Why you need rigid-flex pcbs?
A rigid-flex PCB can help you resolve issues in reducing space, making sure your products can perform well in tough conditions and ensuring they are cost-efficient.
A rigid-flexible combination enables you to use less parts and interconnections and take on more aggressive design challenges, as the rigid-flex PCB is a flexible solution to a number of design issues.
Factors that affect rigid and flexible PCB Cost
When fabricating a rigid-flex pcb, you may need to consider the cost optimization. We will give you an idea of what will affect the rigid-flex pcb cost:
2. PCB board size
3. Finish (HASL, ENIG)
4.Minimum Trace and Space
5.Thickness of the PCB
6.Unique or Custom Specifications
7. Customized requirements
Your Best Rigid – Flex PCB Manufacturer And Supplier in China
Rigid Flex PCB( also called Rigid-flex printed circuit board or flex-rigid PCB), is a combination of rigid PCB and flexible PCB, that are permanently connected to each other, by having conductors on both rigid layers and flexible layers of the circuits.
Rigid Flex PCB For Industrial Valves
And of course these applications normally can afford higher cost, but now in our daily life, we can found consumer products using rigid-flex printed circuit board more and more, such as cars, laptop, cell phone, and batteries., etc.
The use of LEDs in the automotive industry has posed new challenges in the shape and design of printed circuit boards. When installing LEDs in front the automobile headlights, for example, the printed circuit board is bonded to an aluminium heat sink to which the LEDs are then attached. The printed circuit boards offered by Venture have either one, two or three layers (HDI).
Rigid Flex PCB use for Automotive Light
Venture is proud to offer high-quality, high-reliability rigid flex PCB (printed circuit boards), for example:
- Flex PCB with 10 layers rigid PCB
- Single-Sided Flexible Printed circuit board with 6 layers rigid PCB board
- Double-Sided Flexible PCB with 12 layers rigid PCB
- Multilayer Flex PCB with multilayer rigid PCB
Rigid Flex PCB Capability:
|Rigid flex PCB Feature|
|Layers – Flex|
1 – 4
1 – 4
|Layers – Rigid|
4 – 30>
4 – 30>
|Max Board Size|
24” x 40”
609.6 x 1016mm
|Min Board Thickness – 1-2 (layers)|
|Min Board Thickness – 4 (layers)|
|Min Board Thickness – 6 (layers)|
|Min Board Thickness – 8 (layers)|
|Min Board Thickness – 10 (layers)|
|Min Board Thickness – 12 (layers)|
|Min Board Thickness – 14 (layers)|
|Min Board Thickness – 16 (layers)|
|Min Board Thickness – 18 (layers)|
|Min Board Thickness – >20 (layers)|
|Board Thickness Range|
14 – 276mil
0.35 – 7mm
|Max Copper Thickness|
|Min Line Width / Space|
2mil / 2mil
0.05 / 0.05mm
|Min Hole Size|
|PTH Dia. Tolerance|
|NPTH Dia. Tolerance|
|Hole Position Deviation|
5 x 10Sec @288
5 x 10Sec @288
|Warp & Twist|
Venture can produce rigid flex PCB base on our material in stock so you don’t have to wait long lead time on special materials. We have a full range of top rigid & flex raw materials in stock to meet your rigid flex PCB(printed circuit board) application, such as DuPont, Rogers, Isola, Taiflex, Arlon, Panasonic, Thinflex, Aplus Tec, Shengyi, we can also suggest local popular rigid flex PCB raw material manufacturer that fit your projects, to reduce your cost .
|170||TU-862 HF||Taiwan Union|
|FR-4 + BT Epoxy Resin||180||G200|
|FR-4||130||Tlam SS 1KA|
|FR-4||135||H140-1 / FR-4-74|
|FR-4||140||FR-402 / IS402|
|150||TU-747 HF||Taiwan Union|
|175||EM-827/ EM-827B||Elite Material|
|FR-4||176||R5725 Megtron 4|
|200||TU-872 LK||Taiwan Union|
|260||P95 & P25||Isola|
Venture is the perfect place for your rigid flex PCB requirement; we are trusted by thousands of electronic engineers all around the world through our100% quality guaranteed policy. Through our 2 hours rapid response services from our 24/7 sales and tech support team, and excellent after-sales service, we will be your best rigid flex PCB supplier in China. At Venture we can answer any rigid-flex questions that you may have, pls feel free to contact us anytime.
Venture: Your Best Rigid Flex PCB Manufacturer in China
Rigid-flex PCB: The Ultimate Guide
Today’s guide explores all the fundamental aspects of rigid flex PCB.
It aims to give OEM businesses, and large rigid flex printed circuit board importers an in-depth analysis, and insights on sourcing for PCBs.
From basic definition, advantages, disadvantages, material selection, classification, design, layout to assembly – by the end of it all you’ll be an expert in rigid flex PCBs.
Let’s go straight to the main subject of todays printed circuit board guide:
- What is a Rigid Flex PCB?
- Advantages of Rigid-Flex PCB
- Disadvantages of Rigid-Flex Printed Circuit Board
- Types of Rigid-Flex PCB
- Rigid Flex PCB Material
- Rigid-Flex PCB Design and Layout Process
- Choosing Rigid-flex PCB Design Software
- Step-by-step Rigid-flex Designs Process
- Rigid-Flex-PCB design
- Rigid-Flex PCBs Manufacturing Process
- Rigid-flex PCB Fabrication Process
- Rigid-flex PCB Assembly Process
- Rigid-flex Circuit Specification
- Choosing Rigid Flex PCB Manufacturer
- Rigid-Flex PCB Application
What is a Rigid Flex PCB?
Rigid-Flex printed circuit boards are boards made up of both rigid and flexible circuit substrates. More often than not, rigid-flex boards are composed of multiple layers of flexible substrates.
These flexible substrates are then attached to either one or more rigid boards.
This attachment is done either internally or externally. The intended application for the rigid-flex board is crucial in determining how the attachment is done.
Rigid flex PCB
Normally, the flexible components are designed to be constantly flexible.
This flexibility is useful in corners and areas that need extra space. Rigid substrates are useful in areas that require extra support.
With these capabilities, there is a surety that these rigid-flex boards can be curved during the manufacturing and installation processes.
Also, you can achieve this using an application of 3D software. This ultimately enhances the achievement of the desired shape for the intended application.
Advantages of Rigid-Flex PCB
Some of the main advantages of rigid-flex PCBs include the following:
Rigid flex PCB
- Flexibility, which is inherent in rigid-flex circuit boards makes it possible to manufacture a board for an existing device. This is in contrast to making a device while considering the board’s specifications.
- Lightweight – Owing to the fact that rigid-flex PCBs are flexible, they are also lightweight.
- Compactness reduces packing size – The rigid substrate enhances the compactness of these boards. This informs the reduced packaging size.
- Fits smaller & confined areas – Rigid-flex printed circuit boards are also flexible enough to fit into confined and smaller areas. This results in product miniaturization.
In essence, it can be bent and be folded with ease. This enables them to fit into smaller devices.
- Reliability due to absence of solder joints – In its design, rigid-flex printed circuit boards do not have solder joint or connectors. It also lacks contact crimps. This feature ensures the reliability and integrity of applications made of these boards.
- Reduced circuit failure – The integration of both rigid and flex circuitry results into minimization of interconnections. This goes a long way to inform reduced circuit failure in the resulting applications.
- Good thermal stability – The boards use polyimide during the assembly process. Having in mind that polyimide has excellent thermal stability, they can withstand extreme temperatures. This makes it a preference in the manufacture of both military and defense applications.
- Cost effective due to low material requirement – As we have witnessed previously, rigid-flex PCBs needs comparatively fewer materials for assembly. This informs cost effectiveness since procurement and manufacturing costs are reduced.
- Ability to withstand harsh environmental conditions – Rigid-flex boards also have the ability to resist and endure in different environmental conditions. These include radiation and UV rays exposures. They also offer strong resistance against harsh chemicals and oils.
- Allow for component mounting on both sides – During the design process of the boards, they are made in a way that they can enable surface mounting on both sides.
Disadvantages of Rigid-Flex Printed Circuit Board
Now, some of the main disadvantages of rigid-flex printed circuit boards include:
Rigid flex printed circuit board
- Requires and elaborate manufacturing – Two different substrates are involved in the manufacture of rigid-flex PCBs. These include rigid and flex substrates. This makes the production elaborate and time-consuming.
- Complex manufacturing process – Unlike other simpler printed circuit boards, the fabrication process is complex. This requires the use of effective and suitable software. This makes the cost of production expensive.
- Production is labor intensive – Production of rigid-flex printed circuit boards is also material and labor intensive. This is as a result of the sensitivity of the PCB and the variations inherent in rigid and flex substrates.
Types of Rigid-Flex PCB
Some of the most common types of rigid-flex PCBs include:
·Single-Sided Rigid Flex PCB
Single sided rigid flex Circuit boards have only one layer of conductive material. The other side of the board gives room for the incorporation of various electronic components on the board.
Single sided rigid-flex PCBs are composed of one layer of both rigid and flex substrates conjoined together.
Single sided rigid flex PCB
Unlike other types of rigid-flex circuit boards, they can be easily designed and manufactured.
·Double-Sided Rigid Flex PCB
In rigid-flex PCBs, these are made of one layer of rigid substrate and another layer of a flexible substrate.
The rigid layer helps in enhancing compactness while the flex substrate is useful in enhancing flexibility.
Double sided rigid flex PCB
Double-sided rigid-flex circuit boards also allow for more routing traces. This is made possible by the vias which alternate between the two layers.
Double-sided rigid-flex PCBs are preferred for their flexibility and board size reduction capabilities.
Multilayer Rigid Flex PCB
These are rigid-flex circuit boards with more than two conductive layers of whichever of the two substrates.
The substrates act as insulators between one another.
Multi layer PCB
On the rigid layers, there are the conductors.
Rigid Flex PCB Material
Rigid flex PCB
Substrate and Cover Overlay
Some of the most common substrate and cover overlays include:
The most commonly used material for rigid-flex circuits is woven fiberglass. Epoxy resin is used to impregnate this fiberglass thoroughly.
Nevertheless, fiberglass impregnated by epoxy has questionable qualities. This is because it hardly resists sudden and constant vibrations.
It is also a poor shock absorber and cannot support constant movements. For these reasons, during the manufacture of rigid-flex circuit boards, the following materials are used:
This is preferred since it is versatile. It is also tough and can sustain vibrations and constant movements.
Polyimide is also in a position to resist heat. This makes it the best choice for applications meant to be used in fluctuating temperatures.
PET is preferred for its ability to flex and desirable electrical properties. It is also chemical and moisture resistant. This means that it can be used in hostile industrial environments.
When the right substrate is used, there is a surety that the strength and lifespan will be desirable. It takes consideration of factors such as thermal resistance and the stability of the dimensions to get the right substrate.
Other factors to consider include chemical resistance and flexibility.
Cover Lays – these are made by combining flexible films with appropriate adhesives. This cover lays play a number of roles in the assembly of rigid-flex PCBs. It provides the assembly with all-inclusive protection.
Secondly, it provides access to circuitry areas. These include circuit pads which are further processed. The third role is to supplement the dependability and flexibility of the circuitry.
Cover Coats – in some instances, cover lay is not used. In this method, a thin coating of liquid is applied on the surface of the circuitry.
The liquid used is acrylated epoxy. In other instances, acrylated polyurethane is used.
Screen printing method is the most commonly used. The coating is usually thermally cured.
For rigid-flex PCBs, copper is the most preferred material for the board assembly. This preference is due to the fact that it’s a good electrical conductor and has high workability. There are two types of copper foils that are used in the process.
Electrodeposited copper foil is one of them. The second one used is rolled copper foil. These foils have variations in weights and even thickness.
Conductor material for rigid flex PCB
Before use in the assembly process, surface treatment is done to the board. This is done by applying a thin layer of zinc of the foil. This enhances the lifespan of the foil.
Chemical treatment is also done on the foil. This increases adhesiveness and enhance the strength of the bonds. It also reduces the chances of bond degradation and offers protection against oxidation.
In order to get a longer service and lifespan of a rigid-flex PCB, adhesives are essential. Adhesives ensure that secured connections are established between the conductor materials and the substrate.
Sections of PCB – Photo courtesy: Panacol
There are several adhesives that are usable in the manufacture rigid-flex boards. These include:
Temperature resistance inherent is this adhesive makes it the most suitable for the task. It can resist up to 500 Degrees Celsius. This high heat resistance makes it the most preferred in making of a number of sensitive applications.
These include applications used by the military in defense operations and applications used in power generations.
They are also commonly used in multilayer circuits owing to their ability to accommodate thermal expansion.
Compared to polyimide adhesives, these adhesives are relatively cheaper. They are the most preferred in the fabrication of simple rigid flex circuits.
They also have comparatively low bonds strength. Polyester adhesives are also unlikely to resist high and unpredictable temperatures.
However, in recent times, they come in modified forms. This gives them the ability to offer heat resistance.
The modification also increases the chances of versatility. This makes them reliable in the assembly of multilayered circuit boards.
· Acrylic Adhesives
These adhesives are comparatively superior. They have exceptional thermal stability and can resist both corrosion and chemicals. They are very easy to apply and are comparatively cheaper. Combined with their availability, they are popular among manufacturers.
In the manufacture of rigid-flex circuits, this could be the most commonly used adhesive. They equally have the capability of resisting corrosion and both high and varying temperatures.
They are also very flexible and boast of exceptional bond stability. Small amounts of polyester are added to it in order to increase flexibility.
In rigid-flex PCBs, the most commonly used insulators are polyimide film. It is used on the base layer on the single metal layer flex circuits. Polyimide is also used in the inner layers of the multilayered circuits.
FR-4 and the prepreg are combined to come up with the intended insulating layers. This is done on the rigid portion of the rigid-flex circuit.
Rigid-Flex PCB Design and Layout Process
PCB design and layout is an important stage in printed circuit board manufacturing process.
Here are some of the key elements you need to know:
Rigid Flex PCB Design Guidelines
In designing rigid flex circuits, it is imperative that you adhere to the set-out rules as much as you can.
When you are making the corners, make sure that they are not bent. However, when a bend has to be made, you will have to make sure that the bend is curved as opposed to being sharp.
When changing the widths of the traces, it is imperative that you ensure that this is done gradually.
Changing this abruptly is likely to result in a weak spot. In order to reduce costs and to increase the circuit’s flexibility, a minimum of two flex layers has to be used.
Layout Guidelines for Rigid Flex PCB
To successfully create your rigid-flex PCB, there are a number of guidelines that need to be observed.
Rigid PCB Design and Layout
Trace width calculator must be used to get the right results for trace width and spacing between the flexible parts. The solder pads should be completed in either teardrop or rounded styles.
This should also apply to the tracks.
·Annular rings and soldering surface
It is also imperative to ensure that both the annular rings and even the soldering surfaces are made large. The desired thickness should be achieved using stiffeners.
Moreover, it is imperative that you apply a coverlay on the flexible circuit boards in the rigid flex circuits. This grants protection and insulation for the conductors on the outer surface.
During the soldering process, the coverlay is essential in restraining and holding the pads when soldering is being done.
Rigid flexible printed circuit board
The manufacturer will have to ensure that the pads being used include anchoring spurs. These will be of the essence in ensuring that no separation exists in between the material and copper during assembly.
Filleting should then be done on the pads. This will help in reducing stress points and will reduce the chances of breakage during flexing.
The plated vias have to be metalized. This is made possible through the holes that act as a connection between the conductive layers and the flexible circuit.
Blind vias are meant to connect the inner layer exclusive of going via the circuit. One can also use buried vias. These connect every internal layer but ignore the outer layers. Use of these different types of vias is likely to augment space found in the circuit.
Kinds of vias – Photo courtesy: Ray PCB
This gives room for the addition of various component pads. The space can also be used for trace routing.
On the flex circuits of the rigid-flex PCB, it is essential that one avoids the use of vias on the flex substrate. In instances that it must be used, it is advisable to place them on areas that won’t be bent.
Emphasis should be laid on accuracy when calculating the bending radius of the rigid flex circuits. This will help you ensure that there are no breakages. The minimum bending radius should be .05” measuring from the plated through holes.
It should also be ten times thicker compared to the material. If this is observed, then you will be guaranteed of a well-functioning circuit.
When bending the circuit, you should evade doing this at the corners. Copper traces work effectively only when they are put at a right angle to flexible circuit bend.
This should be avoided when you are working with curved traces.
This is because it is likely to stress copper traces when the time for ending comes.
Wrinkles are likely to be formed on the cover coat when a sharp bend is made on the board. The bend is also likely to induce stretching. The cover material is likely to be torn during this process.
This can also break conductors on the outer part of the bend.
A sharp bend on the board can lead to wrinkles in the cover coat. It can also cause stretching, which could in turn lead to tears in the cover material, as well as broken conductors on the outside of the bend.
For the bend to be more reliable, it is advisable that you trim down the thickness of flex.
To realize this, you will first need to reduce the dielectric thickness. You should also balance the weight on both sides of the bend axis.
You should also avoid stacking the conductors atop each other on every layer. You can instead choose to stagger them on all the layers.
In order to expel moisture absorbed by rigid-flex, you will have to dry out any moisture. The moisture is likely to exist since polyimide absorbs it.
This s expelled for four complete hours at around 120 degrees Celsius. When the drying has taken place, the soldering and placement process can be done within eight hours.
Choosing Rigid-flex PCB Design Software
In the manufacture of rigid-flex PCBs, designers are advised to use the most suitable software to make working layouts. Defective layouts are likely to contribute to inefficiency of the rigid-flex boards.
PCB Design software interface
In the rigid-flex design, there exists a number of ECAD software. These software grant you the opportunity to design the board effectively.
They will also help you in fine-tuning the designs. This will allow you to alter board outlines.
ECAD software also offers you a reliable board within the shortest time possible. This software also has the 3D option which is essential in designing reliability of the bends and other sensitive components.
ECAD software is also capable of altering width traces. This is done in a manner that accommodates signals on both rigid and flexible components.
Any rigid-flex design software with these qualities guarantees you an effective design.
You can also choose from the numerous PCB design software available.
Step-by-step Rigid-flex Designs Process
Rigid flex PCB design
Step 1: Preparation of the base material.
Before fabrication process starts, laminate has to be cleaned thoroughly. This pre-cleaning is essential since the copper coils used usually have anti-tarnish features. This is usually done by the vendors to offer protection against oxidation.
However, this impairs the manufacture of rigid-flex PCBs. It therefore has to be removed. This is achieved after following a number of steps.
The first step is the immersion of the copper coil into acidic solution.
Alternatively, the copper coils can be sprayed with acid.
The coils obtained from step one are then micro-etched. Sodium persulphate is used to treat the copper coil in order to achieve this.
Also, the third step involves comprehensive coating of the coil. This is achieved using various oxidation agents. This helps in preventing adhesion and oxidation.
Step 2: Generation of the Circuit Pattern
In this step, circuit patterns are created. There are two main techniques that you will have to use to achieve this. These include:
Screen Printing – this method is preferred for its ability to produce the desired circuit patterns. This is attributed to its ability to deposit accurately on laminate’s surface.
Photo Imaging – this is the oldest technique. However, it is still a commonly used method in depicting circuit traces on laminate. This technique ensures that dry photoresist film which is composed of the intended circuitry is rested on the laminate.
The resulting material is exposed to UV light. Subsequently, the pattern on the photomask is transferred to laminate. The film expunged from the laminate chemically. This leaves the laminate with the intended circuit patterns.
Step 3: Etching the Circuit Pattern
Etching of the copper laminate which contains the patterns of the circuit is etched. Manufacturers of rigid-flex PCBs usually achieve this by dipping the laminate into an etch bath.
Alternatively, they spray them using an appropriate etchant solution. In order to get the required results, etching is done to both sides simultaneously.
Step 4: Drilling Processes
After etching, drilling is the next step. In this step, holes, pads and vias are drilled. To come up with precise holes, you will have to ensure that the drilling tools can sustain high speed.
Use laser drilling methods when creating holes that are ultra-small.
Step 5: Through-hole Plating
In rigid-flex manufacturing, this is a step that must be handled with a lot of care and precision. After the desired holes have been drilled, copper is deposited in them.
They are then chemically plated. The end result is the formation of electrical interconnections across the layers.
Step 6: Application of Cover lay or Covercoat
Protection of both the top and the bottom sides of the flex circuit is very important. This is done by applying a cover lay.
The importance of this is the provision of protection from hostile environments. This cover lay also offers protection against harsh chemicals and even solvents.
Polyimide film enhanced with an adhesive is the most preferred material used as cover lay. Screen printing makes it possible to imprint the cover lay on the surface.
Curing is then done through UV exposure. Specific limits of heat and pressure are applied during the lamination of cover lays.
The difference between cover lay materials and covercoats are clear. Cover lay is a laminated film while covercoat refers to materials that can be directly applied on the substrate’s surface.
The type of coating is determined by considering a number of factors.
These factors include the method used in the manufacturing process and the materials used. The area of application is also considered. Both coats are essential in augmenting the whole assembly’s electrical integrity.
Step 7: Cutting out the Flex
This refers to the cutting of each flex board from the panel on which production is done. This step is essential in rigid-flex production.
Thus, it has to be conducted with care and precision. In high volume production of rigid-flex, hydraulic punching technique is applied.
Step 8: Electrical testing and verification
There are several electrical tests that the board is put through. Factors such as circuit performance are put under scrutiny. The quality is also assessed using the design specifications as the threshold.
When using the traditional methods for designing rigid-flex PCBs, you will mount components to the rigid part. Other mountable parts include connectors and the chassis.
This means that the flexible circuit will only act as an interconnector. This will be essential in mitigating the mass and augmenting vibration resistance. This was commonly used in the past.
In the recent past improved designs have emerged in the design of rigid-flex PCBs. Component scan today be mounted on the flexible circuit area.
This means that more complex multilayer PCBs can be made today as opposed to in the past.
This however sets in new challenges that have to be mitigated in the design process. These challenges are likely to arise when drilling holes and when routing.
The bend lines in the flex circuits are likely to affect routing. Thus, you should avoid placing the components on the bend line. In instances that components are placed correctly on the bend line mechanical stress is likely.
This will affect the surface-mount pads and the through holes. Through hole plaiting can be done to mitigate this stress. You can also bolster the pad support using additional coverlay. This will help in anchoring the pads.
To reduce stress, use hatched polygons. This will be essential in maintaining flexibility when conducting ground plane on the flex circuit. Use curved traces instead of using 90° or 45° angles. When changing the traces widths, use teardrop patterns.
These practices will help you reduce both stress points. For double-sided rigid-flex PCBs, you can stagger the top and bottom layers. This will prevent the traces from lying atop each other thus resulting in a strengthened PCB.
Rigid flex PCB design
Route traces should also be bent perpendicularly to the bend line. This will also mitigate stress.
In the design process also, it is imperative to consider electromechanical factors which are likely to affect both the circuits. Your focus should be on the ratio of bend radius to the thickness.
Chances of failure are increased on the flexible boards when there are tight bends. This is also likely when bend thickness is increased.
Ensure that the thickness of the flex material is a tenth of the bend radius at minimal.
Do not stretch the flex circuit along the outer bend. You should also avoid stretching it along the inner bend.
The thickness of the conductor in the bend area is likely to contribute to influence reliability. Use pads-only plaiting in order to achieve a reduction in thickness and mechanical stress.
Rigid-Flex PCBs Manufacturing Process
Rigid-flex PCB manufacturing process involves series of procedures. Here are some of the most critical aspects you need to know about printed circuit board manufacturing process:
Rigid-flex PCB Component Sourcing
Rigid-flex components are the essential parts that you will need for proper functioning for your PCB. You most definitely lack the ability to make all the components by yourself.
The best you can do is to outsource them. This is common even with companies that manufacture the same PCBs.
The first step in sourcing for your PCB components is the preparation of bill of materials commonly referred to as BOM. This will be a list of all the components that you need for the production of your rigid flex PCB.
Also, this will help you in sourcing for the components and will be a reference point to mitigate omissions.
You can then proceed to source for the components. These components are produced by a number of authorized dealers. You will have to identify and approach a dealer that best suit your need.
A number of factors are taken into consideration at this point. Ensure that the dealer you are sourcing from is authorized to make the components.
Factors such as experience, pricing, warranty and even guarantee should be taken into consideration. Shipping should also be considered.
When you consider all these, you’ll be in a suitable position to get components that will meet your needs.
Rigid-flex PCB Prototype Process
Very sensitive applications are made from rigid-flex circuit boards. Thus, it is imperative to create prototypes before delving into production. With the help of a well-established rigid-flex manufactures you can make the best prototype.
From their experience, they will make the process simple. There are a number of steps involved in rigid-flex prototyping.
Rigid flex PCB prototyping
Step 1: Design
You will first have to come up with the intended design of rigid-flex PCB. Design can be arrived at by the aid of the requisite software.
Step 2: Schematic Design
This provides a description of the intended design that will be used by the manufactures. This entails details of the components to be used during production.
It also provides details of the functions of the board and the way the components will be placed. Remember, it also details the intended panel size and grid.
This makes the first phase of design. A preliminary check is done in order to establish whether there are defects. If any, they are corrected.
Simulations are then run to ensure that the board is working properly. The electronic design is then converted into netlist. This illustrates interconnectivity inherent in the added components.
It is advisable to run these checks on the design regularly until the end of the process. As such, you will be able to fix emerging problems as time goes. This will guarantee you an efficient design process.
Step 3: Bill of Materials
This is a list of the materials and components that you intend to use during production. It is commonly referred to as BOM or bill of materials. In instances that you will be working with a manufacturer, this list will be their point of reference.
BOM photo courtesy: PCB Cart
BOM gives all the essential details of the components. It details quantity which refers to the required components in terms of numbers.
Other details include reference designators, the value of each component and location of every component.
After finishing the BOM and schematic, the necessary parts are gathered by both the component and layout engineers.
Step 4: Routing Design
The routing is then designed through the traces. This will be used to connect all elements in the rigid-flex circuit. There are a number of factors to consider when planning routing.
These include checking on power levels and noise sensitivity. Signal noise generation is also a factor to be considered.
The software programs used in the design of rigid flex circuits use netlist. Most of the programs are able to calculate the maximum number of routes based on the intended number of layers.
This takes a while especially for rigid-flex PCBs owing to the fact that there are a large number of components.
Step 5: Checks
For functionality issues, it is imperative to constantly check the designs before shifting focus to fabrication phase. Thermal issues compose some of the major issues that must be addressed.
The thermal paths and variations n the thickness of copper can contribute to unpredictable temperatures. Electrical rule check must also be performed. The design and layout must also be put under scrutiny.
Step 6: Creating the Photo Film
Refer to the design you provided earlier to come up with a photo film of the rigid-flex PCB. You can achieve this with the aid of a plotter for every layer and the board’s solder mask.
Ensure that the film is a plastic sheet that has been printed with a photo negative of the board. This marks the parts that will be conductive and non-conductive parts.
Step 7: Printing the Inner layers
In this step, you will apply the substrate material with copper. First, copper will be pre-bonded to the substrate. Subsequently, a photoresist layer is applied. This will be essential during hardening using ultraviolet light.
After exposure to UV light, the unhardened photoresist is remover. The hardened photoresist is left covering and protecting the designated points for copper.
You can then remove the hardened photoresist. This will reveal to you copper in the exact places that the design stipulates it to be.
Step 8: Aligning the Layers
For a multilayered rigid-flex circuit board, there is need to align and punch precise registration holes. You will have to perfectly align them. This is essential because it is impossible to correct the inner layers once all layers are merged.
Step 9. Fusing the Layers Together
In this step, you will be fusing the flex and rigid layers together. This is achieved in two distinct stages. The first stage is layer-up and the second one is bonding. In the first step, you first place the outer layer atop an alignment basin.
You will then stack the substrate layer. This is followed by the stacking of copper sheet and more outer layer material. Onto the layer, stack an aluminum foil followed by a copper press plate. The resulting layers can be fit in the pins fixed to the steel table.
In the second step, use bonding press to heat up the stack. In this computer-aided process, pressure is then applied and later on the stack is cooled. The end product is a rigid flex PCB.
Step 10: Drilling the Holes
You can then drill holes on the rigid-flex stack. These holes will necessitate mounting of components. This has to be done with precision. The recommenced measurement is 100 microns diameter.
Use an x-ray locator to get the right hole locations. You will also have to use computer to do the drills. This makes the turnaround time shorter and the holes are drilled precisely.
Step 11: Copper Plating
In this step, a copper layer is deposited on the surface of the panel. This is done using chemical bath. This will help you in ensuring that the whole panel together with the holes and the interior walls are covered.
This will make a coat over fiberglass material in the inside of the panel that had previously been exposed. The whole process is controlled by the computers.
Step 12: Outer Layer Imaging
After copper plating, you should add an additional layer of photoresist. This will help you in imaging the outer layers in accordance to the rigid-flex circuit design provided. This will follow the same procedure used in the earlier stage.
Step 13: Copper and Tin Plating
Another round of copper plating is then done. This photoresist layer will make sure that copper deposits are placed on the preferred parts of the board. The board will then be tin plated. This will offer protection to copper in the next step.
Step 14: Final Etching
Use chemical solutions to wash away excess copper. The tin plaiting done on the previous step will protect copper in the conductive areas. Following procedure, you’ll be able in a position to establish conductive connections.
Step 15: Applying the Solder Mask
In this step, cleaning of the panel is done. It is then applied with epoxy solder mask ink. The rigid-flex board can then be exposed to UV light. This will harden the film. You should then remove all the unhardened parts.
Step 16: Applying the Surface Finish
More plaiting is then deposited. This can either be gold or silver. In some instances, you can also use hot air leveling. This will be essential in ensuring that the pads are uniform. This will give you a surface finish.
Step 17: Applying Silkscreen
You can now proceed to apply silkscreen onto the surface of the rigid flex PCB. This is done using ink-jet writing. This will be essential in conveying important information concerning the board.
Step 18: Cutting
You should first conduct an electrical test. This will help you ascertain whether the board is functioning as intended. Using a router, a separate board is cut from the larger panel. The rigid-flex boards can then be obtained from the panel
Step 19: Assembly
All the components are attached to the rigid-flex board.
Step 20: Solder Paste Stenciling
You should then apply solder paste on the board. This will mix with flux. The solder will subsequently melt and get bonded to PCB surface.
Stainless steel stencil is then placed over the rigid-flex PCB. In so doing, solder paste will be applied on the designated places for components in the finished PCB.
Every open area gets an equal spread of the paste. You can then remove the stencil to leave the solder paste in the desired locations.
Step 21: Pick and Place
For effective picking and placing of the surface mount components, you have two methods at your disposal. You can use a pick and place machine or SMD.
This ensures that the non-connector components are placed on top of the solder paste. It does this in the predestined locations.
Step 22: Reflow Soldering
Surface mount component are attached to the rigid-flex board as the reflow process makes the solder paste solid. You can achieve this by putting the rigid-flex board through a reflow oven. The heaters in the oven melt the solder found in the solder paste. When it finally cools off, the melted solder solidifies. The SMDs are then attached permanently to the board.
Step 23: Inspection and Quality Control
In some instances, reflow soldering can undermine connection quality. This is likely to lead to electrical shorts due to poor connections.
You will thus have to ascertain whether there are no errors. You can do this by conducting manual checks. Automated optical inspections can also be of essence just as x-ray inspections are effective.
Step 24: Inserting Through-Hole Components
In some instances, there are rigid-flex boards that need other components apart from SMD. These components are attached to the board using the through-hole method.
These are plaited through the board. This gives them the ability to send electric signals across both sides of the PCB. Soldering here is done manually. The other option is wave soldering.
This entails putting the board on the conveyor belt into an oven. The bottom of the board is completely covered using molten solder. All the pins are soldered at the same time. This is only used in single-sided rigid-flex boards.
Step 25: Conducting a Functionality Test
In rigid-flex prototyping, this is the last step. It tests the functionality of the prototype. The functionality is supposed to simulate the operating conditions that the board will be subjected to.
After Rigid Flex PCB Prototyping: Testing the Prototype
After prototyping your rigid-flex circuit board, the next stage is testing it before rolling out its full production. The test is conducted in accordance with the reason why it was manufactured.
You should ensure there are no design flaws and identify areas that will need improvement. In the event that you have different designs, run each of them and do a comparison on their performance.
If you happen to detect problems during the tests, there will be need to either correct the flaw or create a new prototype. If the performance of the prototype turns out to be effective, you can proceed to roll out full production of the board.
Rigid-flex PCB Fabrication Process
Since rigid-flex PCBs combine both the properties of rigid and flex boards, they present a unique connection method.
For this reason, they are popular for their ability to work in various applications as they usually improve performance.
However, due to their complex nature, the fabrication process is never simple. There is high technological demand in their fabrication.
This informs the high costs associated with these boards. We hereby delve into the fabrication process.
Rigid flex PCB fabrication
Structure of Flex-Rigid PCB
Through plated vias, the production of rigid-flex PCB is done by bonding the outer rigid with flexible PCB.
Each piece of rigid-flex PCB contains both rigid and flexible parts of the board. this is an indication that several structures have to be put in place. This cannot be achieved unless the necessary fabrication technologies are applied.
Process Design of Flex-Rigid PCB
You should grant attention to new processes involved in the fabrication process. These processes include covering of material cutting and generation of graphics.
This is succeeded with lamination and punching of the cover film.
These processes are performed on the flex circuit. On the low-flow prepreg phase, the plasma is cleaned and roughened. It is then pre-milled and laser cutting is done. Lamination is then done to shield the film. The board lamination is the stiffened.
Based on your design preferences and the requirements of the board, rigid flex PCB is created. This should be executed using reputable rigid-flex PCBs software.
Layout Design of Flex-Rigid PCB
Designing copper clad laminate is then designed in a manner that will feature two options for the widths.
This will be essential in determining recommended range sizes of both the flex and the rigid boards.
Layer up technology is thus commonly used in these PCBs. The structures developed by layer up technology come in two options.
In the first option, four pieces of flex circuit boards are joined together to make a large board. The size of this large board is equivalent to that of the rigid boards.
In the second option, six pieces of flex circuit boards are joined together to make a large board. The size of this board is equivalent to that of the rigid board.
Plasma Cleaning and Roughening
The flex boards that are covered with coverlay are supposed to be subjected to plasma cleaning before lamination. This is done in conformation to the stipulated first cleaning condition.
Plasma roughening is then added on the whole board prior to lamination. This is done by conforming to the second cleaning condition.
Riveting Jig Manufacturing
Both rigid and flexible boards need riveting, it becomes difficult to undertake the two exercises manually. The solution can be found in a riveting jig which will enable you to handle both the PCBs within the shortest time possible.
Requirements for Solder Mask Technology and Design
In rigid-flex PCBs thickness determines the way through which the coating is done. Thickness above 0.5mm is subjected to spraying coating. Thinner boards on the other hand are coated using silk screen technology.
The opening for solder mask window on the flexible board should measure between 4mil and 8mil. You should take this measurement from the board’s axle wire to the rigid area.
When applying De-Cap technology, the light points are supposed to be blocked. In the De-Cap area, ensure that you do not implement a mask window opening. In the absence of the De-Cap design, you should design a silkscreen to block the light.
Pattern Milling Design
In the fabrication process of rigid-flex PCBs, flexible materials are supposed to be laminated with rigid materials.
Rigid materials on the surface e are then eliminated using special methods that leave flex areas exposed.
Surface finish is then implemented within areas flex boards are exposed.
The completed part is then milled out. The end product becomes a rigid flex printed circuit board.
Rigid-flex Printed Circuit Boards Strengthening the Design
In the rigid-flex PCB, you will have to ensure that connection parts are designed to be located on a flexible board. The coating should be done on the copper at the connection points.
As such, they won’t be exposed to the air. This will ensure that no separation occurs between flexible and rigid parts.
Strengthening and Shield Film Design
Strengthening process will help you to strengthen rigidity in the flexible boards. The design file dictates the shield film that ought to be manufactured.
In summary, fabricating flex-rigid PCBs entails a very complex structure which is technology intensive. The materials used also have very grievous financial implications.
Accuracy is the focal point in this fabrication process. This is essential in determining dimensional stability. When all the fabrication steps are observed, reliable electronic products are a guarantee.
Rigid-flex PCB Assembly Process
Once you have the rigid flexible PCB ready, it is now time to place components on it. The 5 steps below will help you understand the rigid flex PCB assembly process.
Step 1: Solder Paste Stenciling
This is the first step in the rigid-flex PCB assembly. It entails the application of solder paste on to the board. Over the rigid-flex PCB, a thin stencil is placed.
This stencil has to be stainless steel. This gives you room to apply solder paste onto the intended parts of the rigid flex PCB. These are the parts on which the components will be mounted.
Solder paste used is made of a grayish substance which contains infinitesimal metallic balls. This is commonly referred to as solder. Ensure that the balls are composed of 96.5% tin, 3% silver and 0.5% copper.
The soldering paste is mixed with flux — this aid in melting of the solder and subsequently leads to surface bonding.
You should ensure that you apply the solder paste at intended places with precision. To achieve this, you can use a mechanical fixture. This will enable you to hold the rigid-flex PCB and the solder stencil in place.
By the aid of an applicator, you will be able to place the solder paste in the predetermined areas. The amounts of paste placed will be precise. The machine will be useful in spreading the paste evenly on the stencil.
You can then proceed to remove the stencil. The predetermined locations will be left covered by the solder paste.
Step 2: Pick and Place
Having applied solder paste successfully on the rigid-flex board, the assembly process proceeds to pick and place machine.
In this step, a robotic device is used to mount surface components onto the rigid flex PCB. These surface mount devices (SMDs) consists of most of the non-connector devices in the PCBs. These are then soldered onto the board’s surface.
The use of machines is preferred in this process owing to their reliability and accuracy. This supersedes hand picking and placing that was common in the past. The machines will also guarantee you a quicker turnaround time and are never fatigued.
With a vacuum grip, let the machine pick and place the components on the rigid-flex board. Subsequently, the machine will apply SMT to the surface of the rigid flex PCB. The components are then placed on the intended locations.
After the solder has melted, rigid flex board is placed on a conveyor belt that moves it through an oven. It is then passed through cooler heaters.
As a result, melted solder is cooled and solidified. A permanent solder joint is created.
This connects the surface mount devices to the rigid-flex board.
Step 3: Inspection and Quality Control
After the soldering of the surface mount components to the rigid-flex PCB, the board should be subjected to functionality tests.
The movements that the rigid-flex board is subjected to during reflow can result in connectivity issues. This can also contribute to electrical shorts.
This is attributed to the fact that misplaced components may result in unintended and fatal connections.
You have a number of inspection methods at your disposal. These methods are as explained hereby.
You can conduct manual checks. As the designer of the rigid-flex PCB, you can conduct a visual inspection after the reflow process. This method is only feasible in instances that you have a small number of these PCBs to inspect.
The method is however inaccurate and unachievable when handling a large number of boards.
The second method is the automatic optical inspections. This is the most preferred inspection method when handling a huge number of rigid flex batches.
The machine applies high powered cameras to assess your rigid-flex PCB. The cameras are strategically located to view the solder connections.
Also, the cameras use different light colors to depict the quality of the solder.
This is done at a relatively high speed. These capabilities make it faster and give it the capability to inspect many boards in a short while.
In fact, the third method is x-ray inspection. Regardless of this method not being commonly used, it is the most effective for complex multilayer rigid-flex boards.
This method grants the viewer an opportunity to visualize the lower layers. As a result, potential flaws are detected.
The subsequent step is the testing of the parts. This is done to ensure that all parts are performing as intended. The rigid-flex board connections are tested to ascertain quality.
Do this regularly after doing the reflow process. It will help you identify potential problems which you will have to address. This will save you time and labor.
Step 4: Through-Hole Component Insertion
In some instances, some rigid-flex PCBs have components that may not be SMDs. These are the plated through-hole (PTH) components. PTHs are holes plated through the board.
This aids in passing off signals from one side of the board to the other. This makes the application of solder paste impossible. This is because the paste will go through the hole without hindrance.
There are several techniques that you will use to solder these components to the rigid-flex board.
The first of these techniques is manual soldering. This is a straightforward process. Each and every PTH will be assigned to one person.
Through hole assembly
This person will be inserting a particular component in these holes. Ones this person is done, the rigid-flex is passed to the next person.
This person will also insert a different component in the designated PTH.
This cycle goes on until all the components are inserted.
The second method at your disposal is wave soldering. This is an automated version of the previous technique. It involves a number of processes. After a PTH component has been put in place the board is moved to another conveyor belt.
This runs the board through an oven in which the board’s bottom is washed with molten solder. As a result, all the pins are soldered. This is restricted to single-sided PCBs.
Step 5: Final Inspection and Functional Test
This step tests the functionality of the board. The rigid-flex PCB is put through simulations that are similar to the function it has been made for. Power and the simulated signals are run through the rigid-flex board.
The electrical characteristics are tested using testers. Unacceptable fluctuations in the voltage signal output and other factors is an indication of failure.
When failure is reported, you can make a decision on the next step to take. This will depend on your set standards and the severity of the failure. The failed rigid flex board can either be improved on or be disposed of.
Disposal means that you will have to restart the assembly procedure. This is the reason as to why various tests are recommended before reaching this last stage.
Rigid-flex Circuit Specification
The maximum board size for a rigid-flex PCB should be 571 x 419mm. Special sizes can however be made on request.
The maximum thickness of the board should be 5.00mm. The lowest number of layers is 1 layer while the highest is 30 layers.
Materials used in the manufacture of rigid-flex PCBs include Fr 4, Fr 4 Mid Tg, and Fr4 Hi Tg. There are also types of Teflon that can be used. These include Rogers, Taconic and Arlon. The polyimides used include arlon and nelco.
Rigid flex PCB Specification
Among the flex polyimides used, you can pick on Rogers, Duponty and Espanex.
Solder resist exists in a number of colours. You can use green, red, yellow, black or white. The minimal thickness should be 15 30 µm while the minimum clearance should be 75 µm.
The minimum line width should measure 100 µm. The resist used should be peelable. There exist different colors for the silkscreen. These include white, black, yellow and red.
The minimum width should be 100 µm while the minimum text height should measure 500 µm. Electrical tests specific to rigid-flex boards include flying probe and dedicated fixture test.
Though optional, high voltage test can be conducted.
Choosing Rigid Flex PCB Manufacturer
1.Experience and Expertise
The total experience of a fabrication shop informs the quality of rigid-flex PCBs it will offer. A rigid-flex PCB manufacturer with many years of experience is likely to be well equipped.
This also informs expert quality in the fabrication process. Expertise and experience therefore guarantee you a quality product.
2.Rigid Flex Manufacturing Capability
Some companies might only have the capability to produce rigid-flex PCB prototypes and not do mass production. This is attributed to lack of cutting-edge production facilities.
Such companies also lack advanced equipment and requisite workforce. If you intend to engage one company to do both prototyping and production, this is not the best option.
You will have to engage a manufacturer with the capability of meeting all your desires.
In the selection of the manufacturer, you should also choose one with minimum order quantity. Preference is always made for manufacturers with the lowest MOQ.
Consider going for one with one piece.
Technical expertise is a very important aspect to consider when choosing a manufacturer. This is usually characterized by qualified and experienced staff.
This will be essential in ensuring that your rigid-flex PCB meets the recommended standards.
The manufacturer should also be able to make follow-ups. This will enable them assist you in instances that you experience hitches with your rigid flex PCB.
5.Rigid-flex PCB Cost
Before engaging a rigid flex manufacturer, it is advisable to research on the market prices. This will enable you to gauge and negotiate prices with the manufacturer.
Relatively high prices could be extortionists while very low prices could be a scam.
6.Uses Good Rigid-flex PCB Packaging
Also there are manufacturers who would want to sell rigid flex components in packages larger than you require. You definitely want to get one that offers a package that you need.
If this consideration is not taken, you will end up paying for what you don’t need.
Rigid-flex PCBs are delicate and sensitive. Thus, they should be packaged with a lot of care before shipping.
Look for a manufacturer that offers shipping services for their clients. They are likely to do the packaging in order.
7.Provides Rigid-flex PCB Quote Faster
With experience and expertise, it can never be difficult to quote costs faster. Manufacturers with these qualities are able to come up with the BOM faster and with precision.
With this they are able to provide the quotation faster.
Rigid-Flex PCB Application
With the increasing need for flexible and more sophisticated electronics, rigid-flex PCBs are popular in many applications.
Let’s mention just a few:
Olympus camera circuit
Rigid-flex PCB in the medical industry
Due to their ability to fit within small devices, rigid-flex PCBs are used in the manufacture of medical wearable. These include pacemakers and cochlear implants.
They are also applicable during the manufacture of other medical equipment. These include imaging equipment and handheld monitors among others.
Rigid Flex PCB in military equipment
For a long time, military equipment have been manufactured using rigid-flex PCBs. This is owed to the reliability offered by the board and its resistance to various fluctuating environmental conditions.
These include weapon guidance systems and communication devices. They are also used in tracking and surveillance systems among other applications.
Rigid-Flex PCBs in the aerospace industry
Just like the military industry, devices in the aerospace industry are exposed to harsh environmental conditions. They are also \sensitive as accidents involving aero planes are always fatal.
Rigid-flex is used in the manufacture of radar equipment and radio communication systems. Noise and vibration testing systems are also manufactured using rigid-flex PCBs.
Rigid Flex PCB in the telecommunication industry
Telecommunication industry equally relies on rigid flex PCBs for effective functioning. This reliance is attributed to the fact that these boards can sustain thermal variations.
The applications include routers and servers, communication satellites and handheld units. Others include base stations and wireless communication devices.
Rigid-Flex PCBs in the automotive industry
Small devices are best made using rigid-flex PCBs. In the automotive industry, there are numerous small devices installed. These include electronic control modules and the comfort control units.
Other units include music systems and LCD displays. Navigation systems and transmission controls also use rigid-flex PCBs.
Rigid-Flex PCBs in manufacturing/industrial
Rigid-flex PCBs are also used in the manufacturing industry to make a number of devices. These include the automation systems and industrial air conditioners.
Other devices include electrical switches and control panels. CCTV surveillance systems used in the industries also rely on rigid flex PCBs.
Rigid-Flex PCBs in consumer appliances
Various consumer appliances are made using rigid-flex PCBs. They include electronic irons, lighting systems and washing systems. Remote controllers for TVs and UV water purifiers equally depend on rigid flex PCBs.
Rigid-flex PCBs are quite complex forms of boards. This is owed to the fact that they combine both flex and rigid substrates. The applications made out of these PCBs are also very crucial especially to the well-being of the users.
Design flaws, negligence in their manufacture, prototyping and sub-standard assembly can result in fatalities. It is imperative that the laid down procedures that we have outlined in this guide are adhered to.
This will help ensure that the applications made from rigid-flex boards are safe and meet the required standards.