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HDI PCB (High-density interconnect printed circuit board)is a fast-growing part of the PCB industry, nowadays our devices are getting more and more portable, at the same time components inside are getting smaller and more lightweight, but providing better performance, all these requirements are needed to be functionality a smaller area, this is just what an HDI circuit board can offer.
In the past, computers used to fill up an entire room, but now, with HDI technology, You can find HDI boards in laptops, cell phones and watches, as well as other portable consumer electronics such as digital cameras and GPS devices.
HDI PCB design had played an important role in providing us with a more efficient life. Below are the main advantages of HDI PCB design:
- HDI PCB designs can reduce layer count and footprint
- HDI PCB designs can better protect signal integrity than alternative through-hole approaches
- HDI PCB designs can result in improved manufacturing yield and board reliability
Your Leading HDI PCB Design Supplier in China
HDI PCB design has a higher circuitry density per unit than traditional PCB design, and HDI PCB design using a combination of buried vias and blind vias, as well as micro vias, Venture has 10 years experiences with HDI PCB manufacturing and also HDI PCB design, with our state-of-the-art laser drilling machine( Mitsubishi), laser direct imaging ( LDI) and dedicated HDI design engineers , we are able to provide you best service from design to manufacture.
HDI PCB : Mitsubishi Laser Drilling Machine
We’re happy to share everything we know from our 10 years experiences, as trusted by thousands of electronic engineers all around the world through our100% quality guaranteed policy. With our 2 hours rapid response services from our 24/7 sales and tech support team, and excellent after-sales service, we will be your valued HDI PCB design and HDI PCB layout partner in China.
At Venture we can answer any HDI PCB design and HDI PCB layout questions that you may have, pls feel free to contact us anytime.
HDI PCB Design – The Ultimate FAQ Guide
What is an HDI PCB Design?
HDI abbreviates High Density Interconnector. HDI PCBs usually have high wiring capacity compared to other boards. This is in comparison with other conventional boards.
HDI boards also have finer spaces and lines. They also have minor vias which have the ability to capture pads resulting in high connection pad density.
This usually improves electrical performance remarkably and effectively minimizes the weight and size of equipment in use.
This makes them a preferred choice when fabricating both your high layer count PCBs and boards with costly laminates.
What are Stacked Vias in HDI PCBs?
Stacked vias are vias used in the event that the required blind via exceeds an aspect ratio of 1:1. This means that the blind vias, in this case, cannot be formed through sequential lamination.
This is because there will be another via starting on the same layer. The layer acts as the blind vias termination layer.
What is High Density Interconnection Technology?
This is the technology used to achieve high wiring density per unit area in a PCB.
It leads to PCBs with finer spaces and higher connection pad density.
Because of these technological improvements, HDI PCBs have a higher frequency, hence better performance
Why use High Density Interconnect Technology?
There are a number of benefits that you derive from using high density interconnect technology. HDI technology first makes a reduction in the size of devices achievable.
This is as a result of high connection pad density which also makes reliability in performance a reality.
These features usually make it possible to manufacture wearable electronics, smart-phones and other handheld electronic devices. Further, the ability to incorporate more transistors makes it a preferred board for electronics manufacturers.
In a nutshell, the advantages of HDI boards can be enumerated as follows:
HDI printed circuit boards
·Denser Trace Routing
HDI PCB allows you to incorporate more components onto the board. This is attributed to the fact that the components can be mounted on both sides of the board.
·Enhanced Power Usage
With the HDI board, you are assured of energy efficiency, especially in devices that rely on a battery.
·Smaller Weight and Size
With the reduced board size, it is a guarantee that you will make devices that can fit in smaller spaces. This is unlike ordinary PCBs. It effectively minimizes the chances of destruction in the event of mechanical shocks.
·Faster Signal Transmission
With high density boards, you can be assured of faster signal transmission. High density interconnection also improves signal quality.
Are there Disadvantages of HDI Printed Circuit Board Design?
Despite the benefits, HDI printed circuit boards come with a number of challenges.
First, the fabrication of these boards is expensive. The high fabrication cost is due to the cost of the equipment required in the fabrication process.
The plaiting process is also a major challenge in this process. It requires that you get the aspect ratios right when doing the laser drilling.
The fibreglass contained in the prepregs is usually too huge for laser drilling. This glass can also change laser direction, resulting in inappropriate shapes for the via holes.
The sensitivity of the via holes is also another challenge. Thermal stress on the via holes is likely to result in stresses.
HDI PCB Layout
How do HDI PCBs and Ordinary PCBs Compare?
High Density Interconnect PCBs are characterized by high-density interconnections of the distribution lines. This is achieved by the incorporation of micro-blind buried holes.
HDI PCBs have both outer and inner layer lines. Through drilling and metallization in the micro-blind buried hole, connections are established between each of the layers.
These boards are also manufactured through a laminate method. The complexity of a board is determined by the number of times the layers are stacked.
Also, the simplest of these boards usually one-time laminate.
Complex HDI PCBs are usually made up of two or more layers of this technology. They adopt advanced technologies to make this a reality.
HDI PCB design
These PCB technologies include stacking holes and plating holes. There is also the use of laser direct drilling.
Usually, any board that requires more than eight layers is manufactured using HDI technology. This reduces the cost of production as opposed to using the common pressing process.
With HDI boards, you can be assured of the use of advanced packaging technology.
HDI PCBs also have better performance capabilities compared to other PCBs due to their enhanced electrical performance and signal correctness. This grants the boards the ability to transmit radio frequencies faster.
These attributes explain the popularity of HDI boards in the manufacture of electronic products in the recent past.
Apart from increasing your board’s density, HDI technology also assures you of precision. It also reduces the size of your machine.
Further, gadgets made from HDI boards will be more compact compared to other boards. It achieves this without compromising performance and efficiency. This explains their use in the manufacture of mobile phones, digital cameras and computers.
Another feature inherent in HDI PCBs but missing in other boards is that you make them using adhesive copper foil. This is important when you will be conducting laser drilling of the board. Usually, this drilling cannot open glass.
Ordinary PCBs, on the other hand, are manufactured using FR4 which entails both epoxy resin and electronic-grade glass.
What is the Difference between Blind and Buried Vias?
Blind via vs. buried via
In HDI technology, you are required to use blind vias to reduce the number of layers. These vias connect the inner layers with exposed surfaces.
However, they never go through the entire board.
Blind vias will also help you in widening breakout channels on both the inner and outer layers of the board.
By reducing the number of layers, blind vias enable you to cut the costs associated with high layer counts.
Unlike blind vias which reduce the layer count, buried vias will help you reduce the aspect ratio. They are essential in connecting internal layers with each other.
However, they do not extend to either top or bottom layers.
The ratio between PCB thickness and drilled hole diameter is the aspect ratio. Whenever the aspect ratio goes beyond 10, the manufacturing costs are likely to shoot.
By the use of buried vias, you will be able to reduce the HDI board’s thickness. This reduces the manufacturing cost.
What are the Keys to Successful HDI PCB Design?
HDI circuit boards usually have high wiring and pad density compared to the ordinary boards. They also have smaller trace widths and spaces.
These features are achieved by incorporating technologies such as blind vias, buried vias and micro vias.
These technological advancements also make them more expensive compared to conventional boards.
There are three main principles that shape the HDI PCB design:
First, unlike in the conventional boards where you have through hole (TH) vias, here you will use microvias. This will increase routing density on the inner layers.
HDI Circuit Board
Secondly, you will have to consider a new layer stackup method, which will help you in eliminating the through hole vias.
Thirdly, ensure that the microvias are placed in a manner that creates channels and boulevards to improve routing.
What are the Different Types of HDI PCBs?
There are a number of HDI board types. These boards can be classified under six main categories.
- Those with through via from surface to surface.
- HDI PCBs with buried vias and through vias.
- Those with two or more HDI layer with through vias.
- Those with a passive substrate with no electrical connections.
- Coreless construction using layer pairs.
When was HDI PCB Invented?
HDI PCB development has been a progressive matter. These improvements have been made on the ordinary PCB boards which were invented in the 1980s.
We can rightly argue that HDI PCBs were invented at the beginning of the 20th century and has been transforming ever since.
Can You Recommend Via Fill Material for HDI PCB Design?
To start with, there are various via fill materials. These include copper filled, non-conductive epoxy, silver filled, conductive epoxy and electrochemical plating.
These via fill materials usually result in vias buried in flat land. This leads to complete soldering of normal lands.
Via fill material will hence enable you to fill the drilled micro vias and vias. This ensures that they get concealed underneath the SMT lands.
Which Features Distinguish HDI PCBs?
HDI boards are high-density interconnect boards.
Compared to other PCB boards, they use micro-blind buried holes to achieve dense interconnectivity.
They have both an internal and outer line and rely on drilling and metallization in the hole to achieve connectivity. This is distinct from the normal PCBs.
You should manufacture these boards using a laminate method. Stacking of the layers needs different levels of technical know-how.
When you are manufacturing ordinary HDI boards, they are one-time laminates.
However, when you are manufacturing high-order laminates, you will have to use a technology meant for two layers or more.
This is characterized by the adoption of technologies such as the stacking holes, plating holes and laser direct drilling.
In the event that a PCB’s layers exceed eight, you will have to adopt the HDI technology. This will effectively help you in reducing the costs associated with pressing the board.
HDI technology will also enable you to use advanced packaging technology.
The electrical performance of the board will also be enhanced compared to ordinary PCBs.
This explains the popularity enjoyed today by HDI PCB in the manufacture of electronic products. It reduces the size of devices made while at the same time enhancing performance.
This product is also compact and efficient. Some of the electronics that have benefited from HDI technology include smart-phones, PCs, and automotive electronics.
Can you Reduce PCB Layers Using HDI PCB?
HDI technology reduces the number of layers in a PCB. Compared to traditional boards, these boards have a high circuit density.
The via-in-pad process helps in ensuring that a multi-layered PCB is reduced. This results in the reduction in the size of the devices.
Instead of compromising the performance of the resulting equipment, interconnectivity improves it. The speed and quality are also improved.
The key aspects that make the goal of reducing the layer counts are the via in pad and blind via.
Via-in-process allows you to place vias on the flat land surface. From this point, you can proceed to plate and fill the vias with conductive or non-conductive epoxy.
Finally, you cap and plate it over to make it invisible.
Blind vias essentially reduce the layer count for your PCB. They will also help you in widening breakout channels on both the inner and outer layers of the board.
By reducing the number of layers, blind vias enable you to cut the costs associated with high layer counts.
Is Laser Drill Technology Important in HDI PCB Fabrication?
In HDI PCB fabrication, you are supposed to drill small micro-vias. This allows you to effectively place components on both sides of the board.
It also helps in reducing the number of layers required. This further translates into a reduction in the size of the device manufactured. You cannot achieve this without laser drilling.
The diameters for blind and buried vias in HDI circuits are very small. They measure about 100um or even less.
This is not achievable when using mechanical drill bits, making laser drilling the solution to these drills.
In the recent past, the use of CO2 lasers has also become common. It can drill between 1500-3000 holes per second, ensuring both precision and quicker turn-around time.
What are the Advantages of Laser Drilling for Vias and Microvias?
You will observe that laser drilling can drill vias and microvias with diameters of less than 50um or less. The vias cover a smaller area of the board, leaving you more space for the high wiring density.
CO2 laser pulse will also help you in ensuring that the surface of the copper foil is processed clean.
The quality of the resulting bind vias is enhanced, and their wall surfaces are smooth. This simplifies the laser drilling process. It also enhances the durability and quality of HDI boards.
With blind and buried vias and microvias, you can stack them above each other. This will achieve the performance of a double-sided PHT.
You also have the alternative of filling the vias with heat-conducting materials to achieve heat dissipation.
How are Blind Vias Made in HDI PCB Fabrication?
Blind vias are essential in connecting one outer layer with an inner layer. You can drill blind vias through laser drilling because these holes have to be very small in diameter.
With a CO2 laser, you will be able to drill blind vias with diameters as small as 50um.
Vias in PCB
What is a Laser Plate?
Drilling smaller holes on the normal PCBs can be very expensive. You will also realize that it is very difficult to improve the board due to the effects of the drilling tool.
HDI boards are drilled differently. They rely on laser drilling technology, which accords HDI boards the name laser plate.
Usually, the diameter of the hole on the HDI board measures 3-5mil, thus reducing the size of the pad. The end result is the distribution of the circuits, which translates to higher density.
Is there Standard Hole Size in HDI PCB Design?
In through-holes vias, the acceptable aspect ratio should be 6:1 to 8:1.
In the same manner, the recommended drill diameter is 0.25 mm. This is the recommended diameter for a standard PCB of 1.60mm thickness.
For the reliability in the pad that you are going to make, make sure that your board does not compromise these regulations.
How has HDI PCB Design Enhanced the Ball Grid Array (BGA) Technology?
The evolution of PCBs has been marked with a number of improvements, leading to better efficiency. HDI boards have high connectivity capabilities.
One remarkable beneficiary of this evolution is ball-grid array (BGA). With the demands of HDI design, BGAs have been improved.
PCB designers have pushed PCB manufacturers to build circuits capable of supporting such fine pitch components.
When the pitch is reduced, interconnection becomes more complex.
The reduction of the pad space leads to a reduction of the vias/holes. These have brought real enhancements to the BGA technology.
What is an HDI PCB?
High Density Interconnect PCBs are circuit boards with high wiring density per unit area. This differentiates them from other PCBs boards.
It usually has fine spaces and has minor vias and capture pads.
This is one of the fastest-growing technologies in the PCB industry. They have blind and buried vias, guaranteeing high circuitry density in comparison to other boards.
Where Can You Use HDI PCB Designs?
HDI PCB designs have a number of applications due to the fact that they provide for dense circuitry, effectively reducing the layer count.
This reduces the size of the devices, making it a preferred choice in almost all the sectors.
Section of HDI PCB
Aerospace industry-Many devices here rely on HDI PCBs. Aeroplanes are prone to fluctuating electric currents. This calls for effective heat dissipation that is found in HDI PCBs.
Some of the devices manufactured from HDI PCBs in the aerospace industry include navigation and communication devices.
Defence-Military applications have to be efficient and reliable. They also have to be convenient in terms of sizes. These qualities can only be found in HDI PCBs.
Military devices used for communication are manufactured from HDI boards. They are also used in manufacturing various devices in military jets and vehicles.
Medical Industry-There are many devices in the medical field that use these PCBs, including medical implants such as pacemakers. Medical equipment such as scanners also use these PCBs.
Consumer appliances-The use of HDI PCBs explains the complex yet small devices that are in use today. With the HDI technology, analogue phones have transformed into digital smart-phones.
This transformation has also been seen in the advancement of personal computers and laptops and smart-watches. Others are home appliances such as LED TVs.
What is the Best Material for HDI PCB Design?
There are very high stakes when selecting the appropriate dielectric material in High Density Interconnect technologies.
HDI boards come with a number of capabilities. However, you will have to ensure that you use the appropriate materials and observe the stipulated regulations.
HDI PCB Design
For your HDI board to perform effectively, you will have to get the right dielectric material. Ensure that these dielectric materials are of high quality compared to other PCBs materials.
With the desire to get high performance, this will most definitely be expensive.
·Material for HDI PCB Design
- Copper foil
This is the electric circuit for the board. It is also the signal line and an essential in grounding and heat dissipation.
- Glass cloth
This is essential for dimensional stability and enhances stiffness. It also minimizes the occurrence of warpages and CTE.
- Resin matrix
This has low water absorption rates and is highly resistant to heat. They are also tough, have very high dielectric properties and high resistance for glass transition temperatures.
Filler is heat resistant, has low water absorption and is highly stiff. It has low CTE and promotes dimensional stability.
It also minimizes the occurrence of warpage and is a good heat dissipater. These four make the best choice for HDI PCB materials.
What is HDI Stackup?
Compared to ordinary PCB, HDI boards have high circuit density per unit area.
Stacking in HDI refers to the provision of dielectric properties and resistance that separate the highly conductive layers.
Is there Maximum Thickness for HDI PCB Design?
Yes. There is a recommended thickness for an HDI PCB design. The recommended thickness is 1.80mm.
What is the Maximum Number of Layers for HDI PCB Design?
The recommended number of layers for HDI PCB design should be twelve layers.
Do HDI PCBs have Microvias?
HDI boards have both blind and buried vias. They also contain microvias. These are usually holes drilled using a laser.
They help to establish electrical connections in between multilayered.
These microvias also make it possible to miniaturize the circuit boards.
They are located in the solder pads.
Are there Special Technologies You Can Use with HDI PCBs?
HDI PCB Dimensions
Owing to the fact that HDI PCBs have a higher circuitry density, they are manufactured using special technologies. Let me take you through some of these technologies.
In any HDI PCB, you will have to provide a multilayered copper filled stack micro via structure. The line space should measure 1.2 /1.2 mil. Also, provide for 4/8 laser via capture pad size. The material options for this include high-temperature FR4 or Halogen.
First-generation microvias: You will first create routing density and reduce the layer count. This is followed by reducing the layer count and enhancing the electrical characteristics.
Second Generation Microvias: Here, you will be able to increase routing on multiple layers. This usually gives room for routing solutions and future applications. This technology gives a solid copper plate the ability to eliminate solder voiding.
Further, a thermal management solution is achieved, and current carrying capacities are improved. This technology also offers a planner surface for BGA.
Deep microvials on the other hand, offer you more dielectric material. It also incorporates small geometry features and improved impedance performance.
This technology also provides RF microvia solutions and a solid copper plate. The current carrying capacity is also improved, and so is thermal management. Again, it provides planer surface for BGA.
Deep stacked microvias: This method technology provides additional dielectric for the RF applications. It ensures that small geometrics are maintained on the multiple layers. It is also capable of improving signal integrity.
This technology further provides a solid copper plate and improved current carrying capacity and thermal management. It also provides planar surface for BGA.
What is the Difference Between Deep Microvias and Stacked Microvias?
Stacked microvias are formed when a blind microvia joins with another blind or buried microvia. The second microvia begins on the layer where the first blind microlayer ends.
Stacked micro vias
You use this where you require a blind microvia that cannot be formed through sequential lamination because it exceeds the recommended aspect ratio.
As opposed to stacked microvias, deep microvias are continuous, rather than a stackup of two other microvias.
Stacked microvias are used in PCB applications that need more than three layers. This usually boosts routing through the layers.
Are there Advanced Capabilities in HDI PCB Designs?
The microvias in HDI PCBs enable additional routing density. They also assist in the routing of fine pitch BGAs. This includes pitch devices with 0.8mm and below.
Different microvia technologies bring different benefits and capabilities that you cannot find in ordinary PCBs. This technology also reduces layer count and improves electrical features.
The second-generation microvias also make it possible to route on multiple layers. They also provide routing solutions for next-generation applications.
Normally this technology also provides a solid copper plate. This helps in preventing probable solder voiding. This also provides a solution to thermal management.
The current carrying capacity is also improved. This technology also provides planar surface for via-in-pad. They can also allow an additional layer through technology.
These capabilities are not easy to attain in normal PCBs.
- In deep microvias technology, there is provision for additional dielectric material.
- It also has small geometry features.
- The impedance performance is also improved.
- This technology also offers you RF microvia solution.
- It also offers the board solid copper plate and enhances current carrying capacity.
- It also helps in thermal management.
- This technology further provides planar surface for the BGA.
These features distinguish HDI PCBs from other boards.
What is the Difference between HDI PCB Designs and High Speed PCB Design?
HDI PCB has a high wiring density per unit area compared to other conventional PCBs. They are further characterized with finer lines and spaces.
The vias and capture pads are also smaller. They further boast of high connection pad density.
High-speed PCBs, on the other hand, refers to PCB designs in which keen interest is paid on signals.
This is achieved by impacting on the physical characteristics of the circuit board like impedance control, matching and spacing.
High speed PCB
How do you Design HDI PCB Prototype?
Before you delve into mass production of HDI PCBs, you will first need to generate a prototype. This will help to ensure that once the actual production starts, it is a sure process.
Let’s see how you design your HDI PCB prototype.
Before you start the design process, you must first choose the right PCB design software for the job. With that in place, this is how you design your HDI PCB.
The first and most important step is plan design for your HDI PCB prototype. After that, you will input your schematic and then create a component list and component libraries.
Next, enter the mechanical data, followed by setting placement rules. After that, continue as follows:
Place the componentsàsimulate high speed geometriesàAdjust sequence and placementàTest the routability and set the routing rulesàRout the boardàTest the routingsàAdd planes for PWR and GNDàCreate area fillsàBack annotate the schematicàCompare the netlistàDesign checkàCreate test pointsàGenerate MFG filesàAudit design.
Using the generated files, proceed to fabricate your HDI PCB prototype.
Are there HDI PCB Design Rules and Regulations?
HDI PCBs are special type of circuit boards designed to provide for dense circuitry and greater functionality within smaller devices.
Also, they are used in sensitive industries such as aerospace, automotive, medical and the military.
Because of the high stakes, the design of HDI PCBs must adhere to certain rules
- First, you will have to choose a via type that will minimize the complexity of the process.
- You should also be careful on the number and types of components you intend to mount onto HDI PCB. The components you use in your HDI design determine the trace widths and the locations. They also determine the types and sizes of the drill holes and the stack up.
- Also, adequate spacing between components is necessary to reduce stress. In the event that you don’t place your vias asymmetrically on the board, there is the likelihood of uneven stress. This can easily translate into warpage.
The dense spacing of the components might result in electromagnetic interference, which negatively affects the signal quality. Parasitic capacitance also affects signal quality.
You must observe the route traces to minimize integrity issues. The main benefit of an HDI PCB is that it uses smaller trace widths in the propagation of signals.
Do this in a manner that will facilitate signal integrity. You will have to use short trace lengths and consistent path impedances.
- It is also important that you use adequate ground planes and isolate the power signal.
- Go for stackup in order to reduce the costs of the materials used. The choice of via you use will impact on the stackup selection, and ultimately, the cost of manufacturing your HDI PCB.
- The type of material used, together with the number of layers, determines the number of lamination cycles. It also determines the number of drilling cycles. You have to keep your budget in mind when making these decisions.
Can High Density Interconnect (HDI) PCB Boards Enhance the Performance of Electronics?
HDI technology significantly impacts on the board capabilities.
With HDI PCBs, you are able to incorporate fine pitch components such as ball-grid array (BGA) and micro BGA. This impact on the performance of electronics manufactured from these boards.
With the use of microvias, the board sizes have been reduced significantly. This has resulted in devices that are physically smaller and weigh less.
This is in contrast to the initial PCBs, which were less complex but bigger in size.
Electronics made from HDI boards, hence, have higher speeds and better performance. The quality is also better compared to those made from ordinary boards.
What are the Standard HDI PCB Quality Standards?
HDI PCBs, like any other PCBs, have quality standards that must be observed. Unlike the ordinary PCBs, HDI PCBs are complex.
Quality Control for HDI PCB
It can never be possible to conduct a manual inspection of the microvias. Further, cross-sectioning also isn’t feasible. This calls for the use of alternative means in verifying these factors during the fabrication process.
The best way to cross-section the microvias is through a test coupon. You can use the IPC’s PCQRR program to conduct this. The standards dictate that not more than 50 defective microvias should exist among a million microvias.
Laser Drilling Quality for HDI PCB
Failure modes in the microvias are usually as a result of the compromised quality of the laser drilling.
When drilling microvias, ensure that you observe the quality criteria for the laser microvias.
You should also observe the measurement methods. It is also important that you observe the set control limits and the sample size.
Vendor Qualification for HDI PCB
As a first-timer, you will encounter challenges when identifying the best HDI fabricator for you. First, you should check on the capability of the fabricator to drill the blind vias.
The vendor should also be able to fabricate HDI boards and to test them. This will also help you in establishing the reliability of the vendor.
How do you Fabricate HDI PCB?
Fabricating HDI PCB
Step 1: Design
Before you fabricate your HDI PCB, you must ensure that it is compatible with the created layout. OrCAD is one of the most reliable software in designing HDI circuit boards.
The design should be approved before you embark on the production.
Step 2: From File to Film
HDI circuit board printing commences only after you have had the schematic files and conducted a DFM check. Use a laser printed film to image the PCB. This will help you in achieving precision and give you the fine details of the design.
The resulting product you should expect from this is a plastic sheet with a photonegative of the intended HDI PCB.
The inner layers’ conductive copper will be represented by black ink. Clear portions indicate the non-conductive material.
For the outer layers, the conductive layers will be denting copper or conductive parts. The black areas denote what you are supposed to etch away.
Every layer of the HDI PCB and the solder mask is assigned a clear or black clean sheet. For instance, in a double-layered HDI PCB, you will have four sheets.
Two layers will be for the conductive layers, while the other two will be for the solder mask.
You can then punch registration holes through every film. This will assist you in aligning the films. These holes will assist you in the imaging process.
Step 3: Printing the Inner layers: Where Will the Copper Go?
In this step, you are preparing for the actual HDI PCB. Clean and decontaminate the copper sided laminate. Ensure that no dust comes into contact with the laminate because that can lead to short-circuiting.
Onto the clean panel, add a layer of photoresist. The photoresist contains photoreactive chemicals which will harden when you expose the board to ultraviolet light.
This will help in ensuring that photofilms and the photoresist match appropriately.
You can fit the films onto the pins, which will hold them over the laminate panel.
This will enable the film and the board to receive the ultraviolet light. The UV light penetrates clear parts of the film, hardening the photoresist on the copper underneath.
The undesignated areas which ought to be hardened are protected by the black ink. This alienates them for removal.
When you are done preparing the board, you should proceed to wash it with an alkaline solution. This will remove all the unhardened photoresist.
You can then perform a pressure wash on the board to remove remnants on the surface, and then dry the board.
The board will be covered with copper in the right places
Step 4: Removing the Unwanted Copper
After removing photoresist, so that the hardened resist remains covering copper, the board moves to the next stage.
This stage involves the removal of unwanted copper. This is achieved using a copper solvent solution.
The needed copper in this process remains covered under the photoresist layer. S
ince not all copper boards are equivalent, you will have to do track spacing in the event that you are using heavier copper boards.
At this point, you can now wash off the protective layer covering the copper. This is accomplished using another solvent. The necessary copper substrate remains glittering on the PCBs surface.
Step 5: Layer Alignment and Optical Inspection
You have now cleaned all the layers. In this step, you will have to align the punches. The registration holes will help you in aligning the inner layers with the outer layers.
For accuracy and precision, you will have to use an optical punch. In the event that the layers are put together with errors, correcting such errors will be impossible.
Put the board through a round of automatic optical inspection. This will help in detecting any defects that you might have overlooked.
Step 6: Layer-up and Bond
It is in this stage that all the separate layers are brought together. Having gone through all the initial procedures successfully, you need to fuse them together.
Your outer layers fuse with the substrate.
There are two main steps involved in this process: layer up and bonding.
The outer layer is composed of fibreglass, which is usually pre-impregnated using epoxy resin. Both sides of the prepreg are covered by thin copper foil with copper trace etchings.
This is the time to sandwich them together.
You should do the bonding on a heavy steel table. This will enable you to fit the layers into the pins effectively. Ensure that everything fits aptly to avert shifting when doing the alignment.
The first thing that goes into the alignment basin is the prepreg. Then the substrate layer follows atop it before you fit the copper sheet.
Mount another prepreg layer atop the copper layer. You can then add aluminum foil and a copper press plate. At this point, you can now press the stack.
Use a bonding press computer in this process in order to achieve automation. This will ensure that the stack is heated up effectively.
After that, apply pressure to cool off the stack at a controlled rate. This paves the way for unpacking. Since all the layers are stuck together, you should unstick them.
In this process, you will be removing the straining pins and discarding the top pressure plate.
Step 7: Drill
In this step, drill holes on the stack board. You will have to do this with precision since all components will rely on them later.
In HDI drilling, the holes must have smaller diameters to achieve maximum use of the board’s space.
Depending on the devices you intend to make from the board, you can make holes with diameters smaller than 50um.
Unlike in other boards, here you will use a laser drill to achieve the small diameters.
The CO2 laser has been the most commonly used drill in HDI circuit board drilling. They are more efficient in terms of production and turnaround time.
These holes will host the vias and the microvias in your HDI board. The holes will also enable you to aptly mount the components.
Step 8: Plating and Copper Deposition
When you are done with drilling, you can move on to plating. In this process, you will be able to fuse together the layers by the use of chemical deposition.
Take the panel through the various stages of chemical baths.
This will translate into deposition of a thin layer of copper which will rest on the surface of the panel. The copper will get into the drilled holes to coat their walls
Step 9: Outer Layer Imaging
In this step, you will apply photoresist on the board. Ensure that you conduct this procedure in a sterile room in order to avert contamination.
Pass the panel through a yellow room which will enable the UV lights to impact on the photoresist.
Protect the black ink transparencies using pins which will help prevent misalignment.
In the period that the panel and the stencil are in contact, the UV rays will harden the photoresist.
You can then pass the panel through a machine that will remove the unhardened resist. Inspect the plate to ensure that the photoresist is removed as intended.
Step 10: Plating
In this stage, you return the board to the plating room. You will have to electroplate the panel. Owing to the fact that the panel had gone through copper plating baths, you should tin plate it.
This will enable you to remove all copper left on the board. With the tin plate, the panel will be able to remain with the copper cover until the next stage.
Step 11: Final Etching
In this stage, tin covers the desired copper. The remaining copper under the resist layer is removed. Use a chemical solution to accomplish this as tin protects the needed copper.
This results in the establishment of the conductive areas and connections.
Step 12: Solder Mask Application
Use an epoxy solders mask ink to sanitize the panels prior to the application of the solder mask. Now expose the board to UV lights.
Unhardened covered portions are removed at this point.
Pass the board through an oven to cure the solder mask.
Step 13: Surface Finish
Plate the panel with either gold or silver. To give it the desired surface finish.
Step 14: Silkscreen
Use an inkjet writer to specify all the required information of the board. You can then coat and cure your HDI PCB.
Step 15: Electrical Test
After completing the fabrication process, conduct electrical tests on the PCB to ascertain its functionality and consistency with the original design.
Step 16: Profiling and V-Scoring
In this stage, you will cut various HDI circuit boards from the panel. You can use either a router or a v-groove to pop the boards out of the panel. You now have your desired HDI circuit board.
What Software is Best for High Density Interconnect (HDI) PCB Design?
There are many different software options that you can use in HDI PCB design. The most recommended one is OrCAD.
What is HDI Stack Up?
This compactness of HDI PCBs can is achieved by the stacking up of layers and vias.
Blind vias, for example, have the ability to connect one exterior layer to an internal layer without going through the whole board.
Buried vias are also able to connect one or more internal layers without connecting to outer layer of the board.
HDI stack up, therefore, is the mounting of many HDI PCB layers, which are connected using copper-filled microvias.
How does Impedance Controlled PCB Compare to HDI PCB?
Controlled impedance ensures signals are propagated without distortion by moderating the trace size, position and tolerance.
These factors are optimized to attain the desired signal integrity.
HDI PCB, on the other hand, depends on its high wiring capacity, finer spaces and lines to achieve signal integrity.
This is mainly through the microvias. These features also minimize the size of the equipment.
Controlled impedance PCB
What are the HDI PCB Design Considerations?
There are three main principles that shape the HDI PCB design.
First, unlike in the conventional boards where you have through hole (TH) vias, here you will use microvias. This will increase routing density on the inner layers.
Secondly, you will have to consider a new layer stackup method. This will assist you in eliminating the through hole vias.
Thirdly, ensure that the microvias are placed in a manner that creates channels and boulevards to improve routing.
What Determines Cost of HDI PCB Design?
When designing HDI circuit boards, you have to establish the costs of different needed components.
Weigh the cost implications that additional parts would have on the general cost.
The cost is also dependent on the prices charged by HDI PCB design contractor. In most cases, the services of the best contractors will be more expensive, but it is worth it.
Another factor that affects the cost is the number and type of vias and microvias on your board. Smaller vias cost more compared to the large vias due to the precision needed in making them.
The height of the stackup will also influence the cost. The stack is informed by processes which entail costs.
The number of layers you intend to have on the board is another factor in determining the cost of production. Having more layers means higher costs.
The type of material also matters.
Fibreglass, for example, is an expensive material. With more layers, you will need more fibreglass, thus increasing the cost of production.
With more laminations, you will be increasing the cost of production.
Ensure that you minimize the trace spaces, especially around fine pitch areas to help minimize the production cost.
Always consider these factors before embarking on designing your HDI PCB.
How Do you Assemble HDI PCB?
HDI PCB assembly mostly takes similar steps as when assembling conventional PCBs.
However, due to the different design characteristics, there are quite some differences in the way these steps are executed and the methods and tools used.
The PCB assembly process takes the following steps:
Fully assembled HDI PCB
Step 1: Solder Paste Stenciling
This marks the beginning of the assembly process in HDI PCBs. Place a thin layer of a stainless steel stencil over the board.
You can then mix the solder with flux and apply on the board. When you do this, the solder will melt, and the result will be surface bonding.
A mechanical fixture will help you ensure that you apply the solder paste with precision by properly holding the HDI board and the solder stencil in place. An applicator will help you place solder paste on the predestined locations.
The parts applied with the solder paste are the parts on which the components will be mounted.
Step 2: Pick and Place
By the aid of a robotic machine, surface mount components will be mounted onto the board. These SMDs are mainly non-connector devices.
The machine used in this process relies on vacuum grip to pick and place the components.
After the solder has melted, put the HDI board on a conveyor belt to the oven.
The machine places the components in the designated places, then passes it through cooler heaters.
Normally, the melted solder cools off and solidifies, thus creating solder joints. The surface-mount devices hence get connected to the board.
Step 3: Inspection and Quality Control
When done with the soldering of surface mount components, subject the HDI board to a functionality test.
This will enable you to detect whether there are unintended connections.
There are a number of inspection methods you can employ here.
One of these methods is by conducting manual checks. This entails visual inspection over the board after the reflow process.
However, this method is not very effective when you have a large number of boards to inspect.
Automatic visual inspection (AOI) is better when handling many HDI PCBs. With the aid of high-powered cameras, you can assess the circuit boards.
The cameras are in strategic positions enabling you to have a fast and perfect and comprehensive inspection.
Another method is X-ray inspection. This is the most effective method, although it is not commonly used in this case.
It is more effective for very complex multilayered HDI PCBs. You can also view the lower layers.
The next step is testing the parts. This helps in ascertaining whether all the components are well-attached and performing effectively.
Step 4: Micro via Component Insertion
This is where you insert microvia components to help in the passing of signals between the various layers.
One of the techniques used here is manual soldering. Each microvia is assigned to a person who inserts a particular component in the microvia.
This is done in a cycle with each person specializing in a particular component. The cycle goes on until all the components are inserted.
Wave soldering is the other technique. This technique is automated and involves a number of processes.
After the components have been put on the board, you put it on a conveyor belt.
The conveyor runs the board into an oven where the bottom of the board is washed with molten solder. The pins are therefore soldered into the microvias.
This method is only suitable for a single layer HDI PCB.
Step 5: Final Inspection and Functional Test
In this step, you will be testing the functionality of the board. Put the HDI PCB under a simulation similar to the function the board will play.
In the event that there are fluctuations in the voltage signal output, this is an indication of the failure of the board.
If the board passes the test, it can be prepared for shipment and ultimate use. If it fails, you can either discard or recycle it depending on the set standards and the extent of failure.
How has Microvias and HDI Technology Changed PCB Designs?
With the invention of HDI circuit boards, there have been many changes in PCB designs.
Unlike in the past, where several conductive layers made up the circuit boards, this is no longer the case. This has been outdated by HDI technologies such as micriovias.
Let us look at some of the existing changes that have marked the HDI PCB era.
With the HDI technology, today there are alternative stack up methods owing to the use of blind and buried microvias.
Through drilled sequential lamination, you are able to wire up higher density boards without using microvias. This also helps to reduce the size of the board.
HDI technology has also brought with it staggered sequential microvia buildup. This is the most common method in the PCB industry.
Another technological influence that HDI has had on ordinary PCBs is co-laminated any-layer microvia buildup.
All these technological influences speak to one major achievement. It has led to minimization of the number of layers in a board.
Other influences include reducing the size of the board and improving conductivity.
What is the Future of HDI PCB Design Technology?
Consumers will always demand changes.
This means that technology should also change. The future looks promising for HDI PCB design technology.
Consumers should expect more complex devices in more compact sizes. This will be made possible with the ability of HDI circuit boards to incorporate components on both sides.
Via processes including via in pad and blind via technology also point towards this future.
The devices made will also be able to transmit signals faster and to minimize signal loss.
How are Non-conventional HDI PCBs Build?
There are a number of processes required in order to build HDI PCBs successfully. The required equipment include laser drills and plugging.
The required processes include laser direct imaging and sequential lamination cycles.
HDI circuit boards also have thin line, tight spacing and have tight annular rings. The specialty rings used in these PCBs are also thin.
Manufacturing this board is both costly and time-consuming.
Can HDI PCB Reduce Dense Trace Routing?
HDI PCBs reduce dense trace routing by first reducing the number of conductive layers for a PCB. This is achieved through the drilling of vias and microvias hence limiting the space required by the board.
How do HDI PCBs Aid in Faster Routing?
In HDI PCBs, we use buried and blind vias and microvias. This gives room for routing within a very small board space.
Because of this, there is stable power supplies and reduction of the distributing inductance. It further improves signal integrity in the high-speed designs.
Can HDI PCB Help in Component Relocation?
HDI circuit boards usually have fine spaces and lines. They are also endowed with minor vias and capture pads. HDI boards also have high connection pad density.
These features help in ensuring maximization of space on the board, thus hindering the relocation of components.
How will HDI PCBs Provide Room for More Component Space?
HDI boards have minor vias that enable them to have components on both sides of the board. The microvias, blind and buried vias further help in ensuring that less space is used.
This results in the creation of more room for components.
What is a Microvia Hole?
This is a blind hole. It is usually drilled on the conductor-insulator-conductor multilayer. Its function is to necessitate electrical connection through an insulator in the conductive circuits.
Microvia hole – Photo courtesy: Hemeixin
What is the Minimum Pad Size Hole on the Outer/Inner Layer?
The pad size hole should measure +0.010 over finished hole size in the case of vias. For the components holes, the pad size should measure +0.014.
This translates to .005 for the annular ring for vias and .007 for the component holes.
What is Copper Wrap?
A plated hole’s external surface copper thickness determines the thickness of the copper wrap. Copper wrap, hence, is the layer of copper that covers the external surface of the filled holes.
This translates into the reliability of the HDI PCB, which has via structures, which also relies on Planarization and surface capping.
What Type of Via Hole Plugging is Recommended?
The via holes are usually filled using hole plugging resin. This hole has to be permanently filled by thermally curable and permanent hole filling material.
Via hole plugging – Photo courtesy: PCB Universe
What is Capped Via hole?
This is the technology used in the design of via in pad owing to flatness of the surface. You will fill the holes with resin and ultimately plate it.
An extra thin copper cap is then imposed to the pad.
Why Should you Source HDI PCB Design from Venture Electronics?
With an experience spanning several years and an able team of experts, Venture Electronics makes perfect BOM for the HDI PCBs.
With this, you can then be sure that no component will be left out of the list.
Venture Electronics is also an authorized HDI circuit board components vendor.
We have the capability of manufacturing all the components necessary for your HDI PCB. Getting all your components under one roof guarantees you convenience.
At Venture Electronics, we have the most reliable turnover capabilities. We will ensure that you get your HDI PCB design within the shortest time possible.
For our overseas clients, you can be assured that we offer perfect packaging and shipping services for the circuit boards. We guarantee that they will reach you safely.
Work with us to get the best quality.
How Long will Venture Electronics take to Design HDI PCB?
Time spent on designing your HDI PCB is dependent on the details provided by you.
However, it takes an average of 10-15 days from the moment the Gerber File is confirmed to be correct.
Does Venture Electronics Provide After Sales Service for HDI PCB Sales?
At Venture Electronics, we help our customers in packaging and shipping the products.
We encourage our customers to contact us in the event that an issue arises with the board.
We promise to correct any flaw that might arise and give you an opportunity to fabricate new boards with us again.
What is Venture Electronics HDI PCB Design Capability?
At Venture Electronics, we have what it takes to drill the via regardless of the size. We are also able to pass your board through all the stages.
These include prototyping, fabrication and the recommended assembly for your HDI circuit board.
Does Venture Electronics offer HDI PCB warranty?
At Venture Electronics, we offer a warranty when we manufacture HDI PCB for you. This cover runs for a whole year.
For any HDI PCB design and fabrication, talk to us today.