Embedded Resistor

The use of embedded resistor PCB is gaining popularity among many applications due to its numerous advantages.

As such, getting the relevant information can be an awkward moment.

However, you don’t have to worry.

Why?

This is because in this guide you will find all the relevant information that you need concerning an embedded resistor.

Have a look.

Embedded resistor PCB

What is an Embedded Resistor?

Embedded resistor refers to a passive device in a printed circuit board that improves the performance of devices. They achieve this by transferring discrete passives from the printed wiring board surface to the PCB.

As this happens, it frees up space on the surface allowing for placement of other active components thus increasing performance.

For it to increase the performance of the PCB, it has to meet a specific tolerance and power ratings. This allows the design and manufacturing of the PCB to meet the circuit signal requirements.

Embedded resistor – Photo courtesy: Gardien

The stability of the material after subjecting it to PCB processes also affects the tolerance of an embedded resistor.

These resistors are also referred to as buried resistors. Apart from the increase in performance of the PCB, there are other benefits that these resistors offer.

Apart fem that,

We will discuss these benefits later in this guide to allow you to have an informed decision on embedded PCBs.

Benefits of Embedded Resistor PCB

As we have seen, embedded resistors offer PCBs increased performance. However, that is not the only benefit that you get from these resistors.

Embedded resistor printed circuit board

Other benefits include:

·Reliability

Embedded resistors aids in improving the reliability of PCBs by eliminating the needs of solder joints. Solder joints tend to wear off with time which affects the reliability of the PCB.

However, by embedding the resistors on your PCBs, there is an assurance of the reliability of the PCB.

·Signal routing

Embedded PCBs can improve signal routing by eliminating SMT vias. This ensures quality signal transmission on the PCB.

·Cross talk

Through the use of buried resistors PCBs, there is a reduction in cross talk and noises that is a common feature of standard PCBs.

The sound produced by regular PCBs can be disturbing while at the same affecting the performance of your application.

However, by using buried resistors, you can eliminate this.

·Elimination of discrete resistors

Discrete resistors can be robust especially when soldering on the PCBs. Not only will it consume your time but also it can affect the performance if not well soldered.

With the use of buried resistors, however, you don’t have to worry about such issues on your PCBs. Embedded resistors offer a lasting solution by reducing the risks of incorrectly soldering the discrete resistors.

·Compatible

Buried resistors are compatible with a wide range of compatibility including lead-free PCBs. You, therefore, don’t have to worry about the compatibility of your embedded PCBs

Classification of Embedded Resistor PCBs

There are several ways that you can classify an embedded resistor PCB.

Let’s examine some of the ways available for classifying embedded resistor PCB. In each section, we take a look at the various types of embedded resistor PCBs available.

Embedded resistor on PCB

Keep reading.

·Number of layers – from single layer to 32 layers

We can use the number of layers of a PCB to classify buried resistor PCB.

Under this classification, your embedded resistor PCBs can either single layers or multiple layers depending on the number of layers it has.

PCB Layers

However, the more the layers, the more complex the embedding process becomes. This is because consideration needs to be taken not to affect the structure of the PCB.

For single layer embedded PCBs, the embedding process can be simple since all you need is to drill cavities and embed the resistors.

When it comes to multiple embedded resistor PCBs, there are several ways for embedding your resistors.

Apart from cavities, you can choose to place your resistors between two layers of your PCBs.

·Single sided embedded resistor PCB

A single-sided embedded resistor PCB is a PCB with only one side having the embedded resistor.

Fabrication of such an embedded resistor PCB is easy since the only requirements are the location and quantity of the resistors.

Single sided PCB

You, however, need to ensure that you have the correct resistors before embedding them into the PCB.

Another factor to consider is the side of the PCB which will inform you of the quantity of the resistor as well as the design to use.

There is a different classification of single-sided embedded resistor PCBs.

That is, single-sided flexibly embedded resistor, single-sided rigid embedded resistor and single sided high Frequency embedded resistor.

You can also have single sided rigid flex embedded resistor PCB, and single-sided aluminum backed embedded resistor PCB.

These type of embedded resistor PCBs are common in simple devices. They include surveillance machine circuits, LED lighting circuits, digital calculators and digital cameras.

Single sided embedded resistor PCB offers several advantages. First, they are easy to design since you don’t need much materials and time to design it.

Also, this design is cheap since it consumes less material.

·Double-sided embedded resistor PCB

A double-sided embedded resistor PCB is one which both sides of the PCB have buried resistors. There are several advantages that your PCB gains by having embedded resistors on both sides.

First, is the maximum utilization of space on both sides of the board which results in better performance. Also, a double-sided embedded resistor PCB allows for the performance of multiple functions on it.

Double sided PCB

There are several ways of embedding resistors on both sides of the PCB as we shall see later in this guide. However, the critical consideration when embedding is to take care not to affect the structure of the PCB.

Double-sided embedded resistor PCBs are relatively expensive than single sided embedded resistor PCBs.

·Nature of the PCB

We can classify buried resistor PCB in terms of the nature of the PCB. Under this, we can have a rigid embedded resistor PCB, flex embedded resistor PCB and rigid-flex embedded PCB.

Flex PCBs consists of flexible plastic that allows for shaping it into different shapes and design. As such, you need to consider the material of your embedded resistors.

The material needs to be flexible for ease of embedding it on the PCB.

Flex embedded resistor PCB have a wide range of applications due to their nature. However, they are relatively expensive in designing and manufacturing them.

Flexible PCB

Rigid-flex embedded resistor PCBs refers to PCBs that are inflexible. While embedding resistors in such PCBs, you need to consider the embedding process.

Rigid flex PCB

It should not affect the components or functionality of the PCB. The rigidness of these embedded resistors, however, limits their functions.

When it comes to rigid-flex embedded PCBs, they share properties of both flexible and rigid embedded resistor PCBs. As such, they have a wide area of application.

All these embedded resistor PCBs can either be single sided or double sided which gives them an additional feature when you are using them.

BOM of Embedded Resistor PCB

For a successful design and manufacturing of an embedded resistor, you need to know the BOM requirements.

BOM refers to the Bill of Materials that your manufacturer needs when fabricating your embedded resistor PCB.

So, how do you go about finding the BOM of an embedded resistor PCB?

First, you need to identify the embedded resistor PCB that you require. This is in terms of the size, the quantity and the nature of the resistors.

BOM – Photo courtesy: RayMing

You will also have to take into consideration the PCB. Ensure all the information that you need for embedding the resistor are in the Gerber file.

Next, you will have to check on the purpose of the embedded resistor. The reason for this is to help you in getting the correct resistance value for your embedded resistor.

After that, you need to ensure that you have a plan on how you are going to design the embedded resistors on your PCB. This is vital in ensuring that you have the correct quantity of resistors that you are going to embed on the PCB.

There are three basic pieces of information that you need to consider when looking for BOM of an embedded resistor.

First is the reference designator. The reference designator refers to the location of the embedded resistors. It usually follows a naming format where you begin with the prefix “R” followed by a unique number.

The second one is the manufacturer’s part number. Your manufacturer needs to know which part to place in the location you have indicated on the resistor.

That’s the essence of the manufacturer’s part number. There will always be several embedded resistors in a PCB; as such, you have to specify which location your manufacturer will place each of these resistors.

Lastly, you have to pay attention to the quantity of the resistors when dealing with the BOM. Quantity is essential for purchasing purposes.

Confirming the quantity makes it easy for your manufacturer to fabricate your embedded resistor PCB. Your manufacturer will be in a better position to counter check the work they are doing.

Apart from these, other pieces of information are vital to BOM. They include the line items, description, hardware detail, and datasheets.

Also, you need to ensure that your BOM contains the package type for your embedded resistor as well as the board layer.

The package type is essential in ensuring that your manufacturer considers all the conditions while packaging your embedded resistor PCB. The importance of this is to minimize the damage that might occur to the buried resistor PCB.

On the other hand, the importance of the board layer is to check on how you want the embedding of your resistor to happen. This will depend on the number of layers your PCB board will have.

Multiple board layers will imply a complex embedding process for your resistor PCB as compared to a single board layer.

Remember, all this information is necessary if you are to have the right BOM for your embedded resistor PCB.

Embedded Resistor PCB Design and Fabrication

Designing and fabricating an embedded resistor is an easy process. However, for you to be successful, you need to pay attention to the particulars to avoid confusion.

A proper understanding of PCB design and fabrication will ensure you get the best printed circuit boards.

Let me take you through the steps that you can easily follow in designing and fabricating an embedded resistor PCB successfully.

1.Isolation of the resistor

The first step when fabricating an embedded resistor PCB is to isolate the resistor. An isolation mask and a layer of seed wafer are crucial at achieving this.

After that, you need to place another isolation mask on top of the first one and a seed wafer. Remember to define the contact holes through the use of a contact mask which forms contact on seed wafer.

2.Deposition of first polysilicon layer

The next step is to deposit the polysilicon layer onto the second insulating layer and its contacts. Also, in this step, doping of an impurity takes place on the layer of the first polysilicon.

3.Patterning

After the deposition, you have to pattern the layer of the first polysilicon which helps in defining the electrical element.

A second polysilicon layer is formed by deposition of an insulating layer along the electrical element.

This polysilicon layer overlies the insulating layer and the second isolating insulator.

4.Doping

The next step involves doping of impurity along the layer of the second polysilicon that connects with the handling wafer. After that, you have to polish the second layer of polysilicon which forms a mirror surface.

5.Insulating layer

In the next step, you have t deposit a layer of insulation connecting the handling wafer. Also, you have to perform a thermal process which bonds the mirror surface and the handling wafer. This happens through an insulating layer.

6.Polishing

In this step, you have to polish the seed wafer till you expose the first layer of the resistor.

7.Preparation of the board

The next step involves preparing the PCB board in readiness for the embedding process. This includes availing all the resistors and your PCB board.

8.Embedding a resistor

A PCB board starts as either a double-sided or a single sided copper layers that you need to embed a resistor into. There are two ways available for fabrication of an embedded resistor.

The first one is creating a cavity, and the other one is placing the resistors in an internal layer during the manufacturing process.

When creating a cavity, there are a few considerations that you need to consider.

First, you need to consider the method of forming a cavity. There are a few methods that you can use in forming cavity on the PCB for embedding your resistor.

You have the Integrated Module board method in which align and place the resistors inside a cavity which is routed to the core by depth routing. After that, you fill the cavity using a molding polymer which ensures chemical, electrical and mechanical compatibility with the material.

An Isotropic solder forms a reliable solder joint

Embedded water-level package (EWLP) is another form of creating a cavity through the PCB in preparation of embedding the resistors. In this method, all the cavity formation steps are done under water.

For this method to be successful, a fan-in is always a mandatory implying that the area for I/O is only available for a chip footprint size.

Embedded resistor PCB structure

Another method of creating a cavity in an embedded resistor fabrication is the Embedded chip buildup. In this method, you mount the resistors into a polyimide film.

After that, you build the other structures from there. Lastly, you have a chip in polymer where you embed the resistors into dielectric buildup layers.

This is different from the other methods in the sense that you don’t have to integrate the resistor into core layers of the PCB.

When using the other method of embedding the resistors by placing them internally, you will have to add additional layers. This ensures embedding of the resistors on the PCB.

For this to be successful, you must do it during the fabrication process.

9.Testing

Testing is an essential aspect of the fabrication process. You need to test the embedded resistor PCB to ensure it functions correctly and efficiently.

Identifying faultiness early enough will help you in rectifying and possibly replacing the faulty embedded resistor.

As we shall see later, the only way to test an embedded resistor is through the use of a multimeter gadget.

Considerations for Embedded Resistor Design

You need to out into consideration several factors before designing an embedded resistor for your PCB. These considerations are vital in ensuring that you fabricate your embedded PCB correctly.

So, what are these considerations?

·The physical layout of the embedded resistor

The physical design of an embedded resistor refers to how the resistor appears before embedding it onto a PCB. It can either be round or rectangular embedded resistor PCB.

A round embedded resistor PCB is a resistor that is round in shape. If you are to consider embedding such a resistor into a PCB, you must ensure you have enough space for that.

PCB design and layout

A flat embedded resistor is easy to embed on your PCB since it is flat in shape implying that it won’t consume much space.

The physical layout may also be in terms of the physical size of your embedded resistor. If you have a large embedded resistor, then you will have to factor that before the embedding process begins.

Similarly, if your embedded resistor is small, you have to consider that during the embedding process. This ensures that you adequately embed your

Type of material to select

There are different types of materials available for the fabrication of embedded resistors at a low cost.

However, the three main types of materials available include carbon composition, metal film and wire wound.

PCB material

Carbon composition resistors consist of either graphite paste or carbon dust. Such resistors are cheap and have a low voltage rating.

Manufacturing of these resistive element consists of mixing fine graphite or carbon dust and a non-conductive clay powder that binds the two together.

The ratio of the conductive material to the non-conductive material determines the overall value of resistivity of the mixture. The lower the ratio of the carbon, the higher the overall resistivity value.

After mixing the two, rolling of the mixture takes place to form a shape that can embed into a PCB. These shapes have wires attached to it.

The function of these wires is to offer the electrical connection needed for the resistor to function.

The only disadvantage of such a material for your embedded resistor is that they have a high tolerance. This means that it is limited when it comes to getting precise and high-value resistors.

Also, the other type of material available for embedded resistors is the metal film. They consist of a conductive metal oxide.

These resistors can be either of the carbon film, metal oxide or metal film. The manufacturing process such embedded resistors consists of deposition of pure metals like an oxide such as tin- oxide or nickel on an insulating material.

After the deposition, you use a laser to cut a spiral helix groove pattern into the film. The effect of this is that there is an increase in the conductivity of the film allowing for a higher tolerance of the resistor.

These embedded resistors have a high ohmic value than the other types of materials.

Wire-wound materials is another way of making your embedded resistors. This is the oldest form of making embedded resistors.

Its manufacturing process involves winding a thin alloy wire on an insulating material. These materials have precision values which are as high as 100kO depending on the number of turns of the alloy wire.

The advantage of this is that they can handle a high electrical current than the other types.

You need to take special care when embedding this type of resistor on your PCB to avoid disruption of the coils.

·Dielectric constant

As a measure of a material’s ability to store energy when in an electrical field, a dielectric constant is an essential consideration in designing an embedded resistor.

Dielectric constant

On average, subjecting a substance with a high dielectric constant to heavy electric fields tends to break easily.

It is therefore essential that when selecting a material for buried resistors, you should pick a material with a lower dielectric constant.

·The coefficient of Thermal Expansion

This refers to the change in the size of an embedded resistor when changes in temperature of a PCB occurs. It is a way of measuring the hardness of the embedded resistor material.

Coefficeint of thermal expansion

It is particularly important when you are considering drilling your PCB ready for the assembling part.

A good embedded resistor is one that has a high Coefficient of Thermal Expansion factor.

Embedded Resistor PCB Quality Testing and Verification

To ensure that the embedded resistor you have fabricated is working and meets all the safety standards, you have to test it.

Testing ensures that you have the correct embedded resistor that functions correctly on your PCB.

Here is how you go about testing your embedded resistor PCB

First, you will need a functioning digital multimeter to test if your resistor is functioning successfully. After that, you will have to disconnect the PCB from a power source.

Embedded resistors and capacitors – Photo courtesy: Sierra Circuits

You can achieve this by either removing the batteries if the application is using a battery or by unplugging from the mains. Wait for a while before proceeding since some applications contain voltage even after disconnecting.

If you attempt to test the embedded resistor while there is still current in the PCB may result in faulty readings.

Next is isolating your embedded resistor. You can achieve this by identifying the end terminals of the embedded resistor. Ensure that you can correctly identify these ends.

The next step involves inspecting the embedded resistor. Check if there are any damages on it by looking for blackening spots or charring around the resistor.

Such damages may be caused by having an excess flow of current. If you notice this, you need to replace the embedded resistor immediately.

After that, you need to check on the embedded resistor for its value. Most resistors have an amount that is printed or color coded.

You need to note the value of the resistor tolerance. This value indicates the variance of the printed value of the resistor since the printed value may not be the precise value.

You need to prepare the digital multimeter. This is the gadget that you will use to measure the resistance of your resistor. You need to ensure that it is fully charged and it switches on.

Once it is on, you have to set the reading on the gadget to the next higher value than that of the printed resistor value. For instance, if the printed value is 10 ohms, you have to set the value of the digital multimeter at even 50 ohms.

Now you can measure the resistance of the embedded resistor. You can achieve this by connecting the two leads of the digital multimeter to the end terminals of the embedded resistor.

Testing PCB

Since resistors lack polarity, you don’t have to match the end terminals to the leads of the digital multimeter.

When reading the value of the digital multimeter after connection, don’t forget to factor in the resistor tolerance. This will give you the accurate value of the embedded resistor.

If your embedded resistor has a correct reading, reattach it to its correct position. If the embedded resistor has a faulty reading, you have to replace it with one that is correct for ensuring you’re your PCB functions.

It is important to note if the embedded resistor has a higher reading, it might be that the resistor is open at some point. This implies that it is faulty; thus you need to replace it.

If the reading is lower than the one printed on the embedded resistor, then the resistor is shorted internally. This is also an indicator of a defective embedded resistor, and thus you should replace it.

Applications of Embedded Resistors

Several sectors utilize embedded resistors in their applications to enhance efficiency. Among the popular areas include:

Embedded resistor PCB application

·Computer industry

Advancement in technology implies that we use computers in most of our functions.

To increase performance, these computers have adopted embedded resistor technology which makes them ideal for our usage.

Embedded resistors not only increase the performance of these PCBs but they also reduce their sizes. Apart from computers, embedded resistor technology is also available in equipment such as servers, workstation, and PC cards.

·Telecommunication industry

This is yet another industry that has gone through technological advancement over the years. Not only are these devices efficient in terms of performance but they are smaller in size such that we can move around with them.

Under this category, you will find embedded resistors in devices such as ATM switching systems and Sonet Multiplexers. Also, they are present in mobile phones and their accessories, telephone boosters and cellular bay stations.

·Military

The military equipment and technology have developed over to become highly sophisticated and efficient in their deployment. To achieve this, certain equipment and devices utilize embedded resistors in their PCBs.

Such equipment and devices include satellites, the radar system, and military specified computers.

·Automotive and aerospace industry

Another common area where embedded resistors are of main influence is in the automotive industry. You will find embedded resistors in such devices like the GPS, audio system, and tire pressure monitoring system.

In the aerospace industry, you will find embedded in devices such as supercomputers and also the aircraft control system.

·Simple electronics

There are some devices that e use in our daily lives that benefit from having embedded resistors in their PCBs. Such devices include heater elements, home theaters, and television sets.

Conclusion

Embedded resistors offer the opportunity of increasing the performance of your PCB while reducing their size.

However, for embedded resistors to be effective, they must meet the recognized standards as well as pass the functionality test. To avoid instances where this fails, you need to engage a qualified manufacturer.

If you are looking for a manufacturer who will offer you quality embedded resistor PCBs for your application, then you are at the right place.

Contact us today for quality and reliable embedded resistor PCBs.