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Design Considerations and Material Selection for High Voltage PCB Design

For high voltage PCB designs, there is a need for precision, as well as careful selection of your choice of PCB material.

Asides from this, know your reasons for wanting a high voltage board, the component selection, procedures for quality testing, design consideration, etc.

This article focuses on high voltage PCB designs and boards. This covers everything from the basic definition and then to its design procedures. Let’s begin!

What are High Voltage PCBs?

Any printed circuit board running at a higher voltage in contrast to the normal voltage for PCBs is regarded as high voltage. Inverters, EV bards, power suppliers are all categorized here. Furthermore, there is no specific digit that makes a PCB qualify to have high voltage. However, some people define  high voltage PCBs as one with at least 100V. Note that this is not official.

When above this value, there are some design practices that you must consider. If not, the printed circuit board will either crumble or fail. Before a designer goes ahead to design a printed circuit board, he or she must understand the following terms. These include basic insulation, functional insulation, altitude, creepage distance, reinforced insulation, double insulation, supplementary insulation, conductive elements, and clearance.

Also, the designer should be able to take note of the base material of high voltage PCBs. Let’s go to the next subheading of how to choose an insulating material for your high voltage design.

Choosing a Material for your High Voltage PCB Design

Creating high voltage PCBs include some stringent conditions that you must adhere to. This is important to make sure that arcs are not formed. This makes sure that the product is reliable and safe.

This means that your high voltage design keeps working perfectly even if it ages. Now, let us consider some of the recommended high voltage materials.

FR4 Laminate

The dielectric breakdown of the FR4 laminate is high. However, in contrast to polyimide and epoxy, it features higher porosity. This is why it is susceptible to any contamination.

Its edge structure is weaker. Anytime the edge has a crack, there is a decrease in its dielectric value. Also, any adjacent electronics may also be carbonized. Note that this is happening due to high voltage or overvoltage events.

BT Epoxy

BT epoxy features strong sidewalls. This is useful for applications having planar coils. This is the best for medium-voltage circuits

Isola Laminates

This is the best due to its ability to extinguish arcs. However, they are expensive. Normally, the Isola laminates are only useful when dealing with double-sided and single-sided boards.

Also, note that when making use of these high voltage pcb materials, there are some environmental factors you should take note of.

When you make use of materials having extremely high standards for insulation, make sure that the pcb material has the ability to sustain high-power or vacuum applications. It can also withstand high voltages.

Design Considerations for High Voltage PCB Design

Before you design a high voltage PCB, there are some considerations that you should make. Let us consider them

Design Guidelines for High Voltage PCB

Consider the operating frequency

This affects the high voltage PCB design. This is because arching done at lower voltages is most likely at a high frequency. This requires good spacing formed in-between the special consideration and signal lines present at the frequency spectrum’s end point.

The DC differential can cause etching. Also, this can lead to electrochemical migration. However, due to the electrochemical migration, the layers will most likely arc.

This decreases the clearance distance and creepage of the board. Some well-known metals that contribute to this electrochemical migration include silver, tin, and in some cases, copper.

This can be reduced by not using pure silver or tin when completing the design. If tin must be used then lace it using low lead contents. This helps in controlling conductive filaments’ emergence.

Derate the Components

This is important if this design is supposed to function in high stress environments. Reduce the greatest value of voltage, current and temperature of that component.

This ensures that the product has a longer lifetime. You can calculate this by making use of the percentage rating.

Furthermore, note that risks linked with boards are due to overvoltage, which causes the board to have arcing. Make sure that derating is done to the maximum and not the average voltage. With this, the high voltage PCB design will survive even when there is overvoltage.

Choose your components

Once you are through with derating, review the high voltage components you have chosen. With high voltage, there is a chance that there is high variability concerning electrical connections found across the board.

This can also lead to field stresses in the board’s components. Voltage fluctuations may also lead to the creation of arc points and lead to the destruction of components.

Design Guidelines for Multilayer High Voltage PCBs

With respect to the spacing of the electrical conductor, boards that have a high voltage difference of 80V between the conductors must have these qualities between them.

  • There should be 0.1 mm between the internal layers
  • The uncoated external layers must have 0.6 mm in-between them
  • Also, the uncoated external layers must have about 0.6mm in-between them
  • Between the coated external layers, there should be 0.13mm in-between them

Note that these values are the minimum that these layers ought to have between them.

Heavy Copper Circuits

The manufacturing of heavy copper is usually done with copper having a weight that falls between the range of 4oz/ft2 and 20oz/ft2. Also, there are instances whereby the copper used weighs between 20 oz/ft2 and 200 oz/ft2. This is what we call extreme copper.

The simple difference between heavy copper PCB manufacturing and other high voltage printed circuit boards is etching. The techniques for plating seem to also differ considerably. It has a high speed plating and differential etching.

During the plating, the fabricator has the opportunity to increase the thickness of the copper.

Temperature Rise and Capacity for Current Carrying

The current tolerance level of a copper circuit depends on the rise in heat that can be sustained. Why is this so? The current flow and heat rise has a positive correlation.

When there is a flow of current along this trace, it results in localized heating. Conduction plays a major role in cooling the high voltage traces and then releases it into the environment.

Also, make sure that a balance exists between the cooling rate and the heating rate.

Circuit Board Survivability and Strength

There are lots of dielectric materials to select from. Moreover, if you have plans to expose the board to extreme environments then make use of exotic material. Also, making use of heavy copper circuits help in avoiding thermal failures. Plating holes to 2oz/ft2 means that there is a zero chance for failure.

Thermal Management

Heat that is released during the board’s operation has to be dissipated. Now, this dissipation must be from a source into the environment. Now, leaving the components to overheat may likely bring failure to the entire system.

When making use of a heavy copper circuit, there will be a reduction in heat loss. Heavy copper circuits make this happen by the conduction of heat away from important components.

High Voltage PCB Component Sourcing

When you are sourcing for the components of high voltage PCBs, it is very important that you develop a BOM (bill of materials). With this, you’ll get an overview of the necessary components needed for your board’s assembly.

Furthermore, the details must include the number of required parts, sizes, and where you should get them. Having a BOM that is properly spelt out, you’ll get a clear view or insight about the whole process.

Most of the time, some components are outsourced from other different manufacturers. However, to get proper guidance, this BOM is a good requirement. This helps the manufacturer to identify the needed things for the high voltage PCB design.

Also, make sure that the company you are sourcing your components from is certified, experienced, and reliable. Note that this bill of material will be used in generating the quotations. Also, when sourcing PCB components from abroad, make sure that this manufacturer has shipping capabilities.

Usually, there are fragile components. Therefore, it is important to have special shipping and packaging. Therefore, ensure that the manufacturer possesses these capabilities. Considering all these, you can be sure that the components you have outsourced will meet your demands and needs.

Sure, the PCB components type you source for has to do with the applications of the printed circuit board. Avoid going for cheap components. This is because when dealing with high voltage PCB components, you must focus on quality before any other thing.

Why should you Design PCBs for Systems of High Voltage?

First reason is that the majority of industries need printed circuit boards that have the ability to hold high voltages. These industries include high voltage applications, power generating companies, military, aerospace industry require these boards. There are cases where making use of other boards can cause a rise in arcing. This could be expensive and bring inconvenience.

Benefits of a High Voltage PCB Design

This PCB design has lots of benefits due to the involvement of heavier copper in contrast to other designs of PCBs.

  • For thermal strains, there is an enhanced endurance. Due to the presence of heavy copper, be sure that your board will easily handle thermal fluctuations.
  • There is an increase in its current-carrying capacity. This quality may not be seen in other boards.
  • Furthermore, high voltage circuit boards feature better mechanical strength. You can find this in PTH holes as well as connector sites.
  • When a higher copper weight is included on the circuitry layer of the board, there is an immense reduction in the product’s size.
  • Vias, which is heavily plated with copper, enhances the transfer of heat to the external heatsinks.

Drawbacks of a High Voltage PCB Design

High voltage PCB designs come with some drawbacks. These include:

Expensive

More materials mean that more money will have to be added to the budget. High voltage printed circuit boards need heavier copper. This increases the cost.

Consumes Time

Fabricating and assembling high voltage printed circuit boards take so much time. Why is this? This is because of the extra modification necessary. These include using heavier copper which is unlike that in other PCBs.

What are the Applications of the High Voltage PCB?

High voltage PCBs are applicable in the following fields.

Power Transformers

These are manufactured making use of high voltage printed circuit boards. You can attribute this to the ability of the board to be able to control any thermal stress.

Most times, power transformers serve as different distribution grids for different power users. It deals with many thermal fluctuations, which must be regulated.

Aerospace Applications

Also, a high voltage PCB design is useful in aerospace applications. Thermal stress, which are usually present in the other boards can lead to many system failures and have fatal outcomes.

It involves using high voltage boards when manufacturing radar systems. Also, they are useful in the manufacturing of communication accessories that are used in aerospace applications and industry. Asides from airplanes, the high voltage boards are useful in spacecraft, as well as other related space equipment.

Military Applications

This type of PCB is useful in the manufacturing of different military applications by the addition of duplicate layers. Note that the layers feature an extra 3-4 oz copper placed in parallel.

This aids in the manufacturing of systems that aid weapon control. High voltage printed circuit boards are also useful in manufacturing power supplies that are used for radar systems.

Also, the manufacturing of military power monitoring systems, battery charges, and distribution panels, is possible through the use of high voltage PCBs.

Conclusion

When manufacturing applications like power supplies, which function under a fluctuating thermal condition or conditions, then the use of high voltage printed circuit boards and conductive elements is very important. This is because they have what it takes to handle these fluctuations.

Furthermore, making use of the right manufacturing process for the board, and then to the process of high voltage pcb assembly, you are sure to have efficiency. This is why you must consider all the aspects highlighted in the article deeply.