Ask Me Anything about Power Distribution

Are you looking to deepen your understanding of power distribution in PCB design? Do you have burning questions about best practices, troubleshooting, or the latest advancements in the field? If so, we have an exciting opportunity for you!

Post your power distribution questions below before June 5th and our experts @steve.carney, @allank, and @atar.mittal will get you the answers!

What are your standard copper thickness options, and can you support thicker copper layers if required?

What is your recommendation in terms of using Embedded Capacitance Material (ECM) to separate a pair of power and ground layers in the PCB stackup? Will the very thin layer thickness and high dielectric constant really result in a significant benefit to reduce the number of discrete bypass and bulk capacitors in the PCB assembly?

Do you have a tool to calculate and verify the current carrying capacity of power traces and planes?

I think it’s a great idea. A typical value might be 10nF per square inch. The dielectric itself is only 0.47 mils thick. I haven’t been able to try it myself, but it sounds like a pretty good bang for your buck.

Yes, We have this tool which can help you calculate Trace Width, Current Capacity Temperature Rise.

(Always request for the stackup from Manufacturer)
The standard copper thickness options for PCBs typically include the following:

1 oz/ft² (35 µm or 1.4 mils)
2 oz/ft² (70 µm or 2.8 mils)
0.5 oz/ft² (17.5 µm or 0.7 mils)

Applications that demand higher current-carrying capacity or improved thermal management. Thicker copper options include:

3 oz/ft² (105 µm or 4.2 mils)
4 oz/ft² (140 µm or 5.6 mils)
greater then 4 oz/ft² (To Be Discuss)

for Higher oz copper you need to discuss with Fabrication team before you proceed,
They will give you stackup as per your need and requirement

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What materials do you recommend for high power applications? Trying to ensure low loss and high thermal conductivity.

Maybe @michael.gay can take this one?

The first thing you need to consider is the stack up regardless of material chosen. E-glass fibers are not the greatest insulator. Why? The plated fiber ends at the PTH or between biased inner layer copper features and a PTH reduce the CAF resistance of the composite. How? Two reasons: The first is what are called hollow filaments. These are microscopic capillaries in the individual glass fibers that make up the yarn of the woven fabric. These create a pre-existing pathway that will result in a CAF failure, usually an infantile failure. The second is a failure along the fiber to resin boundary. The quality of the silane coating on the glass that bonds the resin to the glass fiber is not perfect and there is free space in between the bonds where tiny H2O and Copper ions can easily pass. A poor bond will open that pathway and a good quality bond or wet out with a good quality silane will close down the pathway.

For any inner layer regardless of the copper weight, Isola suggest a minimum “butter coat” of at least 0.2 mils of resin between the glass and the copper foil. Resin has a much higher dielectric strength that glass. Resin ~3000-4000 V/mil, E-Glass fiber 262 V/mil. A volumetric calculation in the critical area should be performed to assure there will be enough resin between high voltage bias to prevent z-axis failures.

Another failure mechanism is contamination. These can be derived from all kinds of sources: paper fibers, clean room suit fibers, human hair, burnt resin, metal process particles, etc. The thinner the dielectric, the more critical the need for a clean room system with Hepa air handling filtration and clean room protocols.

The next factor is the resin system itself. Some resin systems are simply better at preventing CAF formation. These are newer third and fourth generation lead free compatible materials such as Isola IS550H and IS580G. Both products have been tested extensively at high voltage and are in applications up to 15k Volts. These resin systems have optimized silane treatments on the glass and a resin system design with CAF resistance fillers and high strength polymers. These resin systems are used in harsh environments such as automotive and space applications and high thermal cycling applications for chip testing (BIB).

The new generation of materials are not designed with high thermal conductivity. They are higher than typical FR-4 and may offer about 2x better heat dissipation. You will need an expensive ceramic material or copper coins or pallets if you need extensive heat management. However, these materials are typically halogen free and are designed with high Td values and will handle the higher heat of high current applications.

The final factor is spacing. These are going to be resin system specific, and it is advisable to speak to a materials expert and explore the testing the laminate supplier or your fabricator have performed to determine which will meet your specific design requirements. Look into the testing that supports spacing recommendations so that you can have confidence that your design will function without failures.

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Thanks, Michael!

Thank you so much for the detailed answer.