LIVE Q&A: Stack-Up Design

Mark your calendars!

Participate in our next LIVE Q&A on stack-up design where you can ask us questions on:

• Our new Stack-Up Design Guide
• Layer arrangement and SI optimization
• Guidelines for manufacturing
• And much more!

Post your stack-up design questions below before July 10th and our experts @steve.carney, @allank, and @atar.mittal will get you the answers!

Download the Stack-Up Design Guide before the Q&A.

Join Zoom Meeting

Meeting ID: 861 8680 4492

Passcode: 299960

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Inviting our @Top_Members to this live Q&A. It might be happening during night time for some of you but we’d love to see as many of you there as possible!

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How do I determine the optimal number of layers for my stackup to balance SI, power distribution, and manufacturing costs?

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What is the ideal layer arrangement to achieve the best thermal management possible?

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What techniques do you use to reduce the risk of warpage and ensure mechanical stability when you have a complex stack-up?

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What materials do you recommend to customers for signal integrity and thermal management?

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For those two requirements I’d start by looking at Rogers 92ML and TC350. They perform well in those areas.

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That question is compounded by the fact that the manufacturing process probably has more influence on warpage and mechanical stability. As to the layout design it’s important to balance the layout - multiple layers of copper on one end of the board should be avoided. Choosing your materials carefully is very important. As to the mfg. end, heating up and cooling down cycles are critical to warpage control, at least for thin boards.

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We constantly get asked “What is the best…” but in fact there’s usually no answer. It’s going to depend on so many factors. Active or passive cooling? Air flow? Number of layers. Layer material. Surrounding heatsink structures. Materials used. Assuming the surface you place components on is the top, you would want a nice, heavy ground plane close by. If it’s a two layer board, you’re done. If it’s intended for four layers then adding two more heavy ground planes is good. Usually you won’t have that luxury.

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Go here: PCB Stack-Up Design | Sierra Circuits and click on “Layer Estimation”

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Is there a maximum prepeg height when designing a stackup?

For a 1.6mm thick board with 0.35mm pitch BGA, can we use mechanical drill vias in the middle BGA pads? If yes, what would be the via hole size? BGA top layer pads are 0.25mm

Questions asked during the live Q&A:

How does uVia from L1-L2 & L2-L3 and so on affect the lamination steps?

What factors affect cost the most? I heard that picking other than green solder mask, while holding the minimum dam width, saves quite a bit of pricing vs other colors. What is different about the chemistry of green?

Why do you prefer foil outer layers as opposed to core outer layers?

What is the most popular layer count for PCBs with DDR3/FPGA/EtherNet? And layer definition?

Is there any difference in microstrip RF losses versus solder mask color?

Any high level guideline or rule of thumbs to reduce parasitic capacitance and crosstalk?

Can you make green solder mask thinner than other colors to reduce RF losses?

What’s different between a “package fabrication” process vs. a “board fabrication” process in terms of pitch of microvias from L1-L2?

Is it ok to route signals on a power plane if it is really necessary?

What can be done to improve the copper/drill alignment for PCBs with printed microwave filters that are scattered across a board?

Any high level guideline or rule of thumbs to do impedance matching?

For small form-factor PCB, typically used for solder-down modules; what guidelines in the stack-up do you recommend to minimize board warping during the assembly process?

What is your recommendation to make a thin board, 16 mil thick, more stiff. It is a 2 layer board. Where would you add the stiffening layer?

Thanks a lot everyone for joining and participating! I definitely didn’t expect that many people to show up and ask all these great questions. You guys kept us busy for the whole hour, so again, thank you so much for your interest in this event! This makes us want to plan more of these…

And thanks to Roopa, our stack-up manager, Greg, one of our senior design engineers, and @steve.carney, our R&D manager and go-to fab guy. :slight_smile:

If you have more questions, please post in this thread and our experts will answer.

And one more thing: don’t forget to download the full version of our Stack-Up Design Guide here!

My clever interjections below in RED.

Very good job!


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Do I need to download something to see the clever RED interjections? I’m not seeing them in the threaded view of comments or in the video.