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Question

Hello all together,

I'm working on a CmodS6 board for my university course right now. It'd be helpful to now something about the layer design of the Board. I assume it's a multilayer PCB, so at least 1 layer between front and back side, but can anyone tell me something more about it? e.g. common ground plate yes/no?

Hope these information are not somehow confidential or protected, then never mind my question :)

Thanks for any input!

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Hey @TireV

What your are referring to is called the stack-up and refers to the layers of non-conductive prepeg material and copper plating that makes the planes and signal traces. You are correct that as a user of the CMODS6 ( or any small form module for that matter ) has an interest in this part of the board.  The thickness of the module is not necessarily proportional to the number of layers. What is important is how much and how thick the copper on the prepeg layers is because large ground or voltage planes thermally connected to the IC substrate are the only route for thermal energy to be 'wicked' away from the active devices on the module. More layers is not necessarily better.  PC motherboard manufactures for a while there saved cost by using 2 layer boards but there is a lot of engineering and expensive tools required to do this right.

I responded to your question because it's not just a good question but a nice segue into this comment that you brought to mind.

FPGA timing performance is temperature dependent. There are industries that like miniaturized high performance modules and take extreme efforts to minimize and or manage heat. These are very expensive. These modules also [should] come with very detailed testing results that indicate what the upper level of performance the modules can handle and how much heat it dissipates into the system. When someone offers you a very cheap and tiny module you can assume that thermal issues are something to keep in  mind when you use it. It's not just performance that heat has on and FPGA but longevity as well.

I happen to very much like and uses the CMOD-A7 modules, as well as other modules from other vendors. I also keep in mind that it's possible to run into thermal problems if I expect too much out of them. But, like a speciality tool; when you need it it's nice to have around. I have no expectation that a vendor of cheap modules tests much less would specify in their advertising performance, environmental, or thermal information. If I was buying a $100K module with an FPGA then I would insist on this information.

So I offered a narrow slice of a proper reply to your question. I do encourage you to lean more... the information is out there, often as documentation on EVMs that will supply all of the PCB design information as well as the guidelines that were followed in making them.

Edited by zygot

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Consider that the FPGA on your module has 196 balls. The A7 versions have 236. You can answer your own question by thinking about how one gets all of those surface mount pads to ground, voltage and signal traces.

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