Hello, I’ve come across FPGA boards with a 10-layer stack-up resulting in a 1.6 mm thickness. I understand that accommodating more than 10 layers within a 1.6 mm thickness might be challenging. However, for larger FPGA PCB designs, it’s often recommended to opt for 16 or even 22 layers, especially when dealing with numerous peripherals and components with BGA packages. What are the benefits and drawbacks of PCB thickness when comparing 2.4 mm with 1.6 mm?
Well, the biggest benefit of going to 16 layers and a thicker board would be in easier layout resulting in better performance most likely. The biggest drawback is higher cost.
Other benefits include much more likely to be able update the design and spin a new board. More layers might mean the board outline is smaller (e.g. 5” x 10” instead of 6” x 10”). A roomier board is also easier to test or repair. Other drawbacks include more difficult layout, greater weight, and the risk a thicker board might not fit the existing mounting arrangement.
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PCBs can be fabricated into any thickness unless a standard thickness is of importance to your assembly. This can be helpful when thickess is of less concern and total layers might not be known.
Keep in mind that as you increase PCB thickness, that influences other aspects of the design. If using TH vias, those become longer and more difficult to plate (think aspect ratio). Depending on the FPGA pitch, you might need to advance to more complex routing methods like micro vias, or blind, buried vias.
Generally it is best to minimize layer count when practical. Just be aware that adding layers increases fabrication difficulties. Only you can make those decisions since you know your design requirements. If you are unsure, it is best to have a detailed discussion with the fabricator so you can minimize unexpected issues later. Before having a discussion, try to estimate layer requirements and density concerns so they can be evaluated.
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Thanks Allan and Timothy. I called the fab house and they pretty much agreed with what you said. They also reduced the number of layers. Let’s see how that turns out.
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