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PCB thickness

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Hi, I have seen some FPGA boards in which they have 10 layers stackup that ends up to 1.6 mm thickness of the PCB. I don't think more than 10 layers are possible with 1.6 mm thickness. However, for bigger FPGA PCB designs, normally 16 layers or even 22 layers is recommended if there are many peripherals and have other components with BGA packages.

What are the advantages or disadvantages of PCB thickness if we compare 2.4 mm with1.6 mm PCB thickness. 


--- Quote from: joniengr081 on September 22, 2023, 07:54:49 am ---What are the advantages or disadvantages of PCB thickness if we compare 2.4 mm with1.6 mm PCB thickness. 

--- End quote ---

You've asked a question that has no good, definitive answer, and will vary based on the specific circumstance the PCB is used in.

Taking thermal cycling as an example, theory says that a thinner board will be more reliable as the board can flex as the components shrink and grow in relation to the board itself due to thermal expansion and contraction.   However, there is a paper floating around from a couple years ago where the authors ran test boards of varying thicknesses containing various different components through thermal cycles.   The resulting data is confusing, often contradictory, and failures often seems to be more related to the component and/or solder choice than the underlying board.   Some components and solder combinations at certain cycling ranges seemed to confirm the thicker board = less reliable theory, and others seem to contradict or at least not confirm it.

On the other hand, if you look at vibration failures the theory is that a thicker board will have less failures since it is less likely to flex under vibratory loads.   You could pick any different parameter and guess whether a thicker board will do better than a thinner one or the other way around, since it's obvious that a thicker board is bigger, less flexible, heavier, and more complex - each of which is affected by outside stimulus in a different way.

My gut feeling based on everything I've seen is that there aren't a lot of places where board thickness really matters as far as reliability goes as long as you don't push it to extremes. 

For standard processes (nothing fancy), usually the min thickness for 10 layers is 1.2mm.
With 1.6mm you can get 12 layers again with relatively standard processes, possibly 14 with a custom stackup (cost +++).

You can have 10 layers in under 0.6mm if you really want: https://www.rocket-pcb.com/high-end-hdi-anylayer-mass-production-capacity-rocket-pcb

The disadvantage of 2.4mm is mostly additional size and weight. Maybe some component leads aren't designed for that board thickness.

Thicker PCB's are mechanically stronger, stiffer and heavier then thinner PCB's. When you have 6 or more layers, then the price difference is also mostly determined by the PCB size, number of copper layers and the size of the production run (Price drops a lot when you go into manufacturing for a few hundred or or a few thousand PCB's).

As far as I know, the thickness of the PCB is not an important factor at all, except when you want very thin multi layer PCB's. If the combination of the number of layers and total thickness is such that standard prepreg is too thick, then the price very likely goes up significantly.


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