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Microcontrollers and 4 layer boards

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wuchy143

Member
Hi All,

I have always been told that whenever using any type of microcontroller it's a good idea to use at least a 4 layer board. 1. Signal, 2. GND, 3. PWR, 4. Signal. I know that this is trying to battle high frequency noise, crosstalk, EMI, and issues associated with that.

Does anyone have or know of some solid pros and cons of a 4 layer PCB compared to a 2 layer PCB? Or are the ones I mention above a pretty good summary of the two different styles of boards?
 

crutschow

Well-Known Member
Most Helpful Member
It really depends upon the number of traces, the frequency of the signals, and the processor speed. If there's room you may be able to get by with a two sided board if you use a "flooded ground" between traces on both sides of the board for common and just use thick traces for power (with good decoupling to the ground plane at all power pins).
 

BeeBop

Active Member
Hi All,

I have always been told that whenever using any type of microcontroller it's a good idea to use at least a 4 layer board. 1. Signal, 2. GND, 3. PWR, 4. Signal. I know that this is trying to battle high frequency noise, crosstalk, EMI, and issues associated with that.

Does anyone have or know of some solid pros and cons of a 4 layer PCB compared to a 2 layer PCB? Or are the ones I mention above a pretty good summary of the two different styles of boards?
While it may be good, if it were necessary, there wouldn't be the forum on microcontrollers here. :p
A double sided board is accessible; you can see if there are hairline cracks in a trace and repair them. You can fairly quickly reverse engineer a board, or part of one if it has only two layers or less. A four layer board is much more difficult and takes a lot longer, and is often not worth repairing.
I've met and repaired a lot of commercial products with a microcontroller, or microprocessor which have two sided boards. Very rarely a product with a four or six layer board comes into the shop. These often host a chip in a BGA package. Most often the repair is a board replacement.
It can be a lot harder to remove a part from a four layer board, and if you damage a plated through hole when removing a component you may have destroyed the board.
You can make double layer boards in your shop or home without a lot of expensive equipment. You need a board house to make a four layer board.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I have always been told that whenever using any type of microcontroller it's a good idea to use at least a 4 layer board. 1. Signal, 2. GND, 3. PWR, 4. Signal. I know that this is trying to battle high frequency noise, crosstalk, EMI, and issues associated with that.
I would suggest you've been misinformed - microcontrollers are VERY tolerent of layout issues, single sided boards would be perfectly fine for the vast majority of applications. Double sided tend to be used because it's easier for layout programs, there's certainly no need for four layer boards except in exceptionally unusual circumstances.
 

wuchy143

Member
I would suggest you've been misinformed - microcontrollers are VERY tolerent of layout issues, single sided boards would be perfectly fine for the vast majority of applications. Double sided tend to be used because it's easier for layout programs, there's certainly no need for four layer boards except in exceptionally unusual circumstances.
Interesting. Though, if you were in a high EMI environment where noise is making a huge effort to get onto your PCB....or if you had to be as quiet as a mouse and not conduct any noise would a 4-layer PCB be a good design consideration?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Interesting. Though, if you were in a high EMI environment where noise is making a huge effort to get onto your PCB....or if you had to be as quiet as a mouse and not conduct any noise would a 4-layer PCB be a good design consideration?
Probably not, if an environment was THAT bad, then the board would be incased in a fully screened metal box anyway - far more effective than a four layer board.

But it obviously depends on the exact circumstances.
 
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