日本語
Hello Everyone,
I've already done quite a few small and mid-size PCBs for my hobby projects and internal prototypes, but I don't do PCB design for living. I mainly deal with embedded and mixed-signal boards (no RF, no precision analog). Thus, I am far away for being an expert :-)
I am wondering if someone can help me with understanding copper pours design strategies for high performance equipment (lab, medical, industry, 2-6 layers).
Finally the question:
I've seen that there are practically three different strategies for distributing power (mostly COM-GND) on PCBs. I am wondering why and when to use it ?
Type one:
- Usually 4-layer PCB with two internal power planes. One is for positive voltage rail(s) while the second one is common ground. Top and bottom layers do not have practically other than signal traces.
Example:
Type two:
- Multilayer board, where some voltage rails and grounds are also on top and bottom. Internal layers are mixed (planes + traces). Surprisingly, there could have been way more copper (e.g. shielding) but there is not. Typical example is a computer motherboard.
Type three:
- Top and bottom layer (plus internal layers) have a copper pour surrounding all parts (practically copies the board outline) with minimum spacing. Even under BGAs. Copper areas are connected using via stitching technique.
Even in my previous organization dealing with various electronics for industry and railway, there were two groups of engineers and professional PCB layouters with quite opposite opinions.
I don't expect a black-and-white answer but I better look forward interesting discussion.
Thank you in Advance to everyone contributing on this topic
- Comments(1)
A****min
Aug 01.2019, 17:38:42
There are all sorts of reasons and issues.
For high volume, etching copper costs money, so you want to leave as much on as possible.
You ideally want to balance the amount of copper between sides for thermal reasons to reduce warping during reflow.
You ideally want to have uniform copper density across the board for the plating process.
Adding more copper to planes ( e.g. duplicating surface & inner) costs almost nothing and will reduce impedance. This might allow the use of thinner copper (for cost, or to allow thinner traces. Surface planes may also reduce the need for vias ( cost/space), and provide better thermal performance.
Putting power/ground on the outside and signals inside helps sheilding, and can also have advantages in use of surface area to maximise vias etc.
But also a lot may simply be down to style/preference that makes little difference in practice.
