Electronic – Is it better to have a poor top layer copper pour or no copper at all

copperemclayoutpcb

For a few small 2 layers boards I'm doing, I'm using the top layer for parts and signals and a ground pour on the bottom layer with no or very short traces, based on comments and answers to my previous question

Since the top layer becomes too chopped-up with a lot of islands, which makes it practically useless and I'm also trying to minimize the current loop between the ICs and decoupling caps (if I leave the top layer it will connect to the caps and the ground pins separately and not in a single point), so I decided not to use a copper pour on the top layer at all for the mentioned reasons.

The problem with this approach is the manufacturing side of things, if I understand correctly FR4 material could wrap if the copper on both sides of the PCB is unequal (although I don't understand why that doesn't happen with a 4 layer board typical stack-up sig-gnd-vcc-sig), so I'm back where I started

I've been going back to this a lot doing a lot of research but still can't find a conclusive answer and I can't decide what to do.

This is an example board, the one on the right without top copper pour.
enter image description here
Update: based on your comments, I revised the board to avoid breaking the ground as much as possible, but still can't decide on the top layer though.

enter image description here

Best Answer

In general, I would say keep the top-side pour; it certainly does no harm, and it has some secondary benefits, such as less etching required and less thermal stress on the board during reflow.

You do still need to pay attention to current loops and place the vias appropriately, not just scattering them about randomly. Since the FT232R is the only active chip on the board, focus on its outputs. There are two LEDs that are powered by VUSB, and a few outputs associated with the serial port that are powered by VCC. Where do the currents flow when any of these outputs change state? Try to keep the paths as short and direct as possible.

Note in particular, the ground path for the USB connector in your non-pour example. It has to go down, cross below the chip, then come up on the right before it gets to the ground pins on the top of the chip. The top-side pour shortens this considerably. In either case, it would help if you adjusted the vias near pin 1 of the chip so that the bottom pour is continuous there.

One side point about your design: Try to avoid having three etches come together at an acute angle, like you have on your Vcc trace. Make that a right-angle tee connection.