bigmessowires wrote:One problem is that I'm pretty sure Seeed only does rectangular boards for the price they offer-- that's part of why it's so cheap.
Their description implies that they accommodate slots:
Minimum slot 1mm*1mm
In other words, larger slots are okay, but no really long slots are allowed. The little notches needed by a SIMM should be fine.
bigmessowires wrote:Your layout looks pretty good to me. I wouldn't sweat the capacitor placement too much-- closer to the power pins is better, but it'll probably still work fine even if they're further out.
Use really thick traces for the capacitors. One thing you can do is put something like a 39 mil via on end of the Vdd and Vcc pins and put the capacitors on the back of the board, right next to the vias.
bigmessowires wrote:If you do get the 1.2mm thick board, then I'd suggest putting contact pads on both sides, like you planned.
I don't think you should need a 4-layer board. If you have trouble fitting all the traces, try the method of routing everything on the top side horizontally and bottom side vertically, with no diagonal traces.
I agree. Two layers should work fine. My Mac IIfx SIMMs are two layers and they work.
If you look at this image, between the first and second chips from the left, you'll see a bypass cap connected with relatively long thick traces. Also, note the copper fill around the edges of the board.
In the following picture, you can see the bypass cap for the other memory chip near the center of the board. Again, note the fill around the edges and sometimes near the middle of the board. I filled Vcc on the front of the SIMMs and Vdd on the back.
Same thing, but different model, and slightly cleaner layout, because there was more repetition: