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47uf decoupling caps?!

Y

YD

Jan 1, 1970
0
Problem with multilayer boards is two fold:
1. the software I use can only do two layers, unless I want to buy the
full version (currently using free version of Cadsoft's Eagle)
2. multilayer boards are quite expensive. I currently get my boards
through advanced pcb with their student $33 each special program - $33
+ shipping for a 2 layer board with 5 day turn around. I expect cost
for a 4 or 6 layer board would be at least a couple hundred dollars.


Look up Kicad in the yahoo groups. It's free and a lot more active
than FreePCB, which I looked at about a year ago and gave up after
finding Kicad.

- YD.
 
J

Jeff L

Jan 1, 1970
0
rickman said:
Yes, good point, but that uses up a lot of space on the board and tells
you nothing about the thickness of the copper and spacing of the
stackup. There are any number of problems that can happen in
manufacturing. Finding out when the assembled boards dont work is far
too late.

Does anyone know the source of the concern with exposed copper on PCBs?

It can short out to stuff touching the edge such as the chassis,
screwdriver, etc. I suppose burrs and nicks could also cause shorts. A
bridge could also form during HASL finishing. Exposed active copper in a
screw hole is a bad thing......

If it's not connected to anything, then it won't cause a problem, assuming
reasonable spacing between it and active parts of the circuit.
 
R

rickman

Jan 1, 1970
0
nospam said:
They don't have to be big. They don't even have to be inside the board
outline to give the PCB manufacturer a very obvious check he got the
stackup right.

Your exposed copper doesn't have to be inside the board outline either if
you get boards supplied in a biscuit or get supplied the surrounding scrap.
I am a bit dubious about measuring thickness by looking at the edge of the
board. Have you ever done it?

I think you would have to grind or rub it down first because the routing
will burr and spread the copper. Then you need a decent measuring
microscope that you can fit a board into edge on. I suspect it would be
more practical to take a sample from outside the board which you can cut
down, clean up, and fit in a microscope.

I have not had the chance to do this yet. The instructor who taught
this has an inspection microscope just for this purpose that fits in
his toolbox. It looks like an 8 inch long loupe. I believe he said it
had a reticle so he could directly read off the thicknesses. I doubt
that there would be significant burring when the metal is embedded in
layers, but only a test would tell. A saw would cut the boards in a
motion across the thickness and could burr. The router cuts along the
length of the board and is not likely to burr. If it did, it would be
uneven and cause lumpiness in the viewable edge so it would be apparent.
 
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