Homebrew PCBs

On Sat, 19 Sep 2009 14:34:07 +0530, you wrote:

>Hi
>I tried to make my first PCB. It didnt work out. It was the ugliest PCB ever
>made :-(

No, that was one that I tried to make with electrical tape for resist,
many years ago.
>
>I used toner transfer method.
>
>What I learnt.
>1. Dont print the image too dark or else while using the electric press the
>whole thing will spill.
>

You want as much toner as possible, that becomes the resist.  But if
you press too hard, the image spreads.  It can also smear if the paper
moves.

>Mistakes I made
>1. The wholes I drilled were too big

I use 0.030 inch for IC pads, a #70 drill for component leads, and
drills as close to the lead size (but a bit larger) as I can get.  I
try to make sure that the pads are at least 0.050 to 0.066 inches for
home built boards, it gives me extra soldering surfaces for the parts.

I use carbide drills, but they must be used in a drill press.
 

>2. The artwork contains the outlines of the IC and though they are seperated
>in the image during toner transfer they overlapped I think because of extra
>dark copies.

I use EAGLE, and in that, you want to print the dimension (board
outline), BOTTOM, PADS and any VIAS.  That's all you need to print.
What you want is only the traces, pads, and an outline to cut the
board.  VIAS are used for double sided boards only.

The outlines, part values, and so on belong on what's called the "silk
screen layer", which is printed on the board after the board is made.

I also use the flood/fill capability of EAGLE.  I generally make a
polygon that's the size of the board, label it GND, and set the
minimum offset to 0.024 inches.  This gives me a ground plane on the
board, enough room that the traces do not short together, and cuts
etching use.  It also makes some of the circuits more stable because
of the ground plane.

If you don't use EAGLE, then that's something you'll have to look at
in your own program.  Some examples are at www.dragonworks.info in the
section on PC board building (electronics).

Harvey

>
>Questions
>1. What is the drill bit size I should use?
>2. What is the darkness level I should use?
>
>Thanks
>Regards
>Gaurav
>
>
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