> Given that, can you give me some idea as to why it is that some
boards seem
> to be so easy to work on (in terms of repairs etc.) where you can
unsolder
> parts, install new ones and solder them just fine, while at the
same time
> with some of the same kind of parts it seems that no matter how
careful you
> are you end up yanking the plating out of the hole, perhaps lifting
the
> trace on one side, etc. -- using the same tools and methods?
>
> I can ∗see∗ some differences between boards. I can ∗feel∗ some
differences in
> terms of being able to unsolder or to remove the component or
whatever, and
> differences in the weight of the copper, etc. But I don't have the
> experience in making boards to be able to quantify this stuff.
I mechanically etch boards and when I'm done, I peal large sections of
copy off the boards in areas.
FR4 has copper stuck on like bumper stickers. Some will outlast the
cars...
CM2 looks and acts just like FR4, but the copper peals away in large
sheets. I think I had some teflon board material when I got the
machine, that stuff pealed very easily and the boards were bright
white and relitivly slipper, and very smooth.
Fiberglass has a rough surface, so the copper has more places to grab
and hold.
The manual for the machine says to drill first, because if you etch a
pad, then drill, the drill can spin the pad off in some cases.
Anyway, from my experiance, I have learned a few things.
#1) use as large a pad as you can, really large if there will be any
mechanical forces later, like heat sinks or screw terminals or headers
or even DIP sockets where one will be removing the chips.
#2) never allow a mechanical thing to be on the same side as the pad
if you will ever pull on it. The answer to that is to put pads on
both sides and even if you do not plate connect them, solder both sides.
as for the comment about bents pins, I hate people who bend every
other pin of an IC or other component. PITA when removing. BUT.... I
have has high current melt solder, or electrolocys or whatever... and
have found components loose in the board. had they not been bent, the
part would have fallen out. so, for some boards, I would recomend
that action. Very rare though.
Dave