Homebrew PCBs

On Mon, 26 Dec 2011 09:44:59 +0100, you wrote:

<snip>
>Regarding the tedious ESD discussion, I see it as cutting corners. We
>cut corners here all the time, for example who does really bake parts
>before soldering if the moisture sensitivity level would require it?
>Why do most homebrew boards use no solder mask?
>You do always use laser cut solder paste stencils, right?
>

I don't use solder mask because I have no good way to apply it.  My
laser cutting stencil machine seems to have gone walkies, and never
returned home.  Same with my through hole plating setup.

The major problem used to be with the older CMOS and PMOS circuits,
IIRC.  When I worked for Westinghouse, they enforced anti-static
rules.  They did military work, and the QA department did have photos
of chips where the chip was damaged from an ESD discharge.


>It's all a question of risk vs. cost to avoid it (a wire strung to
>your metal table leg does not constitute proper ESD safe working
>environment). Since the consequences are minor, I see no problem with
>avoiding the cost and seeing what happens (which so far is nothing at
>all). Works fine for me and many others, your experience may vary.

Newer chips have some ESD protection built in, and AFAIK, are
certainly more robust in their resistance to casual ESD discharge
(normal handling).  This normal handling can be as simple as using
grounded soldering equipment, touching the ground on the board you're
working with, using anti-static foam, etc., things we'd consider
normal precautions.

Can you do without them?  Certainly, but you're putting more and more
strain on the inbuilt safety mechanisms, which are only so effective.
Since the environment in mid-Florida is not the same as that in
Arizona, YMMV.

I do have some blue LEDS where the manufacturer warns of ESD damage,
and that damage can be any one of early failure, reduced light output,
or outright failure.

The baking of chips for soldering is required only if you do reflow
soldering, because the entire chip will heat up.  Hand soldering does
not heat the entire chip to that extent (evident on multilead chips,
chip resistors and the like do get that hot).

Hot air desoldering is a bit more stressful, though.  It depends on
whether or not you are using a proper nozzle (assume QFP designs) for
your hot air gun to concentrate only on the leads, or one which heats
the entire chip (such as BGA).

I use the recliner arm as a workbench, at times.  The external circuit
impedances seem to be sufficient to minimize external static pickup
for most of the microprocessor circuits I build.


Harvey

>
>ST
>
>On Sun, Dec 25, 2011 at 11:24 PM, clausundercover <cclaus@...> wrote:
>> But when playing with my $5 TI launchpad I stay on my leather recliner with my laptop on one side and with the USB board hanging next to it. I would regret my convenience more by obeying the "rules" then having my board toasted once.
>>
>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>