[sdiy] Solder mask

[Magnus Danielson]

From: "jhaible" <jhaible at debitel.net>
Subject: Re: [sdiy] Solder mask
Date: Sun, 8 Dec 2002 00:34:00 +0100

> > > I scrape with the egde of a sharp X-Acto knife.  Solder mask comes
> > > off in a scrape or two.  Maybe practice on a trash board if you have
> > > never done it, for practice...
> >
> > I second this... altghout I call the knife something completely different.
> > It is usually not very hard to scrape of the mask layer,
> 
> 
> I'm using a screwdriver.
> 
> Now if you think getting to a copper trace thru the solder mask is
> difficult, you'd be surprised what else is possible on pcbs.
> At least *I* was surprised when I saw it.
> 
> While debugging a circuit on a multilayer board, I saw a guy going
> thru several layers with a dremel and making contact to one of the
> inner copper layers. (That was EMC debugging, so tracing the
> signal to a point where it would eventually come out to a surface
> layer was no good.)
> These layers are 35um of thickness - a little too deep and he would
> have gone thru it ...

Well, then you've seen nothing!

One of my very best friends here in life works on the same company as myself.
We (OK, I) onces needed to sense the output of our ASIC, a 568 pin BGA, having
the center distance between the balls separated by 1 mm. Right there in the
middle of all balls where the signal I needed, and it was only attached to
its solderpad, nothing else. This is a 10 layer 2.5 mm thick board. My friend
sat drilling through it for a day, very carefully, got through the board (it's
only a tiny hole since the neighbor copper-traces need to be intact) soldered
on a silver lead onto the ball and attached a lead to it. Nedless to say, this
thing worked straight of the top, I got very valueable debugging done and where
able to point the finger in the right direction of where the problem where
(naturally, not in MY design! ).

This guy would safely drill down to a layer and tap a signal of it, no problem.

> How would you call this - "Archeological Electronics" ?

No, rather the way you have to do things these days. Where getting into even
more crazy sizes, frequencies and signal levels every day.

Doing just audio is such a relief sometimes!

Cheers,
Magnus - a report from the fast lane...