"amdx" wrote in message
...
On 9/11/2012 11:42 AM, Arfa Daily wrote:
Sounds a bit like one of those late night cable programs "When Good
Snakes Go Bad" :-)

We have discussed this topic on here a number of times, and one thing
that usually comes up is how you get the stuff off. There's a switcher
that I do which has a pair of small radial electrolytics 'folded over'
and glued down on top of a whole bunch of surface mount components on
the small drive / control sub-board. Some of the components that are
under the glue run quite hot - a zener for instance - and this has a
double whammy effect on the board in that first it turns the glue brown,
which then becomes conductive, and then it also does a nice job of
conducting the heat into the caps, to ultimately **** those as well.

The glue gets right down between the pins of the PWM / driver IC amongst
other places, and is an absolute bitch to remove, without damaging
assorted gnat's-bollock sized support components in the vicinity.

Well, today, quite by accident, I discovered that my favoured flux
removal chemical - Servisol Deflux 160 aerosol - does a nice job of
softening the glue up. Not quite to the point of actually dissolving it,
but enough that it can then be fairly easily picked off with a fine
scalpel blade, and then scrubbed off with an old toothbrush, once you've
got the thick of it off.

Arfa

Seems like word would have got around about glue on PCB's.
I remember Sony having a service letter about problems caused
by glue on 3/4" Umatic VCR machines in the 70's.
"or was that the 1/2" reel to reel video recorders" :-)
Mikek


Indeed. It's been discussed on here many times over the years, and the fact
that it goes brown, and breaks down into something else that is both
conductive and apparently hygroscopic, is well known amongst service
engineers. Yet still manufacturers use it in places where it is definitely
not to be recommended, such as sources of heat and high voltage, which seem
to exacerbate the problems it causes.

Arfa