On Tue, 1 Dec 1998 [log in to unmask] wrote:

> It's not possible! But it happens....
> Small RF transistors with gullwings and a 2mm circular ceramic body. And
>  a metal cover that is molded on to protect the inside where the chip
> and the bonding is (not the real hermetic version, with other
> words).When these tiny creatures are machine soldered on the boards
> something rare happens. The first sign after soldering is that the
> amplifier gain goes down. OK. What seems to happen is the following.
> When at soldering temperature (approx. 220 Celcius), the molding
> softens, the cap is slighly lifted, the bubbling flux goes in and drops
> on the chip. The temperature decreases,  the molding hardens again, and
> behold, we have a transistor with built-in flux.
>
> I'm a skeptic but my surroundings think this is what happens. If someone
> out there says 'oh, hello, just what we have all the days' so please
> tell me how you tell the semiconductor manufacturer, I dare not yet!
>

Ingemar,
  A few years back, the company I worked for used some Motorola optical
IR LED's to read encoder disks. The through hole parts were soldered in
about .020 < from the surface of the board. When the failure rate got so
bad, they decided to have Motorola do a FA on the parts. Guess what they
found? The epoxy cases were expanding just a little bit at the lead entry
point and flux was getting up inside the part. When it cooled from the solder
process, BINGO, an optic with built-in flux. <-- barrowed that from you...
Motorola basicly told the company that they were mounting the part incorrectly
and told them to read the spec on soldering. (I told them that too) To make
a long story short, I was the only one that could solder the parts in and
get good results. Not bragging, just lucky... Anyway, the company just didn't
want to change things, (that's why I left too) and they most likely still
have the same problem today...

Scott Decker
Senior PCB Designer

AKA: PadMasterson
E-Mail: [log in to unmask]
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