On Sun, 19 Jan 2020 10:10:50 +0000, Cursitor Doom
wrote:

On Sat, 18 Jan 2020 19:35:36 -0800 (PST), wrote:


http://www.ichom.org/Overig-499982/C...HILD-Glob-Top/

The round top is an epoxy glob covering the die, which sits on the flat thick sheet material that holds the leads. 2 tone ones make this easy to see, all black ones not so much.

Ah. Ok. I have a few hundred of those but some obscure part numbers
and all PNP so are unlikely to be called into service here.

Those bring back not so fond memories. The black potting epoxy was
optically transparent to infrared light. I had a hell of a time
dealing with weird problems in the 1960's until I found the light
sensitivity problem with those transistors. It took about a year for
Fairchild to clear their inventory and screw their unsuspecting
customers by continuing to sell these devices. Eventually, they
changed over to the "PN" (TO-92) style package, which initially was
made from silicon epoxy instead of epoxy-B. Silicon epoxy shrinks
slightly at high temperatures, causing the corrosive fluxes from the
wave soldering equipment to creep up the transistor leads by capillary
action, and corrode the leads and chip. We had to x-ray the dead
parts to determine the failure mode and guess the cause. It usually
took about a month for the transistors to rot to death. I had a
difficult time getting Fairchild to understand that having *ALL* the
transistors on a PCB fail almost simultaneously after only a month was
sufficient grounds for suspecting that something might be wrong with
the parts. They eventually switched to epoxy-B, but only after again
unloading their defective inventory on unsuspecting customers. There
was also a problem with the UA2136 IF amp/detector IC, where chips
made in different Fairchild factories produced radically different
performance and stability. I took great pride in personally removing
Fairchild from the approved vendor/manufacturers list, and finding
alternate sources for about $2.5 million/year of their components.
When I mentioned this to the sales rep, he acted like he didn't care
or it wasn't important.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558