From: Ed Kummel (tech_ed_at_yahoo.com)
Date: Sun Jul 11 2004 - 22:51:35 PDT
So then you'll REALLY hate the way we (my hardware
hacker pals and I) used to "unsolder" RAM chips in the
"olden days"
We used to go "dumpster diving" to recover boards that
were covered in RAM chips. 9 chips comprised a single
KB of RAM, so a board that had 36 chips on it was a
4kb card. If one card was bad, the company would toss
the entire 4kb card and pop in a new tested card. My
buddy and I would "reclaim" these cards and extract
the 36 chips from them. The big problem was that these
chips were soldered through on both sides of the
boards. Individual soldering would take hours...and we
just didn't have that kinda time! Especially if there
is a possibility that that chip is that faulty one
that caused the card to be tossed in the first place.
So, we divised a method of removing the chips in
seconds with minimal loss of possible good candidates.
It involves a propane blow torch and a kitchen ice
hammer.
One person holds the board on edge against the ground,
slightly angled with the chip facing the ground (we
put a piece of cardboard there to "cushion" the chip
when it is ejected from the card). The second person
would point the blow torch at the exposed pins and
observe the solder status (melted or solid). The first
person would watch the solder status on the reverse
side. When both sides solder status agree, the first
person would *SMACK* the card with the ice hammer
(sometimes more than once) and the chip would fly from
the card! Sometimes, due to the density of the card,
we could get two or three chips at the same time! I
built a small "go/no-go" chip testing circuit using
mini-lightbulbs (HP still held the patent on LEDs so
they were still very expensive) If all the lightbulbs
lit, then the chip was good (all the addresses
latched)
We got so good at this that we could recover every
good chip on the card (only one bad chip, indicating
that that was the reason for discarding the card)
We recovered dozens of 36 an 72 chip cards this way
and acquired so many chips, we sold them to fellow
hobbiests! Of course, we never told them how we
acquired the chips, but we never had a complaint! We
sold a single chip for $6, or a KB (9 chips) for $45.
(retail was $9/chip or $72 for 1kb) so we made some
pretty serious money...all from late night dumpster
diving and propane blow torches!
Back when your onboard RAM was labled in KBs instead
of MBs, a 16 or 32KB RAM was an impressive machine! My
favorite modification was the "Piggy-back" method of
soldering RAM chips ontop of the existing RAM chips
with the signal pin raised and jumpered to the
neighboring RAM chip and that leading to an unused
address PIN on one of the onboard controller chips.
Using a SPDT switch, you could "switch" between two
banks of 16kb memory addresses!
Ed
web/gadget guru
--- "Humphreys, David" <david.humphreys_at_honeywell.com>
wrote:
<snip>
>
> For those of you who have desoldered chip in this
> 'Radioshaft - You've got questions, we've got blank
> stares' way and
> have been 'successful' it is more down to luck than
> skill and it is very likely that chip integrity has
> been
> compromised.
> The effects are random so it is impossible to
> predict how they have been compromised but, believe
> me, they have.
>
> I understand that few people have this kind of
> equipment but that's what is needed to do the job
> correctly. Anything
> else is sub-standard.
>
> Sorry for the lecture but it is hard to just sit
> back and let folklore turn into reality. No offence
> is meant to anyone.
> I just hate to see bad methods perpetuated. Please
> feel free to use whatever method you wish to remove
> your SMD
> components. At least you now have some science to
> base your decision on.
>
> Regards,
>
> David Humphreys (PCBman)
=====
"A democracy is a sheep and two wolves deciding on what to have for lunch. Freedom is a well armed sheep contesting the results of the decision."
- Benjamin Franklin
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