Content-Transfer-Encoding: 8bit
Message-ID: <200201231621.g0NGLk401787@galahad.joust.net>
Date: Wed, 23 Jan 2002 11:20:35 -0500
To: rsgb_lf_group@blacksheep.org
From: "Steve Dove" <dsp@hifidelity.com>
Subject: LF: Soldering down fine-pitch parts
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Greetings,

I find the best tool for sticking down fine-pitch parts is an intern.
But that's cheating, really.  There is one truly gruesome,
cringe-worthy technique that I've used when pushed, and always
successfully, to stick dsps and fpgas down.  It takes a bit of nerve.

With best eyeballs, aided or otherwise, line up the chip onto the
pads; restrain it (g-cramp etc.) such that it won't budge.  With a
normal-sized iron (no need for a really teensy tip at this point)
solder all the pins along each side in turn down onto all the pads;
the result will be a solid bar of solder along each side of the chip,
engulfing the pins.  Naturally, don't go overboard, but all the
adjacent pins will be stuck to each other as well as the pins being
stuck to their appropriate pads.  Try not to panic or cry.

The next phase is to use solder-wick (the real stuff, not coax
braid) to drain off the excess solder;  gently slide the wick in line
with the pins, not sideways 'against the grain', methodically around
the chip.  Use a magnifying glass to peer between the pins for
sneaky bridges;  wick more if you have to.

Any human attempt at laying these things down will always result
in a long period of squinting, cleaning and picking between its teeth
with a scalpel, including this,  but it is amazing how well this horrible 
method works.  Never lost a device.  Oh, except for the dsp on which 
a mold ejection dimple was more prominent than the 'pin 1' marker, 
resulting in an 80-pin part glued on 180 degrees out . . .

        Cheers,

                Steve