[sci.electronics] Surface Mounts Chips

guest@amos.ling.ucsd.edu (Stranger in Town) (06/29/89)

Thanks to all who mailed me with help on replacing a surface mount chip.  The 
hard drive seems to be working fine now.

Here's what I did:

Using an X-acto knife and a magnifying glass, I carefully cut the leads to
the old chip.  Downward strokes weren't working too well, so I tried
coming up from underneath.  This worked much better on all but the last
lead.  Since almost the entire chip was loose by the time I tried to cut
the last one, I managed to separate the pad from the board.  Fortunately,
the pad wasn't part of the second layer and it was connected to a nearby
larger pad which I could use later.

A couple people suggested "dead-bugging," that is, lying a regular IC on
its top, feet in the air, and soldering wires down to the pads.  Space was
too tight (not enough headroom) to do this, so I used an uglier but just as
functional solution.  I cut fourteen 3" lengths of wirewrap wire and
stripped a small (1/8") from each end.  After cleaning up the pad a bit
(removing the leftover legs and checking for excess solder), I quickly
soldered each wire to a pad, either using the existing solder on the pad or
placing a very small amount on the tip of the iron.  The other ends I
soldered to a DIP socket.

I reassmbled the drive with the new socket sticking out the side.  A regular
chip was plugged in and the drive powered up.  IT WORKED!  I just saved
myself about $280.

The iron I used was Radio Shack's modular type (the kind where the handle,
heat element, and tips must be bought separately) and is ungrounded.  It
was running 23 watts and I bought the special surface mount soldering tips.

Now, if I can just get the OMTI 3527 SCSI card working....  Anybody know
if a Tandon TM 364 is RLL compatible?

Barry Brown
6600hgns@ucsbuxb.bitnet     <== note the new address