DIY Surface Mount Soldering

[David Halliday (Volt Computer)]

I forget the brand name but there is a very clever solder out there for
desoldering SMD parts.  It has a lot better "wetting" ability than standard
solder but has almost zero mechanical strength.  

You reflow this solder onto the pins, it displaces the old solder and then
you can pick the part off the board with ease.

I ran into this in one of Don lancaster's columns - www.tinaja.com



-----Original Message-----
From: Michael B. Irwin [mailto:mirwin1 at istar.ca]
Sent: Sunday, January 10, 1999 11:02 AM
To: irish at eskimo.com
Cc: DIY
Subject: DIY Surface Mount Soldering


It is possible to solder tiny SMD parts using ordinary  equipment if you
have a steady hand, good eyes, a magnifier and patience. I use a cheap
Radio Shack 15 watt soldering iron. File down the (interchangeable) tip
to a needle point and use fine gauge wire solder. Align the chip on the
PCB (with the help of a magnifier) and hold it in place by soldering a
pin at each corner. I have soldered (and replaced) 100-pin QFP (flat
pack) microcontrollers on many occasions using these tools. When solder
bridges occur between pins (as FREQUENTLY happens) use a fine-braid
solder wick to remove the excess solder. The remaining solder will be
enough to secure the pin to the pad.

To remove a QFP a special tool that heats up all pins at once is best.
Otherwise use a very sharp knife to gently cut the pins off each side
to remove a defective chip, and desolder the remains of each pin. The
biggest risk here is peeling the tiny pads off the PCB. Adapters are
available for a number of  many-pin flat packs which have sockets for
the chip and PCB pads or wire-wrap pins for connecting to a main board.
By the way, most DSP evaluation boards have connectors to bring out
control and data lines for interfacing to a larger system. The
difficult-to-do soldering has already been done for you on the board.