Jim Adney wrote:

I'm having trouble understanding this part. Since the 80/20 solder
solidifies at a higher temp than the 63/37, this means that the board
with components must cool down over a larger delta T. Wouldn't this
make any differential expansion problems worse?

And why would they heat the board to less than the melting temp? How
do you get the solder to flow down a PTH that is at a temp below where
the solder solidifies?

Thanks again,
Jim Adney


There is only a small difference in temperature, and the amount of
solder that hits the bottom of the board in a wave solder machine is
considerable, so the board's temperature is above the melting point as
the excess runs off on the trailing edge of the wave. This limits the
heat damage to the circuit board, but the faster cooling 80/20 solder
doesn't give the components much time to move before it solidifies.

Have you ever seen a full blown wave solder machine? They can have
several hundred pounds of molten solder ready to solder board after
board as they move through the machine on the conveyor system. The
boards touch each other all the way through the machine, and the solder
wave is a continuos flow of liquid solder against the bottom of the
boards.

There are cooling fans after the solder operation to reduce the
temperature as the board moves towards the exit, but it takes a while
for them to be cool enough to handle.

I had a several boards that were sent through a wave solder machine
that had a gap between boards and the top of the boards were covered
with solder. They were frequency display boards for the Drake UV-3
radio, and they were setting the machine up for the run. Some of the
boards had over a a pound of excess solder on them. One wasn't quite
that bad, and I managed to clean it up with a vacuum desoldering iron
and a regular solder iron and make it work. It wasn't really worth the
time, I just did it for the challenge.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida