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RE: BGA soldering



Howard,

In a previous life, I had to work on and rework some BGA devices. We
found that a hot air soldering station, the kind with an arm that comes
out over the work area, worked very well for BGAs. The technique that
was used was to make sure the board area was clean of any excess solder
from previous devices and then apply a small amount of a solder paste to
each pad. This solder was meant to melt at a given temperature (below
the damage point of the BGA). To get an indication of when the device
was approaching the solder melting point, a small drop of the same paste
was placed on the top opposite corners of the BGA. When they melted the
part was approaching the correct temperature. Shortly after these
indicator dots melt, the device will be soldered to the board.
Typically, the device will tend to self-center to the pads on the board
because of the wetting action of the solder to the balls on the bottom
of the array (if it was placed within reason to begin with). This seemed
to work very well during prototyping operations and during rework
operations.

A source of parts to try this out on would be any of the hundreds of
cell phones that your friends have laying around after upgrading. Most
of these will have at least one BGA device and maybe several depending
on the manufacturer and the vintage.

You may be able to get enough heat by using a hot air gun used to shrink
the covering on model airplanes or one of the types used to peel paint
off houses. You will have to try and find one that has enough heat but
not too much. Our commercial rework station had a thermostat to control
the temperature. Try to direct the air flow directly on the BGA and not
on the surrounding components as they will of course have the solder
melted on them too.

I think that this is a valuable point no matter which method you are
going to use. After soldering the device, allow it to cool for a little
while. Moving it while the part and board are still hot will probably
cause the BGA device to shift and then you will have to start over. With
an oven, the whole board and all the components will be hot, not just
the area that the air was on using the hot air method.

BGA devices are not impossible to work with, they just take a little
more care, patients and practice.

73,
Steve
KA5YFC
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