Pradeep,
It does not matter how well trained and experienced the operator is.
Whenever manual soldering is performed, it typically is done on a cold
board.
Anytime one brings a single point on a cold board up to reflow
temperatures, some of that heat will be dissipated into the board itself
at that point only.
When that happens, you have created a point that is expanding rapidly
because of the coefficient of thermal expansion (CTE).
If a single point or portion of the board is rapidly expanding, but the
rest of the cold board is not, tremendous stresses are placed on the
board itself.
The board can usually absorb some of these stresses momentarily without
any resultant damage, but if hand soldering is repeatedly performed in
the same area over and over, that portion of the board will get very
hot. When this happens the resultant expansion and stress is too great,
and the board is damaged, typically through delamination of the top
layer or two from the rest of the underlying, cooler layers. This is why
it is better to use a wave-soldering process rather than hand soldering,
as the wave-solder will pre-heat the entire board to avoid large
differences in temperature.
I believe within IPC standard 7711/7721 somewhere it recommends that if
hand soldering needs to be done, that it be done only on scattered
portions, but in an organized pattern that distributes the heat such
that one part of the board does not get too hot.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pradeep
Sent: Friday, March 17, 2006 10:27 PM
To: [log in to unmask]
Subject: [TN]
Importance: High
This is Pradeep from Micropack Limited, India, fabricators of high layer
count MLB's
Few of our customers are following hand soldering of multilayer PCB's
for both through hole components as well as SMD's. Couple of stray cases
of failure of the PTH has been reported and the analysis shows this has
happened only for hand soldered boards.
Few of my queries are
1. The separation is mostly on the adjacent layer to the outer
layers.
2. Why is that it is happening only for hand soldered boards
3. Somebody can help us with some reference articles on the
advantages and disadvantages of both hand soldering as well as machine
soldering.
4. The customer keeps telling that the soldering operator is trained
and with 'years of experience' and can not make a mistake!
He keeps soldering the the pads one by one, evenif the pads are
adjacent ones. We feel by doing so, the area is getting
heated up to higher levels which can be avoided by soldering the pads
which are not close sequentially
Rgds
Pradeep
Micropack Limited
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