Hi Deepak! One additional problem source to look at is the metallurgy of
the solder joints. Get yourself a couple of thermal couples and double
check that you really to reach 235C for 180 seconds - as the TechNet
community as suggested you may be too hot too long. However there is
another possibility - the thermal mass of the assembly is thieving heat and
you are not getting hot enough. There have been several cases where the
gold metallization (you don't mention what the pin metallization is)
actually inhibits wetting because low reflow temperatures or times impact
the diffusion of the gold into the solder making for poor solder wetting
characteristics. Additionally investigate the size of the solder ring
preform - it sounds like you are expecting the solder to flow quite a
distance and it appears you have a large area of solder joint to be formed.
This may also help explain the "dullness" of the solder joint - having a
minimal quantity of solder will result in a large amount of gold in the
solder joint which will affect the visual appearance. It your gold pins
have a thick gold plating you can have the same affect. Good Luck.

Dave Hillman
Rockwell Collins
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DEEPAK KURIYAN <[log in to unmask]> on 08/11/99 06:47:19 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
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Subject:  [TN] Solderability




Hello Technetters,

We are doing a job of soldering around 4500 pins into a Glass Epoxy
Multilayer PCB of size 288 x 200 mm. The pins are first push fit into the
PCB . The pins protrude on both sides of the PCB . On once side the pins
will mate with a connector, and on the other side wires are wrapped on. 1
Solder ring ( 0.9 mm dia ) is then put over each pin . The board is then
put
in a reflow over for 180 sec at 235 deg C. We find that the solder joint
are
not properly formed, and the finish is quite dull. The solder ring is
composed of 62% Tin, 2 % Silver, 34 % Lead. The solder flows out to the
other side of the PCB , but is not quite enough. We also notice
discoloration of the PCB after this cycle.

What are the issues  that we need to be looking at here, to get a better
joint with a better finish . We are completely new to this .

Appreciate some inputs and tips on doing this

With warm regards

Deepak Kuriyan
Framatome Connectors OEN

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