Mike

Unfortunately pictures are not forwarded in TN. However, what you describe is that the surface metallisation of the pin is wetted by the solder but the pin itself does not alloy with the solder. This can have some reasons:

- The solder wets the surface metallisation but the underlying metal is oxidised, contaminated or it is a  metal that doesn't alloy with solder.
- The solder wets the surface but the time above liquidus is too short to allow for the diffusion which is necessary for a solder bond to form with the pin material.
- The metallisation in your case is Au. If the Au plating is thick, an intermetallic layer will form which is very brittle.  If a small force is applied to the joint a brittle fracture with a smooth surface will occur immediately
- We also had hot ruptures in a case where the PCB warped during the soldering process and some solder joints where just about to solidify. The joint was solid, but the pin was the hottest part which means that the interface pin-solder was still muddy. If in some cases the deformation was big enough the pin was halfway lifted out of the joint. It was only under the SEM that we saw the signs of a rupture which can only occur if a material is very close to ist liquidus. But that's very special I suppose.

Best regards

Guenter






EMPA
Swiss Federal Laboratories  for Materials Testing and Research
Centre for Reliability
Guenter Grossmann,  Senior Engineer

8600 Duebendorf
Switzerland

Phone: xx41 1 823 4279
Fax :     xx41 1 823 4054
mail:     [log in to unmask]

>>> [log in to unmask] 14.03.2006 12:49:26 >>>
I am currently having a soldering issue with a Samtec SMT connector.  We
are seeing cracks in the solder joints
on the inner row.  The lead of the connector is only the butt end of the
connector pin that makes contact to the PCB.
I have included some specifications:

(Embedded image moved to file: pic18467.jpg)
The lead pulls out of the solder joint very easily in the length direction.
It leaves a crater in the solder deposit.  The
solder is fully wetted to the pad and pin.  If I bend the pin parallel to
the length it comes out of the joint like the joint
is butter.  The pin is gold plated and the board surface is OSP.  I would
think that the PAD should pull up before the
solder joint fails?  Any ideas or help would be greatly appreciated.

Thank You,

Mike Forrester


PS.  Detail pictures enclosed:

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(See attached file: Samtec J1 Connector.xls)

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