Suzanne Nachbor asked:

>A customer had a board that accidentally got left in an oven for 7 days at
>200F over the 4th of July shutdown.  This board is a multilayer board with
>IR  fused solder finish.
>
>The board was then wave soldered and the solder flaked off the pads leaving
>unsolderable copper surfaces.  Another  board from the extended bake failed
>all adhesion testing prior to solder.  Boards without the extended bake
>passed adehsion testing.  The copper surface on the extended bake boards was
>dark brown (similar to too much heat) to a white haze.
>
>They are trying to explain what happened and have looked for intermetallic
>and are planning on using auger to look for possible surface contaminants.
> Has anyone had a similar experience or insight for further evaluation?

Hypothesis:

Thick Cu6Sn5/Cu3Sn grown during heat exposure by solid phase diffusion,
with separation between the intermetallic phases. Resulting "unsolderable
copper surface" is copper/tin intermetallic.

regards,

Jerry Cupples - [log in to unmask]
Interphase Corporation
13800 Senlac Dr.
Dallas TX 75234
(214) 654-5150
(214) 654-5500 FAX


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