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Date: | 14 Apr 97 13:43 CDT |
Content-Type: | text/plain |
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I have heard reports from a lab technician indicating that he has seen
"rubber" solder joints on some boards we had built. The boards had an
organic coating before soldering. I saw the condition myself, but
have to admit that I am not accustomed to poking at solder joints; I
usually just observe them. In six years of surface mount experience,
I have never seen this condition, nor have I heard of it.
The condition is explained as follows:
Using a relatively blunt object (e.g. not a probe or pick), the
component lead can be moved within the solder joint without visible
fracture to that joint, and without the joint moving off the pad. The
force used is undetermined, but I would consider it relatively gentle,
less than the magnitude of force used when trying to pull a lead out
of a joint.
In some rare cases, the lead slides completely off the pad with the
joint still perfectly attached. I think this indicates a problem with
the surface finish.
In addition, some joints are very malleable; by using a blunt object,
it is easy to dent a joint without visible fracture.
My questions are:
* Has anyone else ever seen this phenomenon?
* Does anyone venture to guess the root cause, or if this might be an
illusion?
Doreen Fisher
Dell Computer Corp.
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