I forgot to add this in my earlier response:
Whenever a part is reworked, this data should always be recorded,
always. And it should be recorded on the traveler or routing for the
assembly and be available to the customer. This breeds accountability.
In other jobs, I required a paint dot be applied to the corner of a
reworked BGA. In other plants, I required use of an indelible marker on
the side of the BGA, with each mark signifying the quantity of reworks
in that particular component location. This provided ready evidence of
the history of rework, and helps the analytically-challenged test
technician to quit telling the rework operator to change out the
component more than once.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Mike Taylor
Sent: Monday, April 17, 2006 9:44 AM
To: [log in to unmask]
Subject: Re: [LF] Tin Pest + Aging Performance--from Jennie Hwang
Hello Werner,
I posted a peripheral question about determining if a peak temperature
could be detected by looking at the microstructure of solder joints.
The answer I am getting is that intermetallic growth is both time and
temperature dependent. Thank you to Ryan Grant and others. I had hoped
to find that there was a way to show that a joint saw much higher
temperature than expected in processing, but that is the board bias. We
also practice assembly operations. In that case, show that the boards
did not see much higher temperature than expected in processing.
I fielded the question from an OEM that procures boards and assembly
services from different contractors. From a practical standpoint we
generated several questions.
1) Can you look at a board that has failed in a lead free process and
see if the board saw the same thermal experience as other boards in the
lot? By thermal analysis? By metallurgical examination?
2) Within a board, could you look at a BGA for example, near a failure,
and see if it saw more thermal experience (rework) than the surrounding
board?
The answer to all the questions is probably "yes", but do you know if an
acceptable procedure has been published that we could reference in
support of an analysis? The answers help direct where to go to find a
solution to prevent a future failure.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier
Sent: Thursday, April 13, 2006 7:46 PM
To: [log in to unmask]
Subject: Re: [LF] Tin Pest + Aging Performance--from Jennie Hwang
Hi Ryan,
And what is the point of this exercise?
Werner
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