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April 1999

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Subject:
From:
"Knowles, Ed" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 5 Apr 1999 15:28:32 -0600
Content-Type:
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Please don't blast me on bringing this subject up again.  I have searched
the TechNet archives and found lots of good information, and also noted that
it is a somewhat sensitive subject, having been around for 30+ years.  We
have a condition that I believe is clearly unreliable based on what I have
read.  The condition is:

- 4 lead LCCC's (leadless with castellations)
- Approximately 50 microinches of glod plating on untinned castellations.
- Untinned parts mass reflow soldered onto PWB's (parts were supplied on
tape and reel, so subcontractors did not see that they were untinned).
- Microsectioning shows a 50 to 100 microinch layer of Au/Sn intermetallic
after soldering, on top of copper/nickel surface.  Au concentration averages
about 25% in this intermetallic region.
- These assemblies will be subjected to high vibration and long term (years)
thermal cycling in actual use.

Replacement of these parts would be expensive since they are on many boards
installed in closed and tested boxes. For this reason, mangement is hoping
that testing will qualify this condition.  I hate to see the affected
program waste time and money, and am afraid they might even get a warm fuzzy
and fly these parts.

Can any of the numerous industry experts in this group give me something
concrete to present to the program such as actual experiences or obtainable
reports?  Is the above condition a no-brainer or is it not as bad as it
looks to me?  I tried getting copies of the 2 reports listed in the
J-STD-001 Handbook, but struck out.

Thank you for your time.

Ed Knowles
Lockheed Martin
[log in to unmask]

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