Here is another one of those sticky DOD questions. We have an assembly, TH,
Mil-Std-2000A, that has been through assembly, test and conformal coat
(UR). As it was being plugged into an end item the operator noticed a
solder ball. How it was seen I'll never know because I can not see it
through a four power glass. That aside, under a microscope we were able to
find 10 or 12 "tiny" solder balls. None of them reduced the conductor with
below an acceptable spacing and all of them are encapsulated in conformal
coat.

Mil-Std-2000A - Paragraph 4.21.4 "Cleanliness of printed wiring, boards and
assemblies. Printed wiring, boards and assemblies shall be free of foreign
matter. This includes grease, silicones, flux residue, dirt, chips, SOLDER
BALLS, insulation residue and wire clippings."

My sensible self tells me that since these solder balls (micro-size) do not
reduce the conductor spacing and they are encapsulated in UR that we will
do more damage reworking these than leaving them alone. I would think that
this is a process indicator and not a real defect.

The Question: Does anyone out there in TechNet land have the specmanship to
work through this or am I all wet?

Thanks in advance for all responses.

Ken Bloomquist
Sr. Principal Process Eng.
PRIMEX Aerospace Company
[log in to unmask]
(425) 881-8990 ext. 6645

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