My first response would be that MIL-STD-2000 no longer exists.
It has been superceded for quite a while now by industry standards such
as IPC610 and ANSI-J. Those standards will state that if they do not
violate conductor spacing and are firmly attached (which conformal would
do a good job of), they are not a reject....

> -----Original Message-----
> From: Kenny Bloomquist [SMTP:[log in to unmask]]
> Sent: Wednesday, June 24, 1998 5:08 PM
> To:   [log in to unmask]
> Subject:      [TN] Mil-Std-2000A Question
>
> 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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