As I suspected, Mil-P-55110 is inactive and the latest revision was
MIL-PRF-55110F(1) dated November 1998. It was replaced by
MIL-PRF-31032/4 which is active. Again, this is a spec covering the
product and not the supplier. A glance through does not reveal the
acceptability or otherwise of so-called "white residues".

I would be suspicious of any company stating they are a 55110-qualified
board manufacturer: a) they are not with it and b) the spec covers only
the products. Do they mean that their products may be made to conform to
the spec, on request?

Brian

> Bogert wrote:
>
> 3/30/002
>
> Folks, we have an OEM who purchased FR-4 printed wiring boards from a
> MIL-P-55110 qualified board manufacturer.  The OEM wave soldered
> the PWAs using HF1189A water washable, organic flux and cleaned the
> assemblies using DI water in an in-line cleaning process.  Subsequent
> Omegameter 600 ionic cleanliness testing passed.  However, almost all
> of the solder side of the PWAs exhibited white residue.  Basically it
> looks like a water mark. While you can remove the residue
> using abrasion, such as by a pencil erasure, it comes back, even after
> several subsequent baking operatioins and additional in-line
> cleaning.  The OEM sent out samples for outside chemical evaluation
> and found minute traces of carbon.  The OEM traced the problem to
> incomplete curing of the LPI solder mask.  The white residue only
> appears on the solder side of the PWA.  There is no evidence of the
> residue on the component side of the assembly.
>
> The OEM proposes that a sample assembly be sent out for SIR testing,
> and that if the test passes, they will request us to accept the
> condition as is.  My concern is that over time in a humid environment,
> we may experience leakage current paths that cound cause operasting
> failures.  The OEM has 20 PWAs that are part of the lot.  However,
> only 6 experience this condition.  It appears that I should reject all
> PWAs that show evidence of the white residue.  I am concerned with the
> presence of carbon, even in trace amounts.  The OEM noted that almost
> everything will show traces of carbon, so not to worry.
>
> Bottom line is, is there any technical concern if the white residue is
> present?  Any input on this topic wo\uld be appreciated.

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