[time-nuts] GPS Timing Antenna Failure - Long

Larry McDavid lmcdavid at lmceng.com
Mon May 14 11:19:18 EDT 2018

Usually, in electronics, when we hear about "whiskers" we think of tin 
whisker growth. That is surely real but not all whiskers are tin. In 
fact, some whiskers are organic rather than metallic; sometimes these 
are even somewhat semi-conducting. Such conductance paths lead to very 
confusing troubleshooting results!

Rosin solder flux, RA (Rosin Activated) or RMA (Rosin Mildly Activated), 
contains organics that aggressively clean oxides from PWB pads and metal 
leads of components. This activated flux is actually corrosive and will 
often do strange things if left in place. It used to be that this flux 
was removed by vapor-phase TCE cleaning but that chemical got into 
ground water and is no longer used for flux cleaning. But, there are 
aqueous saponifiers that can clean rosin flux effectively.

Often, the final water rinse from assembled PWB cleaning is checked for 
conductance, even high ohmic conductance, and cleaning not deemed 
complete until this test is passed. Leaving activated rosin solder flux 
on an assembled PWB is a really bad thing to do.

I don't know what was in the dark brown flux residue I found on my 
Symmetricom antenna board, but it should not have been there. It would 
not have produced tin whisker growth but it could easily have produced 
other conductance paths across the soldered coax pads. Those could have 
been RF paths and not have caused higher dc current draw by the antenna.

Again, I can't be certain the flux residue caused my GPS antenna 
failure, but I believe it very likely and that is supported by the end 
result of fixing the antenna.

Unless someone has something new to add, surely we have beaten this 
topic to death. I was only trying to help others who might have a 
similar GPS antenna failure.


On 5/13/2018 6:42 PM, Hal Murray wrote:
>>   I can't count the number of times flux and whisker  growth has caused
>> problems in circuitry and connectors.
> A whisker might explain things.  Would that also show up as over-current?
> ...

Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)

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