Albert Mok wrote:
>
> Good morning, technetters,
>
> We aer using Alpha 600SMD for detecting the ionic contamination of bare
> PCB.  All boards are D.I. rinse and dried prior for the testing.  The
> reading come out is about 10ug NaCl/sq.in.  However, when the boards sent
> to baking at 110 C for four hours and the boards are tested again, the
> reading drop to 3ug NaCl/sq. in.   We do not suspect inadequate baking at
> the first time.  We bake the boards at 150 C for 65 mins.  The solder mask
> is photoimagable solder mask.
>
> This is not a single case.  Everytime when the contamination is failed,
> then bake the boards again, the result turn to positive.  However, if we
> prolong the baking time at the first baking, it does have this result
> apparently.
>
> Do you have this experience?
>
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Albert:  In your testing, you are washing your boards.  This washing
removes the contamination that your 600 SMD is measuring.  So, each time
you wash the board you have less contamination to be measured during
your next.  Push forward.  Dave F

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