Dear collegues, 
 
I have run into a problem of sporadic ' voiding ' in my through plating 
process. the problem has the following characteristics:
- is observed a few times per month
- affects all materials ( fr4, bt/epoxy, kapton, GI, teflon[s] )
- on kapton-containing builds ( i.e. rigid-flex ) , voiding takes place
predominantly
 on the kapton surfaces. Typically, all the kapton is without coverage.
- I have not (yet ) ben able to establish any correlation with time of day, 
batch maintenance or other obvious influences
- Is independent of type of desmear, plasma or permanganate, even
kombinations
have failed. Therefore,  point of my focus at the pth-line itself.
- The obvious cause would be under catalysation, so an alkaline substitute
for my 
present acid conditioner has been tried. Nice results, but the expected poor
hole wall
adhesions is just not good enough to prevent excessive hole-wall-pullaway
during HASL.
- Supplier is no help ( sorry to say.... ).
 
- Line chemistry is Shipley, Cleaner/cond 815 ( acid) , Etch 3330 (
persulfate/acid stabil. ).
Catalyst 3344 + predip 3340, Accel 19H, copper Cuposit 328 ( 'classic' low
build ), Acid strike 4 microns. 
- Water rinses are all 'fresh' tap-water. ( good quality in our part of the
world )
 
Any advice or hint in this matter is highly welcome
 
regards
 
Torben Østeraa
Printca AS
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