Terry!
Description of Your problem is not clear enough ,especially desciption of
pre-cleaning.At what stage of production this pre-cleaning is applied ? Are
You completly sure ,that Your voids are not from electroless stage ?Try to
run electrical test before tin stripping,this may give You some idea if
really the voids are result of passivation in copper pattern plating.If it
is due to passive surface of copper,check the following :
- PTH line : antitarnish , dryer
-precleaning line before photoresist lamination ( rinses , dryer)
-delays between lamination-exposure and exposure-developing
-check if some of Your boards with voids were re-laminated after stripping
-try to improve acid cleaning and microetch in pattern platin line .

At 20:39 16/12/96 -0800, you wrote:
>Hi. Net:
>
>Recently we have been experiencing some void holes problems
>
>Our process is following:
>
>manual medium PTH build 60 "
>primary image 
>Automated pattern plating copper and etchresist pure Sn
>Striping and Etching
>
>After striping Sn, we find plated copper very low and almost none
especially along the edge (vertical direction). then after we chemically
prepare the surface for LPI, Void comes out.
>
>It seems surface have no trouble picking up Sn, but for Cu plating. 
>
>We try our best to control developing . Everything not too bad except temp
and pressure a little low. Surface still look clean!
>
>For preclean cycle we are using methanesulfnoic chemistry, total etch rate
may be a little low < 10" (we have problem with acid soak solution which
kind functions as etch inhibitor rather promoter)
>
>For copper plating tank. Analysis and hull cell indicate everything OK.
>
>Since it random happen on different jobs with low percentage, It make quite
difficult to quickly point to one stage. Any thoughts?
>
>
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>
Szpruch Edward
Eltek Ltd - Israel
Tel  972 3 9395050
Fax 972 3 9309581
E-mail :  [log in to unmask]

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