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Subject: Tented vias???
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Status: RO

Colleagues:

Our in house SMT assembly facility has asked that we tent our vias on 
top and 
bottom sides to aid in solder bridge reduction.  If bottom tenting is 
not 
possible becaues vias may double as test points, they ask that we still 
tent 
the top (component) side.  They use a no clean process.  

I am concerned that contaminants will be trapped in vias tented only on 
one 
side and cause premature failure down the road.  Normal via size is 
.012.  
What are your thoughts on tented vias???  One side?  Both sides?  Not 
tented 
ever?  Why???  What other problems may we encounter?

Thanks in advance for your opinions.


gary ...


Gary,

I was involved in a research project involving the long term effects of 
no-clean fluxes with Dr. Carl Tautscher and we had discovered that 
there were measurable amounts of eliphatic acid (sp?) found in the 
remaining distillate of the autoclave used in the accelerated life 
test. Although the test specimines had not exhibited severe effects, 
the presence of the substance caused some concern, as the typical test 
methods used in such proceedures actually volitalize the acid and 
distribute it in the surrounding atmosphere. 

If these things are true, then entrapment within the spaces you 
describe could cause concern. 

Carl is by far more qualified than I to discuss this with you, and he 
is an Independent Engineering Consultant:

Carl J. Tautscher
P.O. Box 204
Lynnwood, Wa. 98012
Ph: (206) 776-5190
Fx: (206) 776-2274

Regards,

Edward J. Popielarski
QTA Machine
(714) 364-6614
[log in to unmask]



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