Frank;

Be VERY VERY worried about one sided "tented" or "plugged" vias.

Our work shows high likelihood of entrapping solutions that will etch the pth
and cause opens during assembly or assembly rework.  BGA patters may be worse,
though its not clear yet why (other than statistical via density issues)

HCl, Persulfate and other chemicals can be killers -- common items in
microetches and fluxes.  OSP coated PCB's are the most likely to have
problems.    We've encountered nothing in the coating itself yet that can leach
out and affect the pth.

Best solution is not to tent or plug holes, but with small dia high aspect
ratio holes, even the best coating processes I've seen leave some percentage of
holes with coating blocking them.

This is a reliability exposure the industry is going to have to deal with in
the years to come.  The test industry is going to have to get away from vacuum
fixtures - so we don't keep getting requests to plug vias.

Jim Herard
IBM Microelectronics, Endicott
[log in to unmask]
        Frank.Hinojos @ wj.com
        06-10-97 10:00 PM
Please respond to [log in to unmask] @ internet


To: bmetcalf @ dynachem.mortonintl.com @ internet, Frank.Hinojos @ wj.com @
internet, TechNet @ ipc.org @ internet
cc:
Subject: Re: Tented Via Reliability -Reply

     I was not aware that LPI itself could pose a contamination problem.
     What can the LPI process trap that would be damaging to the via?  I am
     worried about the fluxes and all other contaminants that the "trash
     can" effect can catch during the product's life.

     Frank Hinojos
     Watkins-Johnson Co.


______________________________ Reply Separator _________________________________
Subject: Tented Via Reliability -Reply
Author:  bob metcalf <[log in to unmask]> at INTERNET
Date:    6/10/97 5:16 PM


True tented vias can only be achieved using dry film solder mask. Many
people us liquid photoimageable solder mask to "plug" vias. This is fairly
effective but not as reliable as dry film. The liquid method can lead to
entrapment of contaminants as well as not form a 100% reliable plug.
Plugging with a liquid is dependent on both the solder mask and the skill
of the people applying the mask.

Bob Metcalf
Morton Electronic Materials

>>> Frank Hinojos <[log in to unmask]> 06/10/97 04:18pm >>>
     I would like to use tented vias in my designs for the assembly
     advantages but have heard that the tented via can then act like a
     trash can which collects contaminants and therefore may cause
     reliability problems.  Is this rumor founded?  Are there studies?

     Frank Hinojos
     Watkins-Johnson Co.

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