Steve & Darrel,
I appreciate both your inputs. Sounds like my vendor is correct in
saying 'some people do tent only one side'. Steve, I have to agree with
you about getting contamination into a 12 mil via which has been reduce
in size by solder mask. In fact, I am not so sure I can even clean a 12
mil via (0.062 thick PWB) if it didn't have solder mask tenting. (I am
using a water/saponifier in-line cleaning system.) Maybe my concern
about trapping additional contamination is not valid.
Jim Kittel
>-----Original Message-----
>From: Stephen R. Gregory [SMTP:[log in to unmask]]
>Sent: Tuesday, March 23, 1999 10:21 PM
>To: [log in to unmask]
>Subject: Re: [TN] FW: LPI Tented Vias for BGA's...Part II
>
>In a message dated 3/23/99 4:43:25 PM Pacific Standard Time,
>[log in to unmask]
>writes:
>
>> I'm not sure if either method is better then the other, but from my
>perspective, having tenting on the secondary side presented more of a risk
>then the primary side as far as providing a place for getting "stuff" trapped
>under the BGA was concerned. I suspect Steve has his perspective as well, and
>I have no data to say one way or the other, but we tent the primary side, to
>give you another datapoint.
>
>Regards......DT
>
>Hi Jim, it's me again,
>
>Thinking about what Darrel said, he may have a point. I think a lot of it may
>depend on how big the via's are. You said that the vias in question are
>.012"...that's pretty small. So even if the opening isn't completely closed
>off by the mask, it sure does make the opening smaller than .012''...how
>much
>smaller I don't know.
>
>What I'm thinking, is that when you think about the the physics of surface
>tension of the flux and solder, that's what's preventing "stuff" from getting
>in there, it can't get through openings that small.....I guess I'm thinking
>out loud trying to understand why Darrel doesn't have any problems when vias
>are open on the wave side. Maybe when I had the problems I spoke of, maybe
>the
>vias were a larger diameter...
>
>One last issue with vias open on the wave side (and this may be size related
>too...) is re-reflow of connections that have short trace lengths to a
>topside
>pad...there's a bunch of us that have seen that before...
>
>-Steve Gregory-
>
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