Luo

I have experienced  similar problems on parts smaller or equal to 0603.  The
problem can be traced back to solder paste deposition as you have observed.
I believe the actual problem comes when the screen is lifted, it tends to
lift the paste up because the solder never make full contact and does not
adhere,

We have had great success with .010 holes on 0805 or larger components pads.
I read an SMTA white paper several years ago the solder can not easily wick
back thru  a .010 hole.  So I have used this technique for many years.


The solution is fill the vias,   talk to your fabricator.


Mike Reagan
EDSI




-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 25, 2004 7:06 AM
To: [EMAIL PROTECTED]
Subject: [PEDA] Does Microvia on Pad cause SMT problem?


Dear Members,

We have serveral very high density PCB with microvias on pads, the microvia
is 4 to 5 mil, recently, our SMT house tell us two components contains
microvia on pad are tombstoning after reflow sporadically, and maybe the
reason is the pad with microvia on it need more solder when printing, since
there is a hole on pad, so the stress is unblanced during reflow, thus
tombstone occured.

Does any one have more experience on this? if you use microvia on pad in
your design? I heard copper-Filled Microvias before, No holes observable
after plating, but I do not know how to do this, where can I find more
technical paper about this? Is it very expensive?

Your input is very appreciated!

Best Regards,
Luo.




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