Void is not necessarily a bad thing, the percentage of voiding is. Voids are
a naturally occurring phenomenon of the reflow process it is actually flux
escapement rather than entrapment thus leaving a void in the ball. We
actually like to see small voiding, call us crazy but we believe it may help
to halt crack propagation much like a crack from a pellet on your
windshield, when the crack hits the sphere the energy is diffused.

Unless the voids are large you are probably ok. Reflow temperature and speed
of ramping should be checked, if flux is popping could be indication of too
much heat too fast. 

We use Immersion Silver finish for all of our BGA-fine pitch boards but I
don't think finish has any effect on voids in the balls. Just my humble
opinion.
Dave
Manufacturing Engineer
Circuit Service Inc.


-----Original Message-----
From: Yannick Brisson [mailto:[log in to unmask]]
Sent: Tuesday, January 28, 2003 8:29 AM
To: [log in to unmask]
Subject: [TN] Silly Question


Hi,

   I'm just wondering if someone could answer this silly question...we have
on a board some BGA and other discretes components, when we look at the
X-Ray picture we see that we have void (flux entrapment),  We look at our
BGAs and there are no trace of void before we pass it to the oven.  Our
finnish is a Tin Lead the surface is not flat( HASL), we check our profile
and everything is perfect.  Could our void could came from the finnish? like
this is not a flat surface could we find a void in the pad?? I know this
sound silly but I really don't see where those voids could came of.

  We didn't pass a empty board on the X-ray.


Thanks You

Yannick Brisson
============================
Technicien SMT
Technician SMT
M2S Électronique
2855, Rue de Celles 
Québec, Québec
G2C 1K7
Téléphone: (418) 842-1312 Ext: 264
Télécopie: (418) 842-0123
[log in to unmask]
============================

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