Willis,
Welcome to the black group of the black pads. We've experienced the phenomena lately. The balls were left on the PCB, while the BGA, leg-less, fell off after the soldering. Failure analysis showed clearly balck pads phenomena on the BGA substrate.
Ofer Cohen
Siemens
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of WTSJ-Willis Tam
> Sent: Friday, November 11, 2005 08:31
> To: [log in to unmask]
> Subject: [TN] urgent issue BGA fall out
> Importance: High
>
> > Dear All,
> >
> > Recently, we found a very strange defect with the BGA IC.
> >
> > Here's our process flow: SMT---> De-panel (by V-cut machine)--->
> > Functional test--->final inspection
> >
> > We found around 10 pcs BGA falling out either at the process of
> > de-panel or functional test, defect rate less than 0.1%. The defect
> > only happened in 2 days, It's very strange, all the solder
> balls adhere to PCB. there's no
> > solder ball adhere to the BGA substrate.
> >
> > Investigations from our side:
> > 1. We have been built the same product since April 2004. no
> issue before.
> > 2. Since May 2005, the SMT process was converted to RoHS,
> BGA also has
> > been changed to green type since then, monthly output around 200K.
> > 3. The BGAs were 100% baked under 110 degreeC for 24 hrs before SMT.
> > 4. We use Loctite LF318 solder paste for SMT, the time between 70
> > degreeC to peak 245 degreec is around 250 seconds.
> > 5. The BGA only subjected to 1 time reflow (only 1 side with
> > components) 6, We have reflow fixture to support the board during
> > reflow. there's no warpage issue.
> > 7, Use Vcut machine to separate the units from a 6 up-panel PCB, no
> > extra stress to the board.
> > 8. Use pogo pin to make connection for functional test fixture, no
> > extra stress.
> >
> > Information of BGA.
> > 1. It's a solder mask defined substrate. with ENIG surface
> finishes.
> > 2. 0.8mm pitch, pad size 0.35mm.
> > 3. IC supplier apply solder ball with flux only, without
> solder paste.
> >
> > Would anybody give me some advices, what shall be the most possible
> > root cause? it's a BGA IC issue or a SMT process issue? How
> to improve?
> >
> >
> > Thanks
> > Willis Tam
> >
> >
> >
> >
> >
> >
> >
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> >
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> >
> >
>
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