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November 2005

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Subject:
From:
Ofer Cohen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ofer Cohen <[log in to unmask]>
Date:
Fri, 11 Nov 2005 11:37:38 +0200
Content-Type:
text/plain
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text/plain (103 lines)
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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