> 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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