Could you have a plugged stencil aperture? No solder paste the solder
bump will not collapse.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Wednesday, November 04, 2009 2:11 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Balls - Found word(s) remove list in the Text body
Rex,
Have seen BGAs with balls separating from the substrate side...
Have seen the balls sitting in the trays for the devices...
My guess is that the BGA substrate has a Ni-Au surface finish...
The PCB side adhesion problems will sometime show up on the BGA
substrate side for similar reasons...
If the balls you removed have no solder wetting to the BGA substrate and
they are very smooth and light gray, I think you have a BGA substrate
problem
You can partially confirm this by having the pads of BGAs you removed
cleaned and re-tinned then reballed and reinstalled in the PCAs...
This works in most cases except when you have a bad chip...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Wednesday, November 04, 2009 8:36 AM
To: [log in to unmask]
Subject: [TN] BGA Balls - Found word(s) remove list in the Text body
We have built a batch of pcbs for a customer who supplied the pcbs. They
are 2mm thick 6 layer with 0.2mm vias and ENIG finish. None work fully,
they work intermittently at best.
The customer was suspicious that we had not reflowed the BGAs correctly.
Our under BGA temp on a similar pcb is 245C (We now have some samples to
profile correctly)
The customer is suspicious due to the comment on page 753
http://www.atmel.com/dyn/resources/prod_documents/doc6221.pdf
<http://www.atmel.com/dyn/resources/prod_documents/doc6221.pdf> where
it states a min of 250C
Close x-ray evaluation of the BGAs showed tear dropping along tracks,
uniform balls, everything looked tickety boo.
We offered to remove a BGA to see what was happening underneath.
2 corners showed a similar issue with the ball where it separated from
the BGA rather than the pcb.
The removal technique was to use a PDR IR rework station, under board
heating to bring topside pcb temp to 170C and then a lead free reflow
profile to bring the device up to reflow, manual removal.
I didn't have dye for dye and pry so thought this might show if there
was an ENIG problem.
I was surprised by the almost complete removal of ball at the device and
lack of evidence of solder.
Was this just caused by my investigation processes?
Was the ball device interface broken which prevented it from melting the
ball?
Any other clues?
Thanks
Rex
Hopefully Steve has received the images (sorry about the size!)
Rex Waygood
Technical Manager
Hansatech EMS provides value manufacturing through engineering and
quality
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