And just to add to what Werner has said, I'm always curious if anyone ever tried to estimate the cost of "tweaking" the process versus a possibly simple analysis (like cross-sectioning), which can show much more on the root cause
Regards,
Vladimir
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: Werner Engelmaier <[log in to unmask]>
Date: Wed, 4 Nov 2009 16:52:53
To: <[log in to unmask]>
Subject: Re: [TN] BGA Balls
Hi Bob,
Where do you get "were above the 217 minimum" from? 217 is the Solidus of SAC solders—you cannot solder at that temperature because the Liquidus is higher than that and alloy dependent. As an absolute minimum for reflow [unless vapor phase] you need Liquidus+20C at the slowest heating SJ at the BGA center.
'Verifying conductivity' is insufficient, since the latent defect 'head-on-pillow' will give you functionality in a test—and, yes, 5 C can make the difference.
Werner
-----Original Message-----
From: Robert Kondner <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Nov 4, 2009 11:54 am
Subject: Re: [TN] BGA Balls
Rex,
Wow, what a you know what contest. :-(
They complain about a 5C difference at 250C? Hitting 245 is good IMHO, the
absolute max looks like 260. You were above the 217 minimum.
Do you have any pin test functions like JTAG or ICT to verify joint
conductivity? Testing for manufacturing defects (MDA) using execution of
application logic is difficult at best. If they really think there are
manufacturing defects (opens, short) I would go for something to verify
connectivity parts. If there are many manufacturing defects then you have a
process problem. If there are none then it is an application problem.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Wednesday, November 04, 2009 11:36 AM
To: [log in to unmask]
Subject: [TN] BGA Balls
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
________________________________
Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset BH17 0RY
United Kingdom
Tel:
Fax:
DDI: +44 (0)1202 338200
+44 (0)1202 338202
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www.HansatechEMS.com <http://www.hansatechems.com/>
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