This problem can be seen with ENIG pad finish on BGAs even when you do not
have evidence of black pad. We experienced a situation where a heat sink
was applied to such a BGA using a pneumatic press to attach the sink. This
succeeded in popping the substrate off and left the solder balls on the PCB.
No evidence of classical black pad was found, but this problem was not seen
on any BGAs using electrolytic NiAu.
With use of SAC solder balls, the addition of Cu in the ball could be
further complicating the intermetallic phases present at the solder to Ni
interface with the formation of ternary Cu-Ni-Sn IMCs. When you commingle
this with possible interfacial Ni-Phosphide phases that may result due to
variations in P-content in the Ni, and higher reflow temps, you could
further embrittle the interface.
Best regards,
Leo
Leo M. Higgins III, Ph.D.
Vice President Technical Support Operations
ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, Texas 78704
ph 512-383-4593
fx 512-383-1590
[log in to unmask]
www.asat.com
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of WTSJ-Willis Tam
Sent: Friday, November 11, 2005 3:47 AM
To: [log in to unmask]
Subject: [TN] ??: [TN] urgent issue BGA fall out
Hi Ofer,
What did you do to fix the issue?
Thanks
Willis Tam
-----原始邮件-----
发件人: TechNet [mailto:[log in to unmask]]代表 Ofer Cohen
发送时间: 2005年11月11日 17:38
收件人: [log in to unmask]
主题: Re: [TN] urgent issue BGA fall out
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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