Hello Vladimir,
There is a lot of work going on right now evaluating the impact of the
ternary IMCs. In fact some major system companies are banning the use of Ni
on pads to receive solder. This is causing a lot of work for BGA product
manufacture and second level assembly. With reflow thin Ni3Sn4 layer forms
on the Ni. Then a ((Cu(6-x)Ni(x))Sn5 layer forms due to the presence of Cu
in the SAC. The risk interface is between the two phases, which have very
different microstructures.
Going to OSP coated Cu or direct Au on Cu results in other concerns.
It appears that such an interface results in a thin Cu3Sn layer on the Cu,
and then a thick Cu6Sn5 layer forms between the Cu3Sn and the SAC solder.
In SOME cases it appear that Kirkendall voiding develops between the two
Cu-Sn IMC layers, and for other PCB lots, the voiding does not appear.
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: Vladimir Igoshev [mailto:[log in to unmask]]
Sent: Friday, November 11, 2005 12:48 PM
To: [log in to unmask]; [log in to unmask]
Subject: Re: [TN] RE urgent issue BGA fall out
Hi Leo,
Could you, please, elaborate what you mean? What you've stated sounds rather
unusual, at least from what I know. I've never heard of Cu being "a bad
element causing embrittlement" in solder joints.
Regards,
Vladimir
Sent from my Blackberry Wireless
Vladimir Igoshev, 519-888-7465 ext.5283
-----Original Message-----
From: TechNet
To: [log in to unmask]
Sent: Fri Nov 11 13:35:13 2005
Subject: [TN] RE urgent issue BGA fall out
Based upon past experience, it is not necessary for black pad to be present
for brittle failure to occur with SnPb solder balls. 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
The information contained in this electronic message is CUSTOMER/SUPPLIER
PRIVILEGED AND CONFIDENTIAL INFORMATION intended only for the use of the
individual or entity named above. If the reader of this message is not the
intended recipient, you are hereby notified that any dissemination,
distribution and copying of this communication is strictly prohibited. If
you have received this communication in error, please immediately notify the
sender by electronic mail. Thank you.
-----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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