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April 2001

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Subject:
From:
Bob Perkins <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 9 Apr 2001 14:10:56 -0700
Content-Type:
text/plain
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text/plain (214 lines)
Hi George

Where can I get a copy of the Book?

Thanks

Bob Perkins
SMT Manufacturing Process
Automation Technician
Aimtronics - Delta


-----Original Message-----
From: Wenger, George M (George) [mailto:[log in to unmask]]
Sent: Thursday, March 29, 2001 4:52 AM
To: [log in to unmask]
Subject: Re: [TN] BGA crack- major headache


Rudolph,
After looking at your photos I'd suggest two things:
1. Read "Double Reflow: The Stress Fracture Reliability Problem of the
90's", Wenger et.al., SMI 1995
2. Put Kapton tape on the bottom side of your board covering the area and
vias beneath the BGA before wave soldering.


Regards,
George
George M. Wenger, DMTS Bell Laboratories Princeton
Supply Network Solutions
PO Box 900, Princeton NJ 08542-0900
Route 569 Carter Rd., Hopewell, NJ 08525
(609)-639-2769 (Office), 3210 (Lab), 2346 (Fax)
[log in to unmask]


-----Original Message-----
From: Rudolph Yu [mailto:[log in to unmask]]
Sent: Wednesday, March 28, 2001 2:43 PM
To: TechNet E-Mail Forum.; Wenger, George M (George); [log in to unmask]
Subject: Re: [TN] BGA crack- major headache


Hi George:

The metallization is electrolytic plated NiAu.
The Ni thickness is between 5-15 micron
The thin Au on the top is about 0.5 -1 micron.

Hope these info will help you to help me....

Thanks

Rudolph


------Original Message------
From: "Wenger, George M (George)" <[log in to unmask]>
To: [log in to unmask]
Sent: March 28, 2001 6:39:11 PM GMT
Subject: Re: [TN] BGA crack- major headache


Rudolph,
Do you know if the metallization on the 272 I/O PBGA is electroless or
electrolytic NiAu?

Regards,
George
George M. Wenger, DMTS Bell Laboratories Princeton
Supply Network Solutions
PO Box 900, Princeton NJ 08542-0900
Route 569 Carter Rd., Hopewell, NJ 08525
(609)-639-2769 (Office), 3210 (Lab), 2346 (Fax)
[log in to unmask]


-----Original Message-----
From: Bob Perkins [mailto:[log in to unmask]]
Sent: Wednesday, March 28, 2001 1:10 PM
To: [log in to unmask]
Subject: Re: [TN] BGA crack- major headache


Hi
Have you had a look under the BGA of the reflow quality on that perticular
ball, does it look nasty on the microscope; too much heat, or maybe this
ball has not enough heat.  If the reflow on the bga is not even I would
sugest slowing down the profile and reducing the slope at spike.  Give the
bga a better chance to reflow evenly. It is quite possible to have a ball
close or attached to ground sucking up the heat, or the opposite, a ball
that has a thermal stress on it.

Bob Perkins
SMT Manufacturing Process /
Automation Technician
Aimtronics-Delta

-----Original Message-----
From: Rudolph Yu [mailto:[log in to unmask]]
Sent: Wednesday, March 28, 2001 8:48 AM
To: [log in to unmask]
Subject: [TN] BGA crack- major headache


Here are the facts:

PBGA-272 balls
FR4 with HASL finishes 8 layers

The failure point always happens at the same I/O which is the 2nd last ball
of the top outmost row of the package. It is not located near the edge of
the board or any breakaway point.

Failure mode
Micro fracture found near the intermetallic layer between the BGA package
and the solder ball attached to it.

Around 0.001% of the products we built failed in the field because of this.
None of these were caught during the ICT or Functional test.

The same ASIC is also used on several other Products and have never seen an
issue like this.  Somehow this failure mode with this ASIC only occurs in
one particular product /design.


The ASIC / fab lot-related , ICT pin interference, stress by the breakaway
tab, and stencil cleanliness assumptions had already ruled out after a
controlled lot was built few weeks back.  All boards passed the tests.  But
now some boards started failing in the field.

Why the crack always happen to one single location(ball) with the same
product we built??


We have run out all the possibilities that we can think of. I hope all the
experts in TechNet can share their opinions on this.  Customer kept asking
for the root cause analysis. Right now we just cannot came up with a
reasonable one.

Thanks
Rudolph Yu

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