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January 2008

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Subject:
From:
Paul Edwards <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Edwards <[log in to unmask]>
Date:
Thu, 31 Jan 2008 13:51:25 -0800
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Tim,

What is you peak temperature and ramp rate of the PCB above 130C of your reflow profile? Also what type of PCB material is used?

It could be the drill density in the BGA area is sufficient to increase the z-axis expansion rate which can be 10-20X over the x-y rate for FR4x materials...

Paul

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gervascio, Thomas
Sent: Thursday, January 31, 2008 12:47 PM
To: [log in to unmask]
Subject: Re: [TN] BGA underfill opens- the saga continues

I'm sorry about the confusion and lack of information. To answer a
couple of questions.  I was incorrect it is a 256 I/O over molder
plastic BGA ( OMPAC was an Motorola term- Over Moldered Plastic Array
Component) with a full pad array. The package is 17mm x 17mm x 1.3 mm
(the carrier "PCB" is 0.54mm thick). The spheres are Sn 63/Pb 37
eutectic solder and the sphere diameter is 0.5mm. The solder paste is
Indium SMQ51AC eutectic solder and the board is ENIG finish.

The opens are not related to the underfill since we find the opens
before and after underfill. The failures are found internally at
confidence(final) test.

We have reviewed the cross sections that came with the solder sample
board but a awaiting cross section on the actual failed boards. We are
seeing about a 10 percent fallout due to this. The failed vias are not
localized in any one area under the BGA but always fail under the BGA.
Trapped material in the vias - when going through ESS might- could
entrapped air produce moisture condensation + bias + ionics = corrosion?

The BGA is a single user on the board and is located approximately in
the center of the board. The board is a 12 layer epoxy multilayer.


Tom
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Thursday, January 31, 2008 1:59 PM
To: [log in to unmask]
Subject: Re: [TN] BGA underfill opens- the saga continues

Hi Tom,
You got me utterly confused.
I understand you have opens
HOWEVER,
     are the opens related to the underfill?-then they have to be
fractured SJs; just because you verified the 'underfill profiles' does
not mean that the underfill is doing what you are expecting [see my
reliability column in the March 2006 issue of GSMT&P].

     are the fractures of the vias?-then it is the PCB and has nothing
to do with the underfill. Are you SAC-soldering? Then likely your PCB
design is inadequate for the high soldering temperatures [see my White
Paper on the proper specification of PCBs for lead-free soldering and my
columns in the Sept. 2006 and January 2007 issues of GSMT&P].


Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com



**************
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http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489

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