Hi Ken,

Your description is too general. Do you have a spec on how much force should be required to remove that specific BGA?

How all the analyzes you mentioned had been done?

Do you have a picture showing the problem?
Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

-----Original Message-----
From: "Crandall, Ken" <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Fri, 8 Jul 2011 16:23:49 
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
        "Crandall, Ken" <[log in to unmask]>
Subject: [TN] Micro voids when soldering to hard gold

All -

I have a situation where we are experiencing micro-voids in solder joints after SMT reflow.  Problem manifest itself primarily in BGA to solder ball interface ( at the device junction interface and not the PWB to solder ball interface) confirmed with cross sectioning.  BGA solder joints are weak resulting in electrical failures and removal with minimal mechanical stress.

We are using a Kester 256 HA (62-36-2) solder paste on a electrolytic PWB finish.  The same board with the same process using ENiG does not exhibit this problem.

Ionic, XRF and SIMS analysis does not reveal any surface or interlayer organic contamination.  I have seen old publications indicating this phenomena has been observed before with hard gold chemistries.

DOEs conducted by varying reflow dwell times / surface cleaning / pre-bake does not remedy the situation

Any thoughts or experience with salvaging built CCAs or reclaiming bare boards to eliminate this issue?



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