Hi Gaby,

Just a thought, are you 100% certain that the features which you have
shown are not caused by scoring/scratching/handling on the surface of
the section? Could be some contact on the delicate sample surface
between final polish and observation, perhaps during etch or rinse
steps, or even during mounting onto a slide for viewing (dirt of the
sample press)? This could explain the continuation of a feature from the
solder joint into surrounding mould resin or soldermask. 

Would be worth ruling out and again SEM inspection of the sample would
clarify. Would also be happy to take a quick look at them in the SEM for
you if you don't have access. 

Kind regards,

Stewart

Stewart McCracken
MCS Ltd.

t.   +44(0)131 440 9090
f.   +44(0)131 440 9085
e.  [log in to unmask]
w. www.themcsgroup.co.uk 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gabriela
Sent: 04 July 2009 08:01
To: Administrator
Subject: [TN] Weird solder joints

Dear all,
By cross sectioning BGA solder joints on a failed assembly, I found that
the
suspected joints are not uniform and that they contain unusual
separation
areas.

I suspect mixed assembly and/or bad reflow profile.

Steve was so kind and enabled me to send the links.
Please may I have your opinion?
http://stevezeva.homestead.com/files/small.jpg

 

 <http://stevezeva.homestead.com/files/small1.jpg>
http://stevezeva.homestead.com/files/small1.jpg

 

 <http://stevezeva.homestead.com/files/small2.jpg>
http://stevezeva.homestead.com/files/small2.jpg

http://stevezeva.homestead.com/files/small3.jpg

 <http://stevezeva.homestead.com/files/small4.jpg>
http://stevezeva.homestead.com/files/small4.jpg

 


Gaby


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