Hi Gaby,
I think that you're right - this is certainly unusual and interesting -
and a good chance to learn!
Did you have a chance to look at this in the SEM? - like some of the
other folks, I believe that this would be really helpful in determining
what has caused the features which you've seen.
It's difficult to see why it would have failed electrical test, another
layer of mystery? Seems like there is still sufficient solder volume to
carry signal, and interfaces at BGA and PCB look normal. Is this
device/joint carrying high frequency signals? (could the electrical
fault then be noise through this joint - some kind of skin-effect
perhaps?)
Be really great to see this section in the SEM, we would be happy to
take a look for you free of charge, purely for the learning opportunity
and the greater good!
Another thought, did you have a chance to examine the pad-track
connection on PCB and device? We've examined joints which are fine in
the bulk but have suffered fracture at the connection between track and
pad.
Look forward to hearing how things progress.
Kind regards,
Stewart
Stewart McCracken
MCS Ltd.
Centre House
Midlothian Innovation Centre
Roslin
Midlothian
EH25 9RE
m. +44(0)7711 541735
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: Gabriela [mailto:[log in to unmask]]
Sent: 06 July 2009 17:16
To: 'TechNet E-Mail Forum'; Stewart McCracken
Subject: RE: [TN] Weird solder joints
I am really impressed about you people, being ready to help so much.
Thank you all from all my heart.
No, these specific feature is not due to handling.
I think that the continuation was due to outgassing from the "open" in
the
solder into the mold.
Also, the feature stayed there through all the polishing steps.
Seems to me that this is a first for many of us.
Forgot to tell you: This specific ball failed during ELECTRICAL test.
The exact location-row and ball was given to me.
Two other balls had similar features, but not through all the width. I
don't
know if they passed the electrical test.
Gaby
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stewart McCracken
Sent: Monday, July 06, 2009 5:28 PM
To: [log in to unmask]
Subject: Re: [TN] Weird solder joints
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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