I'd prefer to see SEM images, as optical are not as informative in this particular case. However, those "dark lines" do not look like cracks. The joints appear to have some Pb "concentrated" closer to the PCB interface implying that it could have been a mixed process.
If you don't have access to an SEM you can send them to me.
Regards,
Vladimir
SENTEC
------Original Message------
From: Gabriela
Sender: TechNet
To: [log in to unmask]
ReplyTo: TechNet E-Mail Forum
ReplyTo: Gabriela
Sent: Jul 4, 2009 03:54
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.
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