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March 2008

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TechNet <[log in to unmask]>
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TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 18 Mar 2008 12:37:51 -0400
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TechNet E-Mail Forum <[log in to unmask]>, "Thayer, Wayne" <[log in to unmask]>
Subject:
Re: Solder Mask Defined Pad BGA Reliability
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"Thayer, Wayne" <[log in to unmask]>
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Hi Werner!
 
SM holding a pad down???!
 
No!  The pad is held to the laminate material with CONTACT AREA.  Make the pads as big as you can, then control solder flow with the mask.  And make sure the mask has nice vertical walls and leaves no contamination on the pad.
 
Wayne

________________________________

From: TechNet on behalf of Werner Engelmaier /*
Sent: Tue 3/18/2008 12:32 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Mask Defined Pad BGA Reliability



Hi Wayne,
SMD geometries are stress risers.

If you have a large thermal expansion mismatch, the weakest lik will let go
first. That may be the SJ or the pad adhesion to the PCB (pad cratering) or
BGA. Having a SM hold the pad to the BGA is something of a Band-Aid approach.

Werner



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