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April 2006

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Subject:
From:
Guy Ramsey <[log in to unmask]>
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Date:
Fri, 21 Apr 2006 16:35:08 -0400
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Diamond shape because when the solder wets out to the corners of the land
the pattern is not simply a squashed ball, but has for distinct gray
corners. I first heard this DFM guidance from Glenbrook. But, I have also
heard it argued that these land patterns may produce stress points that
could lead to reduced service life in of the joint. I don't have data to
support the argument against the square or diamond land pattern design. They
are not commonly used.
I will say this, a key hole pattern, that can be produced by a non-solder
mask defined land, can give a similar result. A distinct gray pattern where
the solder wets down the trace leaving the pad.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Scott Decker
Sent: Friday, April 21, 2006 1:40 PM
To: [log in to unmask]
Subject: [TN] BGA and CGA pad questions.


All,
   I was talking with our Manufacturing engineer the other day and the
people that make the SMD re-work station tools, about the pads used for
both BGA's and CGA's. The vendor was saying that diamond pads, (square
on a 45') were better for X-Ray inspection because you can see the pad
verses the pin/ball better during the inspection of the solder joints.
The X-Ray manufacturer' says the same thing, but has anyone done it this
way yet? It sounds good to me, but does anyone have any practical
experience with the diamond pads? How do you figure size between round
to square, etc.? Is it just area calculations or flat side the same as
diameter, etc.? Paste Mask sizing, Solder Mask defined, (not my thought)
or just the standard oversize, etc.? These would be for high-reliability
applications and from what I understand, the CGA is better in that
respect. Any info would be great to hear. Thanks in advance.


Scott Decker
AKA: Padmasterson
Broad Reach Engineering CAE
Ph. 480-377-0400 Ext. 34
FAX. 480-968-4597
Tempe, AZ.


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