BGA Pad Size Does Not Scale With N, M and L?

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I created a land pattern for a Micron memory part BGA and I notice that when I change between N, M and L, there is no change in pad size. It is 0.8mm pitch and 0.45mm ball diameter.

Also, as was mentioned yesterday, I am curious as to whether the pad size should be the same as the Solder Mask, or whether the Solder Mask should create the pad opening on a larger copper pad...

In any case the following table indicates that the pad size should change with N, M and L - what is best to do here? 

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DaveCowl Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 18 Oct 2012 Location: Santa Clara, CA Status: Offline Points: 161	Post Options Post Reply Quote DaveCowl Report Post Thanks(0) Quote Reply Topic: BGA Pad Size Does Not Scale With N, M and L? Posted: 25 Oct 2012 at 2:28pm
	I created a land pattern for a Micron memory part BGA and I notice that when I change between N, M and L, there is no change in pad size. It is 0.8mm pitch and 0.45mm ball diameter. Also, as was mentioned yesterday, I am curious as to whether the pad size should be the same as the Solder Mask, or whether the Solder Mask should create the pad opening on a larger copper pad... In any case the following table indicates that the pad size should change with N, M and L - what is best to do here?



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 25 Oct 2012 at 4:04pm
	IPC-7351 only supports 1-Tier for all Grid Array package pad size calculations. The BGA ball collaspes around the pad edges - The 3-Tier for the BGA only changes the Silkscreen Line Width, Ref Des Height and Local Fiducial sizes for fine pitch BGA's.