[SI-LIST] BGA land pattern
- From: "Umesha" <aumesh@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 12 Sep 2007 03:59:42 +0630
Hello All,
This is not a signal uintegrity question.
The question regarding BGA land pattern design.
On my board I have the footprint of 25 mil pitch 56 pin SSOP package.
Each pad is of 75 mil x 15 mil .
On the existing footprint I am planning to assemble a BGA package of 50 mil
pitch with the ball diameter of 0.5mm (20mil).
This is how I have planned.
Let us say SSOP pins are numbered as 1,2,3,4,....56.
I will mask some portion of each pad of the SSOP package as mentioned below.
Pad 1 of the SSOP package will be masked at the TOP portion (60mil x 15mil
) such that
solderable portion will be of 15 mil x 15 mil.
Pad 2 of the SSOP package will be masked at the BOTTOM portion (60mil x 15mil )
such that
solderable portion will be of 15 mil x 15 mil.
Pad 3 of the SSOP package will be masked at the TOP portion (60mil x 15mil )
such that
solderable portion will be of 15 mil x 15 mil.
Pad 4 of the SSOP package will be masked at the BOTTOM (60mil x 15mil ) portion
such that
solderable portion will be of 15 mil x 15 mil.
Thus I will have 2 rows of square pads on either side of the footprint.
My question is ------
If the BGA component, having the ball diameter of 0.5 mm (20 mil) to be
soldered to this modified footprint, is the masking arrangement proper for
soldering ? If not, what should be the size of the rectangular / square pad
on the board so as to have proper solderability?
Please note that I am having 75 mil x 15 mil pads on the existing card which
I am modifying by applying solder mask.
I have referred the IPC document for this purpose which says for 0.5 mm
nominal ball diameter BGA, land pattern should be 0.4 mm nominal diameter
circuilar pad.
Any inputs in this regard will be helpful.
regards
-Umesha.
Centre for Development Of Telematics,
email :aumesh@xxxxxxxxxxxxxx
aumesh_98@xxxxxxxxx
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