[SI-LIST] Re: BGA land pattern
- From: steve weir <weirsi@xxxxxxxxxx>
- To: aumesh@xxxxxxxxxxxxxx
- Date: Tue, 11 Sep 2007 04:15:15 -0700
Umesha I don't think a square aperture is a good idea.
Steve.
Umesha wrote:
> 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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--
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