Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Homeplate design

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Homeplate design | 25 July, 2007

Hi Folks, I hope someone can help me,

Is the homeplate stencil design (for reduced solder paste) the same for preventing solder balls as it is for reducing tombstones? i.e. the reduction of solder paste under the component termination. I'm trying to reduce tombstones on some 0402 parts on a poorly designed PCB which I am not allowed to change (Pads too far apart). So by implementing the homeplate design am I trying to reduce the pull effect that the solder fillet has on the component or prevent the component from floating on too much solder?

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Homeplate design | 25 July, 2007

Zoinks!! Doing the homeplate design on 0402 will actually make your tombstones WORSE!

Think about it. Your wetting forces are now on the ENDS of the device with no solder paste toward the middle of the device to tack the part down - a gauranteed formula for tomb-a-stoning.

Leave the aperture 1:1 with your pad. With your pads being far apart, you should NOT have to worry about mid-chip balling.

If your pads WERE designed correctly, with correct spacings, and mid-chip balling is a concern, even then, do NOT homeplate. Your best bet would be to shave 1-2 mils off the "inside" of the aperture.

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Homeplate design | 25 July, 2007

Hi Lloyd,

Homeplates will get rid of solder balling. They are only recommended "backwards" for 0402 or smaller (Points point away from each other). If you do this, you will have a full pad width of paste on the pad for the part to stick in. Obviously this will not over come a bad design, so it just depends on your design. Also, check IPC about solder balling. You do get some wiggle room for solder balls.

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