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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Asher Levy

#14966

Stencil opening for 0603,0402 ? | 20 July, 1998

Looking for recommendation, need your on hand experience to decide on narrowing stencil opening relatively to actual pad on pcb for 0603 and 0402 components also info on stencil thickness ? (I have a very dense board with 0603 and 0402 comp.) Thx

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MMurphy

#14968

Re: Stencil opening for 0603,0402 ? | 20 July, 1998

:On a dense board, a great way to reduce solderballing is to either; print paste 1:1 with pad size using a 5mil foil, reduce aperture openings by 10% of pad size or change aperture shape to "Home Plate" design. If none of these work on their own you can try some combination ie. 5mil foil and reduce apertures 10% or 6mil foil,reduce apertures and use "Home Plate" design. Much of your success also has to do with the quality of the paste you are using and whether your laser cut stencil are electropolished. Good Luck!

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Eric

#14969

Re: That is good advice. (End) | 20 July, 1998

| | :On a dense board, a great way to reduce solderballing is to either; print paste 1:1 with pad size using a 5mil foil, reduce aperture openings by 10% of pad size or change aperture shape to "Home Plate" design. If none of these work on their own you can try some combination ie. 5mil foil and reduce apertures 10% or 6mil foil,reduce apertures and use "Home Plate" design. | Much of your success also has to do with the quality of the paste you are using and whether your laser cut stencil are electropolished. Good Luck!

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Russ Miculich

#14967

Re: Stencil opening for 0603,0402 ? | 22 July, 1998

I agree with the response and strongly recommend that you use the "home plate" design to reduce solder ball entrapment, and that the under cut for the 0402's in particular be 80% of the pad size. Solder slump is typically about 1.2 to 1 so spread will be 10% to either side and a reduction in height of about 20%. Example: if pad size is 0.20" wide and you print 0.20" wide paste you will end up with about 0.24" wide - 10% on either side = 0.002" spread x 2. If the height of your stencil is 0.005" then when you print you should end up with about a 0.0045" height pad. This is typically. Results vary depending upon the exact solder paste you use and its density and thixotropic index. Hope this helps. If you are going to the ATE show in Chicago in September I will be giving a brief presentation there. | Looking for recommendation, need your on hand experience to decide on | narrowing stencil opening relatively to actual pad on pcb | for 0603 and 0402 components | also info on stencil thickness ? | (I have a very dense board with 0603 and 0402 comp.) | Thx

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