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Stencil design

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Stencil design | 2 March, 2007


I havea 0.4mm pitch TQFP with heat transfer pad on the bottom side of component.

I will appreciate any suggestions with regards to:

1) stencil thickness (Rest of components on board are 0603 passives and few 40 mil pitch IC's)

2) Stencil aperture openings for the heat pad under the QFP.

Will the solder under the component (on heat pad) create alignement issues for the QFP?


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Stencil design | 2 March, 2007

1- Thickness 0.005" 2- I usually reduce 50% of the thermal pad, but it also depend on original size of thermal pad somehow I have to either create window panel or crosshatch otherwise component wil get wimming during reflow. Hope this will help.

Regards Steve Yen USA STENCILS

This message was posted via the Electronics Forum @

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Stencil design | 6 March, 2007

Hi, What is wimming ?

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Stencil design | 6 March, 2007

Maybe swimming..

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Stencil design | 8 March, 2007

Stencil Thickness should be .005"

A reduction along with cross hatching is a must for the center pad to reduce paste volume as well as to assure even paste deposit while printing on a large pad. With out the cross hatch, the squeegie will most likely pull paste away from the center of the large ground pad.

Not sure on the whole wimming thing!

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