Solder Paste and Stencil questions

Hi, We are in the process of evaluate our solder paste,incoming inspection over the solder paste, stencil requirments:

1- Is anybody using/requiring 1000 Kcps or more on viscosity to your solder paste provider ? Why ?? 2- Is anybody using step stencil and rubber squeegees ? How much is your paste height varition on a PWB ?? And from PWB to PWB ?

Thanks in advance, Jose RG

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| Hi, | We are in the process of evaluate our solder paste,incoming inspection over the solder paste, stencil requirments: | | 1- Is anybody using/requiring 1000 Kcps or more on viscosity to your solder paste provider ? Why ?? | 2- Is anybody using step stencil and rubber squeegees ? How much is your paste height varition on a PWB ?? And from PWB to PWB ? | | Thanks in advance, | Jose RG | Jose,

I'm a stencil vendor, customer feedback says stay away from step stencils. If it is unavoidable, use a metal squeegee. If a metal blade is not available, use a high durometer polyurethane squeegee, 90 duro or higher.

Soft squeegees will scavange paste from the step and cause height variations. The geometry of the step is important too. The apertures in the step must be far enough away from the edge of the step to allow uniform paste pressure by the squeegee.

Engineers with actual experience can be more specific, but aperture size is a better way to adjust paste volumes than step stencils if you can do it. Judging by how few step stencils we sell, it must be very possible and preferable. Dan.

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