Paste accumulation on the squeegee side with a 15mils to 5mils Step stencil

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Hi, We are using a 15mils to 5 mils step stencil with a met... - Aug 12, 2019 by SMTA-Martial SMTA

I've never seen successful printing with a step as deep as y... - Aug 12, 2019 by davef

Forget about a stencil here. The only solution I have for yo... - Aug 19, 2019 by Evtimov

Such huge difference between low and high thickness will def... - Aug 23, 2019 by sssamw

SMTA-Martial

#83243

Paste accumulation on the squeegee side with a 15mils to 5mils Step stencil | 12 August, 2019

Hi,

We are using a 15mils to 5 mils step stencil with a metal blade. The 15mils area the surface is smooth and polish and in the 5mils area the surface is rough and porous because of the laser process. In the 5 mils area where there is no aperture the paste tend to accumulate because the surface is porous. This accumulation of paste increase the thickness of the stencil in those region so the paste volume is higher and it cause some short on the microcontroller. Is anybody come across this kind of issue?

Did you have a solution? (Different squeegee blade, different stencil manufacture process, etc) I think if the surface was smooth in the 5 mils area we wouldn’t have this issue, but I don’t know if the manufacture process allows this.

Regard

This message was posted via the Electronics Forum @ SMTA SMTA

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davef

#83246

Paste accumulation on the squeegee side with a 15mils to 5mils Step stencil | 12 August, 2019

I've never seen successful printing with a step as deep as you seem to be saying. The keep out would have to be jigundous!!!!

SMTnet Technical Library: https://smtnet.com/library/files/upload/Step-Stencils-laserjob.pdf

I'd guess

* Maximum step is: 2 mil [50um]

* Minimum keep out [distance from aperture to the edge of the step]: 25mil [635um]

IPC-7525 Stencil Design Guidelines includes stencil step guidelines

Our friend Chrys Shea presents "SPECIFYING STENCILS TO OPTIMIZE PRINT PERFORMANCE"

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Evtimov

#83317

Paste accumulation on the squeegee side with a 15mils to 5mils Step stencil | 19 August, 2019

Forget about a stencil here. The only solution I have for you is to dispense this paste. There are some super cool Jet printers out there that will do the job.

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sssamw

#83340

Paste accumulation on the squeegee side with a 15mils to 5mils Step stencil | 23 August, 2019

Such huge difference between low and high thickness will definitely cause paste accumulation on the squeegee side. Normally is 2 mil max difference.Yes, dispense maybe help for thicker paste or print two times.

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