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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Solder paste height and metal squeegees

James Lewis

#6029

Solder paste height and metal squeegees | 20 April, 2001

For those of you out there, like myself who are still using 2-d to measure paste ht, I have 2 questions. 1. Typically, what tolerance are you applying to your ht? +- 1 mil, or what? 2. Are you using metal squeegees, and if so, have you found that squeegees at 45 degrees will always add 1 to 1.5 mils of paste ht beyond your stencil thickness no matter what else you do?. Also - have you found that squeegees at 60 degrees will give you the stencil thickness in paste, plus perhaps only a half mil?

We are trying to tighten up our SPC a bit, and reduce some bridges, and I'm hearing a lot of stories, including many about the futility of 2-d measurements (which I understand) and how metal squeegees have basically taken out the impact that a lot of the other parameters, such as pressure, speed, etc, have had. I'm trying to help some "experts" get past the debate and onto the solutions. Somebody give me a sanity check. Thanx!!

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gcs

#6033

Solder paste height and metal squeegees | 20 April, 2001

Just a bullet!

My results are, .005" stencil thickness should measure between .0055" - .006" if your pressure is correct, metal blades and snap-off is set up correctly. Do you have aperture reductions at the QFP locations "typicial industry standards" ? Is your paste slumping ?

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James Lewis

#6037

Solder paste height and metal squeegees | 20 April, 2001

We do some aperture reductions - but it's not the 10% i'm accustomed to. Looks like it should be more than we currently do (I think we do 10% of length, but no width). Don't think we have a slumping problem, and we're not doing snap-off, only contact printing. On a 5 mil stencil - best we get is anywhere from .0055 to .0080, and I'm told we definitely can't hold thickness +- 1 mil, because of 45 degree stencils. Also looking at consistency of board supports as well. ???

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gcs

#6038

Solder paste height and metal squeegees | 20 April, 2001

We always reduce side to side, EXAMPLE: 12 mil width reduced to .010".

Do you guys check viscosity ?

Also maybe your guys are appling to much pressure on the sqweegee blades.

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