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Thickness of solder paste from stencil

mwoodall

#19450

Thickness of solder paste from stencil | 10 April, 2002

We measure the thickness of solder paste printed onto PCBs as a control of the printing process. Generally 6 thou stencils are used and give between 6.2 and 6.8 thou. What thicknesses do other users get?

Cheers!

Mark

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#19454

Thickness of solder paste from stencil | 10 April, 2002

I am curious how you measure your printed paste thickness. We are considering doing the same. As it is now we assure we have squeegee pressure and speed controlled, have not actually measure the printed paste thickness.

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#19460

Thickness of solder paste from stencil | 10 April, 2002

How do you assure you "have squeegee pressure and speed controlled"?

Search the fine SMTnet Archives for background on measuring paste thickness.

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#19461

Thickness of solder paste from stencil | 10 April, 2002

On SMTnet, we've discussed the the frailties of controlling paste height, when volume is a more telling measure.

Sometimes if you seperate too quickly, the paste tries to stay attached to the aperture walls. This creates a 'U' shaped deposit with raised outer edges, rather than a nice 'brick'.

Questions are: * How uniform is this '6.2 and 6.8 thou' measurement across the deposit? * You say 'Generally 6 thou stencils are used ...'. So, what is the thickness of THIS stencil?

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mwoodall

#19462

Thickness of solder paste from stencil | 11 April, 2002

The Alpha metals Hi Check 500 is used to measure paste deposit thickness. The paste height is found from a micrometer reading determined by focussing a beam of light on a track adjacent to a paste deposit and then onto the solder paste.

I've measured the thickness of the stencil round the edges and this matches the thickness as specified, i.e a 6 thou stencil measures as a 6 thou stencil. The stencils are laser cut.

The solder paste deposit is not the same thickness across the PCB. The range figure I gave before of 6.2 to 6.8 was found by measuring the same pad from 80 printed PCBs.

What do other users find as the variation of solder paste deposit?

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BTaylor

#19466

Thickness of solder paste from stencil | 11 April, 2002

We use the ASC vision master 212, our customers wanted a height and volume measurement rather than an inspector doing a visual. We have added this machine to our process, checking height on many preprogrammed locations then this generates a X bar and R chart from the data and then posts it on a file on our network. This gives you real time data to control your process.

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