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SMT electronics assembly manufacturing forum.

Stencil for 10 mils IC

Rchard Eigner


Stencil for 10 mils IC | 12 November, 2000

We are manufacturing a PCB that uses an integrated circuit that has a leg spacing of 10 mils, other components on the PCB are 1206's and 0805's. Is it possible to make the stencil apertures 10 mils apart or is there another way of making the stencil.

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Re: Stencil for 10 mils IC | 13 November, 2000

Hi Richard,

I assume that you deal with a component that has 20mil pitch. In this case depending on your pad design you get from 8 to 10mil spacing for your apertures. With a slight reduction of the aperture (10 to 15% for avoiding shorts)and a 6mil stencil it will work fine. Of course with absolutely misadjusted printersettings for the squegee pressure you can demolish almost every structur but we are working with that kind of spacing very successfully.


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Re: Stencil for 10 mils IC | 13 November, 2000

Richard, From your description of the IC, as Wolfgang indicates it sounds like a 20mil pitch device, the aperture design really depends upon your solder paste particle size, we use a type 3 solder paste with a mesh size of �325 / +500microns. This is with a stencil thickness of 6 thou, an ideal aperture for you with these specifications would be a 9mil aperture. Anything smaller than this (even eight) will not give you good release as the aspect ratio will be wrong (see archives for further details on aspect ratio, but a good rule of thumb is that the apertures should be no smaller in width than three solder particles). If you require an eight thou aperture then you will have to change the particle size of the solder paste and maybe even the stencil thichness, this can lead to further problems, so stick with the 9.

You may also want your stencil manufacturer to radius the corners of the rectangular aperture, this will stop solder paste from clogging up in the corners of the apertures and also give a better release.

Happy printing!


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Re: Stencil for 10 mils IC | 13 November, 2000

Depending on the designers pad size, I generally go for 0.010" aperture with 0.010" spacing - stencil thickness 0.005". This combo with metal squeegees and the "usual suspects" of printer set up and placement details should you you hassle free.

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Re: Stencil for 10 mils IC | 15 November, 2000

"depending on your pad design"...

To me, Wolfgang gave you the biggest secret... I guess he meant the real pad width you get on your board is the start point. Get the average measurement in mils and then cut it from the sides at the percentages he has suggested. Remember, the paste has to FIT on that pad, no matter what the pitch is. Do not apply too much since they'll FALL OFF the edges, but apply enough to build the fillet aLL around.

My designs used to be 14 mil wide pad, the real board used to come with 12-13 mil, and I used to order 11 or 12 mil wide. The trapezoidal shape (bottom of the stencil 12 wide, top of the stencil 11 wide for easy release) is a very good suggestion.

Please be very careful if you go lower widths since it'll be more difficult to release the paste. And keep the screen printer's cover closed during operation...

Good luck.

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