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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Stenciling

Al

#12300

Stenciling | 14 March, 1999

Can sombody help me with this?? When applying solder paste, what factors determine how high off the PCB the stencil is? We use no fine pitch devices. (mostly 603 and 1206 size components) Any help would be greatly appreciated. As you could probably guess we still have much to learn about SMT

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Justin Medernach

#12301

Re: Stenciling | 15 March, 1999

| Can sombody help me with this?? When applying solder paste, what factors determine how high off the PCB the stencil is? We use no fine pitch devices. (mostly 603 and 1206 size components) Any help would be greatly appreciated. As you could probably guess we still have much to learn about SMT | Al, Print on contact, no print gap. This method is the most repeatable. Use metal blades with a .007" thick foil and you'll be all set for the passive components. If you go to .025" pitch or even .020" pitch, use .006" thick foil. Below that, you have to get creative.

Regards, Justin

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Scott Davies

#12302

Re: Stenciling | 16 March, 1999

| | Can sombody help me with this?? When applying solder paste, what factors determine how high off the PCB the stencil is? We use no fine pitch devices. (mostly 603 and 1206 size components) Any help would be greatly appreciated. As you could probably guess we still have much to learn about SMT | | | Al, | Print on contact, no print gap. This method is the most repeatable. Use metal blades with a .007" thick foil and you'll be all set for the passive components. If you go to .025" pitch or even .020" pitch, use .006" thick foil. Below that, you have to get creative. | | Regards, | Justin |

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Scott Davies

#12303

Re: Stenciling | 16 March, 1999

Al,

In general, I would agree with Justin, i.e. contact printing with a 0.007" stencil is great for 0603 - 1206 size components.

However, we also place 0.025" pitch QFP components. We use a 0.006" laser cut stencil and I have found through trial and error that a 1mm print gap tends to give the best printing performance. Of course, a number of other factors, such as the type of paste you are using, will affect quality of printing, but 0.006" seems a good stencil thickness for most general purpose applications, when using metal squeegee blades.

Because of the many variables of the printing process, what works for one person in one part of the world won't necessarily work for everybody else, so don't be afraid to experiment!

Good Luck Scott

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Dan Hughes

#12304

Re: Stenciling | 23 March, 1999

| Al, | | In general, I would agree with Justin and Scott, with the exception that I don't feel a laser cut stencil is required when printing 25 and 20 or even 16 mil pitch. We make a good chem etch stencil that will print fine pitch great if you ever get there. Don't throw your money away on laser cut. good luck...dan. |

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