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Solder paste process

Views: 2833

#58640

Solder paste process | 22 April, 2009

Hi: I would like to know their opinion about the critical variables that I need to control in a screenprinter(solder paste aplication on PCBs) process and how I can control them.

Thanks.

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#58649

Solder paste process | 23 April, 2009

Emilio: Several factors you need to take into account and your process parameters will depend on: Solder Alloy, Is there any Fine Pitch?; BGA?; Smaller chip size?. Tipically you should go for controls in: Solder Temperature and viscosity; blade and stencil conditions; board support; print speed; blade angle; stencil cleaning.

For each one there should be tight controls.

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#58658

Solder paste process | 25 April, 2009

Emilio,

I have a fishbone diagram that I can e-mail to you that shows the MANY variables in the paste print process. There is only one way to determine for certain that the printer is doing it's job, and that is with a true 3D paste inspection process. See http://www.ascinternational.com for our line of paste inspection systems. Best regards, Bill N.

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#58659

Solder paste process | 26 April, 2009

First, in direct answer to your question, DOE printer setup variables (MPM): * Squeegee speed: 0.5 to 1.0 in/sec * Pressure (metal): 1lb/in of blade * Pressure (plastic): 1.6-3 lb/in

Second, supprting earlier responses, most people monitor paste height [volume] to assess how well their print process is staying in control.

Third, we know we're printing correctly when: * Paste at least as big in diameter as your thumb is rolling across the stencil * Paste is filling the apertures * Squeegee pressure wipes the top of the stencil clean * Paste releases from the stencil * Paste is on the board in nice bricks * Bottom of the stencil is clean. Sometimes too little squeegee pressure will not form a good seal and can cause the paste to bleed under the stencil, resulting in solder shorts.

Forth, this links to paste printing papers on Daan Terstegge's excellant jump site: http://www.smtinfo.net/Db/_Solder%20Paste.html

Fifth, this links to good advice from an old friend, Justin Medernach here on SMTnet, on paste printing: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=33254

Finally, search the fine SMTnet Archives to find threads like: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=2984

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#58693

Solder paste process | 30 April, 2009

I have run design of experiments on screen printers and most times people forget about the type of board you are running; the condition of the board; manufacturer of the paste as I have seen Type 4 no-clean no-lead pastes react very differently using the same machine/stencil and settings. Stencil make and manufacturer will also play a big rols in your DOE.

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#58694

Solder paste process | 30 April, 2009

One factor I see missing is separation speed (or snap off speed). I've run experiments with different pastes where it was the biggest factor in standard deviation of print volume for small apertures.

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