Paste Printing @ 45 degrees

Has anybody adopted the method of stencil printing with the board at a 45 degree angle to the squeegee blade? What are the benefits and drawbacks? I've heard you get better fine pitch results.

TX Mark

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| Has anybody adopted the method of stencil printing with the board at a 45 degree angle to the squeegee blade? What are the benefits and drawbacks? I've heard you get better fine pitch results. | | TX | Mark | I have used thetechnique extensively, and you get a more consistent paste shape and fill when the board is turned 45 degrees. The leads that are parallel to the squeegee are usually the hardest to get consistent shape and fill. This reduced the number of unsoldered or insufficient solder joints on 25-25 mil pitch QFP's. It also helped on the SOIC packages that had leads parallel to the squeegee. The only drawback that I saw was it increased the takt time for the operation (due to rotation), but that was minimal when compared to the advantages.

Brian

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| | Has anybody adopted the method of stencil printing with the board at a 45 degree angle to the squeegee blade? What are the benefits and drawbacks? I've heard you get better fine pitch results. | | | | TX | | Mark | | | I have used thetechnique extensively, and you get a more consistent paste shape and fill when the board is turned 45 degrees. The leads that are parallel to the squeegee are usually the hardest to get consistent shape and fill. This reduced the number of unsoldered or insufficient solder joints on 25-25 mil pitch QFP's. It also helped on the SOIC packages that had leads parallel to the squeegee. The only drawback that I saw was it increased the takt time for the operation (due to rotation), but that was minimal when compared to the advantages. | | Brian | Very true. apertures parallel to the print stroke suffer due to reduced filling exposure time. I have seen up to 40 % less volume on parallel deposits in comparison to perpendicular deposits on the same device. 45 degree printing splits the difference between orthagonal devices and gives a more consistent average. Don't forget to have your artwork rotated on the stencil foil (small detail -- but critical!)

Dean

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| Has anybody adopted the method of stencil printing with the board at a 45 degree angle to the squeegee blade? What are the benefits and drawbacks? I've heard you get better fine pitch results. | | TX | Mark | I know we all seek easy/better solutions to apparent problems/issues. I've never seen a need to rotate, at any angle, stencil or board images to effect better prints.

I just haven't seen problems with typical parallel printing. Also, I have seen few, with stencils well designed from qualified suppliers, problems with chemically etched stencil openings for fine pitch, xfinepitch, BGA, and uBGA device types. For me, it all comes down to the right design and process management.

I know this sounds rhetorical, but I've designed and printed for years using chem etching, with laser machining for step downs when required. Electro-polishing is fine, as is electro-forming, but isn't always an answer that works any better for me. I just don't get it when design rules are as they should be.

I'm always willing to try new stuff. I will even try frying pans to effect rework. If it works better, I'll incorporate it into my design rules and process methods, but it has to work. My question is: Does it work and where's the proof it works better before rushing off to do something different?

Earl Moon

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It may be worth mentioning to those that do not have the ability to rotate the PCB, that some folks adjust their aperture design on fine pitch leads by increasing the aperture size for those leads parallel to the X axis, thus allowing consistent volume for both those apertures parallel and perpendicular to the X axis.

Steve A

| | | Has anybody adopted the method of stencil printing with the board at a 45 degree angle to the squeegee blade? What are the benefits and drawbacks? I've heard you get better fine pitch results. | | | | | | TX | | | Mark | | | | | I have used thetechnique extensively, and you get a more consistent paste shape and fill when the board is turned 45 degrees. The leads that are parallel to the squeegee are usually the hardest to get consistent shape and fill. This reduced the number of unsoldered or insufficient solder joints on 25-25 mil pitch QFP's. It also helped on the SOIC packages that had leads parallel to the squeegee. The only drawback that I saw was it increased the takt time for the operation (due to rotation), but that was minimal when compared to the advantages. | | | | Brian | | | Very true. apertures parallel to the print stroke suffer due to reduced filling exposure time. I have seen up to 40 % less volume on parallel deposits in comparison to perpendicular deposits on the same device. 45 degree printing splits the difference between orthagonal devices and gives a more consistent average. Don't forget to have your artwork rotated on the stencil foil (small detail -- but critical!) | | Dean |

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