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0402 stencil design

Russ Roberts

#23247

0402 stencil design | 4 February, 2003

Greetings, I am pretty new to SMT production, and have learned much from this forum. I am getting ready to build a CCA with many 0402 parts that are really close together. I consider these fine pitch. The board also has two QFPS, so my stencil design at those locations uses trapezoidal apertures reduced down to 80% of the pad size. I plan to use a 5 mil laser cut stencil. What are some good guidelines for the 0402 parts? Should I use home plate apertures, reduced apertures, or just leave 1:1? TIA for any links or helpful info.

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Jon Fox

#23254

0402 stencil design | 4 February, 2003

we have some pretty tight 0402 placements and our best fix was to reduce the pad (vertically speaking) from .030x.022 to .020x.022. Fewer tombstones and the paste flows out to the edge of the pads nicely. Only difference is that we have a 6mil stencil.

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#23258

0402 stencil design | 4 February, 2003

You could reduce the paste by about 70%. Solder balling and tombstoning will be the issues to fight. The drivers to these don't change with the component size. Use the fine SMTnet Archives for background.

Aperture Size and Thickness of Solder Paste Stencil Part Type||Pitch||Pad foot print width||Pad footprint length||Aperture Width ||Aperture Length||Thickness range||Aspect Ratio Range||Area Ratio Range PLCC||1.27mm (50thou)||0.65mm (25.6thou)||2.0mm (78.7thou)||0.60mm (23.6thou)||1.95mm (76.8thou)||0.15-0.25mm (5.91-9.84thou)||2.3-3.8||0.88-1.48 QFP||0.635mm (25thou)||0.635mm (13.8thou)||0.635mm (59.1thou)||0.635mm (11.8thou)||0.635mm (57.1thou)||0.635mm (5.91-7.5thou)||1.7-2.0||0.71-2.0 QFP||0.50mm (20thou)||0.254-0.33mm (10-13thou)||1.25mm (49.2thou)||0.22-0.25mm (9-10thou)||1.2mm (47.2thou)||0.125-0.15mm (4.92-5.91thou)||1.7-2.0||0.69-0.83 QFP||0.40mm (15.7thou)||0.25mm (9.84thou)||1.25mm (49.2thou)||0.2mm (7.87thou)||1.2mm (47.2thou)||0.10-0.125mm (3.94-4.92thou)||1.6-2.0||0.68-0.86 QFP||0.30mm (11.8thou)||0.20mm (7.87thou)||1.00mm (39.4thou)||0.15mm (5.91thou)||0.95mm (37.4thou)||0.075-0.125mm (2.95-3.94thou)||1.50-2.0||0.65-0.86 0402|| ||0.50mm (19.7thou)||0.65mm (25.6thou)||0.45mm (17.7thou)||0.6mm (23.6thou)||0.125-0.15mm (4.92-5.91thou)|| ||0.84-1.00 0201|| ||0.25mm (9.84thou)||0.40mm (15.7thou)||0.23mm (9.06thou)||0.35mm (13.8thou)||0.075-0.125mm (2.95-3.94thou)|| ||0.66-0.89 BGA||1.27mm (50thou)||��0.80mm (31.5thou)|| ||��0.75mm (29.5thou)|| ||0.15-0.20mm (5.91-7.87thou)|| ||0.93-1.25 �� BGA||1.00mm (39.4thou)||��0.38mm (15.0mm)|| ||��0.35mm (13.8thou)||0.35mm (13.8thou)||0.115-0.135mm (4.53-5.31thou)|| ||0.67-0.78 �� BGA||0.50mm (19.7thou)||��0.30mm (11.8mm)|| ||��0.28mm (11.0thou)||0.28mm (11.0thou)||0.075-0.125mm (2.95-3.94thou)|| ||0.69-0.92 Flip Chip||0.25mm (10thou)||0.12mm (5thou)||0.12mm (5thou)||0.12mm (5thou)||0.12mm (5thou)||0.08-0.10mm (3-4thou)|| ||1.0 Flip Chip||0.20mm (8thou)||0.10mm (4thou)||0.10mm (4thou)||0.10mm (4thou)||0.10mm (4thou)||0.05-0.10mm (2-4thou)|| ||1.0 Flip Chip||0.15mm (6thou)||0.08mm (3thou)||0.08mm (3thou)||0.08mm (3thou)||0.08mm (3thou)||0.025-0.08mm (1-3thou)|| ||1.0

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RDR

#23264

0402 stencil design | 5 February, 2003

Are these the only packages that you could come up with Dave? What about all the rest?

You're something else. Thanks for doing my work for me!

Russ

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#23277

0402 stencil design | 5 February, 2003

I figure if you need the rest, you don't need these.

These strips are from some laser cutting tool fabricator. They give them to their customers [laser cut stencil fabricators] so the customer can do a good job.

Yall have a nice day now, y'hear?

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Stephen

#23278

0402 stencil design | 5 February, 2003

One thing that worked for me was simply rounding off the pads, making square pads into circlesfor the stencil. It worked but did seem a little strange turning squares into circles for 0603's and 0402's and turning cirlces for BGA's into squares, (but bigger this time).

Stephen

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#23290

0402 stencil design | 5 February, 2003

Stephen's correct. Radiased outer corners on 0402 pads really do seem to improve things. We aim to try "squared-up semicircles".

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