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440-R + Ultrasonics = Safe & Efficient Cleaning
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Smart Sonic
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Dedicated Tool for Process Development
Advanced plating capability at Uyemura Tech Center: Process Development, UBM, pilot production. ENIG, ENEPIG, EPIG/EPAG, RAIG immersion gold; all substrates. On-site analysis.
Uyemura
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| Ask the Experts |
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August 15, 2011 - Updated
August 15, 2011 - Originally Posted
Stepped Stencil Limit
I've used stencils with 1 and 2 mil steps successfully, but recently I've seen a problem with a 3 mil step (8 mil foil stepped down over most of the printed area to a 5 mil thickness). The problem I'm seeing is that the stencil tends to warp around apertures, particularly in areas like fine pitch QFPs, where there are long apertures close together, and the remaining material is a thin strip. This warp makes the stencil act thicker and allow more paste to be deposited, leading to bridges in the fine pitch QFPs. Is there a rule of thumb regarding the amount of step that can be etched into a stencil?
B. B.
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| Expert Panel Responses |
IPC 7525 recommends 35 to 50 mils keep-out for each 1 mil of step.
Bill Coleman
Vice President Technology, Photo Stencil
For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.
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