Phil Zarrow, ITM Consulting With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall, ITM Consulting A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.
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I had an application where we had a nineties designed board with mixed technology, including 4 fine-pitch QFP's as well as 8 .050" pitch J-leaded devices. We used a 5 mil stencil and constantly got shorting on the fine-pitch and insufficient solder on the J-leads (quad 16-pin).
I ordered a 6 mil stencil etched down to 4 mil, leaving islands of 6 mil for the J-leads. I also designed laser cut squeegees that would lift over the J-lead islands. The squeegees had .003" slits that terminated at the top, just under the holder with .100" holes to prevent stress risers.
We suspected that the squeegees would leave lines of paste from the splits, but the splits clogged with paste and never left any features. It cured the shorting of the fine pitch as well as the insufficient J-leads. Both components came from PhotoEtch in Lowell, Ma.
It's worth it to use dedicated squeegee holders in this case, but the blades don't work-harden and distort or crack like they would if they weren't laser cut.
George Garneau, MKS Instruments, USA
Either a rubber or metal squeegee can be used with a stepped solder paste stencil, but most use metal squeegee blades. However, the usable life of a metal squeegee blade is reduced due to accelerated wear caused by the metal squeegee blade impacting the edges of the step areas.
The proper depth of a step is determined by the stencil aperture sizes within the step areas. The foil thickness within the step areas must be thin enough to meet, or exceed, the minimum aspect ratio and/or surface area ratio requirements for the stencil aperture sizes. Most stepped solder paste stencils have step depths in 0.001" increments.
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There's simply no reason to scrap circuit boards when they have contacts contaminated with solder. Restore them using the Gold Contact Plating Kit. CircuitMedic
Once you have made the decision to package your electronics with rigid flex, it makes sense to pick a production partner who can build it right. Printed Circuits, Inc.
Once you have made the decision to package your electronics with rigid flex, it makes sense to pick a production partner who can build it right. Printed Circuits, Inc.
Components encapsulated in plastic or organic compounds are susceptible to moisture damage. So are PCBs, all can cause early field failures. Control MSDs per IPC J-Std-033b.1 and 1601. Super Dry®
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Use the form below to submit a comment.
I ordered a 6 mil stencil etched down to 4 mil, leaving islands of 6 mil for the J-leads. I also designed laser cut squeegees that would lift over the J-lead islands. The squeegees had .003" slits that terminated at the top, just under the holder with .100" holes to prevent stress risers.
We suspected that the squeegees would leave lines of paste from the splits, but the splits clogged with paste and never left any features. It cured the shorting of the fine pitch as well as the insufficient J-leads. Both components came from PhotoEtch in Lowell, Ma.
It's worth it to use dedicated squeegee holders in this case, but the blades don't work-harden and distort or crack like they would if they weren't laser cut.
George Garneau, MKS Instruments, USA
The proper depth of a step is determined by the stencil aperture sizes within the step areas. The foil thickness within the step areas must be thin enough to meet, or exceed, the minimum aspect ratio and/or surface area ratio requirements for the stencil aperture sizes. Most stepped solder paste stencils have step depths in 0.001" increments.
Mike Scimeca, FCT Assembly