Photo Stencil, LLC, a leading full-service provider of high-performance stencils and tooling, announces that the paper Screen Printing Solutions for Small Die and Precision Alignment Challenges, by William Coleman PhD, Photo Stencil and Travis Tanner, Plexus Manufacturing Solutions, Boise, Idaho, is now available on the Photo Stencil website at www.photostencil.com/pdf/Screen-Printing-Small-Die.pdf. The paper details the process the companies followed and the solution they found to print solder fillets on very small gold Kovar tabs.

Plexus was trying to print solder fillets on gold Kovar tabs. The tab was just 0.063 +/- 0.002 x 0.125 +/- 0.002 inches and was plated with 150 micro inches (minimum) of nickel and then plated with 100 micro inches (minimum) of gold. The solder fillet needed to align precisely with the tab. Reflow had to be perfect. There could be no gas pockets or voids anywhere on the fillet. The plan was to use a stencil and a squeegee to transfer the solder onto the fillet. However, getting a successful plot was extremely difficult.

We had set extremely high standards because the fillet of the solder on this part needed to be perfect, said Travis Tanner, CIM/CAM tech Sr., Plexus Manufacturing Solutions. We had tried many stencils and made many plots, but they all resulted in failures. When I was talking to Bill Coleman, VP of technology at Photo Stencil, he happened to ask if we had any issues with anything, and I shared the problem with him. As he started to define a solution, we brought our engineering team into the discussions.    The stencils Plexus had been using had six apertures distributed over the large pad for the Kovar tab (slug). Using this configuration of apertures to print the solder paste did not allow sufficient solder paste solvent to escape during reflow. This caused voids under the Kovar tab and poor solder fillets on the edge of the Kovar tab during reflow. The Photo Stencil team worked closely with the process engineers at Plexus to design several test stencil apertures in an attempt to solve the outgassing problem that was causing the defective fillets and solder voids. Photo Stencil utilized its experience in two areas to resolve the problem. (1) AccuScreen aperture design, which employs a honeycomb type aperture structure. (2) Experience with ground plane aperture designs for quad flat pack no lead (QFN) stencil printing.

For the full paper go to www.photostencil.com/pdf/Screen-Printing-Small-Die.pdf. Photo Stencil will be exhibiting at IPC APEX, San Diego, CA, from February 19-21, 2013, at booth #1215. Photo Stencil experts will be available to discuss your printing challenges. For more information, or to arrange an appointment, contact Photo Stencil at info@photostencil.com or visit the Photo Stencil website at http://www.photostencil.com/apex2013.php.

About Plexus

Plexus services mid-to-low volume, higher complexity customer programs characterized by unique flexibility, technology, quality and regulatory requirements. Award-winning customer service is provided to over 140 branded product companies in the Networking/Communications, Healthcare/Life Sciences, Industrial/Commercial and Defense/Security/Aerospace market sectors.

About Photo Stencil

Photo Stencil, LLC provides high-performance stencils, squeegee blades, thick film and metal mask screens and tooling for the surface mount technology (SMT) assembly, solar, and semiconductor industries. Its innovations include the patented AMTX E-FAB electroform stencils, high-performance, proprietary NicAlloy, NicAlloy-XT, laser-cut, and chemetch stencils, and patented electroformed E-Blade squeegee blade. Stencil design support and customer-specific design libraries are also provided. Founded in 1979, Photo Stencil is headquartered in Colorado Springs and has manufacturing facilities in Mexico and Malaysia. For more information follow us on www.linkedin.com/company/photo-stencil-llc, visit www.photostencil.com, or email info@photostencil.com.