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Printing Takes On New Meanings As PCB Technology Advances

Advanced technology marches on and these advances are rapidly making inroads into PCB assembly. A major impact is being made on solder paste printing due to the challenges finer pin pitch of 0.5 mm and on down present to the PCB design, fab, and assembly house. But at the same time, OEMs demand not only increased reliability on their high-density PCB applications, but also, high, near 100 percent yields.

Keeping up with PCB technologies is of utmost importance to properly serve the OEM. That’s one of the top reasons NexLogic recently installed on its assembly floor a new Speedline Technologies MPM Momentum stencil printer. The new system represents the most advanced stencil printer technology currently available in the industry.

To learn more about what you can expect about printing difficult PCB applications, check out our article appearing in SMT Magazine.

Meanwhile, it is important to get a good understanding of advanced stencil printing for your upcoming PCB applications. Here are a few tips and guidelines to know so you can be better prepared for the next rounds of PCB technology.

  • Understand that solder-charge SMT multiple-pin connectors (Fig. 1) are a major challenge for soldering quality and require thick solder paste. But 0.4 mm pitch CSP and small bump flip-chips need a thinner stencil to achieve a higher area ratio by acquiring sufficient solder paste release.
  • Consider newer and better stencils like 304 series stainless steel designed for laser-cutting and solder paste stencil printing. OEM benefits include time and money savings.
  • New stencil material also provides flatter stencils, allowing for more accurate printing with improved registration and print accuracy.
  • Also, new stencil material offers uniform fine grain structure to yield smoother aperture walls and better paste releasing.
  • To improve the printing process, three standard global fiducial marks should be placed on the three corners of a PCB to help achieve accurate printing paste registration and accurate component placement.
  • Tight control of stencil’s uniform thickness is very important. Thickness tolerance directly affects paste height control tolerance and final quality.

With a well-controlled printing process and other SMT processes, flip-chip/CSP/WLP paste-printing defects can be prevented, while achieving the same yield as the flux-only process yield. This helps to eliminate the high-cost and time-consuming under fill process. It also avoids large capital expenditure ñ using two printers and two stencils: one printer with a thin stencil to print the miniature components and a second in-line printer with a thicker stencil to cover the large solder paste volume requirement.