Circuits Assembly - August 2008 - (Page 42)

Component Advances Molex’s Solder Charge Interface older Charge PCB interface optimizes benefits of density of a BGA tail, but improves on the latter’s shortfalls in processing and manufacturing. The concept consists of a blanked solder mass that gets extruded through a hole near the tip of a terminal until it fills a volume on the opposite side of the pin. The chamfer on the Solder Charge side of the hole provides retention and prevents the solder from backing out of the terminal. While a BGA is manually placed and then heated to adhere to the j-lead on the bottom of a connector, the novel interface is more precise as it uses stamping equipment for adhesion to the terminal, whereas with a stamping die one can be precise to a reported 0.0001". Further, it permits the transmission line to directly reach the PCB, minimally disrupting the design and maintaining the system’s electrical properties. Solder Charge uses standard reflow processing, and reflow profiles are available for all common products. It extends slightly beyond the tip of the terminal to seat within the solder paste on the solder pad; the terminals will lower onto the pad within the reflow oven. In reflow, the solder forms a bugle-shaped solder fillet, providing a 360° engulfment around the terminal and through the hole in the pin for added retention strength. Additionally, the interface is said to provide a significant amount of forgiveness to compensate for variability in the PCB flatness, giving added assurance the PCB adhesion will work. Incorporating the technology is said to offer several benefits over standard BGA attachments, including: • A mechanical design that permits post-processing visual inspection, limiting the need for x-ray. • Increased PCB retention strength – roughly three times as strong as typical BGAs – that reduces stress on solder joints, increases compliancy and lowers applied costs. • Reduced cycle times and fewer rework and secondary processing steps that promote increased output. • Precise formation of stamping die, which offers enhanced precision in the Solder Charge formation and adhesion process. • Flexible solder mass that compensates for board warping. S The interface comes in the HDMezz and SEARAY(1) connectors, in new designs in development, and in SnPb or Pb-free designs. Available from Molex (molex.com). n Continued from pg. 24 Therefore, it’s important to have process-oriented controls and checks and balances, as well as disciplined corrective actions. Process traceability is critical for locating and correcting even the most difficult problems as well. Take, for example, a short between power and ground planes in a 16-layer board. Unless proper process traceability is in place, it is difficult to identify and correct the problem, especially if the board has been assembled. In situations like this, an inordinate amount of time and money is spent because assembled components add a layer of complexity to problem identification, testing and debugging. On the other hand, such issues would have been easier – and less expensive – to troubleshoot provided advanced AOI had been deployed. Advanced AOI can be used to locate opens, shorts and registration issues when innerlayers are constructed during fabrication. For example, when equipment used to print silkscreen on a board is not calibrated, it can result in creating a non-conductive paste or covering on a surface mount pad, creating a current blockage (Figure 2). First-article inspection for prototypes and production is the best way to uncover problematic areas in these and other instances. Equally important, it is an excellent indicator of how efficient a fabricator’s processes are. High first-article yields – say 90%-plus – indicate processes are well defined and controlled. Low first-article yields speak loudly that a fabricator’s equipment, personnel and practices are out of kilter. First-article problems can stem from poorly calibrated equipment, callous or untrained personnel, lack of preventive maintenance and a host of other reasons. Therefore, to avoid PWB procurement issues, it is prudent to institute a well thought-out policy and associated purchasing practices and, at the same time, anticipate a host of adverse purchasing conditions. The worst-case scenario never happens, unless, of course, it does. For example, an undetected minor board error can cascade into a complete PCB order remake. For example (Figure 3), a defect results when part of a trace is clipped by poor process control during fabrication. At times like this, a remake can involve orders ranging from 500 to 5,000 boards. Besides lost time, extra shipping costs cannot be recovered if the board is fabricated overseas. Further, returning boards to an overseas fabricator involves more time and hassle because a laundry list of certifications must be provided to customs officials in these countries. n Zulki Khan is president and founder, NexLogic Technologies Inc. (nexlogic. com); zk@nexlogic.com. The Solder Charge PCB interface eliminates the need for BGA tails, especially in high-speed designs. 42 Circuits Assembly AUGUST 2008 circuitsassembly.com http://molex.com http://www.nexlogic.com http://www.nexlogic.com http://circuitsassembly.com

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Circuits Assembly - August 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Screen Printing Better Manufacturing Auditing a Fabricatior Cutting Machine Programming Time Simultaneous Acoustic Imaging and Surface Mapping Tech Tips Soldering Test and Inspection Process Doctor Pb-Free Lessons Learned Getting Lean Component Advances Product Spotlight Ad Index Assembly Insider Techincal Abstracts

Circuits Assembly - August 2008

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