Circuits Assembly - March 2008 - (Page 44)

Cover Story duction operations. Standalone prototype lines are becoming harder to justify. It is difficult to dedicate multi-million dollar, state-of-the-art placement lines to NPI activities, yet using obsolete equipment offers no benefit to a true product validation on the production line. How do engineers find time on production lines to properly profile the PCB through the reflow process? By running sample assemblies with thermocouples through reflow numerous times to get the right profile, with manual inspection of the solder joints and flux residue to determine the correct target profile. Engineers develop matrix charts on board size, layer count and complexity to approximate the profile so process development time is minimized. How does vapor phase improve this process? With its heat transfer characteristics, and the uniformity at which it accomplishes this, it is easier to understand the profiling relationship between PCBs. Vapor phase reflow profiling can be classified by process type to the point where there are fewer profiles to develop. For instance, standard multilayer 0.062"-thick boards can follow the same Pb-based vapor phase profile regardless of component complexity. Heat load monitoring during soldering permits the systems to profile almost automatically. Ramp rates and soak times at peak temperature can be engineer-defined and controlled by the systems, regardless of product mix. In a true one-piece flow on a prototype, it is much easier to get it right the first time using vapor phase processing. Inadequate reflow temperature or over-temperature on the first article is virtually eliminated. VP and Pb-Free Components Pb-free components are going to be introduced in Pb-based processes. This challenge to engineering and quality is a huge concern and one that needs scrutiny. EMS providers rely on component suppliers to ensure the Pb-free transition on component terminations is seamless to their soldering processes, but that rarely happens. Termination changes require additional modification to solder profiles and flux chemistries to ensure proper wetting of the solder to the Pb-free termination. Nitrogen in convection reflow is becoming more a requirement than an option, and nitrogen is expensive. Vapor phase reflow offers an advantage over convection in this Pb-free transition phase. The inert environment and consistency of heat transfer permit vapor phase to be more forgiving with Pb-free component terminations. Less active no-clean flux chemistries have proved adequate in soldering Pb-free terminations that demand highactivity fluxes in convection reflow. Another advantage of vapor phase reflow is its lower processing temperature. Convection or IR process temperatures can reach 245° to 265°C at the component level. VP temperatures stay at 230°C. The lower temperatures make it possible to use standard FR substrate material rather than (higher Rework & Repair One product line to exceed your expectations and take care of all your lead-free rework and repair needs. All Chemtronics lead-free products are: Engineered for high temperature lead-free applications Specifically designed for all lead-free solder RoHS compliant CALL NOW! Contact ITW Chemtronics today for more information about the new Lead-Free product line. Call our technical hotline at 770-832-4401, or email us at askchemtronics@chemtronics.com. Nothing Cleans Like Chemtronics Soder-Wick®, Flux-Off®, Chemask®, CircuitWorks® and Chemtronics® are registered trademarks of ITW Chemtronics. ©2005 All rights reserved. 800-645-5244 / 770-424-4888 • www.chemtronics.com 44 Circuits Assembly MARCH 2008 circuitsassembly.com http://www.chemtronics.com http://www.chemtronics.com http://circuitsassembly.com

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Circuits Assembly - March 2008 Caveat Lector Letters Industry News Market Watch Talking Heads Focus on Business On the Forefront Screen Printing What Drives the Crowd? Mastering ESD Control in Automated Handling Systems Beating the RoHS Heat Trade Secrets True to Its Roots The Road Abroad - Strategic Alliance or Greenfield Facility? Tech Tips Wave Soldering Test and Inspection Process Doctor Pb-Free Lessons Learned Getting Lean Materials World Equipment Advances Apex Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - March 2008

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