Circuits Assembly - March 2008 - (Page 42)

Cover Story in manufacturing today, with few exceptions that also pertain to convection and IR. Components such as non-sealed switches and SMT sensor devices should be reviewed for compatibility. Also, with the heat transfer characteristics of vapor phase, soldering SMT electrolytic capacitors needs to be monitored closely. It must be understood that components on the PCB during reflow will see the peak temperature set by the boiling point of the fluid used. Benefits to Lean Vapor phase reflow also benefits the Lean Manufacturing environment. A key concern with vapor phase reflow in volume manufacturing is throughput; many manufacturing engineers question how they could accept a reflow process that is going to bottleneck the SMT placement process. The reason for this concern is the inherent design of VP systems exposes the PCB to the vapor process longer than the tact time of the placement processes. To deal with this, vapor phase systems are now designed with throughput in mind. Inline machines are available that can produce double-sided SMT PCB at rates comparable to inline convection and IR reflow processes. These designs include inline batch carrier and inline edge chain systems, designed with sub 30-sec. tact times. Just like any other process machine design, each of these has pros and cons. Batch carrier machines tend to be more mechanical and prone to more maintenance, while inline systems are more gated by the size of the PCB being processed, and less flexible when it comes to changeovers. Lean manufacturing principles in lowto-mid volume manufacturing emphasize minimal changeover time. Changing from product to product needs to be seamless and completed faster than the time taken by upstream processes. It is standard process for a reflow oven to be processing the last PCB of one production lot, while changes for the next lot are being completed on the placement machines. Changeover time can be an issue in convection reflow if the reflow zone temperature changes are significant between the two products and the edge carriers need to be resized. Inline vapor phase systems designed with edge chain conveyors will have the same constraints as inline convection systems, and it is necessary to wait for preheat changes to materialize before the new process starts. Conversely, inline batch carrier vapor phase systems are capable of processing one product lot’s board size changes while another lot is still being soldered. PCB size adjustments can be completed; with IR preheat followed by vapor phase soldering, there is no delay to changeover once the sizing is completed. Lean principles also apply to new product development. It is imperative to maximize capital expenses. To do this, manufacturers must find ways to launch new products on production lines used in sustaining pro- 42 Circuits Assembly MARCH 2008 circuitsassembly.com http://www.dymax.com/conformalcoating 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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