Circuits Assembly - January 2008 - (Page 31)

Cover Story Table 9. Flux Performance Relative to Each CTQ Flux A B D H VOC LRNC VOC OAWS Group <85% Barrel Fill Solder Bridges 1623 1275 484 345 579 590 222 97 Solder Balls 16 16 6 SMD Skips 0 5 6 VOC-free OANC both were significantly better than OANC. Table 10. Phase 2 Normalized and Weighted Score Flux A B D H Low VOC LRNC VOC OAWS Group VOC-free OANC Weighted Score 3.875 3.274 1.216 0.956 Vertical Barrel Fill Preheat effect. In general, the hotter the board, the better solder flows into the plated through-holes. The data show that x-ray defects decreased with higher preheat temperature when using water-soluble VOC (OAWS) or rosin low-VOC (LRNC) fluxes, while they increased with higher temperature when using the organic acid no-clean VOC-free fluxes (OANC). This indicated that OAWS and LRNC fluxes are more heat-tolerant than OANC fluxes. Conveyor speed effect. The slower the conveyor speed, the greater the solder contact time so that the longer the solder has to wet to the barrel walls. This held true for the VOC OAWS and low-solid VOC LRNC fluxes. However, slower conveyor speed increased energy input to the board during preheating. As indicated previously, OANC VOCfree no-clean fluxes were less heattolerant. The data showed the lower conveyor speed was better for OANC fluxes, provided the preheat temperature was lower. Vertical barrel fill decreased significantly for OANC fluxes with higher preheat temperature on the 0.125"-thick OSP board for lead-free SnAgCu wave soldering. Flux selection for improved Pb-free barrel fill. High activity fluxes (OAWS and LRNC) offered ~10% better barrel fill than VOC-free no-clean fluxes on the 0.125"-thick OSP boards. LRNC fill was slightly better than OAWS, but Bridges Preheat effect. For the low VOC LRNC flux, lower board temperature resulted in lower solder bridging for Flux D. Preheat was a much more significant factor with respect to VOC-free OANC than OAWS VOC fluxes. By the same reasoning applied with respect to vertical barrel fill, the OANC fluxes appeared to lose activity if overheated and could not perform their function of facilitating solder flow and smooth solder peel-off from the bottom surface of the PWB. This appeared to be a characteristic of organic acids, where the behavior was similar, but higher solid concentration in the OAWS fluxes survived longer than that of the OANC fluxes, leading to reduced bridging. Conveyor speed effect. For the low VOC LRNC flux, higher conveyor speed resulted in less solder bridging for Flux D. High conveyor speed was better for the OANC VOC-free fluxes by similar argument with respect to vertical fill – more heat energy into the flux resulted in reduced effectiveness. Lower conveyor speed was better for the OAWS flux. Smooth peel-off from the board was more critical than thermal stability. Flux selection for reduced solder bridges. On average, OAWS VOC fluxes exhibited less bridging than LRNC low VOC fluxes. OANC VOC-free fluxes had significantly more solder bridging than the other categories under the high energy process conditions: low conveyor speed, low and high preheat temperature. It was only somewhat higher at low conveyor speed and low preheat temperature. LRNC low residue Flux E had an uncharacteristically high rate of bridging with the combination of low conveyor speed and high preheat temperature. 0 EFD Solder Paste If You Think Our Dispensers Are Great You Should Try Our Solder Request your free white paper titled “Choosing The Right Solder Paste” www.efd-inc.com/ads/ca-0108.html A NORDSON COMPANY 800-338-4353 +1-401-434-1680 circuitsassembly.com Circuits Assembly JANUARY 2008 31 http://www.efd-inc.com/ads/ca-0108.html http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - January 2008

Circuits Assembly - January 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business On the Forefront Screen Printing Better Manufacturing Walking on Water Flux Selection for Lead-Free Wave Soldering An A-to-Z Guide to X-Ray Inspection, Part II Evolution in Action Research Priorities for the Electronics Industry Selective Soldering Process Doctor Pb-Free Lessons Learned Materials World Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - January 2008

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