Circuits Assembly - January 2008 - (Page 30)

Cover Story Table 3. List of Fluxes Evaluated Flux A B C D E F G H I J K L M N O P Q LVRE >50% H 2O >50% VOC HRNC VOC OAWS VOC H 2O LRNC VOC Category OANC Carrier H2O Solids 4.50% 3.70% 3.50% 7.00% 7.00% 4.25% 6.00% 2.90% 19.50% 7.00% 20.0% 22.4% 19.5% 15.0% 15.0% 6.20% 2.40% J-STD-004 Des. ORL0 ORL0 ORL1 ROL1 ROL1 ROM0 ROL0 ORL0 ORH1 ORH1 ORH1 ORH1 ORH1 ROM1 ORL1 ORL0 ROL0 A B C D E F G H I J K L M N O P Q LVRE HRNC OAWS LRNC OANC 4.50% 3.70% 3.50% 7.00% 7.00% 4.25% 6.00% 2.90% 19.50% 7.00% 20.00% 22.40% 19.50% 15.00% 15.00% 6.20% 2.40% VOC VOC VOC H2O VOC 0.783 1.075 1.169 1.461 0.617 0.656 0.656 6 0.632 0.670 0.673 0.773 0.767 0.918 1.326 H2O Table 8. Summary of Phase 1 Results Flux Score Phase 1 1.072 1.200 1.200 2 1.228 Group Solids Base Weighted Table 7. Flux Residue Score Score 1 2 3 4 5 Description No residue Evenly coated with thin residue (minimum white patches) Mostly even but with some slightly brown residue Even, thick residue Uneven, thick residue, flaky brown residue, dross patches Table 4. Factors "Critical to Quality" and Impact Levels CTQ Vertical barrel fill Solder bridges Bottom SMD skips Solder balls Residue Phase 1 5 4 2 2 1 Phase 2 5 4 2 2 N/A N/A – Not assessed in this phase Results and Discussion Table 8 shows how all fluxes performed in Phase 1 screening. The weighted score is based on defects, so the lower the value, the better the flux performance. In general, the water-soluble (OAWS) and high-solid rosin (HRNC) no-clean fluxes performed best, along with the low-VOC emulsion flux. Low-solid rosin no-clean fluxes (LRNC) showed the next best results. Low-solid organic acid VOC-free (OANC) fluxes, along with the high-VOC rosin emulsion no-clean fluxes, ranked lowest. Table A1 in the Appendix shows detail with respect to specific CTQs/ defects. While the high-residue rosin VOC fluxes performed well, customer acceptance would be low because of cosmetic concerns and in-circuit test pin probability issues. Having identified the best of these fluxes, a possible solution for solder quality on the most difficult boards – particularly vertical fill – is identified if the customer is not concerned about the appearance of residue and has measures in place to remove flux residue for pin probeability. One of the rosin emulsion fluxes (Flux P) showed promise; however, it did not pass Bellcore SIR testing and was removed from consideration. The other rosin emul- sion flux, Flux Q, ranked among the lowest performers, and contained 70% VOC, in spite of being listed as a low-VOC flux. There was also evidence that some spray fluxers clogged as a result of the rosin solids of the LVRE type fluxes, which are suspended in the low-VOC solution and are sheared out of solution by the mechanical pump action of the spray fluxer. The top fluxes in each of the remaining categories were used in the Phase 2 verification runs and are highlighted in Table 8 (Fluxes A, B, D, H). As already mentioned, Phase 2 verification was performed according to the matrix shown in Table 5. Table 9 shows Phase 2 verification phase defect results. Each CTQ was again normalized and weighted, and the fluxes were ranked accordingly (Table 10). As indicated, the lower the score, the better the flux performed. Given that the fluxes selected for verification in Phase 2 were among the best on the market, not only was the optimum flux determined for each category, but also the defect data were analyzed to determine process parameters having the greatest influence on the performance of the fluxes. The following sections summarize many of the process conditions considered critical to product quality and the significant factors contributing to each. 30 Circuits Assembly JANUARY 2008 circuitsassembly.com http://circuitsassembly.com

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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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