Circuits Assembly - January 2008 - (Page 28)

Cover Story Flux Selection for Lead-Free Wave Soldering By Douglas Watson, Jasbir Bath and Pan Wei Chih A DoE clarifies the best types, best available flux within each type, and process limits for each. Ed.: The complete article can be found at circuitsassembly.com/ cms/content/view/5895. his article discusses an approach to selecting liquid wave solder fluxes. It includes the design of an internal company test vehicle with a range of component types and design characteristics, preliminary flux performance testing, and results verification on the top-performing fluxes. Included is discussion of the gaps between the capability of existing flux chemistries and requirements of not only Pbfree assembly, but from industry Table 2. Wave Solder Test Vehicle Components Reference standards and customer expectations Description Designator with respect to flux residue and PTH Table 1. Wave Solder Text Vehicle Specifications PCB Board dimension Board thickness Total layers Surface finish Laminate material (core) Solder mask Board Tg Specifications 7” x 5.5” 0.125” 16 OSP (high-temperature rated) FR-406 PSR-4000 (GF5S) ~170°C (High Tg FR-4) 64-pin header DIP16 Axial resistor Bottom-side SMT SO16 SOT23 1206 resistor 0805 resistor 0603 capacitor U1-U12, U30 D1-D20 R50-R88 R100-R139 C301-C320 J2A, J4, J4A U40-U42 R1-R25 T solder quality on more complex assembly designs. Experimentation. The board used for flux testing was the internal company wave test vehicle (TV) (Figures 1 and 2). Table 1 lists general properties of the tested board. The board was available in thicknesses of 0.093", 0.125" and 0.180". Surface finishes could be selected based on the needs of the experiment. The most commonly used surface finishes have been organic solderability preservative (OSP) and immersion silver (ImmAg). The TV was for mechanical testing only and had no electrical functionality. This board and related components (Table 2) were designed to demonstrate the limits of the wave soldering process. The following sections summarize many of the process conditions considered critical to product quality and the significant factors contributing to each. Quantity per Assy. 3 3 25 13 20 39 40 20 28 Circuits Assembly JANUARY 2008 circuitsassembly.com http://circuitsassembly.com/cms/content/view/5895 http://circuitsassembly.com/cms/content/view/5895 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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