Technical Articles

Abstract.  Despite much research and discussion on the subject of reflow profiling, many questions and a good deal of confusion still exist. What is clear is that the pains often associated with profiling can be reduced if there is a strong understanding of the variables that can be encountered during the reflow process, as well as the metallurgical dynamics of the soldering process. This paper shall provide a brief outline of the reflow profile in general, with specific emphasis placed upon the suggested time spent above the melting temperature of the solder. The guidelines for soldering to various surfaces and with alternative solder alloys also are discussed.

General Reflow Guidelines.  While varying reflow profiles may be utilized to achieve optimum soldering results, in general these share many of the same details. For the Sn63/Pb37 and Sn62/Pb36/Ag2 alloys, the typical profile length is 3 ½ to 4...

Abstract.  SMT printing will require reexamination and process adjustment when lead-free soldering is implemented. If a high quality solder paste is used and standard rules for SMT printing are followed, consistent stencil life, aperture release, print definition, high-speed print capabilities and print repeatability may be expected.

Introduction.  As compared to tin-lead solder pastes, lead-free pastes should exhibit similar features on the stencil and many equipment set points should transition well. However, implementation of lead-free solder paste does necessitate some adjustment, as well as providing an opportunity to review and fine-tune several key printing parameters.

Many manufacturers currently use reduced aperture-to-pad ratios to prevent bridging and solder beading. Due to differences in the solderability characteristics of lead-free circuit board finishes and the inability of lead-free solders to spread as well as tin-lead, reduced stencil...

When converting to lead-free wave soldering, several important business decisions need to be made. The first decision pertains to the wave solder pot. Wave solder pots designed specifically for lead-free soldering are resistant to tin corrosion, contain higher-grade stainless steal components, and typically contain lightweight titanium hardware such as nuts and bolts designed to float rather than sink if dropped in the solder pot. It is well understood that Sn-Ag-Cu alloys are aggressive toward the materials found in many older wave solder machines. If implementing a Sn-Ag-Cu alloy for wave soldering, it is recommended that a new wave solder machine, or at the very least a new solder pot, is part of your expenditure.

Lower-budget operations and/or those that currently have a relatively new wave machine that is not fully depreciated may want to continue using current wave soldering equipment after lead-free soldering has been implemented....

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