LEAD-FREE PROCESS AND PRODUCT TRANSITION: Phase II. Paste Characteristic Study by Response Assessment and Printing Optimization by Taguchi Method

摘要

To fulfill the lead-free product and process transition for volume and high-end telecommunication products, few test vehicles with advanced feature for extensive reliability test on representative package types and solder joint were designed. Assessments were performed on various paste types and surface finishes. For paste characterization, SIR, Corrosion, slump, solder ball, printing, wetting, strength, IMC and microstructure were evaluated. Tremendous amount of control variables, are factored into a Design Of Experiment to assess the paste printability. Four different categories of control parameters from stencil tooling (aperature, thickness), paste (type, stirring time, usage dwell time), printer (speed, snap off, cleaning frequency), and operation environment (process humidity and temperature) were treated as main effects and interactions were orthogonally studied. A Taguchi approach with maximizing signal to noise ratio by using the smaller the better solver on STDEV and p-value was used in analysis. Future study approach on thermal optimization, package and solder joint reliability and wave-soldering optimization vs. thermal management strategy also will be presented. Finally, field mechanical stress will be monitored and FEM modeling will be created to assess and infer beyond the limitation of instrumentation. A methodology to established the residual stress under mechanical bending to the reliability scale is proposed. Strengthening mechanism hypothesis for the lead-free Sn-Ag-Cu ternary system was theorized and will be proven in the near future.