Engineering Dual Alloy Solder Paste Systems to Achieve High Reliability, Energy Savings, Withstand High Junction Temperatures
A single solder alloy system like SAC305 has multiple elements (Sn, Ag & Cu) in one alloy where the composition of every solder particle in the paste is SAC305. Mechanical properties of single alloy systems typically can only go one direction – more ductile / less ductile; more brittle / less brittle; higher melting point / lower melting point.
In this study, three dual alloy solder paste systems were developed with an engineered ratio of two alloys with multiple elements per alloy; and different melting points. This facilitated incorporating multiple characteristics – have both hardness and ductility, allow for increased wetting and low voiding, eliminating low melt intermetallic phases (associated with single alloy system), achieve energy efficiency and reliability with lower peak process temperature (<210 deg C).
- DFHR high reliability dual alloy solder paste system was developed for e-mobility to (a) achieve significantly lower voiding (<25%) in air reflow, eliminate vacuum, eliminate 100% X-ray compared to traditional single alloy systems that cause high levels of voiding (40-50%) with high cost overheads; (b) achieve increased thermo-mechanical reliability for increased cycles (-40/+125C, 3300 cycles) with the right balance of hardness for better fatigue performance and also ductility to address CTE mismatches associated with BGA and WLCSP packages.
- DFLT dual alloy solder paste system with lower peak process temperatures (<210 deg C) to achieve energy efficiency (15-25% lower energy costs compared to SAC305) and increased drop-shock and thermo-mechanical reliability. Low melting point Bi-based single alloy systems are brittle and result in poor drop/shocks. Low melting point In-based single alloy systems can have low-melt intermetallic phases that melt as low as 118 deg C. The dual alloy system was engineered to (a) incorporate ductility and exponentially increase drop-shock performance; (b) eliminate low-melt intermetallic phases; (c) form reliable solder joints with a lower peak process temperature of 200 - 210 deg C.
- DFHT high-temperature dual alloy solder paste system to eliminate Pb and use a high temperature Pb-free alloy for die attach in semiconductor discrete packages. High Bi-content single alloy paste systems (that were tested against high temperature high-Pb alloys) for die attach suffer from poor wetting and excessive brittleness. The Pb-free dual alloy solder paste system for die attach was found to be better than / equal to the standard high-Pb alloy on multiple metrics – voiding, tensile strength, shear strength…
