An assessment of lead free solder (Sn3.7Ag0.8Cu) wettability

The National Electronics Manufacturing Initiative (NEMI) standardized lead free solder tin/silver/copper (SnAgCu) ternary system in January 2000. This Sn3.7Ag0.8Cu has higher melting temperature of 217/spl deg/C as compared with current eutectic tin/lead solder (63Sn/37Pb; 183/spl deg/C). Thus, it is a challenge to electronic lead free packaging that requires higher reflow temperature. Optimizing lead-free-reflow-soldering process in second level interconnection is a critical step to ensure reliable solder joint is properly manufactured. This paper presents the assessment of lead free solder wettability. It covers a wide range of soldering parameters with 4 dominant factors and 14 variables. They are 4 different printed circuit board surface coatings (organic surface preservative, OSP; immersion silver, ImAg; electroless nickel immersion gold, ENIG and tin/lead hot air solder leveling), 4 different fluxes in SnAgCu solder pastes, 3 different reflow peak temperatures (225/spl deg/C, 230/spl deg/C and 235/spl deg/C) and 3 different ranges of time above liquidous (30-60s, 60-90s and 120-150s). A test board is designed in these studies. Wetting angles are output parameters and measured using a noncontact laser measurement system.