Automotive Reliability Benchmarks for High-Lead Pb–Sn–Ag Die Attach in PQFN Power Packages: Implications for Pb-Free Transition

Power Quad Flat No-Lead (PQFN) packages utilizing high-lead (High-Pb) Pb–Sn–Ag solders remain prevalent in automotive power semiconductors despite impending regulatory restrictions. With EU RoHS exemptions expiring in 2026–2027, quantitative performance benchmarks for High-Pb die attach become essential for evaluating Pb-free alternatives. We examined alloy composition, reflow temperature, and assembly parameter effects on Pb–Sn–Ag solder joint quality and reliability in automotive PQFN packages. Three solder compositions (Pb–10Sn–2.0Ag, Pb–5Sn–2.5Ag, Pb–2Sn–2.5Ag) were evaluated across reflow temperatures of 340–380°C under controlled nitrogen atmospheres. Assembly variables included stencil aperture designs and die bonding force optimization. Joint quality was assessed through void analysis, bond-line thickness measurement, and die rotation characterization. Reliability evaluation employed thermal cycling (–55°C /150°C, 1,000 cycles). Pb–10Sn–2.0Ag showed superior performance with void fractions decreasing from 5.1% to 0.96% as reflow temperature increased from 340°C to 380°C, accompanied by stable bond-line thickness (54–60 μm). Oxygen concentration (50–500 ppm) minimally affected void formation. Die rotation was effectively controlled through bow-tie stencil apertures (1.61° vs. 2.76° for control) and optimized bonding force (0.75° at 1.2 N). All compositions survived 1,000 thermal cycles without cracking, through Pb–5Sn–0.3Ag exhibited excessive intermetallic compound growth (12–17 μm). Our findings establish baseline performance metrics (void fraction ≤5%, die rotation ≤2°, controlled IMC growth) for qualifying emerging Pb-free alternatives in automotive applications.