Power Module Interconnection Reliability in BTS Applications

• Published in: IEEE transactions on device and materials reliability 2019-09, Vol.19 (3), p.484-493
• Main Authors: Putaala, Jussi, Hagberg, Juha, Kangasvieri, Tero, Raumanni, Juha, Salmela, Olli, Rahko, Matti, Jaaskelainen, Jussi, Galkin, Timo, Nousiainen, Olli, Jantunen, Heli
• Format: Magazinearticle
• Language: English
• Subjects: Acoustic microscopes; Computer simulation; Constitutive equations; Constitutive relationships; Cracks; Creep; Creep (materials); Failure analysis; Finite element analysis; Flanges; Inspection; Interconnections; Lead free; Materials selection; Microscopy; Modules; Optical microscopy; power amplifier; Power amplifiers; Power semiconductor devices; Reliability; Scanning acoustic microscopy; Scanning electron microscopy; Semiconductor devices; Simulation; solder joint; Stress; Substrates; Thermal cycling; Thermal expansion; Thermal mismatch; Thermal stress
• ISSN: 1530-4388; 1558-2574
• DOI: 10.1109/TDMR.2019.2920316

In this paper, the reliability of RF power transistors' solder attachments is characterized through experiments and simulations. Test cases consisted of power amplifier (PA) modules on AlSi10Mg substrates with either a low or high mutual thermal mismatch. The module's flange interconnections were stressed by means of thermal cycling testing (TCT) in the 15 °C-95 °C range. Scanning acoustic microscopy (SAM) was used intermittently to inspect the interconnections of selected structures during cycling breaks. Optical cross-polarization microscopy and scanning electron microscopy were used in the failure analysis of the solder joints. Different materials and dimensional variations were tested in simulations to observe differences in thermal stress. The viscoplastic behavior of lead-free solder in the interconnection was modeled using Anand's constitutive equations. The first cracks could be observed with SAM after 100 cycles. SAM imaging showed that in the worst case, 72% of the interconnection area had cracked at the end of the 1100-cycle TCT. Only a marginal amount of cracks could be observed in PA modules with a better coefficients of thermal expansion match to the substrate. Simulations indicated that it is possible to decrease creep energies significantly and thereby increase the lifetime expectancy of interconnections by selecting the correct materials and structures.