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Power Cycling Reliability Assessment of Various Die-Attach Materials
Keywords: die-attach, SiC, reliability
Thermal performance and reliability of power electronic packages is significantly impacted by the quality of the attach interface between semiconductor devices to a substrate and between the substrate to a heat sink. Attach interfaces experience fatigue due to CTE mismatch between dissimilar materials when subjected to thermal and power cycles over the lifetime of the package. This work investigates the reliability of several die-attach materials through power cycling of SiC diodes attached to a direct bonded copper (DBC) AlN substrate. A standard lead-based solder (SnPb), lead-free solder (SnAgCu), eutectic braze alloy (AuSn), and a polyimide (Epo-Teks P-1011) are the materials chosen for comparison. An initial quality assessment of each die-attach interface was performed using both scanning acoustic and x-ray microscopy. CALCE (Center for Advanced Life Cycle Engineering) software was used to perform a physics of failure based reliability assessment of the solder joints with defined loading conditions to provide an initial estimate of the time to failure prior to conducting power cycling tests. Additionally, finite element heat transfer computations on a simulation model of the package were obtained using SolidWorks and CosmosWorks to compare with the experimental results. The experimental set-up consisted of four diodes bonded to a DBC AlN substrate attached to a liquid-cooled heatsink. The diodes were connected in series with a DC power supply and an IGBT switch. The switch cycled power through the circuit resulting in a determined temperature rise for the diodes as measured by an infrared camera. Individual device power measurements were collected using a data acquisition system to record the voltage drop across each diode and the current in the circuit. Due to the fast thermal time constant of the set-up, thermal equilibrium was rapidly achieved. Thus, an accelerated experimental determination of the performance for the die-attach materials was obtained.
Dimeji Ibitayo, Chemical Engineer
U.S. Army Research Laboratory
Adelphi, MD

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