Transient Liquid Phase Bond Acceleration Using Copper Nanowires

Abstract

Increasing heat flux in power electronics modules is taxing the limits of thermal management technologies. This is the result of wide bandgap semiconductor devices with superior voltage blocking capabilities. These same devices have the capability of operating at elevated junction temperatures when properly packaged. Transient liquid phase (TLP) bonding forms intermetallic compounds (IMC) with high melting temperatures at more conventional processing temperatures. Copper and tin transient liquid phase intermetallic formation in SAC305 solder bonds can be accelerated using copper nanowires. This work explores the feasibility of accelerated transient liquid phase bonding using solder and nanowires. This includes electroforming of nanowires, contact angle analysis of solder on nanowires, void analysis using scanning acoustic microscopy (SAM), and cross-sectional scanning electron microscopy (SEM). SAC305 solder is deposited on substrates with 0.4 μm diameter copper nanowires using a 75 μm stencil and subjected to solder reflow. It is found that atmospheric storage at 260 °C results in regions of complete intermetallic bonding after 2 h. Shear strength of bonds completed with this nanowire transient liquid phase bonding method averages 11.99 kg or 13 MPa.