Interfacial properties of chip bonding using reflow and intense pulsed light soldering: Effects of Cu pillar structure with Ni layer

As the demand for ultra-small/high-performance semiconductor packages increases, soldering technology for controlling the joints interface is being studied. Among them, the intense pulsed light (IPL) soldering using light energy is insufficient. Currently, research on IPL soldering is limited to solder bump structure, and studies on the interfacial reaction of the Cu pillar bump structure are still insufficient. In addition, the studies on the growth rate of the interfacial IMC formed through IPL soldering are insufficient. This study compared the interfacial reactions during chip bonding using reflow and IPL soldering. In addition, the effect of a Ni diffusion barrier layer between the Cu pillar and solder caps in the chip structure was evaluated. In the Cu pillar/solder (CS) structure, intermetallic compound (IMC) layers were observed at the interfaces, including Cu 6 Sn 5 and a very thin Cu 3 Sn layer. In the Cu pillar/Ni/solder (CNS) structure, a Ni 3 Sn 4 IMC layer was observed at the interfaces. Compared to reflow soldering, thinner interfacial IMC layers were formed during IPL soldering due to the shorter soldering time, and thinner IMC layers were formed in the CNS structure than in the CS structure due to the Ni layer reducing atomic diffusion. High-temperature aging (150 ° C for 1000 h) after soldering resulted in IMC layer growth that was linear with the square root of time in all samples. The growth rate of the interfacial IMC layers was faster in the chips bonded by IPL soldering than by reflow soldering. In addition, the growth rate of the interfacial IMC in the CS structure was higher than that in the CNS structure. The IMC grains formed at the joint interfaces under all conditions exhibited random orientations. An evaluation of the mechanical properties of the solder joints confirmed that fracture occurred at the Si chip/Cu pillar interface for all samples, indicating that strong and stable solder joints were formed. Therefore, IPL soldering is considered a promising alternative to reflow soldering in the development of high-performance semiconductor devices. • Interfacial reactions during chip bonding using reflow and IPL soldering compared. • Intermetallic compound (IMC) layers included Cu 6 Sn 5 and a very thin Cu 3 Sn layer. • IPL soldering produced thinner IMC layers than reflow soldering. • Thinner IMC layers were formed in Cu pillar/Ni/solder than in Cu pillar/solder. • All IMC layers showed linear growth upon high-temperature aging after soldering.