Microstructure of Ag Nano Paste Joint and Its Influence on Reliability

Abstract

In this paper, the microstructure of Ag nano paste joint was investigated in pressure-less sintering conditions, and the influence of the microstructure on the joint’s reliability was studied. Firstly, silver nanoparticles (Ag NPs) were synthesized using the redox reaction method. To tightly stack the Ag NPs in nano paste, Ag NPs with sizes of 30~50 nm and submicron-sized Ag particles were mixed. It was found that increasing the sintering temperature or sintering time can reduce the porosity of the bonding layer and the interfacial crack simultaneously, resulting in higher shear strength. When sintering at a temperature of 250 °C, a complete bonding interface was formed, with a 0.68 μm interdiffusion layer. At a higher temperature (300 °C), the bonding interface reached 1.5 μm, providing 35.9 ± 1.7 MPa of shear strength. The reliability of the die attachment was analyzed under thermal shocking from −65 °C to 150 °C for 50 cycles. As the crack could quickly grow through the interfacial defects, the separation ratio was 85% and 67% when sintered at 150 °C and 200 °C, respectively. Because of the reliable bonding interface between the die and the substrate, the Ag nano paste joint formed a slight crack on the edge of the die when sintering at 250 °C. When the joint was sintered at 300 °C, the small voids became large voids, which featured lower resistance to crack growth. Thus, instead of further improved reliability, the separation ratio increased to 37%.

Low-Temperature Sintering of Ag Composite Pastes with Different Metal Organic Decomposition Additions

“…Numerous attempts have been made to lower the sintering temperature by decreasing the size of the Ag particles, but this approach often leads to the agglomeration of Ag nanoparticles at room temperature during synthesis and storage periods. Moreover, synthesizing Ag nanoparticles with diameters below 20 nm is challenging [ 13 , 14 ]. Recent studies have suggested that adding silver salts, such as AgO and AgC 2 O 4 , to Ag pastes can further decrease the sintering temperature by forming Ag nanoparticles through decomposition.…”

A Multilayer Paste Based on Ag Nanoparticles with Cu@Sn for Die Attachment in Power Device Packaging

“…A silver composite paste with micron-sized silver flakes as the skeleton and silver nanoparticles as the binder has been proposed to change the sintering process from being surface diffusion-driven to lattice diffusion-driven to improve the sintering drive [ 2 , 6 , 9 ]. In addition, Tian et al mixed Ag NPs with sizes of 30–50 nm and submicron Ag particles to tightly stack Ag NPs in paste [ 10 ].…”

Study of Thermal Stress Fluctuations at the Die-Attach Solder Interface Using the Finite Element Method

“…In order to meet the requirements of die-attach technologies and the Restriction of Hazardous Substances (RoHS) directive, a series of die-attach materials, such as Sn-Ag, Sn-Ag-Cu (i.e., SAC) solder alloys and sintering silver paste were developed [7][8][9]. Among them, the SAC solder has become a type of widely used lead-free solder in the electronics industry by the virtue of its adequate thermal fatigue properties, strength, and wettability [10].…”