Fracture Mode Of Solder Joints Research Articles

Effect of IMC Thickness on the Mechanical Properties of Microbumps

With the continuous development of electronic products towards high density and small size, the size of interconnecting solder joints also continues to decrease. Under normal service conditions, micro-solder joints will be subjected to multiple loads at the same time, which in turn will cause many reliability problems in the package structure. This paper focuses on the growth pattern of IMC (Intermetallic compounds) during hot-press bonding and analyses its effect on the shear strength and creep properties of copper pillar micro-bumps. Firstly, the solder joints with different IMC thicknesses were obtained by adjusting the bonding parameters during the thermal compression bonding process, and the growth pattern of IMC during the thermal compression bonding process was analyzed. Secondly, shear experiments were conducted on solder joints with different IMC thicknesses, and the effects of IMC on the shear strength and shear fracture mode of solder joints were analyzed. Finally, creep experiments were performed on cylinder-shaped solder joints with different IMC thicknesses under different stress conditions. The results show that throughout the bonding process, copper atoms migrate under the combined effect of temperature gradient (JTM) and concentration gradient (JCM), and IMC shows asymmetric growth, and the growth rate of IMC gradually decreases with the increase of bonding holding time. Under the same temperature conditions, the shear strength of the solder joint shows a trend of increasing and then decreasing with the increase of holding time. In addition, with the increase of IMC thickness, the shear fracture mode of solder joints changes from ductile fracture in the initial stage to tough-brittle combination fracture and finally evolves to brittle fracture. With the continuous increase of stress, the steady-state creep strain rate of all solder joints increases, and the fracture location tends to be closer to the intersection of the solder and the copper pillar from inside the solder joint. With the increase of IMC thickness, the steady-state creep strain rate of solder joints shows a trend of decreasing and then increasing.

Effects of Interconnect Shape and Thermal-Electro-Migration on Solder Creep of Copper-Pillar Flip Chip Joints

With the development of electronic products toward high density and high reliability, the size of interconnect solder joints and interconnect pitch continues to decrease. Under normal service conditions, solder joints are subjected to thermal–electric–mechanical loads simultaneously, resulting in reliability problems for many package structures. This article investigated the effects of interconnect shape and thermal-electro-migration on solder creep of copper-pillar flip chip joints and analyzed the corresponding failure modes and mechanisms. In this article, solder joints with different shapes were obtained by adjusting the thermal compression bonding process parameters, and creep experiments were performed on the solder joints under different temperature and stress conditions. In addition, we have performed thermoelectric coupling experiments and finite element simulations for different shapes of solder joints. Moreover, creep experiments were conducted on three types of solder joints after 10 and 40 h of thermoelectric coupling pretreatment. The results show that the three solder joints exhibit typical creep characteristics under different experimental conditions and the creep strain rate increases with the increase of shear stress and temperature. Under the same conditions, the creep strain rate of the hourglass-shaped solder joint is always higher than that of the other two solder joints. The electromigration reliability of the hourglass-shaped solder joint is the worst, and the electromigration reliability of the cylinder-shaped solder joint is the best. With the increase of thermoelectric coupling pretreatment time, the creep strain rate of solder joints increased significantly, and the fracture mode of solder joints gradually changed from ductile fracture to brittle fracture. Among the three types of solder joints, the creep resistance of the hourglass-shaped solder joints is greatly affected by the thermoelectric coupling pretreatment.

Interface evolution and mechanical properties of Sn–36Pb–2Ag solder joints under different aging conditions

Electronic packaging products are often subjected to reliability evaluation, Sn–Pb solder is widely used in high-reliability military products due to its excellent soldering performance. Sn–36Pb–2Ag eutectic solder joints were subjected to aging experiments at 75 °C, 100 °C, 125 °C, and 150 °C for 100 h, 250 h, 500 h, and 1000 h, respectively. Continuous Cu3Sn and (Au, Cu)6Sn5 compounds were formed on the printed circuit board (PCB) substrate side after aging experiments, and continuous (Au, Ni)Sn4 and (Au, Ni)3Sn4 compounds were formed on the electronic component side. In addition, the Pb–rich phase on the IMC layer side increased with the increase in aging time and aging temperature. Thus, the mechanical properties of the solder joints seriously reduced, and the push force of the fractured solder joint measured in the push–pull force experiment was reduced from approximately 85 N (125 °C–500 h) to approximately 42 N (150 °C–1000 h). The fracture mode of solder joint under 150 °C–1000 h aging conditions was brittle. Furthermore, the diffusion coefficient and activation energy of the Cu3Sn phase and (Au, Cu)6Sn5 phase on the PCB substrate side were calculated.

Effect of Bonding Time on Microstructure and Shear Property of Cu/In-50Ag/Cu TLP Solder Joints

Here, we study the effect of bonding time on the intermetallic compound (IMC) formation and shear property of Cu/In-50Ag/Cu TLP solder joints based on low-temperature transition liquid phase (TLP) bonding of In-Ag composite powder. The bonding process was carried out at a temperature of 260°C using a wafer bonding machine. The results show that the solder joints are composed of an (Ag,Cu)2In phase and a Cu2In phase in the interfacial diffusion reaction zone and an Ag2In phase and In rich phase in the in␣situ reaction zone. It was observed that the (Ag,Cu)2In phase is formed firstly in the diffusion reaction zone when the bonding time is 0.5 min, then transforms completely into the Cu2In phase when the bonding time reaches 30 min. The shear strength increased and then decreased with increasing bonding time. The observed shear fracture mode of solder joints is brittle.

A newly developed rapid uniform thermal cycle test system for electronic components

Electronic components are difficult to heat or cool uniformly and rapidly because of the low heat conduction properties of the materials used in these components. The present study reports a new rapid thermal fatigue test system that circulates a temperature-controlled air shower around test samples to realize both uniform and rapid temperature control. Since the proposed test system allows multi-unit integration of multiple test chambers, the simultaneous evaluation of several samples under various test conditions can be performed efficiently. Based on the results of the temperature profile measured for a practical electronic circuit board, the proposed system is confirmed to enable the target temperature to be approached rapidly while maintaining a uniform temperature distribution. The proposed system shortens the thermal cycle period from 60min to 12min while generating the same degree of crack damage and the same fracture mode of solder joints.

Effect of Pr addition on properties and Sn whisker growth of Sn–0.3Ag–0.7Cu low-Ag solder for electronic packaging

In this study, trace amount of rare earth Pr was added into Sn–0.3Ag–0.7Cu low-Ag solder to enhance properties of solders. Experimental results indicated that optimal amount of Pr addition (~0.06 wt%) can improve properties of wettability, shear force and ductility of Sn–0.3Ag–0.7Cu low-Ag solder. This is because that solder with optimal Pr addition not only had a refined microstructure but also owned a regular and thin interfacial IMC layer after soldering on Cu substrate. Meanwhile, we have explained the change of morphology and thickness of interfacial IMC layer after Pr addition based on Kim and Tu’s kinetic model of interfacial IMC growth. However, it was found excessive Pr addition led to the formation of PrSn3 phase, which was easy to be oxidized and became a great deterioration on the properties referred above. Besides, the fracture mode of solder joint also gradually changed from ductile fracture to cleavage fracture. Moreover, this oxidized PrSn3 became the birthplace of Sn whisker since it provided abundant supply of Sn sources and compressive stress for Sn whisker growth. By the in-situ observation of Sn whisker growth in 0.5 wt% Pr-doped solder joint, we obtained that the incubation period of Sn whisker is very short and its growth rate may have a great decrease with time extending. Besides, it was found after 1 day at room temperature, spindly and rod-like Sn whiskers also grew in 0.5 wt% Pr-doped solder joint besides dot-shaped Sn whisker that grew in 0.5 wt% Pr-doped solder matrix. We suggest this may be related with the extra compressive stress provided by interfacial IMC layer growth in 0.5 wt% Pr-doped solder joint.