Papers by Author: Chun Qing Wang

Abstract: Copper wire bonding has obtained prevalent owning to its economic advantage and superior electrical property. However, the replacement of gold wire with copper wire introduces hardness related issues as copper is much harder than gold. This article reports investigations of the process optimization of ball bonding for 1.8mil copper wire. The results showed that the suitable ranges of the three key parameters were: contact force was 100~120gf, bond time was 15~25ms, and bond power was 100~110dac. When the input energy was too low, it was hard to get effective bonding. However, excessive input energy would cause chip crater and serious extrusion of metallization layer.

Abstract: This paper investigated the process optimization of electronic flame-off (EFO) which was the melting of a wire tip by an electrical spark to form a free air ball (FAB) for 1.8mil copper wire bonding. The results showed that sparking current and sparking time rather than tail length were the key factors to influence the form of FAB. The FAB was skew and coarse with very small diameter when sparking current was 110mA. However, the FAB would be burned-out when sparking current was 180mA. And the appropriate sparking current was proved to be 130mA~150mA. When sparking time was too short (0.8ms~1.0ms), the FAB would appear to be pointed ball or golf ball. However, when sparking time was too long (3ms), the diameter of FAB was much bigger which led to offset ball and golf-bond. The suitable sparking time was proved to be 1.2ms~2ms.

Abstract: In this paper, the characteristics of bond interface and bonding mechanism were investigated with peeling-off method. The fracture was observed and interfacial composition was certified by map scanning of EDX (Energy dispersive X-ray analysis). Based on the features of interfacial characters, the actual joining area mainly distributed at bond periphery; non-bonded at bond center. When the bonding time was lower, the ratio of the bond length to its width was larger and elemental aluminum distributed discontinuously on the bond fracture, primarily at the periphery. After aging, the fractures were also analyzed and Cu2Al3 intermetallic compound (IMC) was identified. The phenomena of bond interfacial tracings were analyzed, and the bonding mechanism was ascribed to plastic flow analyzed by finite element method based on the contact issues.

Abstract: This paper presents bonding technology of aluminum alloy by hot-dipping tin. The dissolution curve of copper in molten tin liquid was obtained in the experiment of hot-dipping Sn. Optimal hot-dipping parameter which was suitable for soldering was designed. To elucidate characteristics of interfacial evolution, the microstructure of the coatings, soldered joint were analyzed using optical microscopy, SEM and EDX. The shear strength of soldered joints was tested as high as 39.9Mpa, which is high enough to achieve the requirement of electronic industry.

Abstract: Reliability optimization design of Ball Grid Array (BGA) solder joints is a major concern in area array electronics packaging technology. In this paper, shapes of the solder joints and their reliability were predicted and analyzed. Through the variations of lower pads’ diameters, the shapes of full array BGA solder joints with different solder volumes were predicted by using surface evolver software. Based on the results of shape prediction, 3-D finite element models were established with MSC.MARC and the distribution of the stress and strain in the BGA solder joints under thermal cyclic loading were simulated. Finally, fatigue lives of the BGA solder joints with different solder volumes were calculated, and the diameter ratios of lower pad to upper pad for these two kinds of BGA assemblies with the best reliability were optimized.

Abstract: The transient temperature field of Al alloy during electron beam welding (EBW) process was simulated using a three-dimensional finite element method. Different from the most previous models which were based on the assumption that the welding pool was solid and neglected the existence of keyhole by meshing the solid as a whole, a dynamic three-dimensional keyhole was applied in this model. The profile of the keyhole was ellipse and its size was determined before simulation based on the results of experiments. Following the heat source, the pre-defined keyhole moved along the welding line. A three-dimensional complex heat source model, including a modified Gaussian distribution source and a uniform source, was used in this study. The result shows that the shape of the keyhole had a direct effect on the temperature distribution and contribution to the special shape of the welding pool in EBW.