Jusheng Ma

Precipitation in Cu–Ni–Si–Zn alloy for lead frame

Abstract The aging of Cu–Ni–Si–Zn alloy for lead frame is investigated. The results showed that the peak of hardening effect occurs after aging for about 1 h and the electrical conductivity increases continuously with aging times. The hardness of the alloy reached a peak at 430–460 °C for 2 h and electrical conductivity reached a peak at 500–550 °C and continuously decreased afterwards. The cold rolling prior to the aging treatment was used to increase the precipitation rate. The precipitates responsible for the age-hardening effect are disc-shaped δ-Ni 2 Si, which has an orthorhombic structure.

Joining of sapphire and hot pressed Al2O3 using Ag70.5Cu27.5Ti2 brazing filler metal

Abstract Sapphire and hot-pressed 99% Al2O3 ceramic were joined using Ag70.5Cu27.5Ti2 bracing filler metal in a vacuum electric furnace. The interface reaction between Ag70.5Cu27.5Ti2 alloy and sapphire, hot-pressed Al2O3 ceramic during brazing is reported. The joining strength and the airtight of the specimen are influenced by the surface condition of Al2O3 ceramic and the factor of active brazing condition.

Preoxidation of the Cu layer in direct bonding technology

Abstract Between the metal melting point and the eutectic temperature of the metal–oxygen, direct bonded copper (DBC) depends on the eutectic composition to join the copper and ceramic. The key of this technology is to import the oxygen to the bonding surface. In this paper, we do some research on the preoxidation law of the copper layer in direct bonding technology, so we can optimize the rang of preoxidation temperature and time. After we investigate the phase diagram of copper–oxygen, by the “conservation of mass” and “level principle”, we find there are some relationship between the preoxidation condition and the bonding process, and we offer a experiential formula to help control the bonding process. Finally, we also analyze the interface reaction production between the Cu layer and alumina ceramic, and discuss some possible reasons.

Electrochemical behavior of Sn-xZn lead-free solders in aerated NaCl solution

Electrochemical corrosion behavior of Sn-xZn solder alloys (i.e. hypoeutectic Sn-6.5Zn, eutectic Sn-9Zn and hypereutectic Sn-12Zn, in wt.%) in aerated 0.5 M NaCl solution was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques, aiming to assess the effect of Zn content on the corrosion behavior of Sn-Zn alloys. Scanning electron microscopy (SEM) equipped with EDX, X-ray diffraction (XRD) were performed to characterize the surface morphology and to identify the chemical composition of the corrosion products, respectively. It is found that increasing Zn contents lead to an increase in corrosion current density and the corrosion potential shifted towards more negative values, revealing that the corrosion rates increase in the order of: Sn-6.5Zn <; Sn-9Zn <; Sn-12Zn. The acquired electrochemical impedances were successfully fitted with an equivalent circuit model. Fitted results reveal that total impedance decreased with increasing Zn content, indicating that Sn-6.5Zn alloy exhibits the highest corrosion resistance. The results are further confirmed by surface morphology characterization of the corrosion products, which shows a more homogeneous product film for lower Zn content. Analysis of the corrosion products indicates that oxide hydroxychlorides are the dominant corrosion products. Based on the obtained results, it is suggested that Sn-Zn alloy with lower Zn content appears to be more attractive in terms of superior corrosion resistance.

Lead-free solder materials for sustainable development of green electronics in China

Building recycle society is the key to ensure the sustainable development of China. The green electronics, including the advanced electronic packaging technology, play a most important role to promote the development of recycle society. In this paper, the development and trend of the green electronic industry, technology and laws in China and other countries are reviewed. New lead-free solder alloys and its application characteristics, also the evaluation methods are illustrated. Some suggestions are put forward.

Researches on system quality control of materials and components for high density packaging

The reliability of the whole electronic system is determined by the electronic devices, components and materials and especially the application properties of materials is the base of high reliability. Failure analysis of electronic packaging shows that failure usually occurs at the interconnections of dissimilar materials. With the development of IC towards high density, high speed, and small size, there is a strong demand for the high performance microelectronic materials, especially for the physical and chemical properties of surfaces, which are the most important for high reliabilities. This paper systematically study the application properties of materials such as leadframe, LTCC substrate, Al anodized oxidation substrate, paste, solder, bump.

Performance analysis of pre-oxidation process direct bonding copper substrate

This paper represented the electrical and heat-resistant performance and uniformity of pre-oxidation process direct bonding copper substrate. Contrasting the difference between the raw alumina substrate and direct bonding copper substrate, there is no obvious change in the dielectric dissipation (tgδ); and a little change in the relative dielectric constant (ε). By the electronic speckle pattern interferometer (ESPI), the changes of pre-oxidation process direct bonding copper substrate were analyzed, there are no obvious defects emerging or extending under 100-300°C thermal shock. It proves pre-oxidation process direct bonding copper substrate can be used in high temperature, high frequency and low resistance bus line application field.

Analysis of new lead-free solder alloy microstructure

Combining with the analysis of solder melting point, spreading rate and tensile strength, a new Sn-Zn lead-free solder system has been developed. The solder melting point is 183 °, it is very close to Pb-Sn eutectic solder melting temperature, the corresponding melting range of this solder is smaller, and it has higher bonding force and other advantages, completely meeting the requirements of the electronic industry. Because the material performances are Influenced by the microstructure, so the alloy microstructure was investigated, and the influencing factors of the alloy microstructure on properties have been found.

Study of New Types Lead-Free Solder Alloys of Sn-Ag-Cu-Al-Ni and Sn-Zn-Bi-In-P

Sn-Ag-Cu lead-free solder alloy is the most potential substitute for Pb-Sn solder, while it still has problems because of its high melting point and poor application properties. We have developed new types lead-free solder alloys of Sn-Ag-Cu-Al-Ni and Sn-Zn-Bi-In-P. The properties of anti-oxidization and stability are enhanced by adding Ni, Al and P. The new Sn-Zn-Bi-In-P lead-free solder has good solderability, low melting point and the same reflow profile as the Sn-37Pb eutectic solder. The bonding strength of the Sn-Zn-Bi-In-P solder joint is 1.5 times higher than that of the Sn-37Pb solder joint. After thermal fatigue, the fatigue life of the former is 25% more than that of the latter. The microstructure and composition of the solder joint interface are also studied. A Zn-rich layer is found at the interface which can prevent the diffusion of Sn and Cu atoms, consequently decrease the thickness of the intermetallic compound layer. The results of EDX and TEM indicate that the intermetallic compound is Cu5Zn8 . The solder paste has been produced and tested on the production line to evaluate its performance

Effect of the texture of indium on its mechanical properties

The mechanics properties of indium bumps connecting optoelectric device is critical to the reliability: Bumps after welding have a very low shear strength, and have a very high tensile strength. The relationship between the texture and strength is studied by analyzing the orientation dependence of resolved shear stress on dislocation slip plane and the effect of shear stress on dislocation initiation. Finally the low shear strength can be explained by that the preferred orientation of glide plane leads to the readiness of dislocation initiation. The high tensile strength can be attributed to the texture strengthening.