Chunqing Wang

Rapid formation of Cu/Cu3Sn/Cu joints using ultrasonic bonding process at ambient temperature

Wafer bonding using Sn interlayer and silicon bond components with Ti/Ni/Cu metallization was achieved by ultrasonic bonding at ambient temperature for 4 s under 0.6 MPa. High-melting-point joint which fully consisted of Cu3Sn intermetallic compounds was formed with a high shear strength of 65.8 MPa and a low electrical resistivity of 67.3 μΩ · cm. Experimental results showed that ultrasonic vibration induced steep temperature rise at rubbing interface, melting solid solder, and sequent ultrasonic effects at the liquid Sn/solid Cu interface dominated the mechanism and kinetics of rapid formation of Cu3Sn joint.

Study of copper free air ball in thermosonic copper ball bonding

In order to meet the new requirements of higher performance and reliabilities for electronic devices, the copper wire ball bonding technology was developed to be an alternative method for the gold wire ball bonding technology because of its economic advantages, strong resistance to sweeping, superior electrical and mechanical performance. But copper wire ball bonding has not been widely implemented in mass production because of some difficulties. The major reason is that the copper is readily to be oxidized during FAB formation process. And the copper oxide would cause non-stick, crater and other reliability problems. Hence, to get standard FAB balls with consistent dimensions and unoxidized ball surfaces was crucial in copper wire ball bonding. In this paper, the impacts of different electronic flame off (EFO) parameters, such as EFO current, preset value of FAB size, gap length and forming gas flow rate and so on, on copper FAB sizes and surface appearance were investigated. It was found that the higher EFO current and preset value of FAB size was needed to form copper FAB balls comparing with gold FAB ball formation. Excessive gap length would cause more heat dissipation during EFO process and had an adverse effect on the copper FAB ball formation for 2 mil copper wire. Low flow rate forming gas would lead to FAB balls with top-ends and high flow rate would cause the tilted FAB ball. Excessive high flow rate would disturb the FAB formation environment. A medium flow rate was suitable for copper FAB ball formation; such as 0.8 l/min was preferred in this study.

Ultrarapid formation of homogeneous Cu6Sn5 and Cu3Sn intermetallic compound joints at room temperature using ultrasonic waves.

Homogeneous intermetallic compound joints are demanded by the semiconductor industry because of their high melting point. In the present work, ultrasonic vibration was applied to Cu/Sn foil/Cu interconnection system at room temperature to form homogeneous Cu6Sn5 and Cu3Sn joints. Compared with other studies based on transient-liquid-phase soldering, the processing time of our method was dramatically reduced from several hours to several seconds. This ultrarapid intermetallic phase formation process resulted from accelerated interdiffusion kinetics, which can be attributed to the sonochemical effects of acoustic cavitation at the interface between the liquid Sn and the solid Cu during the ultrasonic bonding process.

An integrated system for prediction and analysis of solder interconnection shapes

In this paper, an integrated system [predicting solder interconnection shapes (PSIS)] is built to predict and analyze the shape of solder interconnections in electronic packaging. The purposes are to numerically simulate the formation of solder joints, analyze the shape of solder joints and its influential factors and provide an efficient tool for design and manufacturing engineers to improve the integrity of solder interconnections. The formation of solder joints is numerically simulated through a surface evolver program and the calculation is automated with an additional controller. A datafile generator is developed in which the potential energies, geometry of the conjunction and boundary conditions of the initial solder joint can be generated visually and transferred into evolver syntax automatically. A post processor is built to analyze the global three-dimensional (3-D) shape and cross section profiles of solder fillets. Also, the applications for solder interconnection shape prediction of chip component (RC3216) are conducted with this system.

Low Temperature Sintering Cu6Sn5 Nanoparticles for Superplastic and Super‐uniform High Temperature Circuit Interconnections

Brittle intermetallics such as Cu6 Sn5 can be transformed into low cost, nonbrittle, superplastic and high temperature-resistant interconnection materials by sintering at temperatures more than 200 °C lower than its bulk melting point. Confirmed via in situ TEM heating, the sintered structure is pore-free with nanograins, and the interface is super-uniform.

Thermomechanical behaviour of PBGA package during laser and hot air reflow soldering

In this paper, the temperature distribution in laser reflowed solder balls and warpage of the package upon temperature change were simulated using a finite element method, and effects of different laser heating means on the temperature distribution have been discussed in detail. The results of simulation show that solder balls reflowed by laser heating power would not damage the silicon chip and the package and that with laser, the advantages of a short heating time, a lower temperature in the package and smaller deformation were obtained as compared with a traditional heating method such as the hot air reflow method. Also, experiments on a plastic ball-grid-array (PBGA) solder ball laser reflow were carried out. Results show that the surface of the solder bumps obtained by the laser reflow method with proper parameters is much smoother than that obtained by the hot air reflow method.

Effect of solidification on solder bump formation in solder jet process: Simulation and experiment

To investigate the influence of the solidification on the solder bump formation in the solder jet process, the volume of fluid (VOF) models of the solder droplets impinging onto the fluxed and non-fluxed substrates were presented. The high speed camera was used to record the solder impingement and examine the validity of the model. The results show that the complete rebound occurs during the process of the solder droplet impinging onto the fluxed substrate, whereas a cone-shaped solder bump forms during the process of the solder droplet impinging onto the non-fluxed substrate. Moreover, the solder solidification results in the lift-up of the splat periphery and the reduction in the maximum spread factor.

Bonding mechanism of ultrasonic wedge bonding of copper wire on Au/Ni/Cu substrate

Abstract The ultrasonic wedge bonding with d 25 μm copper wire was achieved on Au/Ni plated Cu substrate at ambient temperature. Ultrasonic wedge bonding mechanism was investigated by using SEM/EDX, pull test, shear test and microhardness test. The results show that the thinning of the Au layer occurs directly below the center of the bonding tool with the bonding power increasing. The interdiffusion between copper wire and Au metallization during the wedge bonding is assumed negligible, and the wedge bonding is achieved by wear action induced by ultrasonic vibration. The ultrasonic power contributes to enhance the deformation of copper wire due to ultrasonic softening effect which is then followed by the strain hardening of the copper wedge bonding.

Microstructures, corrosion and mechanical properties of as-cast Mg–Zn–Y–(Gd) alloys

Abstract Long period stacking ordered (LPSO) structure phases were prepared by conventional solidification method in Mg94Zn3YxGd3–x (x=3, 2, 1.5, 1, mole fraction) alloys, the microstructures, corrosion and compressive mechanical properties of which were investigated, separately. The results reveal that the microstructures of the as-cast Mg94Zn3YxGd3–x alloys, with n(Zn)/n(Y+Gd)=1:1, consist of α(Mg) phase, Mg3Zn3RE2 (W) phase, Mg12ZnRE (14H-LPSO) phase and a few bright cube-shaped Mg–Y–Gd phases. The formation and the distribution of LPSO-phase in the alloys can be influenced by the content of Gd. The volume fraction of 14H-LPSO phase increases first and then decreases with the increase of the Gd content. For the electrochemical impedance spectroscopy (EIS) measurement, a R(Q(R(QR))) model was used to fit the test results in 3.5% (mass fraction) NaCl solution at room temperature. The corrosion current densities of all samples are about 10−5 A/cm2. When x(Gd)≤1%, Mg–Zn–Y–(Gd) alloy shows good corrosion resistance, which is better than that of the commercial AZ91D magnesium alloy. The corrosion rate increases when the Gd content is higher than 1.5%. At room temperature, the compressive properties of Mg–Zn–Y–(Gd) alloys increase remarkably with the increase of the volume fraction of LPSO phase. In addition, the pinning effect of W-phase and dispersive cube-shaped Mg–Y–Gd phase is beneficial to improving the mechanical properties of as-cast Mg94Zn3YxGd3–x alloy in deformation process.

Effect of Au-Sn IMCs’ formation and morphologies on shear properties of laser reflowed micro-solder joints

Purpose – The purpose of this paper is to investigate the effect of typical morphologies of Au-Sn IMCs (intermetallic compounds) at the interfaces of solder and pads on shear properties of laser reflowed micro-solder joints. Design/methodology/approach – Sn-2.0Ag-0.75Cu-3.0Bi (SnAgCuBi) solder balls (120 μm in diameter), pads with 0.1, 0.5, 0.9 or 4.0 μm thickness of Au surface finish, and different laser input energies were utilized to fabricate micro-solder joints with Au-Sn IMCs having different typical morphologies. The joints were performed by a shear test through a DAGE bond test system. Fracture surfaces of the joints were analyzed by scanning electron microscopy and energy-dispersive X-ray spectrometry to identify fracture modes and locations. Findings – Morphologies of Au-Sn IMCs would affect shear properties of the joints remarkably. When needle-like AuSn4 IMCs formed at the interfaces of solder and pads, almost entire surfaces presented the manner of ductile fracture. Moreover, shear forces of ...