Papers by Keyword: Wire Bonding

Abstract: Emerging designs of devices require sophisticated bond pad architecture to meet certain specifications, design applications, as well as package requirements. Sophisticated bond pad structures often have thin metal layers and POA circuit bond pads underneath which require careful application of wire bond processing to avoid cracking on the bonding pads during wire bond. Bond pad crack is one of the most detrimental issues at wire bonding, especially with POA devices, so it is important to take into consideration the wire material to be used, the process parameter to be defined, as well as the structure of the bonding pad. This paper aims to resolve and eliminate the bond pad crack by the application Initial Force via Force Profiling, whilst adhering to the output response criteria at wire bond, and not going outside the defined process parameter window. Furthermore, this paper aims to help readers to have a more comprehensive understanding of the Force parameters at wire bond, as well as the different architecture of bonding pads.

Abstract: Kirkendall voids have always been a reliability issue in recent wire bonding technologies in semiconductor package using gold and copper wires. The unpredictable manifestation of these voids has paved the way for a lot of process improvements, parameter optimizations, and material improvements, aiming to alleviate the formation of voids. Predicting when these voids would likely to start to manifest themselves will give us an understanding as to how to improve wire bonding at time-zero, especially on the formation of the intermetallic coverage (IMC) at time-zero. Augmenting different levels of ultrasonic (US) energy at wire bonding gave us different IMC morphologies and thickness at time-zero, which were compared and analyzed through statistical analysis and through a mathematical model. The collective data of each US energy for both time-zero and after each thermal aging, showed when will Kirkendall voids would likely to occur on silver-aluminum [Ag-Al] intermetallics, and if these voids are detrimental to the integrity of the wire bond interphase [Ag3Al] or if it’s still acceptable within the device’s projected lifetime. The survival of the device at the 1000th HTS mark, reveals the reliability of using silver wires for automotive devices in the semiconductor industry today. Furthermore, the overall behavior of [Ag-Al] intermetallics in IM layer thickness can be predicted through an optimized set of parameters at time zero, but its overall numerical behavior can be quite different. Nevertheless, it has been proven through this thesis, that the [Ag-Al] intermetallics can survive 1000 hours of HTS, with different US energy level applications at time-zero.

Abstract: The evaluation of the strength and bondability of gold, Au ball bond requires a new approach to provide a more detail data. Nanoindentation test was used as a new approach to evaluate the strength distribution and bondability of Au ball. Au ball bonds that experienced different value of wire bonding parameter namely bonding force, bonding time, bonding power, and stage temperature were used as samples for the present analysis. The distribution of strength based on hardness and reduced modulus values located at the bonding area of Au ball bonds were found to be related with the values of the wire bonding parameter. Nanoindentation test was found to be a suitable approach to analyze and evaluate the bondability of Au ball bond in a localized and detailed manner. In addition, the responsible mechanism for the thermosonic Au wire bonding can be identified and analyzed by using the results obtained from the nanoindentation test.

Abstract: The in-situ inspection of ultrasonic vibration of wire bonder capillary was carried out using laser interferometer in order to analyze the formation of Au wedge bond. It was observed that the changes in ultrasonic vibration can be used to describe process of bonding formation. The loss of ultrasonic energy was exhibited in ultrasonic vibration waveform of wire bonding on leadframe A. This observation is due to the low frictional energy and high deformation of Au wedge bond on leadframe A. The lower pull strength obtained by Au wedge bond further confirms the reduction of bond formation on leadframe A.

Abstract: This work is a contribution towards the understanding of wire bond integrity and reliability in relation to their microstructural and mechanical properties in semiconductor packaging.The effect of surface roughness and hardness of leadframe on the bondability of Au wedge bond still requires detail analysis. Two type of leadframes namely leadframe A and leadframe B were chosen and scanning electron microscope (SEM) and optical microscope were used to inspect the surface morphology of leadframes and the quality of created Au wedge bond after wire bonding process. It was found that there were significant differences in the surface morphologies between these two leadframes. The atomic force microscopy (AFM) which was utilized to measure the average roughness, R_a of lead finger confirms that leadframe A has the highest R_a with value of 166.46 nm compared to that of leadframe B with value of 85.89 nm. While hardness value of different lead finger from the selected leadframe A and B obtained using Vicker microhardness tester are 180.9 VH and 154.2VH respectively.

Abstract: According to the application of the high voltage SiC devices, studying the package of three kinds of SiC dies with different metals. Experiments show that all die wire bonding and shear strength measurement up to standard, and provide three kinds of packages for different applications, at the same time, filling the needs of producing. The purpose of the shear strength test is to determine the integrity of materials used to attach SiC die to package substrates.

Abstract: This paper reports on the thermal stress comparison between gold (Au) and copper (Cu) wires in wire bonding. The objective of this study is to examine the stress induced during different operating temperatures. ANSYS 11 has been deployed as the simulation tool for this study. This simulation was performed using a three dimensional (3D) non-linear finite element model. The gold and copper wires were attached to an aluminium bondpad on a silicon die. The results showed that when the highest stress concentrates at the area between the ball bond and the bondpad. Moreover, increasing temperature will increase the von mises stress. As for this study, the Cu wire display the greater thermal stress compared to Au wire due to its harder and stiffer material properties.

Abstract: Because of the complexity of bonding process, the mechanism of bonding has been unable to agree. Accoding to previous research, a new bond energy transfer model is established: bond energy equals to energy caused by temperature rising and the friction energy.Then do experiment on bonding time, bonding stress and ultrasonic energy.Experimental results show that as the increase of process parameters, the bonding strength first increases then decrease, which consistent with the hypothesis.

Abstract: The wire bonding process in the package of MEMS accelerometer is analyzed by the finite element software ANSYS/LS-DYNA. Impact on the bonding strength of the ultrasonic amplitude, ultrasonic frequency and the friction between wire bond and bond pad are studied. The strength of wire bond is evaluated through the bond pull test experiment. The test result shows that the analysis on the wire bonding is helpful for improving the quality of wire bonding.

Abstract: Sliver wire was the novel material to replaced gold wire in wire bonding process, and rare earth element was often added to improve the properties of silver wires. The annealing effect (at 225°C~275°C for 30min) on the tensile mechanical properties of silver wires with φ=20μm was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Free-air ball (FAB) of 85μm diameter from 20μm diameter pure silver wire was too huge for bonding process, otherwise the silver wire was added 0.05 wt.% lanthanum to form Ag-La alloy wire to reduce the diameter of FAB. FAB of Ag-La alloy wire with a 55μm diameter, and can avoid short-circuited. In addition, microstructures, tensile properties and the micro-hardness of Ag-La alloy wires indicated that the best annealing temperature was 425 °C.