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In this paper, there are two major investments consisted of ¡§Failure Mechanism of Inner Lead Au-Sn Bonds in Tape Automated Bonding (TCP) Packages¡¨ and ¡§Cu Wire bond microstructure analysis and failure mechanism¡¨. In view of the advantages of low cost, simple manufacturing process and significant miniaturization in size, TCP technology is widely applied in consumer electronic products. Inner lead bonding (ILB) process is especially crucial for the production of high quality TCP packages and components. The ILB process is extremely dynamic since the bonding time is around 0.2 second to complete the thermo-compress and soldering processes. The composition of liquid pool varied with the bond temperature and pressure and is crucial to exhibit different structure. One type of unusual failure bond happened during the process parameters optimization. ILB joints microstructure was examined by electron microprobe (EPMA) for detail phase analysis. The phase formation sequence of normal and failure bonds can be explained from the Au-Sn-Cu ternary phase diagram and thermo-chemistry data of Au-Sn binary. According to Part I study, the hypo-eutectic composition (<30 at% Sn) liquid pool could maintain the normal ILB bonds. And the hyper-eutectic composition (>30 at% Sn) has the potential risk to form this unusual failure bond. In the Part II study, copper wire bonding samples were aged at 205¢XC in air from 0 h to 2000 h. It was found that the bonding of a Cu wire and an Al pad formed Cu9Al4, CuAl, and CuAl2 intermetallic compounds, and an initial crack was formed by the ultrasonic squeeze effect during thermosonic wire bonding. The cracks grew towards the ball bond center with an increase in the aging time, and the Cl ions diffused through the crack into the ball center. This diffusion caused a corrosion reaction between the Cl ions and the Cu-Al intermetallic phases, which in turn caused copper wire bonding damage.

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In the last decade, reliability problems have become a critical subject in power modules. Understanding design weakness and failure mechanisms of thick wire bond are two critical steps in managing the risk of wire bond heel crack which is the topic of this thesis. Although this thesis does not target a specific type of power modules, we note that thick wire bond heel crack failures occur in Insulated Gate Bipolar Transistors (IGBTs). In fact, our aim is to understand failure mechanism in 300μm thick wire bonds with different geometries and materials. Since these wires experience harsh environmental conditions and high load transients, the wires undergo repetitive flexural movement which causes heel crack due to fatigue. For the purpose of understanding this failure mechanism, two experimental setups are built and utilized. The first experimental setup loads the wires using constant currents and observes the response using a scanning laser vibrometer to measure the displacement. The second experimental setup applies repetitive prescribed displacement to the first foot of the wire and detects fatigue failure using a Wheatstone bridge. It is realized that wires have different displacement property depending on their geometry and material. Maximum displacements are observed for Al-H11 instead of CuCorAl and PowerCu.

In the last decade, reliability problems have become a critical subject in power modules. Understanding design weakness and failure mechanisms of thick wire bond are two critical steps in managing the risk of wire bond heel crack which is the topic of this thesis. Although this thesis does not target a specific type of power modules, we note that thick wire bond heel crack failures occur in Insulated Gate Bipolar Transistors (IGBTs). In fact, our aim is to understand failure mechanism in 300μm thick wire bonds with different geometries and materials. Since these wires experience harsh environmental conditions and high load transients, the wires undergo repetitive flexural movement which causes heel crack due to fatigue. For the purpose of understanding this failure mechanism, two experimental setups are built and utilized. The first experimental setup loads the wires using constant currents and observes the response using a scanning laser vibrometer to measure the displacement. The second experimental setup applies repetitive prescribed displacement to the first foot of the wire and detects fatigue failure using a Wheatstone bridge. It is realized that wires have different displacement property depending on their geometry and material. Maximum displacements are observed for Al-H11 instead of CuCorAl and PowerCu.

There are three parts in this thesis: In the first part (Chapter 2), we discuss the port excitation (Wave port vs Lumped port) suitable for sub-millimeter wave operations. We realized on printed circuit board a grounded coplanar waveguide (CPWG) and on gallium arsenic (GaAs) a microstrip line. We performed simulation on these structures using high frequency structure simulator (HFSS), and compared the results with measured ones. From the comparison, we found close match for CPWG insertion loss from 10 MHz to 67 GHz using the Wave port. However, for G-S-G lumped port, only matched up to 40 GHz. The wave port not only was more accurate, but also consumed less time in simulation. Consequently, we employed wave port as our simulation excitation for our sub-millimeter wave QFN design. In the second part (Chapter 3), we focused on design of low cost QFN for sub-millimeter wave applications. We fabricated test structures, which include IC pads and transmission lines, wire bonds, QFN leads, and G-S-G structures on printed circuit board. In HFSS simulation, our specially designed ribbon bonds and QFN configuration show return loss less than -20dB and insertion loss less than -0.4 dB up to 60 GHz. Using the same design principles, we strived to improve the performance of a commercially available QFN, which normally operates at 3 to 6 GHz. The extraction method to obtain the high frequency characteristics was introduced first, and the characteristics of a commercially available QFN (with our wire bond configuration) were then obtained. The insertion loss was less than -20 dB and insertion loss less than -0.5 dB up to 20 GHz. In Chapter 5, we discuss the performance discrepancies between the simulated ribbon bond results and that for fabricated wire bonds. In the third part (Chapter 4), we introduced a method to extract the characteristics of a single backside via and investigated the effects of die attachment on the performance of a single and multiple backside via(s). Using silver epoxy and Cu blank layer as die attach methods, we found it was important to provide a broad path (Cu blank layer), as opposed to a restrict path (like silver epoxy) to reduce the inductance of the backside vias. The conclusion and future work are provided in Chapter 5.

Ultrasonic wire bonding is the most utilized technique in forming electrical interconnections in microelectronics. However, there is a lacking in the fundamental understanding of the process. In order for there to be improvements in the process a better understanding of the process is required. The mechanism of the bond formation in ultrasonic wire bonding is not known. Although there have been theories proposed, inconsistencies have been shown to exist in them. One of the main inconsistencies is the contribution of ultrasound to the bonding process. A series of experiments to investigate the mechanism of bond formation are performed on a semi automatic wire bonder at room temperature. 25 µm diameter Au wire is ball bonded and also 25 µm diameter Al wire is wedge-wedge bonded onto polished Cu sheets of thickness 2 mm. It is found that a modified microslip theory can describe the evolution of bonding. With increasing ultrasonic power the bond contact transitions from microslip into gross sliding. The reciprocating tangential relative motion at the bond interface results in wear of surface contaminants which leads to clean metal/metal contact and bonding. The effect of superimposed ultrasound during deformation on the residual hardness of a bonded ball is systematically studied for the first time. An innovative bonding procedure with in-situ ball deformation and hardness measurement is developed using an ESEC WB3100 automatic ball bonder. 50 µm diameter Au wire is bonded at various ultrasound levels onto Au metallized PCB substrate at room temperature. It is found that sufficient ultrasound which is applied during the deformation leads to a bonded ball which is softer than a ball with a similar amount of deformation without ultrasound. No hardening of the 100 µm diameter Au ball is observed even with the maximum ultrasonic power capable of the equipment of 900 mW. In summary, the fundamental effect of ultrasound in the wire bonding process is the reciprocating tangential displacement at the bond interface resulting in contaminant dispersal and bonding. A second effect of ultrasound is the softening of the bonded material when compared to a similarly non-ultrasound deformed ball.

Ultrasonic wire bonding is the most utilized technique in forming electrical interconnections in microelectronics. However, there is a lacking in the fundamental understanding of the process. In order for there to be improvements in the process a better understanding of the process is required. The mechanism of the bond formation in ultrasonic wire bonding is not known. Although there have been theories proposed, inconsistencies have been shown to exist in them. One of the main inconsistencies is the contribution of ultrasound to the bonding process. A series of experiments to investigate the mechanism of bond formation are performed on a semi automatic wire bonder at room temperature. 25 µm diameter Au wire is ball bonded and also 25 µm diameter Al wire is wedge-wedge bonded onto polished Cu sheets of thickness 2 mm. It is found that a modified microslip theory can describe the evolution of bonding. With increasing ultrasonic power the bond contact transitions from microslip into gross sliding. The reciprocating tangential relative motion at the bond interface results in wear of surface contaminants which leads to clean metal/metal contact and bonding. The effect of superimposed ultrasound during deformation on the residual hardness of a bonded ball is systematically studied for the first time. An innovative bonding procedure with in-situ ball deformation and hardness measurement is developed using an ESEC WB3100 automatic ball bonder. 50 µm diameter Au wire is bonded at various ultrasound levels onto Au metallized PCB substrate at room temperature. It is found that sufficient ultrasound which is applied during the deformation leads to a bonded ball which is softer than a ball with a similar amount of deformation without ultrasound. No hardening of the 100 µm diameter Au ball is observed even with the maximum ultrasonic power capable of the equipment of 900 mW. In summary, the fundamental effect of ultrasound in the wire bonding process is the reciprocating tangential displacement at the bond interface resulting in contaminant dispersal and bonding. A second effect of ultrasound is the softening of the bonded material when compared to a similarly non-ultrasound deformed ball.