Effects of Cu and Pd addition on Au bonding wire/Al pad interfacial reactions and bond reliability (original) (raw)
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The effect of Pd and Cu in the intermetallic growth of alloy Au wire
Journal of Electronic Materials, 2003
This is the new wire evaluation work for the reliability of the wire-bonding process. There is a trend for the plastic integrated-circuit package to function at higher junction temperature with thinner wire. New alloy Au wires have been developed to meet the reliability requirements. Two types of alloy Au wires, Au-Pd and Au-Cu, were evaluated in this study. These samples were aged between 155°C and 205°C under air from 0 h to 3,000 h. According to this study, the phase-formation sequence of Au 2 Al, Au 5 Al 2 , and Au 4 Al intermetallic is similar to the pure Au wire. There is a Pd-rich layer working as a diffusion barrier to slow down the growth rate of intermetallic phases in the Au-Pd wire. The Au-Cu wire also slowed down the growth rate with a different mechanism. Both wires have better reliability based on the microstructure examination. The reliability test results show longer working life at higher temperatures in comparison with the regular Au wire.
Bond strength evaluation of heat treated Cu-Al wire bonding
Journal of Mechanical Engineering and Sciences, 2018
Bond strength evaluation of wire bonding in microchips is the key study in any wire bonding mechanism. The quality of the wire bond interconnection relates very closely to the reliability of the microchip during performance of its function in any application. In many reports, concerns regarding the reliability of the microchip are raised due to formation of void at the wire-bond pad bonding interface, predominantly after high temperature storage (HTS) annealing conditions. In this report, the quality of wire bonds prepared at different conditions, specifically annealed at different HTS durations are determined by measurements of the strength of the interface between the bond wire and the bond pad. The samples are tested in pull test and bond shear test. It was observed that the higher bonding temperature as well as the longer duration of HTS increased the bond strength. This is represented through the analysis of the measurements of ball shear strength. This is due to the fact that ...
Process windows for low-temperature Au wire bonding
Journal of Electronic Materials, 2004
The process windows are presented for low-temperature Au wire bonding on Au/Ni/Cu bond pads of varying Au-layer thicknesses metallized on an organic FR-4 printed circuit board (PCB). Three different plating techniques were used to deposit the Au layers: electrolytic plating, immersion plating, and immersion plating followed by electrolytic plating. Wide ranges of wire bond force, bond power, and bond-pad temperature were used to identify the combination of these processing parameters that can produce good wire bonds, allowing the construction of process windows. The criterion for successful bonds is no peel off for all 20 wires tested. The wire pull strengths and wire deformation ratios are measured to evaluate the bond quality after a successful wire bond. Elemental and surface characterization techniques were used to evaluate the bond-pad surfaces and are correlated to wire bondability and wire pull strength. Based on the process windows along with the pull strength data, the bond-pad metallization and bonding conditions can be further optimized for improved wire bondability and product yields. The wire bondability of the electrolytic bond pad increased with Au-layer thickness. The bond pad with an Au-layer thickness of 0.7 µm displayed the highest bondability for all bonding conditions used. The bondability of immersion bond pads was comparable to electrolytic bond pads with a similar Au thickness. Although a high temperature was beneficial to wire bondability with a wide process window, it did not improve the bond quality as measured by wire pull strength.
Effects of Cu/Al intermetallic compound (IMC) on copper wire and aluminum pad bondability
IEEE Transactions on Components and Packaging Technologies, 2003
Copper wire bonding is an alternative interconnection technology that serves as a viable, and cost saving alternative to gold wire bonding. Its excellent mechanical and electrical characteristics attract the high-speed, power management devices and fine-pitch applications. Copper wire bonding can be a potentially alternative interconnection technology along with flip chip interconnection.
Effects of Pd addition on Au stud bumps/Al pads interfacial reactions and bond reliability
Journal of Electronic Materials, 2004
The main purposes for developing low-alloyed Au bonding wires were to increase wire stiffness and to control the wire loop profile and heat-affected zone length. For these reasons, many alloying elements have been used for the various Au bonding wires. Although there have been many studies reported on wire strengthening mechanisms by adding alloying elements, few studies were performed on their effects on Au bonding wires and Al pad interfacial reactions. Palladium has been used as one of the important alloying elements of Au bonding wires. In this study, Au-1wt.%Pd wire was used to make Au stud bumps on Al pads, and effects of Pd on Au/Al interfacial reactions, at 150°C, 175°C, and 200°C for 0 to 1200 h thermal aging, were investigated. Crosssectional scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA) were performed to identify intermetallic compound (IMC) phases and Pd behavior at the Au/Al bonding interface. According to experimental results, the dominant IMC was Au 5 Al 2 , and a Pd-rich layer was at the Au wire and Au-Al IMC. Moreover, Au-Al interfacial reactions were significantly affected by the Pd-rich layer. Finally, bump shear tests were performed to investigate the effects of Pd-rich layers on Au wire bond reliability, and there were three different failure modes. Cracks, accompanied with IMC growth, formed above a Pd-rich layer. Furthermore, in longer aging times, fracture occurred along the crack, which propagated from the edges of a bonding interface to the center along a Pd-rich layer.
Influence of Intermetallic Phases on Reliability in Thermosonic Au-Al Wire Bonding
2006 1st Electronic Systemintegration Technology Conference, 2006
Since roughly 2002, reliability problems occur often at the ball bonds after wire bonding or reliability testing procedures. Thefailure mainly appears as ball lift-offor reducedpullforce values. Applying Focused Ion Beam (FIB) techniques as well as Scanning and Transmission Electron Microscopy (SEM, TEM) alternative failure modes in addition to Kirkendall voids werefound that could be divided into five morphological categories. Thesefailures include the missing ofany Au-Al intermetallic compound (IMC) formation at the pads after wire bonding, no uniform horizontallvertical IMCformation after wire bonding, micro cracks between the interface IMC and Au ball during reliability stressing, micro cracks between the interface ofthe two IMCs during temperature aging andfinally corrosion ofthe interface IMC/Au ball during temperature aging or humidity testing. Although there is strong indication that part ofthesefailure modes are related to front endprocess steps, the practical limitations resultingfrom separation between semiconductor manufacturing and assembly line require a back end solution. It is shown that the use ofan improved high security (HS) or high reliability wire (HR) contributes significantly to reliability improvement. The wires contain special dopands which reduce the IMC and defect growth. The influence of these wires on the reliability ofbonds will be explained and shown in selected examples.
IEEE Transactions on Components, Packaging and Manufacturing Technology, 2016
Gold wire bonding has been widely used as the first-level interconnect in semiconductor packaging. The increase in the gold price has motivated the industry search for an alternative to the gold wire used in wire bonding and the transition to a copper wire bonding technology. Potential advantages of transition to a Cu-Al wire bond system include low cost of copper wire, lower thermal resistivity, lower electrical resistivity, higher deformation strength, damage during ultrasonic squeeze, and stability compared with gold wire. However, the transition to the copper wire brings along some tradeoffs, including poor corrosion resistance, narrow process window, higher hardness, and potential for cratering. Formation of excessive Cu-Al intermetallics may increase the electrical resistance and reduce the mechanical bonding strength. Current state of the art for studying the Cu-Al system focuses on the accumulation of statistically significant number of failures under accelerated testing. In this paper, a new approach has been developed to identify the occurrence of impending apparently random defect fall-outs and premature failures observed in the Cu-Al wire bond system. The use of intermetallic thickness, composition, and corrosion as a leading indicator of failure for the assessment of the remaining useful life for Cu-Al wire bond interconnects has been studied under exposure to high temperature. Damage in the wire bonds has been studied using an X-ray micro-Computed Tomography (CT). Microstructure evolution was studied under the isothermal aging conditions of 150°C, 175°C, and 200°C until failure. Activation energy was calculated using the growth rate of intermetallic at different temperatures. An effect of temperature and humidity on a Cu-Al wire bond system was studied using the Parr bomb technique at different elevated temperature and humidity conditions (110°C/100%RH, 120°C/100%RH, and 130°C/100%RH), and a failure mechanism was developed. The present methodology uses the evolution of the intermetallic compound thickness and composition in conjunction with the Levenberg-Marquardt algorithm to identify accrued damage in wire bond subjected to thermal aging. The proposed method Manuscript
TEM microstructural analysis of As-Bonded Al–Au wire-bonds
Journal of Materials Science, 2007
In this study the interface morphology of a model 99.999% (5N) Au wire bonded to Al pads in the as-bonded state was examined by scanning/transmission electron microscopy with energy dispersive spectroscopy. Specimens for transmission electron microscopy were prepared using the lift-out method in a dual-beam focused ion beam system. Analysis of the bond microstructure was conducted as a function of the Al pad content and as a function of the bonding temperature. Additions of Si and Cu to the Al pad affect the morphology and the uniformity of the interface. A characteristic-void line is formed between two intermetallic regions with different morphologies in the as-bonded samples. According to the morphological analysis it was concluded that a liquid phase forms during the bonding stage, and the void-line formed in the intermetallic region is the result of shrinkage upon solidification and not the Kirkendall effect.
EFFECTS OF THERMAL AGING ON INTERMETALLIC COMPOUNDS AND VOIDS FORMATION IN AuAl WIRE BONDING
There are several issues related to the mechanical and electrical wirebond failure during wirebonding process. Major factors are associated with AuAl intermetallic system. AuAl intermetallic compounds (IMC) can easily form at room temperature and can be accelerated with the elevated temperature. In this paper, pattern of intermetallic compounds growth and potential degradation due to voids in thermosonic ball bonding were studied on AuAl intermetallic compounds. The thermosonic ball bonding process used 99.99% gold wire and aluminized pad of Si chip. Results after HTS at 150ºC for 500 hours demonstrated that voids were generated around the diffusion layer because of the Kirkendall effect and severe voids was clearly exhibited after thermal aging at 150ºC for 1000 hours. Prolong aging time can lead to bonding failure associate with Kirkendall voids.
Degradation of Al-1%Si wires bonded onto copper pads
2017
The current load and its influence on degradation of Al-1%Si wires bonded onto copper pads is presented in this paper. The current load was chosen to occur the electromigration phenomenon during ageing. Our attention was paid to the direction of current from Cu pad to Al wire, and as well as reversed from Al wire to Cu pad. The dependencies of electrical resistance (ΔR/R0) relative change vs time as well as dependencies of mechanical strength vs time for different types of current stresses (direct current IDC and pulse current IPULSE) were obtained and evaluated. The results were evaluated in relation to all above mentioned conditions moreover thermal ageing at 100°C/1000 h was applied and evaluated too.