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Gold-coated silver wire was developed to alleviate the high cost of Au wire used in semiconductor packaging. Ball-bonding and stitch-bonding techniques were used to fabricate the dummy packaging material, comprising 97.3 % Ag, 97.3% Au-Coated Ag, and 99.99 %Au wires. The wire ball shear test (BST), the wire ball pull test (BPT), and the microstructural attributes of the ultrasonic bonding interfaces were compared with the initial properties, both before and after the highly accelerated stress test (HAST), conducted at 130 ℃ and 85% relative humidity (RH). The initial bonding strength for all the wire variants was ?23~24 gf. Following the HAST, the bonding strength of the Ag wire, the Au-coated Ag wire, and the Au wire decreased by approximately 75 %, 47 %, and 17 %, respectively. The microstructure analysis revealed that cracks developed and propagated at the ends of the interface and that the Au-rich Au-Al intermetallic compound (IMC) inhibited the propagation of the crack at the ACA/Au wire interface. Additionally, it was discovered that the presence of the Ag-Au-Al IMC at the interface of the ACA wire reduced Kirkendall voids, which act as a barrier to Au-Al interdiffusion.

Several attempts have been made to lower the price of materials in the semiconductor market. Among them, the wire used for interconnection has a disadvantage of high material price in the field of using gold. Many packages have evolved to other technologies to improve performance and are moving away from wire bonding process, but many packages still use bonding wires. In the bonding wire market, in order to reduce prices, gold is being replaced by inexpensive copper, and now the market for copper wire coated with precious metals considering workability is dominant. [1], [5] However, due to the rigid nature of copper, packages with sensitive wiring structures are difficult to apply. [2] Silver alloy wire and noble metal coated silver wire have been developed to lower the wire price of these sensitive packages. [3] In the case of the recently developed noble metal coated silver wire, unlike a silver alloy bonding wire, a spherical ball shape can be realized without using inert gas when forming a Free Air Ball. Due to these advantages, it has recently been in the spotlight as a wire for replacing Au wire. [3] In this paper, experiments were conducted on the bonding conditions of silver wire coated with noble metals. The bondability of the prepared noble metal-coated silver wire according to the Free Air Ball formation conditions was verified. Specifically, evaluation was performed according to the current change at the time of Electronic Flame Off, the type of inert gas, and the size of the Free Air Ball. The evaluation confirmed the optimum bonding conditions for the application of the noble metal coated silver wire.

To suppress the bonding strength degradation of solder joints in automotive electronics, we proposed a mid-temperature quaternary Pb-free Sn-0.5Cu solder alloy with minor Pd, Al, Si and Ge alloying elements. We manufactured powders and solder pastes of Sn-0.5Cu-(0.01,0.03)Al-0.005Si-(0.006–0.007)Ge alloys (T m = 230°C), and vehicle electronic control units used for a flame-retardant-4 printed circuit board with an organic solderability preservative finish were assembled by a reflow soldering process. To investigate the degradation properties of solder joints used in engine compartments, thermal cycling tests were conducted from −40°C to 125°C (10 min dwell) for 1500 cycles. We also measured the shear strength of the solder joints in various components and observed the microstructural evolution of the solder joints. Based on these results, intermetallic compound (IMC) growth at the solder joints was suppressed by minor Pd, Al and Si additions to the Sn-0.5Cu alloy. After 1500 thermal cycles, IMC layers thicknesses for 100 parts per million (ppm) and 300 ppm Al alloy additions were 6.7 μm and 10 μm, compared to the as-reflowed bonding thicknesses of 6 μm and 7 μm, respectively. Furthermore, shear strength degradation rates for 100 ppm and 300 ppm Al(Si) alloy additions were at least 19.5%–26.2%. The cause of the improvement in thermal cycling reliability was analyzed using the (Al,Cu)-Sn, Si-Sn and Al-Sn phases dispersed around the Cu6Sn5 intermetallic at the solder matrix and bonding interfaces. From these results, we propose the possibility of a mid-temperature Sn-0.5Cu(Pd)-Al(Si)-Ge Pb-free solder for automotive engine compartment electronics.

Au Bonding wire, which has been widely used in the semiconductor PKG market, is being converted into Cu Bonding wire due to a sharp increase in Au price. The price of Cu is cheaper than Au and Pd coated wire products with improved reliability and workability have been introduced, bringing a large portion of Au Bonding wire usage. However, the sensitive structure of the PKG still uses Au Bonding wire, because of the problem of pad cratering due to the high workhardening of Cu, so the Au Bonding wire cannot be converted to a cheap Cu Bonding wire despite the high Au price. Recently, Ag alloy Bonding wire has been widely evaluated as a low cost Bonding wire for PKG with sensitive structure. However, like the Cu Bonding wire, a gas kit and an inert gas are required to prevent oxidation when forming a FAB (Free Air Ball, the following notation is unified FAB) for ball Bonding. In addition, the high-humidity reliability level of silver alloy Bonding wire is lower than that of Au Bonding wire. In this study, we evaluated the metal coated silver bonding wire as a next generation low cost bonding wire product to replace Au Bonding wire. In order to improve the disadvantages of the Ag alloy Bonding wire in which the elliptical FAB is formed when the inert gas is not used in the 1st ball Bonding, the noble metal coating is performed on the high purity Ag alloy Bonding wire. Gas free Bonding characteristics and high humidity reliability performance were evaluated according to the kind and thickness of noble metal. In the evaluation of high humidity reliability, metal coated silver Bonding wire showed a high humidity reliability performance more than 2 times compared to the conventional silver alloy Bonding wire. Metal coated silver Bonding wire is expected to be an alternative to the new low cost Bonding wire in the PKG market due to gas free Bonding and improved high humidity reliability performance.

Bonding wire, one of the bonding materials, has been rapidly changed from Au to Cu due to an increase in gold price. Although Pd coated Cu (Au-Pd-Cu) wires, which comprise the largest market share among Cu bonding wires, show high reliability compared to bare Cu wire in high-humidity reliability, the reliability issue still appears in certain area. In the case of Pd coated Cu wire, studies have reported that the Pd distribution on the free air ball (FAB) surface is an important factor for improving the reliability. This study confirmed that the distribution of FAB could be controlled according to the wire manufacturing conditions, and that the Pd distribution further changed depending on the change of EFO conditions. The study further confirmed that the denser Pd distribution outside bonded ball induces the higher chemical resistance at the interface between bonding pad and the bonded ball, which improves the reliability at high temperature and high humidity after PKG.

The breakup behavior of a molten metal jet into a still gas was studied numerically. Droplet formation was modeled by imposing a sinusoidal waveform perturbation or an amplitude-modulated waveform perturbation. The effect of the temperature on the jet breakup behavior was examined by modeling the liquid metal properties, including density, viscosity, and surface tension, as a function of the temperature. The process by which a molten metal jet was ejected from an orifice exit was modeled to include the wetting of the molten metal on the orifice surface at the gas interface using a dynamic contact angle ( θ D ). The effects of the oscillation amplitude ( A = 0.10–0.30), the Strouhal number ( St = 0.20–0.50) and the Weber number ( We = 11.63–129.19) were studied. The imposition of a periodic perturbation yielded linear or nonlinear breakup behavior in the molten metal jet. The conditions found to be optimal for the continuous generation of uniform droplets were identified by optimizing the uniformity of the main droplet, the regular distance between main droplets, the presence of satellite droplets, and the coalescence of the droplets due to surface instabilities and hydrodynamic interactions. The effects of the modulated amplitude ( B ) and the frequency ratio ( N ) on the coalescence and separation of neighboring droplets were examined.

The application of an alternative method of bond monitoring during high-temperature aging is reported using a custom made test chip with piezoresistive integrated CMOS microsensors located around test bond pads. The sensor detects radial stresses originating from the bond pad and can resolve changes because of intermetallic compound (IMC) formation, voiding, or crack formation at the bond interface. Optimized Au ball bonds are aged for over 2000 h at 175 °C. It is found that stress sensors next to the bonds are capable of showing the stages of IMC growth, consumption of pad Al layers, and monitoring the formation of low-density and Al-rich IMC (AuAl2) which shows an advanced stage of aging. In particular, a first stress signal increase corresponds to the conversion of all Al above the diffusion barrier into IMCs. The second increase in stress signal after a period of stability corresponds to conversion of all Al below the barrier into IMCs. The IMC formation in these periods causes shear strength increase. After complete bond Al consumption, the bond, however, reaches maximum strength. As bond degradation starts, e.g., by lateral IMC formation, voiding, and oxide formation, as well as because of lateral pad Al transformation to IMC, the signal exhibits a strong decrease. The findings are corroborated by results obtained from classical methods such as interruptive or destructive testing including visual inspection, shear testing, cross sectioning, and by bond resistance monitoring.

Cu wire is replacing Au wire in the microelectronic industry due to its lower cost. However, during Cu ball bonding one of the main challenges is the increased stress that can damage the pad and underpad layers. Past work showed that using ultrasound super-imposed together with impact force (pre-ultrasound) results not only in a softer bonded ball, but also in a flatter ball/pad interface. In this study, Cu ball bonding processes are optimized with five levels of pre-ultrasound. The wire material is 99.99% pure Cu wire, 25.4 μm in diameter. It is shown that by using pre-ultrasound of 37.5% bonds with adequately high shear strength (120 MPa) are achieved and the amount of splash is reduced by 31%. Using pre-ultrasound allows for lower bonding ultrasound levels that result in less stress on the pad and underpad materials.

Bulk all-solid-state batteries made with mechanochemically prepared Li2S-P2S5 glass-ceramic electrolytes 1‐3 are a safe alternative to conventional Li-ion batteries because sulfide based glass-ceramic electrolytes are pure ionic conductors, non-volatile, non-flammable, and stable versus lithium metal. However, the use of lithium metal anodes in all-solid-state batteries (ASSBs) is not straightforward because dendritic lithium can penetrate porous cold-compacted glassceramic electrolyte separators. To demonstrate this point, an interfacial instability that was observed by a previous study may be better characterized as an internal short. 4 To improve cell cycleability and survivability a recent study has demonstrated that the vapor deposition of thin lithium films onto Li2S-P2S5 glass-ceramic solid-state electrolyte (SSE) pellets can improve electrolyte-lithium electrode in

We investigated the effect of Pd concentration in Pd-doped Ag wires on the humidity reliability and interfacial corrosion characteristics between Ag wire and Al metallization. Additionally, we confirmed no corrosion problem between Ag wire and noble metal (Pd, Au) metallization, even after a pressure cooker test (PCT). The chemical composition of the tested Ag wires was pure Ag, Ag-1wt% Pd and Ag-3wt% Pd. These wires were bonded to Al and noble metal (Au, Pd) metallization using a thermo-sonic bonder. The interfaces were characterized by focused ion beam (FIB), high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The interface corrosion of Pd doped Ag wires was significantly reduced as the Pd concentration in the Ag wires increased. Furthermore, the Ag wires on the noble metal (Au, Pd) metallization exhibited stable reliability during the PCT.

This paper reports a Si-Ti-Ni ternary alloy developed for commercial application as an anode material for lithium ion batteries. Our alloy exhibits a stable capacity above 900 mAh g−1 after 50 cycles and a high coulombic efficiency of up to 99.7% during cycling. To enable a highly reversible nano-Si anode, melt spinning is employed to embed nano-Si particles in a Ti4Ni4Si7 matrix. The Ti4Ni4Si7 matrix fulfills two important purposes. First, it reduces the maximum stress evolved in the nano-Si particles by applying a compressive stress to mechanically confine Si expansion during lithiation. And second, the Ti4Ni4Si7 matrix is a good mixed conductor that isolates nano-Si from the liquid electrolyte, thus preventing parasitic reactions responsible for the formation of a solid electrolyte interphase. Given that a coulombic efficiency above 99.5% is rarely reported for Si based anode materials, this alloy's performance suggests a promising new approach to engineering Si anode materials.

Inhomogeneous microtexture evolution during the cold drawing process usually results in lean, sway, or sweep failure. The longitudinal fiber texture has higher stiffness than the texture and its proportion and distribution in the cross-section are critical for the bonding stability of fine gold wire. We investigated the inhomogeneous microtexture evolution of gold wire that was cold drawn through an asymmetric diamond die. In this study, the distributions of the and textures in a2 0μm diameter fine gold wire are the variables and their effects on the bonding stability of the wire were estimated by electron backscattered diffraction (EBSD) and finite element method (FEM) simulations. The use of a focused ion beam apparatus enabled a high quality of band contrast of the EBSD to be achieved in the exact half cross-sectional area of the fine gold wire. The detailed three-dimensional FEM results show that the asymmetric distribution of the textures plays a crucial role in increasing the spatial displacement of the gold bonding wire.

We report the direct observation of microstructural changes of LixSi electrode with lithium insertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the LixSi particles with lithium insertion. Because lithiation-induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high-capacity Si anodes in lithium-ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials.

This study examined the effects of inclusions on the gold wire drawing stress using the Finite Element Method (FEM). Al2O3 and SUS304 are used as the model inclusion materials, which are frequently found on the fracture surfaces of drawn wire. The wire drawing stress showed a strong correlation with the size and yield stress of the inclusions. In the case of Al2O3, a larger diameter induced more drawing stress in the wire, whereas in case of SUS304, a larger diameter induced less drawing stress in wire. The difference was estimated quantitatively by comparing the amount of equivalent plastic strain (PEEQ) in the wire, which is the result of an interaction between the wire and inclusion. This result shows that the reason of difference in drawing stress variation is due to the yield stress of the inclusion.

Given the cost and performance advantages associated with Cu wire, it is being increasingly seen as a candidate to replace Au wire for making interconnections in first level microelectronics packaging. A Cu ball bonding process is optimized with reduced pad stress and splash, using a 25.4 μm diameter Cu wire. For ball bonds made with conventionally optimized bond force and ultrasonic settings, the shear strength is ≈140 MPa. The amount of splash extruding out of bonded ball interface is between 10 and 12 μm. It can be reduced to 3–7 μm if accepting a shear strength reduction to 50–70 MPa. For excessive ultrasonic settings, elliptical shaped Cu bonded balls are observed, with the minor axis of the ellipse in the ultrasonic direction and the major axis perpendicular to the ultrasonic direction. To quantify the direct effect of bond force and ultrasound settings on pad stress, test pads with piezoresistive microsensors integrated next to the pad and the real-time ultrasonic force signals are used. By using a lower value of bond force combined with a reduced ultrasound level, the pad stress can be reduced by 30% while achieving an average shear strength of at least 120 MPa. These process settings also aid in reducing the amount of splash by 4.3 μm.

The development of novel Cu wires for thermosonic wire bonding is time consuming and the effects of shielding gas on the electrical flame off (EFO) process is not fully understood. An online method is used in this study for characterizing Cu free air balls (FABs) formed with different shielding gas types and flow rates. The ball heights before ( H FAB ) and after deformation ( H def ) are responses of the online method and measured as functions of gas flow rate. Sudden changes in the slopes of these functions, a non-parallelity of the two functions, and a large standard deviation of the H FAB measurements all identify FAB defects. Using scanning electron microscope (SEM) images in parallel with the online measurements golf-club shaped and pointed shaped FABs are found and the conditions at which they occur are identified. In general FAB defects are thought to be caused by changes in surface tension of the molten metal during EFO due to inhomogeneous cooling or oxidation. It is found that the convective cooling effect of the shielding gas increases with flow rate up to 0.65 l/min where the bulk temperature of a thermocouple at the EFO site decreases by 19 °C. Flow rates above 0.7 l/min yield an undesirable EFO process due to an increase in oxidation which can be explained by a change in flow from laminar to turbulent. The addition of H 2 to the shielding gas reduces the oxidation of the FAB as well as providing additional thermal energy during EFO. Different Cu wire materials yield different results where some perform better than others.

A real-time signal of the stress caused by a ball bond is recorded during long-term high temperature storage (HTS) without destroying the ball bond, using a piezoresistive integrated CMOS microsensor located next to the Al bond pad (test pad) on a test chip. The sensor is sensitive to in-plane shear stress changes Δτxy that arise due to tensile or compressive stress at the test pad. While performing HTS at 200 °C during 400 h, significantly different stress signals are observed with a ball bond (test structure) compared to those observed without a ball bond (reference structure). Simultaneous to Δτxy the contact resistance of the bond was directly measured with a four-wire method in which two connection paths lead to the test pad and a second wire bond is made on top of the test ball bond. The contact resistance values measured at room temperature (25 °C) before and after HTS are 2.1 mΩ and 6.1 mΩ, respectively. Effects influencing the stress signal during HTS include volume changes by the growth of intermetallics. The stress increase initially observed during HTS shows bond shrinking corresponding to growth of Au-rich phases which was previously reported to result in volume shrinkage. A subsequent phase of signal drop is observed starting after 200 h, indicating the presence of a different mechanism partly reducing the stress built up previously, and attributed to lateral growth of Al-rich intermetallics, partially consuming the pad Al outside the bond region, and resulting in volume expansion. Finite element models are developed to support the interpretation of the stress signal features. One of the models simulates the shrinking of Au–Al material due to phase transformation. When calibrated to experimental data, the peak underpad Tresca stress level generated during such contraction is 53 MPa, located 2.4 μm inside of the 55 μm diameter bond zone.

Finer pitch wire bonding technology has been needed since chips have more and finer pitch I/Os. However, finer Au wires are more prone to Au-Al bond reliability and wire sweeping problems when molded with epoxy molding compound. One of the solutions for solving these problems is to add special alloying elements to Au bonding wires. In this study, Cu and Pd were added to Au bonding wire as alloying elements. These alloyed Au bonding wires—Au-1 wt.% Cu wire and Au-1 wt.% Pd wire—were bonded on Al pads and then subsequently aged at 175°C and 200°C. Cu and Pd additions to Au bonding wire slowed down interfacial reactions and crack formation due to the formation of a Cu-rich layer and a Pd-rich layer at the interface. Wire pull testing (WPT) after thermal aging showed that Cu and Pd addition enhanced bond reliability, and Cu was more effective for improving bond reliability than Pd. In addition, comparison between the results of observation of interfacial reactions and WPT proved that crack formation was an important factor to evaluate bond reliability.

Presently, Sn-Ag-Cu (SAC) solders are most commonly used as the interconnect materials in the semiconductor package. However, their thermal fatigue and drop impact resistant properties depends on the Ag content and therefore, most semiconductor package assemblers are forced to implement multiple SAC alloys depending on intended performance. Sn-xAg-Cu solders with high Ag content (x>3 mass%) give good temperature cycling (TC) reliability but poor drop impact reliability whereas Sn-xAg-Cu solders with low Ag content (x

Solid solution-type alloying in Au wire matrix is one of the well-known methods for improving the mechanical properties of Au wire as well as the reliability of bonding interface. Palladium (Pd) uses as a typical alloying element of Au bonding wire manufacturing which makes solid solution hardening effect in Au matrix. The behavior of Pd at the Au wire-Al pad bonding interface during the thermal aging, and the effect of Pd on Au/Al interfacial reactions were investigated. Two types of Au wires, Au-0.25wt%Pd (Low Pd content) and Au-0.95wt%Pd (High Pd content), were used for the fabrication of wire-bonded test vehicles (TVs). The wirebonded TVs were thermally aged at 175°C up to 1200hours, and the formation of a Pd-accumulation layer was investigated at Au-Al bonding interface by using a cross-sectional scanning electron microscope (SEM) and an electron probe microanalysis (EPMA). The accumulation of Pd atoms was confirmed at the TVs fabricated with the Au wire with high Pd content. According the results of a transmission electron microscope (TEM), the thickness of Pd accumulation layer was about 500nm and it located between Au wire (Au-0.95wt%Pd) and Au8Al3 intermetallic compound (IMC) layer. Au4Al IMC did not detected in Au-0.95wt%Pd wire TVs. In TV with Au-0.25wt%Pd wire, the phenomenon of Pd accumulation was not observed at bonding interface after thermal aging but Au4Al formed at the interface between Au-0.25wt%Pd wire and Au8Al3 IMC. After long-term thermal aging, the bonding interface was degraded by the oxidation phenomena. According to the cross-section analysis, it was mainly due to the oxidation of Au4Al IMC and, therefore, the Au-Al bonding interface becomes vulnerable to this kind oxidation.

Thermosonic wire bonding is a well-known process which combines heat, ultrasonic energy and force to bond small wires to complete an electrical path from a metalized surface on a microchip to another metalized surface on the substrate of the circuit and the bonding occurs through the process of atomic diffusion. The bonding wire materials presently used in the industries are primarily gold (Au) and recently the use of low cost copper (Cu) and palladium coated wire (PdCu) have increased significantly. However, due to the increasing price of Au and reliability concerns with the Cu and PdCu wire has led to the search of alternative bonding wire materials in which silver (Ag) or silver alloy wire (Ag alloy) has emerged as the preferred choice. Cu and PdCu wire induces a higher stress on the bond pad and underlying structure due to its inherent hardness value. Ag has similar mechanical properties as Au while it's cheaper and has higher thermal and electrical conductivity as compared to Au. When compared to Cu, Ag is similar in conductivity, but softer in terms of mechanical properties. The pure Ag bonding wire has some issues such as unstable free air ball (FAB) shape and poor reliability. To overcome these issues, alloyed Ag wire (Ag-Au-Pd) was developed and their FAB formation, bondability and reliability were studied. The package used is BGA type and the pad composition is Al-1%Si-0.5%Cu. Ag alloy wire delivers good and stable bonding capability using nitrogen as ambient gas. Both the bonded ball and stich bonding show good bond integrity. The reliability is determined by the high temperature storage life test (HTSL) test. Intermetallic compound (IMC) growth behavior during reliability test is characterized by the scanning electron microscopy (SEM) and energy dispersive spectrometer analyses (EDS). Two types of IMCs Ag2Al and Ag3Al were observed. No failure or voids are observed in the bulk IMC or metal-IMC interface after the HTSL test at 150C for 1000 hrs. Additionally these IMCs are fabricated in bulk and their resistivity and co-efficient of thermal expansion (CTE) properties are characterized to understand the likely source of failure of the Ag-Al bond. The CTE of the Ag3Al is lower than the Ag2Alwhich could be attributed to the lower stretching of lattice constant of former at higher temperature. The interface between the Al and Ag2Al is likely source of crack generation and failure because of the high CTE difference between them. The resistivity of the Ag3Al phase was found to slightly higher than Ag2Al. The information regarding the properties of Ag-Al IMCs are important for the finite element and quantum mechanics based first principle calculation and to ultimately predict their behavior in real life situation. The Ag alloy wire show floor life time of minimum 10 weeks based on bonded ball shape, workability and bondability test and there is no visible appreciable degradation of pull strength and bonded ball shape overtime. Ag alloy wire bonding has the potential to become an emerging technology as an option in microelectronic packaging.

Recently Silver (Ag) wire has drawn attention to the packaging industry because of the bonding quality and long term reliability concerns with the Cu and Pd coated wire. Ag wire has low cost, high thermal and electrical conductivity as compared to Au while their mechanical properties such as hardness, elongation and breaking load are similar to Au. In the present study, free air ball (FAB) formation, bonding behavior and reliability of Ag alloy wire (Ag-Au-Pd) bonding was studied. The careful control of electronic flame off (EFO) current, time and gas flow rate leads to spherical FAB ball formation without defects. The Ag alloy wire delivers good and stable bonding capability using nitrogen as ambient gas. Both the bonded ball and stich bonding show good bond integrity. The reliability is determined by the high temperature storage life test (HTSL) test. Intermetallic compound (IMC) growth behavior during reliability test is characterized by the scanning electron microscopy (SEM) and energy dispersive spectrometer analyses (EDS). Two types of IMCs Ag2Al and Ag3Al were observed. The Ag alloy wire show floor life time of minimum 10 weeks based on bonded ball shape, workability and bondability test.

The rapidly solidified Si-xTiNi (x = 0.2-0.45) alloy ribbons were fabricated via melt spinning process. The thickness of the melt-spun ribbons was about 12.5 microm, and the sound section was selected for the experiment. The microstructures of the ribbons were analyzed using XRD, FE-SEM, and HR-TEM: The primary silicon particles of 30 nm-100 n min diameter were finely dispersed in the inactive buffering matrix of Si7Ni4Ti4 phase. The charge/discharge energy capacity and electrochemical properties were significantly influenced by the relative ratio of NiTi to silicon. With increasing the total amount of Ni and Ti content up to 45 at%, the amount of Si7Ni4Ti4 phase increased and the cycle performance was improved. The Si7Ni4Ti4 phase acted as a buffer for the volume expansion/contraction of Si occurring during the alloying and dealloying, and it could prevent a significant deterioration in cycle performance of the battery.

This paper presents the microstructures and electrochemical properties of Si-Ti-Ni alloys of various compositions prepared by a rapid solidification process. Si-15Ti-(0-25 at%)Ni alloy ingots prepared by arc-melting was melt-spun to produce thin strip of -15 Om thickness. The Si-Ni-Ti alloy electrode were fabricated by mixing the active powdered materials (88 wt%) with ketjen black (4 wt%) as a conductive material and polyamide-imide binder (PAI, 8 wt.%) dissolved in N-methyl-2-pyrrolidinone (NMP). Results showed that the microstructures of melt-spun Si-Ti-Ni ribbons consist of silicon, TiSi2, Si7Ni4Ti4, and NiSi2 phases depending on the composition. As the content of nickel increased in silicon matrix, TiSi2 phase disappeared while Si7Ni4Ti4 and NiSi2 phases are generated. The cycle efficiency of Si65Ti15Ni20 and Si60Ti15Ni25 alloys was significantly improved because of the increased volume fraction of Si7Ni4Ti4 and NiSi2 phases and fine particulated silicon phase.

The phase change due to varying content of titanium in Si-Ni-xTi alloys and its effect on the electrochemical behavior has been investigated. Specimens were prepared by melt-spinning to reduce the microstructure scale. Results showed that silicon particles of 50-100 nm diameter and dendrites of somewhat larger scale were formed in the Si-Ni-Ti alloys ribbons. The microstructure of Si70Ni15Ti15 alloy ribbons was composed of silicon particles finely dispersed in Si7Ni4Ti4 phase. The cycle performance was improved by the formation of TiSi2 or NiSi2 phase at the presence of Si7Ni4Ti4 phase, either of which combined with Si7Ni4Ti4 phase effectively accommodated the volume change of silicon particles during cycling. The reduced scale of silicon particles contributed to the enhanced cycle efficiency as well.

With 20μm diameter PCC wire, spherical (well-shaped) free-air balls (FABs) were obtained in both forming gas and N 2 at flow rates between 0.25–0.75 l/min and 0.4–0.5 l/min, respectively. With Cu wire, in comparison, sperical FAB are obtained in forming gas with flow rates between 0.25 and 0.5 l/min while in N 2 gas, FABs are always pointed or golf-clubbed (mis-shaped). Using a shielding gas with Au wire makes the FABs mis-shaped. The FAB deformability is measured as the amount of deformation under a given load. Au had the highest deform-ability. The FABs made with PCC wire in N 2 had generally the same deformability as Cu FABs in forming gas. The force required to achieve a pre-defined deformed ball height (target) is named “force for target deformation”, F TD , and set to half the FAB diameter. Compared to "deformability", the F TD method is more similar to the standard tensile or compression tests that determine yield strength. Deforming a PCC FAB obtained with 0.4 1/min N 2 to the target ball height requires 615 ± 32 mN, a value not significantly different from that for a Cu FAB obtained in 5 l/min forming gas. For comparison, the target deformation requires 394 ± 16 mN for a Au FAB.

In this study, we reported that effect of solder ball sizes on the intermetallic growth of Sn-Ag-Cu solder balls during thermal aging. Various size (400, 300, 200, and 100 um diameter) solder balls of 98.5 wt.% Sn, 1 wt.% Ag, and 0.5 wt.% Cu(SAC105) were bonded on the Cu/OSP (Organic Solderability Preservative) and ENIG (Electroless Ni Immersion Gold) pads by solder reflowing and then subsequently annealed at 150°C for up to 500 h. In the case of the reaction with Cu/OSP, there was no significant difference of the total Cu 3 Sn IMC thickness regardless of solder ball size. Unlike the reaction with Cu/OSP, the IMC growth of fine size solder balls on ENIG pads was faster than larger size solder balls during a thermal aging test. The composition of Cu-Ni-Sn IMCs formed at the ENIG pads was changed from Cu-rich phase ((Cu, Ni) 6 Sn 5 ) to Ni-rich phase ((Ni, Cu) 3 Sn 4 ), as solder ball sizes decreased and aging time increased. This study showed that the solder ball size significantly affects the IMC thickness, types of IMC phases, and IMC composition at the ENIG pad during a thermal aging test.

To qualify interconnect technologies such as microelectronic fine wire bonds for mass production of integrated circuit (IC) packages, it is necessary to perform accelerated aging tests, e.g., to age a device at an elevated temperature or to subject the device to thermal cycling and measure the decrease of interconnect quality. There are downsides to using conventional ovens for this as they are relatively large and have relatively slow temperature change rates, and if electrical connections are required between monitoring equipment and the device being heated, they must be located inside the oven and may be aged by the high temperatures. Addressing these downsides, a miniaturized heating system (minioven) is presented, which can heat individual IC packages containing the interconnects to be tested. The core of this system is a piece of copper cut from a square shaped tube with high resistance heating wire looped around it. Ceramic dual in-line packages are clamped against either open end of the core. One package contains a Pt100 temperature sensor and the other package contains the device to be aged placed in symmetry to the temperature sensor. According to the temperature detected by the Pt100, a proportional-integral-derivative controller adjusts the power supplied to the heating wire. The system maintains a dynamic temperature balance with the core hot and the two symmetric sides with electrical connections to the device under test at a cooler temperature. Only the face of the package containing the device is heated, while the socket holding it remains below 75 degrees C when the oven operates at 200 degrees C. The minioven can heat packages from room temperature up to 200 degrees C in less than 5 min and maintain this temperature at 28 W power. During long term aging, a temperature of 200 degrees C was maintained for 1120 h with negligible resistance change of the heating wires after 900 h (heating wire resistance increased 0.2% over the final 220 h). The device is also subjected to 5700 thermal cycles between 55 and 195 degrees C, demonstrating reliability under thermal cycling.

Wire bond reliability testing typically consists of aging bonds in a high temperature environment for long time periods, removing samples at intervals to assess bond shear strength and characterize the bond cross sections. In this way, the degradation of the bond can be monitored at discrete time intervals, and it is determined whether the bond will be reliable under long term operation at lower temperatures. This process is labour and time consuming. An alternative process is reported using piezoresistive integrated CMOS microsensors located around test bond pads. The sensors are sensitive to radial compressive or tensile stresses occurring on the bond pad due to intermetallic formation, voiding, and crack formation at the bond interface. Two sets of identical test chips are bonded with optimized Au ball bonds and aged for 2000 h at 175 °C. One set is connected to equipment which monitors signals from the stress sensors, along with the contact resistance of the bonds. The other set of chips is destructively tested by shear tests and cross sectioning. It is found that the stress sensors are capable of indicating which stage of intermetallic growth is currently being experienced, by relating the signal to the relative density of the intermetallic compounds (IMCs) which form during aging. The sensors can detect the consumption by IMCs of each Al layer in a multilayer pad, and can monitor the formation of AuAl 2 which indicates an advanced stage of aging. Sensor signals combined with contact resistance measurements provide a valuable tool for preliminary reliability studies, and give real-time insight into microstructural changes. Drop in shear strength of a ball bond is detected by a change in the microsensor signal combined with a contact resistance increase.

Due to increasing cost of gold and technological demand for finer pitch application, Au bonding wires with finer diameter are needed. In such demands, Au bonding wire manufacturing companies produced ultra-fine Au wires with diameter of 12 μm (0.5 mil). However, interfacial reactions between ultra-fine Au wires and Al pads may cause serious reliability problems as wire diameter get smaller. Decrease in bond reliabilities may be caused by interfacial failures such as Kirkendall voids and oxidation of Au 4 Al IMCs. For the application of ultra-fine Au wires in real products, studies on interfacial reactions of ultra-fine Au wires/Al pads and effects of Pd addition on Au wire/Al pad interface which is previously proven to be enhancing bond reliabilities are necessary. In this study, interfacial reactions and failures of two types of 4N ultra-fine Au wires(12 μm)/Al pads with different bonding types were analyzed, and effects of Pd addition on interfacial reactions and failures are also investigated by using 3000, 6000, and 10000 ppm of Pd added Au wires. High temperature storage test (HTST) at 175D under air-ambient was performed to simulate an accelerated thermal exposure characteristic of device operation conditions. Intermetallic compound (IMC) phases and Pd behavior at the Au wire/Al pad interface were identified using various analytical tools. Ball pull test (BPT) was conducted to evaluate bond reliabilities depending on bonding types, wire compositions, and aging times. According to experimental results, two types of ultra-fine Au wires/Al pads showed different bonding reliabilities depending on initial inter-metallic coverage. It was found that initial intermetallic coverage determined the interface bond reliability because interfacial oxidation problem depended on initial intermetallic coverage. Addition of Pd on Au wires/Al pads significantly affected bond reliabilities depending on Pd contents. 3000 ppm of Pd added Au wires/Al pads resulted the best bond reliabilities and strongest resistance against the interfacial oxidation due to the Pd accumulation at Au 4 Al grain boundaries. However, 10000 ppm of Pd added Au wires/Al pads showed low bond reliabilities because separated Pd-rich island grains formed among Au 4 Al grains resulting in less protection of Au 4 Al from oxidation.

Recently, the application of Ag bonding wires in electronic devices has been attempted as alternative to Au bonding wires to reduce the material cost of Au. Nevertheless, Ag bonding wires have not been applied to devices due to interface corrosion problems between the Ag wire and Al pad during humidity reliability tests, such as the PCT (Pressure Cooker Test). As the technology for alloying Pd element in Ag wire has developed recently, the corrosive failure problem at the interface in the PCT has been improved significantly. This study examined the behavior of IMCs(intermetallic compounds) and interface corrosion between an Ag wire and Al metallization under humidity conditions (100%RH, 121'C). The chemical compositions of the Ag wires tested were pure Ag, Ag — 1wt%Pd and Ag-3%Pd. These wires are bonded to Al and noble metal(Au, Pd) metallization using a thermo-sonic bonder. The interfaces were characterized by FIB(Focused ion beam), HRTEM (High Resolution Transmission Electron Microscope) and EDS (Energy Dispersive X-ray Spectroscopy) The findings show that, (1) the interfacial reliability between the Ag wire and Ag metallization was improved considerably. The interface corrosion was suppressed significantly as the Pd content was increased. (2) Ag wires on a noble metal(Au, Pd) pad have stable reliability in PCT.

Ball bonding processes are optimized on Al pads with a 25.4 µm diameter Cu wire to obtain maximum average shear strengths of at least 120 MPa. To quantify the direct effect of bond force and ultrasound on the pad stress, ball bonding is performed on test pads with piezoresistive microsensors integrated next to the pad and the real-time ultrasonic signals are measured. By using a lower value of bond force combined with reduced ultrasound level, the pad stress can be reduced by 30%. An ultrasound/bond force process window for low-stress copper ball bonding is determined, which shows that a proper optimization of ultrasound and bond force leads to Cu ball bonds of high quality while transmitting lower stress to the pad during the bonding process.

Ultra-fine pitch Au wire has become inevitable in the electronic packaging industry due to decreasing electronic package dimension and increasing cost of gold. However, fine pitch Au wire with diameter less than 0.5 mil. (12 μm), bonded on Al pad, showed low inter-metallic coverage, and it caused distinctive interfacial failures: the oxidation of Au 4 Al and overgrowth of inter-metallic compound (IMC). In order to enhance the interfacial failure, addition of Pd was proposed due to its known effect as the diffusion barrier. In this study, 0 ppm, 3000 ppm, 6000 ppm, and 10000 ppm of Pd was added to 0.5 mil. Au wire as alloying element and subsequently aged under high temperature storage test (HTST) in air and vacuum condition at 175 °C. By the observation of Au/Al interface using scanning electron microscope (SEM) and reliability test using ball pull test (BPT), it was confirmed that major failure mode was the oxidation of Au 4 Al for air-aging and overgrowth of IMC for vacuum-aging; however, it was observed that the interfacial failures were affected by the addition of Pd. For air-aging, the oxidation rate was in order of 10000 ppm (fastest) > 0 ppm = 6000 ppm > 3000 ppm (slowest) of Pd showing that the interfacial failure due to the oxidation was affected by Pd contents. For vacuum-aging, higher Pd contents decreased overgrowth of IMC and number of ball-lift. Detailed effects of Pd for the oxidation rate were analyzed using transmission electron microscope (TEM). Au wire with 2500 ppm of Pd was analyzed as most oxide-stable Pd composition, and was observed to form segregation of Pd mass at the grain boundary of Au 4 Al, and the segregation protected Au 4 Al from the oxidation. However, the sample with 10000 ppm of Pd made separate Pd-rich grain, and it didn't prevent the oxidation and even caused quicker oxidation than the sample without Pd.

There have been many studies on replacing Au bonding wire with other bonding wire materials, because the cost of Au has dramatically increased by approximately 2~3 times in recent years. When replacing part of the bond pad with a noble metal, Ag bonding wire is of particular interest due to its superior electrical properties, lower cost and similar mechanical properties as compared with Au. Ag bonding wire is thermosonically bonded to 3 kinds of bond pad (Al, Au and Pd) and aged at high temperature (175°C). Then, the bondability and interface reactions are characterized at each bond pad. In the case of Ag-Al bonding, 2 kinds of intermediate phases were observed and the composition ratios of Ag and Al in these phases were 4:1 and 2:1, respectively. After 300 hrs of aging, cracks were formed in these intermediate phases and ball-lift failure occurred. However, in the case of the noble metal bond pad, a solid solution was formed between the Ag wire and bond pad and no voids or cracks were formed. This shows the robust bonding characteristics. The diffusion layer was observed and the diffraction pattern was analyzed by TEM (Transmission Electron microscopy). The Au-Al bond reliability was also characterized by a comparative study. In this study, Ag bonding wire is proposed as an alternative to Au bonding wire for noble metal pads. Also, the thermal reliability is reviewed and the failure mechanisms are verified with various bond pads.

To reduce material cost of Au bonding wire, Au-Ag alloy wire had been tried to use in electronic device, in alternative for Au wire. Nevertheless, Au-Ag alloy wire had not been applied to device due to failure problem during high humidity reliability test, like PCT(Pressure Cooker Test) for a while. Recently, as the technology adding Pd element to conventional Au-Ag was developed, corrosive failure problem at interface between wire ball and Al pad (metallization) was solved in PCT. Finally, mass production of Au-Ag-Pd wire starts to grow up. The study on reliability and behavior of intermetallic compounds(IMC) have not been performed in terms of thermal Aging or HTST(High Temperature Storage Life Test) yet. This study investigates IMC & voids behavior between Au-Ag-Pd wire and Al metallization under thermal aged condition (175'C). The chemical compositions of gold wires tested are 99.99% Au, Au-30wt.%Ag and Au-30wt.%Ag-5.5%wt.Pd, respectively. The wires are bonded on Al metallization by using thermosonic bonder, IMC behavior was characterized by FIB(Focused ion beam), TEM (Transmission Electron Microscope), EDS (Energy Dispersive X-ray Spectrometer) The findings reveal that, interfacial reliability between Au-Ag-Pd wire and Al metallization is considerably improved, compared with 4N Au or Au-30%Ag, Growth of IMCs as well as the voids formation are significantly suppressed.

Various Au bonding wires which have different diameters from 25 um to 12 um, and purity of 2N and 4N are used for studying possible problems in ultra fine wire bonding. As wire diameter gets finer, grain size gets finer and portion of direction in wire texture is increased due to high working ratio. Moreover, as wire diameter gets finer, eccentricity of FAB (Free Air Ball) get worse and, for soft 4N wire, neck broken issue is occurred in 12 um bonding due to low neck strength, and for hard 2N wire, bond-off issue is occurred due to bad initial bondability. Also initial IMC (Intermetallics) coverage gets worse and HTST reliability is dramatically dropped in ultra fine wire application. Therefore, soft 2N wire which has relatively low FAB hardness and Pd-based dopant composition could be an alternative to solve these issues in ultra fine wire.

Recently, Sn-Ag-Cu solders have been widely used as lead-free candidates for the Ball-Grid-Array (BGA) interconnection in the microelectronic packaging industry. However, widely used Sn-Ag-Cu solders such as with 3.0-4.0 wt% Ag in microelectronics exhibit significantly poorer drop test reliability than SnPb solder due to the low ductility of Sn-Ag-Cu solder bulk. The brittle failure of solder joints occurs at intermetallic compound (IMC) layer after drop test. Because the brittle nature of IMC or defects around IMC transfers a stress to the interfaces as a result of the low ductility of solder bulk. For the improvement of the drop test reliability by solder alloys, the low ductility of solder bulk and the IMC control at the interface are needed. In this paper, the bulk property of solder alloys and interfacial reactions with ENIG of Sb-added Sn-Ag-Cu solder were studied and finally, drop test was performed. Low Ag solder such as Sn1.0Ag0.5Cu and Sn1.2Ag0.5Cu0.5Sb showed higher ductility than high Ag solder such as Sn3.0Ag0.5Cu. In the interfacial reaction, all of the solders had (Cu,Ni)6Sn5 IMCs and P-rich Ni layer, however, Sn1.2Ag0.5Cu0.5Sb solder showed the lowest P-rich Ni layer thickness, because less Ni participated in the formation of (Cu,Ni)6Sn5 IMCs. In the drop test, the longer lifetime was in order of Sn1.2Ag0.5Cu0.5Sb, Sn1.0Ag0.5Cu, and Sn3.0Ag0.5Cu. Sn1.2Ag0.5Cu0.5Sb solder showed the best drop test reliability compared with other two solders due to the thinnest P-rich Ni layer. The failures of all packages occurred along P-rich Ni layer which is the most brittle phase at the solder/ENIG interface.

The trend of high integration and miniaturization of semiconductors has accelerated the development of gold bonding wire with smaller diameter. For the stable bonding of fine wire, it is important to characterize the wire with various diameters during the bonding process. To investigate this relationship, the experiments were done for the various sizes of wire diameter and FAB. The wire size and the FAB size were chosen for the test from 15 /spl mu/m to 25 /spl mu/m and from 1.4 WD (wire diameter) to 2.0 WD, respectively. The results showed that as the size of FAB became smaller, the size deviation of FAB increased and FAB itself was tilted to one side. When FAB was formed at the same parameter, the length of HAZ became shorter for the wire with the high temperature of recrystallization. It is also revealed that the length of HAZ decreased for the smaller size of FAB. This phenomenon is considered to be related to the beat generated during the FAB formation.

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