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Free air ball (FAB) and bonded strength were performed on an Ag-10Au-3.6Pd alloy bonding wire (diameter of 0.025 mm) for different electronic flame-off (EFO) currents, times and bonding parameters. The effects of the EFO and bonding parameters on the characteristics of the FAB as well as the bonded strength were investigated using scanning electron microscopy. The results showed that, for a constant EFO time, the FAB of the Ag-10Au-3.6Pd alloy bonding wire transitioned from a pointed defined ball to an oval one, then to a perfectly shaped one, and finally to a golf ball with an increase in the EFO current. On the other hand, when the EFO current was constant and the EFO time was increased, the FAB changed from a small ball to a perfect one, then to a large one, and finally to a golf ball. The FAB exhibited the optimal geometry at an EFO current of 0.030 A and EFO time of 0.8 ms. Further, in the case of the Ag-10Au-3.6Pd alloy bonding wire, for an EFO current of 0.030 A, the FAB diameter exhibited a nonlinear relationship with the EFO time, which could be expressed by a quadratic function. Finally, the bonded strength decreased when the bonding power and force were excessively high, causing the ball bond to overflow. This led to the formation of neck cracks and decrease in the bonded strength. On the other hand, the bonded strength was insufficiently when the bonding power and force were small. The bonded strength was of the desired level when the bonding power and force were 70 mW and 0.60 N (for the ball bonded) and 95 mW and 0.85 N (for the wedge bonded), respectively.

In this work, we report a methanol-facilitated approach to directly use aqueous Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) (PEDOT:PSS) in the silver/epoxy composites for preparation of highly electrically conductive adhesives (ECAs) and an investigation of the interaction between PEDOT:PSS nano-gels and silver microflakes. PEDOT:PSS nano-gel (18

The high price of Au has motivated many to look for alternative bonding wire materials in the field of microelectronics packaging. In the present study, the reliability performance of palladium coated silver (PCS) wire in high temperature storage test (HTST) is carried out using 18 μm diameter fine pitch PCS wire. Fine pitch ball bonds are made on Al metallization, with bonded ball diameter (BBD) of 32 ± 0.5 μm and ball height (BH) of 8 ± 0.5 μm. The aging temperature used in HTST is 170 °C and both shear and pull test are used to evaluate the aged ball bonds at regular time intervals. The shear force increases from 9.9 gf at 96 h to 12.5 gf at 192 h, and remains almost constant until 1344 h, and starts dropping gradually until 10.9 gf at 1848 h. The pad lift percentage recorded in pull test gradually drops from 90 % at 96 h to 20 % at 1008 h, and increases to 90 % at 1848 h. The chip side fractography after shear test indicates that the main failure modes are through pad at 96 h, through ball bond at 504 h, and half of both at 168 h, respectively. Cross-sectional images show that the thickness of the intermetallic compound (IMC) layer growth follows parabolic relationship and the rate constant is 0.10 ± 0.02 μm/h½. Gaps are observed along the periphery of the ball bond interface where no IMC is observed. The IMCs are located at the center of the ball bond interface, and the width is 16.0–19.3 μm at 96 h and 17.2–22.7 μm at 1344 h, respectively.

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.

Thermo-chemical properties of the Al nanoparticle and NiO nanowire composites modified by the micro-sized copper additive were investigated experimentally. Their onset temperatures of ignition and energy release data per mass were characterized using differential thermal analysis measurements. These microstructures and chemical compositions of reaction products were analyzed using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The fuel-rich Al/NiO/Cu composites produced two types of metallic spheres. Copper spheres were formed from melting and solidification of the copper additive, while AlNi composite spheres were identified by the energy dispersive X-ray spectroscopy and X-ray diffraction analyses. It was found that the amount of the copper additive did not significantly influence the onset temperature of thermite peaks, but caused a dramatic change in energy release. The aforementioned ignition and energetic properties were compared with these from the Al nanoparticle and CuO nanowire composites.

Carbon modified TiO2 nanobelts (TiO2-C) were synthesized using a hydrothermal growth method, as a support material for palladium (Pd) nanoparticles (Pd/TiO2-C) to improve the electrocatalytic performance for methanol electrooxidation by comparison to Pd nanoparticles on bare TiO2 nanobelts (Pd/TiO2) and activated carbon (Pd/AC). Cyclic voltammetry characterization was conducted with respect to saturated calomel electrode (SCE) in an alkaline methanol solution, and the results indicate that the specific activity of Pd/TiO2-C is 2.2 times that of Pd/AC and 1.5 times that of Pd/TiO2. Chronoamperometry results revealed that the TiO2-C support was comparable in stability to activated carbon, but possesses an enhanced current density for methanol oxidation at a potential of −0.2 V vs. SCE. The current study demonstrates the potential of Pd nanoparticle loaded on hierarchical TiO2-C nanobelts for electrocatalytic applications such as fuel cells and batteries.

With the rapid development of advanced microelectronic packaging technologies, research on fine-pitch wire bonding with improved reliability is driven by demands for smaller form factors and higher performance. In this study, thermosonic wire bonding process with a 20 μm wire for fine-pitch interconnection is described. To strengthen stitch bonds made in a gold–silver bonding system when the bonding temperature is as low as 150 °C, ball bumps (security bump) are placed on top of the stitch bonds. The ball–stitch bond and bump forming parameters are optimized using a design of experiment (DOE) method. A comparison of pull test results for stitch bonds with and without security bumps shows a substantial increase of the stitch pull force (PF) due to the use of security bonds. By varying the relative position of the security bumps to the stitch bonds via wedge shift offset (WSO), a WSO window ranging from 15 to 27 μm results in stitch PF higher than 7 gf, which is equivalent to an increase in average stitch PF of 118%.

Thermal stability and reaction properties of Al–CuO system, a mixture of 50–200 nm aluminum nanoparticles passivated by nitrocellulose and 12 nm copper (II) oxide, were investigated with microstructure characterization, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Transmission electron microscopy observation confirmed that the passivation coating successfully hinders the oxidization. TGA revealed that the passivation shell does not influence the ignition temperature of the thermite reaction. Reaction chemistry of the nano-thermite was elucidated by heating the composite both in inert ambient and vacuum. It was found that the thermite reaction

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 effect of substrate material pick up by the Cu wire tail on the hardness of the subsequently formed free air ball (FAB) is investigated with scanning electron microscopy (SEM) and micro-hardness test. The Cu wire bonds are made on Au metallization. Wire residue is not found on the imprint the tail bond leaves on the metallization, but fracture of the substrate metallization is evident. SEM images of the Cu wire tail end clearly show Au residue (pick up). The amount of Au pick up is estimated higher than 0.03% of the volume of a subsequently formed 50 μm diameter FAB, exceeding typical impurity and dopant concentrations (0.01%). Lowering the impact force process parameter is found to strongly increase the amount of substrate material pick up. Cu free air balls (50 μm in diameter) formed with an estimated Au pick up volume of 50 μm 3 are found to be between 1.2 HV and 4.3 HV softer than those without pick up. However, the hardness varies significantly more than that of FABs without pick up.

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.

In this study, security bumps are used for strengthening the stitch bonds of two 20 micron diameter insulated Au wire bonding example processes. Bump bonding as a variant of the ball bonding process has been commonly used in the microelectronic industry to make bumps on dies that will later be flip-chip bonded. The optimized stitch bond parameters combined with the security bumps placed upon the stitch bonds substantially improve the second bond strength demonstrated on the two example processes on two different types of wire bonding equipment. A comparison of pull test results shows that security bumps increase stitch pull force up to 100%. The effect of varying the relative position (shift) of the security bump relative to the stitch bond location is investigated for one process. The window with the highest pull force improvement is ranging from 16 to 31 micron shift towards the ball bond. Looping with insulated wire is faster than with bare wire because of less effort to mitigate the risks of wires touching each other and producing a short. If two wire loops touch each other e.g. after molding, the wire insulation prevents shorts. Therefore, the looping requirements of the example processes with security bumps can be relaxed by reducing the number of kinks (reverses) from four to two. Due to the reduced looping complexity, the overall UPH increased with insulated wire by about 3.0 % and 4.9 % for the two processes, respectively. This increase is in spite of the time required for the additional security bumps, and compared to bare wire processes without security bumps but with more complex looping.

Cu bonding wire is more and more used for interconnections to integrated circuits (ICs) to reduce cost and increase performance compared to Au wire. To eliminate underpad damage for Cu wire applications, it is worthwhile to reduce the hardness of the free-air ball (FAB). Short heat affected zone (HAZ) and high HAZ breaking load are often required for advanced microelectronics packaging in order to decrease the loop height and thereby the package thickness. Online measurements of deformability and HAZ breaking force at temperatures close to the bonding temperature of 220^oC are new tools used in this study to evaluate the effects of electronic flame off (EFO) current and firing time on the Cu FAB deformability and the HAZ length and tensile strength. FABs with 50@mm diameter formed from a 25@mm diameter Cu wire with a breaking load of 118.6mN were used. EFO currents and firing times ranged from 40 to 250mA and 0.11 to 0.90ms, respectively. Average FAB deformability factors, HAZ breaking forces, and HAZ lengths were in the rounded ranges of 36.64-44.09% (with a deformation force of 0.60N), 107.7-116.8mN, and 167-215@mm, respectively. When produced with 250mA current during 0.11ms, the FABs are 7.01-7.89% more deformable than when produced with 45mA during 0.9ms, the HAZ breaking force is 7.53-9.37% higher, and the HAZ length is 7-90@mm shorter.

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.

Two types (A and B) of 25-μm-diameter bare Au bonding wire and their corresponding insulated wire were used to produce 50-μm-diameter free-air balls (FABs) for heat-affected zone (HAZ) and FAB deformability analyses. Insulated wires showed no significant difference in HAZ length compared with bare wire for type A, while their difference lay in the range of 4% to 12% longer for type B. The HAZ breaking load of bare wire is 0.3% to 1.8% smaller than that of insulated wire for type A and not significantly different for type B even though the HAZ length is shown to be larger for insulated wire B. The deformability of the FAB from insulated wires is 1.0% to 2.1% smaller than that from bare wires for type A and 2.1% to 3.4% larger for type B.

The characteristics of the crescent bond process with insulated Au wire are investigated. Au wire with a sub-micron thick insulation coating is bonded on standard Ag plated leadframe diepads at 493 K. The wire loops are oriented perpendicular to the ultrasonic horn. The pull force obtained with a basic bonding process of insulated Au wire and bare Au wire are optimized by iteration and compared. Subsequently, the process is modified for the application with insulated wire. To increase the pull force an insulation layer removing stage (cleaning stage) is inserted before the bonding stage. The cleaning stage consists of a scratching motion (shift) toward to the ball bond in combination with ultrasound. The pull force obtained in this way with the insulated wire is 90:1 � 7:9 mN which is 2:4 � 2:0 mN larger than that obtained with bare Au wire. [doi:10.2320/matertrans.MRA2008087]

In situ sensors can measure wire bond reliability nondestructively during thermal aging. Conventional thermal aging of ball bonds requires ovens heating the entire microchip along with the wire bonds, also affecting interconnects for in situ sensors. To protect the interconnects and on-chip logic components of in situ sensor chips, conventional thermal aging is kept below a safe temperature limit of 200 °C. At higher temperatures, the doped Si components change their characteristics and transistors stop working. Localized on-chip heating is introduced to circumvent these drawbacks using a new microheater to increase the safe temperature limit for nondestructive reliability assessment with in situ sensors. The effect of temperature on surrounding components is reduced. The microheater is a rectangular design resistive heater made from N+ silicon. In addition, a pad resistance measurement is introduced that indicates bond aging more conveniently than previously reported bond resistance measurements.

The method is based on a microheater integrated next to a wire bonding pad (test pad) on a test chip. It is fabricated in CMOS technology without additional micromachining. The microheater consists of two polysilicon resistor elements, placed at opposite sides of the pad, operated in parallel using a constant voltage, each element extending over 30 × 70 μm with a resistance of ≈140 Ω at room temperature, and is operated based on Joule heating. The polysilicon is located at least 20 μm but not more than 50 μm from the pad aluminum. To characterize the microheater, Al serpentine resistors are placed on and between the heaters next to the pad, serving as resistive temperature detectors, having resistances of about 9.4 Ω at room temperature. With a constant operation voltage of 15 V, ≈140 mA of current and ≈2.1 W of heating power are generated, resulting in a heat flux of ≈500 MW/m2. The thermal resistance of the heater is 200 K/W (i.e., loss coefficient of 5 mW/K). The maximum temperature measured on one of the microheater resistors was above 396 °C and was reached using 18 V within less than 5 s of voltage application starting at room temperature. When heating from 101 °C to 138 °C, even faster heating is possible, allowing the performance of highly accelerated thermocycles. These cycles are applied to a ball bond on the test pad. Compared to the 20 min cycles used by a standard test, the new microheater device performed cycles lasting 10 ms (5 ms on, 5 ms off) which is 5 orders of magnitude faster. The released energy is typically 10 mJ per cycle. A 50 μm diameter ball was made using 25 μm diameter Au wire and bonded to the test pad. The effect of the microheater-cycling on the contact resistance values of ball bonds is described. Starting with typical contact resistance values around 2.5 mΩ, the increase observed is between 4% and 7% after 5 × 106 10 ms cycles (≈14 h).

Palladium coated Copper (PCC) bonding wire is a popular low cost alternative for Gold wire. The quality of an innovative Pd coating technique on Cu (Direct PCC) wire is evaluated by comparing free air ball (FAB) deformability and stitch bond strength to those of Cu wire. The coating is applied to commercial Cu wire which is either thermally treated or as-delivered. FABs of 40 μm diameter are produced in two different shielding using 20 μm diameter direct PCC (DPCC) and bare Cu wires. The FABs are deformed under a force of 400 mN. The DPCC FAB made in forming gas deforms 0.60 to 1.92% more than the Cu FAB, indicating a slightly softer bonded ball. The stitch bonds are made on Ag of a QFN substrate and on Au of an BGA substrate at 200 °C and 175 °C, respectively. The stitch bond strength of PCC wire is 11–26 % higher than that of Cu wire.

A 25 μm diameter Ag wire is coated with a nano-layer of Pd to form a Palladium coated Silver bonding wire (PCS). A new method is used in which the coating is directly attached to the bonding wire without subsequent drawing process. Palladium coated Silver wire produced with this direct coating method (DPCS) is tested for use in wire bonding. The target free-air ball (FAB) diameter in this study is 50 μm. Before forming the FAB, the vertical distance from wire end to the fixed electrode is chosen to be 50 μm — which is intentionally short — to artificially introduce a higher than optimal FAB variation. Under these test conditions, the diameters of FABs produced with PCS in air are found to be more consistent than those obtained with Au wire, having a standard deviation of about 1 % of the FAB diameter compared to 3 % for Au. These results show the PCS wire forms FABs with excellent uniformity in air, ie. without the use of any shielding gas. The bond process results are improved, too. Average values for the stitch pull force and neck pull force of PCS are 55 % and 35 % higher, respectively, than those of Au. The shear force is ≈8 % higher than that obtained with Au. The PCS bonds pass a 24 h thermal bake at 175 °C in Nitrogen with neck pull and ball shear force values of 12.5 gf and 27.9 gf respectively, higher than those obtained with Au. The fusing current for 25 μm diameter 2.92 mm long wires at 25 °C is measured for Au, Cu, and PCS wires. As Silver is the most conductive of all metals, the fusing current for PCS wire is highest, its average is found to be 1.24 A, i.e. 37 % higher than that of Au wire and 18 % higher than that of Cu wire.

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.

Microelectronic wire bonding is an essential step in today's microchip production. It is used to weld (bond) microwires to metallized pads of integrated circuits using ultrasound with hundreds of thousands of vibration cycles. Thermosonic ball bonding is the most popular variant of the wire bonding process and frequently investigated using finite element (FE) models that simplify the ultrasonic dynamics of the process with static or quasistatic boundary conditions. In this study, the ultrasonic dynamics of the bonding tool (capillary), made from Al(2)O(3), is included in a FE model. For more accuracy of the FE model, the main material parameters are measured. The density of the capillary was measured to be rho(cap) = 3552 +/- 100 kg/m(3). The elastic modulus of the capillary, E(cap) = 389 +/- 11 GPa, is found by comparing an auxiliary FE model of the free vibrating capillary with measured values. A capillary "nodding effect" is identified and found to be essential when describing the ultrasonic vibration shape. A main FE model builds on these results and adds bonded ball, pad, chip, and die attach components. There is excellent agreement between the main model and the ultrasonic force measured at the interface on a test chip with stress microsensors. Bonded ball and underpad stress results are reported. When adjusted to the same ultrasonic force, a simplified model without ultrasonic dynamics and with an infinitely stiff capillary tip is substantially off target by -40% for the maximum underpad stress. The compliance of the capillary causes a substantial inclination effect at the bonding interface between wire and pad. This oscillating inclination effect massively influences the stress fields under the pad and is studied in more detail. For more accurate results, it is therefore recommended to include ultrasonic dynamics of the bonding tool in mechanical FE models of wire bonding.

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.

Strong crescent bond and strong tail bond are crucial for maintaining reliability and bondability of the wire bond and stability of the bonding process, respectively. This study investigates the optimization of tail breaking force and pull force of the crescent bond with insulated X-WireTM. The pull force and the tail breaking force are individually optimized by an iteration method. The results are compared with the results of bare Au wire. Ultrasonic power which is a measure of ultrasonic amplitude, combined with a cleaning stage during bonding plays a significant role in initiating the removal of the insulated layer of X-WireTM during the crescent bonding process. The pull force and the tail breaking force of insulated X-WireTM are 91.4 plusmn 11.78 mN and 59.15 plusmn 5.35 mN, comparable to those of bare Au wire.