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Mayer M.,University of Waterloo | McCracken M.,University of Waterloo | Persic J.,Microbonds
Journal of Electronic Packaging, Transactions of the ASME | Year: 2013

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 lm with a resistance of ̃140 ω at room temperature, and is operated based on Joule heating. The polysilicon is located at least 20 lm but not more than 50 lm 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 ̃2.1W 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, 5ms off) which is 5 orders of magnitude faster. The released energy is typically 10 mJ per cycle. A 50 lm diameter ball was made using 25 lm 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 2.5mω, the increase observed is between 4% and 7% after 5̃106 10 ms cycles (̃14 h). © 2013 by ASME. Source

Liang R.,University of Waterloo | Hu A.,University of Waterloo | Persic J.,Microbonds | Norman Zhou Y.,University of Waterloo
Nano-Micro Letters | Year: 2013

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 perfor- mance 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. Source

Nan C.,University of Waterloo | Mayer M.,University of Waterloo | Zhou N.,University of Waterloo | Persic J.,Microbonds
Microelectronic Engineering | Year: 2011

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%. © 2011 Elsevier B.V. All rights reserved. Source

Nguyen N.H.,University of Waterloo | Nguyen N.H.,Hanoi National University of Education | Hu A.,University of Waterloo | Persic J.,Microbonds | Wen J.Z.,University of Waterloo
Chemical Physics Letters | Year: 2011

This Letter presents the thermal stability and energetic reaction properties of palladium coated aluminum nanoparticles. The classical MD simulations are conducted using a new EAM force field. The results reveal that, when the initial temperature is higher than 600 K and lower than 900 K, a two-stage reaction may occur. At the first stage, the reaction rate is determined by the solid-state diffusion of Al atoms. At the second stage where the particle temperature is greater than the melting point of Al, the alloying reaction between the liquid Al core and the Pd shell happens with a much faster rate. © 2010 Elsevier B.V. All rights reserved. Source

Huang Y.,University of Waterloo | Shah A.,University of Waterloo | Mayer M.,University of Waterloo | Zhou N.,University of Waterloo | Persic J.,Microbonds
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2010

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 Al2O3, 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 pcap = 3552 ± 100 kg/m3. The elastic modulus of the capillary,Ecap = 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. © 2006 IEEE. Source

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