Novel Methods in Ball Bond Reliability Using In-Situ Sensing and On-Chip Microheaters

Wire bonding is the process of creating interconnects between the circuitry on a microchip and PCB boards or substrates so that the microchip can interact with the outside world. The materials and techniques used in this bonding process can cause a wide variation in bond quality, so wire bond reliability testing is very important in determining the quality and longevity of wire bonds. Due to the fact that microchips are encased in protective resins after bonding and their substrates attached to the larger device as a whole, once any single wire bond fails then it could jeapordize the entire device as the wire bonds cannot be individually replaced or fixed. Current methods of reliability testing are lengthy and often destroy the entire sample in the process of evaluation, so the availability of novel non-destructive, real-time monitoring methods as well as accelerated aging could reduce costs and provide realistically timed tests of novel wire bond materials which do not form Intermetallic compounds (IMCs) as rapidly as Au wire on Al substrates. In this thesis, five new chip designs for use in wire bond reliability testing are reported, focusing on the first joint made in a wire bond, called the ball bond. These chips are scaled either to test up to 55 test bonds simultaneously or just one at a time, introducing different requirements for microchip infrastructure capabilities, such as on-chip sensing/data bus, multiplexer, and switches able to operate under High Temperature Storage (HTS) which ranges from temperatures of 150-220 ºC. There are different heating requirements for each of these microchips, needing to be heated externally or containing on-chip microheaters to heat only the ball bond under test, and not the rest of the microchip or surrounding I/O pads. Of the five chip designs, sample chips were produced by an external company. Experimental studies were then carried out with two of these chip designs. They were specifically made to test novel methods of determining ball bond reliability using in-situ, non-destructive sensing, in real-time, while the ball bond undergoes thermal aging. Pad resistance as an analysis tool for ball bond reliability is proposed in this thesis as a new way of evaluating ball bond quality and allows for the testing of electrical connection without the need for specialized measurement probes or difficult bonding processes that contact resistance measurements require. Results are reported for pad resistance measurements of a ball bond under very high temperature storage (VHTS) at 250 ºC, a temperature exceeding typical HTS ranges to accelerate aging. Pad resistance measurements are taken using the four-wire measurement method from each corner of the bond pad, while reversing current direction every measurement to remove thermo-electric effects, and then calculating the average square resistance of the pad from this value. The test ball bond is aged using a novel on-chip microheater which is a N+ doped Si resistive heater located directly underneath the bond pad, and can achieve temperatures up to 300 ºC while not aging any of the I/O pads surrounding it, which are located ~180 µm away. A 50 Ω resistor is placed 60 µm away from the heater to monitor the temperature. The use of a microheater allows the aging of novel wire types at temperatures much higher than those permitted for microchip operation while thermally isolating the test bond from the sensing and power bonds, which do not need to be aged. Higher temperatures allow the aging process to be sped up considerably. The microheater is programmatically cycled between 250 ºC (for 45 min) and 25 ºC (for 15 min) for up to 200 h or until the pad resistance measurements fail due breakdown of the bonding pad. Intermetallic compounds forming between the ball bond and the pad first become visible after a few hours, and then the pad becomes almost completely consumed after a day. The pad resistance is measured every few seconds while the sample is at room temperature, and the increase in pad resistance agrees with the fact that Au/Al IMC products are known to have much higher resistance than both pure Au or Al. Also discussed are some aging results of Au wires and Pd coated Cu (PCC) wires bonded to Al bonding pads and aged at a temperature of 200 ºC in an oven for 670 h. The oven aged Au ball bonds also saw IMC formation on the surface of the bonding pad, much like the microheater tests. The PCC ball bonds became heavily oxidized due to lack of Pd on the surface of the ball, the wire portions did not oxidize much. In conclusion, the new structures have been demonstrated to age ball bonds faster than with conventional methods while obtaining non-destructive data. Specifically, the new microheater ages a test bond at an accelerated rate without having an observable effect on the I/O connections used to monitor the test bond. Pad resistance measurements correlate to the aging of the test bond and ensure the electrical integrity of the joint is checked.1 yea

Update - Body of Knowledge (BOK) for Copper Wire Bonds

Copper wire bond technology developments continue to be a subject of technical interest to the NASA (National Aeronautics and Space Administration) NEPP (NASA Electronic Parts and Packaging Program) which funded this update. Based on this new research, additional copper bond wire vulnerabilities were found in the literature - Crevice corrosion, intrinsic degradation of palladium coated copper wire, congregation of palladium near ball bond interface leading to failure, residual aluminum pad metallization impact on device lifetimes, stitch cracking phenomena, package delamination's that have resulted in wire bond failures and device failure due to elemental sulfur. A search of the U.S.A. patent web site found 3 noteworthy patents on the following developments: claim of a certain IMC (Intermetallic Compound) thickness as a mitigation solution to chlorine corrosion; claim of using materials with different pHs to neutralize contaminants in a package containing copper wire bonds; and a discussion on ball shear test threshold values for different applications. In addition, an aerospace contractor of military hardware had a presentation on copper bond wires where it was reported that there was a parametric shift and noise susceptibility of devices with copper bond wires which affected legacy design performance. A review of silver bond wire (another emerging technology) technical papers found that an electromigration failure mechanism was evident in device applications that operate under high current conditions. More studies may need to be performed on a comprehensive basis. Research areas for consideration are suggested, however, these research and or qualification/standard test areas are not all inclusive and should not be construed as the element (s) that delivers any potential copper wire bond solution. A false sense of security may occur, whenever there is a reliance on passing any particular qualification, standard, or test protocol

過度液相焼結法によるパワーモジュールと銅ヒートスプレッダの低温及び低圧力接合

早大学位記番号:新7685早稲田大

Modeling the SAC microstructure evolution under thermal, thermomechanical and electrical constraints

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CO Gas Sensor for Consumer Electronic Applications

Gas sensors in smartphones and other mobile devices have the potential to contribute to improving the quality of life and security. This calls for a high degree of miniaturization and a reduction in power consumption. In this work, various aspects of miniaturized, resistive CO gas sensors based on metal oxides (MOX) were investigated. Deposition took place through pulsed laser deposition (PLD) on structures of platinum that were patterned using a lift-off process. The influence of the resist geometry on the metal structures was demonstrated by experiment and simulation. With regard to the MOX thin films, the focus was set on SnO2. Both its electrical and gas-sensing properties were highly influenced by the deposition parameters: Higher deposition pressures (>10 Pa) are leading to higher base resistances and to a higher sensor signal for CO in dry air. These properties correlated with the nanoporous morphology of the material. For measurements in humid air, the response to CO was reduced compared to dry air. Different noble metal additives, in particular Pd, were introduced by sputtering, thereby significantly improving properties. CO-sensitivity in humid air was also demonstrated for highly porous WO3. In a parameter study, the impact of the heated membrane geometry on the power consumption of the sensor was further investigated in simulation and experiment.Gassensoren in Smartphones und anderen mobilen Geräten haben das Potential, zukünftig Lebensqualität und Sicherheit zu verbessern. Dafür ist ein hoher Grad an Miniaturisierung und die Reduzierung der Leistungsaufnahme notwendig. In dieser Arbeit wurden verschiedene Aspekte miniaturisierter, resistiver COSensoren auf Basis von Metalloxiden (MOX) untersucht. Herstellung erfolgte mit gepulster Laserabscheidung (PLD) auf Platinstrukturen, die mit einem Lift-Off-Prozess strukturiert wurden. Per Simulation und Experiment wurden Einflüsse der Lackgeometrie auf die Metallstruktur aufgezeigt. Bei den untersuchten MOX-Dünnschichten lag der Fokus auf SnO2. Dessen elektrische und gassensitive Eigenschaften hängen stark von den Abscheidungsbedingungen ab:Höhere Abscheidungsdrücke (>10 Pa) führen zu höheren Grundwiderständen sowie zu einem höheren Signal für CO in trockener Luft. Diese Eigenschaften korrelieren mit der nanoporösen Morphologie des Materials. Bei Messungen in feuchter Luft reduzierte sich das CO-Signal im Vergleich zu trockener Luft. Durch den per Sputtern aufgebrachten Zusatz von Edelmetallen, insbesondere von Palladium (Pd), konnten die Eigenschaften deutlich verbessert werden. COSensitivität in feuchter Luft konnte für hochporöses WO3 ebenfalls gezeigt werden. In einer Parameterstudie wurde in Experiment und Simulation zudem der Einfluss der geheizten Membrangeometrie auf die Leistungsaufnahme des Sensors untersucht

Activity of halide-free flux at copper and tin surfaces

The activity of halogen-free carboxylic acid flux is considered one of the most important aspects in controlling flip chip joint quality recently. In this work, we examined the CuOx removal effectiveness of carboxylic acid solutions at Cu substrates using electrochemical methods at elevated temperatures from 100ºC to 180ºC. Reaction kinetics of CuOx removal were investigated by chronopotentiometry and gravimetric analysis. FTIR was used to study the surface chemistry, and spectrophotometry was used to understand reactant and product solubility. Kinetics of carboxylic acid solution such as adipic acid or maleic acid in polyethylene glycol (PEG) with and without complexing agents such as ethanolamine was investigated. Carboxylic acid-based solutions with ethanolamine show oxide removal rates similar to hydrochloric acid solutions at temperatures above 140ºC. Results indicate the combination of proton-donating complexing agents with carboxylic acids can increase oxide removal rates an order of magnitude over solutions without complexing agents. Sn (II) and Sn (IV) voltammetry shows Sn2+ and Sn4+ can form Sn-carboxylate complex and dissolve into the solution. XPS results indicate under high temperature (180 ºC) and relatively low pH (~2.50), carboxylic acid can clean the surface of Sn as well as halide acid. Equilibrium coefficients between the complexes are obtained and potential-pH diagrams for adipic acid and maleic acid in PEG are presented

Properties and behaviour of Pb-free solders in flip-chip scale solder interconnections

Due to pending legislations and market pressure, lead-free solders will replace Sn–Pb solders in 2006. Among the lead-free solders being studied, eutectic Sn–Ag, Sn–Cu and Sn–Ag–Cu are promising candidates and Sn–3.8Ag–0.7Cu could be the most appropriate replacement due to its overall balance of properties. In order to garner more understanding of lead-free solders and their application in flip-chip scale packages, the properties of lead free solders, including the wettability, intermetallic compound (IMC) growth and distribution, mechanical properties, reliability and corrosion resistance, were studied and are presented in this thesis. [Continues.