Christopher Kaestle

Optimized thin-film diffusion soldering for power-electronics production

This paper gives an overview on diffusion soldering or transient liquid-phase soldering (TLPS), where the conventional electronic production processes have been optimized for being capable of producing highly durable pore-free TLPS bonds. The growth of intermetallic phases (IMP) with control of temperature and time has been investigated in production line perspective. The samples processed under optimized vacuum based vapor-phase soldering along with realization of thin solder layers down to less than 10μm are demonstrated. As a result, pore-free diffusion soldered joints filled with Cu6Sn5 and Cu3Sn phases near the chip-substrate interface have been realized. Formations of IMP with changes in optimized solder profile, solder paste, chip metallization, substrate roughness and solder paste thickness are discussed.

Reliable packaging technologies for power electronics: Diffusion soldering and heavy copper wire bonding

Production of a reliable power module capable of achieving higher switching frequencies and higher junction temperatures is limited by the present assembly and packaging methods, mostly in the areas of the die-attach and the top level interconnections. The present study aims to display the advances in packaging technologies of diffusion soldering and heavy copper wire bonding in the view of material characterization, process optimization and quality improvement. In diffusion soldering, the growth of intermetallic phases through thin-layer paste deposition and solder profile optimization with vapor phase soldering were investigated. Solder paste inspections were performed to evaluate the errors during deposition process for thin layers and influences on soldering process and related post-failure modes. In heavy wire copper bonding, the impact of substrates with a mechanically polished surface of reduced roughness was investigated. Furthermore the influence of applying the bond force in a ramp style was examined and inspected with the pull and shear forces. The bond width was also monitored in order to receive a non-destructive quality feature for the process monitoring. All test series were accompanied by a close control of the tool wear-out and its influence on process stability.

Comparative analysis of the process window of aluminum and copper wire bonding for power electronics applications

Todays state-of-the-art top level interconnect technology in power modules is an aluminum wire wedge/wedge bond process. Being the bottleneck for realizing even higher switching frequencies and thus higher junction temperatures made possible by upcoming wide bandgap semiconductors, innovative packaging technologies such as copper wire wedge/wedge bonding are a key issue in pushing the technological frontier of power electronics even further. With its higher electrical and thermal conductivity as well as its lower coefficient of thermal expansion copper wire bonding bears the chance of a significant improvement in one of the most sensitive lifetime limiting areas of power modules. In contrast coppers higher youngs modulus as well as a higher strain hardening require increased bond parameters resulting in new challenges for the bonding process. A smaller and more sensitive process window is expected to be the other side of the coin. This study aims to display the advantages and challenges of the aluminum and copper wire bonding process for power modules with special focus on a comparative analysis of their process windows. To obtain statistically significant conclusions all tests are performed in randomized rotatable central composite response surface design of experiment studies. A comparison of attainable shear forces as well as observed failure modes will be the bases to define criteria for acceptance that are applicable for the used wire bond material. This deep understanding of all process and process influencing parameters will be needed in order to set up and evaluate a reliable and optimized production process for power modules.

Investigations on ultrasonic copper wire wedge bonding for power electronics

Driven by applications in the field of renewable energy, power distribution, consumer electronics and the automotive industry, the demand for reliable and economic power electronics packaging solutions is growing rapidly. The present study aims to display a new technology for chip top-side interconnects by using heavy wire copper wedge/wedge bonding. Therefore a response surface design of experiment study was set up to evaluate the influence of the main parameters time, ultrasonic power and bond force on the bond process quality. With this information an optimized set of machine parameters was derived, with respect to maximized pull and shear forces. Furthermore, investigations on the correlation between the bond parameters and the destructive test failure modes were conducted. All tests were accompanied by a monitoring of the tool wear-out. This allows to assess the process stability as well as the process reliability. The aim is to identify the most significant parameters and to find an optimized parameter set in order to improve future die interconnection technologies for power electronics manufacturing.

Evaluation of influencing factors on the heavy wire bondability of plasma printed copper structures

Power semiconductor devices and systems enable the efficient conversion and management of electrical energy. Power electronic applications range from fewer watts up to several mega- and gigawatts. Driven by a continuous electrification of society, power electronics are not only found in the automotive and energy sector, but also in industrial and lighting applications, as well as consumer electronics. In power electronic devices wire bonding is the established and predominant top-level interconnect technology due to a high process stability and low production costs. Characterized by a great process flexibility it might also be the predominant interconnection technology of coming additive manufactured devices and structures if wire bonding proves to be capable of connecting printed layers that form the basis of additive functionalized and even three-dimensional power device layouts. This paper will therefore display the influencing factors, as well as the possibilities and challenges that come along with the process combination of cold active atmospheric plasma printing with large wire aluminum bonding. For the investigations, copper layers are additively printed on Al2O3 ceramic substrates. Based on the printing parameters the most influential characteristics of the printed layers are derived. The influence and effectiveness of various steps of post processing such as grinding and cleaning are discussed. Last, a production series of 300 μm aluminum wires is bonded on the generated copper layers. The process stability as well as the interconnection quality is evaluated by destructive pull and shear tests and metallographic cross sections.

Feasibility Investigations on Selective Laser Melting for the Development of Microchannel Cooling in Power Electronics

The introduction of new generation semiconductormaterials into power electronics brings not only performanceimprovements but also technological challenges for the thermalmanagement as the urge for high temperature operating powermodules and packaging systems increases. The limiting factorfor the performance and application range is not anymore thechip temperatures but the restrictions of the state-of-the-artpackaging systems. Especially for high power applications, thetemperatures can rise to more than 200 °C at the interconnectlevel. In this paper, as a contribution towards the aboverequirements, the selective laser melting (SLM) technique hasbeen used to fabricate a heat sink concept which would not befeasible with conventional production techniques. Here thefeasibility of producing a heat sink concept with SLM based onmicro-cooling technology is successfully introduced and thethermal management performance is demonstrated. Theadvantages mainly for the volume and weight reduction alongwith performance improvement are highlighted.

Cyber-Physical Electronics Production

Cyber-physical manufacturing networks bear the chance to change the face of tomorrow’s electronic and mechatronic products as well as their production systems. The ability to integrate miniaturized sensors and printed communication technologies into materials, machines, and products leads to autonomous cyber-physical systems with an image in the virtual world and a real-world counterpart down on the shop floor. An efficient sensor data consolidation is in the position to establish self-learning control loops across global production networks in order to increase process robustness as well as process flexibility and thus allowing for instant product changes with an ideal lot size of one. Low-cost solutions for smart autonomous vehicles enable the breakup of classical production lines. One of the major challenges of these disruptive changes is securing the manageability of the possible data and information overflow. Novel socio-cyber-physical assistance systems will ensure the operation of these smart factories.

A Comprehensive Study on the Automation Potentials and Complexities of Advanced and Alternative Die-Attach Technologies for Power Electronic Applications

The field of power electronics packaging presents intricate and interdisciplinary challenges. System costs, reliability and performance are strongly determined by various aspects such as mechanical design, materials, thermal management and interconnect technologies. The overall costs of the product depend mainly on the complete process chain in the module development. Automation as well plays an important role and facilitates higher production rates, efficient use of materials, better product quality, and reduced factory lead times. This paper focuses on emerging interconnection technologies of bonding semiconductor components to power electronic substrates like diffusion soldering, conductive adhesive bonding and reactive multi-layer bonding. An overview on the automation potentials and complexities in individual technologies for the manufacturing of reliable and cost-effective power modules is given and discussed. Thus, a basis is created for choosing optimal die-attach technology depending on economic and technologic demand by comparing the state-of-the-art and advanced technologies.