Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Transient thermal storage of excess heat using eutectic BiSn as phase change material for the thermal management of an electronic power module
    ( 2018)
    Wunderle, B.
    ;
    Springborn, M.
    ;
    May, D.
    ;
    Heilmann, J.
    ;
    Manier, C.-A.
    ;
    Abo Ras, M.
    ;
    Oppermann, H.
    ;
    Sarkany, Z.
    ;
    Mitova, R.
    Novel concepts in power electronics rely heavily on the availability and processability of new materials and packaging technologies to meet the requirements of increasing performance and reliability at lower form factor, weight and cost. Today's main technological route for converter modules is still the power die soldered and wire-bonded to a DCB substrate. New applications or semiconductor technologies like e.g. SiC, however, require enhanced thermal management using standard commercial casings within the same, usually very limited thermal budget. This paper is the final of a series of publications dealing with a novel thermal management concept for power electronics enabled by the use of advanced packaging technologies as well as smart handling of power transients, making use of a TEC and a thermal buffer using a low melting BiSn eutectic as phase change material to store excess heat temporarily exploiting the PCM's enthalpy of fusion. This concept is exemplified on a typical six-pack converter module for industrial applications (4 kW, 1200 Volts) to be integrated into a standard easyPIM casing while being able to cope with overload power pulses. This paper summarises the whole system approach, references back to literature for details finishes the series of papers with the reliability analysis of the buffer technology. Thus, all stages of product development covering design, technology and performance are finally highlighted.
  • Publication
    A Novel Concept for Accelerated Stress Testing of Thermal Greases and In-situ Observation of Thermal Contact Degradation
    ( 2018)
    Wunderle, B.
    ;
    May, D.
    ;
    Heilmann, J.
    ;
    Arnold, J.
    ;
    Hirscheider, J.
    ;
    Li, Y.
    ;
    Bauer, J.
    ;
    Ras, M.A.
    Thermal greases allow a low stress bond at low bond line thicknesses (BLT) at medium thermal conductivities and simple application, all of which make it an alternative to solders, thermal adhesives or pads. It is widely used in power and microprocessor applications, most of which involve large areas to be used for heat transfer. However, for years thermal overload failure of power modules and chips has been a pressing problem due to pump-out of thermal grease as die or module thermal interface material (TIM): Most thermal greases are Bingham fluids and thus not solids, so they can be squeezed out from in between the gap, driven by thermo-mechanical action of the adjacent layers as e.g. DCB substrate or silicon chip with the heat sink. Today, thermal greases have to be qualified in lengthy stress tests in a product relevant environment which consumes substantial resources as often a system test is required. Therefore, a fast test is necessary which accelerates testing and thus allows a fast screening of commercial greases on one hand, and guidelines for material development on the other. For that purpose this paper addresses this topic in a combined simulative and experimental way, where at the same time a novel test procedure is proposed for accelerated grease pump-out testing (GPOT) in the framework of a completely new approach, combining loading with in-situ failure analytical techniques and decoupling thermal from mechanical loading. This allows for the first time a realistic loading of greases during accelerated testing. The method is demonstrated on various commercial and custom greases, varying their composition and structure, and benchmarked against industry standard thermal cycling tests.
  • Publication
    Thermo-mechanical characterisation of thin sputtered copper films on silicon: Towards elasto-plastic, fatigue and subcritical fracture-mechanical data
    ( 2018)
    Wunderle, B.
    ;
    May, D.
    ;
    Zschenderlein, U.
    ;
    Ecke, R.
    ;
    Springborn, M.
    ;
    Jöhrmann, N.
    ;
    Pareek, K.A.
    ;
    Heilmann, J.
    ;
    Stiebing, M.
    ;
    Arnold, J.
    ;
    Dudek, R.
    ;
    Schulz, S.
    ;
    Wolf, M.J.
    ;
    Rzepka, S.
    Thin metal layers, especially those made of copper, are omnipresent in today's packaging applications as e.g. RDL structures, conductor traces on flexible and stretchable substrates, chip finishes or terminal metallisation, serving electrical, thermal or mechanical purposes. During operation, thermo-mechanical stress will cause failures in the Cu layers and interfaces over time. As Cu is very process and size dependent, its resistance to fatigue failure needs to be characterised with samples which have undergone identical processing steps as those in the real application. For that purpose, simple specimens and fast testing routines are necessary, some of which may need special loading stages for varying the load variables of interest such as stress amplitude and temperature. This paper addresses fatigue characterisation of thin Cu films on silicon under typical processing conditions on simple and inexpensive but industry-grade samples. Along with them, custom built test stands have been used to handle those specimens appropriately within a specimen-centred approach.
  • Publication
    Modelling and characterisation of a grease pump-out test stand and its use for accelerated stress testing of thermal greases
    ( 2017)
    Wunderle, B.
    ;
    Heilmann, J.
    ;
    May, D.
    ;
    Arnold, J.
    ;
    Hirscheider, J.
    ;
    Bauer, J.
    ;
    Schacht, R.
    ;
    Vogel, J.
    ;
    Ras, M.A.
    Thermal greases allow a low stress bond at low bond line thicknesses (BLT) at medium thermal conductivities and simple application, all of which make it an alternative to solders, thermal adhesives or pads. It is widely used in power and microprocessor applications, most of which involve large areas to be used for heat transfer. However, for years thermal overload failure of power modules and chips has been a pressing problem due to pump-out of thermal grease as die or module thermal interface material (TIM): Most thermal greases are Bingham fluids and thus no solids, so they can be squeezed out from in between the gap, driven by thermo-mechanical action of the adjacent layers as e.g. DCB substrate or silicon chip with the heat sink. Today, thermal greases have to be qualified in lengthy stress tests in a product relevant environment which consumes substantial resources as often a system test is required. Therefore, a fast test is necessary which accelerates testing and thus allows a fast screening of market-available greases on one hand, and guidelines for material development on the other. For that purpose this paper addresses this topic in a combined simulative and experimental manner, where at the same time a novel test procedure is proposed for accelerated grease pump-out testing (GPOT) in the framework of a completely new approach, combining loading with in-situ failure analytical techniques and decoupling thermal from mechanical loading.
  • Publication
    Phase change based thermal buffering of transient loads for power converter
    ( 2014)
    Wunderle, B.
    ;
    Springborn, M.
    ;
    May, D.
    ;
    Mrossko, R.
    ;
    Abo Ras, M.
    ;
    Manier, C.-A.
    ;
    Oppermann, H.
    ;
    Mitova, R.
    This paper deals with the system design, technology and test of a novel concept of integrating silicon power dies along with thermo-electric coolers and a phase change heat buffer in order to thermally manage transients occurring during operation. The innovative power-electronics concept features double-sided cooling as well as new materials and joining technologies to integrate the dies such as transient liquid phase bonding/soldering and sintering. To avoid a cold plate at the backside, a new low-cost, low-footprint thermal storage device has been developed and optimized by simulation to meet the requirements given by this application. Coupled-field simulations are used to predict thermal performance and are being verified by especially designed test stands.
  • Publication
    Double-sided cooling and transient thermo-electrical management of silicon on DCB assemblies for power converter modules: Design, technology and test
    ( 2014)
    Wunderle, B.
    ;
    Springborn, M.
    ;
    May, D.
    ;
    Manier, C.-A.
    ;
    Abo Ras, M.
    ;
    Mrossko, R.
    ;
    Oppermann, H.
    ;
    Xhonneux, T.
    ;
    Caroff, T.
    ;
    Maurer, W.
    ;
    Mitova, R.
    This paper deals with the system design, technology and test of a novel concept of integrating Silicon power dies along with thermo-electric coolers and a phase change heat buffer in order to thermally manage transients occurring during operation. The concept features double-sided cooling as well as new materials and joining technologies to integrate the dies such as transient liquid phase bonding/soldering and sintering. Coupled-field simulations are used to predict thermal performance and are verified by especially designed test stands to very good agreement.
  • Publication
    Modelling and characterisation of smart power devices
    ( 2012)
    Wunderle, B.
    ;
    Ras, M.A.
    ;
    Springborn, M.
    ;
    May, D.
    ;
    Kleff, J.
    ;
    Oppermann, H.
    ;
    Töpper, M.
    ;
    Caroff, T.
    ;
    Schacht, R.
    ;
    Mitova, R.
    This paper deals with the system design, technology and test of a novel concept of integrating Si and SiC power dies along with thermo-electric coolers in order to thermally manage transients occurring during operation, thus turning it into a smart power device. The concept features double-sided cooling as well as new materials and joining technologies to integrate the dies such as transient liquid phase bonding/soldering. Coupled-field simulations are used to predict thermal performance and are verified by especially designed test stands to very good agreement. This paper is the first in a series of planned publications on the ongoing work in the project.
  • Publication
    Advanced mixed-mode bending test: A rapid, inexpensive and accurate method for fracture-mechanical interface characterisation
    ( 2012)
    Wunderle, B.
    ;
    Schulz, M.
    ;
    Keller, J.
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    May, D.
    ;
    Maus, I.
    ;
    Pape, H.
    ;
    Michel, B.
    This paper presents a comprehensive method for obtaining urgently required critical interface delamination data of material pairings used in electronic packaging. The objective is to thereby enable rapid, inexpensive and accurate lifetime prediction for that failure mode. A new testing method is presented which allows maximum mode-angle range and enhanced throughput testing under multiple loading conditions, the coverage of which is usually a rather lengthy and resource-demanding procedure. The approach is specimen-centred in the sense that the accent is put on test-specimens which are easily manufacturable industrially, rather than having to adapt them to a special testing machine. The concept is also scalable, i.e. it has potential to work also for smaller samples cut from real devices. We show the first version of a newly developed test-stand and discuss the obtained results for copper-molding compound interfaces in the light of the current state of the art used for delamination testing in electronic packaging.
  • Publication
    Automated test system for in-situ testing of reliability and aging behaviour of thermal interface materials
    ( 2011)
    AboRas, M.
    ;
    Haug, R.
    ;
    Schacht, R.
    ;
    Monory-Plantier, C.
    ;
    May, D.
    ;
    Wunderle, B.
    ;
    Winkler, T.
    ;
    Michel, B.
    Thermal interface materials (TIMs) are widely needed to improve thermal contacts for facilitation heat transfer in electronic packaging, such as that associated with the flow of heat from microprocessor to a heat spreader or a heat sink in a computer. Due to thermal mismatch between these components mechanical strain occur which cause pump-out, cracks or delamination of TIM. In order to qualify the reliability and aging of TIMs, traditional power cycle test is commonly used to detect potential thermal failures. This traditional power cycle test is a time consuming process due to its long heating and cooling time. Therefore a new automated test system for in-situ reliability testing of TIMs is developed and will be presented in this paper. The new test system is designed to be able to analyze the aging and reliability behavior of most common TIMs. The TIMs can be measured in-situ and under real conditions as they are used in real applications.
  • Publication
    In-situ measurement of various thin bond-line-thickness thermal interface materials with correlation to structural features
    ( 2008)
    Wunderle, B.
    ;
    Kleff, J.
    ;
    Mrossko, R.
    ;
    Abo Ras, M.
    ;
    May, D.
    ;
    Schacht, R.
    ;
    Oppermann, H.
    ;
    Keller, J.
    ;
    Michel, B.
    Thermal characterisation of thermal interfaces becomes even tougher a challenge at low bond line thicknesses and higher thermal conductivities of the interface materials as more accurate measurement techniques are required. As in parallel the quest for high conductivity adhesives and greases is ongoing, a correlation between thermal bulk or interface properties and structure is in high demand. We have developed test-stands for various classes of thermal interface materials. These permit characterisation for materials with thin bond line thickness and high thermal conductivity still using steady state techniques. The methods are benchmarked for greases, adhesives and sintered silver. For the latter, the technology development is described. Then, structural features such as particle density and porosity are examined. It will be the aim to compare and correlate them to thermal resistance. Part of the work has been accomplished within the running EU. Project "Nanopack".