Metallic Interconnection Technologies

Besides die attach soldering and Al heavy wire bonding, new packaging concepts are pursued to built power electronics systems which shall provide improved thermal performance and higher reliability. By replacing the wire bond with an area contact on both sides of the chips the thermal performance can be improved.

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Apart from ensuring the best possible system design, understanding material, mechanical and thermomechanical behavior on package, component and module levels is critical for ensuring overall system reliability. Thermally and thermo-mechanically induced failure mechanisms can lead to premature failure and limit lifetime.

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Depending on the field of use optoelectronic components have very different requirements. Datacom lasers und photodiodes need to be single mode compatible and the accuracy of the assembly must be better than one micrometre to fulfil today’s requirements for data rates.

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The research area “reliability” is particularly significant at Fraunhofer IZM, as different materials with diverse thermal, mechanical and thermomechanical properties are used in the packaging process. Ensuring that the resulting systems function reliably in increasingly harsh environmental conditions (high temperatures, vibration, high current densities and voltages) for a predetermined operating time is always at the forefront of research and development, regardless of the application area the system is intended for. The development process is approached systematically. From the very beginning, physics-of-failure models are used as a tool for selecting materials with suitable properties in terms of thermomechanical tension and thermal performance.

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Heat spreaders are widely used in microelectronics to distribute heat loss as well as possible so that thermal resistance is minimized. A material is a heat spreader if it spreads the heat (distributes it over a larger area), so this task is usually performed by a material with good thermal conductivity, e.g. copper, aluminum, silicon or (artificial) diamond.

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Main goals for a Formula 1 power module are highest power density and lowest weight. Volume and weight of presented converter could be reduced by roughly 50 percent compared to previous versions.

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Accelerated tests can be used in order to simulate the thermal, climatic and mechanical field stress of electronic assemblies. In combination with FEM- calculation a life-time prediction can be derived. Failure analysis can be used for optimization of material choice and/or technology.

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Optimized thermal management is particularly important in power electronics. Improving the thermal connection between the package/module and the cooling structure can increase the service life of the overall system many times over.

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SMD failure analyses comprehend analyses in the context of impaired PCB solderability, early failures of plated-through holes and microvias as well as investigations of failed solder joints after field stress.

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Soldering materials to create solid-state  bonds is a technique that dates back thousands of years. Even today, soldering is the most popular means of interconnecting electronic components. In the electronic packaging industry, the process is applied at all levels of integration, from interconnection between the chip and housing and/or wiring (1st level packaging), to interconnection between the 1^st level package and the carrier and/or any additional components (2nd level packaging).

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The demands on electronic and mechatronic systems are increasing steadily. Today, such systems are even expected to operate reliably at temperatures of up to 300°C. Silver sintering is an ever more popular means of achieving this and represents an alternative to conventional solder processes in power electronics.

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From the beginning of solid state lighting IZM was involved in LED development. Assembly processes for LEDs with highest power and power density were developed as well for LEDs in harsh environment or just to make mass production more reliable but cost-effective, too.

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Qualification of surfaces with regard to bondability (bond testing), assembly of prototypes and small series, feasibility studies, process development, technological advice, schoolings. Fully automatic wire bonding, production under laboratory and manufacturing conditions. Wire diameters from 17,5 – 500 µm, wire materials: Al, AlSi1, Au, AuPd1, Cu, Pd Procedures: Ball/Wedge, Wedge/Wegde, ribbon, heavy wire, studbumps Options: fine wire/fine pitch bonding, low/short/long loop bonding, deep access bonding.

Due to the low switching losses when using the novel wide band-gap semiconductor generation made from gallium nitride and silicon carbide, respectively, it is possible to increase the switching frequency of power electronic systems significantly. As a consequence, the size of passive components, especially of the bulky ripple inductors, can be reduced, for the reason that less energy needs to be buffered in the system. The focus of the ECPE lighthouse project "Industrial Demonstrator on System Level" was on an additional power density increase by means of innovations in filter topology, semiconductor control and pareto front optimization of the overall system.

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One of the world’s leading automotive suppliers, Marelli, has launched the first power module for electric and hybrid traction applications in motorsports. The new module was developed together with the Fraunhofer Institute for Reliability and Microintegration IZM. Based entirely on silicon carbide, the module enables higher conversion efficiencies and is smaller and lighter – a successful innovation for both motorsports and vehicles in general.

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The use of SiC semiconductors in drive inverters is becoming increasingly popular. SiC offers the possibility of increasing the power density and efficiency in the system through lower switching and conduction losses compared to silicon FETs. The converter built at Fraunhofer was realised in a 6-phase topology. With the appropriate electric motor, this results in several advantages for the electric power train.

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• Lσ power module < 1.7 nH
• PCB Embedding: Smart p² Pack® Technology by SE AG
• Power range up 231 kVA (for a 6 phase inverter)
• Highest on-board function integration: Damped DC-Link, gate power supply, gate driver, 2 temperature sensors (one per switch), embedded current sensor, fast analogue short-circuit detection, signal insulation and digitalization

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When developing merchantable power electronic systems, a multitude of partial conflicting requirements must be taken into account. High efficiency, robustness, reliability, low cost, long life, high power density and good EMC behaviour have to be valued and weighed against each other for a specific application.

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The VORTEIL project (‘Vertikale Oberflächenemitter für Robuste Temperaturstabile Effiziente Integrierte Lasersystems’ – Vertical Cavity Surface Emitters for Robust, Thermally Stable Efficient Integrated Laser Systems) is funded by the Federal Ministry of Education and Research to develop high-performance lasers based on VCSEL technology (cf. ill. 1). Lasers of this type can be used for such diverse application as a low-impact cleaning of monumental antique buildings or ignitions for large-scale combustion engines within the whole cylinder capacity at once.

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In the framework of the Quality and Test Center (QPZ) for electronic assemblies we offer:

• Failure analyses of electronic assemblies
• Failure analysis of LED packages
• Solderability and wettability analysis
• Acceptability of electronic assemblies
• Microstructure analysis of solder joints
• Surface analysis using XPS
• X-ray, C-SAM, CT, FIB, SEM
• Reliability testing and analysis
• Reflow soldering processes
• Void-less soldering
• SIR, Electromigration

Wire Bonder

• F&K Delvotec G5
• Kulicke & Soffa
• Hesse

Testing

• Pull- and sheartester Dage
• Ultrasonic Welding

Die Bonder

Life-Time-Testing

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