Wire Bonding as Dynamic Process of Hardening and Softening

Ultrasonic wedge-wedge bonding of AlSi1 wires is characterised as a dynamic process of hardening and softening. The bonding parameters ultrasonic energy and bond force are acting in the opposite direction: While the bond force causes wire hardening ultrasonic energy causes softening and a better plasticity of the wedge. Increasing ultrasonic power is resulting in reduced wedge-hardness, i.e. the Aluminium wedge is more softened than using lower ultrasonic power. In the first phase of wire bonding the wedge is pre-deformed and cold worked by the bond force. After ultrasonic energy has been switched on, recrystallisation starts at the interface. During the bonding time hardening and softening processes alternate and a maximum in hardness is measured after 15 ms. Hardening and softening processes correlate well with the grain structure, the measured grain sizes and a typical plateau in the z-deformation curve of the contact. At the end of the wire bonding process the wedge is recrystallised and softer than the predeformated wedge, but harder than the as-received wire

Demonstration of glass-based photonic interposer for mid-board-optical engines and electrical-optical circuit board (EOCB) integration strategy

Due to its optical transparency and superior dielectric properties glass is regarded as a promising candidate for advanced applications as active photonic interposer for mid-board-optics and optical PCB waveguide integration. The concepts for multi-mode and single-mode photonic system integration are discussed and related demonstration project results will be presented. A hybrid integrated photonic glass body interposer with integrated optical lenses for multi-mode data communication wavelength of 850 nm have been realized. The paper summarizes process developments which allow cost efficient metallization of TGV. Electro-optical elements like photodiodes and VCSELs can be directly flip-chip mounted on the glass substrate according to the desired lens positions. Furthermore results for a silicon photonic based single-mode active interposer integration onto a single mode glass made EOCB will be compared in terms of packaging challenges. The board level integration strategy for both of these technological approaches and general next generation board level integration concepts for photonic interposer will be introductorily discussed

Modular microsystems with embedded components

Each system is designed to fulfill the desired purpose. It is defined by its inputs, outputs, structure, environment, boundary, and the including elements (subsystems). Due to the ongoing miniaturization and integration the complexity of subsystems increases continuously. This paper is intended to demonstrate the build-up of modular Microsystems. By using the embedding technology, each subsystem (module) is interchangeable and stackable. Therefore, the functionality of the entire system depends solely on the selected modules. Moreover, the enhancement, expansion or redesign can be accomplished by replacing existing or adding new modules. The communication between the individual modules is based on the standardized I²C bus. Additionally, a USB interface has been implemented to manage the data transmission between the embedded camera module and a computer. The whole system recognizes each module and performs accordingly. The user can access sensor values, watch the video stream, and change the parameters of each module via a Graphical User Interface (GUI) on his computer. To achieve the build-up of the modular Microsystems we only used packaged active and passive components. Depending on the complexity of each module a core of up to eight layers is build up. The components are then soldered onto both sides of the core. At this point the components are embedded using a laminating press. The afterwards even surface is then structured again, to enable the stacking of the modules. Each step of the entire assembly process is done via state of the art circuit board processing technologies, including laser drill and laser-direct imaging

Influence of bonding process parameters on chip cratering and phase formation of Cu ball bonds on AlSiCu during storage at 200 °c

Wire bonding remains the predominant interconnection technology in microelectronic packaging. Over the last 3 years a significant trend away from Au and towards Cu wire bonding has become apparent. This has been due to general efforts to lower manufacturing costs and price increases for raw materials like Au. Although much research has been carried out into wire bonding over recent decades, most has focused on Au ball/wedge bonding. The results of this research have shown that bonding parameters, bonding quality and reliability are closely interconnected. However, the different material properties of Cu compared to Au, such as affinity to oxidation and hardness, mean that these insights cannot be directly transferred to Cu bonding processes. Thus, further research is necessary. This paper discusses a study of bonding interface formation under various bonding parameters. Cu wire was bonded on AlSiCu0.5 metallization and a bonding parameter optimization was carried out to identify useful parameter combinations. On the basis of this optimization, different samples were assembled using parameter combinations of low, medium and high US-power and bonding force. An interface analysis was subsequently carried out using shear testing and HNO3 etching. Intermetallic phase growth was analyzed on cross sections of devices annealed at 200 °C for 168 h and 1000 h. Contacts bonded with low bonding force and high US-power tended towards cratering during shear testing. Bonding force proved to have a significant effect on intermetallic phase formation whereas US-power was found to exert only a minor influence. The intermetallic phase formation of annealed samples was analyzed using EDX and interpreted on the basis of phase formation kinetics. Three main intermetallic phases were identified

Micro-Nanostructural Investigations of AlSi1 Bondcontacts

The wedge microstructure of AlSi1 wire bonds as well as the interface between the bonding wire and the Cu/Ni/Au metallization layer especially for Chip on Board (COB) assemblies was investigated by Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and micro-hardness measurements. With increasing ultrasonic power the results indicate recrystallization of the grain structure and decreasing micro-hardness inside the bonded wedges contacts. The very fine grain structure in the interface region is the precondition of a closed interface, high bond strength and reliable bond contacts. The interface between the AlSi1 wire and the Cu/Ni/Flash-Au metallization layer of the optimized bonds consists of a closed crystalline Au layer. Above this Au layer, a second zone consisting of intermetallic phases was analyzed and identified by electron diffraction as Au8Al3. After a few milliseconds first spots of the 30- 50 nm thick intermetallic phase are grown. The covered area increases during the bonding time and results for perfect bond contacts in a gold layer completely overcast by the Au8Al3 phase

Die attach for high power VCSEL array systems

Vertical Cavity Surface Emitting Lasers (VCSEL) are commonly used for sensing, data-com and other low power applications. VCSELs are highly reliable and have great potential for low cost and robust solutions. Therefore, there is a growing interest to use them for high power demanding tasks such as pump modules for solid-state laser surface cleaning or heating applications. By arranging single VCSELs in arrays, high power VCSELs systems in kilowatt range can be built [1]. In order to realize highly reliable High Power VCSELs arrays systems with an optimized optical output an excellent thermal management is necessary. Therefore the VSCELs modules are mounted with metallic interconnection technologies like silver sintering and soldering using AuSn and SnAg-Solder for an advanced heat transfer and cooled with micro structured water copper cooler [2][3]

Metallkundliche Phänomene und Grenzflächenreaktionen beim US-Bonden von 25µm-AlSi1-Draht

Gerade für komplexe Module der Mikrosystem- und Hochfrequenzanwendungen werden beim Aufbau mit Chip & Wire Technik immer feinere Drähte und kleinere Anschlussgeometrien (z.B. auf Mikrowellenchips und auch auf HDI-Leiterplatten) verwendet. Damit reduziert sich automatisch die während des Bondens aktivierte Grenzfläche und das Materialverhalten im Mikro- und Nanobereich gewinnt enorm an Bedeutung. Das Paper stellt neue Erkenntnisse zu metallkundlichen Vorgängen beim Bonden von AlSi1-Draht vor. Mittels aufwendiger Gefügeuntersuchungen, wie z.B. Focused Ion Beam (FIB) Präparation in Kombination mit Rasterelektronenmikroskopie (REM) und Transmissionselektronenmikroskopie (TEM) aber auch Lichtmikroskopie und Martenshärtemessungen, können Einflüsse von Werkstoffeigenschaften und Prozessparametern ermittelt werden, was zu einem besseren Verständnis der Verbindungsbildung zwischen den Fügepartnern führt. Die Untersuchungen erlauben Aussagen zu Ver- und Entfestigungsvorgängen, sowie zu den strukturellen Veränderungen im Draht und in der Grenzfläche zur Metallisierung. Dies erweitert die Vorstellungen im derzeitigen Phasenmodell zur Ausbildung einer hochwertigen Bondverbindung. Die Rückkopplung zur Anwendung entsteht durch veränderte Vorgaben für die Materialauswahl und zu den angewendeten Qualitätskriterien

Modern wire bonding technologies - ready for the challenges of future microelectronic packaging

Increasing I/O numbers and device complexity, higher clock frequencies, and the trend to product miniaturization in microelectronics as well as microsystems strongly require a quantum jump from current Wire Bonding technology. High quality manufacturing (speed and reliability) of wire bonds, especially in the range of pitches below 50 µm, depends on advanced materials, high precision bonding tools, and sophisticated equipment. Together with modern product engineering, optimized technology development and extreme quality parameters, high process yield/stability can and must be achieved. This paper covers new developments and trends of materials and bonding equipment as well as bond quality and reliability