Stefan Schmitz

Development and Status of Cu Ball/Wedge Bonding in 2012

Starting in the 1980s and continuing right into the last decade, a great deal of research has been published on Cu ball/wedge (Cu B/W) wire bonding. Despite this, the technology has not been established in industrial manufacturing to any meaningful extent. Only spikes in the price of Au, improvements in equipment and techniques, and better understanding of the Cu wire-bonding process have seen Cu B/W bonding become more widespread—initially primarily for consumer goods manufacturing. Cu wire bonding is now expected to soon be used for at least 20% of all ball/wedge-bonded components, and its utilization in more sophisticated applications is around the corner. In light of this progress, the present paper comprehensively reviews the existing literature on this topic and discusses wire-bonding materials, equipment, and tools in the ongoing development of Cu B/W bonding technology. Key bonding techniques, such as flame-off, how to prevent damage to the chip (cratering), and bond formation on various common chip and substrate finishes are also described. Furthermore, apart from discussing quality assessment of Cu wire bonds in the initial state, the paper also provides an overview of Cu bonding reliability, in particular regarding Cu balls on Al metalization at high temperatures and in humidity (including under the influence of halide ions).

Microstructural evolution of ultrasonic-bonded aluminum wires

Abstract The evolution of microstructural gradients, especially crystallographic texture gradients, after ultrasonic wire bonding process and after active power cycling (APC) of high purity, heavy aluminum (Al) wires is studied by electron backscatter diffraction (EBSD) and nanoindentation. The results improve the knowledge about microstructural changes and arrangements after wire bonding and during APC. After ultrasonic deformation by wire bonding, the evolution of a distinct rotated cube (RC) textured area within the wedge was proved by EBSD analysis. The RC texture is discussed as a result of shear deformation and oriented grain growth. Decreased hardness within the RC textured area provides evidence for local softening effects during wire bonding. During APC, besides crack propagation, grain coarsening as well as local low angle boundary migration occurs and the wedge texture changes to an overall random orientation. Effects of microstructure on the crack growth behavior were discussed and suggestions for the improvement of wire bond reliability were derived.

Early-state crack detection method for heel-cracks in wire bond interconnects

Reliability of electronic systems is finally limited due to thermo-mechanical fatigue of interconnections. Besides soldered interconnections wire bonding is one of the most commonly used interconnection technology in electronics. Due to thermo-mechanical loading wire bond technology suffers from cracking in the heel region and delamination in the interface. To increase lifetime and lower ecological impact of electronic systems, a condition monitoring concept is needed, which is able to determine the remaining lifetime of an interconnection. The scope of this paper lies in the development of a parameter measurement system for early-state crack detection in the heel region of wire bond interconnections. This parameter measurement system uses signal components generated by cyclic opening and closing of growing cracks. So it becomes possible to determine the remaining lifetime of the interconnection, which is directly connected to the lifetime of the whole system. Furthermore an analytical model is presented, which supports the experimental setup. Measured cracks are investigated by metallographic cross-sectioning of wire bonds and focused ion beam (FIB).

Correlation between mechanical properties and microstructure of different aluminum wire qualities after ultrasonic bonding

Abstract Three different heavy aluminum wire qualities were investigated regarding their microstructural evolution after ultrasonic bonding by electron backscatter diffraction and nanoindentation. The results complete the findings of our recent research regarding the effect of bonding mechanisms on the wire bond microstructure and its local mechanical properties. Local elastic-plastic material parameters of the bonded wires were approximated on the basis of the elastic anisotropy of crystals and a correlation between hardness and stress.

Investigating wire bonding pull testing and its calculation basics

This study found that standard wire pull testing models introduced more than 20 years ago are insufficient under certain circumstances, including the larger wire bond angles used in applications for automotive control units, pressure sensor devices and COB. The techniques assessed were those given in the German industrial specification DVS Merkblatt 2811 and the international standards MIL-STD-883G and ASTM-F459-06 by comparing the calculated results with actual wire bond pull tests results. The detrimental impact of such failures on standard wire bonding quality control parameters (e.g. the typically used cpk value) can be significant. A new FEM model was developed to investigate possible solutions to the shortfall in accuracy. The data thus obtained was then fed into a new analytical model, based on the Capstan model, which is easily transferred to standard industry and research settings. All measurements, calculations and simulation results were correlated.

New processes and materials for semiconductor components

To date, public interest in the development of new electronic systems has been primarily focused on advances in semiconductor technology and microsystem technology. However, in coming years, attention will shift to approaches that flexibly, cost-effectively and reliably integrate semiconductors into a miniature system. In this article, the Fraunhofer Institutes for Reliability and Microintegration (IZM) discuss this trend, also known as heterointegration, which will require new manufacturing processes and materials.

Neue Verfahren und Werkstoffe für Halbleiterkomponenten

Bislang standen bei der Realisierung neuer elektronischer Systeme die Fortschritte im Bereich der Halbleitertechnologie oder Mikrosystemtechnik im Mittelpunkt des Interesses. In Zukunft werden hingegen Ansatze fokussiert, die Halbleiterkomponenten flexibel, kostengunstig und zuverlassig zu einem miniaturisierten System zusammenfassen konnen. Das Fraunhofer-Institut fur Zuverlassigkeit und Mikrointegration (IZM) beschreibt diesen, auch Heterointegration genannten Trend, der durch neue Fertigungsverfahren und Werkstoffe erst ermoglicht wird.