A brief review of selected aspects of the materials science of ball bonding

Breach, C.D.; Wulff, F.

doi:10.1016/j.microrel.2009.08.003

Cited by 93 publications

(43 citation statements)

References 122 publications

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“…Fig. 10 shows an example from a recently published review of ball bonding materials science [13] and examples of similar squeeze out can be seen in as-bonded copper ball bonded packages in industry and in recent literature such as the study by Hang et al [14].…”

Section: The Ball Bonding Processmentioning

confidence: 78%

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What is the future of bonding wire? Will copper entirely replace gold?

Breach¹

2010

Gold Bull

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Thermosonic ball bonding is a major interconnect process in microelectronics packaging and is positioned to remain one of the key process technologies available to package designers in the near future. However, the main wire material used in fine pitch (FP) and ultra-fine pitch (UFP) ball bonding is gold and with significant increases in gold price, gold ball bonding has become a more costly process that has a considerable economic effect on the assembly of packages used in consumer electronics. An alternative wire material to gold is copper, which is much cheaper and has several technical benefits including better electrical conductivity and has been widely used in discrete and power devices with wire diameters typically larger than 30μm in diameter for many years. However, copper wire behaves quite differently than gold due to its different physical properties, some of which are beneficial and others detrimental to bonding performance. In this article, we briefly review some of the advantages and difficulties with using copper wire advanced packaging and explain why copper cannot replace gold in many applications and why gold offers significant benefits.

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Section: The Ball Bonding Processmentioning

confidence: 78%

“…The graph in Fig. 19 [13] shows that intermetallic growth for gold and copper ball bonds is generally parabolic but very much slower with copper. Examination of etched specimens of copper ball bonds in Fig.…”

Section: Reliability Studies 2003 To Presentmentioning

confidence: 99%

What is the future of bonding wire? Will copper entirely replace gold?

Breach¹

2010

Gold Bull

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“…In the past decade thermosonic ball bonding has become a key technology for microelectronics devices to create electrical connections between [3,4]. Compared to their soft and ductile parent materials, Al-Cu intermetallics highly differ in their physical properties: volumetric shrinkage, M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT increased hardness and brittleness [5] highly affect the performance and reliability of such interconnects [6].…”

Section: Introductionmentioning

confidence: 99%

Role of intermetallics on the mechanical fatigue behavior of Cu–Al ball bond interfaces

Lassnig

Pelzer

Gammer

et al. 2015

Journal of Alloys and Compounds

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The mechanical fatigue behavior of Cu-Al interfaces occurring in thermosonic ball bonds -typically used in microelectronic packages for automotive applications -is investigated by means of a specially designed fatigue test technique. Fully reversed cyclic shear stresses are induced at the bond interface, leading to subsequent fatigue lift off failure and revealing the weakest site of the bond. A special focus is set on the role of interfacial intermetallic compounds (IMC) on the fatigue performance of such interfaces. Therefore fatigue life curves were obtained for three representative microstructural states: The asbonded state is compared to two annealed states at 200 ℃ for 200 h and at 200 ℃ for 2000 h respectively. In the moderately annealed state two IMC layers (Al 2 Cu, Al 4 Cu 9 ) could be identified, whereas in the highly aged state the original pad metallization was almost entirely consumed and AlCu is formed as a third IMC. Finally, the crack path is traced back as a function of interfacial microstructure by means of electron microscopy techniques.Whereas conventional static shear tests reveal no significant decrease of the bond shear force with increased IMC formation the fatigue tests prove a clear degradation in the cyclic mechanical performance. It can be concluded that during cycling the crack deflects easily into the formed intermetallics, leading to early failure of the ball bonds due to their brittle nature.

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“…At present, wire bonding is used in 75 % of discrete and integrated circuit (IC) devices due to its technology maturity, established equipment, flexibility, and reliability [3][4][5]. There are three basic wire bonding techniques: thermo-compression, ultrasonic, and thermosonic [6][7][8]. Popular wire materials have been aluminum (Al) and gold (Au) [9,10].…”

Section: Introductionmentioning

confidence: 99%

A solid-state bonding technique of large copper wires for high power devices operating at high temperature

Lee

2015

J Mater Sci: Mater Electron

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Solid-state processes of bonding 1 mm copper (Cu) wires on Cu substrates and silicon (Si) chips, respectively, were developed. To overcome Cu oxidation issue, the bonding surface on the wire was plated a silver (Ag) layer. An annealing step followed to make the Ag layer much easier to deform and conform to the Cu or Si bonding surfaces. The bonding process was performed at 300°C with 6.89 MPa. Wire-bond cross sections were studied using optical and electron microscopy, respectively. The images obtained exhibit nearly perfect Ag-Cu bonding interface. For wire-bonds made on Cu substrate, in-plane (shear) pull test measured a breaking of force 20.7-23.7 kg, comparable to the 22.5 kg breaking force of the Cu wire itself. Breaking forces on vertical (peel) pull test are about one-half of in-plane pull test results. For wire-bonds made on Si chip, breaking forces are about 80 % of those made on Cu substrate. Fracture modes were evaluated in details. 90 % of the wire-bonds broke with three modes mixed together: near Cu-Ag plating interface, inside Ag layer, and Ag-Cu bonding interface. Thus, the bonding interface is as strong as other regions of the wirebond. This solid-state wire bonding process is expected to have valuable applications in high power and high temperature devices and modules where the wire-bonds have to stand alone without protection due to lack of high temperature molding compound and reinforcing materials.

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A brief review of selected aspects of the materials science of ball bonding

Cited by 93 publications

References 122 publications

What is the future of bonding wire? Will copper entirely replace gold?

What is the future of bonding wire? Will copper entirely replace gold?

Role of intermetallics on the mechanical fatigue behavior of Cu–Al ball bond interfaces

A solid-state bonding technique of large copper wires for high power devices operating at high temperature

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