Critical temperatures in thermocompression gold stud bonding

Abstract

A study on temperature dependence in gold-gold ͑Au-Au͒ thermocompression bonding was performed. Gold studs were bonded to two kinds of surfaces-cofired gold on alumina and electroless nickel covered with immersion Au on silicon. A critical bonding temperature was observed for both substrates. No bonding occurs when the temperature is below this threshold value, whereas bond strength increases with bonding temperature beyond the threshold. This critical temperature can be related to the activation of organic films on the bonding surfaces. Under similar bonding conditions, the critical temperature is lower for a harder substrate than for a softer substrate, primarily because of larger interfacial shear stresses. This is supported by the observation on the interfacial shear stress distribution at the bonding interface based on finite element simulation models of substrates with different hardness.

Direct metal-to-metal thermocompression bonding studies

“…Results shown inFigure 4-3 indicate that the bond strength increases with chip temperature, with higher strength obtained at higher bonding pressures. This temperature dependence of the bond strength is in agreement with the behavior reported by Zhang[86], interpreted to be due to the necessity to rupture barrier films prior to bonding.School of MaterialsScience & Engineering: PhD Dissertation 76 ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Tensile strength of bonded joints bonded at 310 MPa and 516MPa in variation with bonding temperature A comparison between the bond strength of traditional direct gold stud-gold and SAMs-assisted gold-gold bond was carried out.…”

Optimum pressure in low temperature direct metal bonding

“…A ring of copper /gold material was found on the substrate while a cylinder of copper/gold material was left on the central of the bump imprint on the chip side. It has been shown in earlier studies that interfacial shear stress which contributes to deformation and shearing of the contamination layer radiates from the peripheral towards center [11,12]. The relation between the ring and the amount of interfacial shear stress was further discussed in the previous papers [11].…”

Modeling, design, and demonstration of low-temperature Cu interconnections to ultra-thin glass interposers at 20 μm pitch

“…Au is chemically noble and can be deposited easily with either dry or wet process. Extra-high stress is not required to break down native oxides to form direct Au-Au bonding [8,9]. Therefore, Au, in combination with Cu interconnections, is the optimum metal for direct bonding, compared to other alternatives including Al, Ni, Ti, and Pd [10][11][12][13][14][15].…”