Zn-Al based alloys as Pb-free solders for die attach

Abstract

The present study examines the potential of Zn-Al based alloys for replacing Pb-containing solders used in the die-attaching process. Four alloys (Zn6wt.%Al, were cast and characterized in terms of microstructure and mechanical behavior. Based on the criteria of thermodynamics (phase diagram extrapolations) and mechanical behavior (flow curves), it was possible to select the Zn-Al-Ga alloy as best meeting the requirements concerning melting range necessary for die attach and mechanical properties. A wire with 0.76-mm thickness was produced successfully by extrusion. However, the alloy, in the form of wires, is subject to substantial embrittlement after extruding to a degree that further handling becomes impossible. The reason for the embrittlement was investigated using x-ray techniques (x-ray diffraction and x-ray photo spectroscopy (XPS)) and transmission electron microscopy. The temperature dependence of the Ga solubility in the hexagonal close-packed (hcp) Znrich phase in combination with the affinity of Ga to the surface of the Al-rich and Zn-rich phases is held responsible for the embrittlement. A remedy for the embrittlement could be a reduction of the solubility at high temperatures in the Zn-rich phase. This will be attempted by adding small fractions of further alloying elements in future work.

Effect of Cu Addition to Zn-12Al Alloy on Thermal Properties and Wettability on Cu and Al Substrates

“…[8,9] The major contribution of the Vianco team, [10] which worked on alloys in the temperature range above 573 K (300°C), is noteworthy. Yet their new ecological alloys still did not yield very good results, so further research has been conducted by Takaku, [11] Kang, [12] and Savaskan, [13] to improve the alloy properties.…”

“…The proposed eutectic ZnAl alloys have a higher melting point, of 654 K (381°C), after the addition of Cu, and they demonstrate good corrosion resistance and high mechanical strength. [8][9][10] The intermetallic phases (IMPs) in the Cu-Zn system have a very important role in the joining of metals. [11][12][13][14] Therefore, the formation of IMP layers on a Cu substrate has a significant impact on the properties of the joints.…”

Characteristics of Zn-Al-Cu Alloys for High Temperature Solder Application

“…For this reason, several studies on Zn-(Sn, Al, Mg, Ga) based high temperature solders have been reported. [10][11][12][13][14] Vianco defined an ultra high temperature solder working properly between 573 K and 623 K and suggested a Zn-Al based alloy for the possible alloy system. 15) It has been reported the tensile strength, creep resistance, dimensional stability and corrosion resistance of Zn alloy are improved by the addition of Al/Cu elements.…”

Shear strength of Cu-to-Cu joints using mixed Ag particle paste

“…For example, Au-, Zn-and Bi-based alloys have been investigated, but their widespread use is unlikely because of their inferior properties and high costs [2][3][4][5][6][7][8][9] . New joining process using thin films and sintering process using metal particles have also been proposed as solder alternatives [10][11][12][13][14][15] .…”