Formation and Growth of Intermetallics in an Annealing-Twinned Ag-8Au-3Pd Wire Bonding Package During Reliability Tests

Abstract

Wire bonding on Al pad packages with an innovative annealing twinned Ag-8Au-3Pd alloy wire results in a sufficient interfacial intermetallic layer at the initial as-bonded stage, while its growth during the further temperature cycling test and pressure cooker test is very slow. Even after prolonged high-temperature storage at 150°C for 500 h, the thickness of its intermetallics is only around 1.7 µm. In contrast, a very thin CuAl 2 intermetallic layer appears at the interface of the Pdcoated Cu wire bonded package, and a thick layer of Au 8 Al 3 intermetallic compounds forms in the Au wire package, which grows to a thickness of around 4.0 µm after high-temperature storage at 150°C for 500 h. Energy dispersive X-ray spectrometry analyses indicate that AgAl 2 , Au 8 Al 3 , and CuAl 2 are the main intermetallic phases formed in the packages bonded with Ag8Au-3Pd, and Au and Pd-coated Cu wires, respectively. However, an additional Pd-containing Ag 2 Al layer found at the AgAl 2 /Al interface of Ag-8Au-3Pd wire bonded package can interrupt its intermetallic reaction, and the annealing twins can further slow the intermetallic growth.Index Terms-Ag-8Au-3Pd alloy wire, annealing twins, intermetallic compounds, wire bonding.

Microstructural evaluation and failure analysis of Ag wire bonded to Al pads

“…A cluster of alloying Au and Pd elements was not observed, and these alloying elements were considered to be uniformly distributed even after the HTSTs. It was therefore suggested that the elemental addition of Au and Pd could increase the resistance to oxidation and sulfuration of the Ag bonding wire [19]. The alumina layer still remained after 2000 h, suggesting that the thermal energy during HTST at 150 and 175°C did not affect it, even though the IMC was grown by atomic inter-diffusion through or beside the alumina layer.…”

“…Recently, a variety of Ag alloys have been designed for better bonding wire and improved properties. Additionally, the Ag-Al bond reliability has been evaluated [14][15][16][17][18][19]. Technologies based on Pd coatings and the addition of Ag bonding wire have been introduced, which improve the efficiency of the fabrication process and the Ag-Al bond reliability [14,15].…”

“…Technologies based on Pd coatings and the addition of Ag bonding wire have been introduced, which improve the efficiency of the fabrication process and the Ag-Al bond reliability [14,15]. Annealing twinned Ag-8Au-3Pd bonding wire has been reported to improve the properties of wire and the Ag-Al bond reliability [16][17][18][19]. However, the alloying addition of Au in Ag bonding wire may still increase the cost, and the development of a costeffective Ag alloy is necessary.…”

A study on intermetallic compound formation in Ag–Al system and evaluation of its mechanical properties by micro-indentation

“…However, the Ag-Al IMC phases reported are not conclusive. One research group indicated Ag 4 Al and Ag 2 Al phases [18] and others showed AgAl 2 , Ag 2 Al and Ag 3 Al phases at the Ag/Al interface [19,20]. Moreover, although many studies have reported the reliability test results of the Ag-Al wire bonds [18][19][20][21], the mechanical properties of the Ag-Al intermetallics are still unclear.…”

Thermosonic ball bonding behavior and reliability study of Ag alloy wire

“…There are few studies regarding the Ag wire as compared to Au and Cu [4][5][6][7][8][9][10]. Cho et al [4] reported that Pd alloying of the Ag wire was effective in improving the reliability of Ag ball bond.…”