Guh-Yaw Jang

Solid-State Reaction in an Au Wire Connection with an Al-Cu Pad During Aging

In integrated-circuit packages, wire-bonding techniques are the preferred methods for making electrical connections between the chip and the lead frame. The influence of aging at 150°C up to 3,000 hr on interfacial reactions of Au wire bonded with the Al-Cu pad was investigated herein. To observe various intermetallic compounds (IMCs) with field-emission scanning electron microscopy, polished samples were ion-milled through precision etching and coating techniques. Three IMCs, i.e., (Al,Cu)Au4, (Al,Cu)3Au8, and (Al,Cu)Au2, were found between the Au wire and the Al-Cu pad in the as-assembled wire bond. After 168 hr of aging, Al3(Au,Cu)8 formed between (Al,Cu)3Au8 and (Al,Cu)Au2 in the center of the wire bond. In fact, the Al-Cu pad, (Al,Cu)Au2, and Al3(Au,Cu)8 IMCs were completely reacted after 500 hr of aging. (Al,Cu)3)Au8 was thus transformed into (Al,Cu)Au4. Near the edge of the wire bonds, (Al,Cu)Au2 formed between the Al-Cu pad and (Al,Cu)3Au8 during 500 hr of aging. For aging longer than 1000 hr, Al3(Au,Cu)8 was detected between (Al,Cu)3Au8 and (Al,Cu)Au2. It was noted that the Al3(Au,Cu)8 IMC gradually grew with aging. With the aid of microstructure evolution and quantitative analysis, the interfacial phase transformation between the Au wire and the Al-Cu pad could be probed. In addition, the growth kinetics of (Al,Cu)Au4 and (Al,Cu)3Au8 in the center of wire bonds were also evaluated and discussed.

Role of Cu contents in the isothermal metallurgical reaction for the flip chip Sn-3.0Ag-[0.5 or 1.5]Cu joints with Cu/electroless Ni-P/immersion Au bonding pad during aging

Cu/electroless Ni/immersion Au metallization is usually used as bonding pad on the substrate side of flip chip solder joints. Sn-Ag-Cu solder is one of the promising candidates to replace the conventional Sn-Pb solder. Isothermal interfacial reaction in Sn-3.0Ag-(0.5 or 1.5)Cu solder joints with electroless Ni/immersion Au surface finish after aging at 150degC was investigated in this study. Intermetallic compounds (IMC) of (Cu_1-y,Ni_y)₆Sn₅, (Ni_1-x,Cu_x)₃Sn₄ and P-rich layer formed between the solder and the EN layer in both Sn-Ag-Cu joints during aging. For the Sn-3.0Ag-0.5Cu joints after more than 2000 h aging, (Ni_1-x,Cu_x)₃Sn₄ IMC gradually grew. Through the investigation of cross-sectional microstructural observation and quantitative analysis, the interfacial microstructure and the elemental distribution between the solder and bonding pad could be clearly revealed. It was demonstrated that Cu content in the solders near the solder/IMC interface played an important role in the growth of (Ni_1-x,Cu_x)₃Sn ₄ and (Cu_1-y,Ni_x)₆Sn₅