A Study of the Sulfidation Behavior on Palladium-Coated Copper Wire with a Flash-Gold Layer (PCA) after Wire Bonding

Palladium-coated copper wire with a flash-gold layer (PCA) is an oxidation-resistant fine wire that simultaneously has the properties of palladium-coated copper wire (PCC) and gold-coated copper wire. This research used an extreme sulfidation test to compare corrosion resistance between the PCC and PCA wires. In addition to closely examining the morphology of the wires, the internal matrix after the sulfidation test is also discussed. In doing so, the PCA wire was bonded onto the aluminum pads and the sulfidation test was conducted. Then, we observed its morphology and elemental distribution and found that the flash-gold layer of the PCA wire effectively enhanced resistance to sulfidation corrosion. Because the copper ball had an alloying effect on the ball bonding, it produced different shapes of sulfide after the sulfidation test. The degree of corrosion on the wedge bond was different because of the presence or absence of the coated layer. In contrast, the flash-gold layer of the PCA wire enhanced the bonding force and retained low resistance characteristics after the sulfidation test.

Solid-State Microjoining Mechanisms of Wire Bonding and Flip Chip Bonding

Low-temperature microjoining, such as wire (or ribbon) bonding, tape automated bonding (TAB), and flip chip bonding (FCB), is necessary for electronics packaging. Each type of microjoining takes on various aspects but has common bonding mechanisms regarding friction slip, plastic deformation, and friction heating. In the present paper, solid-state microjoining mechanisms in Au wire (ball) bonding, FCB, Al wire bonding (WB), and Al ribbon bonding are discussed to systematically understand the common bonding mechanisms. Ultrasonic vibration enhances friction slip and plastic deformation, making it possible to rapidly obtain dry interconnects. Metallic adhesion at the central area of the bonding interface is mainly produced by the friction slip. On the other hand, the folding of the lateral side surfaces of the Au bump, Au ball, and Al wire is very important for increasing the bonded area. The central and peripheral adhesions are achieved by a slip-and-fold mechanism. The solid-state microjoining mechanisms of WB and FCB are discussed based on experimental results.

High Temperature Storage Reliability of Bond Resistance of Palladium-Coated Copper Ball Bonds

Reliability of wire bonds made with palladium-coated copper (PCC) wire of 25 μm diameter is studied by measuring the wire bond resistance increase over time in high temperature storage at 225 °C. Ball bonds are made on two bond pad thicknesses and tested with and without mold compound encapsulation. Bond pads are aluminum copper (Al-0.5%Cu), 800 nm and 3000 nm thick. The wirebonding pattern is arranged to facilitate 4-wire resistance measurements of 12 bond pairs in each 28-pin ceramic test package. The ball bonding recipe is optimized to minimize splash on 3000 nm Al-0.5%Cu with shear strength at least 120 MPa. Ball bond diameter is 61 μm and height is 14 μm. Measurements include bond shear test data and in-situ resistance before and during high temperature storage. Bonds on 3000 nm pads are found to be significantly more reliable than bonds on 800 nm pads within 140 h of aging.