Comparison of Gold and Copper Wire Bonding on Aluminum and Nickel- Palladium-Gold Bond Pads for Automotive Application

摘要

New automotive requirements expect plastic packages to survive higher operating temperatures with extendedthermal duration. Mission profiles for under-the-hood and transmission application historically specified minimalduration at maximum junction temperature, such as 50 total hours at 150C, while keeping most of the total operatingduration at lower temperatures. Further module integration and more stringent environmental requirements pushmodules and thus plastic packages closer to the heat source. As such, new mission profiles include more than 3500total hours at 150°C. To satisfy new automotive requirements, plastic packages must meet AEC Grade 0 or higher.One key limitation of the conventional plastic package is the use of gold bond wire on aluminum bond pad. Au-Alintermetallic degradation due to intermetallic transformation in high temperature storage condition remains the mainreliability concern. More reliable intermetallic systems have been proposed that change the wire material and/or thebond pad metallization. An alternative wire material to gold, copper, has many benefits including low cost, highelectrical and thermal conductivities and excellent reliability with aluminum pad metallization. Pad re-metallizationusing nickel/palladium, nickel/gold or nickel/palladium/gold over aluminum bond pad or copper bond pad offers anoble and reliable metal interconnect. This study focused on evaluating Au and Cu wire bonding on low-K-copperwafers having two types of bonding surfaces, the conventional aluminum pad and aluminum pad re-metallized withelectroless nickel / electroless palladium / immersion gold. Ni thickness ranging from 1μm to 3μm was evaluated.Defects on as-plated Ni/Pd/Au bond pads such as color difference and surface roughness were determined to be dueto nodule growth and plating non-uniformity. Wire bonded strip-level thermal aging was conducted to compare thehigh-temperature performance of the four interconnect types. Packages underwent extensive reliability stressconditions. Cross-sectioning through the ball bonds was also conducted to examine the welding region between theball bond and bond pad. Defects in plating and wire bonding processes causing package reliability failures wereidentified. Recommendations for plating and wire bonding processes were derived to ensure high quality andreliable interconnect exceeding AEC grade 0 requirements.