High temperature reliability of aluminium wire-bonds to thin film, thick film and low temperature co-fired ceramic (LTCC) substrate metallization

Reliable interconnects are essential for microelectronic systems intended for long life times in harsh environment applications. Intermetallic growth accelerates as the temperature increases, and the material system must be carefully selected to avoid mechanically and/or electrically weak connections. The dominating chip metallization is aluminium, and aluminium wire-bonding is therefore recommended to obtain a mono-metallic system at chip level. A suitable substrate metallization compatible with aluminium wire-bonds at high temperatures (HT) should therefore be found.Test substrates with low temperature co-fired ceramic (LTCC) silver conductors plated with nickel/gold, gold and aluminium thin film, gold thick film, and silver thick film plated with copper/nickel/gold have been manufactured. Wedge/wedge aluminium wire-bonding were performed with 25 μm aluminium wire on the substrates before they were subjected to long term ageing at temperatures up to 250 °C for 6-12 months. Bond-pull strength and electrical resistance were measured during ageing on selected components.The present work shows that long term reliable aluminium wire-bonds for 250 °C operation is feasible both with thin film, thick film and LTCC substrate technology. For the screen-printed conductors, a plating system with nickel is necessary. Aluminium wire bonded to gold thin film displays reliable long term high temperature performance for gold thicknesses up to ∼1 μm.