Abstract: AlN high temperature co-fired ceramic (HTCC) substrates with high thermal conductivity and thermal expansion coefficient matched with the chip are the preferred substrate material and packaging material for high power multichip module. In this paper an electroless Ni-B/ electroless Pd/ electroless Au-ENEPEG coating is deposited on the surface of the tungsten conductor of AlN HTCC substrates to provide goal solderability. The nickel electroless solution system and the process conditons of high temperature heat treatment are studied. The thickness of the nickel layer is optimized. The results show that high temperature heat treatment promotes the diffusion of the thin nickel layer to the tungsten conductor on the substrate surface, thereby improving the adhesion between the electroless plating layer and the substrate. The coating has good adhesion and meets the requirements of gold wire bonding and tin-lead soldering, which provides technical support for the development of microwave high-power module.