A method for forming a direct bonded aluminium substrate for use in a power semiconductor device, the method comprising: inserting a substrate assembly into a furnace having a plurality of process zones, the substrate assembly including a first aluminum substrate and a second aluminum substrate that are electrically isolated from each other by a dielectric substrate, wherein the first aluminum substrate and the second aluminum substrate are each coated by an Al-Si alloy or an Al-Mg alloy opposing to the dielectric substrate, wherein a top boat is placed on the upper aluminum substrate, and a bottom boat is placed below the lower aluminum substrate, wherein the top boat weighs more than the bottom boat and wherein the top boat and the bottom boat are made of graphite, and providing the substrate assembly successively into each of the plurality of process zones to bond the first and second aluminum substrates to the dielectric substrate at the same time, thereby obtaining a direct bonded aluminum substrate, wherein the plurality of process zones includes: - a preheating zone to gradually ramp up the temperature of the substrate assembly, - a primary heating zone to bring the substrate assembly to a temperature between an eutectic temperature of the Al-Si or Al-Mg alloy and the melting temperature of aluminum, and - a cooling zone to gradually cool the substrate assembly and solidify the eutectic melt, wherein an inert gas is flowed into the primary heating and cooling zones of the furnace to facilitate the bonding of the aluminum substrates to the dielectric substrate without providing a vacuum environment. inserting a substrate assembly into a furnace having a plurality of process zones, the substrate assembly including a first aluminum substrate and a second aluminum substrate that are electrically isolated from each other by a dielectric substrate, wherein the first aluminum substrate and the second aluminum substrate are each coated by an Al-Si alloy or an Al-Mg alloy opposing to the dielectric substrate, wherein a top boat is placed on the upper aluminum substrate, and a bottom boat is placed below the lower aluminum substrate, wherein the top boat weighs more than the bottom boat and wherein the top boat and the bottom boat are made of graphite, and providing the substrate assembly successively into each of the plurality of process zones to bond the first and second aluminum substrates to the dielectric substrate at the same time, thereby obtaining a direct bonded aluminum substrate, wherein the plurality of process zones includes: - a preheating zone to gradually ramp up the temperature of the substrate assembly, - a primary heating zone to bring the substrate assembly to a temperature between an eutectic temperature of the Al-Si or Al-Mg alloy and the melting temperature of aluminum, and - a cooling zone to gradually cool the substrate assembly and solidify the eutectic melt, - a preheating zone to gradually ramp up the temperature of the substrate assembly, - a primary heating zone to bring the substrate assembly to a temperature between an eutectic temperature of the Al-Si or Al-Mg alloy and the melting temperature of aluminum, and - a cooling zone to gradually cool the substrate assembly and solidify the eutectic melt, wherein an inert gas is flowed into the primary heating and cooling zones of the furnace to facilitate the bonding of the aluminum substrates to the dielectric substrate without providing a vacuum environment.