next referring to fig3 an under bump metallurgy layer 306 is formed on the active surface of the silicon wafer 300 said under bump metallurgy layer 306 mainly comprises an adhesive layer 306 a for example a titanium layer or a copper layer a barrier layer 306 b and a wetting layer 306 c said under bump metallurgy layer may comprise a titanium layer a nickel vanadium and a copper in sequence moreover the under bump metallurgy 306 layer may also comprise an aluminum layer a nickel vanadium layer and a copper layer in addition the mentioned above under bump metallurgy layer 306 can only comprise two layers made of a titanium layer and a copper layer which comprises an adhesive layer and one electrically conductive layer or said under bump metallurgy layer comprises four layers made of an aluminum layer a titanium layer a nickel vanadium layer and a copper layer next referring to fig4 a photo resist layer 308 is formed on the portions of the under bump metallurgy layer 306 which are disposed above the bonding pads 302 in order to expose the residual portions of the barrier layer 306 b and the wetting layer 306 c not covered by the photo resist layer afterwards as shown in fig5 the photo resist layer is taken as a mask to remove the residual portions of the barrier layer 306 b and the wetting layer 306 c not covered by the photo resis layer so as to expose the adhesive layer 306 a for example the nickel vanadium layer of the under bump metallurgy layer can be removed by the etchant made of a sulfuric acid.