be made of lead free solder for example tin copper sn cu alloy tin antimony sn u2014 sb alloy tin bismuth sn u2014 bi alloy tin indium sn u2014 in alloy tin zinc sn u2014 zn alloy tin silver sn u2014 ag alloy tin bismuth silver alloy tin bismuth antimony alloy tin bismuth zinc alloy tin bismuth indium alloy or tin silver copper alloy it is noted that the present invention provides the ubm layer for the tin containing bumps for reducing the formation rate of the inter metallic compounds referring to fig2 the ubm layer 220 includes an adhesion layer 222 a barrier layer 224 and a wetting barrier solder layer 226 the adhesion layer 222 is disposed on the bonding pad 216 and the material for forming the adhesion layer 222 is selected from the following group consisting of titanium ti titanium tungsten ti u2014 w alloy chromium cr titanium nitride tin tantalum nitride tan tantalum ta aluminum al copper cu and mixtures thereof the adhesion layer 222 can also be a composite layer made of the aforementioned materials if the bonding pad 216 is made of aluminum the material for forming the adhesion layer 222 is selected from the following group consisting of titanium titanium tungsten alloy chromium titanium nitride tantalum nitride tantalum and aluminum if the bonding pad 216 is made of copper.