the solder joint 320 connecting the pin 121 with the substrate 110 the metal patterns or lines on the substrate 110 are electrically connected to the pin 121 as shown in fig3 there is a remaining metal layer 210 on the substrate 110 which indicates only a portion of the metal layer 210 is introduced into the solder joint 320 as to fig4 there is no metal layer 210 on the substrate 110 which indicates the entire metal layer 210 is introduced into the solder joint 320 additionally it should be noted that the method of the present invention may not induce the intermetallic phase of the solder material 220 substrate 110 interface and the metal layer 210 is kept at the solid solution phase after the first thermal process and the first soldering process mentioned above a second thermal process and a second soldering process may be performed on demand as discussed above the operation temperature of the second thermal process should be carefully controlled to prevent the solder joint 320 formed in the first thermal process from melting since the present invention elevates the eutectoid temperature of the solder joint 320 formed in the first thermal process to be higher than the eutectoid temperature of the solder material 220 the eutectoid temperature decrease in the prior art would not occur thus the operation temperature of the second thermal process could be precisely held below the eutectoid temperature of the solder material 220 in other words an advantage of the present invention lies in the easy control of the operation temperature of the second thermal process in addition the eutectoid temperature of the solder joint 320 may be elevated.