two recesses 27 28 in a bottom face thereof the two recesses 27 28 are surrounded by the annular groove 24 the two recesses 27 28 are located corresponding to the two plateaus 15 16 of the two leads 11 12 and the annular groove 24 is located generally corresponding to the two middle sections 110 120 of the two leads 11 12 each recess 27 28 has a depth larger than a thickness of a corresponding blocking layer 17 18 and the annular groove 24 has a depth larger than that of the two recesses 27 28 the second mold 21 defines a large chamber 23 in a top face thereof the chamber 23 has a depth equal to a height of each lead 11 12 so that the two leads 11 12 can be substantially totally received in the chamber 23 the second mold 21 has a horizontal inner face 230 defining a bottom of the chamber 23 and a plurality of vertical inner faces 232 defining laterals of the chamber 23 as shown in fig4 the first mold 22 and the second mold 21 are brought to move towards each other until the first mold 22 and the second mold 21 join together the two leads 11 12 are completely received in the chamber 23 of the second mold 21 and the two blocking layers 17 18 are totally received in the two recesses 27 28 respectively the bottom sections 114 124 of the two leads 11 12 abut against the horizontal inner face 230 of the second mold 21 and the middle sections 110 120 of the two leads 11.