| 摘要 |
PROBLEM TO BE SOLVED: To provide paste solder having a low melting point and reflow temperature and joining strength. SOLUTION: The paste solder is composed by mixing leadless solder alloy powder of an Sn-Ag-Cu system, Sn-Ag-Bi-Cu system or Sn-Cu system, for example, an Sn-3.5Ag-0.75Cu system and low m.p. solder alloy powder of an Sn-Bi system having the melting point lower than the melting point of the alloy solder described above, for example, an Sn-58Bi system and Sn-40Bi system. If the alloy powder of the low m.p. solder among the composition is used, the m.p. of the solder may be lowered and therefore, the preheating temperature for heating of printed circuit boards with waste heat may be kept low and in addition, the working temperature (peak temperature) at the reflow treatment is lowered and the reflow time may be shortened. Further, the working temperature may be lowered and therefore the damage of packaging parts by heat may be prevented and the oxidation problem of the parts may by overcome. In addition to these characteristics, the paste solder has the characteristic that the joining strength of the packaging parts may be enhanced by limiting the contents of bismuth.
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