| 摘要 |
PROBLEM TO BE SOLVED: To decrease generation of solder balls ensuring solderbility and to improve reliability of an electronic circuit by making a solder alloy contain specified amount of Cu. SOLUTION: Cu containing ratio in a solder alloy is to be 0.5-2.0 wt.%. Under a melted state of this powdery solder, Cu in the solder alloy precipitates and generates fine particles, and Sn-Pb eutectic alloy is excellent in wettability and spreadability with regard to Cu, and makes the surface of precipitated Cu particles strongly wet accordingly. For reason of that, Cu particles seize fused materials of Sn-Pb eutectic alloy, apparent surface tension of fused solder becomes large, solder balls once generated become liable to be merged with solder adhered to pads and electonic parts, and then, as a result, generation of extricated solder balls is suppressed. In consequence, electronic parts are soldered to a printed circuit board of a fine pattern without generation of short- circuit between pads or others.
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