To obtain an alloy not containing toxic Pb and expensive In, having a low melting point, superior in mechanical properties and thermal fatigue characteristics and suitable for a low temperature soldering operation by composing the alloy of Ag, Zn and Bi each having a specific composition ratio and the balance Sn.
The solder can be obtained by adding Zn and Bi to a silver based solder with Sn/Ag. Ag brings the effect of a low melting point, increases strength and improves glossiness. For that purpose, the solder is designed to contain 2-4% Ag, 0.5-2% Zn and 2-6% Bi, and the balance Sn essentially. As a result, the melting point is as low as that of alloy H; the mechanical strength, namely, the tensile strength as well as the elongation, is superior; and particularly, the mechanical properties are excellent after retention at a high temperature; so that a solder can be obtained that excels in thermal fatigue characteristics. Consequently, it allows a soldering operation under a comparatively low temperature, reducing possibility of damaging a printed circuit board, and extending the life of an IC chip.
NAKAHARA YUNOSUKE
NINOMIYA RYUJI
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