PROBLEM TO BE SOLVED: To provide a uniform and thin Au-Sn alloy thin film, while securing excellent bondability as a joint layer by an Au-Sn alloy on a metallization layer of an LED element or a substrate.SOLUTION: Screen printing is executed in a predetermined area on the metallization layer of Au, by using Au-Sn including alloy paste of mixing Au-Sn alloy powder including Sn:20-25 wt%, having a residual part having a composition composed of Au and having a particle size of 10 μm or less and an RA flux of 15-30 wt%, and next, the Au-Sn alloy thin film having a thickness of 5 μm or less and having at least an eutectic structure, is formed by being solidified after heating and melting the Au-Sn alloy powder.
