Abstract: A method for determining the condition of a reflow furnace so as to prevent the semiconductor element from tilting due to different collapsed amounts of solder bumps in the single semiconductor element of multiple chip modules mounted on the semiconductor element on the substrate. For the carrying direction in the reflow furnace using a carrying belt, temperature analysis for time duration is performed for the solder bumps at both the front and rear, and then the condition of the reflow furnace is determined so as to close at both the times for reaching the solder melting temperature and the times for maintaining the solder melting temperature.