To prevent bubbles from being mixed into a solder for soldering the terminal of a chip, located at a step and a soldering part by applying an ultrasonic vibration to bubbles confined in a molten solder formed on the outer circumference of an electronic device mounted on a board at the time of immersion, thereby removing bubbles.

After being thrust into a solder 6, a board 11 is applied at the step part thereof, with an ultrasonic vibration from a horn 27 of an ultrasonic vibrator, disposed in the proximity of the solder flow 6 in order to remove bubbles 32. When the board 11 is pulled up after being immersed into the solder flow 6 to such an extent as the ultrasonic vibration is also applied to other terminal part of a chip 9, the bubbles 32 are removed again and the chip 9 is placed in a space 23 defined by the board 11, an upper guide 22, a lower guide 21 and the solder flow 6, thus completing the soldering of the chip 9 and a printed wiring 16. According to the method, the bubbles 32 are eliminated from the solder for soldering the chip 9 and the printed wiring 16.