Abstract: The present invention relates to an ultrasonic soldering tool for soldering wires to a solder tab of an electrochromic device located between the layers of an insulated glass unit. The soldering tool includes an ergonomically designed handle and soldering tip head to increase operator comfort during use while also providing features to ensure that the surface of the insulated glass unit is not contacted by the soldering tip. One embodiment of the invention provides an automatic feed soldering tool which may have a soldering tip with a trough to create an ideal solder joint. The invention also includes a clamp for securing a wire to a substrate in a correct position while serving as a guide for the soldering tool to provide further protection from errant contact between the soldering tip and the insulated glass unit. The invention also includes a method of creating an ideal solder joint.