3. Touch the soldering iron to one of the board's pads, not the solar cell's pins. Carefully, apply solder to the point between the soldering iron tip and the solar cell's pin. As the solder liquefies, slide the iron's tip towards the SOIC pin. Remove the iron and examine your solder joint. When the solder is solid, test for a strong connection, by tweaking the pin with a wooden tooth pick.