Use a rosin core solder used for electrical purposes such as 60/40 that melts at 370 degrees Fahrenheit. Never use acid core solder that is used for plumbing. Silver solder is not recommended and is normally used for jewelry. I use it for soldering two metal pieces together. You can use solid core 60/40 solder and brush on paste or liquid flux. Acid core solder can oxidize and contaminate the contacts.