While silver bearing solder is somewhat stronger, I often use plain old rosin core electrical solder with no problems or failures over many years. As mentioned above, cleanliness is of paramont importance; and, yes flux is required for easy success. I shy away from acid core or acid flux due the the requirement for complete neutralization after soldering to preven rust and corrosion--difficult to accomplish. If you use a torch, be carefull, to much heat can be as detrimental as to little.