[Espeefan]

Silver solder has a higher melting point, which is good for high current applications. Most solder sold through hobby shops today does not contain any lead at all. Reason being there is a trend to get away from all things containing lead, for safety reasons. There is a huge difference in the soldering ease of your typical 40/60 solder (that's 40% tin/60% lead) vs. silver solder. Thankfully, 40/60 solder is still readily available in hardware stores.

If you are having a problem with melting the factory solder joints, you probably don't have enough heat. Also, the heat sinks are definitely soaking up the heat your iron is trying to put into the joints. Remove the heat sinks and give that a shot. Ever notice how hot the heat sink is after you've soldered a joint to the board?

I would recommend you use a soldering iron that puts out at least 35 watts. Sometimes 35 watts isn't quite enough for all jobs, like soldering capacitors to motor cans, or building battery packs.

It's also possible your iron's tip is worn out or just plain dirty/corroded. Cheap irons use cheap tips, which wear out very fast. If the coating is gone, it's time for a new tip. Always, always tin your tip, whenever you put the iron back into the holder, and before you unplug the cord. Anytime you are not using your iron to make a joint, keep the tip tinned. Clean it before you make a solder joint, and then tin it when you are done. Do this and your tip will last a long time, will stay clean, and will always be more efficient at transfering heat. That's the name of the game.