How do I solder this 21 pin modchip?

the one this modchip works is u kno plug the 21 pin ribbon into the mod chip then plug the modchip into the little slot where the 21 pin ribbon is suppose to go. Then there is a wire that go from the chip itself to the 5v point. The thing is that the guide that came with it just prompt me to plug the wire into the 5v box. It's a snuggy fit but after sometimes it'll come loose. i was wondering if there is some way to solder it so it wont slip. I tried soldering to the 5v prong but the solder wont stick.
You should be able to solder to the 5v 'prong'.

You probably need to heat it for a bit longer as it is solid metal, rather than a piece of wire. I soldered the 5v wire on my mod directly to the power supply.