Okay, You're probably here because there's something wrong with the soldering technique or something wrong with your equipments. Make sure the solder 60/40 Tin-Lead mix Soldering which is is 40% tin - 60% lead and should already contains cores of "flux" which helps the molten solder to flow more easily over the joint.
If that still doesn't help then try this technique which help keep the solder where it should be and not down into the PCB board as what may have had happen with the original relay.
You will need a strand of copper wire. This is used to fill the gap. The copper wires can be used as a wick as long as they're used with a rosin paste flux.
You may need a razor blade. This will ensure a clean wire strand cut to prevent electrical shorts.
Steps: Fill the gap with a strand of copper wire: Wrap a strand around the terminal. Press the strand into the gap with a needle tip instrument. After soldering (step 3) cut off the remaining wire with a razor blade. The strand keeps the solder from escaping below and allows for a perfect smooth joint not achieved from the factory.