Soldering surface mount components isn’t difficult, but it will require a good eye, a steady hand and a soldering iron with a small and clean tip. In a proper joint, you want the solder to adhere to both the PCB pad and the component lead rather than having the solder ball up on the end of the component and not adhere to the PCB pad.
First, apply a small bead of solder to one of the PCB pads for the component being installed. The bead should be approximately 0.020” to 0.030” high. Apply some liquid rosin based flux from a flux pen to the solder bead and to the other pads for the component.
Next, using a pair of tweezers, pick up the component to be installed and place it over the appropriate pads. With the component in position, move the soldering iron to the solder bead on the PCB pad. Apply a small amount of heat from the iron to flow the bead, while at the same time lower the part onto the board and make sure it is aligned properly.
Remove the soldering iron and allow the solder to cool. Inspect the joint, at this point you aren’t concerned with the quality of the actual solder joint, but the positioning of the component. The component should be flush against the PCB, with all of it’s ends properly contacting the pads. The component should be straight and centered between the two pads.
Apply a good amount of liquid flux to both ends of the component. Heat the unsoldered end of the component and the corresponding pad with the soldering iron, carefully wipe on a small amount of solder. You want to have a small tight fit, rather than a glob of solder.
After the second end of the component is soldered, go back to the original solder joint and reheat the PCB solder. The flux will allow the solder to flow freely. If there isn’t enough solder, add a little more. However, if you find that you have a large blob of solder at either end it can be removed with a solder wick. Just apply flux to the blob and the wick, position the wick over the blob and press lightly on the wick with your iron. When the heat runs through the wick the solder blob will then melt and be drawn off the wick. If you wind up removing too much solder, just re-apply a small amount of new solder to the joint.
When the joints have cooled, inspect them carefully to make sure they are solid and are making contact with the PCB board. If you aren’t sure about the connection, apply more flux and reflow the joints until you are satisfied.
