Soldering Tips

 1. Don't trust heat settings on the Solder Iron. I always test the iron by melting a small amount of solder to see how it would react. I tin a wire or two, maybe even do a quick practice solder to similar components on to a blank board. Use just enough heat to melt the solder quickly. Melting point of solder depends on its composition, ie. Tin:Lead ratio. 63/37 is 180 degrees Celsius, 60/40 is 190 degrees Celsius. But this heat does not account for loss in transfer as well as any connected heat sinks, so temperature needed might be much higher. Your soldering iron temperature should work nicely.

2. Main thing for a good solder is very quick heat transfer to the solder and keeping heat from spreading and damaging other components. So the proper size tip and having a tinned tip is key to having the tip contact and transfer heat into the solder. The solder tip will have an oxide layer after some use, especially at higher soldering temperatures. This oxide layer prevents contact and heat transferring. When the solder tip touches the desired place to transfer heat, apply a small amount of fresh solder into the corner, to help increase heat conduction, very very very helpful. I do this almost all the time.

3. Tip size makes a difference as the area of contact but also a small thermal storage. If you need to solder grounds or areas that have a lot of heat sinks, a larger tip to store the heat will be necessary. If the tip is too small, when thermal contact is made the temperature will drop too much at the tip. This is not usually an issue with any SMDs though.

4. If too much heat is used during soldering the insulation of wires melts, plastic burns, components burn. Too much heat can be temperature but also can be exposure time (dwell time.) Think of it as energy input, so temperature multiplied by the dwell time. Hotter fast soldering is much better than lower temperature long exposures.

5. Too little heat, or movement while the solder is cooling will cause a cold solder joint, where the solder has micro cracks. Cold solder connections are no good for vibrations, and can have unwanted resistance and can completely fail continuity over time. A cold solder joint will have a dull luster to it, instead of a shiny smooth look of proper solder connection. Cold solders are also caused sometimes when a circuit overheats, and then cools while vibrating, leaving a micro crack along the connection not visible to the eye. This is why a lot of electronics stop working, but can be easily fixed with a quick re-flow of the solder at the failed connection. Fixed many power supplies with just a reheat of solder.

6. Cleaning all copper pads with alcohol is a must. Then optionally apply rosin-flux to the only area needed to be soldered, but rosin-core wire solder usually works fine without. Do not use regular flux as it will cause corrosion over time, unless properly cleaned off.

7. Always pre-tin wires and connections. Then cut wires to length and place components. Then solder the connection, by applying heat to the pre-tinned area, wait until the solder is liquid and shiny, remove heat. Very important to wait, do not be impatient as many solder joints may look cooled but are not solid, and if the connection is tested for integrity or moved it will cause an unwanted cold solder joint.

8. The iron might heat other components closely connected so sometimes, so I use Normally Closed Tweezers to act as a heatsink to direct excess heat from other components, just clip it to the conductor to stop heat passing through it. As well there is a thermal tape I use sometimes for covering plastics, to prevent melting with hot air or an oven. Sometimes even just a piece of old board or paper is a great heat shield for surrounding components during soldering.