Introduction to Soldering Electronic Circuits Department of Electrical and Computer Engineering Kettering University Soldering Tools and Supplies Good quality pencil-type soldering iron Small gauge resign core solder Damp sponge Safety glasses Needle nose pliers/wire cutters Bench top vise for extra hands Braided de-soldering wick
Soldering Safety Always wear safety glasses Solder on a fire resistant surface (never directly on a bench or desk top) Never leave a hot iron unattended Use caution when laying down or picking up a hot iron (tip temperatures are 700 800 degrees F) Use a soldering iron stand if available Replace the cord if it becomes worn or burnt Do not overload electrical outlets A clean tip is important A clean tip assures good thermal contact between iron and component Clean the tip regularly by wiping on a damp sponge
Holding the soldering iron Hold the soldering iron in a relaxed position, like holding a pen Steady your arm by resting it on the work surface Correct component placement Place the components through the holes on the top side of board Check the alignment of polarized components Components should be nearly flush with the board surface Bend the leads outward on the bottom side to hold components in place while soldering
Incorrect component placement Here the components are not placed flush with the board surface See the previous slide for correct, flush component placement Tin the tip Melt a small amount of solder on the tip before beginning; called tinning the tip This procedure reduces oxidation on the tip and improves heat transfer to the component
Soldering technique The component lead should be between the iron and the solder Heat the component lead and the PCB trace for a short time (max. 2-3 seconds) Touch the solder to the component lead (not the tip of the iron) Soldering technique (cont.) Feed a small amount of molten solder to the joint Some solder will be drawn up into hole, the rest will form a cone around the lead Pull the solder away first, then pull the iron away
Good solder joint A good solder joint should be shiny and cone shaped Wiggle the component slightly to test for good mechanical connection Trim the excess lead length with wire cutters Bad solder joint A bad (cold) solder joint will be dull and glob-like The board may be discolored from overheating These symptoms will lead to unreliable electrical and mechanical connection
De-soldering If you make a mistake, solder can be removed from a connection using braided desoldering wick De-soldering Place the braided desoldering wick on the solder to be removed Heat the wick to melt and draw the solder into the wick Continue to use fresh wick until all solder is removed and component lead is free
Completed board This is an example of the top side of a completed board Components are neatly aligned with correct polarity and placed flush with the board surface Completed board This is an example of the bottom side of a completed board Solder joints are shiny and cone shaped Board is not discolored from over-heating Excess leads are neatly trimmed off There are no unwanted solder bridges between connections
Finishing Up Before finishing, invest some time in checking over your work. It could save you hours of trouble-shooting and re-work later. Look for solder bridges between connections, cold solder joints, missed connections, and reversed polarity on components. Touch up any solder connections that seem less than perfect. Once power is applied.it may be too late!