Soldering

SOME NOTES ON SOLDERING PCBs and other things:
  • use resin core electronic solder. I use 1 to 0.7mm for fine work including PCB circuits.
  • the resin is the FLUX to help remove oxides from the surface. It is in small “veins” within the solder (60%tin 40%lead).
  • if you melt the solder onto the tip of the soldering iron, all the flux goes up in smoke!
  • to make a good electrical join, clean the surface to be soldered using a scouring pad / fine wet & dry abrasive paper/ “Ajax” or similar abrasive powder / fibre glass brush (horrible things that shed dangerous tiny pieces of fibreglass).
  • clean the tip using a wire pad (or use a damp sponge)
  • “tin” (coat) the tip of the soldering iron with a tiny bit of solder (this helps to conduct the heat to the join)
  • heat the join area with the tip of the iron and simultaneously feed in some solder to the joint.
  • Only use a liquid flux if it is non corrosive – I only use that when soldering rail or brass kits. Such a flux needs to be washed off with water.
  • In the photo below the solder has been fed briefly to the gap between the tip and the copper. In this case to prepare a spot ready to receive the leg of a component.
    This simple Circuit Board will be used to step down the 12 Volts form the main power Bus to 5 Volts to operate servos on the layout.
    A component (an electrolytic capacitor) has the two radial leads separated and cut short such that each goes to a different pad.
    The component has been held in place with self closing tweezers.
    The tip of the soldering iron is briefly cleaned – then a tiny amount of solder added to “wet” the tip – apply the tip to the join – feed in some 0.7mm solder.
    Doing it this way feeds the flux to the joint as well as the solder.
    A GOOD join should be smooth and have a nice shine to the surface.
    Same again on the second leg making sure that each leg of the component only connects to a separate pad.
    This method is like working with what are called SMDs (Surface Mount Devices) except that our discrete components are 10s or 100s of times bigger!
    The electrolytic capacitor is in position and the Voltage Regulator is being prepared on the right. On a normal PCB the legs would go through holes and be soldered to tracks on the reverse side. In this case the legs are being bent to straddle 3 pads.
    And here are all the parts in place on the PCB. To the left is a diode (passes current one way only) which serves to protect the circuit if it is accidentally connected to 12V with the wrong polarity. A larger electrolytic capacitor is behind the diode.
    Sharp eyes will make out 7805 on the IC (integrated circuit) – the “5” indicates that the output voltage is 5V. This is the voltage required to operate servos and this board provides that power to the servos.

    This is the circuit diagram for the project described above including the “pinouts” of the 3 leg 7805 voltage regulator IC. Feed it with 7-35V DC and it will deliver 5V DC.
SOLDERING BRASS / RAIL / WHITE METAL:

Coming soon

 

 

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Rick Fletcher

Born in the steam era and developed an interest in railways when given a clockwork Hornby "set". Surrounded by steam when travelling to school (by train of course) and holidays were always by steam train as we had no car. How lucky was I?

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