Friday, October 19, 2012

Soldering Guide for LEDs



[While you do not have to solder your wiring, here are directions in case you want to solder]

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece. Soldering differs from welding in that the workpieces are not melted. There are three forms of soldering, each requiring higher temperatures and each producing an increasingly stronger joint strength:
  • soft soldering, which originally used a tin-lead alloy as the filler metal
  • silver soldering, which uses an alloy containing silver
  • blazing, which uses a brass alloy for the filler.
The alloy of the filler metal for each type of soldering can be adjusted to modify the melting temperature of the filler. Soldering appears to be a hot glue process, but it differs from gluing significantly in that the filler metals alloy with the workpiece at the junction to form a gas-tight and liquid-tight bond.
Soft soldering is characterized by having a melting point of the filler metal below approximately 400 °C (752 °F), whereas silver soldering and brazing use higher temperatures, typically requiring a flame or carbon arc torch to achieve the melting of the filler. Soft solder filler metals are typically alloys (often containing lead) that melt at temperatures below 350°C/662°F.
In the soldering process, heat is applied to the parts to be joined, causing the solder to melt and to bond to the workpieces in an alloying process called wetting. In stranded wire, the solder is drawn up into the wire by capillary action in a process called wicking. Capillary action also takes place when the workpieces are very close together or touching. The joint strength is dependent on the filler metal used, where soft solder is the weakest and the brass alloy used for brazing is the strongest. Soldering, which uses metal to join metal in a molecular bond has electrical conductivity and is water-tight and gas-tight.
Equipment:
1) How many different types of soldering irons are there and which are ones to avoid when soldering small wires?
There are hundreds of kinds of soldering irons on the market:
·      small craft sized irons sometimes called "pencil irons" sold at Home Depot, Radio Shack, Hobby Lobby, Michaels, etc. are cheap and easy to use.
·      larger "heavy duty" irons (get a lot hotter than is good for LEDs
·      ESD Digital Regulated iron
                                                      ESD stands for Electrostatic Sensitive Device. Regulated means you can set the temp accurately. This type of iron is best for use when soldering wires onto an LED. LEDs are heat + discharge sensitive. (This does not mean that an ESD is necessary for the wires, only for work on the diode itself. That is why having the wires and resistors already done for you is so nice.)
I own an ancient soldering iron which gets hotter the longer it is on. For soldering of wires at the connection points: I can use my old iron, but I’ve found I need a light touch, usually soldering and then unplugging the iron, plugging it in and making the next solder, etc.
Anyone who already has the "pencil iron" can use this. However, if you intend to do lots of wiring, think about the ESD iron.
2) Is it necessary to solder on a particular surface, or is there a surface
you would recommend?
Soldering surface can be as little as a piece of cardboard or as much as a ceramic tile. Cardboard can be changed often, giving a clean surface for work. Take a look at the wire stripping video. http://www.modeltrainsoftware.com/kynarwire.html  Scroll down to the second item on the page to see video. She was using a paper towel.
3) What sort of solder do you recommend?
 I get "benzomatic" at Home Depot in the tools area. It comes in a small cheap roll. It has 40% rosin core (flux already inside of it) and is a lead-tin type, which sticks better than non-lead. I researched lead in solder and safety concerns. The lead does not become airborne when you heat the solder. The flux is what is in the smoke you see. The lead stays inside the solder itself. So if you wash your hands and avoid eating or smoking or touching your eyes or nose while soldering, you will not ingest any lead!

4)I like the idea of the flux in the solder, but why is flux necessary?
Flux is a reducing agent designed to return oxidized metals to their metallic state. Rosin Flux makes the solder "stick" better by etching the metal a bit. It ‘seals’ the metal connection and prevents future oxidization and thus improves the electrical connection and mechanical strength. The two principal types of flux are acid flux, used for metal mending and plumbing and rosin flux used in electronics.

Steps in Soldering:
  • bare about 1/3 inch of each wire to be connected
·      slide shrink insulation piece onto one side of wires to be connected and away from soldering area
  • lay together the wires which are to be connected
  • solder them by holding the solder near the wires and heating it with the soldering iron
  • cool a minute
  • give a little tug to make sure solder is solid
  • slide shrink insulation over the connection
  • hold shrink insulation over a lit match in order to shrink it tightly onto the connected wires

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