Cert. No.: FM 78329
Soldering is the act of heating two metals with a solder alloy to form a strong electrical or mechanical connection. To achieve good soldering, one must know the following steps in soldering:
Selection of soldering irons
- Use a soldering gun when the job requires more control of the amount of heat, such as joining wires.
- Use a low wattage soldering iron when you need to do intricate jobs such as circuit board repairs.
- Use a 30/40W soldering iron for model construction, radio repair applications.
- Use a 60/80W soldering iron for other workshop applications.
- Use higher power for work that requires high heat retention at the tip.
Selection of tips
Choose the tip shape that can offer the maximum contact between the tip and the metals to be soldered. Having a large enough contact area can deliver just the right amount of power/heat to make a good soldering joint. A tip that is too large in contact area may damage the PCB. A tip that is too small in contact area may be too cold for making the joint. There are two major types of soldering tips:
- Nickel Plated Copper Tips
These nickel-plated copper tips are economical soldering tips. Oxidation occurs on the surface of the tips easier during soldering. You may file away the oxidation.
- Iron Plated Long Life Tips
Long life tips are iron-plated copper tips. They are much more durable than regular copper tips. They are pre-tinned at the tip by the manufacturer to allow easier wetting of solder to the tip. Never file a long life tip, as this will damage the plating of the tip.
Selection of solder
- There are two major types of solder: regular tin/lead alloy solder and special lead-free solder.
- Solder usually comes in wire form and bar form.
- Solder bars are for industrial production line use.
- Solder wires are for DIY and repair maintenance use.
- There are two types of solder wire: rosin-core and acid-core.
- Always use a rosin-core solder for soldering electrical wiring or copper and tin flat metals.
- Use acid-core solder only on galvanized iron and other hard-to-solder metals.
- Special lead-free solder is an environmentally friendly product, which does not contain lead.
Preparation of the joint to be soldered
- Be sure the material you are soldering is completely clean from dirt, grease, oxidation, etc. The surface must be scraped, sanded, or treated with flux, before applying solder.
- Solder does not stick to coated surfaces.
- When soldering electrical wire, separate the wires to be soldered and scrap them clean. Each section of the wire should be ¡§tinned¡¨ with a thin layer of solder and then twist the sections of wire together.
- Make sure the tip is fitted all the way into the soldering iron and that the tip is tightly screwed. Failure to do so may affect the life time of the soldering iron.
- Plug in the soldering iron and let it heat up on its stand for a few minutes for the tip to reach the working temperature.
- "Tin" the tip by applying a thin layer of solder to all sides of the tip. ¡§Tinning¡¨ should be done frequently throughout the soldering process.
- Use a soldering helper (Third Hand) to hold the joints to be soldered.
- Hold steady the tip of the soldering iron under the joint to be soldered and heat the joint from below.
- Feed solder wire from the top.
- Let solder melt into the joint.
- Remove the wire, and then the solder iron.
- "Tin" the tip again while the tip is still hot.
- Let the soldered joint cool down undisturbed.
- Rest the hot soldering iron on the stand to cool down naturally before storing away.
Care for tips
- Always "tin" the tip before, during, and after soldering to prevent the tip from oxidation.
- Oxidation of the tip will result in poor wetting of solder and hence affect the quality of the soldering joint.
- Do not feed solder wire directly to the tip surface. The flux inside the solder wire will speed up the oxidation of the tip.
- Occasionally, after the soldering iron is cooled down, remove the tip from the soldering iron to prevent the tip from "freezing".