Soldering 101

Earlier this year,I bought a basic soldering equipment for a project,and as soon as got hold of it,I realized I actually didn't know how to solder. In my mind it seemed as easy as those skills that you never really get to study, boy was I surprised.

Nevertheless,I got digging to understand some basic but important concepts to make my work rather simple.And therefore came up with a 'guide' below(It mostly leans towards PCBs);

Important terms:

1.Soldering-The process of joining two materials(metals) together using a special fluid/filler metal(solder) to form an electrical bond.

2.Flux-A chemical (acidic) compound(usually paste/liquid) that helps prepare the metal surfaces for soldering by removing oxides, promoting wetting, and enhancing the flow of solder.

3.Solder-The filler metal(leaded or lead-free ) to be melted by the soldering iron.Include; antimony, bismuth, brass, copper, indium, tin or silver.

4.Soldering Iron-the hand tool used to melt the solder,usually powered by electricity.

5.Brass Sponge-used for wiping the tip of the soldering iron to remove oxide layer

FLUX

Fluxes essentially fall into three basic categories or flux types,each with a trade off(s):

• Low-Solids/No-Clean FluxesPros: Doesn't require cleaning after soldering due to less activity i.e use of alcohol which evaporates quickly.Sometimes require addition of Rosin to provide lasting protective barrier(This will then require cleaning).
• Rosin Fluxes (Full/High-Solids Rosins)Rosin Fluxes provide excellent soldering, with an equivalent ability to clean the metals to be soldered; has the benefit of acting as protective barrier during soldering and after soldering can entrap ionic residues, preventing them from destructive reaction.Con: Leaves residue thus require cleaning

• Water Soluble fluxes-

Water Soluble fluxes are excellent for soldering, and provide the best soldering possible. They have a great amount of activity that readily cleans the metals to be soldered, and virtually never burn off during the soldering process.

Cons: Generally very aggressive, corrosive, persistent and will continue to react after soldering,and thus have to be cleaned throroughly.

Soldering Techniques

There are many processes that make soldering achievable.

1. Reflow soldering- process begins by applying flux and solder to the pads. The pcb is then placed in a reflow oven?and hot air melts the paste to form solder joints.?The process occurs by raising the temperature to pre-determined levels. For more detailed explanation: Reflow Soldering (by Neoden USA)-It's the most prevalent method for PCBs as it's suitable for SMT assembly.
2. Wave Soldering-Just as shown in the picture below ,a 'wave' of solder is applied to the PCB components to form connections then followed by cooling.

-Pre heating is necessary to reduce thermal shocks.

-Used mostly for THT components,and for simultaneous(Mass) soldering,although it requires lots of monitoring due to the need for temperature adjustments.

3.Brazing- this is a method that resembles welding whereby higher temperatures (>450 C)are used to join metal using a filler metal.

4.Hand soldering-Most common for small applications,especially THT components.

Basic Summary to start Hand Soldering At Home

• Get all essential tools- this include soldering iron,flux,solder,sponge etc
• Ensure your work is clean and safe-this can be done by using an extracting equipment to limit fumes to avoid inhalation(of course unless you got a robot to do the work).Order also reduces risk of injuries by electrical or fire
• Apply the flux to the surface to be soldered to avoid oxidation and remove impurities
• After the iron is ready,make contact with the metal(surface) to preheat the 2 points of contact
• Place the solder wire to melt thus making the electrical joint.
• Wait for a few seconds to cool or use dryer depending on the scale of components.

Conclusion

Soldering is one of the simplest but essential skill especially for anyone related to PCBs,design and engineering.

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