Soldering is an essential process in the PCB fabrication and assembly process. It helps to combine two or more metal items by melting and then flowing a filler metal, called the solder, into the joint. The melting point of the filler metal is relatively lower.
Soldering helps to form a permanent connection among the electronic components. You can consider solder to function as connective tissue. It is like a conductive glue that helps join parts to the substrate and brings circuit continuity on the PCB. Solder helps secure the connection to not break down because of vibration or other mechanical forces.
While the process may seem easy at the forefront, the PCB engineer must take care of various intricate details to perform it effectively. PCB soldering is the core process of electronics assembly, and you can buy IPC solder kits equipped with the necessary equipment to execute the soldering process.
The solder is melted using heat from an iron connected to a temperature controller. You need to heat up beyond its melting point, almost at 600° F, which helps melt it. When it cools down, it forms the solder joint. In some cases, you need to remove the solder, which you can do using a desoldering tool.
Types Of Soldering
Soldering is generally of three types and varies with the temperature applied.
- Soft soldering (90 °C – 450 °C) uses the lowest filler metal melting point, which is typically around 400°C. The filler metals are lead alloys with liquidus temperatures that are under 350°C. The components tend to experience low thermal stress. But, it does not make strong joints, and hence it is not suitable for various mechanical load-bearing applications. It is also not meant for high-temperature use.
- Hard (silver) soldering (>450 °C) uses bonding metal typically made from brass or silver. It needs a blowtorch to achieve the right temperature for melting the solder.
- Brazing (>450 °C) makes use of metal with a higher melting point than other soldering types. In this method, the metal being bonded is heated instead of being melted. Once you sufficiently both the materials, you need to place the soldering metal between them, which functions as the bonding metal.
Metals Used In Soldering
Filler metals that are used in soldering are generally lead-based (lead solder). However, due to stringent regulations under the RoHS directive that curbs the use of toxic lead-based substances, these lead-containing solders are increasingly being replaced by lead-free solders. The lead-free solders consist of various materials such as copper, tin, silver, antimony, bismuth, or indium.
What Is Flux?
Flux is a chemical cleaning agent, purifying agent, or flowing agent. It is helpful before and during the soldering process. Soldering needs to form an excellent metallurgic bond. The solder joint does not break loose and does not suffer fluctuation in electrical continuity because of mechanical, temperature, and other stresses.
The flux protects the metal surfaces by removing any oxidation. It also slightly etches the surface for enabling wetting. “Wetting” allows the solder to flow over the surfaces of the contacts and the soldering tip.
- Use the soldering iron carefully. It can heat to around 400°C, which can injure you or start a fire. Remain cautious when using the iron.
- When not in use, remember to unplug the soldering iron.
- Place the power cord appropriately in places where it cannot be tripped over.
- Do not touch the soldering iron tip when it is on a power line. If you touch a power cord with a hot iron, it triggers the risk of burns and electric shock.
- Place the soldering iron on its stand when it is not in use.
- Do not put the soldering iron down on your workbench.
- The working environment where you carry out the soldering process must be a well-ventilated area.
- As the solder melts, the flux may create smoke which can irritate. Tilt your head instead of placing it above your work to avoid breathing.
- The lead-based solder is toxic and poisonous. Wash your hands after you use them.
Understanding Solder Blends
Solder generally has three primary materials, that is lead, tin, and flux. However, it also contains various additives that complement its conductivity. Some of the commonly used alloy additives include:
- Antimony helps to increase the solder’s mechanical strength. It does not impact its wettability and also helps to prevent tin pests.
- Bismuth helps to improve wettability and also lowers the melting point. It is also helpful in inhibiting the growth of tin whiskers.
- Copper helps in lowering the melting point. It also leverages ‘wettability’ in the molten state.
- The presence of Nickel in solder alloy helps in protecting UBM (under bump metallization) layer from dissolution.
- Silver augments the mechanical strength but is less ductile than lead. It helps in improving fatigue resistance during the thermal cycles in lead-free solders.
These are a few essential things you should know about the soldering process. It would help if you were mindful of these aspects to robustly perform the soldering tasks and ensure that soldered interconnections are robust. It will help ensure better electronic conductivity across the board. Also know Smart Ways To Lower Medical Bill Debt.