For soldering electrical joints, rosin-based fluxes are commonly used.
Understanding Soldering Flux for Electrical Work
Soldering is a fundamental process for creating secure electrical connections. Flux plays a critical role in this process by cleaning the metal surfaces and preventing oxidation during heating. Without flux, solder would not properly flow and bond to the components and PCB pads.
The Role of Flux
The primary functions of flux include:
- Cleaning: Dissolving existing oxides and contaminants on the metal surfaces.
- Protection: Forming a protective barrier that prevents re-oxidation during the soldering process.
- Improving Solder Flow: Reducing the surface tension of the molten solder, allowing it to wet the joint properly.
Rosin-Based Fluxes: A Traditional Choice
Historically and still widely, rosin-based flux is a preferred choice for soldering electrical and electronic assemblies. The provided reference highlights the origin of this traditional flux:
- The most basic soldering flux used is the natural rosin derived from pine tar resin.
- Pine tar resin is dissolved in a solvent and then distilled to yield the clear, water-white rosin used in soldering flux.
This natural rosin, also known as colophony, is mildly acidic at soldering temperatures, making it effective at cleaning oxides without being excessively corrosive. After soldering, the residues left by rosin flux are generally non-corrosive and non-conductive, which is crucial for the long-term reliability of electrical circuits.
Types of Rosin Flux
Rosin fluxes come in several variations:
- Rosin (R) Flux: Basic rosin dissolved in a solvent. Mildly active.
- Rosin Mildly Activated (RMA) Flux: Contains a small amount of activator in addition to rosin. Offers slightly better cleaning power than R flux. Residues are typically non-corrosive.
- Rosin Activated (RA) Flux: Contains more activators than RMA. Provides stronger cleaning action but may leave residues that require cleaning, especially in sensitive applications.
For most general electrical soldering, RMA flux is a popular choice due to its balance of activity and residue properties.
Other Flux Types (Briefly)
While rosin is traditional for electrical work, other flux types exist, such as water-soluble fluxes and no-clean fluxes.
| Flux Type | Primary Base | Common Electrical Use? | Residue Properties |
|---|---|---|---|
| Rosin (R) | Pine Resin | Yes | Non-corrosive, Non-conductive |
| Rosin Mildly Activated (RMA) | Pine Resin + Activator | Yes (Common) | Generally Non-corrosive |
| Rosin Activated (RA) | Pine Resin + More Activator | Yes (Higher activity needs) | May require cleaning |
| Water-Soluble | Organic Acids | Yes (Often requires cleaning) | Requires cleaning (corrosive) |
| No-Clean | Various | Yes | Minimal, intended to be left on |
When selecting a flux, compatibility with the solder alloy and the cleaning requirements of the assembly are important factors. However, based on tradition and widespread use for electrical joints, rosin-based fluxes, particularly RMA, remain a standard.
