www.pcbnet.com: The Basics Of Solder Flux

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What is a PCB?

Most electronic products run with the aid of circuit boards. A PCB or printed circuit board is a board made from non-insulating, heat-resistant material such as fiber glass. These are also referred to as substrates. PCB substrates may be single-layered or multi-layered, depending on the type of device that you intend to use them for. Copper or any other conductive metal is used to create conductive traces to facilitate electrical flow. Once the copper traces or conductive pathways are etched on the board, it is thus called “printed circuit board.”

The process through which PCBs are assembled and fabricated involves a soldering process. This is essential to any PCB process and it is important to solder the components properly onto the board to avoid any flaw or defect. To better understand what solder flux is and what it is for, www.pcbnet.com has come up with this guide to help you perform this process with success.

What is a Solder Flux?

PCB Assembly
PCB assembly and soldering uses a type of chemical called “solder flux.” The primary function of solder flux is to clean and eliminate any oxide on the surface of the board. These oxides that are deposited on the PCB may not allow proper solder joints, leading to poor conduction of electricity through the board’s circuits.

Solder flux aids in de-oxidizing the metals attached to the board, including copper tracks and component leads. It also allows for better wetting action and soldering. (Wetting action refers to the ability of removing oxides and preparing a clean board surface prior to soldering.) By eliminating the oxides and other contaminants on the surface, the molten solder remains wet when introduced to the surface mount components and their leads.

Types of Solder Flux

There are three main categories of solder flux based on their activity: rosin, water soluble and no-clean flux. To ensure reliable and faultless finished products, we at www.pcbnet.com always use the solder flux, which is most appropriate for a particular project.

Rosin Flux

This type of flux chiefly consists of natural resin extracts obtained from the oleo-resin of pine trees. Rosin flux has 3 subcategories:

• Rosin (R) Flux – This is the least active and contains only rosin. R flux is commonly used for clean surfaces and it leaves no residue behind.

• Rosin Mildly Activated or RMA Flux – RMA flux contains enough activator, which allows it to clean the plated lands or solder-coated areas and the component leads and terminations. This enables the molten alloy or solder to wet those areas.

• Rosin Activated or RA Flux – RA flux is the most active of all rosin flux types, and it leaves terrible amounts of residues on the board after the soldering process.

Water Soluble Flux

PCB
Also called organic acid flux (OA flux), water soluble flux mainly consists of organic materials, excluding resin or rosin. This flux provides fine soldering results as they have satisfactory flux activity. It also promotes agreeable wetting action. However, water soluble flux can become too aggressive, which calls for further precaution throughout the cleaning procedure to prevent any contamination.

No-Clean Flux

No-clean flux, as the name suggests, does not require any cleaning after the soldering process is done. It does not leave any residue and is thus more convenient to use.

How to Choose Flux for Soldering

You have to consider several factors when choosing the type of flux to use for soldering:

• Board Type (single-sided, multi-layered, double-sided)

• Type and density of the electronic components due for soldering

• Soldering process to be used (SMT, wave soldering, hand soldering)

• Solder ability of components or metals to be connected

Cleaning of Soldering Flux

After doing the soldering process, it is important to clean the surface and other parts of the board and make sure that no residue is left that can affect the function of the PCB or cause short circuit. Except if you use no-clean flux, you need to clean the board with aqueous cleaners or a solvent cleaning agent. Most soldering flux vendors and manufacturers also supply and sell flux cleaners.

About PCBNet

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