Solder Flux
No-Clean, Water-Soluble and Rosin-Based flux
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Solder Flux
Solder fluxes play a critical role in ensuring high-quality solder joints by removing oxides and promoting wetting between metal surfaces. They are essential in both manual and automated soldering processes, where they enhance reliability, reduce defects, and improve electrical performance.
Our range of solder fluxes includes both no-clean and water-soluble formulations, designed to meet the specific needs of wave soldering, reflow, and touch-up operations. These fluxes deliver excellent activation, consistent spread, and minimal residue, helping manufacturers achieve high throughput with reduced cleaning and rework.
No-clean fluxes are optimized for applications where post-solder cleaning is undesirable, offering low residues and high insulation resistance. Water-soluble fluxes, on the other hand, provide strong activation for difficult-to-solder surfaces and can be easily removed with standard aqueous cleaning systems.
Each formulation ensures superior solderability, stable performance over a wide temperature range, and compatibility with a variety of surface finishes and alloys, making them ideal for electronics assembly, PCB manufacturing, and rework operations.
Product Selector Guide
| Product | Application | Flux Type | Key Features |
Frequently Asked Questions
What is the difference between water-soluble flux and no-clean flux?
Water‐soluble fluxes are designed with higher activity and leave residues that must be cleaned (typically with aqueous cleaning systems). They often provide excellent wetting, ideal for difficult assemblies. No-clean fluxes are formulated with low solids and benign residues so that cleaning may not be required, which simplifies process flow, however they may demand cleaner surfaces and tighter process control.
Do all liquid fluxes work in a lead-free soldering process?
Not all liquid fluxes are optimized for lead-free soldering. Lead-free alloys such as SAC305, SAC405, and SnCu require higher soldering temperatures and exhibit different wetting behaviors compared to traditional SnPb alloys. As a result, the flux must have a stronger activator system, higher thermal stability, and controlled residue chemistry to maintain proper wetting and avoid issues such as bridging, solder balling, or incomplete hole fill.
Are all fluxes suitable for both wave and selective soldering applications?
Not necessarily. While both wave and selective soldering processes share the same objective, forming reliable through-hole solder joints, the thermal exposure, flux delivery method, and dwell time differ significantly between them. In wave soldering, the flux is generally applied by foam or spray fluxers over the entire underside of the PCB, requiring good spreadability, heat resistance, and low residue activity to cover large board areas uniformly. In contrast, selective soldering delivers flux in a localized, controlled pattern (through micro-spray or drop-jet systems), so the flux must feature precise jetting behavior, minimal spattering, and high stability during longer preheat cycles and localized solder contact.
What do the classifications ROL0, ORL0 etc mean?
These are classifications from IPC/ANSI standards (such as IPC-J-STD-004) specifying the flux activation level and residue type. For example: ROL0 means rosin (RO) based, low flux activity (L), no halide (0). ORL0 means organic (OR) base, low flux activity (L), no halide (0). These classifications help define cleaning requirements and reliability expectations. For more information please refer to General understanding on fluxes.
How does pad finish affect flux performance and selection?
The pad finish on a printed circuit board, such as HASL, ENIG, OSP, or immersion silver, has a direct impact on how flux performs during soldering. Each finish presents different surface chemistries, oxide growth rates, and solderability characteristics, which determine how easily molten solder can wet the pad surface. Flux is responsible for removing surface oxides and contaminants, creating a clean and active metal surface that promotes proper solder wetting. If the flux formulation is not compatible with the specific pad finish, it can lead to issues such as insufficient wetting, solder bridging, dewetting, or voiding. For example, ENIG finishes typically require fluxes with strong activators to penetrate the nickel-gold interface oxides, while OSP surfaces demand fluxes that can gently remove the organic layer without damaging the copper beneath. Selecting the right flux ensures consistent wetting, stable solder joint formation, and improved long-term reliability across various board finishes and component metallizations.
Do solder fluxes comply with RoHS requirements?
Yes, Most modern solder fluxes are fully RoHS compliant, as they are formulated without restricted substances such as lead, cadmium, or mercury defined under the EU RoHS Directive. Fluxes are primarily made of organic resins, activators, and solvents, so they typically fall well within compliance limits.
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Role of Flux in wave soldering
Flux plays a critical role in wave soldering, where printed circuit boards (PCBs) are passed over a molten solder wave to form solder joints between components and pads.
During this process, metal surfaces (component leads and pads) are often covered with oxides that prevent proper solder wetting.
Flux is applied before preheating and soldering to:
Remove oxides and contaminants from metal surfaces.
Prevent reoxidation during heating.
Improve solder wetting and flow across pads.
Reduce the surface tension of molten solder for smooth solder coverage.
Without proper fluxing, solder bridges, skips, or poor wetting are common defects.
Where Flux is Used in Wave Soldering.
In wave soldering, the flux is a key enabler for reliable solder joint formation. It is applied directly to the PCB before the board enters the preheating and solder wave stages. he primary purpose of flux is to clean metal surfaces, removing oxides and contaminants that would otherwise prevent proper wetting.
Flux also protects surfaces during the soldering process by preventing reoxidation and promoting uniform solder flow. Depending on the type and formulation, flux may contain solvents to facilitate even application, activators to enhance oxide removal, and stabilizers to maintain performance under heat.
The fluxing stage is closely coordinated with preheating, which helps activate the flux and evaporate volatile solvents. Proper flux application ensures that when the PCB passes over the molten solder wave, the solder wets correctly, flows smoothly, and forms strong mechanical and electrical connections.
The table below summarizes the key stages where flux is used in wave soldering and its role at each step:
Process Stage | Description | Flux Function |
Fluxing | Flux is sprayed or foamed onto the underside of the PCB before preheating. | Removes oxides and deposits activators on solderable surfaces. |
Preheating | PCB is heated to activate flux and evaporate solvents before entering solder wave. | Activates flux chemistry and drives off volatile solvents. |
Solder Wave | PCB passes over molten solder wave. | Flux residues protect joints and improve solder wetting. |
Flux Types Used in Wave Soldering
Flux Type | Cleaning Requirement | Common Use |
No-Clean Flux | Minimal residue; cleaning often not required. | Consumer, telecom, and cost-sensitive assemblies. |
Water-Soluble Flux | Requires post-solder cleaning with DI water. | High-reliability applications (automotive, medical, aerospace). |
Rosin-Based Flux | Optional cleaning; good wetting and reliability. | Traditional applications, through-hole assemblies. |
Solvent Systems in Flux
Flux formulations often include solvents to help evenly apply the flux, control viscosity, and promote quick activation during preheating. The type of solvent used also impacts drying speed, VOC emissions, and environmental compliance. Understanding the solvent system is important when selecting flux for wave soldering, as it affects process efficiency, residue characteristics, and compatibility with your cleaning or no-clean process.
The table below summarizes the common solvent types used in fluxes and their key characteristics:
Solvent Type | Description | Environmental Impact | Example Use |
Solvent-Based (Alcohol) | Contains isopropanol (IPA) or similar solvents for fast drying. | Higher VOC emission. | Common in no-clean fluxes. |
Low-/No-VOC Flux | Uses water or glycol ethers to reduce volatile organic compounds. | Environmentally friendly; slower drying. | Compliant manufacturing lines. |
Water-Based Flux | Minimal VOC, slower drying; needs longer preheat. | Green alternative. | Selective or wave soldering with extended preheat. |
Flux Classification (IPC J-STD-004C)
IPC J-STD-004C classifies fluxes based on flux type, activity level, and halide content. Understanding flux classification helps customers select the right flux for their specific soldering application. By knowing the flux type, activity level, and halide content, users can match flux performance to board materials, component types, and reliability requirements, while minimizing defects and ensuring compliance with industry standards.
Classification Symbol | Flux Type | Activity Level | Halide Content | Example |
ROL0 | Rosin | Low | <0.05% | Mild, no-clean rosin flux |
ROL1 | Rosin | Low | >0.05% | Rosin flux with moderate halide activators |
ROM0 | Rosin | Moderate | <0.05% | Moderate activity, halogen-free |
ROM1 | Rosin | Moderate | >0.05% | Moderate with halides for better wetting |
ORL0 | Organic | Low | <0.05% | No-clean, halogen-free organic flux |
ORH1 | Organic | High | >0.05% | High activity, water-soluble flux |
INH1 | Inorganic | High | >0.05% | Very active, non-electronic applications |
Flux Activity Level (Meaning and Measurement)
What is Activity Level?
Activity level indicates how chemically aggressive a flux is in removing oxides from metal surfaces.
How It’s Measured
Titration or Ion Chromatography is used to determine halide/acid content.
SIR (Surface Insulation Resistance) and Corrosion Tests per IPC standards assess electrical reliability after exposure.
The higher the activity, the stronger the cleaning action, but also higher the residue risk.
Activity Level | Cleaning Strength | Residue Reliability | Typical Application |
Low | Mild oxide removal | Excellent reliability | Clean copper surfaces, no-clean process |
Moderate | Balanced removal | Moderate reliability | General electronics, mixed technology |
High | Aggressive oxide removal | Requires cleaning | Oxidized leads, high-reliability assemblies |
Example:
A ROL0 flux (Rosin, Low activity, no halide) is ideal for modern, clean PCBs with ENIG finish.
An ORH1 flux (Organic, High activity, halide-containing) suits heavily oxidized surfaces or OSP boards, but must be cleaned post-soldering.
Halogen in Flux
Halogens (chlorine, bromine, etc.) are often added to increase flux activity. They act as strong oxide removers, improving wetting and solder spread.
However, residual halides can cause corrosion or electrochemical migration on PCBs, leading to reliability issues, especially in fine-pitch or high-impedance circuits. That’s why many manufacturers now specify halogen-free fluxes to meet IEC 61249-2-21 and JPCA-ES-01 standards.
How to Choose the Right Flux
Selecting the right flux starts with understanding your process requirements and substrate materials. Use these key criteria as a guide:
Selection Criteria | What to Consider | Why It Matters |
Application Type | Wave soldering, Selective soldering, or Semiconductor packaging | Each requires different activation strength, residue characteristics, and thermal stability |
Soldering Process | Wave, Selective, Reflow, Flip-chip | Determines flux viscosity, deposition control, and heat resistance |
Residue Requirement | No-clean, Water-soluble, or RMA | Impacts post-solder cleaning and visual inspection |
Substrate & Finish | Cu, Ni, Au, ENIG, or Al pads | Influences wetting behavior and corrosion potential |
Halide Content | Halide-free or activated | Affects corrosion risk and ionic cleanliness |
Operating Temperature | 150°C–350°C | Ensures flux remains stable without charring |
Compliance | RoHS, REACH, Halogen-free | Meets global manufacturing and export standards |