Solder Flux

No-Clean, Water-Soluble and Rosin-Based flux

Improves wetting and removes oxides

Solder Elements Solder Flux Solder Spheres Tape and Reel Solder Pastes

Soldering Flux (Liquid Flux)
Product	Flux Type	IPC Class	Solids (%)	Acid No. (mg KOH/g)	Halide (%)	Process	Clean Required	Key Advantage
ALPHA NF3000 Water-Soluble Flux	Organic Acid (OA)	ORH1	24%	High	2.2 ± 0.3	Wave	Yes	Strong oxide removal across a wide thermal window
KESTER 186 Soldering Flux	Rosin (RMA)	ROM1	36%	55	0.5–1.0	Dip, Foam or Wave	Optional	QPL approved RMA flux per MIL-F-14256 ensuring non-corrosive, non-conductive residues
KESTER 951 Soldering Flux	No-Clean	ORL0	2%	14.3	<0.05	Wave & SMT assemblies	No	High SIR performance for automotive, computer and telecom applications
KESTER 977 Soldering Flux	No-Clean	ORL0	3.25%	27 ± 1.0	<0.05	Wave & SMT assemblies	No	VOC-free, high SIR, designed to reduce solder bridging
KESTER 979 Solder Flux	No-Clean	ORL0	4.5%	40 ± 3.0	<0.05	Wave / Selective	No	VOC-free, Bellcore GR-78 compliant with excellent SIR for critical communication and data center equipment
KESTER NF372-TB Soldering Flux	No-Clean	ROL0	3.9%	16.6	<0.05	Wave, Selective & Hand	No	Bellcore GR-78 compliant, long dwell capability, lead and lead-free compatible
KESTER 985M Soldering Flux	No-Clean	ORL0	3.6%	20	<0.05	Wave, Selective & Hand	No	Bellcore GR-78 compliant, minimizes solder bridging
KESTER 959T Soldering Flux	No-Clean	ORL0	2.9%	21 ± 1.0	<0.05	Wave, SMT & Hand	No	Minimizes micro-solder balls
KESTER 2331-ZX Soldering Flux	Water-Soluble	ORH1	33%	High	>0.5	Dip, Foam or Wave	Yes	Strong oxide removal for critical computer and telecom assemblies
KESTER 952-S Soldering Flux	No-Clean	ORL0	<2%	15.0	<0.05	Dip, Foam or Wave	No	Special Organix flux for photovoltaic (PV) tabber and stringer equipment
KESTER 2235 Soldering Flux	Water-Soluble	ORH1	11%	High	1.6	Dip, Foam or Wave	Yes	Low solids water-soluble flux with high ionic cleanliness per MIL-P-28809
KESTER 182 Soldering Flux	Rosin	ROL1	25%	High	0.05	Dip	Optional	Meets IPC J-STD-002 and J-STD-003 for solderability testing

Tacky Soldering Flux (Paste Flux for Rework)
Product	Flux Type	IPC Class	Viscosity (P)	Initial Tackiness (g)	Acid Number (mg KOH/g)	Halide	Cleaning Required?	Application Method	Key Advantage
KESTER TSF-6852	Water-Soluble	ORH1	220	61	Very Low	Halide-free	Yes	Stencil print / dispense	Reliable BGA/PGA sphere attach with strong print definition
KESTER TSF-6522RH	No-Clean	ROL0	285	100	75.4	Halide-free	No (optional)	Stencil print / dot dispense / pin transfer / syringe	Optimized for BGA/PGA rework and surface mount packages
KESTER TSF-ULR18	Ultra-Low Residue No-Clean	ROL0	300–500	140–160	20–50	Halide-free	No	Fine-pitch stencil / dipping	Designed for high-density miniaturization, ultra-fine copper pillar, microball bump flip chip and FCOL/FCQFN packages
KESTER TSF-6502JCR	No-Clean	ROL1	High (Printable)	High	Low	Halogenated	No (optional)	Stencil print / dot dispense / pin transfer / syringe	Bellcore GR-78 compliant; balanced general-purpose BGA/CSP flux

Rework Flux
Product	Flux Type	IPC Class	Viscosity (poise)	Acid Number (mg KOH/g)	Cleaning Required?	Application Method	Key Advantage
KESTER RF771	Water-soluble rework gel	ORM0	285	42.0	Yes – batch washer or in-line cleaner using DI or soft water	Syringe/manual application; BGA rework	Strong oxide removal, excellent wetting for repair work; compatible with Kester water-soluble cored wire solders and water-soluble paste

Flux-Pen
Product	Flux Type	IPC Class	Solids (%)	Acid No. (mg KOH/g)	Halide (%)	Application Focus	Cleaning Required?
KESTER 186 Flux-Pen	Rosin (RMA)	ROL1	36	55	0.5–1.0	General hand soldering and rework of leaded and lead-free conventional and surface-mount circuit board assemblies	No
KESTER 951 Flux-Pen	No-Clean	ORL0	2	14.3	<0.05	PCB touch-up and laboratory work	No
KESTER 952-D6 Flux-Pen	No-Clean	ORL0	3.1	21.4	<0.05	General hand soldering and rework of leaded and lead-free conventional and surface-mount circuit board assemblies	No
KESTER 2331-ZX Flux-Pen	Water-Soluble (OA)	ORH1	33	High	>0.5	Oxidized pads and difficult-to-wet joints	Yes

Flux Cleaners
Product	Cleaner Type	Residue Compatibility	Material Compatibility	Typical Applications / What It Cleans	Recommended Cleaning Method
ALPHA SC-7525 Cleaner	Aqueous	Water-soluble (OA) flux residues	PCB materials, metals, plastics	Water-soluble flux residues and general PCB soldering residues	Spray, immersion, ultrasonic bath
KESTER 5252 Cleaner	Solvent-Based	Rosin (R), RMA, and No-Clean residues	PCB materials, metals, limited plastics	Rosin and No-Clean flux residues, misprinted solder paste, wave soldering flux	Spray, wipe, manual cleaning
KESTER 5252M Cleaner	Solvent-Based	Rosin (R), RMA, and No-Clean residues	PCB materials, metals, limited plastics	Rosin and No-Clean flux residues, wave soldering flux, and organic contaminants from PCB assemblies	Spray, wipe, manual cleaning

Note:

These cleaners are flammable and should be stored in cool, well-ventilated areas away from sparks, flames, and heat sources. Always refer to the Technical Datasheet (TDS) for complete handling instructions and safety information.

The flash point indicates the temperature at which vapors can ignite, while the boiling point affects evaporation rate and drying speed during cleaning. Material compatibility is indicative; always test on critical components before full-scale use.

Process Advantage: These cleaners dry quickly, helping improve throughput, reduce waiting time between cleaning and assembly steps, and minimize residue spotting during production.

Solder Pot Maintenance / Dross Reduction
Product	Appearance / Form	Melting Point / Working Temp	Flash Point	Compatible Solder Types	Brief Application Method	Process Benefit / Notes
KESTER 5744 Solder Saver	Clear liquid	Dissolves at solder pot temp (~240–260 °C SnPb, ~250–280 °C lead-free)	~105 °C	SnPb, SAC alloys, other standard alloys	Add to solder pot; stir or circulate; removes dross/impurities	Reduces dross, improves pot life, maintains solder quality

Note:

Add only during normal soldering operations. Avoid overheating outside solder pot. Follow TDS instructions for safe handling and correct dosing. Keep away from sparks and flames, and ensure good ventilation.

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.

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