Difference between solder paste No clean vs water-soluble

What is the difference between no-clean and water-soluble solder paste?

Solder paste plays a critical role in the PCB [Printed Circuit Board] assembly process, serving as a vital component in ensuring the reliability of the produced PCBs. Understanding the differences between various types of solder pastes is essential for selecting the most suitable option for specific assembly requirements. There are many types of solder paste offered in the market, but our focus today will be on how the no-clean solder paste and water-soluble solder paste differ from each other.

Water Soluble:

water-soluble, no-clean solder paste

Water-soluble solder paste, also referred to as “washable” or “Cleanable” solder paste, allows for the removal of flux residue with deionized water following the reflow process. The water-soluble solder paste is a traditional choice and is particularly useful in applications where the removal of flux residue is necessary to mitigate potential risks to the circuit board’s reliability and functionality.

The removal of the flux is crucial since it is considered to be an impurity or contaminant on the circuit board and, to op that off, exposing the circuit board to multiple water wash cycles could be risky unless the components are compatible with the water washing processes. Using water-soluble solder pastes comes from the requirements imposed by the designer to lower the risk of reliability defects, especially for high-performance electronic devices, and to ensure the circuit board is free from not only flux but also from other harmful particles.

No-clean Solder Paste:

water-soluble, no-clean solder pastes

The no-clean solder paste, also sometimes known as “low solids flux” or “low activated flux” solder paste is better and more reliable in the circuit board assembly process as it leaves behind minimal residue after the reflow process. The solid content is between 2% to 4% typically. There are also ultra-low-solids fluxes with about 0.5% solid content, designed for wave soldering processes that operate in a nitrogen atmosphere with extremely low oxygen content [<50 ppm oxygen]. The residues from the no-clean solder paste are designed to be non-corrosive, resinous residue around solder joints harmless to the end products. Having to use them is considered to be cost-effective and process-friendly as it eliminates the need for a post-soldering cleaning process, especially densely packed SMD boards. 


In summary, the main difference lies in residue management, with no-clean focusing on minimal residues that don’t require cleaning, and water-soluble focusing on residues that can be easily removed with water-based cleaning processes. The choice depends on the specific requirements of the application and the capabilities of the manufacturing process.

water-soluble, process, cleaning PCB board, reflow process, wave soldering
Single-layer mixed assembly using a water-soluble solder paste

CAPLINQ manufactures both the no-clean and washable solder paste. The no-clean solder paste options are SP-SAC305 and SP-SAC307. The water-soluble solder paste option offered now is SP-SAC305-WS. These solder pastes are lead-free and designed for excellent printing capabilities that guarantee high reliability with a low iconic activator system. Please find our other solder paste portfolio in our Solder Paste category.

We are constantly expanding our portfolio and we can develop or introduce the most common solder paste alloys. Contact us with your design limitations and application requirements to see how we can help you move forward toward a more efficient and sustainable future.

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