Solder paste plays an important role in ensuring the reliability of printed circuit boards (PCBs). There are different varieties of solder pastes, and understanding the differences between these types is essential for selecting the most suitable option for specific assembly requirements. In this article, the differences between the two most common types of solder pastes, water-soluble and no-clean, are discussed.
Water-Soluble Solder Paste
Water-soluble, also referred to as “washable” or “cleanable”, solder paste allows for the removal of flux residue with deionized water following the reflow process. This solder paste is a traditional choice that 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 flux is considered as an impurity or contaminant on the PCB. However, exposing the PCB to multiple wash cycles could be risky if the components are not compatible with the water washing processes. Designers choose water-soluble solder pastes to reduce the chance of reliability problems, especially in high-performance electronic devices. This ensures the circuit board is clean, removing both flux and other harmful particles.
No-clean Solder Paste
No-clean, also sometimes known as “low solids flux” or “low activated flux”, solder paste leaves behind minimal residue after the reflow process. As such, this type is considered better and more reliable for the PCB assembly process. No-clean solder pastes typically contain 2–4% solids. For wave soldering processes that operate in a nitrogen atmosphere with extremely low oxygen content (<50 ppm), no-clean solder pastes with ultra-low soldi content (0.5%) can be used. Residues from no-clean solder pastes are designed to be non-corrosive, and hence harmless to the end products. Additionally, using them is seen as a cost-effective and process-friendly solution since it removes the need for a cleaning process after soldering, which is particularly beneficial for densely packed SMD boards.
Summary
In summary, the main difference between washable and no-clean solder pastes lies in residue management. No-clean pastes leave minimal residues that don’t require cleaning, whereas water-soluble options contain residues but they can be easily removed through water-based cleaning processes. The choice depends on the specific requirements of the application and the capabilities of the manufacturing process.
CAPLINQ manufactures both the no-clean and washable solder pastes. 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. 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.
