{"id":1408,"date":"2023-08-15T12:06:09","date_gmt":"2023-08-15T04:06:09","guid":{"rendered":"https:\/\/www.jingpengpcb.com\/?p=1408"},"modified":"2026-10-02T19:36:51","modified_gmt":"2026-10-02T11:36:51","slug":"surface-tension-and-viscosity-in-pcba-welding","status":"publish","type":"post","link":"https:\/\/www.jingpengpcb.com\/en\/blog\/surface-tension-and-viscosity-in-pcba-welding\/","title":{"rendered":"How to Reduce Surface Tension and Viscosity in PCBA Soldering"},"content":{"rendered":"

During the PCBA (Printed Circuit Board Assembly) soldering process, the surface tension and viscosity of the solder are two key performance indicators. High-quality solder should have low surface tension and viscosity to ensure that it spreads fully and wets the soldering surface when melted. Although surface tension is an inherent property of a substance and cannot be completely eliminated, we can take certain measures to reduce its impact.<\/p>\n

\"PCB<\/p>\n

Methods for Reducing Surface Tension and Viscosity<\/h2>\n

During the PCBA soldering process, there are several key measures that can help reduce the surface tension and viscosity of the solder, thereby achieving better soldering results.<\/p>\n

1. Increase the temperature<\/h3>\n

By increasing the welding temperature, the spacing between molecules in the solder can be increased, reducing the attractive force between molecules in the molten solder and those on the surface. This lowers the solder\u2019s viscosity and surface tension, making wetting easier to achieve.<\/p>\n

2. Adjust the proportions of the metal alloys<\/h3>\n

The proportion of metals in the alloy also affects the surface tension of the solder. For example, pure tin (Sn) has high surface tension, but increasing the lead (Pb) content can reduce the surface tension of the solder. In Sn-Pb solder, the surface tension decreases significantly when the lead content is increased to approximately 37%.<\/p>\n

3. Add a surfactant<\/h3>\n

Adding surfactants can effectively reduce the surface tension of the solder and help remove the oxide layer on its surface, thereby further improving the solder's wetting properties.<\/p>\n

4. Improve the welding environment<\/h3>\n

Using methods such as nitrogen shielding or vacuum brazing can reduce oxidation at high temperatures, thereby improving the wettability of the brazing material and lowering its surface tension.<\/p>\n

The Role of Surface Tension in Welding<\/h2>\n

Surface tension has the opposite effect on solder wetting; therefore, in soldering, high surface tension inhibits the solder\u2019s wetting ability and affects the formation of solder joints. Whether in reflow soldering, wave soldering, or manual soldering, surface tension has a detrimental effect on the soldering process.<\/p>\n

However, in reflow soldering, surface tension can be harnessed. When the solder paste reaches its melting temperature, the equilibrium surface tension creates a self-alignment effect. This means that even if a component is placed with a slight deviation, surface tension will automatically pull it back to a position close to the target location. As a result, the reflow soldering process has relatively less stringent requirements for placement accuracy, which facilitates high levels of automation and high-speed production.<\/p>\n

However, it is important to note that an imbalance in surface tension can lead to welding defects, such as component misalignment, tombstoning, and bridging.<\/p>\n

Factors Affecting Wave Soldering<\/h2>\n

In wave soldering, differences in the size and height of SMC\/SMD components\u2014or situations where taller components block shorter ones\u2014can obstruct the flow of the tin wave, and surface tension can affect the wetting of liquid solder on the backside of the components. This may lead to soldering defects such as missed solder joints.<\/p>\n

Conclusion<\/strong><\/p>\n

Surface tension and viscosity play a crucial role in PCBA soldering. By increasing the temperature, adjusting the alloy ratio, adding surfactants, and improving the soldering environment, we can reduce the surface tension and viscosity of the solder, thereby achieving better soldering results and quality.<\/p>\n

\n

Frequently Asked Questions<\/h3>\n
    \n
  1. How can the surface tension of solder be reduced?<\/strong> The surface tension of solder can be reduced by raising the temperature, adjusting the alloy composition, or adding surfactants.<\/li>\n
  2. How does surface tension affect welding?<\/strong> High surface tension can inhibit the wetting ability of solder and affect the formation of solder joints; however, in some cases, surface tension can also have beneficial effects.<\/li>\n
  3. What is the self-alignment effect in reflow soldering?<\/strong> In the reflow soldering process, when the solder paste melts, the self-alignment effect caused by surface tension allows components to automatically return to a position close to their target location, which helps improve placement accuracy.<\/li>\n
  4. How does surface tension affect soldering in wave soldering?<\/strong> In wave soldering, high surface tension can affect the wetting of liquid solder on the backside of components, leading to soldering defects.<\/li>\n<\/ol>","protected":false},"excerpt":{"rendered":"

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