A factorial design investigating solder paste volume under varied squeegee pressure and squeegee types.

It is generally agreed that, on average, 40% to 60% of the defects generated by a surface mount production line can attributed to the solder paste screen (stencil) printing process. This process comprises different key elements designed to work together to generate the most optimal performance and results. These elements include the following:

Selecting the right paste requires an understanding of its properties.

A solder paste’s viscosity and thixotropic properties influence its performance in different production environments.

Viscosity is a measure of a fluid’s resistance to flow. Think of it as a fluid’s “thickness” or “thinness.” A fluid that flows slowly, like molasses, has a high viscosity, while one that flows easily, like water, has a low viscosity.

While cheaper to use, uncoated stencils can have a detrimental effect on printing performance.

In a recent study focused on optimizing solder paste transfer efficiency, the initial phase used factory-applied coated stencils to isolate and understand the effects of solder alloy powder size on print performance. This approach ensured precise data by minimizing stencil-induced variations.

Our follow-up study explores the implications of using uncoated stencils, which are used in many manufacturing settings.

Factory-applied nanocoated stencils are designed to enhance the release of solder paste, while uncoated stencils are still widely used due to their cost-effectiveness. The choice between these stencils can play a significant role in determining the quality and efficiency of solder paste application.