Solder paste | Determining dynamic viscosity of solder pastes with ViscoQC and a spiral adapter measuring system
Solder pastes of reliable quality are essential for a seamless production process of printed circuit boards (PCBs). Therefore, this report aims to support the manufacturing of solder pastes and PCBs by providing a quality control method using the rotational viscometer ViscoQC.
Viscosity is a critical property of solder pastes, as it directly influences printability and joint quality, and therefore overall performance in electronic assembly processes. A paste with improper viscosity and flow behavior can lead to insufficient solder volume, bridging, slumping, or poor stencil release, all of which compromise the reliability of the final solder joint. During printing the paste should flow easily, so a high shear force is applied to fill the stencils. After filling, the paste should recover its structure to avoid slumping.
A widely used method for determining the viscosity of solder pastes is rotational viscometry with a spiral adapter system according to IPC-TM-650. The spiral adapter is specifically designed for solder pastes, as they are difficult to evaluate with conventional geometries. With such a system, the paste is sheared between a spiral spindle and a stationary chamber, enabling a stable measurement of viscosity.
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