What is Wetting?

Wetting is the study of how a liquid spreads out on a solid substrate. In the case of Printed Circuit Boards, Wetting refers to the how well the molten solder paste is able to bond with the PCB or component. During the soldering process, the molten solder wets the target area, and causes an interfacial reaction at the target-solder interface, forming a soldering joint. 

Solderability characteristics of PCB surface finishes impact the solder alloy’s wetting behavior. A particular surface finish must allow molten solder wetting within the given time using a specified flux. Other factors, which affect the wetting properties are temperature, the amount of oxygen in the soldering atmosphere, solder reflow profile, and solder-alloy composition.

Characteristics of a Wetting-friendly Solder

• Stable solder paste viscosity for a longer duration
• Excellent wettability (solidification time)
• Reduced cracking and side balling due to less flux residue

Nowadays, manufacturers perform ‘Wetting Balance Testing’ to validate the solderability features of the surface finishes. Click here to learn more about the Wetting Balance Test.