What is expected of solder wetting the tinned portion of a wire?

The expectation for solder wetting the tinned portion of a wire is that it should penetrate to the inner strands. This penetration ensures a strong and reliable electrical and mechanical connection. When solder adequately wets the tinned surface, it provides a complete fillet that enhances the bond between the solder and the wire strands.

This thorough wetting is critical for several reasons: it increases the surface area of contact, which improves conductivity, and it contributes to the overall mechanical strength of the joint. Good wetting also helps to ensure that there are no voids or weak points within the solder joint, reducing the risk of failure during service.

In contrast, if the solder only coats the outer strands, the connection may not be robust enough, leading to potential failures under stress. Avoiding contact with the inner strands reduces the effectiveness of the joint, and creating a thick layer on the surface does not guarantee that there is adequate bonding throughout the entire joint. Therefore, the proper wetting of solder must include thorough penetration to the inner strands for optimal performance of the connection.