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48 The PCB Magazine • February 2016 The force required to remove the sphere is used as an indication of the solder joint strength. The higher the force required to dislodge the solder sphere, the stronger the solder bond is between the surface finish and the solder. Two types of pad features are used in this ball shear test. One type of pad is the metal- defined pad while another is the solder mask defined pad. It's worthwhile to differentiate the two pad features because it affects the sol- der shear integrity. Figure 8 illustrates the main difference between the two pad features. Metal- defined pads are features on the panel that are shaped or made up of the substrate metal itself, whereas solder mask defined pads are features shaped by the solder mask. In the latter case, a Figure 6: Wetting balance from 0–12 mto. The left column depicts as-plated samples and the right column is after 3x reflow. Cyanide-free iMMersion gold suitable for pCb surfaCe finishing