When designing PCB test fixtures, choosing the correct type of spring probe can significantly improve probing reliability.

Test probes are available with a variety of style of head, to suit different requirements. To probe on a plain pad a sharply pointed tip is optimum. The point helps to cut through flux and other potential contaminants. This type of tip typically also has a tri-cornered taper rather than a smooth conical shape, which make it also suitable for probing test pads with plated holes. The sharp edges cut into the side wall of the plated hole.

Probing on component leads is typically discouraged, but if you have to then a waffle style tip may be optimum. This tip has a surface with multiple points that can still punch through contaminants but is less likely to get pushed off center than a pointed tip.

The waffle style works well for probing leads of through-hole components with wire leads, where the position of the lead is not well controlled. For components with rigid pins, such as connectors, a cup-style probe may also be suitable. This has no sharp points to deal with contaminants, but is does self-align on the pin, making short circuits between densely-placed adjacent probes less likely.

For general purpose use, the tri-cornered pointed tip that Merifix supplies is the most versatile.