Bead Probe Technology-Advantages-Disadvantages-
circuit Board Pcb
Bead probe technology
Bead probe can be used in circuits where the pin-pitch is too fine to allow standard test pads. This is becoming more common as pin pitches continue to reduce, particularly in embedded devices. Typically bead probe widths are the width of the PCB traces with a length of about three times this. This allows a high degree of flexibility in their positioning, and can in some cases be applied retrospectively to existing layouts. Because of their small size, bead probes do not affect the signal quality of the signals transferring within the PCB trace. This is especially useful in high speed input/output (HSIO) interconnects, where a standard test pad would interfere with the signal.
The soldering process that forms the bead probe leaves a coating of flux. Depending on the manufacturing process used, this flux can have varying levels of hardness. Flux with a waxy hardness can reduce the deformation force from the bead, preventing proper contact with the test probe during the first pass contact. This becomes less of an issue on subsequent contacts as the flux is displaced. Test probes with serrated ends of an appropriate size can also aid in measuring bead probes where flux is an issue.
Bead probes require the trace being tested to be located on the surface. This makes it unsuitable for testing high-density boards with many obscured or internal traces and buried vias.