Agilent Medalist Bead Probe Technology is a significant advancement in In-Circuit Test (ICT). Bead Probes provide an alternate method of increasing the number of contact points available for ICT systems. Because shrinking geometries are beginning to limit the number of test pad locations available on a circuit boards, beads hold the promise of extending the life of ICT and enhancing contact coverage.
 Beads are small 'beads' of solder that sit on top of a trace. They are essentially electrically neutral at all frequencies of interest to a board designer, and can therefore be added freely to the circuit board without concern for signal integrity.
Beads are added in two basic steps, the Placement/Solder Mask step and the Paste Stencil design step. Prior to building the bare boards, the beads must be placed and the Solder Mask defined with the bead relief points. Prior to fabricating the board, the solder stencil must incorporate the appropriate shapes to transfer metal to the bead probe during reflow. Different tools and different users are involved in each phase.
Bead Placement
Bead placement occurs in the circuit board design phase just after the board layout. The board designer or test engineer can accomplish this step without involvement from a process engineer.
Stencil Design
Stencil design requires information about the materials and thicknesses of the layers being used in board fabrication, so this step is best accomplished by the fabrication house just prior to actual fabrication.
|
