As long as people are discussing vias in PCB, I'll raise a different question which occurred to me recently.
Modern electronic manufacturing methods often include a testing step in which the stuffed board is checked for connectivitiy using either a "bed of nails" test fixture, or with a "flying probe" robotic probe. These tests are totally automated, and are performed by very expensive machines manufactured specifically for testing PCBs. Both types of test use little brass probes which look like pogo sticks to touch little round pads you attach to each and every track. These round pads are maybe 30 -- 50 mils in diameter. The pads live only on the surface metal layers, and the soldermask is cleared away from the pad so that the probe may make contact. Using these pads and your netlist, the machines can verify that your newly assembled PCB doesn't have any shorts, connections are correct, etc. [1] So my question: Has anybody here tried placing test pads on their PCBs? I have a feeling most people using PCB are doing so for hobby/student projects. However, professional-level boards destined for mass manufacture need this feature. I suppose one could just create a "testpad" element in PCB to place & hook to every net. However, since the test pad doesn't appear in the netlist, PCB will complain every time you refresh the netlist, and it will make DRC checking a real PITA. Therefore, I have a feeling that any testpad element needs to be recognized as a special structure by PCB. Any thoughts? Has anybody tried to place testpads for manufacturing test? Stuart [1] Note: The test pads I am talking about are *not* test points which you place in your circuit to hang scope probes off of. They are used more or less exclusively by your PCB assembly house for ICT -- in circuit testing.
