Automatic adjustment method for elimination of the centering error during the electrical test on printed circuit boards

An automatic adjustment method for eliminating centering error during an electrical test on printed circuit boards (PCBs), particularly with SMT (surface mounting technology), utilizing surface contact bumps or pads for connection of the components, comprising the following steps:

• associating each pad of a centering profile described by a function .rho.=f(.theta.), the function f(.theta.) describing .rho., where .rho. is the distance of the edge of the pad from a nominal point of contact between a test needle and pad, and .theta. the angular direction variable from 0 to 360.degree.,
• performing the electrical test and classifying the pads as either having errors of open circuit and being open or having no errors of open circuit and being okay,
• calculating the .rho..sub.max and .rho..sub.min curves, corresponding to a lower envelope of the centering profiles of the pads found to have no errors of open circuit, and upper envelope of the centering profiles of the pads found to have an error of open circuit, respectively,
• determining an area A given by the intersection of a region bounded at the top by .rho..sub.max and that bounded at the bottom by .rho..sub.min, the area corresponding to the possible displacements of the test needles with respect to the nominal points of contact of the corresponding pads,
• determining an optimal correction .rho..sub.opt, .theta..sub.opt, among those admissible, and
• directing displacement of a PCB position control means by said .rho..sub.opt and .theta..sub.opt quantities.