Mutual inductance coupling probe for testing the integrity of through-hole plating in printed circuit boards

Claim 1

A mutual inductance coupling-probe device having a longitudinal axis, a probe tip portion and a body portion for non-destructively testing the structural integrity of throughhole plating in plated circuit boards, and comprising a non-magnetic, highly electrically-conductive envelope encasing said probe device and having an enlarged body portion and a narrow probe tip portion; two mutually electrostatically shielded electromagnetic structures within said envelope, each said structure having a yoke about which is wound a winding positioned in the enlarged body portion, said yoke narrowing into an elongate section of a parallel pair of mutually electrostatically shielded legs extending longitudinally of said probe, said structures being side-by-side and mutually parallel, a distal end of each leg of said pair of legs terminating in a terminal stub section oriented perpendicularly of said elongated section and radially of said longitudinal axis by a common radial extent in a wall of said probe tip portion of said envelope, and in an axially spaced array, the arrays of said structures being of a common axial disposition and being mutually angularly displaced about said longitudinal axis by substantially 90*, said structure being of a material of high magnetic permeability and high electrical resistivity; said body portion of said envelope also enclosing a switched alternating current excitation source for exciting one of said windings and further enclosing means responsive to said second winding for indicating the magnitude of an induced EMF detected in said second winding; and a distal end of said probe tip portion being adapted to be inserted in and rotated within a plated through-hole of a circuit board for effecting mutual inductance coupling between said arrays.