Method for detecting power plane-to-power plane shorts and i/o net-to power plane shorts in modules and printed circuit boards

Abstract

A method of locating in a non-destructive and non-invasive manner power plane-to-power plane shorts or I/O net-to-power plane shorts found in a printed circuit board or a multi-chip-module by way of a magnetic field generating probe is described. Thousands of nets can be simultaneously tested to detect not only the presence of a short but also to accurately pinpoint its position. For high resistance shorts, the probe is provided with a pot core housed inductor located at its tip, and is used at low frequencies to minimize the effect of the capacitive impedance between the power planes. For low resistance shorts, the probe is used at high frequencies, delivering equal but opposite current to each of two matched inductors at the tip of the probe to maximize mutual inductive coupling while minimizing electrostatic capacitive coupling with the board or module. In both cases, the highest current stress is on the probe rather than on the expensive and fragile package under inspection. This allows the test to be both more sensitive to high resistance shorts at low frequencies and is less destructive, thereby being less likely to blow filamentary shorts due to high current stresses through the board or module.