Method of and apparatus for testing for integrated circuit contact defects

1. A method of testing the continuity of a connection between an integrated circuit pin and a circuit board where the integrated circuit pin is connected to a plurality of integrated circuit pinsfonning a first group, the method comprising the steps of:

identifying a second group of integrated circuit pins having electrical properties relatable to the first group;

applying one or more first test signals to the first group of pins and measuring one or more respective first voltage differences occurring between the first group of pins and a reference voltage;

applying one or more second test signals to the second group of pins and measuring one or more respective second voltage differences occurring between the second group of pins and a reference voltage; and

on the basis of the measurements, extracting and comparing a non-linear characteristic of the first and second groups of pins to obtain a measure of said continuity.

2. An apparatus for testing the continuity of connections in a circuit path within a product, said path comprising a plurality of integrated circuit device pins forming a first group connected to a first circuit node such that current flows via the pins and through associated semiconductor junctions to a second circuit node, the apparatus comprising:

a first tester for applying M test signals to the first group of pins and measuring M voltage differences occurring between the first circuit node and a reference, where hi is an integer greater than zero;

a second tester for applying N test signals to a second group of pins expected to have a behavior identical to or relatable to the first group of pins and measuring N voltage differences occurring between a second circuit node connected to the second group of pins and a reference, where N is an integer greater than zero; and

a processor responsive to the voltage differences for deriving or comparing a non-linear characteristic of the first and second groups of pins to obtain a measure of said continuity.

3. An apparatus as claimed in claim 2 , in which the first and second groups comprise the same number of device pins.

4. An apparatus as claimed in claim 3 , in which each device connection in the first group has a corresponding device connection in the second group being members of the same or similar family of device technologies and of similar function.

5. An apparatus as claimed in claim 3 , in which the first and second non-liner characteristics are compared and a faulty connection is indicated by the data processor if the difference between them exceeds a first threshold.

6. An apparatus as claimed in claim 3 , in which the M test signals and the N test signals are substantially identical current waveforms.

7. Apparatus as claimed in claim 2 , in which the M test signals and the N test signals are DC signals of switchable value and voltage offsets are calculated from the voltage differences, the offsets are compared and a faulty connection is indicated if the difference in offsets exceeds a threshold value.

8. An apparatus as claimed in claim 3 , in which the M test signals and the N test signals comprise an AC component superimposed on a DC component and the magnitude of harmonic components of the voltage differences are compared and a faulty cotuiection is indicated if the difference in harmonic components exceeds a threshold value.

9. An apparatus as claimed in claim 2 , in which the comparison of non-linear characteristics is performed directly by extracting a non-linear characteristic based on forming a difference between the first voltage difference and the second voltage difference.

10. An apparatus as claimed in claim 2 , wherein the first and second testers are adapted such that the test signals applied to the groups of pins comprise discrete time samples of a sinusoidal or other waveform having little or zero low-order harmonic content and the testers are further adapted to use the measured voltage differences as discrete samples in reconstructing the response to a sinusoidal or other waveform having little ar zero harmonic content input for harmonic analysis.

11. An apparatus as claimed in claim 2 , further comprising a further test signal generator for generating a probe current which is injected via a further device connection into a selected integrated circuit, and wherein the continuity test is repeated and the selected integrated circuit is indicated as having an unacceptable connection if the nonlinear characteristic varies by more than a first predetermined threshold, or is indicated as having an acceptable connection if the non-linear characteristic varies by more than a second predetermined threshold of opposite sign to die first predetermined threshold.