Scanning method for screening of electronic devices

1. A method, comprising:

applying a stimulus waveform, using a signal generator, at least between two pins of a circuit;

applying a probe to a grid of multiple grid points, wherein each grid point is a spot on the circuit;

monitoring an electrical output produced by the circuit in response to the stimulus waveform for each of multiple grid points where the probe is applied;

performing a power spectrum analysis (PSA), to produce a power spectrum amplitude in each of one or more frequency bins, on the monitored output for each of the multiple grid points;

deriving a respective pixel value from the PSA for each of the multiple grid points;

constructing an image from the pixel values; and

displaying the image.

2. The method of claim 1 , wherein:

the probe is a beam of electromagnetic radiation, an electron beam, or an ion beam,

applying the probe comprises impinging the beam onto the circuit, and

the output is monitored at least on two pins of the circuit.

3. The method of claim 2 , wherein the probe is a beam of infrared, visible, or ultraviolet light.

4. The method of claim 2 , wherein:

the method further comprises selecting a frequency bin for the PSA, and

the respective pixel values are derived from power-spectrum amplitudes in the selected frequency bin.

5. The method of claim 2 , wherein:

the method further comprises performing a PSA on the monitored output without applying the probe, so as to obtain a dark PSA amplitude in each of the one or more frequency bins;

the respective pixel value for each of the multiple grid points is derived from a power-spectrum amplitude produced by the PSA in each of the one or more frequency bins; and

for each of the multiple grid points, the power-spectrum amplitude produced by the PSA in each of the one or more frequency bins is normalized to the dark PSA amplitude in a respective one of the one or more frequency bins before said power spectrum amplitude is used to derive a respective pixel value.

6. The method of claim 1 , wherein:

at each of the multiple grid points, the PSA is performed over a plurality of frequency bins, thereby to produce a vector of power spectrum amplitudes;

the method further comprises performing a principal component analysis (PCA) on the vectors of power spectrum amplitudes, thereby to identify one or more principal components, wherein each of said one or more principal components can be assigned a principal component weight;

the method further comprises mapping each said vector to an n-tuple of principal component weights, wherein n equals 1, 2, 3, or 4; and

the respective pixel values are derived from the n-tuples.

7. The method of claim 6 , wherein n=1 and the pixel values are displayed as gray-scale values.

8. The method of claim 6 , wherein n=3 and the pixel values are displayed as color values.

9. The method of claim 6 , wherein n=4, and the pixel values are displayed as a combination of color values and height values in a three-dimensional representation.

10. The method of claim 6 , wherein:

the PCA is performed so as to identify the n principal components that maximally account for variability in the vectors over the multiplicity of grid points; and

the mapping of each said vector to an n-tuple of principal component weights is carried out such that at least one of the principal component weights in the mapped n-tuple is a weight for one of the n principal components that maximally account for variability in the vectors over the multiplicity of grid points.

11. The method of claim 10 , wherein before performing the PCA, the vectors of power spectrum amplitudes at the respective grid points are normalized relative to a response of the circuit to the stimulus waveform absent application of the probe.

12. The method of claim 1 , wherein the stimulus waveform is periodic.

13. The method of claim 1 , wherein the stimulus waveform is non-periodic.

14. The method of claim 1 , wherein the stimulus waveform is applied as an on-normal stimulus.

15. The method of claim 1 , wherein the stimulus waveform is applied as an off-normal stimulus.

16. The method of claim 1 , wherein the grid points correspond to locations on an integrated circuit that is scanned by the probe.

17. The method of claim 1 , wherein at least some of the grid points correspond to discrete circuit elements on a circuit board that is scanned by the probe.

18. The method of claim 1 , further comprising making a disposition of the circuit based on the displayed image.

19. A method, comprising:

applying a stimulus waveform, using a signal generator, at least between two pins of a circuit;

applying a probe to a grid of multiple grid points, wherein each grid point is a spot on the circuit;

monitoring a radio-frequency output produced by the circuit in response to the stimulus waveform for each of multiple grid points where the probe is applied;

performing a power spectrum analysis (PSA), to produce a power spectrum amplitude in each of one or more frequency bins, on the monitored output for each of the multiple grid points;

deriving a respective pixel value from the PSA for each of the multiple grid points;

constructing an image from the pixel values; and

displaying the image,

wherein the probe is used to sense the output produced by the circuit in response to the stimulus waveform, and wherein the monitoring of the circuit output comprises monitoring a signal from the probe.

20. The method of claim 19 , wherein the probe is a radio-frequency antenna.