  The adoption of 3D packaging technology necessitates the development of new
approaches to failure electronic device analysis. To that end, our team is
developing a tool called the quantum diamond microscope (QDM) that leverages an
ensemble of nitrogen vacancy (NV) centers in diamond, achieving vector magnetic
imaging with a wide field-of-view and high spatial resolution under ambient
conditions. Here, we present the QDM measurement of 2D current distributions in
an 8-nm flip chip IC and 3D current distributions in a multi-layer PCB.
Magnetic field emanations from the C4 bumps in the flip chip dominate the QDM
measurements, but these prove to be useful for image registration and can be
subtracted to resolve adjacent current traces in the die at the micron scale.
Vias in 3D ICs display only Bx and By magnetic fields due to their vertical
orientation and are difficult to detect with magnetometers that only measure
the Bz component (orthogonal to the IC surface). Using the multi-layer PCB, we
show that the QDM's ability to simultaneously measure Bx, By, and Bz is
advantageous for resolving magnetic fields from vias as current passes between
layers. We also show how spacing between conducting layers is determined by
magnetic field images and how it agrees with the design specifications of the
PCB. In our initial efforts to provide further z-depth information for current
sources in complex 3D circuits, we show how magnetic field images of individual
layers can be subtracted from the magnetic field image of the total structure.
This allows for isolation of signal layers and can be used to map embedded
current paths via solution of the 2D magnetic inverse. In addition, the paper
also discusses the use of neural networks to identify 2D current distributions
and its potential for analyzing 3D structures.
