Thermal analysis and measurements of spiral inductors using built-in and IR sensors

The aim of this paper is to present and compare a contact and a contactless method of rapid thermal characterisation of spiral inductors. A series of spiral inductors of different geometries were fabricated on FR4 PCB and aluminium based MCPCB substrates of different thickness. Next their thermal characteristics were measured using a JESD51-1 compliant contact method implemented in the T3STER tester. The same measurements were repeated using a contactless approach, with a thermographic camera. Next, the results obtained with both methods were compared, showing the advantages and drawbacks of each method. Spiral inductors are widely used for different applications, at different circuit levels, integrated on chip, on PCB or in ceramic packages. Because of their relatively large sizes compared to neighbouring elements, they are becoming a source of non-negligible interferences - both electromagnetic and thermal - especially if used as part of power circuits. Knowing that the principal causes of electronic system failures are namely dust (6%), humidity (19%), vibration (20%) and temperature (55%) - the last of those factors being clearly dominant - it is obvious that it has to be taken into account in the design process. Because of specific spiral inductors geometry, whit three to four orders off magnitude difference when comparing their thickness to external length or width, spiral simulations are numerically ill-conditioned and very time consuming, especially if full 3D calculations are required. One of the solutions of this problem consist in rapid prototyping and direct thermal characterization of structures containing spirals, based on their thermal response