Multilayer PCB Thermo-Mechanical Analysis

An optical sensing system relied on a densely populated 10-layer PCB to hold a precision image sensor in tight alignment. Before any thermal or structural behaviour could be predicted, the board itself had to exist as an accurate 3D model — something no off-the-shelf CAD library could provide, since every copper layer, dielectric interface, via, and pin pattern was unique to this design.

The work centred on turning raw Gerber manufacturing data into a geometrically faithful CAD assembly, then finding a way to carry that complexity into a coupled thermal-structural FEM model without exceeding the computational limits imposed by hundreds of thousands of small, intricate features.

The PCB was rebuilt through a systematic Gerber-to-CAD workflow: each layer's manufacturing drawing was converted to 2D vector geometry, imported into parametric CAD, and extruded into a solid body. Vias and pin holes were cut through Boolean subtraction operations directly against the solid layers, and the ten copper layers were assembled with their dielectric prepreg interfaces into a single, fully detailed 3D model — ultimately a 400 MB STEP file capturing the complete geometric structure of the board, including its intricate via patterns and layer-to-layer interactions.

That level of geometric detail, while accurate, was too heavy to simulate directly once the optical sensor and surrounding components were added: repeated attempts at a fully detailed thermo-mechanical model ran into memory overload. Rather than compromise on the geometry, the modelling strategy was split in two: the detailed PCB assembly was used purely as a characterisation tool, meshed with over 830,000 shell and solid elements (S4R, S4, S3, and C3D8 element types) and linked layer-to-layer via tie constraints to capture how the real, heterogeneous stack-up behaves under a controlled thermal load.

From that detailed model's response to a known temperature differential, effective orthotropic properties were back-calculated for the board as a single homogenised solid — in-plane and through-thickness thermal expansion coefficients and elastic moduli that reproduce the detailed assembly's deformation behaviour without carrying its full mesh cost. This homogenisation step, verified by comparing the detailed and homogenised models' deformation response side by side, gave a PCB representation light enough to support full system-level simulation while preserving the accuracy the optical alignment requirements demanded.

Sensor-level material properties were derived separately from manufacturer datasheet data covering the silicon die, glass lid, ceramic package, and lid-attach epoxy, allowing the homogenised PCB and the detailed sensor package to be combined into a single coupled thermo-mechanical model for the next phase of analysis.