HDI routing for a miniature flex PCB.

Miniature boards compress electrical, mechanical and manufacturing constraints into the same small area. Routing density cannot be considered separately from layer structure, return paths, component placement, thermal flow and the behaviour of flexible regions.

The internship focused on planning that system before detailed routing, so the stack-up and interconnect strategy supported the physical form rather than fighting it later.

The public scope includes multilayer stack-up planning, rules-driven HDI routing, blind and buried via use, miniature flexible PCB layout and thermal management decisions.

The central task was to keep these decisions connected. A via choice changes manufacturability and available routing channels; a flex transition changes mechanical and copper constraints; a thermal path can compete with signal or placement priorities.

I start by mapping the interfaces and the constraints that cannot move, then separate them from preferences that can be traded. Stack-up, reference planes and critical routes need to be coherent before local routing density is optimised.

Review is most useful when it tests the reasoning behind the layout: whether return paths remain credible, whether flex and rigid regions are treated differently, and whether thermal and assembly considerations are visible rather than deferred.

Miniaturisation is not simply the same circuit drawn smaller. It changes which physical effects dominate and makes communication between electrical, mechanical and manufacturing decisions more important.

The lasting lesson is to treat layout as systems engineering. Geometry is the final expression of many earlier decisions, not a substitute for making them explicitly.