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Substrates, by definition, form the base of all electronic devices. Whether discussing silicon wafers for semiconductors, glass-and-epoxy materials in printed circuits, or the base of choice for interposers, all these materials function as substrates.
While other substrates have come and gone (polyimide paper, unreinforced PTFE, epoxied paper, and Bakelite for printed circuits, and germanium, selenium, and gallium arsenide for semiconductors), silicon (for semiconductors), and FR-4 (for printed circuits) have remained the de facto standards for the industry. These represent the majority of substrates in use over the past 25 years or more.
The industry seemed content with these substrate choices as long as Moore's Law held. But now, after years of relative stability in substrates across all aspects of the electronics industry, multiple simultaneous advances in materials are breaking through.
Moore’s Law No More, Now What?
With Moore’s Law having reached its practical limits in monolithic silicon, new approaches (heterogeneous integration, advanced packaging) and new substrate materials are in demand to keep the miniaturization momentum. For both semiconductors and PCBs (or interconnects), glass is one contender that may be far less complex than some of its predecessors.
Planarity is a key advantage of glass. Glass delivers such extreme planarity because, as an amorphous material, it has no underlying weave like FR-4. The glass fiber weave comes with localized unevenness and a tendency to deform under heat—traits that become even more apparent on traditional substrate materials as PCB feature sizes get significantly smaller and larger.
To continue reading this article, which originally appeared in the September 2025 issue of PCB007 Magazine, click here.
