2.1 The Bedrock – Substrates and Stackups

The Printed Circuit Board (PCB) is not merely a carrier for components; it is a precision-engineered structural element. Just as a skyscraper relies on its foundation, the reliability of an electronic device depends on the physical properties of its substrate. Failure at this level is catastrophic, often requiring the scrapping of the entire unit.

FR4: The Reinforced Concrete

The industry standard substrate is FR4 (Flame Retardant type 4).

• Composition: A composite material consisting of woven fiberglass cloth (providing tensile strength) impregnated with an epoxy resin binder (providing rigidity).
• Thermal Stability (Tg): The "Glass Transition Temperature" is the point where the rigid board becomes soft and rubbery. High-performance electronics require High-Tg materials (>170°C) to withstand the intense heat of lead-free soldering without warping or delaminating.

The Vertical City: Multilayer Stackups

A PCB is built in layers, similar to a multi-story building.

• The Core: The central rigid layer, typically thick FR4 with copper on both sides.
• Prepreg: Sheets of "uncured" fiberglass and resin placed between copper layers. During the lamination press process, the resin melts and glues the layers together into a solid block.
• Cost Implication: Each additional pair of layers adds a lamination cycle, increasing manufacturing time and yield risk. An 8-layer board is exponentially more complex to align and press than a 4-layer board, driving up the bare board cost.

Final Checklist