This comprehensive guide explores PCB fundamentals, from basic single-layer boards to advanced HDI designs, covering key materials like FR-4, aluminum, and ceramic substrates. We detail the complete manufacturing workflow, essential certifications (UL, ISO 9001/14001, IATF 16949), and diverse applications in consumer electronics, 5G networks, automotive systems, and aerospace. The article highlights technical specifications, industry standards, and emerging trends like flexible circuits and high-density interconnects, providing engineers and procurement professionals with critical insights for PCB selection and implementation.