A printed circuit board is a laminated stack that couples copper foil to dielectric layers so electronic components connect, power, and shed heat with predictable behavior. The practical answer to what PCB is, is copper, FR-4 or polyimide substrate material with glass fibers, solder mask, a silkscreen layer, plated vias, and a surface finish for dependable soldering.
| Layer or material | Typical spec | Primary role | Where it appears |
| Copper layer | 12–70 µm, ED or RA | Routes signals and power as copper traces | Outer layers, inner layers |
| Core or prepreg | FR-4, polyimide, PTFE; Dk 2.9–4.3 | Insulating material with controlled dielectric constant and thermal conductivity | Stack backbone |
| Plated vias | 20–25 µm Cu | Interconnect through holes drilled | Multilayer builds |
| Solder mask | LPI, 10–25 µm | Protection, solder dams, AOI contrast | Over copper features |
| Silkscreen | Epoxy ink | Reference marks for assembly and rework | Board legend |
What are circuit boards and multi-layer stack-ups?
Circuit boards are engineered laminates that place materials so signals meet electrical targets while parts gain mechanical support. A multi layer stack-up defines layer order, thickness, and copper weights for impedance, loss, and thermal expansion control. For accelerated DFM and stack selection, evaluate PCB design services offered by Conclusive when planning stack-ups that must work on the first spin.
What is copper foil and what does it control?
Copper foil is the conductive skin that governs current capacity, high-speed loss, and EMI, with profile and copper thickness setting performance on each layer of copper. Teams without internal bandwidth often ask “what is software outsourcing?” since layout, embedded code, and test automation tend to move together from prototype to bring-up.
What are the main dielectrics and how do they differ?
FR-4, polyimide, and PTFE differ on dielectric constant, loss, Tg, Td, moisture uptake, and CAF resistance, which shape reliability at high temperatures. FR-4 suits most digital work, polyimide tolerates extreme heat and long reflow cycles, and PTFE or hydrocarbon-ceramic blends serve high frequency applications that need low loss and stable permittivity.
What is a flex board made of?
A flex board uses polyimide cores with adhesiveless copper, coverlays instead of solder mask, and localized stiffeners. Rigid flex architectures join bendable sections to rigid islands so connectors and dense components survive motion across multiple layers.
What are solder mask, legend, and surface finishes?
Solder mask preserves insulation resistance, prevents bridges, and boosts automated optical inspection contrast, while the silkscreen layer speeds placement for integrated circuits and passive components. ENIG favors fine-pitch BGA work, immersion silver suits RF paths, OSP stays simple, and lead-free HASL wets well with less planarity.
What is the manufacturing process that ties materials together?
PCB manufacturing sequences lamination, drill, desmear, through-hole plating, LDI imaging, etch, mask, finish, electrical test, and final inspection. Stack choices set drill aspect ratio, plating targets, and yield for single-sided, double-sided, and complex layer boards.
Material selection checklist
- Dk and Df window plus copper profile for bandwidth and loss
- Tg, Td, and z-CTE for via life through reflow
- Trace geometry and conductive layers for current, EMI, and density
- Finish choice versus pitch, RF loss, and shelf life
- Mask color and thickness for AOI across outer and inner layers
- Via strategy and aspect ratio for yield at volume
Most Asked Questions
Is PCB made of plastic?
No – A PCB uses a glass-fiber reinforced epoxy base (FR-4) with laminated copper; plastics appear as epoxy resin and solder mask rather than a standalone sheet.
Are PCBs fiberglass?
No – They use fiberglass cloth embedded in epoxy to form the substrate, while the working layers are copper.
What does a PCB contain?
A PCB contains copper layers and plated vias bonded to a fiberglass-epoxy substrate, plus solder mask, silkscreen, and a surface finish like ENIG, immersion silver, OSP, or lead-free HASL.
What material are PCB traces made of?
PCB traces are made of copper, typically electrodeposited or rolled-annealed, with thickness from 12–70 µm based on current and impedance targets.
