Everything you need to know about PCBs — types, multi-layer technology, blind and buried vias, step-by-step manufacturing, materials, and real-world applications — from India's specialist MLB manufacturer.
A printed circuit board (PCB) is a flat, rigid or flexible board that mechanically supports and electrically connects electronic components. Thin conductive pathways — called traces — are etched from copper sheets laminated onto a non-conductive substrate, typically FR4 (fiberglass-reinforced epoxy resin).
PCBs replaced earlier point-to-point wiring and made modern electronics possible. Every smartphone, satellite, automobile, medical device, and computer contains at least one printed circuit board. The board provides both the structural foundation and the electrical highways that allow components — resistors, capacitors, integrated circuits, connectors — to work together as a system.
The complexity of a PCB ranges from a simple single-layer board in a household appliance to a 22-layer multi-layer PCB inside a satellite transponder or defence radar system — the kind Fortran Cirkit Electronics manufactures.
PCBs are classified by their layer count, rigidity, and the materials used. Each type serves different performance, space, and reliability requirements.
One copper layer on one side of the substrate. Used in simple, low-cost electronics: calculators, LED lighting, power supplies.
Copper on both sides with plated through-holes (PTH) connecting them. Used in most consumer electronics, industrial controls, and automotive modules.
Three or more copper layers laminated together. Essential for aerospace, defence, telecom, and high-speed computing. Layer counts range from 4 to 22+.
Built on flexible polyimide film. Bends and folds for wearables, cameras, and medical implants where rigid boards cannot fit.
Combines rigid and flexible sections in one assembly. Reduces connector count and enables 3D packaging in space-constrained designs.
Aluminium or Copper-Invar-Copper core for superior heat dissipation. Used in high-power LED lighting, power electronics, and automotive systems.
Teflon (PTFE) or ceramic substrates for RF, microwave, and antenna applications. Maintains signal integrity at GHz frequencies.
High Density Interconnect boards with microvias, fine lines, and laser drilling. Used in smartphones, tablets, and advanced military electronics.
A multi-layer PCB (also called an MLB — multi-layered board) is a printed circuit board containing three or more conductive copper layers separated by insulating prepreg and core materials, bonded together under controlled heat and pressure in a lamination press.
While a simple double-sided board has two copper layers, a multi-layer board can have 4, 6, 8, 10, 12, 16, 18, 20, or even 22+ layers. The additional layers provide:
Multi-layer PCBs are the standard for demanding applications: satellite transponders, radar systems, avionics, 5G base stations, medical imaging equipment, and high-performance servers. Fortran Cirkit's production record is 22 layers, and we regularly fabricate 18 and 20 layer boards with blind and buried vias for defence programmes.
A via is a small plated hole that creates an electrical connection between different layers of a multi-layer PCB. The three main types of via determine how signals travel through the board's layer stack.
A through-hole via passes completely through the board from the top surface to the bottom. It is the simplest and most common type, drilled mechanically and then electroplated with copper. Through-hole vias are visible on both sides of the board.
A blind via connects an outer layer to one or more inner layers but does not pass through the entire board. It is visible from only one side — hence "blind." Blind vias are used when routing density is high and space on the opposite surface must remain available for other components or traces.
A buried via connects two or more inner layers only and is completely hidden within the board stack-up. It is not visible from either outer surface. Buried vias are manufactured by drilling and plating individual inner layer pairs before the final lamination, making them more complex and costly to produce.
Both blind and buried vias significantly increase the routing density and design freedom of a multi-layer PCB, which is why they are standard in military, aerospace, and high-performance applications. At Fortran Cirkit, we manufacture sophisticated 16 and 18 layer boards with both blind and buried vias for elite defence projects.
PCB manufacturing is a precision-driven, multi-stage process combining photolithography, electrochemistry, and CNC machining. Here is how a multi-layer PCB moves from design file to finished board.
The circuit layout (Gerber files) is verified, panelised, and prepared for manufacturing. Design rule checks ensure the layout meets production tolerances for trace width, spacing, hole sizes, and layer registration.
Copper-clad laminates are coated with photoresist, then exposed to UV light through a photomask (photo-tool) that transfers the circuit pattern. The exposed photoresist is developed, leaving the trace pattern protected.
Unprotected copper is chemically dissolved away, leaving only the designed copper traces and pads on the inner layers. The remaining photoresist is then stripped off.
Inner layers are inspected, then stacked with prepreg (pre-impregnated bonding sheets) in precise alignment using registration pins. The stack is bonded together in a lamination press under controlled temperature (typically 170–190°C) and pressure for several hours.
Through-holes and vias are drilled using Computer Numeric Control (CNC) drilling machines with carbide micro-drill bits. Hole diameters can be as small as 0.35 mm for precision applications. For blind vias, controlled-depth drilling or laser drilling is used.
The drilled board is chemically cleaned, then copper is electroplated into the holes and onto surfaces. This creates the electrical connections between layers. The plating process is followed by tin or tin-lead plating to protect the copper during outer layer etching.
The outer layers go through the same imaging and etching cycle as the inner layers — photoresist application, UV exposure, development, and copper etching — to create the final surface traces and pads.
A protective solder mask (typically green, though other colours are available) is applied and cured, leaving only the pads and test points exposed. Component reference designators and other markings are screen-printed as the legend (silkscreen) layer.
Exposed copper pads are coated with a surface finish to prevent oxidation and improve solderability. Common finishes include HASL (Hot Air Solder Levelling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).
Every board undergoes bare board electrical testing — checking for opens (broken connections) and shorts (unintended connections). Additional quality checks include visual inspection, impedance measurement, cross-section analysis, and compliance verification against IPC standards.
The choice of substrate material determines a PCB's electrical, thermal, and mechanical performance. Different applications demand different material systems.
The most widely used PCB substrate. FR4 is a glass-reinforced epoxy laminate with good mechanical strength, electrical insulation, and moisture resistance. Suitable for most general-purpose and many multi-layer applications. Standard Tg (glass transition temperature) is around 130–140°C, with high-Tg variants reaching 170°C+ for lead-free assembly.
A high-temperature substrate used for flexible PCBs and rigid boards that must withstand sustained thermal stress. Polyimide has a Tg above 250°C and excellent dimensional stability. Used in military, aerospace, and downhole drilling electronics.
Teflon-based substrates (Rogers, Taconic, Arlon) have very low dielectric constant and loss tangent, making them ideal for RF, microwave, and antenna applications operating at GHz frequencies. Fortran Cirkit manufactures Teflon boards and pioneering Teflon composite multilayers — combining Teflon, ceramic, and FR4 in a single stack-up.
Metal-core PCBs use an aluminium or Copper-Invar-Copper (CIC) base for superior thermal conductivity. The metal core efficiently draws heat away from power components. Used in high-power LED arrays, motor drives, power converters, and automotive electronics.
Ceramic substrates (alumina, aluminium nitride) offer exceptional thermal conductivity, high-frequency performance, and chemical resistance. Used in high-power RF modules, sensor packages, and extreme-environment electronics.
Multi-layer printed circuit boards are the backbone of systems where reliability, performance, and compactness are non-negotiable.
Satellite transponders, avionics, navigation systems, and space-grade communication modules. ISRO's INSAT series uses multi-layer PCBs from Fortran Cirkit.
Radar systems, electronic warfare, secure communications, and missile guidance. Boards must survive extreme shock, vibration, and temperature cycling.
5G base stations, optical transceivers, high-speed routers, and network switches require high-layer-count boards with controlled impedance.
MRI machines, CT scanners, patient monitors, pacemakers, and diagnostic instruments demand high-reliability multilayer boards.
Engine control units (ECUs), ADAS, infotainment systems, and EV battery management systems increasingly rely on multi-layer and metal-core PCBs.
Motor drives, PLCs, power inverters, and automation controllers use MLBs for noise immunity and compact power routing.
A printed circuit board (PCB) is a flat board made of insulating material — typically fiberglass-reinforced epoxy (FR4) — with thin copper traces etched onto its surface. These traces form the electrical pathways that connect electronic components such as resistors, capacitors, and integrated circuits. PCBs are the foundation of virtually every modern electronic device.
A multi-layer PCB is a circuit board containing three or more conductive copper layers separated by insulating material and bonded together under heat and pressure. Multi-layer PCBs (also called MLBs) allow far more complex circuits in a compact form factor. They are essential for aerospace, defence, telecommunications, and high-speed computing, with layer counts ranging from 4 to 22 or more.
A blind via connects an outer layer of a PCB to one or more inner layers, but does not pass through the entire board — it is visible from only one side. A buried via connects two or more inner layers and is not visible from either outer surface. Both types increase routing density and are used in high-reliability applications such as military and satellite electronics.
PCB manufacturing involves several key steps: (1) Design and CAM processing of the circuit layout, (2) Inner layer imaging — transferring the pattern onto copper-clad laminates using photolithography, (3) Etching to remove unwanted copper, (4) Layer alignment and lamination — bonding multiple layers under heat and pressure, (5) CNC drilling of through-holes and vias, (6) Electroplating to deposit copper in drilled holes and on surfaces, (7) Outer layer imaging and etching, (8) Solder mask application and legend printing, (9) Surface finishing (HASL, ENIG, OSP), and (10) Electrical testing and quality inspection.
The main types of PCB are: single-sided (one copper layer), double-sided (two copper layers with plated through-holes), multi-layer (3+ layers, used in complex electronics), flexible PCBs (built on polyimide film for bendable applications), rigid-flex PCBs (combining rigid and flexible sections), metal-core PCBs (with aluminium or copper core for thermal management), and high-frequency PCBs (using Teflon or ceramic substrates for RF/microwave applications).
Common PCB substrate materials include FR4 (fiberglass-epoxy, the most widely used), polyimide (for high-temperature and flexible boards), PTFE/Teflon (for high-frequency RF and microwave circuits), ceramic composites, and metal cores such as Copper-Invar-Copper or aluminium. The conductive traces are almost always copper, typically 1 oz (35 µm) or 2 oz (70 µm) thick.
Multi-layer PCBs are used across many industries including aerospace and satellites (ISRO, NASA), defence and military electronics, telecommunications and 5G infrastructure, medical devices (MRI machines, pacemakers), automotive electronics and electric vehicles, industrial automation, consumer electronics, and high-performance computing and data centres.
Fortran Cirkit Electronics, established in 1987 in Chennai, India, specialises in multi-layered PCBs up to 22 layers. Our specialities include blind and buried via MLBs, Teflon and Teflon composite multilayers, metal core boards, polyimide multilayers, edge-plated boards, flexi-rigid assemblies, and our proprietary AL-Back (Anodized Aluminium Bonding) technology. We serve ISRO, BEL, DRDO, HAL, and leading IITs.