Commercial PCB Production
From Prototype to Printed Circuit Board
Once a circuit design has been validated on a breadboard or stripboard prototype, the next step in commercial production is to manufacture a printed circuit board (PCB). A PCB replaces the hand-wired connections of a prototype with precise copper tracks that are reproduced identically on every board, reducing errors and enabling mass manufacture. The OCR specification covers two production methods — photo etching and CAM milling/routing — and three types of PCB: single-sided, double-sided, and flexible.
Photo Etching
Photo etching (also called the photochemical process or UV etching) uses ultraviolet light and a chemical etchant to transfer a track pattern onto a copper-clad board. The process has several distinct stages. First, the PCB layout is printed as a positive or negative image onto a transparent film (the photomask). Second, the copper-clad board — coated with a UV-sensitive layer called photoresist — is placed under the photomask and exposed to UV light. The effect of UV light depends on the photoresist type. Third, a developer removes the soluble areas, exposing the copper that will be etched while photoresist protects the intended tracks. Fourth, the board is immersed in an etchant solution — typically ferric chloride or ammonium persulphate — which dissolves all exposed copper, leaving only the copper beneath the protective resist. Fifth, the remaining photoresist is stripped away to reveal the finished copper tracks. Finally, holes are drilled for through-hole components. Photo etching produces very fine, accurate tracks and is the dominant method in commercial PCB production.
The five stages of photo etching are: (1) print photomask; (2) UV exposure — UV light changes the photoresist pattern; (3) develop — remove the soluble resist; (4) etch — dissolve unprotected copper in etchant chemical; (5) strip remaining resist to reveal copper tracks. Etchant chemicals are hazardous — proper safety precautions (gloves, goggles, neutralisation and disposal) are always required.
CAM Milling/Routing
CAM milling (Computer-Aided Manufacture milling or routing) uses a CNC (computer numerically controlled) machine fitted with a small cutting bit to physically remove copper from a copper-clad board. The PCB design file is sent directly to the milling machine, which follows the track outlines precisely, cutting away the copper between tracks so that only the desired conductive paths remain. The advantages of CAM milling are that no chemicals are required (making it safer and more environmentally friendly), it produces a board very quickly from a design file, and it is well-suited to school or workshop use for one-off prototype PCBs. The disadvantages are that the track resolution is coarser than photo etching (minimum track spacing is limited by the cutter size), and the process is slower and less cost-effective for large-volume production than photo etching.
Photo etching is favoured for commercial mass production because it can produce very fine tracks (important for densely packed components), is fast for large batches, and the same photomask can be reused to make hundreds of identical boards. CAM milling is favoured for low-quantity, rapid-prototyping situations — particularly in schools and small engineering workshops — because there are no hazardous chemicals involved, no need for a darkroom or UV exposure unit, and the board is ready almost immediately after the CNC program finishes. For an exam question comparing the two, always link your choice to the scale of production and the track resolution required.
Types of PCB: Single-Sided
A single-sided PCB has copper tracks on one side of the insulating board only. Components are mounted on the opposite (component) side and their leads pass through holes to be soldered to the tracks underneath. Single-sided boards are the simplest and cheapest to manufacture. They are suitable for circuits that are not very complex — where all the routing can be achieved without tracks needing to cross. Their limitation is that complex circuits cannot be routed on a single side without track crossovers, which are not possible without bridges or additional wiring.
Three PCB types: single-sided (copper one side — cheapest, suits simple circuits); double-sided (copper both sides — suits complex circuits, can use vias to connect layers); flexible (copper tracks on thin flexible substrate — suits wearables and curved enclosures, but more expensive and harder to manufacture).
Types of PCB: Double-Sided and Flexible
A double-sided PCB has copper tracks on both sides of the board. Connections between the two layers are made through small plated holes called vias. Double-sided boards greatly increase the routing density that can be achieved — complex circuits such as microcontroller development boards and motor controllers are typically double-sided. The manufacturing process is more involved (both sides must be etched and aligned precisely), and cost is higher than single-sided. A flexible PCB uses a thin, flexible polymer substrate rather than the rigid fibreglass (FR4) of standard boards, allowing the circuit to bend, fold, or conform to a curved surface. Flexible PCBs are used in products where space is very restricted or the board must flex during use — for example, inside a fold-up phone, a camera module, or a wearable health monitor. They are more expensive to manufacture than rigid boards and can be damaged by repeated sharp bending.
The choice of PCB type is driven by circuit complexity, product form factor, and budget. If the circuit is simple (such as a basic LED driver or a small sensor module) and cost is a priority, a single-sided PCB is appropriate. If the circuit is complex — many components, dense interconnections — a double-sided PCB allows the routing to be split between layers. If the product must fit inside a curved or flexible enclosure, or the circuit board itself must flex during use (such as a fitness tracker wristband), a flexible PCB is required despite its higher cost. In exam answers, always justify your chosen PCB type with a specific reason linked to the product scenario.