A printed circuit board, or PCB, is the computer equivalent of a nervous system. It is the foundation on which tiny electronic components — the resistors, microchips, connectors, and capacitors — are attached. It is astoundingly complex, with some parts so minuscule that they can only be seen under a microscope.
Robotics is the heart of PCB manufacturing. No human being has the agility to place thousands of perfectly spaced, geometrically aligned wires into paper-thin layers of copper and insulation, but automation makes it all possible.
Benefits of robotics
Automated machinery has the following advantages over human workers:
- Speed: A rapid placement machine can install thousands of components on PCBs per hour. Robots are simply unmatched when it comes to working speed.
- Dexterity: Because some electronic components are so minute, specialized machinery is required to solder them onto a printed circuit board. Machines can also print tiny letters and markings on a PCB to show where the components will be placed. Without robots, computers would never be small enough to fit in people’s pockets.
- Inexhaustibility: Machinery can work tirelessly without breaks. Unlike people, machines don’t get sick, get distracted by emotions, or suffer from boredom even after hours of repetition.
- Safety: Sealants, adhesives, and soldering equipment can pose health and safety risks to human workers. Using robotics to do the job prevents workplace accidents.
- Visibility: X-ray machines can detect soldering defects such as excess solder application, open circuits, solder bridges, and voids. They can also see component issues as well as CSP and BGA defects. This machinery can inspect multiple boards at once, allowing product lines to be deployed in minutes.
- Accuracy: Accurate optical inspection (AOI) can point out near-microscopic defects that would be difficult to see with the naked eye. An AOI camera uses photogrammetry to calculate the height of different components on a printed circuit board. It also uses software to detect parts that aren’t contacting the PCB. Consequently, AOI can catch flaws like uneven soldering, tombstones, and tilted or missing components.
- Consistency: Machinery can replicate the same results repeatedly. Pick-and-place robots can continuously move products from one location to another. Laser marking machines print a unique serial number on each PCB to make them traceable. Every part of the PCB manufacturing process is highly repetitive, but the devices make it consistent.
All these qualities make automated machinery an essential part of PCB manufacturing.
How PCB manufacturing uses automation
A PCB allows all the components to communicate with the system on a chip (SOC) and other microchips via hundreds of copper wires. It’s made up of several conductive layers.
The top and bottom layers are used for mounting components. They feature a coat of solder mask — usually blue or green — to provide insulation while keeping mounting pads for parts accessible.
There is also a power plane and ground plane inside the PCB. The remaining copper layers carry all the communication traces or signal wires. Epoxy resin and insulating fiberglass are between these layers to prevent electricity flow.
Automatic machinery is the obvious choice when putting all these tiny pieces together. Here are the steps of the manufacturing process that rely on robotics:
1. Imaging and Develop/Etch/Strip (DES)
After people design the PCB, review it and print it out, it’s time to start making the board. First, laser-direct imaging gets to work on the panels. A machine develops the dry film and etches any exposed panel copper. It then strips the remaining dry film so the copper pattern stays behind, which will become part of the inner layers.
2. Automated Optical Inspection (AOI)
This process only applies to multilayer PCBs. AOI inspects the layers of a multilayer board before laminating them together. It does this by comparing the PCB design data to the image it’s viewing on the panel. This process is important since it allows manufacturers to notice and correct defects. For example, the AOI might detect pinholes or tiny cuts in the etched pattern.
3. Chemical Treatment
An oxide chemical treats the inner layers of multilayer PCBs before they are laminated. This increases the roughness of clad copper, which will improve the bond strength of the laminate. It helps prevent the layers from separating at the manufacturing process’s end.
The numerous layers in a multilayer PCB have to be bound together. A hydraulic press uses high temperatures and pressure to bond the conductive core materials with alternating layers of epoxy-infused fiberglass sheets, causing them to fuse. After cooling, multilayer and double-sided PCB manufacturing will follow the same process.
Drilled holes are an important component of PCB designs. They’re used for mounting the PCB in its housing and attaching parts.
They also link two or more layers by allowing copper wires to pass vertically through the board. This process is called vertical interconnect access (VIA). There are three types of VIA holes:
- Through hole: This connects all layers of the PCB.
- Blind VIA: This type of hole connects a top or bottom layer to a middle layer.
- Buried VIA: A buried VIA connects internal layers. It’s the only type of hole that isn’t connected to the top or bottom part of the board.
Advanced precision drilling systems make these precise holes. They employ solid carbide cutting tools that are specifically designed for use on PCBs.
6. Electroless Copper Deposition
The electroless plating process involves chemically depositing a thin layer of copper on all the exposed surfaces of the PCB. The walls of the holes are also coated, allowing them to be electroplated. The copper coating is incredibly thin —between 80 to 100 millionths of an inch thick.
7. Dry Film Outer Layer
A laminator machine coats the outer layers of the copper panel with dry film. Then, laser direct imaging exposes it. This exposed film stays behind while the unexposed film is developed.
This process prepares the panel for electroplating.
During electroplating, a machine plates copper onto the PCB’s hole walls and the conductive pattern. This step ensures the circuitry’s design requirements are met.
The PCB is connected to a cathode bar. Then, a copper plating bath uses a DC power supply to apply current, which deposits copper plating onto the board. Next, the PCB enters a tin plating bath which deposits a coating onto it. This will become the etch barrier for the next step in the PCB manufacturing process.
9. Stripping and Etching
A machine strips the board of the resist, and the exposed copper that isn’t covered by tin is etched away. Next, the machine chemically strips the remaining tin that covers the holes and traces.
10. Applying Solder Mask and Legend
A machine applies a liquid photo imageable (LPI) solder mask to protect the copper surface. This photosensitive, epoxy-based resist completely covers the panel, which undergoes a tack-cure cycle.
A film tool or laser-direct imaging exposes the panel to a UV light source. This process removes all unexposed solder masks. An oven bakes it to ensure the solder mask hardens, cures and sticks to the board.
Next, a screen printing process applies the legend, which consists of letters or symbols that serve as reference points during the assembly process.
11. Applying Surface Finish
A machine applies the surface finish to the PCB via a chemical process. It prevents the remaining exposed copper from oxidizing.
12. Electrical Testing
Technicians move the PCB into a machine that tests its electrical conductivity. It uses multiple moving probes to touch different spots on the copper circuitry and send an electrical signal between them. This identifies short and open circuits.
A CNC machine routes each board out of the larger panel into the required size and shape. It also cuts slots and beveled edges.
Technicians and machines look over the final product to catch any errors before shipping it off. This is critical when evaluating PCBs used in flight control systems or medical devices.
Anyone who uses a smartphone has benefitted from the use of robotics. Although PCB manufacturing is technically possible without automation, it would be a slow, laborious process with little output. Machinery allows for speed, consistency, and extreme precision when making printed circuit boards smaller and more powerful. Thanks to robotics, the world is more connected than ever.