PCB manufacturing is a fascinating process. From custom PCB design to fast market-ready production, MIS offers consignment or turnkey solutions to support every stage of PCB production.
In this article, we take an in-depth look at how it all works from a bare circuit board to a ready-to-use, functional PCB.
Table of Contents:
- Understanding the PCB manufacturing process
- The basic layers of a PCB
- Solder resist
- Designing a PCB
- DFM: Design for Manufacturability
- The 2 broad phases of the PCB manufacturing process
- A] PCB fabrication:
- Printing the design files
- Pre-bonding copper traces on the substrate
- Layer stacking & drilling of registration holes
- Chemical baths & outer layer imaging
- B] PCB assembly
- SMT or Surface Mount Technology
- Through-hole technology
- PCB testing
- Automated Optical Inspection (AOI)
- X-Ray tests
- In-circuit tests
- Flying probe
- Jtag boundary scan
- Packaging & delivery
- MIS: Your trusted partner in the PCB manufacturing process
Understanding the PCB manufacturing process
The ubiquitous printed circuit board (PCB) or the ‘chip’ as we call it, is a marvelous piece of engineering. Can you imagine that tiny electronic components soldered onto a green insulated board control how our smart electronic gadgets operate!
Assembling a PCB is a complex process involving three main stages: PCB design, manufacturing and testing. We go through these stages iteratively until we develop a PCB that functions as per the product designer or OEM’s specifications. But before we begin, let’s understand what the basic circuit board is made up of.
The circuit board is simply a flat sheet of insulating material with a layer of copper foil on which we install electric components in the assembly stage.
In its most basic form, the PCB consists of four layers heat-laminated together to create a single board.
- Substrate: The substrate is the basic layer that gives structure and sturdiness to the PCB and holds the components together, most commonly made of fibreglass or flexible materials like polymers.
- Copper: The copper layer is the most important as it acts as the conducting material to carry electric charge to and from various components attached to the board. Copper traces create tracks which perform the function of wires. Copper has high conductivity, which ensures that signals flow without losing electricity.
- Solder mask: The solder mask (or solder resist) provides insulation to the copper tracks from the solder, metallic parts, and other conductive parts. It forms a protective layer that ensures only those specific areas of the board are exposed to the solder.
- Silkscreen: This layer is used as a legend to indicate part numbers, settings, instructions for engineers and manufacturing teams. It uses a non-conductive epoxy ink in colours varying from yellow to white to black,
Designing a PCB
Creating high-performance electronic products starts with innovative circuit board design. OEMs, PCB designers or one-stop PCB service providers like MIS create customized design plans and layouts based on the functional requirements of the end product.
A DFM (Design For Manufacturing) review ascertains that the PCB design is fit for manufacturing. It eliminates unforeseen delays due to design issues that would require re-engineering and cuts down production costs.
The PCB layout and Gerber files are reviewed by the client and then sent for prototyping.
We first produce a lab PCB test unit and demonstrate to the client the feasibility of the design and its readiness for mass production. Next, the prototype is sent for PCB testing and verification. The design is then debugged and revised based on the test results. This iterative process ensures that there are no manufacturing issues once the PCB goes into mass production.
The 2 broad phases of the PCB manufacturing process
The PCB manufacturing process consists of 2 broad phases: Circuit board fabrication and PCB assembly. Let’s dive into each of these.
The PCB fabrication process starts once the design of the circuit board is approved after prototype production and testing.
PCB fabrication is usually a process that OEMs prefer to outsource to a contract manufacturer. These days, OEMs prefer to use an end-to-end PCB assembly services provider who handles all stages of the production process and delivers a ready-to-use, tested and functional PCB.
The PCB design files are printed on a plotter printer, in which the black ink signifies the traces and circuits of the PCB, and clear ink marks the non-conductive areas. For the outer layer of the PCB, the reverse pattern is followed (black ink areas are etched away). In this way, each layer of PCB and solder mask receives its own clear and black film sheet. Finally, the films are punched with a registration hole to keep them properly aligned.
This process maps out the copper trace pathways that will conduct charge to various components on the board.
The copper is pre-bonded on the substrate base of the board, and the solder mask prevents the copper from bonding to the non-conductive areas of the board.
For multi-layer boards, the separate layers are fused together using a bonding press computer which molds the layers together. Finally, holes are precision-drilled on the board. This is critical as the components must fit precisely into these holes during the assembly stage. A computerized drilling machine ensures that the holes are drilled exactly as per the original design file.
More chemical baths and outer layer imaging preps the board further. In the final etching stage, chemical solutions are applied to remove the excess copper. At the end of this complex process, the conductive areas of the board and the connections are distinctly seen.
Finally, the finished PCB is marked with a legend that gives engineers or manufacturers vital information about the board and its components. This process is called silkscreening and uses ink to make these marks.
During the assembly process, the electronic components are mounted to the bare board through a soldering process. It is a crucial step in the PCB assembly process as a soldering flaw can cause the end-product or device to malfunction or perform in an unintended way.
We can use different soldering techniques to attach electrical components to a PCB.
For mass production, we usually use Surface mount technology which involves soldering electronic components directly onto the surface of the PCB. This method is also amenable to automation. Pick-and-place machines can easily pick up electronic components and place them on the board. A solder paste stencil machine applies tiny amounts of solder paste onto the board. An inspection machine ensures that the right amount of solder paste is applied. Quality control at this stage of assembly is vital—if there’s too little or too much solder paste, defects or malfunction could result.
Once the components are placed, the board passes through a reflow oven which gradually increases the board’s temperature until the solder paste melts. As the board cools again, the solder material solidifies to create a strong bond between the solder material and the component, fixing it to the board.
We may use through-hole technology for prototyping or low-volume production. This technique requires drilling holes on the circuit board for components with ‘legs’ or wired leads. The wires or leads pass through the drilled hole. Although this technique works best for manually assembled PCBs, wave soldering machines are available if we need to produce higher volumes using this method.
Once soldering is complete, we test if all the components on the board function as per the original design. Modern PCB assembly and soldering factories have automated IoT devices that use test scripts. This process is much faster and more effective than manual electrical tests. We use five powerful tests to make sure the final PCB functions effectively:
- We have Automated Optical Inspection (AOI) machines that visually inspect the board for missing components, incorrect positioning of components, wrong parts, lead defects, solder integrity, and more.
- X-ray testing machines use high-resolution scans to screen assembled BGAs and large boards. They can detect short circuits, opens caused by insufficient reflow, doming or voids.
- In-circuit tests detect manufacturing process faults quickly and accurately, using an electrical probe to check whether the PCB was correctly fabricated.
- Flying Probe PCB testing is an electro-mechanical controlled probe that accesses components on a PCB assembly accurately and quickly.
- In the JTAG Boundary scan test, we use powerful PCB boundary scan hardware and software products such as ScanMaster & ScanManager.
PCB packaging and delivery are highly controlled aspects of PCB quality control practices. PCBs are fragile and need special packaging to protect them from damage during shipping, transportation, and storage.
In-transit damages can lead to heavy losses in terms of money and time lost in replacements. A single damaged consignment of circuit boards can affect the entire supply chain for the OEM.
At MIS, we use a combination of anti-static packaging material and anti-moisture desiccant bags, vacuum-sealed to protect against moisture. In addition, we add padding material to make the package shock-proof, so the PCBs inside are protected during handling and transportation.
Our final shipments also include a comprehensive set of PCB assembly documents, including Bill of Materials (BOM), PCB Gerber and CAD data, PCB schematics and fabrication drawing, test specs, quality specs, and regulatory requirements.
MIS: Your trusted partner in the PCB manufacturing process
Trust an experienced PCB manufacturer like MIS Electronics with your PCB design, manufacturing and assembly requirements. We provide high-quality components and advanced electronic component assembly solutions. And, because we’re a turnkey electronics manufacturer, we also have advanced testing capabilities backed by superior customer service.
MIS Electronics manages your entire PCB manufacturing process from custom design to shipping, with safe, reliable, and on-time delivery.
Get a free quote from MIS Electronics, your local Canadian one-stop PCB shop.