Printed Circuit Boards are made to provide support and connection between electronic components. PCB board, itself made from non-conductive material to isolate each component from the other, only connects those which are supposed to be part of the board by conductive traces of copper. In such a way, PCBs become the foundation of almost all electronic devices. This guide covers all the basic aspects of PCB manufacturing including design, manufacturing process, cost, equipment, etc.
What is PCB Manufacturing?
The PCB manufacturing is systematically complicated, which includes designing, testing, assembly and inspection. The PCB manufacturing process begins with schematic design done. Subsequently, the PCB manufacturers begin to turn the virtual PCB board design into a physical PCB board. Typically, PCB manufacturing pursues mass production, producing standard PCBs. However, most of the time, custom PCB manufacturing still has a strong place in electronic industry because those specialized boards are able to meet different electrical and mechanical requirements.
PCB Manufacturing Process Steps
A lot of processes are performed to fabricate PCB. Each step requires different specialized tools and operation rules but aims to build interconnected electrical structures with accuracy, precision, and without any flaws.
To have well-functional, optimized, and improved PCBs, designers need to understand all steps of PCB manufacturing so they can collaborate effectively and efficiently with fabricators to have state-of-the-art finished PCBs with minimal flaws.
- Before PCB manufacturing, the manufacturer required PCB design files in Gerber format. Once finished PCB designing, after creating an electronic circuitry schematic, one can export a Gerber file using software tools like Altium Designer and Ki-Cad.
- First step in PCB manufacturing involves preparing the raw materials such as laminate material, copper foil, plating material, and solder mask ink. There are different kinds of laminate materials like FR-4, Polyimide, PTFE, and Ceramic-filled PTFE. PCB laminate is considered as the backbone of PCB board, as it provides the foundation and board-like shape. Copper film is used to make conductive traces and layers of PCB, as PCB laminate is non-conductive. Plating solutions are merely electroplating baths namely copper plating solution, Tin-lead plating, and nickel or gold plating.
- After the preparation of raw materials, laminate material undergoes a cleaning procedure, which results in the removal of oil and debris.
- Applying photoresist to a copper surface is the next step in custom PCB manufacturing. This can be done with different methods like spin coating, electrodeposition, and roller coating. This photoresist coating is of two types, dry film coating and liquid coating. Dry film coating is like a sticker application while the liquid coating is more complex and provides more resolution. After coating, the board is exposed to ultraviolet light which hardens the part of the PCB with resist and dissolves the unexposed parts. Till this point, the PCB circuit layout is transferred on a copper surface.
- The next step involves etching away exposed copper with no resist using some chemical bath. Once this etching is done, the PCB layout design with isolated copper is obtained by stripping away the remaining photoresist using another solvent.
- Before lamination, automated optical inspection (AOI) is done to detect any defect in inner layers. After testing, accepted inner layers are laminated by stacking each layer with desired conductive traces and passing them under high pressure and temperature to create bondage among them. Lamination requires a controlled environment and care like controlled temperature, pressure, and ramp rates.
- In the next step of PCB manufacturing, holes are drilled. Generally, this is done mechanically by using drilling machines. Different types of machines and technologies are used for different kinds of holes. Plasma technology is used for buried vias and blind vias.
- Drilled holes must be conductive and for that, a thin layer of electroless copper is used to make holes conductive for electrical signals. Metals like palladium can also be used for this purpose.
- After processing the inner layers, the outer layer of the PCB undergoes a similar set of processes as discussed above. Application of photoresist, exposure to UV, etching, and stripping away of remaining resist, and after that outer layer AOI is performed which ensures that outer layer of PCBs complies with the proposed design, and detects any extra copper residue on layers and also checks for any improper electrical connection.
- In the next step, here comes the application of solder mask and silkscreen. A solder mask is applied after cleaning the panel thoroughly, then with the help of UV light, extra solder mask is detected and removed. This mask also provides an extra layer of protection for copper traces from oxidation and corrosion. Silk screen is used to print important information on fabricated PCBs like corresponding value ratings, warning symbols, and logos.
- Depending on the customer’s budget and design requirements, the board undergoes conductive material plating like hard gold plating, immersion silver, lead-free HASL, immersion tin, and ENEPIG (electroless nickel electroless palladium immersion gold). Each plating material has its pros and cons and provides copper protection.
- At this point PCB is manufactured and proper coating and cured. Now comes the electrical testing. An electrically isolated circuit is being tested in this step. This electrical reliability test can be performed in different ways like the In-Circuit Test (ICT) and Flying Probe Test. Both tests are performed to check almost similar characteristics of PCB but in different manners. In the flying probe test, two moveable testing probes are used to test circuit continuity, resistance, impedance, and capacitance. This method is faster, more flexible, and more efficient than ICT.
Besides the electrical reliability test, there is another test named “bed of nails” to check the PCB’s physical strength against high pressure at different test points. To perform this test, high pressure is applied to several spring fixtures, which are attached to different test points on the PCB.
- In the last, a final quality inspection was performed to check if the PCB met the required standards. This inspection involves visual inspection, dimensional inspection, and X-ray inspection. In visual inspection, a trained technician examines the PCB visually and checks for the solder mask, plating errors, vias, and pad damage. Dimensional Inspection involves the verification of trace width, annular rings, hole diameters, and other dimensional-related aspects. While X-ray inspection is used to identify if there are any hidden flaws in the PCB, this inspection can also check for flaws in inner layers.
- After the final quality control, the final product is ready for packaging and delivery to the customer.
PCB Manufacturing Cost
It is crucial for us to understand the cost of making a PCB board before giving a quote. The price varies from one PCB manufacturer to another based on several factors. Please refer to the following main factors which affect the PCB manufacturing cost greatly.
PCBs are produced by many kinds of materials, such as FR-4, polyimide, ceramic, aluminium, copper-based, PTFE, and other reinforced ore hybrid materials. All these material costs are different and will affect the printed circuit board cost significantly.
One factor affecting PCB manufacturing cost is the number of layers. Compared with single-sided or double-sided boards, it spends much more time and money manufacturing multi-layer boards. As more layers are added to the board, more production steps are required in the PCB layer stack-up. And extra manufacturing cost occurs.
Surface finish is essential to protect the PCB board from oxidation and corrosion and extend the service life of the board. There is a wide range of surface finish options available, including HASL, lead-free HASL, immersion gold, ENIG, hard gold, immersion silver and so on. Different surface finishes require additional manufacturing processes and additional manufacturing costs.
Another factor that affects custom PCB manufacturing costs is the number of boards. When it comes to low-volume PCB assembly, it is costly but suitable for prototyping. As for high-volume PCB assembly, the price is much cheaper because mass production is cost-effective. The cost per board is lower.
PCB Manufacturing Equipment
As we all know, PCB manufacturing is a complex task. There are many steps from base material cutting to final testing. Some basic equipment related to PCB manufacturing is as follows:
- drilling machine (mechanical and laser)
- etching equipment (chemical and plasma)
- plating machine (electroless, electroplating)
- exposure and developing equipment
- automated optical inspection (AOI) equipment
- E-testing machine
- flying probe tester
- solder paste printing machine
- automatic pick and place machine
- reflow soldering oven
- all kinds of testing equipment
All in all, I think you may have a basic understanding of PCB manufacturing after reading this article, such as what is PCB manufacturing, PCB manufacturing processes, the cost of PCB manufacturing, and the equipment used in PCB manufacturing. However, it would be better to visit some professional PCB manufacturing companies.