The words PCB manufacturing and assembly are used regularly in casual discussion during the PCB process and production time but, they are two different mechanisms in the PCB industry. Both of these steps are essential steps in bringing a printed circuit board from the design phase to a functional electronic product. In one case PCB manufacturing involves the physical creation of the bare board itself and in the other case, PCB assembly talk about the process of attaching electronic components to the manufactured board which turns them into a fully functional device.
What is PCB Manufacturing?
PCB manufacturing is the process which involves the fabrication of the actual PCB. Here, the flat and layered board acts as the foundation for electronic components. This step during the process focuses on creating the physical structure that will house electrical pathways, known as traces and connecting points which are known as pads for the electronic components. For actual PCB fabrication, PCB manufacturing and assembly are inseparable.
Materials Used in PCB Manufacturing
One of the most commonly used materials in PCB manufacturing and assembly is FR4. It is a fibreglass-reinforced epoxy laminate which plays the role of an insulating core for the board. Materials like flexible polymers, ceramic substrates, or metal-core PCBs will be utilized in high-performance or specialized applications. The conductive layer will be typically made of copper which forms the circuitry of PCB. The copper layers are itched to create electrical pathways for the components depending on the design. At last, a solder mask and silkscreen layer are applied to protect the board and to label the places according to the location of the component. Material selection is important for PCB manufacturing and assembly so we need to pay attention to it.
PCB Manufacturing Process
The key steps involved in the PCB manufacturing process are given below.
- Design Translation: The PCB design is translated into a format that manufacturing machines can interpret, typically using Gerber files. These files contain all information regarding the layers, traces, pads, holes and any other feature of the board.
- Substrate Preparation: The process starts with the preparation of the core material for the board and this is coated with a layer of copper on both sides in the case of double-sided or multilayer boards.
- Copper Etching: Unwanted copper is removed from the board to create the desired circuitry pattern using a process called photoengraving or chemical etching. This process involves applying a photoresist to the copper surface and this will result in exposing the board to UV light through a stencil of the design and the excess copper will be etched away with a chemical solution.
- Holes Drilling: In the holes drilling step, precise holes are drilled in the board to create a vertical connection between layers and mounting points for through-hole components.
- Layer Stacking: Under high heat and pressure, multiple layers of etched copper and insulating substrate are laminated together. This process will provide us with a solid, multi-layer structure.
- Plating and Surface Finishing: The exposed copper pads and vias are plated with a thin layer of copper to make sure that the board is ready for soldering. The plating is done with materials which include tin, gold or silver to prevent oxidation as well. The surface finish will be HASL (Hot Air soldering Leveling) or ENGI (Electroless Nickel Immersion Gold) applied to the pads.
- Solder Mask and Silkscreen: The solder mask is used to insulate the board and avoid unintentional soldering bridges during assembly. The silkscreen, on the other hand, adds markings on the board to indicate where components should be placed. The silkscreen markings will be included with the reference, number and orientation of the components.
- Testing: The finalized PCBs will undergo electrical testing before it is shipped to the desired location. The testing methods will include flying probe testing and open or short circuit detection to ensure that the traces are connected correctly and that there are no short circuits present.
Purpose of PCB Manufacturing
The main purpose which PCB manufacturing serves is providing the foundation for the entire electronic assembly process. The process focuses entirely on building the structure and electrical pathways for the PCB without which the electronic components could not function together. The main result we can expect from PCB manufacturing and assembly is the bare board itself which is manufactured specifically to meet the design specifications.
What is PCB Assembly?
As mentioned above, PCB manufacturing and assembly are inseparable. The next step or procedure that we go through right after PCB manufacturing is the assembly of the board. In this step, the electronic components are mounted onto the naked board according to the Gerber file and turned into a functional circuit. The assembly of the board involves placing and soldering various components like resistors, capacitors, ICs and microprocessors, inductors, fuse, connectors etc. to the circuit.
Types of PCB Assembly
There are mainly two types of PCB assembly and manufacturing. This type is purely dependent on the type of components being used.
- Surface-Mount Technology (SMT): SMT is the most commonly used method in the latest PCB assembly and manufacturing. In this type of assembly, the components with small, flat leads are soldered directly to the surface of the printed circuit board without the necessity of drilled holes. The advantage of this PCB assembly and manufacturing methodology is that this will allow for a high density of components on both sides of the board which makes it ideal for compact and complex designs.
- Through-Hole Technology (THT): In through-hole PCB assembly and manufacturing, the components will have leads which pass through pre-drilled holes in the PCB and are soldered to pads on the opposite side when it is placed on the board. This method will be required by components which are comparatively large to mount like connectors, transformers, transistors etc. They are more outdated when compared to SMT but will provide a solid connection for the components with the board.
In many cases, PCBs use a combination of both SMT and THT components, depending on the design and performance requirements.
PCB Assembly Process
The PCB assembly and manufacturing process involves several steps:
- Solder Paste Application: We utilize the solder paste for the PCB assembly and manufacturing of surface-mount components and for that, a thin layer of solder paste is applied to the pads on the board. The application of paste is done using a stencil which is a thin film of the clear-cut SMT pads mirrored to it. The main purpose of the solder paste is to hold the tiny little components like resistors, capacitors, inductors etc. while assembling and to solder and form electrical connections for the components with the pad when they are melted using a hot air gun or heat plate machine.
- Pick and Place Machine: A pick and place machine is used in the PCB assembly and manufacturing process to place surface-mount components onto the board. These machines are highly accurate and can place thousands of components in a small amount of time. This is a highly advanced and time-saving process considered to normal pick and place method which we are still practicing in some industries.
- Reflow Soldering: Once the components are placed properly on the board, they then pass through a reflow oven. This oven will heat up the PCB to a level that the solder paste applied for soldering will melt down and then form some solid electrical connections between the components and the board. This PCB assembly and manufacturing process will enhance the SMT connection and make it stay in place.
- Through-Hole Component Placement: Here, the components are sometimes manually or automatically inserted into the drilled holes in the PCB board and the leads of these components are soldered there using either manual soldering (mainly used for prototypes or smaller unit production) or wave soldering (for bulk production).
- Quality Control: After assembly with the components, the PCB will undergo various inspections to ensure the quality of the component placement and solder joints. Various inspection methods for quality control of PCB assembly and manufacturing include automated optical inspection, X-ray inspection, manual visual inspection etc.
- Testing: The fully assembled PCB is tested based on factors which influence its functionality. In-circuit testing is a method used to ensure the board operations. This method will also make sure that there is no defect present in the assembled product like short or open circuit, incorrect placement of the components etc.
