PCB is a printed circuit board that helps connect different electrical components. The board is a combination of laminated material, and the copper foil laid on a non-conductive substrate.
A PCB is the main part of any electronic device, so it has to be perfect. It should have functional components and microelectronics circuits to perform well. Development of PCB goes through different processes that you should know well. PCB manufacturing has 4 stages, including design, manufacturing, PCB assembly, and PCB testing.
First Stage- Design
PCB design involves different steps, such as schematic design, layout planning, the placement of the components, routing, and manufacturing files.
PCB schematic design: It is a blueprint of PC design that shows all PCB components with symbols. The schematic design is always according to the technical requirements of the user.
Layout planning: After the schematic design, you have to develop the layout of a PCB that includes physical components’ models, the shape of the PCB, and the structure of a PCB.
Placement of components: It involves planning the placement of various components. You decide on the PCB layers according to your requirements. The right placement of the components ensures a flawless board, decreasing the production cost.
First of all, the designer places the fixed components in the layout, including switches and connectors.
Then, the critical components are placed, such as memory chips, microprocessors, as well as power supplies.
Then the supporting components of the PCB are placed, like inductors, capacitors, and resistors.
In the end, the decoupling capacitors and terminating resistors are placed.
Routing: Once the components are placed, you have to connect all components through trace routing. There are four ways to do so, such as manual routing, auto-interactive routing, semi-automatic, and batch-auto routing. You can choose any method according to your Printed Circuit Board and budget.
Design: In this stage, you have to plan for the number of board layers, dimension of the board, and types of components. You can use a special app in this case, such as EDA or electronic design automation. The designer often adopts the SMT instead of a through-hole technology, depending on your requirements. Once the design is over, you can export the design files to CAD or Gerber format.
Preparation of manufacturing files: This is the last stage of design where the designer exports the Gerber files for manufacturing. The manufacturer needs these files to develop a printed circuit board.
Stage 2-Manufacturing of Circuit Board
Once the manufacturer receives all design drawings, he starts making PCB. It involves different stages as described below:
Design Imaging: The manufacturer uses a plotter to convert the PCB design files into films like they resemble the photo negatives of the schematic design. The printer uses black and clear inks for inner and outer layers. Copper traces and circuits are shown with black ink, whereas the non-conductive parts are shown with clear ink.
Printing of Inner Layers On Copper: It is the initial stage of PCB manufacturing. The engineer uses a substrate material to make a laminated board. Like, epoxy resin or fiberglass are common in this case. The design of the PCB is printed on the board, and then he pre-bonds copper on a board’s both sides. After that comes the etching of copper, and then the board is protected through a photo-sensitive film.
Ultraviolet Light: the manufacturer then exposes the resist-covered PCB to UV light to strengthen the photo-reactive material. Then the board is cleaned with an alkaline solution to get rid of unnecessary copper particles. The expert checks the board to remove any errors and then goes to the next stage. The main aim of UV blasting is to develop a PCB Board according to the schematic drawing.
Inner layer’s etching: copper’s inner layer needs chemical etching for removal. The process of photoresist prevents the essential copper from etching. The board size determines the amount of the solution and etching time which is less for small boards but more for large boards.
Some other manufacturing processes include:
· Alignment of layers
· Optical testing
· Layer pressing and lamination
· Plating of PCB
· Imaging of external layer
· Etching of external layer
· Solder mask
· Silk screening
· PCB finishing
· Quality testing
· Packaging of PCB
· Shipping of PCB
Stage 3-PCB Assembly
The assembly of a PCB involves four stages, such as soldering, placement of components, solder pasting, and testing. Let’s review them in detail.
Solder Pasting: It is like t-shirt screening, as it involves solder paste stenciling. The stencil is made of stainless steel and it’s very thin. You have to use the stencil to apply the paste in areas where different components will be installed. In this process, flux is used for melting the paste to help it bond to the PCB.
Placement of the Components: Once you are done with the solder paste, you need a pick and place the tool for the components. Generally, it is SMT or surface mount technology where components are placed on the PCB surface. Initially, it used to be a manual process and assemblers used tweezers to pick and place different components on the board. However, new technology has made this process automated due to robotics and it’s more precise and consistent.
Soldering of PCB: After the placement of components, you have to place the PCB on a conveyor belt to help a board move to a reflow oven that heats the board. The heating helps melt the solder paste, and bond the components on the board permanently. However, if the board has more components other than SMDs, it would need a through-hole insertion that involves more advanced soldering.
Testing of PCB Quality: Sometimes, the components are misplaced during reflow when the PCB is moving. This issue may cause a poor connection, or no connection at all, or the parts are not well-connected. So, you need to inspect the PCB to ensure a flawless function. A PCB can fail this test even if it passed other tests, and a failed PCB goes to scrap or you have to recycle it with all essential processes until you get a flawless circuit board.
Stage 4-PCB Testing
Manufacturers use different methods for PCB testing to ensure that it will function correctly. These methods include in-circuit, optical inspection, flying probe, turn-in, x-ray, and a functional test.
In-Circuit: It is also known as ICT, or you can call it the bed-of-nails inspection. In this method, PCB is pressed on the bed of probes. It is highly accurate because it checks all components of a PCB. You can also test the BGAs with this method. Moreover, it also tests the solder integrity of the bottom-terminated components.
However, this test is expensive and time-consuming. Moreover, it does not test the non-electrical parts and connectors.
AOI, Automated Optical Inspection: This testing method involves a visual inspection of the board. It is done with the help of HD cameras, LED lights, UV, and high-level infrared. The test is contact-free and helps check poor solder joints or missing parts. It also tests the smt assembly issues and it’s very accurate.
However, it only inspects the preprogrammed errors and can’t check defects regarding glue or sealing.
Flying Probe Test: It involves probes that help test the upper and lower surface of a PCB. This PCB testing method is cost-effective, consumes less time, is easy to do, and is compatible with many applications of PCB assembly. However, it is slower than other testing methods and not ideal for complex testing.
Burn-In Test: In this test, PCB is exposed to a high temperature to see if it works well. It ensures a lifetime product and enhances the brand because of an effective end product.
However, this test is costly and can affect a PCB by damaging its components. Moreover, it can be less reliable due to voltage scaling.
Inspecting Through X-Ray: It involves an x-ray machine that inspects a PCB. It thoroughly checks soldering which is hard to detect with AOI. The x-ray inspection is ideal for thick or multilayered PCBs. It also detects the voids or bubbles and can also check the components under a shield.
However, it needs expensive x-ray machines and can cause hazards in the workplace.
Functional Test of PCB: It involves functional testers that you connect to the edge connector. It creates an electronic environment for which a PCB is made. It inspects the functional errors and identifies the analog issues. It also checks issues with digital circuitry.
However, it is very costly and needs high-end tools, which are too expensive. It needs a proper understanding of the working atmosphere of the DUT.
The development of a PCB involves different processes, including design, printing, assembling, and testing. Each stage is further divided into different parts, and you have to understand all stages to create a flawless PCB.
The board is a combination of laminated material, and the copper foil laid on a non-conductive substrate. A PCB is the main part of any electronic device, so it has to be perfect.