In this electrical era, every need depends on electronics. Each electronic has a PCB known as a Printed Circuit Board. This article will discuss the Printed Circuit Boards Assembly (PCBA) Process.
Every electronic equipment can see a green part holding many small components. This green plate is known as PCB. So, keep reading to learn the PCB assembly process in detail.
PCB Design Basics
In the PCB design, the basic unit is the base consisting of several layers. These layers play a role in the overall functioning of the PCB. However, we’ll discuss these layers further.
The substrate is the main rigid board on which various PCB components are scattered. This layer is made up of FR-4 material and provides overall firmness to the PCB.
- Copper Foil: It is the second layer that covers the top and bottom of the PCB as copper foil.
- Solder Mask: The third layer at the top and bottom of the PCB provides a non-conductive area and helps separate copper traces to avoid any short circuits.
- Silkscreen: We usually see white labeling on the PCB as C1, R1, or company logo. This white labeling is made of silkscreen.
Thus, these are the layers that are included in the PCB. Now, we’ll discuss the three primary types of PCB.
- A rigid PCB is a base covering most of the Printed Circuit Boards Assembly (PCBA) Process. However l, it is made up of few materials. These include FR-4, fiberglass, phenolics, or epoxies.
- Flexible PCB: These are made up of Kapton-like material. It can also tolerate high-temperature levels with a thickness of about 0.005 inches.
- Metal Core PCB: These are alternatives to rigid PCBs. It is made up of a metal core like Aluminium. However, it is very effective in dispersing heat.
Before the Assembly Process
Before starting the Printed Circuit Boards Assembly (PCBA) Process, there are some measures that you have to take. These primary steps assist the PCB assembly manufacturer in scanning overall functionality. Various PCB assembly companies need a design file with some additional requirements. Thus, the manufacturer can check the design file and work on any issues that can affect the functions of the PCB components.
Thus, it is the step for the DFM check of the PCB. The manufacturer scans the overall design for any missing features or errors within the DFM check. These errors can damage the functions of the PCB more or less depending on the issues.
Moreover, the PCB assembly begins after deep scanning for these issues or errors. The actual process starts when the manufacturer clears each issue, which you can see below.
PCBA Process Steps
Before the assembly process, the circuit board is called a prototype circuit board. The printed Circuit Boards Assembly (PCBA) Process is the solder paste application on the prototype circuit board and other components like resistors and capacitors.
Step 1: Solder Paste Stenciling
In the first step, the solder is applied to all the areas where you want to put the components on the PCB. The solder paste is applied on a stainless steel stencil. After this, a mechanical fixer put the stencil and PCB together. This job is done with the help of an applicator.
Now, the applicator applies the solder paste evenly on the PCB so that all the targeted areas are filled with the paste. However, the solder paste comprises 96.5% tin, 3% silver, and 0.5% copper. Moreover, the lead is not included in it.
Step 2: Pick and Place
After spreading the soldered place, the next step is to put the components on the PCB with the help of a pick-and-place machine. To do so, the PCB assembly manufacturer inputs the design file into the device. By scanning the design file, the machine picks and places the components at the exact location.
When these machines are not introduced, it is done by expert technicians very carefully. As a result, the technician faced eyesight issues and a high level of fatigue along with the slowed process.
Thus, it made the process more threatening to the errors. However, with the advent of these machines, PCB assembly is now accurate and convenient. Moreover, these machines can work 24/7.
Step 3: Reflow Soldering
After placing the components and the solder paste on the PCB board, the next step is reflow soldering. It is a process in which the PCBs and the components are put on the conveyor belt that moves them in the oven and creates a 250°C temperature.
Thus, this temperature is enough to melt the solder paste. This melting will help the PCB to adjust all the components and make joints. After this, it went to the coolers, where these joints would be cooled in a controlled manner.
Thus, this cooling will create permanent joints between the components and the PCB. However, if the PCB is two-sided, the other side will be treated similarly after this process. But the side which will be treated first is the one with fewer components.
Step 4: Inspection and Quality Control
After the reflow soldering process, there is a need for some inspection. Because of the movement, the small components on the PCB may cause some flaws, which have to be removed with some inspection. A PCB assembly manufacturer can do three types of reviews at this stage.
- Manual Inspection: Manual inspection is not feasible because of the small components. It will be hard for the technicians to work at such a trim level. However, it will be applicable if the board has THT features.
- Optical Inspection: This method is feasible for a large volume of PCBs. Various high-quality cameras are installed in a machine that views the joints from each direction. However, this inspection will take a short time because of its accurate and fast work.
- X-ray Inspection: This inspection is done to see the inner layer defects. It required technicians to analyze if there was any fault or issue in the inner layer. If the scanning is not done correctly, it may cause faulty PCBs.
Step 5: Through-Hole Component Insertion
At the 5th step of PCB assembly, Through-Hole component insertion is done. These components are also known as Plated Through Holes. These components will pass through the holes in the PCB. Each hole is connected to the other spot via the copper traces.
When these components are inserted in the holes, an electrical network of the holes and the components will be made.
Step 6: Final Inspection and Functional Test
After completing all the steps mentioned above, the final thing to do is inspect the functional test. The available test will give the electrical signals to check the output and specific connectors.
For this, there is a need for some lab instruments like a DMM function generator, Oscilloscope. This testing is essential to check if there is still any fault, issue, or error.
Thru-Hole Technology (THT) Assembly Process
The components containing leads coming out and inserted in the small holes of PCB is called Thru-Hole Technology Assembly Process. To accomplish this, there is a need to collaborate on manual and automatic procedures.
- Placement Of Components: This step requires manual handling by engineers. The engineers quickly place the components in the targeted locations per the design file. However, to have precise results, this placement should be done per the regulations of this process.
- Inspection And Rectification: After placing all the components, the circuit board is placed in a matching transport frame to scan the accuracy of the components’ placement. Thus, it will be easy to rectify the issues.
- Wave Soldering: At the end, these components are soldered with the help of waves. The board will slowly move from the waves of high temperature of about 500°F. After this, all the details are firmly attached to the board.
Surface Mount Technology (SMT) Assembly Process
In the Surface Mount Technology Assembly Process, all the steps are automatic compared to the previous process.
- Solder Paste Printing: The components are mounted on the board with the help of solder paste printing. A template is used for the accurate placement of the solder paste. However, the quality products are inspected with the help of a solder paste inspector.
- Mounting Components: After the solder paste printing, it is sent to the pick and place machine where the components are mounted.
- Reflow Soldering: After mounting the components, the board is passed through an oven with a temperature of about 500°F. It will cause the details to attach firmly to the board.
Conclusion
After completing the Printed Circuit Boards Assembly (PCBA) Process, all the products are delivered to the targeted locations. During all these steps, all the employees work hard and examine each step accurately to avoid any fault. The work is done so precisely that the products are made to satisfy the customers.