Have you been wondering about the foundation and manufacture of electronic devices? Do you know what an electronic device comprises? In our day-to-day activities, we often interact with different electronic appliances or devices such as televisions, laptops, mobile phones, smartwatches, refrigerators, and many others. However, many people are still not aware of how the appliances are manufactured. When manufacturing these electronic devices or appliances, technicians use printed circuit boards (PCBs). PCBs are simple circuit boards on which we mount different electronic components such as resistors, inductors, integrated circuits, transistors, and many others. These PCBs are assembled in special rooms with ample assembling equipment.
We will look at the assembly of these PCB assemblies in the PCB assembly house. It also becomes prudent to explore the different equipment present in this house.
What is PCB assembly?
Printed circuit board assembly (PCBA) is the process of mounting electronic apparatus onto bare boards. One can mount electronic components on a bare board through-hole or surface mount (SMT). We refer to an assembly with both ways of connection as a high mix printed circuit board.
What is a PCB assembly house?
A PCB assembly house is a facility where manufacturers assemble electronic components and PCBs. In these houses, you will find equipment for PCB assembly work, such as mounters, reflow ovens, printers, and others. It is easy to confuse a PCB assembly house with a PCB board house. The board house is a facility where experts carry out PCB fabrication. The method of manufacturing is according to their volume. We can classify PCB boards as either panel or PCB boards.
Equipment in the PCB assembly house
In the process of assembling PCBs, manufacturers employ the following nine equipment:
Manufacturers use the solder paste printing machine to apply the solder paste onto the PCB. Solder paste is a gray goo that sticks components to the bare board. It is a mixture of powdered metal alloys, say, tin, silver, and lead. Before applying the paste, they place a PCB stencil on the board. While applying the paste, they use the automated paste printer to hold the PCB and the PCB stencil in place. Then, in spreading the paste, the machine passes a blade across the stencil, depositing the paste in its place.
Solder Paste Inspection machine (SPI)
SPI machine contains cameras that can capture images in three dimensions. It, therefore, evaluates the alignment, amount, and thickness of the solder paste. These three factors talk more about the solder paste’s quality. Suppose there is an imperfect alignment or an improper solder volume, this machine senses and highlights the faulty areas. Consequently, the manufacturer addresses the issue early enough. We will therefore get high-quality PCBs.
Before placing the components, we use the glue dispensing machine to apply glue patches on the board. We later stick the components on these patched as they await soldering. Soldering the components even on both sides of the board is easier since the components cannot fall off.
This machine picks up a component and accurately places it on the solder paste on the bare board. Amazingly, this machine is very swift. It can place approximately 30,000 components within one hour. Furthermore, this machine is compatible even with the tiniest components.
Reflow soldering machine
Having placed all the required components like xilinx fpga on the board, we move them along a conveyor to an oven we call the reflow soldering machine. It melts the solder paste at keenly observed temperatures. As a result, the paste hardens uniformly and forms strong connections between the components and their particular pads. The machine has different temperature sets that enable it to dry the paste, preheat it, melt it, wet it, and cool it, ensuring that the components and the board are in good contact.
Wave soldering machine
In this machine, manufacturers set up a solder wave within a molten solder tank. Later, they pass PCBs over it so that the lower part of the board touches the solder wave and connects the components with their specific pads and holes. However, in current PCBs, manufacturers rarely use this machine. Instead, they go for reflow soldering due to their compatibility with finer surfaces that they use to manufacture PCBs.
Automated Optical Inspection machine (AOI)
Having assembled the PCB boards, what remains now is inspecting and testing them. Due to the complexity of the PCB boards, we must employ automatic inspection. We achieve this using the AOI machine, which detects faults early enough, giving the manufacturers a chance to rectify them before distribution. The AOI machine uses cameras with a high resolution to capture the board’s surface and keep this image for analysis. The machine later compares the image with that of a correct reference board.
In-Circuit Testing machine (ICT)
To test the functionality of the inner circuit, we use the bed of nails structure. The structure has an arrangement of spring-loaded pins that contact a single circuit node due to their arrangement. Manufacturers then press each PCB on this bed and easily test their electrical continuity or any short circuits.
Functional validation Test machine (FVT)
The FVT machine consists of connectors where we interface the PCB and investigate whether it works as expected. In this stage, this machine does not look for physical defects such as discontinuity. Instead, it loads the PCB with software that tests whether it works in its application areas. “Hot mock-ups” are the most popular functional tests that simulate the final product in which we use the PCB. No matter how you customize the FVT machine, it shares the common system’s components, hardware, and software.
We may have ample knowledge of using various electronic appliances and devices. However, this is not enough. It is important to understand the make-up of these devices and what lies behind their operation. We have realized that these electronic devices consist of assembled printed circuit boards (PCBs) that enable them to perform specific tasks. We have looked at what we mean by PCB assembly and where it happens. In the PCB assembly house, where this assembly happens, we have seen that many pieces of equipment perform different tasks during the preparation of the PCBs and the ultimate assembly process. For example, applying the solder paste on the bare boards, inspecting the quality of the printed solder paste, and dispensing of glue on areas where the components sit awaiting soldering.
Others are processes such as picking and placing the electric components on the bare board, reflow soldering, wave soldering, inspecting the assembled PCB, and testing whether the PCB works according to the design. Therefore, this article equips us with all we need to know about the PCB assembly house.