Printed circuit board assembly has continued to be the core of all electronic devices. Without these boards, these devices will not exist. Electronics are part of our everyday lives. From the smallest devices to the largest devices, PCBs play a crucial role. Printed circuit boards are the small green board available in these devices.
However, there is a difference between a PCB and a PCBA. While PCB is a bare board without any components, PCBAs are PCBs featuring several electronic components. These boards are crucial for the development of electronic devices. Therefore, PCB assembly entails the process of mounting electronic components on a bare printed circuit board. We will be focusing on printed circuit board assembly in this article.
What is PCB Assembly?
A printed circuit board assembly is a circuit board that features electronic components required for the functionality of a board. Also, PCB assembly may refer to a process that involves mounting of necessary components on a board. A bare circuit board is useless without electronic components. The electronic components mounted on the bare board are responsible for the functioning of the PCBA.
Therefore, PCB assembly entails the placement of different components on a bare board to develop a functioning board. Also, the functioning board is referred to as PCBA. Printed circuit board assembly is the finished board that has all components soldered and installed. Component placement can be either done mechanically or manually.
Furthermore, a PCB board features conductive pathways which are further integrated with a non-conductive substrate to create the assembly. What creates a fully functioning electronic device is the placement of the electronic components. PCB assembly is a process that occurs during the development of electronic devices.
One can say, PCB assembly involves putting components together to create something functional. However, PCB assembly requires integrating the right technology. There are two major types of technologies integrated in PCB assembly. These are surface mount technology (SMT) and through hole technology (THT).
PCB assembly is totally different from circuit board manufacturing. PCB manufacturing involves processes like PCB prototype creating, PCB design, PCB layout, and more. On the hand, PCB assembly process involves the mounting of electronic components on a printed circuit board.
PCB Assembly Technologies
Surface Mount Technology
SMT Manufacturing is known as a method for mounting electronic components on a printed circuit board. It involves the placement of electronic components directly on a PCB surface with the help of automated machines. Surface mount technology integrates an automated process. Therefore, it is much faster than THT. Also, SMT began to gain popularity in the electronics industry in the 1980s after its advent in the 1960s.
This PCB assembly technology doesn’t involve the drilling of holes on a board. It simply picks and places electronic components on a PCB surface. Furthermore, SMT is a flexible and automated process that enables higher connection densities. Also, this assembly process enables assemblers to place complex circuits in very small components.
In addition, this PCB assembly technology enables the miniaturization of electronic devices. Surface mount devices (SMDs) are the electronic components placed on this board. SMDs don’t have leads, therefore, they are directly mounted on the PCB surface. Surface mount technology is crucial for advanced circuit boards.
Through Hole Technology
THT is a process that requires the drilling of holes in a circuit board. It is an older PCB assembly technology. Also, THT helps to create stronger connections between components. The THT process can be semi-automated or fully automated. Also, this PCB assembly technology involves inserting components through holes.
This PCB assembly process is an old concept; therefore, it is suitable for some certain scenarios. Also, this technology makes it easy to attach the details of a printed circuit board to the inner layers of circuit. Through hole technology is ideal for components exposed to mechanical stress. Furthermore, this PCB assembly technology is ideal for conducting prototyping and tests.
In the through hole technology, the assembler inserts wire elements in part. This process involves inserting pin through hole components via drilled holes. The assembler then affixes he leads to the pads on the other side. After this, soldering takes place. In THT, manual soldering or wave soldering is the ideal option. Soldering helps to keep the electronic components in place.
Mixed Technology
This PCB assembly technology involves the combination of both surface mount technology and through hole technology. The constant development in technology has resulted in the demand for more complex and compact boards. Some PCBs feature both SMD components and through hole components.
Differences between SMT and THT
There is a big difference between SMT and THT as regards several factors. It can be very difficult to choose one of these PCB assembly technologies for your project. However, it is important to know the differences between these two technologies. This will help you choose the one that suits your project.
Higher pin count
The pin count is one of the differences between SMT and THT. SMT has more pin count than THT. As technology continues to evolve, the use of leads in printed circuit boards has been eliminated.
Technical cost
Through hole technology is a process that entails drilling of holes on a board. These holes help to hold components firmly. However, it takes more time to drill holes. The cost and time of drilling holes contribute to the technical cost of THT. SMT process is less time-consuming since a pick and place machine helps to complete the process.
Automation
The surface mount process solely depends on automation unlike THT technology. Also, this process involves use of several automated machines like pick and place machine.
Component placement
THT offers a stronger bond between through hole components due to its method of inserting components. Also, this process involves inserting PTH components through already drilled holes in the PCB. On the other hand, SMT involves the placement of SMD components directly on a PCB surface.
Soldering process
There is a huge difference between SMT and THT in terms of the soldering method they integrate. SMT involves reflow soldering while THT involves wave soldering or manual soldering. In reflow soldering, the PCB passes through a reflow oven where the solder melts. After then, the circuit board goes through a cooler in which the molten solder becomes solid.
SMT Assembly Process
The printed circuit assembly process involves several steps.
Solder paste stenciling
The first step in PCB assembly process involves applying solder paste. However, this step is only applicable for SMT. THT doesn’t require the application of solder paste. The assembler applies the solder paste on areas where the components will be.
Placement of components
After applying the solder paste, the assembler will place the surface mount components directly on the PCB surface. This step involves the use of pick and place machine. In THT, the assembler uses hand to place the components. This usually requires careful precision. SMT involves the integration of a robotic machine.
Reflow soldering
In this step, the board moves through an oven. The oven heats the solder and transforms it into a liquid state to ensure great connection between the components. After this, the PCB passes through a cooler. The cooler helps to solidify the molten solder paste. The solder paste must be in a solid state as this helps to ensure the components stay in place.
Inspection
This step helps to detect any defect in the board. Inspection involves evaluating the functionality of the circuit board. Also, some defects like shorts and open circuits can occur during the reflow process. These defects are side effects of the movement of the board in the reflow oven. Also, there could be other defects like misplaced components.
Final inspection and functional tests
The final step in the SMT assembly process is performing final inspection and functional tests. Functional tests help to evaluate the functionality of the board. Also, these tests put the circuit board in the normal circumstances it will operate. During this test, power signals will pass through the circuit board while testers will check the electrical characteristics of the circuit.
Steps in THT Assembly Process
Drilling of holes
This involves drilling holes in the PCB. Also, these holes feature several specifications. A document known as drill file helps to specify the sizes and location of the hole.
Placement of leads
This step involves placing leads in the drilled holes. Also, the through hole components must have long leads. Place the through hole components and ensure the leads are well placed on the holes according to the specification in the design. The assembler can do this manually or automatically.
Wave soldering or manual soldering
Rather than using soldering paste, through hole components integrate a different soldering method. The two different soldering methods is wave soldering and manual soldering. Manual soldering is process that involves the insertion of one component in a specified plated through hole.
Wave soldering involves a different process. It is an automated process of soldering the board. Here, the assembler places the board on a conveyor belt. This belt passes through an oven. In this oven, molten solder goes over the PCB’s bottom. Then all pins on the bottom of the PCB solders. Wave soldering is ideal for double sided boards.
Inspection and cleaning
In this process, the PCB assembly goes through inspection to be sure the PCB assembly functions as required. It is important to get rid of any debris or particles left on the board.
Printed Circuit Board Assembly Challenges and How to Prevent Them
PCB assemblers experience some failures and challenges during PCB assembly process. It is important to know these failures and how to prevent them.
Joint solder fracture
Solder joint fracture can be a result of the differences in a board’s thermal coefficients. Also, this problem can cause failure in a printed circuit board if subjected to high temperatures. Another cause of solder joints fracture can be manual soldering. One of the ways to prevent solder joint fracture is to integrate automatic equipment for soldering the electrical parts on a board. Also, apply the appropriate amount of solder paste on the board.
Short circuit
This is a common occurrence during PCB assembly. Short circuits occur due to high current spikes, solder bridges, or moisture. Also, this problem can damage the whole PCB. You can prevent this occurrence by performing a visual inspection to detect any hanging parts on the PCB surface. Furthermore, you might need to perform electrical testing for early detection of short or open circuits.
De-wetting
De-wetting can occur the electronic components are faulty. Solder joints will become loose when de-wetting occurs. Contamination, overheating, and corrosion are the causes of de-wetting. A careful board inspection can help to detect this problem.
PCB bend or crack
A printed circuit board can bend or crack during PCBA process. Crack or bend in circuit boards usually occurs as a result of physical and mechanical stress. The best way to prevent bends and cracks is to pre-bake and store the circuit board in a humidity-controlled place.
Unsuitable copper weight
The appropriate weight of the copper foil determines the flow of electricity on a board. An unsuitable copper weight will not enable the circuit board function well. Therefore, use the ideal copper weight.
How Much Does PCB Assembly Cost?
The cost of PCB assembly depends on several factors. Also, PCB assembly cost ranges from about 5 dollars to hundreds of dollars. This price range is a result of several factors which include:
PCB complexity
Complex circuit boards often require complicated PCB assembly process. For instance, complex boards like rigid-flex, high density interconnections, and high frequency boards requires more time to assemble. Also, PCB assembly cost will be higher if the circuit requires drilling.
Assembly methods
The type of assembly technology integrated determines PCB assembly cost. SMT is less expensive than THT since SMT requires the use of automated machines. THT assembly process consumes more time as it requires the drilling of holes on the PCB.
Customization
Customization will also contribute to the cost of PCB assembly. Also, if your request for custom PCBs, you should get ready to pay more because your PCB assembler will likely spend more to meet your demands,
Turnaround time
If your request to get your printed circuit board delivered within a short time, you will likely pay more for PCB assembly. This is because PCB assemblers will need to abandon some orders to focus on your orders. Sometimes they will even need to work overnight just to meet up with the deadline.
Number of layers
This is another factor that can contribute to PCB assembly cost. More layers means more time and cost. For instance, the cost of assembling a multilayer circuit board assembly will be more than that of a single layer PCB assembly.
Labor costs
Labor costs vary according to region. This factor can contribute to the cost of PCB assembly. For example, the cost of labor in Europe and the U.S is more expensive than that of South Asia.
Crucial Considerations when Choosing a PCB Assembly Service
Getting reliable and efficient PCB assembly services for your PCBA project is crucial. It is impossible to produce electronic devices without a PCB assembly. Since PCB assembly is a crucial part of most electronic devices, it is important to choose a professional PCB assembler for your project.
Choosing a professional PCB assembler will help you save PCB assembly cost. This is because this assembler guarantees quality. Here are factors you should consider when choosing a PCB assembly service provider.
Certification
Reliable PCB assemblers should have some PCB certifications like UL, IPC, ISO, and RoHS. This helps to indicate your assembler’s adherence to certain standards in the industry. Also, this assures you that your assembler adopts good quality control methods.
Technologies
Ensure you make inquiry about the type of equipment and processes integrated by your assembler. Advanced equipment can enhance the efficiency of the PCB assembly. For instance, advanced SMT equipment helps to ensure components are precisely placed on the PCB surface.
Customer support
Ensure your PCB assembler maintains a good working relationship with its customers. A good assembler will always prioritize the interests of its customers. Also, some PCB assemblers offer after sale services to their customers.
Expertise
This is another factor you should look out for in your PCB assembler. Ensure you work with an assembler that has vast expertise in circuit board assembly. Work with a professional PCB assembler who has the skills and knowledge required in assembling circuit boards. Also, expertise is crucial in complex PCB assembly projects like HDIs, high-frequency boards, and multilayer PCBs.
Versatility
Hire a PCB assembler that offers diverse PCB assembly services. For instance, some PCB assembler offer PCB assembly services like BGA assembly, THT assembly, SMT assembly, and more.
Conclusion
Assembled boards are crucial for the functioning of an electronic device. The final outcome of the PCB assembly process is an assembled board. Also, PCB manufacturing is entirely different from PCB assembly. The PCB assembly process is a vast one. It entails several steps. We hope you have been able to gain vast knowledge of PCB assembly after reading this article. We at RayMing offer vast PCB assembly services.
