What are PCBA Services?
It’s important for HDI PCB designers and engineers to understand the different processes and services involved before the final circuit takes shape. They are responsible for the first part, i.e., design. The fabricators are responsible for the second part – creating the circuit, with all the layers, traces, vias, and through-holes in place for the last part (Assembly). Once the components are assembled/installed over this black circuit board, it takes on the last, completed form – PCBA (Printed Circuit Board Assembly). There is often little distinction between the fabricators and assemblers as both services are usually provided by the same companies/businesses. However, PCBA services are still a distinct set of services involved in circuit development, and designers should know how these services work and what they include.
What is PCBA (Printed Circuit Board Assembly)?
A PCBA (Printed Circuit Board Assembly) is the completed PCB circuit, with all the components assembled/installed on the fabricated circuit board. The addition of “A” to the PCB marks the important distinction that exists between a plain circuit board that by itself only represents one element of the circuit (perhaps the most important element, essentially its backbone), and the completed circuit.
Even though the two refer to separate products, only one of them can be considered stand-alone and functional, while the other is basically an incomplete product. A PCB circuit, no matter how sophisticated and electrically and mechanically sound, cannot perform the requisite function unless the circuit components are assembled. Yet it has to be perfect (as per specs) for the PCBA (Printed Circuit Board Assembly).
A Printed Circuit Board Assembly (PCBA) can be further categorized based on the component assembly approach (through-hole, SMT, or both). Also, a PCBA may represent the last step in the production cycle of a circuit but not the product it’s designed for. The PCBA may have to go through further development steps before it can be installed in the final product.
PCBA Production
Printed Circuit Board Assembly (PCBA) production refers to the process of producing/creating the final form of a circuit. It’s also called the “assembly process” (or assembling process). There are multiple steps to this production process, and they differ for the two different types of PCBA.
THT PCBA vs. SMT PCBA
THT stands for Through Hole Technology while SMT is Surface Mounted Technology. They refer to two different types of component assembly mounting techniques/technology and two different types of component families. This has a significant influence, not just on the assembly process but on the PCB manufacturing as well.
THT PCBs are created with the holes in place. When creating the THT PCBA, the components are inserted into the relevant through holes. The process can be both manual and automated. Once the components are in place, the soldering process starts. Again, that process can also be manual or automated in nature. The soldering completes the electrical as well as mechanical connection of the component to the board. Components in the THT PCBAs are more mechanically secure because of the way they are inserted and then soldered onto the board. This is important for certain environments. However, there are drawbacks as well, like the component footprint.
The assembly process is a bit different for SMT PCBA. It starts with the application of the “bonding agent.” The most commonly used one is solder paste, which is a tin and lead alloy. The paste is applied carefully on board segments allocated to various compounds, and the amount of the paste is proportional to the designated space. A stencil printer is responsible for applying this paste automatically and takes multiple factors into account when applying the paste, including the component’s geometry and dimensions.
Once the paste is in place, a pick-and-place machine starts adding the component to the surface of the board. The components in an SMT PCBA are bonded only to the surface and are not physically inserted into the board and the power of their adhesion is highly influenced by the bonding agent and the soldering process. It’s sound enough for most applications, but for circuits that may have to perform in environments where frequent and substantial mechanical jerks are common, other steps need to be taken to mechanically secure the components beyond what the bonding agent and soldering are able to do.
The last step in the SMT PCBA process is soldering. The SMT PCBA, with both the components and soldering paste in place, goes through a reflow oven, where the paste melts, creating a strong bond between the component and the board. The SMT PCBA is able to accommodate a relatively denser collection of components compared to THT assemblies.
PCBA Production Best Practices
It’s important to understand the different “options” available for assembly and for mounting and bonding the SMT components. Soldering paste isn’t the only available option, and cost, as well as effectiveness, electrical characteristics, mechanical tolerances, and several other factors influence these and other factors. The best practices may differ for THT and SMT PCBAs, but some general principles that apply to both are:
- The most influential best practice starts from the design phase. If you adhere to the best Design For Manufacturing (DFM) practices, all PCBA production steps are likely to go well, including the assembly process.
- Choosing the right components and taking all the factors, like the footprint of their entire housing into account. A component with a small footprint may have a bulky heat sink or housing that may not cause problems in the design but in the later stages of PCBA production.
- Choosing the right bonding option for SMT PCBA production is also critical.
- Thermal management is also something you have to manage in the design process because once the PCBA production is complete, you would have very little room (if any) for effective thermal management.
- Communicating any special requirements early in the process. There are several things that are completed even before the PCBA production process, like masking in the circuit so if you want them to adhere to a specific nomenclature for your circuit assembly, the instructions should be communication beforehand.
There are several other best practices as well, though they lean more towards the people responsible for PCBA production, rather than the designer.
PCBA Services
Printed Circuit Board Assembly (PCBA) services may vary from vendor to vendor. They may include:
DFM Consultation and Support
Some of the key PCBA services start way before the assembly process and DFM consultation is a great example. Many Printed Circuit Board Assembly (PCBA) vendors offer DFM guidance and consultation services. They help designers create designs that are easy and practical to manufacture and assemble, forestalling many complications and ensuring that the process, from design to final PCBA product goes smoothly.
Manufacturers also have design guidelines available that designers can follow to ensure that the later processes go smoothly but DFM consultation is a distinct service. It signifies the active role manufacturer/PCBA services provider can play in the design process/stage.
Independent Assembly Services
Independant assembly services are when a Printed Circuit Board Assembly (PCBA) vendor only takes over the assembling part. You get your circuit fabricated and tested by a different vendor/PCB manufacturer, and once it’s completed per your design, they are shipped/transported to you or the assembler directly, and they focus on the PCBA finalization. It’s relatively rare because most PCB manufacturers also offer assembly services nowadays, but designers might choose this PCBA service if the manufacturer doesn’t have the assembly capabilities they are looking for. It can be anything from handling a special type of bonding agent for SMT PCBAs to component availability and cost.
Turnkey Assembly Services
Turnkey assembly services, or more accurately, turnkey PCBA services, are when a single vendor takes care of all aspects of the PCB development process. The client is only responsible for sharing the design adhering to the tolerances and other constraints defined by the manufacturer. Afterward, the vendor takes over. They will complete the PCB fabrication, its testing, assembling, and then final testing, and send you the final PCB designed to your specs. Some turnkey PCBA service providers may even make slight adjustments to your design (with your consent) to avoid any assembling or manufacturing challenges they might foresee.
Consignment Assembly
Consignment assembly is when the client takes the responsibility for sourcing all the components required for Printed Circuit Board Assembly (PCBA). They would ship or hand over these components to the PCBA services provider, and they simply assemble the final circuit. This is different from most other types of services, where the service provider is responsible for sourcing the components as well. This is useful from a cost perspective or when the designer is particular about component quality. However, it does increase the legwork and the designer’s/client’s involvement in the PCBA production process.
Hybrid Assembly
Hybrid assembly is when the client sources some of the components while the manufacturer sources the remaining ones. This is practical for very expensive, hard-to-find, or custom components. It may also allow for better cost control.
Both consignment and hybrid assemblies are PCBA services classified primarily based on the sourcing of the components for assembly.
End-to-End Assembly
End-to-end assembly can be considered an extension of turnkey services, where the PCBA (Printed Circuit Board Assembly) service provider does more than assemble and test the final circuit. They may package it for specific installation conditions or install it in the equipment/product the PCBA was designed for. This requires more capabilities and resources than typical PCBA services but can be useful for highly sensitive or sophisticated services. Circuit manufacturers may have a better understanding of how to safely mount and connect the circuit to the equipment it’s designed for.
Testing
Final testing is a critical part of the PCBA (Printed Circuit Board Assembly) completion process. There are testing steps related to PCB fabrication before it as well, but the final testing only happens when all the components are mounted. This includes but is not limited to:
Inspection: A visual inspection of the finished PCBA allows the assembler/tester to identify problems like damaged components, inadequate solder joints, housings and components with insufficient clearances, and several other problems that may prevent the PCBA from functioning as it should.
Electrical Testing: Electrical testing of the PCBA involves ensuring that all electrical connections (involving the components) are sound. There are no stray currents and leaks that may undermine the circuit or disrupt other components. Faulty soldering or damaged components (Especially when they are in series) can significantly undermine the PCBA’s functionality and they are identified at this stage.
Thermal Testing: Thermal testing focuses on the heat dissipation characteristics of the PCBA. This is especially critical for assemblies that include components that may generate significant amounts of heat. Or PCBA with tight thermal tolerances. This testing may also be focused on specific components or parts of the circuit that might be more vulnerable to heating.
Environmental Testing: Depending on where the PCBA is expected to be mounted or installed, it may experience adverse forces other than that. This includes mechanical jerks, rotations, vibrations, etc. Testing for these parameters ensures that the PCB will remain functional when deployed to the target environment.
X-Ray Testing: X-ray testing allows for the inspection of solder joints inside the PCB layers as well and ensures that everything is well under the hood. It can also allow for more comprehensive testing in SMT PCBAs.
Functional Testing: The most comprehensive testing process is related to the PCBA’s intended functionality. This may involve testing the circuit’s functionality in different conditions, testing it to the limit of its operational conditions, etc. In some cases, this testing may be used to set the limits of its functionality in various conditions.
Signal Integrity/Noise Testing: In some cases, signal integrity and noise tests are conducted to ensure that unwanted levels of noise are either not produced or effectively dissipated within the circuit. This is critical for sensitive circuits where higher noise levels might compromise functionality.
Then, there are certain desirable characteristics of PCBA services, including:
- Quick turn
- Prototyping
- Bulk production
Final Words
PCBA (Printed Circuit Board Assembly) represents the final stage and final form of the circuit that’s ready to be deployed to the environment or installed in the equipment/system it was created for. To ensure that there aren’t any issues in this process and the final product, it’s important to take great care when choosing PCBA services. Relevant capabilities, cost, delivery times, and support are some of the key factors that might influence your decision. However, if you have specific requirements like DFM support or incorporating a novel assembly approach, you may have to dig deeper into the portfolios and past projects of shortlisted PCBA service providers.
