Author：WELLSDate：2023-12-14 09:31:08
PCB and PCBA are integral components in the electronics manufacturing sector, fulfilling critical functions in the design and function of electronic devices. For emerging engineers, designers, and manufacturers, comprehending the distinctions between PCB and PCBA is imperative, enabling informed decision-making during new product development or existing product improvements. In this blog, we will introduce PCB and PCBA separately and make a detailed comparison of these two in terms of diverse aspects.
PCB stands for printed circuit board, it is a thin and flat board made of non-conductive materials that provide a base for the mechanical structure and electrical connectivity of electronic components. The non-conductive materials used for PCB substrates include fiberglass, epoxy resins, or other insulating materials, which allow the etching or printing of conductive copper pathways over their surface. These copper pathways are known as traces and they electrically link together various circuit board components that are soldered to the PCB. The key purpose of a printed circuit board is to act as a robust yet lightweight platform for organizing intricate circuitry by mounting electronic constituents in designated locations.
According to the number of conductive copper layers, it can be classified as:
Single-sided PCBs: As the name suggests, they have copper tracks on only one side of the insulating substrate. They are low cost and simple, used in basic circuits.
Double-sided PCBs: These have conductive tracks on both sides of the substrate. Allow for more complex interconnections between components versus single-sided.
Multilayer PCBs: Consist of multiple copper layers bonded together, allowing much denser and complex circuitry. Used in advanced electronics and allows high-speed signals.
Based on the different materials used, printed circuit boards can be categorized as metal PCB, fr4 PCB, ceramic PCB, and so on.
PCB is composed of the following layers. In this section, we mainly introduce the materials used in each layer:
Substrate Layer
It is often constructed from insulating materials such as FR-4 glass epoxy, ceramics, or composites, which serve as a structural foundation.
Conductive Layer
The conductive layer consists of copper foil affixed to the substrate, which is then meticulously etched to create pathways and landing points for circuit interconnections.
Solder Mask Layer
It is a protective epoxy-based coating that envelopes the surface of the PCB, leaving designated spots for attaching components and guarding against inadvertent short circuits.
Silkscreen Layer
The silkscreen layer imparts essential component details, such as labels, logos, and board outlines, utilizing ink or paint, aiding in both assembly and the identification and resolution of issues.
The PCB manufacturing process encompasses many steps, demanding a high level of professionalism. Below, we have outlined the general sequence of these processes:
Design – The PCB layout is designed using CAD software based on circuit schematics and requirements. This involves component placement, routing, and track layout.
Prototyping – Initial PCB prototypes are made to test the design before full production. This validates functionality.
Etching – The conductive copper layer is chemically etched to form the traces and pads that connect components.
Lamination – The etched conductive layer is glued to the insulating substrate using high heat and pressure.
Drilling – Holes are precisely drilled for mounting components and vias for connections.
Plating – The walls of drilled holes are plated with copper to facilitate connectivity between layers.
Solder mask – An epoxy layer is applied over the entire PCB surface except soldering points to prevent shorts.
Silkscreen – Paint or ink prints identifiers like component symbols, labels, and logos to aid assembly.
Testing – Each completed PCB is electrically tested for defects before release.
A PCBA (printed circuit board assembly ) is a populated printed circuit board that contains all the necessary electronic components that provide the functionality of the board. It consists of a printed circuit board, on which components like ICs, resistors, capacitors, transistors are soldered. Additional parts like connectors, buttons, LEDs may also be assembled. The leads of the electronic components are electrically and physically attached to the PCB’s contact pads and conductive tracks by melting solder to form a joint. Once all components are soldered to the board and it is tested for proper functionality, it is called a PCBA. PCBAs are an essential step in electronics manufacturing, designed and assembled by electronics manufacturing service companies before the final product is put together.
Based on different assembly techniques, PCBA can be divided into 3 types:
SMT PCBA
SMT (Surface Mount Technology) PCBA uses surface mount components that are soldered directly onto the surface of the PCB without any holes. Components are small, allow high density packing and make the board compact. This process is automated.
THT PCBA
THT (Through Hole Technology) PCBAs use leaded components with pins that are inserted into holes drilled in the PCB. The protruding leads are soldered on the opposite side. Components with large sizes are assembled manually.
Mixed-technology PCBAs
Mixed PCBAs use both SMT and THT components soldered onto the same PCB. Smaller surface mount parts are combined with larger through-hole parts needing mechanical strength. This takes advantage of both technologies on one board. Assembly involves both automated and manual soldering.
The PCBA production process generally consists of the following steps:
Solder Paste Application – Solder paste containing tin, silver, copper is printed on the PCB board in required areas using a stencil. This will hold components.
Component Placement – Surface mount components are automatically picked and placed onto the solder paste areas on the PCB.
Reflow Soldering – The PCB goes through a reflow oven which heats up to melt the solder paste and securely attach components.
Inspection – Optical and X-ray inspection checks for soldering defects and component faults. Ensures quality.
Through Hole Assembly – Components are inserted into holes in the PCB manually or by wave soldering to attach them.
Functional Testing – The fully assembled PCBA is tested by simulating operating conditions to verify proper electrical functioning.
Manufacturing Process
PCB fabrication revolves around crafting the bare circuit board itself, involving tasks like designing the board’s layout, etching copper traces, and adding insulating layers. This process is typically automated and marked by high precision. In contrast, PCBA takes the PCB as its starting point and proceeds to populate it with electronic components and connectors. PCBA can be a manual or automated assembly process, depending on the project’s scale and complexity.
Components and Complexity
PCBs consist solely of the bare board with copper traces, without any electronic components populated on them. While PCBAs incorporate a range of electronic components assembled on the PCB through soldering. This transforms the bare board into a functional electronic system, with complexity ranging from simple assemblies to dense arrangements with many components and integrated circuits.
Cost and Time Considerations
PCB fabrication is generally more cost-effective and time-efficient compared to PCB assembly. PCB costs are lower due to simpler design and material expenses. PCBA involves higher costs for components and labor-intensive assembly processes. Additionally, PCBA lead times are longer due to the component integration and extensive testing required.
Determining whether to use a PCB or a fully assembled PCBA depends on your project needs and production approach. If you just need the foundational circuit board to build upon later, a bare PCB is likely suitable, allowing customization and component integration flexibility. However, if you want a ready-to-go electronic assembly without needing to source and solder components, a PCBA is preferable, as it saves development and assembly time.
For simple DIY projects with few components that you want to choose yourself, bare PCBs offer prototyping flexibility. But for complex projects with tight timelines, PCBAs may be the best solution to accelerate development.
The decision also depends on production volume – PCBAs are ideal for mass production while bare PCBs make sense for low-volume prototyping. For DIY assembly of simple PCBAs, you can solder components onto custom designed PCBs. But for complex PCBAs, working with a professional PCBA manufacturer like Wells is recommended. We have the expertise and tools for reliable and scalable PCB assembly. Contact us now to get a quote for our PCB and printed circuit assembly services.
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