PCB vs PCBA | Difference Between PCB and PCBA

Introduction

PCB vs PCBA where PCB stands for Printed Circuit Board and PCBA stands for Printed Circuit Board Assembly.

A PCB is a rigid board made of insulating material, typically fiberglass, which has conductive tracks or pathways etched onto its surface. It serves as a foundation for electronic components to be mounted and interconnected to create a functional electronic circuit. The PCB provides mechanical support and electrical connections between components.

On the other hand, PCBA refers to the complete assembly of electronic components onto a PCB. It involves the process of soldering or attaching the individual electronic components, such as resistors, capacitors, integrated circuits, and connectors, onto the PCB according to a specific circuit design. The PCBA process also includes inspection, testing, and quality control to ensure that the assembled board functions correctly.

PCB refers to the bare board without any components, while PCBA refers to the PCB with electronic components assembled on it. PCBs are the foundation for electronic circuits, and PCBA is the final product that integrates the components onto the PCB for a functional electronic device.

PCB vs PCBA
PCB vs PCBA

Designing Process of PCB

The PCB manufacturing process involves several steps, from designing the circuit layout to the final fabrication of the printed circuit board. Here’s a general overview of the PCB manufacturing process:

Circuit Design

The first step is to design the circuit layout using computer-aided design (CAD) software. This involves creating a schematic diagram that outlines the connections between components and the desired circuit functionality. These diagrams pass the information about electrical connection between passive devices, integrated chips and terminals. These schematics are made in software’s like Eagle, Altium designer, Portal etc. 

A schematic design of circuit (courtesy OrcAD)
A schematic design of circuit (courtesy OrcAD)

PCB Prototyping

Before mass production, it is common to create a prototype PCB to verify the design. Prototyping involves manufacturing a small number of PCBs to test functionality, performance, and compatibility with components.

PCB Design of Electrical circuit
PCB Design of Electrical circuit

Gerber File Generation

Once the design is finalized, the CAD software generates Gerber files. These files provide detailed instructions to the PCB manufacturer, specifying the layout, copper traces, drill holes, and other important details.

*.GBR Gerber File
*.GBR Gerber File

Designing Process of PCB Assembly

Generation of Centroid File

This file is only generated for the assembly process. The Centroid file, also known as the Pick and Place file or XY file, is a data file used in PCB assembly (PCBA) to provide precise component placement information to the assembly equipment. It contains the coordinates and other relevant information for each component on the PCB, allowing the assembly machine to accurately position and mount the components during the manufacturing process. 

The Centroid file typically includes the following information for each component:

RefDes 

A unique identifier or reference designator for each component on the PCB. This helps correlate the component with its corresponding location on the board.

 X and Y Coordinates

The X and Y positions of each component’s centroid (center point) on the PCB. These coordinates are often given in millimeters or inches relative to a reference point on the board.

Rotation

The rotational orientation of each component, usually specified in degrees. This information indicates the correct alignment of the component during placement. 

Layer

A notation indicating whether the component is to be placed on the top (component side) or bottom (solder side) of the PCB.

Centroid File generated for PCB Assembling
Centroid File generated for PCB Assembling

BOM Generation

BOM stands for Bill of Materials. It is a comprehensive list of all the components, parts, and materials required to build a product or assembly. The BOM provides detailed information about each item, including part numbers, quantities, descriptions, and sometimes additional specifications.

The BOM serves as a crucial reference document throughout the product development and manufacturing process. Here are some key aspects of a BOM:

Component Information

The BOM includes the names, part numbers, and descriptions of each component or part required for the product. This information helps identify and locate the necessary components.

Quantities

The BOM specifies the quantity of each component needed for the product. It ensures that an adequate number of components is procured or manufactured for assembly.

Reference Designators

Each component in the BOM is associated with a reference designator, which is a unique identifier or label used to locate and identify components on the PCB or assembly.

Manufacturer and Supplier Information

The BOM may include the preferred manufacturers and suppliers for each component. This helps in sourcing and procurement activities, ensuring the use of approved and reliable sources.

Subassemblies and Assemblies

In more complex products, the BOM can include subassemblies, which are smaller assemblies that are later combined into larger assemblies. This hierarchical structure provides a detailed breakdown of the product’s structure.

Additional Information

The BOM may contain other relevant information, such as component specifications, alternate part numbers, component costs, lead times, and any special notes or instructions.

The BOM is used by various stakeholders involved in the product development and manufacturing processes, including design engineers, procurement teams, manufacturing personnel, and suppliers. It helps streamline the procurement process, ensures accurate component selection, aids in inventory management, and facilitates efficient assembly and production.

The BOM can be created and managed using specialized BOM management software or through spreadsheet applications. It is typically revised and updated as the product evolves, with changes made to component selections, quantities, or suppliers as required.

BOM generated for PCB Assembly
BOM generated for PCB Assembly

PCB Fabrication

The fabrication process begins with the manufacturing of the bare PCB. It involves the following steps:

Substrate Preparation

A copper-clad laminate sheet is selected as the base material. It is typically made of fiberglass-reinforced epoxy resin.

Cleaning

The laminate surface is cleaned and prepared for the subsequent processes.

Copper Cladding

A thin layer of copper is bonded to the laminate surface, either through an electroplating process or by lamination with pre-clad copper sheets.

Photoresist Application

A layer of photoresist material is applied to the copper surface.

Exposure and Imaging

The Gerber files are used to create a photomask, which is aligned and exposed to UV light through a process called photolithography. This exposes the photoresist, creating a pattern that matches the copper traces and component pads.

Etching

The board is submerged in an etchant solution that removes the unprotected copper, leaving behind the desired traces and pads.

Solder Mask Application

A layer of solder mask, usually green in color, is applied to the board surface, covering all areas except the copper pads.

Silkscreen Printing

Component labels, markings, and other identifying information are printed onto the board using a process called silkscreen printing.

Surface Finish

A final surface finish is applied to protect the copper traces and prevent oxidation. Common surface finishes include HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).

PCB Component Assembly

Once the bare PCB is ready, electronic components are mounted onto it through the process known as PCBA (Printed Circuit Board Assembly). This involves the following steps:

Solder Paste Application

If surface mount devices (SMDs) are used, solder paste is applied to the appropriate pads using a stencil.

Component Placement

SMDs and/or through-hole components are placed on their designated positions with the help of automated assembly machines or manual labor.

Soldering

The components are soldered to the PCB using different techniques, such as reflow soldering (for SMDs) or wave soldering (for through-hole components).

Inspection and Testing

The assembled PCBs undergo visual inspection and functional testing to ensure proper soldering, component placement, and functionality.

PCB Testing

After assembly, the PCBs go through various tests, including electrical testing, in-circuit testing (ICT), functional testing, and sometimes, environmental testing to ensure they meet the required specifications and quality standards.

Final Packaging

Once the PCBs pass all the tests, they are cleaned, marked, and packaged according to the specific requirements of the customer or the intended application.

It’s important to note that the PCB manufacturing process can vary depending on the complexity of the design, the specific requirements, and the manufacturing capabilities of the PCB manufacturer.

Conclusion

The main difference between PCB (Printed Circuit Board) and PCBA (Printed Circuit Board Assembly) lies in their stages of production and functionality:

PCB (Printed Circuit Board)

  1. PCB refers to the physical board that serves as a foundation for electronic components. 
  2. It is a flat board made of non-conductive material, typically fiberglass-reinforced epoxy. 
  3. PCBs have conductive pathways, known as traces, etched or printed on the board, providing electrical connections between components. 
  4. The primary purpose of a PCB is to support and interconnect electronic components in an electronic circuit. 
  5. The PCB is manufactured in a process that involves etching or printing conductive patterns on copper-clad laminate sheets, and it includes various layers with traces running between them.

PCBA (Printed Circuit Board Assembly)

PCBA refers to the complete assembly of electronic components onto the PCB.

  1. It includes the placement of surface mount devices (SMDs) or through-hole components on the appropriate locations of the PCB and soldering them in place to establish electrical connections.
  2. The PCBA process follows the manufacturing of the bare PCB, and it is the final product ready for use in electronic devices.
  3. PCBA involves several steps, such as component placement, solder paste application (if using SMDs), soldering, inspection, and testing.
  4. The PCBA process can be automated using specialized machines or done manually, depending on the complexity and volume of production.

In summary, a PCB is the physical board with conductive traces used as the foundation for electronic components, while PCBA refers to the completed assembly of components on the PCB, making it a functional electronic circuit. The PCB is designed and fabricated first, and then it undergoes the PCBA process to become a fully operational electronic device

Cost comparison

The cost comparison between PCB (Printed Circuit Board) and PCBA (Printed Circuit Board Assembly) can vary depending on several factors. Here are some considerations to keep in mind:

PCB Cost

The cost of the PCB itself depends on factors such as board size, complexity, number of layers, and material used. Larger boards or boards with more layers generally require more materials and processing steps, which can increase the cost.

Special features like blind vias, buried vias, controlled impedance, and high-frequency materials can also contribute to higher costs. Prototype or low-volume PCB production may have higher unit costs compared to mass production, as fixed costs are distributed across a smaller number of units.

PCBA Cost

PCBA cost includes not only the cost of the bare PCB but also the cost of components, assembly labor, and additional processes. Component cost can vary significantly based on the type, quantity, and quality of components used.

SMDs (Surface Mount Devices) tend to be more cost-effective compared to through-hole components due to automated assembly processes. Assembly labor cost depends on the complexity of the design and the required level of manual intervention. Additional processes like solder paste application, soldering, inspection, and testing add to the overall PCBA cost.

Testing complexity and requirements can also influence the cost. For instance, more rigorous testing procedures or specialized testing equipment may increase the overall PCBA cost.

In general, the cost of PCBA is higher than the cost of the bare PCB alone. The additional expenses associated with components, labor, assembly, and testing contribute to the increased cost. However, it’s important to note that the exact cost comparison will depend on the specific project requirements, volume of production, component selection, and manufacturing processes used.

It’s advisable to consult with PCB manufacturers like us MorePCB to obtain accurate cost estimates based on the specific design and production needs.

Experience exceptional PCB manufacturing and assembly services with MorePCB! 

Contact us today to bring your electronic designs to life. 

Let us be your trusted partner for high-quality PCB solutions!

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