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Presensitized PCB: An Ultimate Guide

What is a Presensitized PCB?

A presensitized PCB, also known as a photosensitive PCB or pre-sensitized Copper Clad board, is a printed circuit board (PCB) that has been pre-coated with a light-sensitive photoresist layer. This photoresist layer is crucial in the PCB fabrication process as it allows for the precise transfer of the desired circuit pattern onto the copper surface of the board.

Presensitized PCBs offer several advantages over traditional PCB manufacturing methods, including:

  1. Improved accuracy and precision in circuit pattern transfer
  2. Faster and more efficient production process
  3. Reduced environmental impact due to less chemical waste
  4. Cost-effective for small to medium-sized production runs

Composition of a Presensitized PCB

A typical presensitized PCB consists of several layers:

Layer Material Function
Base Material FR-4, Aluminum, or Flexible Substrate Provides mechanical support and insulation
Copper Foil Copper Conducts electrical signals
Photoresist Light-sensitive polymer Allows for precise circuit pattern transfer
Protective Film Polyethylene (PE) or Polyester (PET) Protects the photoresist layer from damage

How Presensitized PCBs are Manufactured

The manufacturing process for presensitized PCBs involves several steps:

Step 1: Substrate Preparation

The base material, typically FR-4, aluminum, or a flexible substrate, is cut to the desired size and shape. The substrate is then cleaned to remove any contaminants or debris that may affect the adhesion of the copper foil.

Step 2: Copper Foil Lamination

A thin layer of copper foil is laminated onto the substrate using heat and pressure. The thickness of the copper foil can vary depending on the intended application, with common thicknesses ranging from 0.5 oz/ft² to 2 oz/ft².

Step 3: Photoresist Application

The presensitized copper clad board is then coated with a light-sensitive photoresist layer. This is typically done using a roller coating or curtain coating process to ensure an even and uniform distribution of the photoresist across the surface of the board.

Step 4: Protective Film Application

A protective film, usually made of polyethylene (PE) or polyester (PET), is applied on top of the photoresist layer to protect it from damage during handling and storage.

Using Presensitized PCBs in PCB Fabrication

The use of presensitized PCBs in the PCB fabrication process involves several key steps:

Step 1: Circuit Design and Artwork Preparation

The desired circuit pattern is designed using electronic design automation (EDA) software. The artwork, which represents the circuit pattern, is then prepared in a format suitable for use with a photoplotter or laser photoplotter.

Step 2: Exposure

The presensitized PCB is exposed to light through the artwork, typically using a UV light source. The areas of the photoresist that are exposed to light become soluble in the developer solution, while the unexposed areas remain insoluble.

Step 3: Development

The exposed presensitized PCB is then developed using a developer solution, which removes the soluble portions of the photoresist, leaving behind the desired circuit pattern.

Step 4: Etching

The developed PCB is then subjected to an etching process, where the exposed copper areas are removed using an etchant solution, typically ferric chloride or ammonium persulfate. This leaves behind the copper circuit pattern protected by the remaining photoresist.

Step 5: Photoresist Removal and Finishing

After etching, the remaining photoresist is removed using a stripping solution, revealing the final copper circuit pattern. The PCB can then undergo additional finishing processes, such as solder mask application, silkscreen printing, and surface finish application (e.g., HASL, ENIG, or OSP).

Advantages of Using Presensitized PCBs

Using presensitized PCBs in the PCB fabrication process offers several advantages:

  1. Improved Accuracy and Precision: The use of presensitized PCBs allows for the precise transfer of the desired circuit pattern onto the copper surface, resulting in higher accuracy and precision compared to traditional PCB manufacturing methods.

  2. Faster Production: The presensitized PCB manufacturing process is faster and more efficient than traditional methods, as it eliminates the need for manual application of the photoresist layer.

  3. Reduced Environmental Impact: The use of presensitized PCBs results in less chemical waste compared to traditional methods, as the photoresist application process is more controlled and efficient.

  4. Cost-Effective for Small to Medium-Sized Production Runs: Presensitized PCBs are particularly cost-effective for small to medium-sized production runs, as they eliminate the need for the additional equipment and labor associated with manual photoresist application.

Factors to Consider When Choosing Presensitized PCBs

When selecting presensitized PCBs for your PCB fabrication project, there are several factors to consider:

  1. Base Material: Choose the appropriate base material (e.g., FR-4, aluminum, or flexible substrate) based on your application’s requirements, such as thermal, mechanical, and electrical properties.

  2. Copper Thickness: Select the appropriate copper foil thickness based on your application’s current carrying requirements and desired trace width and spacing.

  3. Photoresist Type: There are two main types of photoresist used in presensitized PCBs: positive and negative. Positive photoresist becomes soluble when exposed to light, while negative photoresist becomes insoluble. Choose the appropriate photoresist type based on your specific design requirements and manufacturing process.

  4. Spectral Sensitivity: Ensure that the spectral sensitivity of the photoresist matches the wavelength of the light source used in your exposure process for optimal results.

  5. Storage and Handling: Presensitized PCBs are sensitive to light and should be stored in a cool, dark place. Handle the boards with care to avoid damaging the photoresist layer.

Troubleshooting Common Issues with Presensitized PCBs

When working with presensitized PCBs, you may encounter some common issues. Here are some tips for troubleshooting these problems:

  1. Incomplete Development: If the photoresist is not completely developed, it may be due to insufficient exposure time, incorrect developer concentration, or inadequate development time. Adjust these parameters as needed to ensure complete development.

  2. Over-Development: If the photoresist is over-developed, it may result in loss of fine details or widening of traces. Reduce the development time or developer concentration to prevent over-development.

  3. Poor Adhesion: If the photoresist does not adhere properly to the copper surface, it may be due to contamination or improper storage conditions. Ensure that the presensitized PCB is clean and has been stored correctly.

  4. Undercut or Overcut: If the etched circuit pattern shows signs of undercut (narrowing of traces) or overcut (widening of traces), it may be due to incorrect exposure time, developer concentration, or etching parameters. Adjust these parameters to achieve the desired results.


  1. What is the shelf life of presensitized PCBs?
    Presensitized PCBs typically have a shelf life of 12 to 18 months when stored under proper conditions (cool, dark, and dry environment). However, it is always best to consult the manufacturer’s specifications for the exact shelf life of a particular product.

  2. Can presensitized PCBs be used for Multilayer PCBs?
    Yes, presensitized PCBs can be used for the fabrication of multilayer PCBs. The process involves laminating multiple presensitized PCBs together, aligning the layers, and then exposing, developing, and etching the desired circuit pattern.

  3. What is the minimum feature size achievable with presensitized PCBs?
    The minimum feature size achievable with presensitized PCBs depends on several factors, including the type of photoresist, exposure equipment, and etching process used. Typically, presensitized PCBs can achieve minimum feature sizes ranging from 50 µm to 100 µm (trace width and spacing).

  4. Are presensitized PCBs suitable for high-frequency applications?
    Yes, presensitized PCBs can be used for high-frequency applications. However, the choice of base material and copper thickness becomes critical in these applications to ensure the desired electrical performance. Materials with low dielectric constant and dissipation factor, such as PTFE or Rogers laminates, are often used for high-frequency presensitized PCBs.

  5. Can presensitized PCBs be used for flexible circuits?
    Yes, presensitized PCBs can be used for the fabrication of flexible circuits. Flexible presensitized PCBs use a flexible base material, such as polyimide or polyester, and are processed using similar exposure, development, and etching techniques as rigid presensitized PCBs. However, the handling and processing of flexible presensitized PCBs require additional care to prevent damage to the flexible substrate.

In conclusion, presensitized PCBs offer numerous advantages in the PCB fabrication process, including improved accuracy, faster production, reduced environmental impact, and cost-effectiveness for small to medium-sized production runs. By understanding the composition, manufacturing process, and key considerations when using presensitized PCBs, you can optimize your PCB fabrication process and achieve the desired results for your specific application.