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Electronic manufacturing industry
PCB Photoresist

The production of printed circuit boards (PCBs) depends heavily on photoresists. For electrical devices to work, creating the essential conducting patterns on the PCB surface is necessary. The two types of PCB Photoresist, their uses, the developer solution, how photoresist is made, and how to remove it from a printed circuit board are all covered in this article.

Table of Contents

What is PCB Photoresist

A part of a printed circuit board is a PCB Photoresist. They apply it to the PCB’s copper-clad surface, either wet or dry. Depending on whether it is positive or negative, photoresist changes chemically when exposed to ultraviolet (UV) light through a photomask, becoming more or less soluble. The development procedure only involves removing the exposed or hidden areas of the copper surface, leaving the desired pattern intact. This diagram shows the required wire routing for safe device operation. Because it helps to identify the proper circuits on PCBs and protects the integrity of electrical connections, PCB Photoresist is a crucial component.

What is PCB Photoresist
What is PCB Photoresist?

What are the two types of photoresist

Although PCB Photoresist can be “positive” or “negative,” “negative” is the more common type. Positive resistance becomes more water-soluble when exposed to ultraviolet light, making it simpler to remove during the development process while maintaining the desired image. Positive resist renders the image’s UV-exposed and unexposed areas less soluble. After development, negative resist only leaves the desired design on the substrate. The expected results of the circuit pattern and the needs of the PCB layout determine whether a positive or negative resist type is superior.

When and how are photoresist used in PCB fabrication

Electrical lines are etched into the copper-clad surface of printed circuit boards using a photoresist. The procedures needed to create printed circuit boards (PCBs) with photoresists are as follows:

Preparation of Substrate: The first steps are cleaning and checking for contamination on the base, typically a copper-clad board.

Photoresist Applying: The printed circuit board (PCB) ‘s copper side must have photosensitive material first. With a dry or wet sheet, you can achieve this. A uniform photoresist layer is produced when the liquid is rotated onto the surface. The dry film method involves laminating a photoresist-coated film onto a copper surface before the lamination procedure.

Absorption of UV radiation: The photomask’s shape, which enables ultraviolet light to reach the PCB, is ideal. Only a tiny portion of the photoresist is protected from UV light penetration by the photomask, which acts as a pattern.

Development: After UV exposure, The PCB is placed in a fixer for additional processing. The developer will only remove the exposed or visible parts of the photoresist, whether you use positive or negative resist.

This method reveals a copper surface using a photomask.

Etching: Copper loses its visible surface through etching. The electrical pathways the photoresist defines are retained after removing extra copper.

Stripping: Following the etching procedure, the PCB is cleaned with a chemical solution, and any extra photoresist is eliminated. After this step, the copper lines on the circuit plan will be immaculate.

Using the PCB Photoresist’s light sensitivity to produce precise conductive lines on the PCB, this manufacturing process makes it possible to fabricate the intricate electrical circuits required for the operation of electronic devices.

What developer solution for PCB photoresist

Use either positive or negative resistance depending on the software option you choose. Alkaline development fluid and positively charged positive resist are two common varieties of positive resist. This alkaline solution only removes the visible photoresist, leaving the desired pattern on the copper’s surface. It is typical to use corrosive solutions to develop negative resistance. The exposed portions of the photoresist deteriorate in this acidic solution. This reveals the intended design of the copper base. How and which photoresist components are eliminated during development depends on the developer solution used.

How is PCB photoresist made

To create a PCB Photoresist, photosensitive materials and polymers are either mixed to create a liquid solution or coated on a carrier film to produce a dried film. It is necessary to dissolve photosensitive compounds in a solvent, purify the resulting solution, and store it in the proper containers to make liquid photoresist. The production of dry film photoresists requires coating a carrier film with a substance that responds to light in a controlled environment. You can store photoresist for dry film in coils or sheets. These photosensitive properties must be present during the entire PCB fabrication process for the photoresist to undergo the desired chemical transformation when exposed to ultraviolet light.

What is the difference between positive and negative photoresist PCB

The development procedure separates positive and negative PCB Photoresist by removing each photoresist from each. UV-exposed areas cause positive photoresist PCB to become more water-soluble. This enables growth in regions that aren’t exposed to UV light. The crucial layout, which shows where the electrical lines are on the PCB, is still etched into the copper. PCB was less soluble in the negative photoresist when exposed to UV light. Uncovered copper is removed during growth, leaving only the desired shape. PCB Photoresist can be positive or negative depending on the needs of the circuit design and the desired output of the electrical pattern.

What material is used for PCB photoresist

Photosensitive polymers and compounds make up the majority of PCB Photoresist. These elements change chemically when exposed to UV radiation because of their sensitivity. The reactive mixture is either sprayed on a carrier film or mixed with a solution for dry film photoresists. Higher quality, resolution, or sensitivity could be required during PCB fabrication to change the photosensitive material. Using a PCB Photoresist, sensitive to ultraviolet light, allows for the precise definition of electrical pathways on a printed circuit board (PCB) surface after using a photomask.

How thick should PCB photoresist be

The limitations of the PCB design, the required level of precision, and the application’s processing requirements all affect the width of the PCB Photoresist. Most PCB Photoresist has a thickness of between a few micrometers (m) and tens of m. For applications requiring greater detail clarity, thinner photoresist layers are superior.

In contrast, denser layers are selected for applications requiring more excellent processing and handling safety. Determining the ideal diameter is crucial for a solid connection to the base, distinct electrical channels, and simple removal during the growth and cleaning processes. Both the PCB fabrication process and the type of photoresist used determine the thickness of the photoresist layer.

How thick should PCB photoresist be
How thick should PCB photoresist be?

How do you remove photoresist from PCB

One of the most critical steps in PCB fabrication is removing the photoresist. This process, also known as “stripping,” involves chemically dissolving the photoresist on the copper surface. The type of PCB Photoresist determines the best course of action. Negative resistance requires an acidic fluid, while favorable opposition requires an alkaline solvent. When submerged in the right stripping solution, a PCB Photoresist will degrade and flake off the copper surface. You could heat or stir the substance to hasten the process. After the photoresist has completely deteriorated, the PCB will be meticulously cleaned to remove all traces. The copper lines that make up the design’s circuit architecture are visible once the photoresist has been completely peeled off and can be used for additional processing or the assembly of electrical parts.

Conclusion

A crucial element in the creation of printed circuit boards is PCB Photoresist. It is essential to create high-tech circuits to imprint patterns on the surface of copper and expose it to ultraviolet light. The PCB’s intended use will determine whether to use positive or negative resistance. When used correctly, photoresist makes it possible to create exact electrical channels, which enhances the dependability and usability of electronic devices.

FAQ

A part of a printed circuit board is a PCB Photoresist. They apply it to the PCB's copper-clad surface, either wet or dry. Depending on whether it is positive or negative, photoresist changes chemically when exposed to ultraviolet (UV) light through a photomask, becoming more or less soluble.

Although PCB Photoresist can be "positive" or "negative," "negative" is the more common type.

Photosensitive polymers and compounds make up the majority of PCB Photoresist. These elements change chemically when exposed to UV radiation because of their sensitivity.

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