Question 1

Inner Layer Process (IV): AOI Inspection and Brown Oxide Treatment--FAQ

Accepted Answer

1. What happens after the inner-layer circuit is etched?

After etching and stripping, the circuit pattern is formed on the inner layer of the PCB. However, the inner layer still needs to be inspected and treated before it can be laminated into a multilayer PCB.

2. What is AOI inspection?

AOI stands for Automated Optical Inspection. It is an automated inspection process that uses high-resolution cameras and image-processing software to check PCB circuits for defects.

3. What defects can AOI detect?

AOI can detect problems such as:

Short circuits
Open circuits
Copper residues
Nicks or damage in the circuit pattern

4. Why is AOI inspection important?

AOI finds defects before the inner layers are laminated together. Detecting problems at this stage helps prevent defective boards from continuing through production and reduces material waste and scrap.

5. What happens after the AOI inspection?

If the inner layer passes AOI inspection, it undergoes a surface treatment called brown oxide treatment or black oxide treatment.

6. What is brown oxide treatment?

Brown oxide treatment is a chemical surface treatment applied to the copper surface of an inner PCB layer. It creates a micro-roughened oxide layer on the copper.

7. Why is the copper surface roughened?

The roughened surface improves the ability of the resin to adhere to the copper during the multilayer lamination process. Better adhesion helps the layers bond together securely.

8. What could happen if the brown oxide treatment is insufficient?

If the oxidation treatment is insufficient, the copper surface may not bond properly with the resin. This can weaken the connection between PCB layers.

9. What could happen if the copper is over-oxidized?

Excessive oxidation can damage the copper surface. Therefore, the chemical composition and treatment time must be carefully controlled.

10. How do AOI and brown oxide treatment improve PCB reliability?

AOI helps ensure that the inner circuits are free from important defects before lamination. Brown oxide treatment improves bonding between the copper and resin. Together, these processes help reduce problems such as delamination and voids and contribute to reliable multilayer PCB construction.

11. Why are these processes important if they are near the end of inner-layer fabrication?

Although AOI and brown oxide treatment may seem like final steps, they are critical quality-control processes. Problems detected or prevented at this stage can have a major effect on the reliability of the finished multilayer PCB.

12. What is the main purpose of AOI and brown oxide treatment?

AOI: Checks the inner-layer circuit for defects.

Brown oxide treatment: Improves copper-to-resin adhesion during lamination.

Together, they help ensure that multilayer PCBs have accurate circuits, strong interlayer bonding, and good long-term reliability.

Question 2

Inner Layer Process (IV): AOI Inspection and Brown Oxide Treatment

Accepted Answer

After etching and stripping, the inner layer circuits are formed, but the process does not end there. The next step involves Automated Optical Inspection (AOI).
Using high-resolution cameras and image comparison software, AOI automatically detects defects such as short circuits, open circuits, nicks, or copper residues.
This inspection ensures that defects are identified before lamination, significantly reducing scrap risk.

Once the inspection is passed, the inner layer panels undergo brown oxide (or black oxide) treatment. This process forms a micro-roughened oxide layer on the copper surface to enhance adhesion with the resin during multilayer lamination.
Proper control of the chemical composition and treatment time is essential; insufficient oxidation may result in poor adhesion, while excessive oxidation can damage the copper surface.
Although AOI and brown oxide treatment appear to be concluding steps, they are in fact critical safeguards for multilayer board reliability.

These processes ensure strong interlayer bonding, prevent delamination or voids, and are indispensable parts of the inner layer fabrication process.

Question 3

Inner Layer Process (III): Etching and Stripping--FAQ

Accepted Answer

1. What is PCB etching?

PCB etching is the manufacturing process that removes unwanted copper from the inner layer after photoresist development. Only the copper protected by the photoresist remains, forming the designed conductive circuit pattern.

2. Why is etching important in PCB manufacturing?

Etching directly determines the final trace width, spacing, and circuit geometry. Accurate etching is essential for maintaining electrical performance, signal integrity, and overall PCB reliability.

3. What chemicals are commonly used for PCB etching?

An acidic cupric chloride solution is one of the most widely used etchants for inner-layer PCB fabrication. Its concentration, temperature, and spray conditions must be carefully controlled to achieve consistent and precise copper removal.

4. What happens if the etching process is not properly controlled?

Poor process control can lead to over-etching, which makes traces narrower than designed, or under-etching, which leaves residual copper that may cause electrical shorts. Both conditions can negatively affect product quality and yield.

5. What is photoresist stripping?

Photoresist stripping is the process of removing the hardened photoresist after etching is completed. This reveals the finished copper circuitry and prepares the PCB for the next manufacturing processes.

6. Why is complete photoresist stripping important?

Incomplete stripping can leave chemical residues on the copper surface, which may affect lamination quality, adhesion, impedance consistency, and long-term product reliability.

7. What is AOI inspection after etching and stripping?

Automated Optical Inspection (AOI) uses high-resolution imaging to inspect the finished circuit pattern. It identifies defects such as opens, shorts, missing copper, or irregular trace edges before the PCB proceeds to the next production stage.

8. How do etching and stripping affect PCB performance?

These processes define the final conductor geometry of the PCB. Precise etching and thorough stripping help ensure stable impedance, reliable signal transmission, and consistent electrical performance, especially for high-speed and high-density circuit designs.

9. Can fine-line PCBs be manufactured with high etching accuracy?

Yes. Modern PCB manufacturers use tightly controlled etching equipment, optimized process parameters, and AOI inspection to produce fine-line circuits with high dimensional accuracy and repeatability.

10. What process comes after etching and stripping?

After the inner-layer circuitry has been verified through AOI inspection, the PCB typically proceeds to inner-layer surface treatment (such as black oxide) and lamination, where multiple layers are bonded together to form the multilayer PCB structure.

Learn more: https://www.explus.com.tw/faq/Inner-Layer-Process-III-Etching-and-Stripping.html

Question 4

Inner Layer Process (III): Etching and Stripping

Accepted Answer

Once the circuit pattern is clearly defined through exposure and development, the process proceeds to etching.

The purpose of etching is to remove the exposed (unprotected) copper, leaving only the intended conductive traces.
The most common etchant is an acidic cupric chloride solution, and precise control of concentration, temperature, and flow rate is crucial for maintaining accurate line width. Improper control may lead to over-etching (resulting in thinner lines) or residual copper (causing potential short circuits).

After etching, the photoresist stripping process removes the hardened photoresist, exposing the final copper circuitry.
Although this step may appear straightforward, incomplete stripping can leave residues that affect subsequent lamination or impedance stability.
Therefore, the etching and stripping stages are often followed by Automated Optical Inspection (AOI) to verify that circuit edges are clear and that there are no open or short circuits.
This step essentially determines the final shape of the circuitry and plays a vital role in defining the PCB’s electrical characteristics.

Question 5

Inner Layer Process (II): Exposure and Development --FAQ

Accepted Answer

What is the exposure process in PCB inner layer manufacturing?

Exposure is the process of transferring the PCB circuit pattern onto the dry film photoresist. After the dry film is laminated onto the copper-clad laminate, UV light is projected through a photomask that contains the circuit image. The exposed areas of the dry film become chemically hardened, while the unexposed areas remain soluble for the next development proces

Why is exposure important?

The exposure process determines the accuracy of the PCB circuitry. Proper exposure ensures:

Precise line width and spacing
Accurate circuit pattern transfer
Consistent dimensional stability
High production yield
Reliable electrical performance

Poor exposure may result in broken traces, short circuits, or dimensional deviations.

What factors affect exposure quality?

Several factors influence exposure performance, including:

UV light intensity
Exposure time
Photomask alignment accuracy
Dry film quality and thickness
Surface cleanliness after pre-treatment
Equipment calibration

Careful control of these parameters helps maintain consistent image quality throughout production.

What is the development process?

Development removes the unexposed portions of the dry film after exposure. A developer solution dissolves the unhardened photoresist while leaving the exposed circuit pattern firmly attached to the copper surface.

The remaining dry film acts as a protective mask during the subsequent etching process.

Why is development important?

A properly controlled development process ensures:

Complete removal of unwanted photoresist
Well-defined circuit patterns
Clean copper surfaces for etching
Stable manufacturing quality

Insufficient development may leave residual photoresist, while excessive development can damage fine circuit features.

What happens after development?

Once development is complete, the PCB panel undergoes inspection to verify that the circuit pattern has been accurately transferred. The panel then proceeds to the inner layer etching process, where the exposed copper is chemically removed to form the final inner layer circuitry.

How does ExPlus ensure consistent exposure and development quality?

ExPlus applies strict process control throughout the exposure and development stages by utilizing:

High-precision exposure equipment
Controlled UV energy and development parameters
Routine equipment calibration
Continuous quality inspection during production

These measures help achieve accurate circuit transfer, stable manufacturing quality, and high reliability for multilayer PCB production.

Question 6

Inner Layer Process (II): Exposure and Development

Accepted Answer

After pre-treatment, the inner-layer copper surface is laminated with a dry film photoresist, a UV-sensitive material that protects areas not intended for etching.

Once laminated, the board is aligned with a photomask film representing the circuit pattern and exposed to ultraviolet (UV) light. The exposed areas harden to form a protective layer, while the unexposed portions dissolve in the developer, revealing the bare copper. This stage determines the accuracy and clarity of the circuit pattern.

Therefore, light intensity, exposure time, lamination pressure, and development speed must all be tightly controlled. Insufficient or excessive exposure can cause blurred or distorted circuit edges, directly affecting impedance characteristics and line width/spacing tolerances.

As modern PCBs demand higher performance for high-frequency and high-speed signal transmission, the precision of the exposure and development process has become even more critical.

For this reason, manufacturers regularly calibrate exposure and development equipment to maintain accuracy and consistency.

Question 7

Inner Layer Process (I): Panel Cutting and Pre-Treatment-FAQ

Accepted Answer

What is panel cutting in PCB manufacturing?

Panel cutting is the process of cutting large PCB laminate sheets into smaller production panels suitable for inner layer fabrication and subsequent PCB processing steps.

Why is pre-treatment important before the inner layer process?
Pre-treatment removes oxidation, dust, oil, and contaminants from the copper surface to improve dry film adhesion and ensure accurate circuit imaging.

What does micro-etching do during PCB pre-treatment?
Micro-etching slightly roughens the copper surface to enhance bonding between the copper layer and the dry film photoresist used in imaging.

What problems can occur without proper pre-treatment?
Improper pre-treatment can cause poor dry film adhesion, uneven etching, open or short circuits, and reduced PCB reliability.

What process comes after panel cutting and pre-treatment?
After pre-treatment, the PCB proceeds to dry film lamination, UV exposure, developing, and etching to create the inner layer circuit patterns.

Learn more: Inner Layer Process (I): Panel Cutting and Pre-Treatment

Question 8

Inner Layer Process (I): Panel Cutting and Pre-Treatment

Accepted Answer

The first step in the inner layer PCB manufacturing process begins with large copper-clad laminates. Since the original panels are typically oversized, they must first be cut into appropriate working dimensions according to production requirements using a cutting machine.

Following cutting, the panels undergo pre-treatment, a critical process designed to ensure that the copper surface is clean, roughened, and uniform. Pre-treatment generally consists of three main stages: mechanical brushing, chemical cleaning, and high-pressure dust removal.

Mechanical brushing removes the oxide layer and increases surface roughness.
Chemical cleaning eliminates oil, fingerprints, or other contaminants.
Dust removal ensures that fine particles are completely cleared from the surface.

These treatments are essential for ensuring proper adhesion of the dry film photoresist and maintaining the precision of subsequent circuit patterns.
Poor surface preparation may lead to defects such as photoresist peeling, short circuits, or incomplete circuitry during the exposure and etching stages. Although pre-treatment may appear simple, it is in fact a key determinant of product quality and a vital part of the entire PCB fabrication process.

Question 9

Key Factors Affecting PCB Shelf Life

Accepted Answer

Key Factors Affecting PCB Shelf Life

1. Surface Finishing Method (Most Critical Factor)

Different surface finishes vary in their sensitivity to oxidation and humidity, which directly affects the PCB’s shelf life.

2. Storage Environment

· Temperature: Maintain between 20–25°C
· Humidity: Keep below 60% RH
· Packaging: Vacuum sealing with desiccants can effectively extend shelf life
· Light and Dust Protection: Avoid direct sunlight and dust exposure, as these accelerate surface deterioration.

3. Storage After Opening

Once the vacuum seal is broken, PCBs become exposed to air and moisture, causing oxidation to progress more rapidly. · OSP boards: Recommended to be used within 24–72 hours after opening · ENIG and HASL boards: Can last slightly longer, but should be used within one week · Unused boards: Should be re-sealed under vacuum and stored in a dry cabinet

Note: Using PCBs beyond their recommended shelf life may result in poor solderability, increased contact resistance, or functional failure.

Question 10

Green PCB: The Starting Point for Sustainable Electronics

Accepted Answer

Behind the rapid growth of the electronics industry, the Printed Circuit Board remains an indispensable core component.

However, the traditional PCB manufacturing process often involves high energy consumption, extensive use of chemicals, and the generation of difficult-to-treat electronic waste. To achieve environmental protection and sustainable development, the concept of the Green PCB has emerged—becoming a key direction in the industry’s transformation.

The term “Green PCB” refers to circuit board products designed with environmental protection and resource circularity in mind throughout all stages, including material selection, process design, and waste management. This involves the use of lead-free solder, halogen-free substrates, and the development of recyclable or biodegradable bio-based materials.
Furthermore, the integration of smart manufacturing technologies and energy-efficient equipment helps reduce both energy consumption and waste emissions.

In today’s era of growing ESG (Environmental, Social, and Governance) awareness, Green PCBs represent not only a tangible commitment by enterprises to environmental responsibility but also a valuable opportunity to open new markets and enhance brand value.

From electric vehicles and 5G communications to wearable devices, the demand for eco-friendly materials in electronics continues to rise.

The era of green electronics has arrived.
Those who take the lead in implementing sustainable design in PCB manufacturing will gain a significant competitive advantage in the global market.

Knowledge