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

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 4

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 5

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 6

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 7

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 8

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.

Question 9

PCB Applications and Industry Demand

Accepted Answer

With technological advancements and industrial upgrading, the applications of PCBs have become increasingly diverse—expanding from traditional consumer electronics to high-end sectors such as aerospace, medical equipment, and new energy industries.

According to market research, 5G, electric vehicles (EVs), and AIoT (Artificial Intelligence of Things) technologies are the three major driving forces behind the recent growth of the PCB industry.

For example, in the electric vehicle sector, a single car typically contains over a hundred PCBs, including power control boards, battery management systems (BMS), and charging modules. These PCBs must not only withstand high voltage and temperature but also meet stringent requirements for reliability and stability.

As a result, many PCB manufacturers are shifting toward advanced HDI (High-Density Interconnect) and FPC (Flexible Printed Circuit) technologies to meet market demands for compact, lightweight, and high-performance electronic devices.

Question 10

What is a PCB? The nervous system of electronic products.

Accepted Answer

The Printed Circuit Board (PCB) is an indispensable component in modern electronic devices.

It functions as the "nervous system" of electronic products, connecting and supporting all electronic components such as resistors, capacitors, and chips.
The primary function of a PCB is to allow electrical current to flow between various components through conductive pathways (copper traces), thereby enabling different circuit designs.

Common PCB materials include FR-4 (fiberglass fabric) and polyimide, among which FR-4 is the most widely used due to its excellent heat resistance and insulation properties.
From mobile phones and computers to automobiles and medical equipment, PCBs can be found in virtually all electronic devices.

Their stability and reliability have a significant impact on product quality and safety.

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