The PCB pre-treatment process plays a crucial role in determining the efficiency and quality of the overall manufacturing process. The success of this step greatly impacts both the production timeline and the final product quality. This article outlines the potential issues that may arise due to factors such as human errors, machine malfunctions, material properties, and environmental conditions during the PCB pre-treatment stage. Addressing these challenges effectively can ensure a more streamlined operation and improve overall results.
### 1. Overview of Pre-treatment Equipment
Various equipment is used during the PCB pre-processing stage, depending on the specific manufacturing line. Common examples include the inner layer pre-processing line, electroplating-copper pre-processing line, double-sided (D/F) line, and the solder mask treatment line. These systems are essential for preparing the PCB surface before the subsequent processes, such as copper deposition, solder mask application, or etching.
### 2. Example of Solder Mask Pre-treatment Line for Hardboard PCBs
Taking the hardboard PCB solder mask pre-treatment line as an example (note that processes can vary depending on the manufacturer), the typical steps include:
– **Brush grinding (2 groups)**
– **Water washing**
– **Pickling**
– **Water washing**
– **Cold air knife**
– **Drying section**
– **Solar disc rewinding**
– **Discharge rewinding**
Each step is designed to ensure optimal surface preparation for the application of the solder mask. However, issues may arise at any of these stages that can affect the final product quality.
### 3. Issues with Brush Grinding Process
The brush grinding process often utilizes gold steel brushes, typically with brush wheels rated #600 and #800. These tools are responsible for roughening the PCB surface, which is crucial for ensuring proper ink adhesion to the copper surface. However, improper use of the brushes can lead to several problems:
– **Impact on Surface Roughness**: The effectiveness of ink adhesion largely depends on the surface roughness achieved by the brushing process. If the brush wheels are not maintained properly, they can create uneven surface roughness, leading to inconsistent ink bonding.
– **Brush Wheel Wear**: Over time, brush wheels lose their effectiveness, which can result in defects such as uneven roughening or deformation of the circuit pattern. Prolonged use without proper maintenance can lead to “dog bone” defects, where areas of the PCB are inadequately roughened, causing issues during later stages.
– **Color Mismatch After Printing**: If the brushing process is inconsistent, the copper surface may exhibit color discrepancies after the ink is applied, impacting the aesthetic quality of the PCB and potentially affecting its functionality.
### 4. Importance of Regular Maintenance and Testing
To avoid these issues, it is critical to regularly inspect and maintain the brush wheels. Before starting the brushing operation, a **brush mark test** should be performed. For double-sided (D/F) PCBs, a **water break test** is also necessary. This test ensures that the width of the brush mark is within the ideal range, typically between **0.8mm to 1.2mm**, though variations can occur depending on the specific product.
Once brushing is complete, the level of the brush wheel should be checked and adjusted if necessary. Additionally, lubricating oil must be applied regularly to maintain optimal brush performance.
### 5. Potential Issues with Water and Spray Pressure
The water used during the brushing operation should be at the correct temperature. Insufficient heating of the water or inadequate spray pressure can result in the production of copper powder during the process. Even small amounts of copper powder can lead to significant issues, such as micro short circuits or failed high-voltage tests on the finished PCB.
To prevent this, it is essential that the spray pressure is appropriately set to ensure an effective fan-shaped spray pattern. Additionally, the water temperature and spray angles must be carefully monitored to avoid the accumulation of copper dust on the PCB surface.
### Conclusion
The PCB pre-treatment process, while essential for ensuring the quality of the final product, can present several challenges if not carefully managed. Common issues such as improper brush wheel maintenance, inconsistent surface roughness, and incorrect water temperature or spray pressure can all negatively affect the outcome. By maintaining proper equipment, regularly testing surface conditions, and addressing environmental factors, manufacturers can achieve better results, improve operational efficiency, and avoid costly defects in the final product.
In the PCB pre-treatment process, one common issue that may arise is the oxidation of the board surface, which can lead to the formation of bubbles or cavitation after the H/A (hot air) drying stage. The following are key contributing factors and solutions based on my experience:
1. **Incorrect Positioning of the Solid Water Retaining Roller**:
If the solid water retaining roller in the pre-treatment section is incorrectly positioned, it can result in an excessive amount of acid being transferred to the washing section. This imbalance can lead to acid residue remaining on the board. Additionally, an insufficient number of washing tanks or inadequate water flow can exacerbate this problem, as it hinders the proper removal of contaminants.
2. **Poor Water Quality and Contaminants in the Washing Section**:
The quality of water used in the washing section plays a crucial role in ensuring a clean copper surface. If the water is contaminated or contains impurities, foreign particles can adhere to the copper, which may later cause defects such as oxidation or poor adhesion of subsequent layers.
3. **Issues with the Water Absorption Roller**:
A dry or water-saturated water absorption roller cannot effectively remove excess water from the PCB. This results in excess moisture both on the surface of the board and within the vias, leading to residual water that cannot be properly evaporated during the subsequent air knife drying step. As a result, cavitation typically manifests as tears around the edges of the vias.
4. **High Temperature at Discharge**:
If the PCB temperature remains high during the discharge stage and the boards are stacked immediately, this can lead to oxidation of the copper surface. It is essential to ensure proper cooling procedures are followed to prevent this.
### Solutions and Best Practices:
– **pH Monitoring**:
A pH detector should be used to monitor the acidity of the washing water. This helps in controlling the chemical balance, ensuring optimal conditions for the treatment process.
– **Infrared Measurement of Board Temperature**:
Utilize infrared sensors to measure the residual temperature of the PCB surface. This helps in assessing whether the board is too hot, which can cause oxidation.
– **Solar Disk Reeling Device**:
Installing a solar disk reeling device between the discharge and stacking areas can effectively cool the boards before they are stacked, reducing the risk of oxidation.
– **Water Absorption Roller Maintenance**:
It’s essential to maintain proper wetting conditions for the water absorption roller. Ideally, two sets of suction wheels should be used alternately to ensure effective cleaning and drying.
– **Air Knife and Drying Section Checks**:
Before daily operations, confirm the correct angle of the air knife to ensure optimal drying. Regularly inspect the air ducts in the drying section for any detachment or damage, as this can impede airflow and reduce the efficiency of the drying process.
By addressing these key areas—water quality, equipment maintenance, and proper process parameters—the risk of oxidation and cavitation can be minimized, ensuring high-quality PCB production.
