To address cleaning issues in PCBAs, several traditional methods and practices have been employed. Below are the key steps:
1. **Washing Method**: When cleaning the PCBA, it’s essential to tilt the board rather than laying it flat. This helps prevent pooling of cleaning solution on the surface. Placing a paper towel in the washing station can assist by allowing the excess solution to flow off the board efficiently.
2. **Frequency of Cleaning**: Avoid over-washing the boards with the same cleaning solution. The frequency of replacement should be increased based on the level of contamination, ensuring the cleaning solution remains effective without causing potential damage to the PCBA.
3. **Improving the Washing Formula**: It’s crucial to assess the current formula of the cleaning solution. Working with suppliers to enhance the chemical composition can improve the cleaning efficiency and volatility of the solution, allowing for better cleaning results while preventing residual damage.
### 2. Solving the Whitening Issue After Cleaning:
Whitening of the circuit board’s surface is a common issue after cleaning, but it can be effectively managed by adopting more advanced cleaning agents and techniques. Here’s a structured approach to addressing this problem:
1. **Use of Water-Based Cleaning Agents**: To combat whitening, water-based cleaning agents have proven to be both safe and effective. These agents are compliant with key environmental regulations such as ROHS, REACH, and SONY 00259, making them a reliable choice for environmentally-conscious cleaning processes. Their high cleaning efficiency ensures that the whitening problem is completely resolved, offering a sustainable and reliable solution.
2. **Environmental and Regulatory Compliance**: Water-based cleaners not only solve the whitening issue but also meet critical environmental standards, making them suitable for industries aiming to adhere to stringent environmental guidelines.
3. **Optimal Equipment Selection**: Using the right cleaning equipment in combination with water-based solutions further enhances the cleaning process. The choice of cleaning machinery plays a vital role in achieving the desired results without compromising the integrity of the PCBA.
By incorporating these strategies, the issue of whitening on PCBA surfaces can be effectively managed, leading to improved overall board quality and compliance with industry standards.
### White Residue on PCBA Surface After Cleaning: Causes and Solutions
In the electronic component manufacturing process, a common issue arises after wave soldering of PCBA circuit boards: the appearance of white marks on the board surface following manual cleaning with a cleaning agent. These white marks, which are most noticeable around the solder joints, can severely impact the visual acceptance of the board.
### 1. Causes of Whitening After Cleaning
White residue on PCBA boards is a frequent phenomenon, typically resulting from flux by-products. The most common substances involved include polymerized rosin, unreacted activators, and reaction products between flux and solder such as lead chloride or bromide. These substances can absorb moisture, causing them to expand in volume or even undergo hydration reactions, further exacerbating the appearance of the white residue. The persistence of these residues on the PCB surface can be linked to improper cleaning, overheating, or extended exposure to high temperatures during the soldering process. Infrared spectrum analysis has confirmed that rosin and other residues undergo transformations before and after soldering, contributing to this whitening issue.
### 2. Key Factors Contributing to White Residues
White residue can appear in various stages of the manufacturing process, whether immediately after cleaning, during storage of no-clean boards, or even during rework. Four primary causes are responsible for these residues:
#### 2.1. Rosin in Flux
Rosin, a major component of flux, is typically a transparent, hard, and brittle substance that lacks a defined crystal structure. Although rosin is thermodynamically unstable and prone to crystallization, it generally remains in a glassy state. When the cleaning process is incomplete, the solvent evaporates, leaving behind crystalline rosin, which appears as a white powder on the PCB. Additionally, if the PCB is stored in a high-humidity environment, rosin may absorb moisture and transition from its colorless glassy state to a crystalline form, leading to visible white residues. Importantly, while these crystalline residues are unsightly, they do not affect the board’s performance due to the insulating properties of rosin.
#### 2.2. Denatured Rosin Compounds
During the soldering process, rosin can react with the flux, leading to the formation of denatured rosin compounds. These compounds have very low solubility and are difficult to clean, often remaining on the PCB as white residues. While these residues may be persistent, they are organic in nature and do not compromise the board’s reliability. Thus, while they pose a cosmetic issue, they do not affect the electrical or mechanical performance of the board.
#### 2.3. Organometallic Salts
In the process of soldering, organic acids react with metal oxides on the soldering surface, forming organometallic salts that are soluble in liquid rosin. After the soldering process, these salts remain in a solid solution with the rosin, and are typically removed during cleaning. However, if the soldering surface or components are highly oxidized, the concentration of reaction products will be higher, and excessive oxidation of rosin can lead to the formation of undissolved metal oxides. This situation can result in persistent white residues, which may reduce the overall reliability of the board.
#### 2.4. Metal Inorganic Salts
Another source of white residues is the formation of metal inorganic salts, which may result from the interaction of metal oxides in solder and flux with halogen-containing activators. These halogen ions, such as chlorine (Cl), bromine (Br), and iodine (I), are commonly found in fluxes used in the assembly process. Though these residues are not initially white, they react with water or moisture to produce strong acids. These acids then interact with the oxide layer on the solder joints, forming acid salts that manifest as white residues on the board surface. Such residues are especially prevalent when halogen-containing fluxes are used, even in cases where the flux is marketed as “environmentally friendly.”
### 3. Conclusion and Best Practices
The whitening of PCBA boards after cleaning is primarily caused by the residual flux components, including rosin and other by-products that react with moisture. While these white residues are mostly harmless to the board’s functionality, they do affect the visual quality, which may be a concern during final inspection.
To minimize these issues:
– **Optimize the cleaning process:** Ensure that the cleaning agent fully removes all flux residues, and adjust cleaning parameters to prevent incomplete solvent evaporation.
– **Control humidity levels:** Store PCBs in a controlled environment to prevent rosin crystallization and moisture absorption.
– **Use low-halogen or halogen-free fluxes:** Consider switching to halogen-free flux options to minimize the risk of metal ion contamination and acid formation.
By understanding and controlling the factors that contribute to white residues, manufacturers can improve the appearance and long-term reliability of PCBA products.
