1. Copper sulfate electroplating holds a crucial role in PCB electroplating. The quality of acid copper electroplating directly impacts the quality and mechanical properties of the electroplated copper layer on PCB boards, which in turn affects subsequent processing.
2. Therefore, controlling the quality of acid copper electroplating is a key aspect of PCB manufacturing and represents a challenging process for many large-scale factories.
3. Drawing from years of experience in electroplating and technical services, the author offers a summary aimed at providing insights to the PCB electroplating industry.
4. Common issues encountered in acid copper electroplating include: 1. Rough plating; 2. Copper particles on the board surface; 3. Electroplating pits; 4. Whitish or unevenly colored board surfaces.
5. Solutions and preventive measures for these issues are discussed based on these conclusions and brief analyses.
1. Rough electroplating: Typically, a rough board surface is due to excessive electroplating current. Reduce the current and use a card meter to check for abnormalities. A consistently rough board is rare, but the author encountered it once at a customer’s site, later attributing it to low winter temperatures and insufficient brightener content. Reworked boards not properly cleaned can also exhibit similar issues.
2. Plating copper particles on the board surface: Various factors can cause copper particles on the board surface, from copper sinking to the entire pattern transfer process. The author observed such particles in a large state-owned factory, specifically due to copper sinking.
3. Copper particles from the copper immersion process might stem from any step in the immersion treatment. Alkaline degreasing can cause roughness in both the board surface and holes, particularly if water hardness is high and drilling dust is excessive, especially with untreated double-sided boards. Internal roughness and spot-like dirt can also result from poor quality micro-etching agents or excessive impurities in ammonium persulfate (sodium). It’s recommended to use at least CP-grade chemicals, as industrial-grade alternatives might lead to failures. High copper content or low temperature in the micro-etching bath can cause slow precipitation of copper sulfate crystals, leading to a turbid and polluted bath. Activation solutions often suffer from pollution or improper maintenance, such as filter pump leaks, low specific gravity, or high copper content, which produces particulate matter or impurity colloids on the board surface and hole walls, resulting in roughness.
4. Dissolving or accelerating issues: If the bath solution becomes turbid over time, it’s often due to fluoroboric acid attacking the FR-4 glass fiber, increasing silicate and calcium salt levels in the bath. Additionally, high copper content and dissolved tin in the bath can contribute to copper particles on the board surface. Excessive activity in the copper sinking tank, airborne dust stirring, and suspended solids in the tank liquid can also be factors. Adjusting process parameters, increasing or replacing air filters, and filtering the entire tank can provide effective solutions.
5. After copper deposition, ensure that the dilute acid tank for temporarily storing the copper plate is kept clean. If the tank liquid becomes turbid, replace it promptly. Avoid prolonged storage of copper immersion boards to prevent oxidation. If oxidation occurs, it makes copper particle removal more difficult. Copper particles from the copper sinking process are generally uniformly distributed and regular in appearance. To address these issues, small test boards can be processed separately for comparison. For on-site faulty boards, a soft brush can be used.
6. Graphics transfer process: Excess glue from development, residual film that can still be plated, or improper cleaning after development can cause oxidation on the board surface, especially if the plate is left too long after pattern transfer. Poor cleaning or heavy air pollution in storage conditions can exacerbate this issue. Strengthening water washing, scheduling, and acid degreasing intensity can help resolve these problems.
2. Therefore, controlling the quality of acid copper electroplating is a key aspect of PCB manufacturing and represents a challenging process for many large-scale factories.
3. Drawing from years of experience in electroplating and technical services, the author offers a summary aimed at providing insights to the PCB electroplating industry.
4. Common issues encountered in acid copper electroplating include: 1. Rough plating; 2. Copper particles on the board surface; 3. Electroplating pits; 4. Whitish or unevenly colored board surfaces.
5. Solutions and preventive measures for these issues are discussed based on these conclusions and brief analyses.
1. Rough electroplating: Typically, a rough board surface is due to excessive electroplating current. Reduce the current and use a card meter to check for abnormalities. A consistently rough board is rare, but the author encountered it once at a customer’s site, later attributing it to low winter temperatures and insufficient brightener content. Reworked boards not properly cleaned can also exhibit similar issues.
2. Plating copper particles on the board surface: Various factors can cause copper particles on the board surface, from copper sinking to the entire pattern transfer process. The author observed such particles in a large state-owned factory, specifically due to copper sinking.
3. Copper particles from the copper immersion process might stem from any step in the immersion treatment. Alkaline degreasing can cause roughness in both the board surface and holes, particularly if water hardness is high and drilling dust is excessive, especially with untreated double-sided boards. Internal roughness and spot-like dirt can also result from poor quality micro-etching agents or excessive impurities in ammonium persulfate (sodium). It’s recommended to use at least CP-grade chemicals, as industrial-grade alternatives might lead to failures. High copper content or low temperature in the micro-etching bath can cause slow precipitation of copper sulfate crystals, leading to a turbid and polluted bath. Activation solutions often suffer from pollution or improper maintenance, such as filter pump leaks, low specific gravity, or high copper content, which produces particulate matter or impurity colloids on the board surface and hole walls, resulting in roughness.
4. Dissolving or accelerating issues: If the bath solution becomes turbid over time, it’s often due to fluoroboric acid attacking the FR-4 glass fiber, increasing silicate and calcium salt levels in the bath. Additionally, high copper content and dissolved tin in the bath can contribute to copper particles on the board surface. Excessive activity in the copper sinking tank, airborne dust stirring, and suspended solids in the tank liquid can also be factors. Adjusting process parameters, increasing or replacing air filters, and filtering the entire tank can provide effective solutions.
5. After copper deposition, ensure that the dilute acid tank for temporarily storing the copper plate is kept clean. If the tank liquid becomes turbid, replace it promptly. Avoid prolonged storage of copper immersion boards to prevent oxidation. If oxidation occurs, it makes copper particle removal more difficult. Copper particles from the copper sinking process are generally uniformly distributed and regular in appearance. To address these issues, small test boards can be processed separately for comparison. For on-site faulty boards, a soft brush can be used.
6. Graphics transfer process: Excess glue from development, residual film that can still be plated, or improper cleaning after development can cause oxidation on the board surface, especially if the plate is left too long after pattern transfer. Poor cleaning or heavy air pollution in storage conditions can exacerbate this issue. Strengthening water washing, scheduling, and acid degreasing intensity can help resolve these problems.
