Copper electroplating is the most widely used pre-plating layer to enhance coating adhesion. It is a crucial component of the copper/nickel/chromium system, providing both protection and decoration. A flexible copper coating with low porosity is vital for improving adhesion and corrosion resistance between layers. Copper plating is also utilized for local anti-carburization, metallizing printed board holes, and as the surface layer of printing rollers. Additionally, chemically treated colored copper layers coated with organic film can be used for decorative purposes. This article will delve into common issues encountered in PCB copper electroplating and their solutions.
1. Common problems of acid copper electroplating
Copper sulfate electroplating is essential in PCB electroplating, as its quality directly impacts the electroplated copper layer and related mechanical properties, influencing subsequent processing. Thus, controlling the quality of acid copper electroplating is a critical aspect of PCB electroplating and a challenging process for many large factories. Common issues with acid copper electroplating include: 1. Rough electroplating; 2. Copper particles on the plate surface; 3. Electroplating pits; 4. Whitening or uneven coloration of the plate surface. Solutions and preventive measures for these issues are briefly analyzed below.
1. Rough plating
Typically, rough board edges result from excessive electroplating current. To address this, reduce the current and check the current display with a card meter for abnormalities. Although roughness on the entire board is rare, it has been encountered in specific cases and requires thorough examination.
1. Tomorrow, the winter temperature will be low, and the brightener content may be insufficient; occasionally, the surface of some reworked faded sheets may not be cleaned properly, leading to similar issues.
2. Electroplating Plate Surface Copper Particles
Copper particles on the board surface can arise from various factors throughout the process, from copper immersion to pattern transfer. In a large state-owned factory, copper particles on the plate surface were traced back to copper immersion issues. Copper particles caused by the immersion process can originate from any treatment step. Alkaline degreasing might cause roughness on the board surface or in holes, particularly if water hardness is high and drilling dust is excessive (especially if the double-sided board isn’t de-smeared). Internal roughness and slight stains can be removed; main issues during microetching include poor-quality microetching agents (like hydrogen peroxide or sulfuric acid) or excessive impurities in ammonium persulfate (sodium), which should generally be at least CP grade. Industrial-grade materials can lead to other quality failures. Excessive copper content or low temperature in the micro-etching tank can cause slow copper sulfate crystal precipitation, leading to a turbid, polluted tank liquid. Activation solution issues often arise from pollution or poor maintenance, such as leaks in the filter pump, low specific gravity of the bath liquid, or high copper content (especially if the activation tank has been in use for over 3 years). This can produce particulate suspended matter or colloidal impurities that adhere to the plate surface or hole walls, causing roughness. Dissolving or accelerating issues occur if the bath solution remains too long, with fluoroboric acid attacking FR-4’s glass fiber, causing silicate and calcium salt to increase. Additionally, increased copper content and dissolved tin can lead to copper particles on the board surface. Copper immersion tank problems typically stem from excessive activity of the tank liquid, air stirring, and high suspended solid particles. Process adjustments, air filter element replacement, and thorough tank filtration can effectively address these issues. The dilute acid tank used for storing copper plates post-deposition should remain clean, with timely liquid replacement to prevent turbidity. Copper immersion boards should not be stored for extended periods to avoid oxidation and difficulty in treating oxide films, which can lead to copper particles on the board surface. Copper particles from the copper immersion process, aside from surface oxidation, usually exhibit uniform distribution and strong regularity. Such pollution can be assessed with small test boards for step-by-step comparison. On-site faulty boards can be cleaned with a soft brush. In the graphics transfer process, excess glue during development (even a very thin residual film) can be plated and coated during electroplating, or inadequate cleaning after development and extended plate storage can cause oxidation. The solution involves enhanced water washing, planning, scheduling, and intensified acid degreasing.
3. Electroplating Pits
Electroplating pits can arise from several processes including copper immersion, pattern transfer, pretreatment, copper plating, and tin plating. Poor cleaning of the copper immersion hanging basket can lead to palladium copper contamination during microetching, resulting in pits. Graphics transfer pits are often due to equipment maintenance issues and poor developing cleaning, such as glue stains from the brushing machine’s suction stick, oily dust in the air knife fan, or inadequate cleaning of the developing machine. Pre-treatment for electroplating, with sulfuric acid-based bath solutions, can result in turbid solutions and board surface pollution, especially if hangers are poorly encapsulated, leading to dissolving and diffusion of encapsulant and contamination of the tank liquid. These non-conductive particles can cause varying degrees of electroplating pits.
4. Whitish or Uneven PCB Surface Color
The acid copper electroplating tank might exhibit issues such as misaligned air blast tubes, uneven air stirring, or leaks in the filter pump that cause air to be drawn in, leading to fine air bubbles that adhere to the PCB surface or edges, especially around lines and corners. Inferior cotton cores, if not thoroughly treated or if contaminated with anti-static agents, can affect the bath solution and cause plating defects. To resolve this, increase aeration and remove surface foam promptly. Post-soaking in acid and alkali, whitish or uneven board surface colors can result from polishing or maintenance issues, and sometimes from cleaning problems after acid degreasing or micro-etching. Misalignment of the polisher, severe organic pollution, and excessively high bath temperatures can also be contributing factors.
1. Common problems of acid copper electroplating
Copper sulfate electroplating is essential in PCB electroplating, as its quality directly impacts the electroplated copper layer and related mechanical properties, influencing subsequent processing. Thus, controlling the quality of acid copper electroplating is a critical aspect of PCB electroplating and a challenging process for many large factories. Common issues with acid copper electroplating include: 1. Rough electroplating; 2. Copper particles on the plate surface; 3. Electroplating pits; 4. Whitening or uneven coloration of the plate surface. Solutions and preventive measures for these issues are briefly analyzed below.
1. Rough plating
Typically, rough board edges result from excessive electroplating current. To address this, reduce the current and check the current display with a card meter for abnormalities. Although roughness on the entire board is rare, it has been encountered in specific cases and requires thorough examination.
1. Tomorrow, the winter temperature will be low, and the brightener content may be insufficient; occasionally, the surface of some reworked faded sheets may not be cleaned properly, leading to similar issues.
2. Electroplating Plate Surface Copper Particles
Copper particles on the board surface can arise from various factors throughout the process, from copper immersion to pattern transfer. In a large state-owned factory, copper particles on the plate surface were traced back to copper immersion issues. Copper particles caused by the immersion process can originate from any treatment step. Alkaline degreasing might cause roughness on the board surface or in holes, particularly if water hardness is high and drilling dust is excessive (especially if the double-sided board isn’t de-smeared). Internal roughness and slight stains can be removed; main issues during microetching include poor-quality microetching agents (like hydrogen peroxide or sulfuric acid) or excessive impurities in ammonium persulfate (sodium), which should generally be at least CP grade. Industrial-grade materials can lead to other quality failures. Excessive copper content or low temperature in the micro-etching tank can cause slow copper sulfate crystal precipitation, leading to a turbid, polluted tank liquid. Activation solution issues often arise from pollution or poor maintenance, such as leaks in the filter pump, low specific gravity of the bath liquid, or high copper content (especially if the activation tank has been in use for over 3 years). This can produce particulate suspended matter or colloidal impurities that adhere to the plate surface or hole walls, causing roughness. Dissolving or accelerating issues occur if the bath solution remains too long, with fluoroboric acid attacking FR-4’s glass fiber, causing silicate and calcium salt to increase. Additionally, increased copper content and dissolved tin can lead to copper particles on the board surface. Copper immersion tank problems typically stem from excessive activity of the tank liquid, air stirring, and high suspended solid particles. Process adjustments, air filter element replacement, and thorough tank filtration can effectively address these issues. The dilute acid tank used for storing copper plates post-deposition should remain clean, with timely liquid replacement to prevent turbidity. Copper immersion boards should not be stored for extended periods to avoid oxidation and difficulty in treating oxide films, which can lead to copper particles on the board surface. Copper particles from the copper immersion process, aside from surface oxidation, usually exhibit uniform distribution and strong regularity. Such pollution can be assessed with small test boards for step-by-step comparison. On-site faulty boards can be cleaned with a soft brush. In the graphics transfer process, excess glue during development (even a very thin residual film) can be plated and coated during electroplating, or inadequate cleaning after development and extended plate storage can cause oxidation. The solution involves enhanced water washing, planning, scheduling, and intensified acid degreasing.
3. Electroplating Pits
Electroplating pits can arise from several processes including copper immersion, pattern transfer, pretreatment, copper plating, and tin plating. Poor cleaning of the copper immersion hanging basket can lead to palladium copper contamination during microetching, resulting in pits. Graphics transfer pits are often due to equipment maintenance issues and poor developing cleaning, such as glue stains from the brushing machine’s suction stick, oily dust in the air knife fan, or inadequate cleaning of the developing machine. Pre-treatment for electroplating, with sulfuric acid-based bath solutions, can result in turbid solutions and board surface pollution, especially if hangers are poorly encapsulated, leading to dissolving and diffusion of encapsulant and contamination of the tank liquid. These non-conductive particles can cause varying degrees of electroplating pits.
4. Whitish or Uneven PCB Surface Color
The acid copper electroplating tank might exhibit issues such as misaligned air blast tubes, uneven air stirring, or leaks in the filter pump that cause air to be drawn in, leading to fine air bubbles that adhere to the PCB surface or edges, especially around lines and corners. Inferior cotton cores, if not thoroughly treated or if contaminated with anti-static agents, can affect the bath solution and cause plating defects. To resolve this, increase aeration and remove surface foam promptly. Post-soaking in acid and alkali, whitish or uneven board surface colors can result from polishing or maintenance issues, and sometimes from cleaning problems after acid degreasing or micro-etching. Misalignment of the polisher, severe organic pollution, and excessively high bath temperatures can also be contributing factors.
