Analysis and Treatment of Common Plastic Electroplating Failures:
- No copper layer is deposited on the part surface. This type of failure is generally caused by the failure of the sensitizer or activator solution. It may also be caused by low pH, temperature, formaldehyde, or copper sulfate content in the electroless copper plating solution, or excessive chelating agent content.
To address this type of failure, first check whether the sensitizer, activator, or colloidal palladium solution is functioning properly. Use a small amount of freshly prepared sensitizer and activator solution (or colloidal palladium solution). If a copper layer is deposited on the roughened plastic part after treatment with the freshly prepared sensitizer and activator solution, the original sensitizer or activator solution has failed and should be adjusted or replaced.
If the surface of a roughened light-colored plastic part turns brown after treatment with the original sensitizer and activator solution, the sensitizer and activator solution are not expired and the electroless copper plating solution should be inspected.
When inspecting the electroless copper plating solution, first check the pH and temperature. Adjust the pH to around 12 and the temperature to around 30°C. Then, add an appropriate amount of formaldehyde and conduct a trial plating. If copper still fails to deposit on the part, analyze the color (light color) or composition of the electroless copper plating solution to determine if the copper sulfate content is low. If so, add an appropriate amount of copper sulfate salt. This analysis and treatment can eliminate the problem of copper plating failure on the part.
- During electroless copper plating: Partial copper plating failure on a part’s surface is different from complete copper plating failure. Causes of this failure include: inadequate degreasing; poor roughening; insufficient sensitization or activation time; stress on the plastic part itself; or an imbalance in the composition of the electroless copper plating solution.
Failure to plate due to incomplete degreasing only occurs on a few parts or in localized areas of the part; oil may not be present on all surfaces.
Therefore, this type of failure is rare and can be eliminated through effective degreasing measures. If stress in the plastic itself causes plating failure, it often occurs on similar parts. This can be corrected by heat-treating a small number of parts to relieve the stress, then inspecting and troubleshooting using the usual roughening, sensitization, activation, and electroless copper plating procedures. Imbalanced electroless copper plating bath composition often manifests as slow copper deposition.
If copper begins to form on the plastic part within 5 minutes during electroless copper deposition, it’s not a problem with an imbalanced copper plating bath composition. If no copper layer forms on the plastic part after more than 15 minutes, it could be due to a low pH, low temperature, low formaldehyde content, low copper sulfate content, or excessive chelating agent content. These issues can be corrected by analyzing the solution and adjusting the proportions accordingly.
Also, insufficient chromic acid in the roughening bath, too low a temperature, or too short a roughening time can result in poor roughening, resulting in partial copper plating failure.
Different plastics require different roughening temperatures and times. For most domestic ABS plastics, a roughening temperature of 60°C to 65°C and a duration of 20 to 30 minutes is sufficient. Higher roughening temperatures can easily lead to over-roughening and deformation of the plastic part.
However, for Japanese electroplating-grade ABS plastic, a temperature of 60°C to 65°C is too low, which can easily result in poor roughening of the part. Roughening at 70°C to 75°C is generally recommended. Of course, this also depends on whether the part deforms. For parts prone to deformation, the roughening temperature should be lower and the duration longer.
For parts that are less susceptible to deformation, a higher roughening temperature and a shorter duration are recommended. Some factories maintain a roughening temperature of 82°C to 85°C and shorten the duration to 2 to 5 minutes. These roughened parts, after electroless copper plating, achieve faster and better brightness when electroplated with bright copper.
Thus, the temperature and duration of the roughening solution should be carefully controlled according to the specific plastic material to prevent electroplating failures caused by poor roughening. During the electroplating process for plastic signage, a factory received plastic parts from a supplier that were not regular injection molded parts. Instead, they were machined onto an injection molded plate and polished. Conventional electroplating processes for injection molded parts were used for electroplating.
The results revealed that the parts appeared normal before roughening, but after chemical roughening, several yellowing areas appeared on the surface. The electroless copper plating in these areas turned black, and after electroplating, plating defects occurred.
Despite repeated adjustments to the chemical roughening process, including extended heat treatment times to relieve internal stress and intensified chemical reduction steps, little progress was achieved. An investigation into the manufacturing process for the plastic blanks revealed that the ABS injection molded plate used to make the blanks contained small amounts of black material inclusions due to incomplete cleaning of the injection molding machine’s barrel.
Although surface defects were eliminated after machining and polishing, the high internal stress in these areas during roughening easily led to over-roughening, resulting in microcracks or loosening. During the activation process, in addition to the reaction, some unreacted solution seeped into the cracks, and even washing and formaldehyde reduction could not completely remove it.
This prevented the electroless copper plating process from proceeding normally, and a black, non-conductive Cu20 layer formed in that area, causing localized plating failure. The factory later switched to an electroless nickel plating process for metallizing plastic parts, avoiding the aforementioned problem.
This is because the reducing agent (sodium hypophosphite) in the electroless nickel plating solution has a much greater reducing power than the formaldehyde in the electroless copper plating solution, thus eliminating this problem.
Also, insufficient sensitization and activation time can often result in partial copper plating failure on plastic parts. Sometimes, even after a single sensitization and activation, no activated silver forms in certain areas, resulting in partial copper plating failure.
To eliminate this type of problem, after the first sensitization and activation, rinse with water and then repeat the second, and even third, or fourth, sensitization and activation treatments. This ensures that catalytic silver atoms are present on all surfaces of the roughened plastic part, eliminating the problem of partial copper plating failure.
- Poor adhesion between the coating and the plastic: Poor adhesion between the coating and plastic is a common problem on plastic parts. Common causes include: incomplete surface degreasing; improper plastic injection molding conditions; insufficient or excessive surface roughening; and the presence of oil in the electroless copper plating solution, all of which can cause blistering, peeling, and other problems in the coating.
Incomplete degreasing of parts is generally a rare and occasional problem, and can be avoided by strengthening pre-plating degreasing measures. Poor adhesion caused by improper injection molding conditions often occurs in the same area on each part, and can occur on many parts. To determine if this is the cause, take a small number of parts, place them in an oven to remove stress, and then perform roughening, sensitization, activation, electroless copper plating, and electroplating to observe the adhesion of the coating.
Poor coating adhesion caused by insufficient roughening often appears on concave surfaces. If the coating is peeled off, the plastic surface in these areas is usually smoother. However, poor coating adhesion caused by excessive roughening is more likely to occur on the tips and edges of the part, leaving these areas with a rough appearance after peeling.
To verify whether roughening is adequate, dry the roughened part in sunlight or in an oven. If the surface turns white after drying and a fine powdery substance appears on the tips and edges of the part that can be wiped off by hand, the part has been over-roughened and the roughening temperature or time should be reduced.
If a few areas of the dried surface turn white while the majority of the surface remains the natural plastic color, the roughening is insufficient and the temperature should be increased or the time should be extended.
What roughening temperature and time should be used? It’s best to test a small number of parts in batches at different roughening temperatures and times. Find the temperature and time that achieves both hydrophilicity and a uniform whitening after drying without any powdery residue. Then, maintain these temperatures and times for roughening.
Using air agitation can improve the crystallization of the electroless copper layer, reduce copper powder, and extend the life of the copper plating solution. The mechanism by which agitation improves the crystallization of the electroless copper layer and extends the life of the plating solution is that it helps quickly remove hydrogen produced by the reaction, acting as a secondary reducing agent in the bath. However, its presence can lead to localized overactivity of the bath. Furthermore, the air used for agitation must be strictly purified. Otherwise, oil from the air compressor can be introduced into the copper plating solution, resulting in a rough, loose copper layer and poor adhesion.
Because the electroless copper plating solution is alkaline, saponified oils will react with soap to form soap and glycerin. Non-saponified oils will partially emulsify under prolonged air agitation, resulting in foam in the solution.
Therefore, if foam is observed in the copper plating solution and the copper layer appears rough, loose, and poorly bonded, the air passing through the solution should be checked for oil. If oil is present, air purification should be strengthened. Furthermore, the solution should be treated with activated carbon to remove oil contaminants and eliminate the problem of poor coating adhesion.
The crosshatch method can be used to check the adhesion of the coating on plastic parts. This method involves making 10 horizontal and vertical scratches with a sharp blade at 1mm intervals. The scratches must expose the plastic substrate. The plastic substrate is then bonded with the specified adhesive tape. A pass mark is considered acceptable if at least 90% of the coating remains intact or no coating falls off when the tape is pulled away.
Thermal cycling tests can also be used to assess the adhesion of the coating on plastic parts. Generally, the plastic parts are placed at -30°C for 1 hour, then at room temperature for 1 hour, then at 70°C for 1 hour, and finally at room temperature for 1 hour. High adhesion requires four cycles without blistering.
- Dark brown powder on the copper layer. This problem can be caused by: excessive loading of parts during electroless copper plating; excessive roughening; excessive pH or temperature of the copper plating solution; excessive copper salt content and insufficient complexing agent; excessive reducing agent content or contamination of the copper plating solution with activation solution.
To analyze and address this problem, first check whether the electroless plating load on the parts is excessive. If it is indeed excessive, reduce the number of parts plated to see if the problem can be eliminated. Then, shorten the chemical roughening time to check whether the plastic parts are excessively roughened. If none of the above causes are present, inspect the electroless copper plating solution.
Generally speaking, contamination of the copper plating solution by activation solution is different from abnormalities in the composition and operating conditions of the electroless copper plating solution. The latter usually accelerates the copper plating speed, and excessively high speeds can lead to the formation of a dark brown powdery layer. If the electroless copper plating speed is not fast, activation solution contamination may be the cause.
From the perspective of abnormalities in the composition and operating conditions of the electroless copper plating solution, it has been found that a high pH value in the electroless copper plating solution is prone to this type of problem. Therefore, the pH value of the electroless copper plating solution must be strictly controlled (around 12) during production. Never raise the pH value of the electroless copper plating solution to achieve a faster copper plating speed.
If a dark brown powdery copper layer still appears when the pH value of the electroless copper plating solution is controlled at around 12, it may be necessary to add a chelating agent to the electroless copper plating solution. Alternatively, the plating solution can be appropriately diluted to keep the temperature below 30°C. These measures can help eliminate this problem.
- The main causes of black powder on the electroless nickel coating are: high temperature or pH of the electroless nickel plating solution, excessive nickel sulfate and sodium hypophosphite content in the solution, etc.
These factors can cause the electroless nickel plating solution to react violently, leading to rapid decomposition and the formation of solid nickel particles. These particles are trapped in the solution and become black powder in the nickel coating.
To troubleshoot this problem, first control the pH and temperature of the plating solution, then analyze and adjust the solution composition, and then filter the solid particles from the electroless nickel plating solution.
- Pitting in Plastic Coatings (Copper or Nickel) Pitting on the surface of plastic parts is primarily caused by the substrate material, pre-electroless plating process, and copper and nickel plating. Small holes, small spots, and inclusions on the plastic substrate can all cause pitting. During roughening, small spots on the part surface become non-wetting, activation, and uncoated spots after electroless plating. Later, pitting occurs during electroplating. These pitting occurs as pits.
Eliminating pitting during this process requires strengthening pre-plating inspection of the substrate material and pre-electroless plating processes. Plastic parts are also prone to pitting during the copper and nickel electroplating processes after electroless plating. Low or high phosphorus content in the phosphorus anode used for copper plating can lead to abnormal anode dissolution, resulting in the formation of cuprous oxide particles, which can cause pitting in the copper layer.
Also, brightener imbalances in the plating bath or brightener decomposition products can cause pitting in the coating. These factors must be strictly controlled to eliminate surface pitting in the electroplated copper layer.
Pitting in the electroplated nickel layer is related to iron impurities in the nickel plating bath, brightener decomposition products, the bath pH, insufficient wetting agent, and solid particles in the bath. Similarly, the methods described in Chapter 4 should be followed to troubleshoot this type of pitting.https://solidcomould.com/product/armrest-8/
