Plastic electroplating common fault analysis and treatment:

1. The surface of the parts can not be plated with copper layer; The cause of this kind of failure is generally caused by the failure of sensitizing liquid or activation liquid, and may be caused by the pH value, temperature, formaldehyde, copper sulfate content is too low or the content of complexing agent is too high in the electroless copper plating liquid. The treatment of this kind of failure should first check whether the sensitized liquid, activation liquid or colloidal palladium solution is normal. With a small amount of newly formulated sensitization and activation solution (or colloidal palladium solution), if the coarsened plastic parts are able to deposit a copper layer after being treated with the newly formulated sensitization and activation solution, proving that the original sensitization or activation solution has failed, these solutions should be adjusted or replaced. If the roughened light-colored plastic parts, after being treated with the original sensitization and activation solution, the surface of the parts can turn brown, indicating that the sensitization and activation solution has not failed, the electroless copper plating solution should be checked. In the inspection of electroless copper plating solution, first check the pH value and temperature of the solution, the pH value of the solution is adjusted to about 12, the temperature is controlled at about 30¡æ, and then add an appropriate amount of formaldehyde after trial plating, if the parts still can not be deposited on the copper layer, it should be from the color of electroless copper plating solution (light color) or composition analysis, determine whether the copper sulfate content in the plating solution is low, if the content is low, Appropriate amount of main salt of copper sulfate should be added. After such analysis and treatment, the phenomenon that the parts cannot be plated with copper can be eliminated.

2. When electroless copper plating. Parts surface local plating copper layer parts local plating and completely plating is different, the reason for this failure is: parts surface local plating may not be oil removal is not complete; Poor coarsening; Insufficient sensitization or activation time; Plastic parts themselves have stress or chemical copper plating solution composition imbalance. The plating caused by incomplete oil removal of parts only occurs in a few parts and parts of the local position, not all parts have oil on the surface, therefore, the phenomenon of this failure is a few, can take good oil removal measures to eliminate; If the plastic itself is not plated due to stress usually appears in similar parts of the parts, a small number of parts can be taken after heat treatment to remove stress, and then according to the commonly used coarsening, sensitization, activation and electroless copper plating to check to eliminate this fault; The composition imbalance of electroless copper plating liquid is usually manifested as a slow copper deposition speed. If in the chemical deposition of copper, the surface of the plastic parts began to sink copper within 5 minutes, it is not the problem of copper plating liquid composition imbalance; If there is no copper layer on the surface of the plastic parts in more than 15min, it may be the reason that the pH value of the electroless copper plating solution is too low, the temperature is low, the formaldehyde content is low, the copper sulfate content is low or the complexing agent content is too high, and the analytical solution can be adjusted in proportion to eliminate this fault. In addition, the chromic acid content in the coarsening solution is insufficient, the coarsening temperature is too low or the time is too short, there will be poor coarsening, resulting in the local surface of the parts can not be plated with copper.

Different plastics need to use different coarsening temperature and time, most domestic ABS plastics, coarsening temperature only needs to be 60 ¡ã C ~ 65 ¡ã C, the time is 20min ~ 30min, coarsening temperature again high, easy to cause excessive coarsening, plastic parts deformation. However, Japan's electroplating grade ABS plastic, with 60¡æ ~ 65¡æ temperature is a little too low, easy to cause bad coarsening parts, generally 70¡æ ~ 75¡æ coarsening into good. Of course, it also depends on whether the parts are deformed, if the parts are easy to deform, the coarsening temperature should be lower and the time should be longer. For some parts that are not easy to deform, the coarsening temperature can be higher, and the time is shorter. Some factories control the temperature at 82 ¡ã C ~ 85 ¡ã C when coarsening, and the time is shortened to 2min ~ 5min, so that the coarsening parts, after electroless copper plating bright copper will be bright quickly, the brightness is good. Therefore, in the coarsening, should be based on different plastic materials, master the temperature and time of the coarsening solution, in order to prevent the plating failure caused by poor coarsening. A factory in the process of electroplating plastic signs, the plastic parts sent by the matching factory are not regular injection parts, but parts that are machined and polished on the injection plate, using the conventional electroplating process for injection parts. Results found that the parts in the roughing before the appearance is very normal, but once the chemical rough chemical process, the surface of the parts appear several yellow spots, electroless copper plating in the area of the coating is black, after electroplating there is leakage plating failure. Although the chemical coarsening process has been adjusted many times, the heat treatment time to eliminate internal stress has been extended, and the chemical reduction process has been strengthened, but little effect has been achieved. After the investigation of the production process of plastic blanks, it is learned that the ABS injection plate made of blanks has a small amount of black inclusions on the injection plate due to the endless cleaning of the material bore of the injection molding machine. Although the mechanical processing and polishing, the surface of the parts can not see the defects, but in the process of coarsening due to the large internal stress in the area, it is easy to coarsene too much, forming a fine crack or loose. In this way, in addition to the reaction in the activation process, there is a part of the unreacted solution permeated in the crack, although it can not be completely removed by washing and formaldehyde reduction. So that electroless copper plating can not be carried out according to the normal reaction process, and the formation of a black non-conductive Cu20 layer in the area, resulting in the occurrence of local leakage plating phenomenon. After the plant to use electroless nickel plating process for metallization of plastic parts, to avoid the occurrence of the above faults. This is because the reducing capacity of the reducing agent (sodium hypophosphite) in the electroless nickel plating solution is much greater than the formaldehyde in the electroless copper plating solution, thus eliminating this failure.

In addition, sensitization and activation time is not enough, often there will be plastic parts local plating on copper phenomenon, sometimes after a sensitization and activation of plastic parts, in the local formation of activated silver atoms, so that there will be local plating on copper phenomenon. In order to eliminate this kind of failure, you can in the first sensitization and activation, after washing and then repeat the second sensitization and activation treatment, and even the third, fourth sensitization and activation treatment, so that the coarse plastic parts, the surface of various parts have a catalytic role of silver atoms, so as to eliminate parts of the phenomenon of local plating copper.

3. Coating and plastic bonding force poor plastic parts coating bonding force is a common fault phenomenon, the general reason for this failure is: plastic parts surface oil removal is not complete; Plastic injection molding conditions are improper; Insufficient surface roughening or excessive roughening; There is oil in the electroless copper plating liquid, etc., will cause the coating foaming, peeling and other faults. General parts degreasing is not completely accidental few phenomena, can be used to strengthen the plating before degreasing measures to avoid this failure; Injection molding conditions caused by improper coating bonding force is not good often appear in the same part of each part, and there will be many parts have this failure phenomenon, whether this reason can take a small number of parts, put in the oven after removing stress, and then coarse, sensitized, activated and electroless copper plating, and electroplating to observe whether the coating bonding force is good. Parts coarsening is not enough to produce the coating bonding force is not good often appear on the concave surface of the parts, if the coating is stripped, the plastic surface of these parts is usually smooth, and the coarsening caused by excessive coating bonding force is not good is more in the tip and edge of the parts, after stripping the coating, these parts show a rough appearance.

Test whether the coarsening is appropriate way is to put the coarsening parts in the sun or in the oven to dry, if the dry surface is white, the tip of the parts and the edge of the fine powdery material, this powder can be wiped by hand, it indicates that these parts have been coarsening too much, should reduce the coarsening temperature or shorten the coarsening time. If the surface of the parts after drying, there are a few parts white, most of the surface is still the natural color of plastic, it indicates that the coarsening is not enough, should be increased coarsening temperature or extend the coarsening time.

What kind of coarsening temperature and time to choose? It is best to take a small number of parts, in batches under different coarsening temperatures and times to test to find out the coarsening temperature and time that makes the coarsening parts both hydrophilic and uniformly white after drying, and then to control the coarsening under such temperatures and times. The use of air stirring has certain benefits for improving the crystalline structure of electroless copper plating layer, reducing copper powder and extending the service life of copper plating solution. Electroless copper plating relies on stirring to improve the crystallization of the coating and extend the life of the plating solution. The mechanism is that it can help quickly remove the hydrogen generated by the reaction in the plating solution, which plays the role of the second reducing agent in the plating solution. But its existence will lead to the local plating solution activity is too strong; In addition to strictly purify the air of mixing, otherwise, if the oil in the air compressor is brought into the copper plating liquid, the copper plating layer will be rough, loose, and the binding force is not good. Because the electroless copper plating liquid is alkaline, if the oil into the copper plating liquid is saponified oil, saponification reaction will occur to produce soap and glycerin, if the oil into the solution is non-saponified oil, then in a long time under the air stirring will be partially emulsified, so that the copper plating liquid foam. Therefore, when it is observed that there is foam in the copper plating liquid, and the copper layer is rough and loose, and the binding force is not good, it should be checked whether there is oil in the air of the copper plating liquid, if there is oil, it is necessary to strengthen the air purification, and it is also necessary to carry out activated carbon treatment of the copper plating liquid to remove the oil and eliminate the failure of the coating binding force.

Check the binding force of the coating of plastic parts can use the grid method, that is, the sharp edge spacing lmm horizontal and horizontal row l0, the scratch must be exposed to the plastic matrix, and then use the specified adhesive tape pressure adhesive, when the adhesive tape is opened at least 90% of the coating does not fall off or no coating is qualified. In addition, the thermal cycle test can also be used to assess the binding force of the coating of plastic parts, the general requirements of the plastic plating parts placed at -30¡æ lh, and then placed at room temperature for 1h, then at 70¡æ lh, and finally to room temperature lh for a cycle, with high binding performance requirements is that after 4 cycles of coating can not bubble for qualified.

4. There is dark brown powder on the copper plating layer. The reason for this failure is that the parts are loaded too much when electroless copper plating; Excessive coarsening; The pH or temperature of the copper plating solution is too high; The content of copper salt is too high and the content of complexing agent is too little; The reducing agent content is too much or the copper plating solution is stained by the activation solution. When analyzing and dealing with this kind of failure, it is necessary to first check whether the loading amount of electroless plating parts is too much, if the loading amount is indeed too much, it is necessary to reduce the number of electroless copper plating parts to see whether this failure can be eliminated; Then take to shorten the chemical roughening time to check whether the plastic parts are excessive, if not for the above reasons, it is necessary to check the electroless copper plating solution.

Generally speaking, the copper plating solution is polluted by the activation liquid and the chemical plating liquid composition and operating conditions are different, the latter usually accelerates the copper plating speed, the speed is too fast and leads to the formation of dark brown powdery copper layer, if the speed of electroless copper plating is not fast, it may be caused by the activation liquid pollution. From the chemical copper plating liquid composition and operating conditions caused by such failures found that the pH value of the chemical copper plating liquid is too high, it is easy to occur such failures, so the production needs to strictly control the pH value of the chemical copper plating liquid (around 12), do not in order to pursue faster copper plating speed, and the pH value of the chemical copper plating solution is higher. If the pH value of the electroless copper plating solution is controlled at about 12, there is still a dark brown powdery copper layer, it may be necessary to supplement the complexing agent in the electroless copper plating solution, and the plating solution can be appropriately diluted to control the temperature of the electroless copper plating solution below 30 ¡ã C. These measures are conducive to the elimination of this fault.

5. There is black powder on the electroless nickel plating layer. The main reasons for this failure are: the temperature of electroless nickel plating solution is high or the pH value of the plating solution is too high, and the content of nickel sulfate and sodium hypophosphite in electroless nickel plating solution is too high. These factors will make the reaction of electroless nickel plating solution intense, resulting in the rapid decomposition of the solution, so that the solution produces solid nickel particles, and these particles pinch into the black powder in the nickel plating layer. The way to eliminate this kind of failure is: first, you need to control the pH value and temperature of the plating solution, and then analyze and adjust the composition of the solution, and then filter the solid particles in the electroless nickel plating solution.

6. Plastic coating (copper or nickel) pitting plastic parts surface coating pitting main sources are: substrate material, electroless plating before the process, copper plating and nickel plating. Small holes and small spots on the plastic parts matrix, inclusions, etc., may cause pitting of the coating; When coarsening, there are small points on the surface of the parts that are not wet and activated to the small points without plating caused by electroless plating, and then the pitting points are formed; And these pitting points exist in the form of pits. To eliminate the pitting caused by this link is to strengthen the pre-plating inspection of the base material and the treatment of the pre-electroless plating process. Plastic parts after electroless plating copper and nickel plating process is also prone to pitting links, the use of phosphate-containing anode plate in copper plating, if the phosphorus content is low or too high, resulting in abnormal anodic dissolution, easy to produce cuprous oxide particles, resulting in pitting of copper plating layer. There are brightener imbalance or brightener decomposition products in the plating solution will cause the coating pitting, which should be strictly controlled to eliminate the surface pitting failure of the electroplating copper layer. The pitting of nickel plating layer is related to iron impurities in nickel plating solution, brightener decomposition products, plating solution pH value, insufficient wetting agent, solid particles in plating solution, etc., and it is also necessary to remove the pitting fault of this coating according to the method in chapter 4.

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