The multi-layer ceramic casing is a multi-layer ceramic metallized base and metal parts (outer lead frame, sealing ring, heat sink, etc.) are brazed with silver-copper solder. The metallization material is generally tungsten (W) or molybdenum (Mo)-manganese (Mn), and the outer lead and the sealing ring material are generally iron (Fe)-nickel (Ni)-cobalt (Co) alloy or iron (Fe). - Nickel (Ni) alloy material, the heat sink material is generally tungsten (W) - copper (Cu) or molybdenum (Mo) - copper (Cu) alloy material. In a variety of materials, it is necessary to first plate nickel in gold plating , and to ensure that the quality of the coating meets the requirements of the product standard, which is difficult. In the plating problem of the common quality problems in electroplating, the problem of peeling and air bubbles in the coating is discussed in the electroplating production process after the appearance of the electroplating after the appearance of the inspection or high temperature aging.
2 Multi-layer ceramic shell plating process
The electroplating process of the multilayer ceramic casing is generally first nickel plated and then gold plated. In order to ensure that the product's bonding, capping, solderability, moisture resistance, salt spray resistance and other performance indicators meet the requirements, the nickel plating of the outer casing is usually nickel-plated nickel sulfamate with low profit, gold plating is usually low hardness pure gold (gold) The purity is 99.99%) gold plated. The plating process of the multilayer ceramic casing is as follows:
Plasma cleaning → ultrasonic cleaning → solder cleaning → flowing tap water cleaning → electrolytic degreasing → flowing tap water cleaning → pickling → deionized water cleaning → pre-nickel plating → deionized water cleaning → double pulse nickel plating → deionized water cleaning → pre-gold plating → Deionized water cleaning → pulse gold plating → deionized water cleaning → hot deionized water cleaning → dehydration drying.
This process ensures that the residual amount of plating solution after plating is as small as possible.
3 Causes of electroplating bubbles
In the multi-layer ceramic shell electroplating production process, the plating bubbles, mainly nickel-plated bubbles, are generally rare in the case of nickel plating and gold plating production.
The reason for the nickel-plated layer bubble is generally related to the poor treatment in the early stage and insufficient cleaning between the pre-treatment steps. Secondly, excessive impurities in the nickel plating solution can also cause bubbles; third, the pre-treatment solution is used for a long time, impurities. Too much can also cause bubbles; third, the pre-treatment solution is used for too long, too much impurities, not replaced in time, not only does not achieve the purpose of pre-treatment, the day of contamination contaminated the product and caused bubbles. The nickel-plated cheongsam of the multi-layer ceramic shell is generally divided into metalized area bubbles, lead frame and sealing ring bubbles, solder area bubbles and heat sink bubbles according to the distribution part and the base material. Due to the difference of the base material, bubbles are generated. The reasons are not the same.
3.1 Metalized area bubbles
The reason for the bubbles in the metallized area is due to the large internal stress in the nickel plating layer. The bonding force between the nickel layer and the bottom metal is insufficient to eliminate the thermal stress in the nickel layer during the high temperature aging, so that bubbles appear at the stress concentration. Generally speaking, such bubbles are most likely to appear in the ceramic metallization zone when using bright nickel plating. When using nickel sulfamate plating, it is most likely to occur in the ceramic metallization zone. When nickel sulfamate is used to plate dark nickel, the nickel plating layer has a small stress, and this problem generally does not occur.
3.2 Lead frame and sealing ring foaming
The lead frame and the sealing ring are foamed because the surface is contaminated and uncleaned. The pretreatment process in the normal plating process cannot remove such contaminants, or the pretreatment process is abnormal, resulting in unclean dirt removal. It is a poor bonding force between the nickel plating layer and the base metal, thereby causing foaming.
3.3 solder area foaming
The soldering area of ​​the solder is due to the pre-process--the brazing process is not strict in the process of component assembly and brazing, the brazed parts are not clean, or some of the particles (C) adhere to the solder surface during the brazing process. After electroplating, bubbles are generated at the portion where the graphite particles are contaminated in the solder region.
3.4 Heat sink foaming
Tungsten-copper or molybdenum-copper as a heat sink device for ceramic casings, which is liable to cause peeling or foaming during electroplating, because both materials are difficult to plate metal, and therefore, in a ceramic housing with a heat sink Special pretreatment must be performed prior to plating.
In summary, the causes of electroplating blistering are: the surface of the outer casing caused by the contamination caused by the previous process is not clean, and the pre-plating treatment fails to remove the contaminants to cause foaming; If the solution, time, temperature control or improper operation of each process is not good, the contaminant on the surface of the outer casing can not be cleaned and cause foaming; the graphite particles on the outer casing of the brazing, the stains on the fingers, etc. The pretreatment process is difficult to process cleanly, thereby generating foaming; the impurity ion concentration of the positive nickel plating solution increases as the number of products to be plated increases, so that the hardness of the nickel plating layer increases, thereby increasing the stress of the nickel plating layer. , causing foaming.
Therefore, in order to solve the problem of nickel plating foaming of the outer casing, it is necessary to start from the previous process, and at the same time, control the pretreatment process and the nickel plating process.
4 Measures to solve the blistering of the plating layer
4.1 Strict process hygiene
In the production process of ceramic casing, it is necessary to make strict regulations on the process hygiene of each process, and it is not allowed to directly touch the product by hand. At any time and under any circumstances, it is necessary to wear the finger cot to contact the product.
Before the shell is brazed, the assembly positioning graphite boat and graphite parts must be strictly cleaned. When processing and assembling the graphite boat, the graphite particles on the surface of the boat are left more. In order to avoid the contamination of the product by the graphite particles, the team graphite boat must be strictly cleaned. Secondly, the assembly positioning graphite boat and its parts must be dehydrogenated. To reduce other contaminants on the surface of graphite parts during processing; third, to regularly clean the brazing furnace, remove graphite particles in the furnace, and prevent the stone in the furnace
The ink particles are stained onto the product.
The metal parts must be cleaned during assembly, the metal parts and solder used should be strictly cleaned, and the finger cots should be assembled for assembly.
4.2 Strict brazing process
The brazing of the metal parts of the multi-layer ceramic shell can be brazed by a nitrogen-protected brazing furnace or a hydrogen-protected brazing furnace. However, when brazing with a nitrogen-protected brazing furnace, the purity of nitrogen must be 99.99% or more. In the brazing process, the brazing process must be strictly carried out, especially if the brazing furnace temperature is not too high. Generally speaking, when using Ag72/Cu28 solder, the soldering temperature should not exceed 950 ° C, and the time should not exceed 5 minutes. This is because when the temperature is too high or the time is too long, when the solder melts from the solid state to the liquid state, gasification occurs on the one hand, causing honeycomb structure inside the solder to reduce the brazing strength; on the other hand, the graphite particles invade the molten solder. Floating on the surface of the solder, after the solder is cooled, it is partially covered by the solder, and the other part is floated on the solder surface, which cannot be removed during the pre-plating treatment, so that bubbles are generated in the place where the graphite particles are present after the nickel plating. This graphite particle bubble cannot be solved by conventional plating pretreatment processes. We have tried to use oxygen plasma cleaning, hoping to oxidize the graphite particles, but the effect is not obvious. This problem can only be solved with a strict brazing process.
4.3 Strict pretreatment process
The pre-treatment process of the shell plating has a direct relationship with the cleanliness of the coated surface of the shell, which is the key to solving the blistering of the plating. Therefore, a strict and effective pre-treatment process is the fundamental guarantee for solving the electroplating foaming. The pre-treatment process described above: plasma cleaning → ultrasonic cleaning → solder cleaning → flowing tap water cleaning → electrolytic degreasing → flowing tap water cleaning → pickling → Deionized water cleaning is a mature process that we have been using for many years. However, the mature process is not static and must be properly adjusted according to product and environmental conditions.
For example, when the room temperature drops to 0 ° C in winter, the pickling solution should be appropriately warmed or the acid treatment time should be appropriately extended to improve the acid treatment effect, otherwise, it will be difficult to remove the oxide layer on the metal surface. For example, when the graphite particles on the product are seriously stained during the brazing process, a sawdust polishing process may be added before the plasma cleaning to remove the graphite particles. In short, the pre-treatment process should be adjusted according to the product and environmental conditions to ensure the cleanliness of the product being plated.
In the pre-treatment process, it is also necessary to pay attention to the replacement of the alkali solution and the acid solution according to the quantity of the plated product. Otherwise, the effect of the pre-treatment may not be achieved, but the plated surface may be contaminated with impurities.
4.4 Optimize nickel plating process
Optimized nickel plating process is also one of the measures to solve nickel plating foaming. When using low stress sulfamate nickel plating, a pre-nickel plating process can be added before positive nickel plating, which is beneficial for solving foaming in metallized areas. .
4.5 Strengthening the maintenance of nickel plating solution
In order to ensure the best coating quality of the outer casing, it is necessary to strengthen the maintenance of the nickel plating solution. It is necessary to periodically analyze and adjust the parameters of the solution to be within the range specified by the process. Secondly, according to the quantity of the plated product, the solution is Activated carbon treatment to remove organic impurities in the solution; third, according to the quality of the product and the amount of the product to be plated, the solution is subjected to a small current treatment to remove the impurity metal ions in the solution to ensure the purity of the nickel plating layer. Reduce the stress on the nickel plating layer and reduce the possibility of foaming.
4.6 Nickel plating and gold plating production should be carried out continuously
Nickel plating and gold plating of the outer casing should be carried out continuously to reduce the occurrence of foaming of the gold plating layer. In the event of power outage or equipment failure, once the nickel plating and gold plating production cannot be carried out continuously, the product should be immersed in deionized water. When the fault is removed, the product is pickled with acid solution and rinsed with deionized water. After that, immediately proceed to the next process of production.
4.7 Pretreatment of tungsten-copper or molybdenum-copper heat sink with heat sink ceramic housing
The ceramic housing with heat sink should be pre-treated before soldering. It must be coated with a layer of nickel and then brazed to reduce the possibility of foaming.
5 Discussion
In the electroplating production process of the multilayer ceramic casing, when nickel plating and gold plating are continuously produced, the nickel plating layer is foamed due to the uncleaned surface being plated; secondly, when the concentration of impurity ions in the nickel plating solution is too high
It also causes foaming of the nickel plating layer. Therefore, to solve the problem of blistering of the nickel plating layer, the following measures must be taken:
a. Strict process hygiene, reducing pollution of the outer casing being plated;
b. Strictly braze the metal parts of the outer casing to reduce the contamination of the graphite particles on the external surface;
c. Strict pre-treatment process to ensure the cleanliness of the coated surface of the shell:
d. Strengthen the maintenance of the nickel plating solution, ensure that the parameters of the nickel plating solution are within the process range, reduce the content of organic impurities and impurity metal ions in the solution, ensure the purity of the nickel plating layer, and reduce the internal stress of the nickel plating layer.
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