Study on Foaming of Secondary Metallization Nickel Plating in Ceramics for Electrovacuum Devices

Research on Foaming of Secondary Metallization Nickel Plating on Ceramics for Electrovacuum Devices Yang Weiying, Wu Zhi, Zou Guijuan, Zeng Min (Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621900, China) Chemicals and Secondary Metals The analysis of XPS XRESEM and other methods shows that the secondary metallization foaming of ceramics is related to the thickness of the deposited layer's substrate and deposition layer, and the specific morphology of molybdenum after one-time metallized sintering of ceramics is more comparable to that of molybdenum particles. The looseness of the large particles and the electrochemical properties of molybdenum determine that the thickness of the deposited layer on the molybdenum must be within a suitable range of -9m in order to reduce the stress in the deposited layer and ensure a good nickel layer and molybdenum after sintering. Combining the nine air tightness and sealing strength is one of the main characteristics of the electric vacuum device. This feature requires that the components for the electric vacuum should be ceramic one by one, avoiding leakage and low sealing strength as much as possible during the processing process. The factor is that the foaming of the nickel plating layer in the secondary metallization process of ceramics is one of the factors. It is also a special waste product of the secondary metallization of ceramics, ie the electroplating of nickel. The phenomenon is that the ceramic nickel plating layer is burned twice. The reason behind the partial blistering (uneven bubble size) may be the contamination of the metallized layer with contaminated plating solution and excessively thick nickel plating. In the process and production, the first three can basically overcome the latter. The thickness of the coating is not easy to control in production. In order to explore whether the excessive thickness of the coating can cause foaming of the nickel layer, this paper combines the production practice to carry out the corresponding process experiments, and theoretically explains the plating substrate and the over-thick Relationship between electroplated nickel layer and blistering after secondary sintering 1 Experiment 1.1 Preparation of sample 75% alumina ceramic or 97% alumina ceramic was cleaned with surfactant or organic solvent. After heat treatment, certain methods were used. Mo-Mn and other metal powders and pastes are coated on ceramic parts and sintered once again to obtain a conductive metal layer on the ceramic. Electron scanning microscope (SEM) and X-ray photoelectron spectroscopy are used prior to electroplating of nickel. (XPS) Composition and morphology analysis of the once metallized surface layer.

1.2 Experimental methods In the experiment, the metallization layers after primary metallization were analyzed by means of SEM and XPS, and their composition and morphology were analyzed. The thickness of the metallized layer was measured by a light microscope and an XRF thickness gauge, and then metallization was performed. The ceramic electroplating nickel and nickel electroplating solution are prepared according to the dark nickel plating formulation. The plating tank is a square tank bath. The pH value temperature and the current density are all performed within the process range. The values ​​of the various coating thicknesses in the experimental results are different. The current density and plating time are obtained.

After sintering, the ceramic is sintered according to the sintering process and the quality of the sintered material is recorded. Then, the thickness of the nickel layer is measured using an XRF thickness gauge. For details of the process test, see Table 1 below. Table 1 Nickel layer after nickel plating and sintering under different conditions of ceramics Thickness and quality of the experiment number of times the number of samples (a) average thickness of the nickel layer (am) mass after sintering 184., 9.0 in this range of plating is not blistering 2163., 11.914 samples of nickel plating thickness 3. Female 9. 0 not Foaming; 1 sample nickel plating thickness is 1 (> 11.9Mm plating is not blistering; 1 sample nickel plating thickness is 9.10-6m blistering 3165.14.06 samples nickel plating thickness is 5. 9.5Mm is not foamed; 1 sample nickel plating layer thickness is not foamed at 9.3 11.5Mm; 9 sample nickel plating layer thickness is foamed at 10-13.6Mm 4167., 15.34 sample nickel plating layer thickness is at 7.9.7 ,Ym did not blistering; 7 samples of nickel plating thickness was not blistering at 9.8 14.0Mm; 2 samples of nickel plating thickness bubbled at 9.413.7Mm; 3 samples of nickel plating thickness from 13.b15.3Mm Foam 5209091.86 kinds of nickel plating thickness of 9.2-13.5Mm non-foaming; 1 sample nickel plating thickness of 9.2 11.6Mm blistering; 11 samples of nickel plating thickness 1.3 experimental results of any kind of plating, must It must be known on which substrate (generally metal) the deposition of the metal is performed. Different metal substrates have different surface electrochemical characteristics, and the stress in the deposited layer and the binding force between the substrate and the deposited layer are not Since ceramics are non-metals, direct nickel plating on ceramics cannot be achieved, and a conductive metal layer must be obtained on the ceramic by a certain process in order to be nickel-plated, so the exploration of secondary metallization foaming must be carried out from a metallization. Process and Principle Start At present, in the production and research of electric vacuum devices, a large number of ceramic primary metallization processes are used to produce various ceramic metal sealing products by one-step sintering metal powder method. Mo-Mn activated metalized powder method is commonly used One of the main components of the Mo-Mn-activated metallized powder method is MoMn, and in addition there is a small amount of active components such as S2CaOAl23. Usually, a layer of MoMnSi2CaO, Afc3 mixed metallized layer is applied on the ceramic by coating. Then, a sintering process is performed to analyze whether the surface layer after the primary sintering is a gold oxide or a mixture of a metal and an oxide. Using SEM and XPS methods, etc. After sintering, the surface layer was analyzed and the results showed that the surface layer was composed of metal Mo, MnSi2CaO Al23, etc. The other components were located in the transition layer because: During the primary sintering process, complex physical and chemical changes occurred between the metallized layer and the ceramic. Mn, which is uniformly mixed in the metallization layer before sintering, is oxidized to Mn2 in a metallizing atmosphere, migrates to the intermediate layer during the sintering process and forms a transition layer with other components S2CaOAl23, and Mo is sintered as metal under the metallization conditions. After the primary sintering of Mo*, the molybdenum located in the surface layer is different from the usual molybdenum in density and grain size. According to the data, the molybdenum in the metallized layer is 50% to 6% of the density of the dense molybdenum (%), and the sintered molybdenum is porous. The molybdenum layer. The SEM method was used to compare the morphology of molybdenum layers and metallic molybdenum after primary metallization: it was a metallized molybdenum-shaped ceramic after primary metallization sintering and scanning of metal Mo. The molybdenum layer obtained by the metallization process has a certain thickness, and the thickness of the ceramic metallization molybdenum layer obtained by the Mo-Mn activation metallization powder process method is analyzed by using SEM and XRF thickness gauges, and the thickness of the Mo layer is only Tens of micrometers from the above theoretical analysis and some test results show that: the nickel-plated ceramic substrate for electro vacuum is different from the general industrial nickel-plated substrate, the former is obtained through a certain process to obtain a special plating Nickel substrates have a relatively large particle size, the substrate is loose, and is tens of microns thick (very thin). Generally, the nickel-plated substrate is directly on the dense metal with a thickness of more than millimeters. ongoing.

The quality of the plated layer after sintering is analyzed in the following table: 76 samples were made under several conditions within the process range. After plating, 32 samples with a nickel layer below about 9 Mm were obtained. No blistering; among the 30 samples of 9~13.5m in the nickel layer, 17 are not blisters after re-sintering and 13 are foamed; the nickel layer is 14 samples above about 13.5Mm, all from the second sintering The results of the foam show that the quality of the sintered product (foaming or not) has the following rules: The nickel layer is in the proper range, eg, less than 9 Mm, and does not foam after the second sintering; the thickness of the nickel layer is too thick, for example, over 13.5 m. After the secondary sintering, foaming occurs; between these two thickness ranges, there is a transitional range in which the coating may be foamed or may not be foamed. Therefore, the following conclusions are drawn: The foaming phenomenon of the ceramic nickel layer after sintering is related to the thickness of the nickel layer to be plated. The thickness of the plating layer is mainly determined by the current density and the plating time, as long as the current density is controlled and the plating time ( With high current density and relatively short plating time, the thickness of the coating can be controlled, the coating will not blister after sintering, the relationship between the current density and the plating time is not well controlled, the coating is too thick, and blisters easily after sintering, the quality of the coating Can not be controlled 2 Analysis and discussion Ceramic nickel layer is too thick, easy to blisters after sintering, for this particular phenomenon, can be explained from the basic principle of plating: In the plating process, metal ions can only adhere to the cathode at a favorable position. On reaching a growing point and combining there into the growing lattice, the initial lattice growth is lateral, creating a thick layer of atoms, but at some point if the lateral process is disturbed, because All plating solutions must contain impurities that are strongly adsorbed on different parts of the cathode surface. When the growing surface encounters such adsorbent material, Lateral growth is terminated. Due to the influence of adsorbed substances, the growth layers gather into clusters and form a ladder. Finally, they aggregate into grains, and atoms on grain boundaries between grains and grains deviate from normal crystal alignment. And there are other defects within the grains, mainly dislocations, twins and co-deposited heteroatoms or molecular groups, due to the mismatch of these lattice parameters or the entrainment of foreign substances, such as oxides or hydroxides, Water, sulfur, or metal impurities that prevent the formation of a normal lattice and produce stress in the deposited layer. Therefore, the electrodeposited layer tends to be in a state of stress when it is plated out. This kind of stress that is independent of the substrate is called internal stress. Or residual stresses, which may be partially or completely present or remain in the deposited layer. The one we are familiar with is the macroscopic stress and the structural reasons for the generation of macroscopic stress. It is not yet fully understood that the macroscopic stress can cause the deformation and crack of the coating, and the loss of the binding force with the substrate is the nickel-plated layer after the secondary sintering of the ceramic. The surface morphology, on the surface shows a secondary sintering cracks throughout the entire nickel-plated surface after the secondary sintering of the nickel-plated layer of the surface, which is the scanning electron microscope photographs in the sintering process between the substrate and the nickel layer 3 SEMimageofNicoating forces cannot constrain the phenomenon caused by the stress in the nickel layer. This not only indicates that there is stress in the ceramic nickel layer, but also that the nickel layer of this structure is easily foamed due to the force (or heat) although there is stress in the plating layer. There is also a certain binding force between the coating and the base metal, so a good coating does not fall off due to mechanical forces (such as tensile stress in the coating) or deformation but when the nickel deposit has excessive tensile stress, not only can the coating be comprehensive Cracking, but also the deformation of electroformed parts from the impact of macroscopic stress on the coating analysis, coating foaming and macroscopic stress if the stress is nickel layer The main reason for foaming after sintering, but the stress is present in thin and thick coatings, but after sintering there is a thin coating does not blistering, and thicker coating is very easy to blistering phenomenon. It can be explained by the model. Ceramic nickel plating is performed on a large, very rough surface of the particles. Many large molybdenum particles penetrate deep into the nickel layer like a needle. If the thickness of the nickel layer is appropriate, it just covers the top of the large molybdenum particles. The molybdenum particles that have penetrated into the nickel layer reduce the stress in the nickel layer. In this case, the bonding force between the nickel layer and the base material is greater than the stress existing in the nickel layer, so the nickel layer with the appropriate thickness does not easily blisters if nickel is plated. When the layer is too thick, no molybdenum eliminates the stress in the excessively thick nickel layer. Therefore, the stress in the easy-to-bubble coating after sintering and the binding force between the plating layer and the substrate are present both before and after sintering. And hydrogen burning also plays a role in reducing the stress, but the production of nickel layer is good after electroplating, and the metal molybdenum surface after burning a metallized has a special surface state (such as porous, rough surface), energy Obtaining a nickel layer of a better thickness directly on the molybdenum surface is otherwise impossible. Electroplating nickel directly with metal molybdenum can illustrate this point. Because the molybdenum surface of metal molybdenum is much smaller than the latter or the surface is much smoother than that of molybdenum surface after metallization, the molybdenum metal is The useful nickel layer is very thin. When the thickness is less than 1m, it is not easy to peel, and when it is more than 1um, it is easy to peel off. In terms of the electrical parameters, the plating time must be short in the production practice to improve the ceramic or metal and Molybdenum brazing performance, when electroplating on molybdenum, to control the current density and plating time, the nickel layer to be plated is thin, otherwise the nickel layer from the hydrogen burning from the skin, leading to product scrap 4 conclusions of a metallurgical process The nickel-plated substrate (with pores on the surface, large molybdenum particle size, and roughness) X has a large influence on the quality of the secondary metallization nickel plating, controlling the secondary metallization under the condition of a primary metallization process The quality of the product, the thickness of the nickel layer is controlled within the appropriate range is very important. In addition, the quality of the secondary metallization products is also related to the plating parameters that affect the internal stress of the nickel deposits, such as temperature, pH value, inorganic impurities, etc. of the chloride content in the bath. To reduce the stress, the electrical parameters should be controlled The most suitable range.

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