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Electroplating technology, as a kind of functional finishing technology, has been widely used in electronic products because of its excellent wear resistance, corrosion resistance, uniform coating thickness and high density. With the rapid development of electronic industry, the requirement of electroplating technology is higher and higher. NCVM, as an excellent surface treatment process, has advantages that other processes do not have. It is widely used in electronic products. There are many parts using NCVM process on mobile phones.
1. What is NCVM
NCVM is English Non conductive vacuum metalization, also called discontinuous or non-conductive plating coating technology, is a kind of common vacuum plating of high and new technology. Vacuum plating, referred to as VM, is the abbreviation of vacuum metalization. It refers to metal materials in vacuum conditions, the use of chemical, physical and other specific means of organic conversion, so that the metal into particles, deposition or adsorption on the surface of plastic materials, forming a film, that is, we call the coating film. Vacuum non-conductive electroplating, also known as NCVM, its processing technology is higher than that of ordinary vacuum electroplating, and its processing process is much more complicated than that of ordinary process.
2. Technological process of NCVM
The following schematic diagram is the actual picture of NCVM process flow:
The membrane diagram is as follows:
In many cases, in order to improve the adhesion of the bottom and middle paint and improve the product's resistance to water boiling, many factories use a layer of primer on the coating layer (thickness 1-2um);
3. Common problems of coating and cause analysis
1). The coating is yellow or blue
Coating material quality is too yellow, too little will be blue. In addition, if the vacuum plating furnace is poor in air tightness, or the vacuum gauge is abnormal, the vacuum degree in the furnace chamber is not enough, which will cause the overall coating blue;
2). Less plating
When coating, the product placement layer spacing is too small will lead to less plating on the top and bottom of the product, need to increase the layer spacing by adding sleeve between the two layers to improve; Some products are more complex structure, causing some parts of the back evaporation source less plating, generally by reducing the product placement density to improve;
3). Pressure test breakdown of coating layer
Coating layer is too thick resulting in a small resistance film, the test was conducted. In general, we need to reduce the quality of the plating material, reduce the thickness of the coating layer to improve its resistance. Under normal production conditions, there will be a very small probability of pressure test NG, through the coating machine for two no-load vacuum can solve the abnormal; Therefore, in the proofing and production process, it is necessary to test the withstand pressure of each furnace product, and the requirement should be at least 30KV without breakdown
4). Coating surface after fog
The lack of UV curing energy of the non-metallic luster primer results in the incomplete curing of the UV primer, which can be improved by improving the primer energy. Some large or complex structure of the surface need to pay attention to adjust the Angle and distance of UV, etc. to ensure that the spray surface can be irradiated enough UV light, if some parts of the irradiation will cause fog, no metallic luster phenomenon;
4. The structure design of NCVM
1）. Material material is generally PC or PC+GF(10%), avoid PA+GF; Mainly due to the high hardness of PA+GF material, the surface polarity is small, not conducive to the adhesion of paint;
2）. Texture of material surface: the product surface is required to be smooth, and the highlight is the decorative feature of NCVM.
3）.NCVM components are not made of metal materials. Firstly, NCVM is adopted for metal keys, which is repetitive and wasteful in technology.
4）. The main shell material of NCVM shall be made, whose edges and corners shall be at least R0.5, decorative products shall be at least R0.3, and the width shall be at least 1.2mm, to ensure the vibration and wear test of the whole machine;
5）. Part PL surface should be inverted R0.1 or do 0.2 straight extension to avoid tooth edge problem caused by sharp Angle;
6）. The R Angle of the contour is greater than 0.3(recommended 0.4-0.5);
7）. Try to avoid continuous thickness of glue;
8）. The color of NCVM should not be too dark. If the proportion of pigment slurry added is more than 3%, there is a risk of boiling and foaming, and losing 100 grams.
9）. NCVM for big plane, hole edge and right-angle edge location will have oil accumulation problems, so try to avoid using it.