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In order to obtain the coating with high adhesion strength, in addition to considering the two internal factors of creating the adsorption conditions and eliminating the stress of the film in the process of forming the film, measures should be taken from many external factors affecting the adhesion strength of the film
1. The substrate shall be strictly required
Substrate sort is more "material is widely used, its shape will be different according to the use, such as decorative plating film corrosion resistant film substrate is plated parts of itself, and half guide Hugh and integrated circuit, a copy piece generally adopts the thin sheet, it with membrane attached as part of the circuit and also to have certain requirements on the performance of the substrate, such as requirements have a lower surface roughness and smoothness (that is, the surface is not a right degree), especially for thin film circuit with the substrate, the surface should be smooth, should achieve the highest to the lowest on unit area distance is less than 25-1500nm;, the material structure should have a high density. Secondly, the substrate should have a high chemical stability, do not react with the film material, is not limited by the use of chemical reagents in the process of the thin film circuit, but also requires the substrate to have a certain thermal stability and thermal shock resistance, in order to withstand the process of baking and heating;High thermal conductivity, to prevent circuit components from overheating, and there should be a certain mechanical strength, prevent breakage;And the thermal expansion coefficient should be equal to that of the film to prevent the film from spalling under stress;If mass production of substrate costs should be low.
2. The substrate shall be carefully pretreated for plating
Substrate into the coating chamber before, no matter how to its surface coating requirement, should be careful before plating processing (cleaning) through the process to achieve the purpose of the workpiece to oil decontamination and dehydration due to exist on the surface of oil will not only destroy the vacuum chamber of a vacuum, and the oil under the thermal state decomposition can also make membrane layer growth in the process of adding impurities, dirty greasy including dust, perspiration and workpiece surface And so on.Decontamination requires removal of oxidation layer, burr and loose tissue on the surface of the substrate.Then after the coating process of electrons, ions bombardment so that the surface of the substrate before the coating appears molecules
Grade atomic grade cleanliness, which is an important measure to improve the coating firmness.
The pollution sources of substrate surface are mainly as follows:
1) All kinds of dust adhered to during processing, transmission, packaging and placement of parts.
2) lubricating oil polishing paste and grease sweat stains adhered to by parts during processing, storage and transportation
3) Oxidation film formed on the surface of parts in moist air;
4) Gas absorbed and adsorbed on the surface of parts.
Above these filth basically can use go oily or chemical clean a method to get rid of it should note is in clean workpiece while must also be opposite the tool container that USES at the same time clean and maintain cleanness, also cannot achieve the purpose that clean otherwise.
3. The substrate is heated during film formation
Substrate temperature, grain size, grain growth process speeds up, reduce the membrane coagulation defects, recrystallization enhanced, so as to further perfect the formation of the membrane and thus can reduce the internal stress of membrane and substrate temperature is too high, and the thermal stress in the membrane increase to reduce the total stress of membrane, the heating temperature of substrate to optimum when, generally no higher than 400℃.
4. Control evaporation source temperature and vapor pressure
Heat the evaporating source to the evaporating temperature (steam pressure &(temperature), some of the metal atoms to escape the solid phase, at a certain velocity fly a higher evaporation source temperature, not only on the number of metal atoms to escape, escape and the kinetic energy of metal atoms is big, therefore with over heat barrier of energy, in the base sheet forming strong chemical adsorption but evaporation source temperature is exorbitant, can make the vapor pressure increases rapidly, the deposition rate is accelerated, and affect the performance of the membrane and stress for this, must according to the different nature of the membrane, control corresponding evaporation temperature and vapor pressure.
5. Base film between substrate and film
Pre-coating the base film on the substrate is one of the technological measures to increase the adhesion strength of the membrane base interface. For example, when vacuum ion-plating technology should be used to prepare silver-plated aluminum electrical connectors, the solubility of silver in aluminum is only 1% around, if on the aluminum silver directly, its adhesion strength is poor Solubility in the aluminum and copper) is 5.6%, aluminum solubility in the copper is 9.4%, the solubility of silver in copper is 8%, so first copper plating on aluminium as base film, then can greatly improve the joint silver plated with silver coating on the surface of the aluminum parent metal adhesion performance And like a gold-plated copper palladium in glass or ceramic The adhesion is bad, then first and then backing film Gold-plated copper palladium, again can improve the adhesion strength At the bottom of the membrane materials currently used multi-purpose chromium molybdenum nickel titanium, tantalum, etc metal.
6. Heat treatment is carried out on the substrate after film forming
After film deposition, necessary annealing treatment can be carried out, the temperature can be slightly higher than the deposition temperature, or the plating parts after film formation can be placed in 400℃ high temperature baking 8 hours for high temperature film fixation. The mechanism is to intensify the thermal motion of membrane base molecules, mutual diffusion at the interface and form the alloy layer with high strength.
7. Dust, moisture and oil - proofed during coating process
Clear coating indoor dust, set the workshop of high cleanliness, keep clean indoor height is the super size requirement of plating film Air humidity larger area, except to the substrate before plating vacuum indoor wall and each component in the vacuum chamber cleaning, seriously want to bake to gas Oil, to avoid the oil into the vacuum chamber, pay attention to the oil return oil diffusion pump, diffusion pump for heating power high measures must be taken One meter of coating machine for the production experiment, with five layer of aluminum plate as a mechanical barrier "is to make sure that the oil diffusion pumpThe steam can not return to the vacuum chamber, which reduces the extraction rate, but improves the adhesion between the membrane bases.