Photo-imaging etching resisting plating ink (hereinafter referred to as wet film) is a new type of anti-corrosion and anti-electroplating masking material for circuit board manufacturing that appeared in the early 1990s. At that time, the technical leaders and departments of the former Ministry of Electronics were promoted as a new process in the industry, and also organized professionals to visit and use professional manufacturers Guilin Radio 5 Factory to conduct professional study. After more than ten years passed, the wet film is famous for its excellent anti-corrosion and anti-electroplating performance, high resolution and various coating forms (roller coating, curtain coating, screen printing, spraying, etc.) as well as general and inexpensive equipment. , Widely used in the circuit board industry. The popularization and application of wet film shows the development of the pattern transfer process and has entered a new milestone. It provides an ideal mask material for the production of thin wires and promotes the development of integrated circuit and microelectronics technology. It is a major achievement in the development of circuit materials. . In recent years, with the enthusiastic service and vigorous promotion of ink printers, wet films have also been used in the manufacture of signs, panels, and decorative paintings, and they have received great results. So far, printing, building materials and related fields are also being used, and the speed of development is staggering. 1, the wet film corrosion resistance and for a variety of masks 2, higher resolution 3, anti-plating properties 4, the choice of wet film
1.1 resistant to a variety of acidic etching solution
The prominent point of the wet film is that it is resistant to a variety of acidic etching solutions: acidic copper chloride etching solution, ferric chloride etching solution, nitric acid series etching solution, and sulfuric acid hydrogen peroxide etching solution. These etching liquids are used for the etching of circuit boards, and some of them are used for the etching of steel, stainless steel, aluminum signs, and panels.
1.1.1 Alkaline etching solution
When the outer layer of the double-sided board and the multilayer board are etched, the plating layer is used as a resist layer, and the etching solution is an alkaline copper chloride etching liquid. In the inner layer production of multi-layer boards, wet films are mostly used as masks to make patterns. Due to the thick copper layer, the wet film is completely resistant to alkaline copper chloride etching under certain conditions. This not only saves one device (acid etching machine), reduces the production area, and eliminates the auxiliary equipment (reproducing device). The adjustment and maintenance of the etching solution also reduce the pollution.
1.2 Masks for Signage Panels
In recent years, wet film has been commonly used in masks for panels, panels, metal paintings, filters, grids, and integrated circuit frames. Past masks for the manufacture of these products have been made of bichromate as the sensitizer and polyvinyl alcohol. According to the theory of sensitization, the sensitized portion is cross-linked to become trivalent chromium, and the desired pattern remains on the surface of the board; and the unsensitized portion is washed away by hexavalent chromium after development. Replacing the wet film now not only shortens the production cycle and avoids the emission of hexavalent chromium, but also greatly contributes to environmental protection and eliminates the poisoning of operators. At the National Signage Technology Symposium held in Jiangyin in April this year, the director and representatives of the delegation were very loud about it. A wet film manufacturer distributed about 30 samples at the meeting and sold it hot. It seems that the moment of ending with dichromate as a sensation is not far off.
1.3 Masks for Mold Making
The good corrosion resistance of the wet film does not appear in the direct etching of the circuit board, because the general copper thickness is 18um, 35um or less. The most prominent are the masks used in the manufacture of press roll molds (pressure roll molds for embossing of leather, fabrics, plastics, and paper, etc.) with etching depths of 0.2-0.4 mm and equipment for etching with nitric acid (materials made of 45# steel , tool steel more). The etching method is pressed roller rotation immersion method, the time is about 5 to 10 minutes, the etching for large-scale integrated circuit frame is mostly used for ferric chloride temperature 40 ~ 45 °C, time 4 ~ 6 minutes range (material: iron nickel Alloy, 0.4-0.2mm thick) double-sided etching.
1.4 Mask for Electro-Etching
In the etching of signage and panels, the disposal and discharge of waste liquids is a big problem. It is even more prominent in small cities that have unconditionally looked back and deal with waste etching liquids. In recent years, the electro-etching (also called electrolytic etching) process that has swept the industry has solved this problem. A device can be purchased for a few thousand dollars. This is because the electroetching solution is a non-contaminating etchant and thus there is no need to solve the etchant treatment and discharge. However, the mask for electrical etching is pre-etched with an automatic vinyl cutter, and then affixed to the etched surface for electro-etching, thus limiting mass production (mass costs are too high). Fine words and finer and more complex patterns cannot be processed. After wet film is used, whether it is a single piece or a large quantity, no matter whether the pattern is intricate or not. All can operate freely. In addition, the large-area etched signboard panel where the wet film is used for the positive pattern (ie, pattern projection) can show its excellent performance: the bottom surface is flat and the side etching is small.
Another outstanding advantage is the higher resolution, which allows the circuit board to process fine lines and create fine metal painting conditions. There is no such mask compared to economic value. With a single-sided direct etch (including the inner layer of a multilayer board), 2 mil line widths and lines can easily be made. These data are obtained in real production rather than tests and samples.
In recent years, I have been able to contact the most prominent example of the grid manufacturing products: stainless steel or iron-nickel alloy material, thickness of 0.02 ~ 0.05mm, using a wet film as a mask, hollow lines after etching rough 0.015 to 0.012 mm. In addition, in the manufacture of metal paintings, it can also be manufactured in a hierarchical version, and its products are exquisitely collectible. The razor covers, filters, acoustic panels, and metal business cards are now made with wet films as masks.
Pattern plating masks that are layered on double-sided and multilayer boards, more and more manufacturers use dry film to wet film. With the advancement of science and technology and the requirement of environmental protection, the emission of fluoride is forbidden on the agenda. The original tin-plated lead solution not only pollutes the water source but also affects the operator's health due to the presence of fluoride. Therefore, it is changed to contain no fluoride. Pure tin plating is imperative. At present, many manufacturers have switched to pure tin plating, and production practices have proven that wet film as a mask for pure tin plating has been approved by the circuit board industry. In addition, it has been used as a copper, nickel, and tin-lead plating (still used by some manufacturers) in the process.
3.1 Plating for Signage
Its plating resistance adds new processing methods and new varieties for the manufacture of signs and panels. With its good resistance to etch and plating, it has also been used for signs and panels for good results, such as black nickel etched panels or signs on copper plates.
The flow is: etching convex pattern → black nickel plating → film removal → protection of copper surface. The gold and black plated signs or panels with this word and pattern dimension are completed. The effect is beautiful and has outstanding features. It is really fine (it can also be made into gold and the rest of the board is black ).
Good plating resistance is also used in high-grade plated gold plating. The brand of a certain institute in Beijing is gold-plated, and it always maintains its true color. The choice of gold plating is a means of manufacturing high-end signs by signage, but its aesthetic cost is not high.
4.1 The primary condition for selection is the environmentally friendly wet film
Among the many wet film brands, how to choose the wet film suitable for their own products is the main problem in use. This should be based on the characteristics of their own products to choose, in the same product its performance may not be the same, but the primary condition is to choose a low toxicity, non-toxic or less polluted wet film, although it is the primary condition but it is difficult because Most brands contain benzene, ether or a large amount of organic solvents that have caused environmental pollution. Some manufacturers have explicitly stated the names and contents of organic solvents on the labels, but there are also a considerable number of brands that are low-toxic or wet films that are moving toward low toxicity. However, the use of large amounts of diluents (organic solvents) cannot be underestimated. The second condition is the unity of price and quality performance.
4.2 Wet film selection for single-sided, inner circuit boards, signage panels (for direct etching)
The mask used for direct etching must be selected to have good leveling, ie screen printing or roller coating, which can be quickly leveled on the board surface. Because it is used for direct etching its coating thickness is about 5 ~ 10um. Some manufacturers use thinners to increase the coating area (with a consequent reduction in costs), and the amount of diluent added by conventional wet films should not exceed 5% of the total amount, because users often add 10% to 25% of the product. The range of coating area has been expanded from 20 to 25 m2 to 25 to 30 m2, and the thickness can also be reduced to about 4 to 7 years.
4.2.1 Dilution Added Control
The thinner is preferably supplied by the original wet film manufacturer (alternatively, environmental protection or low toxicity). Adding too much diluent will result in a decrease in exposure energy or a decrease in the etch resistance. Especially when used for roller coating, the groove of the roller is different (some without grooves) with different diluents. It can also be added according to the different amount of the product.
Bubbles appear during dilute stirring, which is the cause of stirring. When mixing, it should be in one direction. If the mixture is used positively or negatively, according to the theory of fluid mechanics, the flowing liquid encounters a reaction force and will generate whirlpools, so bubbles appear. Bubbles should normally disappear within 40 seconds of screen printing. If it is still for 10 minutes, it may be a problem with the wet film itself or improperly added diluent.
4.2.2 The fineness of the wet film
According to the conventional ink supplier's instructions, the superscript fineness is less than 5um. This fineness is useful for masking general lines and dots, but when used for fine lines and fine dots, the above fineness is relatively marginal. Tiny burrs appear on the edges of lines and dots after development. In this case we should choose 2.5um ~ 3.0um fineness. For the convenience of operation, it is necessary to measure the wet film purchased by the available fineness meter.
4.2.3 Selection of diluent
In the above discussion, it is best to use thinners for wet film. The diluents sold on the market mostly contain ethers and benzene hydrocarbons. It is best not to use them or use them less. Wet film is a film-forming material that combines UV and thermal curing and contains a certain amount of solvent. These solvents not only have odor and toxicity (according to different brands of different solvents), seriously endanger the health of workers and the surrounding environment. As early as the 1980s in Germany, statistics, the use of paint and ink solvent up to 40 tons per year. The United States, Sweden, and other countries also have legislation that strictly restricts the addition of organic solvents and stipulates that inks and coatings containing benzene-containing hydrocarbons must not exceed 5%.
China's "Hygienic Standards for Design of Industrial Enterprises" also stipulates the maximum allowable value of toluene, formaldehyde, benzene, and benzene homologues within 1m during the operation. With the rapid development of China's industry, there has been a great improvement in the operation of the ground. The air in the ventilation room is fresh, but the most fundamental problem is to ask the research department or experts to research and develop non-toxic or low-toxicity wet film. Improvement is the only way out