Development of soldering materials for the electronics industry

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Development of soldering materials for the electronics industry [Copy link]

Development of soldering materials for the electronics industry

[Source: Beijing Chaoyang Soldering Flux Factory] [Author: unknow] [Time: 2004-12-28 14:10:15] [Clicks: 7169]

With the continuous progress of science and technology, electronic products are developing towards miniaturization and high reliability, which puts forward higher and newer requirements for soldering materials used in the electronics industry. This article briefly introduces the development of three aspects: flux, solder alloy and paste solder. During the brazing process, flux removes oxides, prevents reoxidation, and allows molten solder to quickly replace the flux and fill the brazing seam. Therefore, flux is an indispensable and important material in the brazing process of electronic products. There are many flux manufacturers (companies). The most famous ones abroad are American company A, Kester, British Malticore, Japanese Senju, German Stanmol, etc. Domestically, the designated manufacturers of the former Ministry of Electronics include Beijing Chaoyang Flux Factory, Jiangsu Haimen Sanyang Chemical Factory and several other units. At present, the annual demand for flux produced by electronic assembly is more than 200 tons. Different types of flux can be selected according to different use processes. According to their main components and characteristics, they are usually divided into three categories. 1.1. Inorganic soldering flux Inorganic soldering flux contains inorganic acid and inorganic salt, such as hydrochloric acid (HCI), phosphoric acid (H3PO4), ammonium chloride (NH4CI), zinc chloride (ZnCl), etc. It can be made into liquid, paste and dry powder. It has the advantages of wide temperature range, brazing by various heating methods, and brazing temperature up to 3000C. It is still used in the production of some parts of metal products, electrical appliances and electronic products. This type of flux is highly corrosive. When using it, you should pay attention to its residues must be carefully removed. At present, the development direction is to develop low-corrosive and easy-to-clean inorganic soldering flux for specific products and processes. Organic soldering flux Organic soldering flux contains organic acid, organic base, organic halide, and their derivatives. Such as adipic acid (C6H10O4), C6H14O4 (suberic acid), urea (CO(NH2)2), diethylamine hydrochloride (C4H11CHCI), etc. This type of flux is generally made of a combination of multiple materials. Its characteristics are medium deoxidation ability, lower activity than inorganic ones, and significantly lower corrosiveness than inorganic ones. When brazing at temperatures below 3000C, if used properly, it has good fluxing properties. In recent years, many newly developed no-clean and water-cleanable fluxes belong to this category. The advantage of no-clean flux is that the soldering liquid does not need to be cleaned, which not only reduces costs but also is beneficial to environmental protection. In the development of this type of flux abroad, the solid content has dropped from 20% to about 2%, and it has developed from low halogen content to halogen-free type. However, in order to meet market demand, low-halogen, high-solid content products are still retained, which is conducive to users to choose at will under the premise of no-cleaning. At present, no-clean soldering flux is widely used in the United States, Japan, Western Europe, etc. Since the 1990s, my country has developed several halogen-free no-clean soldering fluxes, whose activity and solid content are comparable to similar foreign products, but there is still a gap in process adaptability, storage stability and the state of soldering liquid residues. In the future, research and development work should be strengthened, and more types of no-clean soldering fluxes should be produced under the premise of strictly implementing relevant standards to facilitate the promotion and application of such fluxes. Water-cleanable flux has the advantages of strong activity, good process adaptability, good stability and environmental protection requirements. It can be used for component packaging welding and wave soldering when assembling printed circuits, and the soldering liquid must be cleaned with water. At present, most water-cleanable fluxes on the market have a solid content of up to 10-30%, and some of them are corrosive at room temperature. Therefore, a new type of water-cleanable flux is developed to reduce its solid content and halogen content and inhibit corrosion. This product will have a broad market. Resin flux At present, resin flux is still mainly rosin-based. According to relevant standards or specifications, it can be divided into three types: R-type pure rosin-based flux, RMA-type medium-active rosin-based flux, and RA-type active rosin-based flux. Different types of flux can be selected for different requirements. In the assembly and production of electronic products, RMA and RA types are mostly selected. Although RA type has excellent soldering performance, when assembling high-reliability circuit boards that meet the requirements of MIL-P-28809, RMA type flux is generally used, and it is required to be cleaned with Freon or CFCs after soldering. As the circuit density becomes higher and higher, CFCs will be banned. Some flux manufacturers, while developing new cleaning agents that do not contain Freon or CFCs, have developed new resin fluxes with low solid and halogen content, very little solder residue, and electrical properties that meet the requirements to meet market demand. Solder alloy containing gold for electronic industry. Its main material has reached the international advanced level in my country and is exported to developed countries. Mainly due to the backward development of flux, the overall level of tin-lead solder is still lagging behind that of developed countries. In order to improve the production level of tin-lead solder in my country as soon as possible, we must give full play to the overall advantages of the whole industry, strengthen technical exchanges and cooperation, and seek common development. We should give full play to the role of technical supervision departments at all levels, jointly resist and crack down on counterfeit and shoddy products, and protect the interests of our national industry and users. At present, the market capacity (including export) of various tin-lead solders and their products is about 10,000 tons. There are many varieties of solder alloys, usually composed of Sn, Pb, Sb, In, Ag, Bi, Zn, Cb and other elements. According to different composition ratios, they can be made into a series of alloys with different melting points and strengths, and can be processed into various forms such as ingots, strips, wires (with or without cores), powders, sheet rings, balls, etc. Soft solders used in the electronics industry are mainly tin-lead solders. The main components, impurity content, melting temperature, supply status, main properties and uses of this series of alloys are clearly stipulated in the standards or specifications of various countries. In recent years, in order to meet the welding requirements of microelectronics, high-precision electronic products and certain special processes, as well as people's awareness of environmental protection, some trace elements are added to the original alloy to improve the thermal fatigue resistance and other properties of the solder joints. Lead-free solder alloys have been developed. 2.1. Solder alloys for wave soldering. Generally, 1# tin and 1# lead are used as raw materials to make 63SnPb alloy and 60SnPb alloy. Usually, different processes are used, and the impurity content in the alloy is also different. In the wave soldering process, the molten solder is in a dynamic state, so its oxidation resistance is particularly important. For this reason, a lot of research has been carried out at home and abroad, adding elements such as P and Bi for static tests to form a thin oxide film on the surface of the molten solder to prevent the solder from oxidizing, which is effective when the solder is in a static state. However, during wave soldering, the surface of the molten solder is in a state of continuous flow. Therefore, users still use antioxidants to isolate the molten solder from the air to achieve the purpose of preventing oxidation. At present, the anti-oxidation effect of some products is not ideal. Therefore, efficient and low-cost antioxidants still need to be developed. 2.2. The performance of active solder wire mainly depends on the selection of core flux. Different fluxes are selected according to different uses. According to GB3131-88 standard, the flux content in active solder wire is usually 1.5-2.5%. The main indicators for evaluating the quality level of solder wire at home and abroad are: expansion rate, insulation resistance, electron mobility, ion contamination, corrosiveness and halogen content. The key technology in production is to prevent the additives in the flux from being oxidized or decomposed when preparing the flux and drawing the welding wire, so as not to lose the flux activity. In order to implement the Montreal Protocol, various countries have carried out the research and development of no-clean solder wire. Beijing Chaoyang Flux Factory has developed no-clean active solder wire and is now in mass production. With the development and popularization of surface mount technology (SMT), new requirements are put forward for the amount, variety and quality of solder paste. For this reason, several foreign manufacturers (companies) with a good reputation for solder paste quality have continuously developed and developed type-specific solder paste to meet market demand. The development of solder paste in my country has a history of many years. Due to the small investment, the ability of continuous development and large-scale production has not been formed. Therefore, the quality, variety and production capacity cannot meet the market demand. At present, the annual demand for solder paste in my country is nearly 100 tons, and only a small part of it is domestically produced. Solder paste is a slurry composed of solder alloy powder and carrier material. The content of the latter is generally 8-15%. Its use and performance depend on the quality of the alloy powder components, as well as the chemical composition and ratio characteristics of the carrier material. 3.1. Solder alloy powder solder paste is mainly used in electronic assembly production. Taking surface mount technology as an example, solder paste is placed on the pad by printing or dispensing, and then the components are mounted on the pad. During reflow soldering, the solder alloy concentrated in the solder paste carrier connects the pins or terminals of the mounted components to the pad. It can be seen that the composition and quality of the alloy powder will affect the performance of the solder paste. For this reason, the composition, powder size, shape and surface state of the alloy powder are clearly defined in the IPC-SP-819 and my country's SJ/T standards. In addition, the oxygen content and fine powder in the powder have an impact on solderability, ball count, etc. At present, the composition and use of solder alloys in commonly used solder pastes are shown in Table 1. Table 1 Alloy composition solid-liquid temperature range (0C) brazing temperature (0C) Characteristics and uses 63Sn/37Pb 60Sn/40Pb 50Sn/50Pb 183 183 - 188 183 - 215 200 - 215 200 - 220 215 - 245 Widely used in surface mounting and general circuit assembly, with the advantages of low cost and good performance. Not suitable for welding gold and silver-based conductors 63Sn/37Pb/2Ag 179 190 - 215 Suitable for high-density circuits, can be used for welding base conductors, gold-plated parts are not suitable. The influence of alloy powder content in solder paste on the quality of solder joints is shown in Table 2. Table 2 It can be seen from the table that the final thickness after reflow varies from 50% of the solder paste thickness (90% metal content) to 22% of the solder paste thickness (75% metal content). It can be seen that a slight change in the metal content in the solder paste has a significant impact on the quality of the solder joint. 3.2. Solder paste carrier material Solder paste carrier material is composed of activator, binder, thixotropic agent and solvent. Therefore, the solderability, viscosity, printing performance, storage performance and so on of solder paste depend to a great extent on this material. By changing the composition and ratio of solder paste carrier material, solvent-cleanable, no-clean and water-washable solder paste can be made. No-clean solder paste should meet relevant technical indicators. Under appropriate process conditions, it should be free of solder balls, non-corrosive residue, non-hygroscopic, good drying, high insulation resistance and low ion contamination. Users can determine it after testing according to product quality requirements and process conditions. Water-washable solder paste, the residue after welding is easy to clean with water, non-corrosive, and can achieve high reliability. At present, a few domestic thyristor module manufacturers have adopted water-washable solder paste. From the perspective of market demand, no-clean and water-washable solder pastes will have a broad market. At present, the production of soft solder materials for my country's electronic industry still lags behind market demand. In addition to my country's poor industrial foundation. There are still some problems, such as insufficient investment in research and development, slow transformation of research results into productivity, and unregulated market. Therefore, the whole industry is waiting for joint efforts to accelerate the development of soft soldering materials for the electronic industry.