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Composition, classification and important parameters affecting the properties of solder paste
Composition, Classification and Important Parameters Affecting the Properties of Solder Paste
1. Alloy solder powder: A. spherical B. prism 2. Activator: (flux) Removing the oxide layer on the surface of solder powder and welded parts reduces the surface tension, increases the wettability of components pins and pads, and improves the welding reliability. 3. Film-forming agent and adhesives: Placing alloy solder powder for further oxidation, and having a certain bonding effect, is conducive to the temporary fixing of the position of components to avoid displacement. 4. Wetting flux: Increasing the wettability of solder paste between the welded parts is beneficial to the expansion of alloy solder powder, good solderability and cleaning of residual after welding. 5. Thixotropic flux: The properties of solder paste's viscosity varying with time, temperature, shear strength and other factors. 6. Solvents and thickeners: Solution activator, film-forming agent, adhesive, wetting agent, thixotropic agent and other additives to make the flux and alloy solder powder uniform mixture. 7. Other additives: improve the corrosion resistance of solder paste, gloss of solder joints and flame retardancy, and sometimes add anti-corrosive extinction agent brightener or flame retardant to the flux formulation, whose composition is basically the same as that of general flux. 1. Welding Activity (Unactivated Moderately Activated Full Activated) 2. Cleaning methods: Organic solvent cleaning water cleaning semi-water cleaning and non-cleaning, etc., from the perspective of environmental protection, water cleaning semi-water cleaning and non-cleaning are the trend of development. 1. Viscosity: (Thixotropic flux) Solder paste is a fluid which has rheological properties and can flow under external forces. 2. Density: Composition ratio of alloy solder powder and flux content. The density of solder paste directly reflects the composition of alloy powder and flux content in solder paste. It can also be used as an important parameter to affect the performance of solder paste. 3. Melting point: It depends on the composition and proportion of solder powder. 4. Shape and viscosity of alloy solder powder: and surface oxidation degree play a key role in the performance of solder paste, especially the shape and particle size of solder powder are usually important parameters of solder paste. 5. Thixotropy index and slump: as a thixotropic fluid, solder paste thixotropy index is an important parameter. 6. Working life and storage life: working life is 12-24H. The judgment basis is that the time from solder paste applied to PCB to patch is 12-24H, which is also closely related to working environment temperature and humidity. Storage life: 2-5 C can be maintained for 6 months. Low temperature storage is conducive to preventing oxidant volatilization and prolonging service life. The solder paste should be warmed up to 4H before use, otherwise: A. Viscosity does not meet the requirements. B. Viscosity decreases after water absorption Definition of solder paste: paste or paste which is uniformly mixed with metal powder paste flux. SMT process is not only a missing welding material, but also has a certain viscosity at room temperature. At welding temperature, with the volatilization of solvents and some additives, solder components and PCB pads are connected together to form a permanent electrical connection. Characteristic application of solder paste 1. Pre-application characteristics: A. It has a long storage life and can be stored for 3-6 months at 2-5 ° C. B. Hygroscopicity, non-toxic, odorless, non-corrosive. 2. Characteristic of coating and reflow preheating process: A. Can use screen printing, leaky plate and other coating methods to work without spilling unnecessary solder paste. B. It has a long working life. It can be stored for a long time at room temperature after printing and coating, and its performance remains unchanged. C. The solder paste should keep its original shape and size without collapse after printing and during reflow preheating. 3. Property of reflux heating: A. Good wettability B. No solder spatter C. Forming a minimum number of solder balls 4. The characteristics after reflow welding: A. Better welding strength ensures that components do not fall off due to vibration and other factors. B. The stability of the residual after welding is better, the non-corrosive insulation resistance is higher and the cleaning property is better.
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