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Solder paste is a new type of soldering material that was developed with SMT. It is a mixture of solder powder, flux and other surface activators, thixotropic agents, etc., which are mixed to form a paste mixture. It is mainly used for soldering electronic components such as resistors, capacitors and ICs on the surface of PCBs in the SMT industry.
We all know the importance of solder paste to SMT parts, a good solder paste can make the components better paste on the PCB board,to produce high-quality products. However, there are many types and specifications of SMT solder paste in SMT OEM factory, the same SMT solder paste used by SMT OEM factory in SMT OEM,there are differences in alloy composition,particle size,viscosity,cleaning pipeline, and so on, and the price is also very different. How to correctly choose the right solder paste for SMT parts has a great impact on product quality and cost.
Solder Paste
How to choose the right solder paste for SMT parts?
1.The first thing you should do is to determine the alloy composition of the solder paste used in SMT manufacturing. Alloy is the formation of solder data, it is soldered with the metal interface to form an alloy layer, while the alloy composition also determines the soldering temperature, and commemorative products should first determine the alloy composition. Alloy composition is mainly based on electronic products and technology to choose, should try to choose and component welding compatible alloy composition, and at the same time should also consider the welding temperature and other process factors.
2.Reasonable selection of flux in SMT solder paste.Solder paste printability, solderability depends mainly on the flux in the paste, antique products in the determination of the alloy composition of the paste should be selected after the production process to adapt to the flux.
Selection, according to the printed circuit boards and components storage time and the degree of surface oxidation to choose its activity: general products using RMA type, high-reliability products to choose the R-type, printed circuit boards, components stored for a long time,the surface of the serious oxidation is the use of RA-type, and should be cleaned after soldering.
3.Determine the ratio of alloy composition and flux in SMT solder paste.Alloy composition and flux ratio directly affects the paste viscosity and printability.
4.According to the process of applying solder paste and SMT parts assembly density to choose the viscosity of the solder paste. There are many kinds of tubes for applying solder paste, and different application tubes have different requirements for the viscosity of solder paste.
5.Consider the temperature requirements of PCB and components, as well as the frequency of reflow soldering. Commonly used solder pastes are Sn63Pb37 and Sn62Pb36Ag2. For Palladium or silver thick-film terminations and components with poor solderability, silver-containing solder pastes should be used, while silver-containing solder pastes should not be selected for gold-plated boards.
6.According to the PCB on the cleanliness of the requirements and reflow soldering after different cleaning process to choose: the use of no-clean process, to select the halogen-free and strong corrosive compounds of no-clean solder paste. When solvent cleaning process is adopted,solvent cleaning type solder paste should be selected. When adopting water cleaning process, water-soluble solder paste should be selected.BGA,CSP generally need to select high-quality no-clean silver-containing solder paste.
7.Whether the assembly density of SMT has narrow spacing will affect the selection of solder paste alloy powder particle size. Usually there are four levels of fineness,if there is a narrow pitch,usually choose 20-45 microns of powder particles.
8.Select the viscosity of the solder paste according to the process of applying the paste and the assembly density; high density printing requires high viscosity,while undercoating requires low viscosity.
9.Select according to the environmental protection requirements, for the lead-free process, can not choose lead-containing solder paste.
10.As electronic parts are getting smaller and smaller in size, 0402 components can now be used, and these components need to pass the high-temperature and high-humidity environment test, so in the selection of solder paste, special attention should be paid to checking its surface insulation resistance (SIR) value of the performance of the situation.
Selection of a suitable solder paste should be made in conjunction with the specific SMT foundry environment,with reference to the activity, viscosity, powder shape, fineness and melting point of the solder paste for the foundry.