Very practical electronic component surface mount technology
The full name of SMT is Surface mount (or mounting) technology, which means surface adhesion (or placement) technology. SMT is a surface mount technology (short for Surface Mount Technology) called surface mount or surface mount technology. It is currently the most popular technology and process in the electronics assembly industry. In general, the temperature specified in the SMT workshop is 25 ± 3 °C.
SMT placement machine
Solder paste: The materials and tools required for solder paste printing, such as solder paste, steel plate, scraper, wiping paper, dust-free paper, cleaning agent, and mixing knife. The composition of the solder paste comprises: metal powder, solvent, flux, anti-sagging agent, active agent, and the main component thereof is tin powder and flux, and the volume ratio is about 9:1 by weight. The flux begins to volatilize in the constant temperature zone for chemical cleaning action; the main role of the flux in the soldering is to remove oxides, destroy the surface tension of the tin, and prevent reoxidation. The rosin-based flux can be divided into four types: R, RA, RSA, and RMA; the lead solder has a Sn/Pb ratio of 63/37 and a melting point of 217 °C. The lead-free solder Sn/Ag/Cu was 96.5/3.0/0.5 and the melting point was 217 °C.
When the solder paste is removed from the refrigerator, it must be warmed and stirred after two important processes. The purpose of the temperature recovery is to return the temperature of the refrigerated solder paste to normal temperature for printing. If the temperature is not returned, the solder balls are easily generated after the PCB is reflowed. The principle of using solder paste is first in, first out. The solder paste currently on the market actually has only 4 hours of tack time.
SMT production workshop
Steel mesh and PCB: The common manufacturing methods of steel mesh are: etching, laser, electroforming, and the commonly used SMT steel mesh is made of stainless steel. The thickness is 0.15 mm (or 0.12 mm). SMT general steel mesh opening is 4um smaller than PCB PAD to prevent the phenomenon of poor solder balls. The commonly used PCB material is FR-4; the purpose of PCB vacuum packaging is dustproof and moisture proof. The PCB warpage specification does not exceed 0.7% of its diagonal. Components: Common passive components (Passive Devices): resistance , capacitors, inductors, diodes, etc., and these components are sucked by the pick-up machine nozzle, referred to as nozzle or nozzle; active components (Active Devices) are: transistor, IC, and so on. The relative humidity and humidity of the component drying oven is <10%. After the IC unpacking, the humidity on the humidity display card is greater than 30%, indicating that the IC is damp and moisture.
SMT high speed placement machine
Heating furnace: The temperature curve of the reflow furnace is the most suitable for the maximum temperature of 215 °C. When the tin furnace is inspected, the temperature of the tin furnace is 245 °C. The RSS curve is the temperature rise → constant temperature → reflux → cooling curve; the ideal cooling zone curve and the reflow zone curve mirror relationship.
Patch Red Glue: SMT SMD Red Glue is a kind of poly-dilute compound. Unlike solder paste, it is cured after being heated. Its freezing point temperature is 150 ° C. At this time, red glue begins to change from paste to solid. . SMT patch red plastic has viscosity fluidity, temperature characteristics, wetting characteristics and the like. According to this characteristic of red plastic, in the production, the purpose of using red plastic is to make the parts firmly adhere to the surface of the PCB to prevent it from falling.
Use on printing machine or dispenser: In order to maintain the quality of the adhesive, please store it in the refrigerator (5±3 °C); before taking it out of the refrigerator, it should be warmed for 2 to 3 hours at room temperature; Use toluene or ethyl acetate to clean the hose.
SMT workshop component management
Dispensing squeegee: Add a back plug to the dispensing tube to obtain a more stable dispensing amount; the recommended dispensing temperature is 30-35 ° C; when dispensing the dispensing hose, please use a special glue moisture installation machine to disassemble to prevent Air bubbles are mixed in the glue. The recommended wiper temperature is 30-35 ° C. Note: After the red glue is removed from the refrigerated environment, it cannot be opened before reaching the room temperature. To avoid contamination of the original product, do not return any used patch adhesive to the original packaging.
SMT features: high assembly density, small size and light weight of electronic products, the size and weight of patch components are only 1/10 of the traditional plug-in components, and with the advancement of technology, components will become smaller and smaller, generally after SMT The volume of electronic products is reduced by a large margin, and the weight is reduced by 60% to 80%. High reliability and strong seismic resistance. The solder joint defect rate is low. High frequency characteristics are good. Reduced electromagnetic and radio frequency interference. Easy to automate and increase productivity. Reduce costs by 30% to 50%. Save materials, energy, equipment, manpower, time, etc.