Introduction to the basic knowledge of SMT
1 Generally speaking, the temperature specified in the SMT workshop is 25 ± 3 ℃.
2. When solder paste is printed, the materials and tools to be prepared are solder paste, steel plate, scraper, wiping paper, dust-free paper, cleaning agent and mixing knife.
3. The commonly used solder paste alloy composition is Sn / Pb alloy, and the alloy ratio is 63/37.
4. The main components of solder paste are divided into two parts of tin powder and flux.
5. The main role of flux in soldering is to remove oxides, destroy the surface tension of molten tin, and prevent further oxidation.
6. The volume ratio of tin powder particles to Flux (flux) in the solder paste is about 1: 1, and the weight ratio is about 9: 1.
7. The principle of taking solder paste is first-in first-out.
8. When solder paste is used in unsealing, it has to go through two important processes to reheat and stir.
9. The common manufacturing methods of steel plates are: etching, laser, electroforming.
10. The full name of SMT is Surface mount (or mounting) technology, which means surface adhesion (or mounting) technology in Chinese.
11. The full name of ESD is Electro-static discharge, which means electrostatic discharge in Chinese.
12. When making SMT equipment program, the program includes five parts, the five parts are PCB data; Mark data; Feeder data; Nozzle data; Part data.
13. The melting point of lead-free solder Sn / Ag / Cu 96.5 / 3.0 / 0.5 is 217C.
14. The relative temperature and humidity of the parts drying oven shall be <10%.
15. Commonly used passive components (Passive Devices) are: resistance, capacitance, point sense (or diode), etc .; active components (Active Devices) are: transistors, IC, etc.
16. The material of commonly used SMT steel plate is stainless steel.
17. The thickness of commonly used SMT steel plate is 0.15mm (or 0.12mm).
18. The types of electrostatic charge are friction, separation, induction, electrostatic conduction, etc. The impact of electrostatic charge on the electronics industry is: ESD failure, electrostatic pollution; the three principles of electrostatic elimination are electrostatic neutralization, grounding, and shielding.
19. Inch size length x width 0603 = 0.06inch 0.03inch, metric size length x width 3216 = 3.2mm 1.6mm. 20. The 8th code “4” of ERB-05604-J81 excludes 4 circuits with a resistance of 56 ohms. The capacitance of capacitor ECA-0105Y-M31 is C = 106PF = 1NF = 1X10-6F.
21. The full name of ECN Chinese: Engineering Change Notice: The full name of SWR Chinese: Work Orders for Special Needs, which must be signed by relevant departments and distributed by the document center to be valid.
22. The specific content of 5S is sorting, rectification, cleaning, cleaning and literacy.
23. The purpose of PCB vacuum packaging is to prevent dust and moisture.
24. The quality policy is: comprehensive quality control, implementing the system, providing the quality required by customers; full participation, timely handling, and achieving the goal of zero defects.
25. The three-quality policy is not to accept defective products, not to manufacture defective products, and not to export defective products.
26. 4M1H refers to (Mandarin): human, machine, material, method and environment in the cause of fish bone inspection in the seven methods of QC. 27. The composition of solder paste includes: metal powder, solvent, flux, anti-sag agent, active agent; by weight, metal powder accounts for 85-92%, and by volume metal powder accounts for 50%; of which metal powder mainly The composition is tin and lead, the ratio is 63/37, and the melting point is 183 ℃.
28. When using solder paste, it must be taken out of the refrigerator and returned to temperature, the purpose is: to restore the temperature of the cold solder paste to normal temperature, in order to facilitate printing. If it does not return to temperature, the defect that is likely to occur after PCBA enters Reflow is tin beads.
29. The document supply modes of the machine are: preparation mode, priority exchange mode, exchange mode and quick connection mode.
30. SMT PCB positioning methods include: vacuum positioning, mechanical hole positioning, bilateral clip positioning and board edge positioning.
31. The resistance of the silk screen (symbol) is 272, the resistance value is 2700Ω, and the resistance (the silk screen) of the resistance value of 4.8MΩ is 485.
32. The silk screen on the BGA body contains information such as the manufacturer, the manufacturer ’s part number, specifications, and Datecode / (Lot No).
33. Among the seven methods, the fishbone diagram emphasizes the search for causality;
34. CPK refers to: the current process capability under actual conditions;
35. Flux begins to volatilize in a constant temperature zone for chemical cleaning action;
36. Ideal cooling zone curve and The mirror relationship of the reflow zone curve;
37. The solder paste of Sn62Pb36Ag2 is mainly used for ceramic boards;
38. The rosin-based flux can be divided into four types: R, RA, RSA, RMA;
39. The RSS curve is heating → constant temperature → reflow → Cooling curve;
40. The PCB material we currently use is FR-4;
41. The PCB warping specification does not exceed 0.7% of its diagonal;
42. Laser cutting made by STENCIL is a method that can be reworked;
43. The current BGA ball diameter commonly used on computer motherboards is 0.76mm;
44. ABS system is absolute Coordinates;
45 ceramic chip capacitor ECA-0105Y-K31 error is ± 10%;
46. The PCB of the computer currently used, its material is: glass fiber board;
47. SMT parts packaging its tape-reel diameter is 13 inches, 7 Inch;
