Jul 5, 2026News & Insights

100 Essential SMT Knowledge Points for SMT Professionals

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100 Essential SMT Knowledge Points for SMT Professionals
  1. The full name of SMT is Surface Mount Technology, which means surface mounting technology in Chinese.
  1. The SMT process consists of the board feeding system - solder paste printer - high-speed machine - universal machine - reflow soldering - board collection machine.
  1. The specific contents of 5S are sorting, organizing, cleaning, maintaining cleanliness, and cultivating a good work ethic.
  1. The specific contents of 7S include sorting, organizing, cleaning, maintaining cleanliness, cultivating a good work ethic, ensuring safety, and saving resources.
  1. The specific contents of 8S are organization, tidying, cleaning, sanitation, discipline, safety, economy, and efficiency.
  1. What is the maximum exposure time for the solder paste at room temperature? (24 hours)
  1. The current thickness of the SMT steel mesh commonly used in mobile phones is 0.12mm.
  1. What is the thickness range for the tin paste printing? (The thickness of the steel mesh is 0.12mm.) (100um - 160um)
  1. The tools for SMT component repair include: soldering iron, hot air gun, solder suction line, tweezers, PCB board holder, ball placement steel mesh, and small scraper.
  1. What are the different methods for cleaning the steel mesh? (Dry cleaning, wet cleaning, vacuum cleaning)
  1. During visual inspection, what is the distance between the inspected PCBA board and the eyes? (30cm ~ 50cm); What is the angle? (45°)?
  1. ROHS Introduction: The 2002/95/EC Directive on Restricting the Use of Certain Hazardous Substances in Electrical and Electronic Equipment 13.13. WEEE Introduction: The 2002/96/EC Directive on Waste Electrical and Electronic Equipment. 14. The main function of flux in welding is to remove oxides, break the surface tension of molten solder, and prevent re-oxidation.
  1. What is the fundamental for the effective operation of the ISO9000 quality system? (What should be done must be done, and what is done must be recorded.)
  1. The common manufacturing methods for steel meshes include etching, laser processing, and electroforming.
  1. What are the seven QC tools? (1. Lookup table method; 2. Classification method; 3. Control chart; 4. Pareto chart; 5. Scatter plot; 6. Fishbone diagram; 7. Histogram.)
  1. How often is the static rubber sheet's impedance value tested? (Every three months)
  1. What is the qualified range for the impedance value of the static rubber sheet? (106Ω - 1011Ω)
  1. The main components in the solder paste are divided into two parts: tin powder and flux.
  1. What is the maximum cumulative exposure time for PCBs? (48 hours)
  1. What are the thicknesses of the steel mesh? (0.1mm; 0.12mm; 0.15mm; 0.17mm)
  1. How many points at least need to be measured for the thickness of the solder paste? (5 points)
  1. What is the acceptable impedance for the soldering wire? (Less than 2Ω) What is the acceptable range for the static voltage of the soldering wire? (Below 2mv)
  1. The 5 W's in production? (What - Production Object; Who - Production Subject; How - Method; Where - Space; When - Time)
  1. Quality is the lifeblood of an enterprise;
  1. What is the standard for component misalignment? (Acceptable if it is less than 25% of the solderable end width of the component or less than 25% of the pad width; otherwise, it will be rejected.) (Only for the horizontal direction)
  1. The principle for using solder paste is "first in, first out".
  1. What is a tombstone? (The end of the component is raised) 31. What is SPC? (Statistical Process Control)
  1. The thread board includes: date, time, model, target output, actual output, efficiency, pass rate, and remarks.
  1. What is the specified environmental temperature for the SMT workshop? (18℃ - 25℃)
  1. What is the specified environmental humidity level for the SMT workshop? (40% - 80%)
  1. The FUJI NXT has 30 modules. Among the 4 production lines, M3 has 24 and M6 has 6.
  1. In the SMT process, improper setting of the reflow profile may cause micro-cracks in the components in the preheating zone and the cooling zone.
  1. When the efficiency of the thread board is lower than 85%, it is marked in red.
  1. The packaging methods for SMT components mainly include tubular, disc-shaped, and roll-type.
  1. When the pass rate of the thread inspection board is below 97%, it will be marked in red.
  1. Characteristics of static electricity: Low current, highly affected by humidity;
  1. The upper box can hold up to 50 layers, and it is guaranteed that there will be no collision between any two layers.
  1. When using the solder paste after opening the package, two important steps must be carried out: warming up and stirring.
  1. PCB turnover cart, each compartment can hold a maximum of 100 layers. During the placement process, ensure that there are no collisions between adjacent layers.
  1. The true meaning of quality is to do it well the first time.
  1. The success or failure of 5S lies in maintaining the unwavering commitment to 5S.
  1. When applying solder paste, the materials and tools required for the process are as follows: 1. Solder paste 2. Steel mesh 3. Scraping tool
  1. Cleaning paper 5. Cleaner 6. Mixing blade
  1. When loading materials, ensure that the spacing of the Feeder is consistent with the spacing of the materials.
  1. Uneven heating at both ends of SMT components can lead to: open circuits, misalignment, and warping.
  1. What is ISO? (International Standards Organization)
  1. The assembly machine should first attach the smaller components, and then the larger ones.
  1. What is BOM? (Bill of Materials)
  1. In the normal inspection II-level sampling plan (based on the sampling standard MIL-STD-105E table), when the number of samples submitted for inspection is 20 pieces, the number of samples to be inspected is 5 pieces; when the number of samples submitted for inspection is 200 pieces, the number of samples to be inspected is 32 pieces.
  1. In the sampling standard MIL-STD-105E, the term "AC" (Acceptance number) represents What? (Number of qualified judgments); What does RE (Rejection number) stand for? (Number of unqualified judgments)
  1. The full name of ESD is Electro-static discharge, which means "static electricity discharge" in Chinese.
  1. The melting point of lead-free solder Sn/Ag/Cu 96.5/3.0/0.5 is 217℃; the melting point of lead-containing solder paste alloy with composition of Sn/Pb 63/37 is 183℃.
  1. Semi-automatic printing machines are divided into left scraper and right scraper, while fully automatic printing machines are divided into front scraper and rear scraper.
  1. The storage temperature of the solder paste in the refrigerator should be between 0℃ and 10℃; the re-warming time before using the solder paste is 2 hours.
  1. The commonly used material for SMT steel mesh is stainless steel.
  1. The types of static charges include friction, separation, induction, and electrostatic conduction, etc. Static charges have an impact on electronic workers. The impacts of the industry are: ESD failure, electrostatic contamination; The three principles of electrostatic elimination are electrostatic neutralization, grounding, and shielding.
  1. The full Chinese name of ECN is: Engineering Change Notice; the full Chinese name of SWR is: Special Work Requirement Form. It must be signed and approved by relevant departments and distributed by the document center before it becomes valid.
  1. The purpose of vacuum packaging the PCB is to prevent dust and moisture.
  1. The quality policy is: Do not accept defective products, do not manufacture defective products, and do not allow defective products to be released. Product;
  1. Among the seven QC tools, in the fishbone method for analyzing causes, 4M1E refers to (in Chinese): People, Machines, Materials, Methods, and Environment.
  1. When using the solder paste, it must be taken out of the refrigerator and allowed to warm up. The purpose is to restore the temperature of the cooled solder paste to normal so as to facilitate the printing process. If it is not warmed up, defects such as solder beads may occur after the PCBA undergoes reflow.
  1. The PCB positioning methods for SMT include: vacuum positioning, mechanical hole positioning, double-clamp positioning and edge positioning of the board.
  1. The resistor marked with the symbol 272 has a resistance value of 27 * 100 = 2.7 KΩ. The symbol (soldering mark) for a 4.8MΩ resistor is 485.
  1. Among the seven QC tools, the fishbone diagram emphasizes the identification of cause-and-effect relationships;
  1. CPK stands for: The process capability index under the current actual conditions;
  1. The flux begins to evaporate in the constant-temperature zone, initiating the chemical cleaning process.
  1. The ideal cooling zone curve and the reflux zone curve are in a mirror-image relationship.
  1. The RSS curve represents the sequence of events: heating up → constant temperature → reflux → cooling.
  1. The warpage specification for PCBs must not exceed 0.75% of its diagonal length.
  1. Currently, in the mobile phone boards processed by Zhenhua, the most compact pitch (spacing) of the socket pins is 0.4mm, and the most compact pitch of the BGA pins is 0.5mm.
  1. After the IC is unpacked, if the humidity indicator on the card shows a value greater than 30%, it indicates that the IC has been exposed to moisture and absorbed moisture.
  1. The weight ratio of tin powder to flux in the solder paste composition is 90% : 10%, and the volume ratio is 50% : 50%.
  1. The early surface mount technology originated in the military and aerospace electronics fields in the mid-1960s.
  1. The commonly used paper tape tray with a width of 8mm has an element feeding spacing of 4mm for 0603 components and 2mm for 0402 components.
  1. The most commonly used material for electronic components in SMT is ceramics.
  1. The SMT section has no directional restriction;
  1. The rated air pressure typically used for SMT equipment is 5 kg/cm².
  1. Common inspection methods in SMT: Visual inspection, X-ray inspection, AOI (Automatic Optical Inspection);
  1. TQC (Total Quality Control) means comprehensive quality control, while TQM (Total Quality Management) means comprehensive quality management.
  1. The main engineering purposes of each zone in the general reflow oven Profile: a. Preheating zone; Engineering purpose: Volatilization of solvents in the solder paste. b. Constant temperature zone; Engineering purpose: To activate the soldering agent, remove oxides; To evaporate excess moisture. c. Re-welding area; Engineering purpose: Melting of solder. d. Cooling zone; Engineering purpose: Formation of alloy solder joints, connection of part pins to the solder pads.
  1. In the SMT process, the main causes of the generation of solder beads are: poor PCB pad design, poor design of hole openings on the steel plate, excessive placement depth or placement pressure, too steep upward slope on the Profile curve, solder paste collapse, and too low solder paste viscosity. 85. The steel mesh size used by Zhuhua in the MPM printing machine is 29 inches by 29 inches.
  1. The six harmful substances restricted by the EU RoHS directive are:
  • Lead (Pb) Maximum allowable content: 1000 PPM - Mercury (Hg) Maximum allowable content: 1000 PPM - Cadmium (Cd) Maximum allowable content: 100 PPM - Hexavalent chromium (Cr6+) Maximum allowable content: 1000 PPM - PBDE (Polybrominated Diphenyl Ethers) Maximum allowable content: 1000 PPM - PBB (Polybrominated Biphenyls) Maximum allowable content: 1000 PPM
  1. What needs to be emphasized in the RoHS process is: a) 1. Identification 2. Area planning 3. Confirmation of materials and auxiliary materials usage 4. Use of tools
  1. The full name of SMD is Surface Mount Device, which means "surface-mounted component" in Chinese.
  1. The quality policy is: Build a Chinese brand, produce Chinese high-quality products.
  1. The quality targets are: The pass rate of the first inspection batch should be above 95%, and the customer satisfaction rate should be above 98%.
  1. HSF Policy: Observe laws and regulations, prevent pollution, continuously improve the environment, respect nature, put people first, provide environmentally friendly products
  1. HSF Objectives: a) The concentration values of hazardous substances in HSF products fully comply with the EU ROHS directive, the "Measures for the Control of Pollution from Electronic Information Products" in China, and the ROHS requirements of the customers. b) The major pollution sources in the HSF production process of the company have been 100% controlled. c) The company will 100% recall all HSF products whose hazardous substance concentration exceeds the limit.
  1. HSF stands for Hazardous Substance Free, which in Chinese means: Free of Harmful Substances
  1. PCBA stands for Printed Circuit Board Assembly, which means "printed circuit board assembly" in Chinese.
  1. The currently commonly used sizes of the reel feeders are as follows: 8mm, 12mm, 16mm, 24mm, 32mm, 44mm, 56mm
  1. The curing temperature for the adhesive tape is 120℃ to 150℃.
  1. 0402 components are packaged in reel form with a standard quantity of 10,000 pieces per reel.
  1. In electronic components, C: represents capacitor, R: represents resistor, L: represents inductor, D: represents diode, Q: represents transistor, U: represents IC, V: represents rheostat, VD: represents voltage stabilizing diode, LED: represents light-emitting diode.
  1. In the PDCA cycle method, "P" (plan) means planning, "D" (do) means action, "C" (check) means inspection, and "A" (act) means execution.
  1. The opening time of temperature and humidity control spaces such as moisture-proof boxes, refrigerators, and ovens shall not exceed 2 minutes.
  1. For temperature and humidity sensitive components, the temperature and humidity control card turns pink when the humidity exceeds the limit.
  1. The components can be put back into production only after being removed from the oven and left for one hour; those not urgently needed should be vacuum-packed or stored in a moisture-proof box.
  1. During the visual inspection, components with a 25% deviation from the solder pads on their sides will be rejected; 104. In the keypad board, the standard for tin plating on the outer ring of the keyboard gold fingers: When there are no special requirements from the customer, the company's document "Visual Inspection Standard for Gold Finger Boards" (numbered as SMT-QWI-019) shall be followed.
  1. The printed PCB board can only be kept for a maximum of 2 hours (before being soldered)
  1. What are the types of BGA welding defects? BGA displacement; insufficient soldering with false welding; presence of foreign objects; short circuit (with soldering connection); bubbles; solder beads.
  1. The welding quality standards are as follows: The solder points must be shiny; smooth, with evenly distributed and uniform tin slag; free of air holes; free of contamination; and the welded objects must not be scorched.
  1. What are the differences between the resistance specifications marked "100" and "1000"? The former has an error of 5% for a resistance of 10 ohms, while the latter has an error of 1% for a resistance of 100 ohms.
  1. What parameters does the capacitor specification include? Capacity, tolerance, withstand voltage, material, and package type.
  1. The Chinese name for BGA is Bottom Ball Grid Array;
  1. What does FAA stand for? First Article Inspection;
  1. What is 3G? It refers to the third generation mobile communication technology.