SMT (short for Surface Mounted Technology) is the most popular technology and process in electronic assembly industry at present.

What are the characteristics of SMT?

Electronic products have high assembly density, small volume and light weight. The size and weight of the patch component are only about110 of the traditional plug-in. After SMT, the volume of general electronic products is reduced by 40%~60% and the weight is reduced by 60%~80%.

High reliability and strong anti-vibration ability. The defect rate of solder joints is low.

Good high frequency characteristics. Reduce electromagnetic and radio frequency interference.

It is easy to realize automation and improve production efficiency. Reduce the cost by 30%~50%. Save materials, energy, equipment, manpower, time, etc. Computer mounter, as shown in the figure.

Why use SMT:

Electronic products pursue miniaturization, and the previously used punch plug-ins can no longer be reduced.

Electronic products are more versatile, and the integrated circuits (ic) used have no perforated components, especially large-scale and highly integrated IC, so surface mount components have to be adopted.

For mass production and automatic production, the factory should produce high-quality products with low cost and high output to meet customer demand and strengthen market competitiveness.

The development of electronic components, integrated circuits (ic) and diversified applications of semiconductor materials.

The revolution of electronic science and technology is imperative to catch up with the international trend.

Basic process components of SMT:

Screen printing (or dispensing)->; mount->； (curing)-> Reflow soldering->; Cleaning-> Detection->; Repair something that is badly repaired.

Screen printing: its function is to print solder paste or chip glue on the pads of PCB in order to prepare for the welding of components. The equipment used is a screen printing machine (screen printing machine), which is located at the forefront of SMT production line.

Glue dispensing: glue is dripped at the fixed position of PCB, which is mainly used to fix components on PCB. The equipment used is a dispensing machine, which is located at the front end of SMT production line or behind the test equipment.

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Installation: Its function is to accurately install the surface assembly components to the fixed position of PCB. The equipment used is a mounter, which is located behind the screen printer of SMT production line.

Curing: Its function is to melt the patch adhesive, so that the surface mount component and PCB board are firmly bonded together. The equipment used is the curing furnace, which is located behind the mounter in the SMT production line.

Reflow soldering: Its function is to melt the solder paste, so that the surface assembly components and PCB board are firmly bonded together. The equipment used is a reflow oven, which is located behind the mounter in the SMT production line.

Cleaning: its function is to remove welding residues harmful to human body on the assembled PCB, such as flux. The equipment used is a cleaning machine, and the location can be not fixed, online or offline.

Inspection: Its function is to inspect the welding quality and assembly quality of the assembled PCB. The equipment used includes magnifying glass, microscope, on-line tester (ICT), flying needle tester and automatic optical detection.

(AOI), X-ray inspection system, function tester, etc. This position can be configured in a suitable position on the production line according to the needs of detection.

Rework: Its function is to rework the PCB board whose fault has been detected. Tools used include soldering iron, maintenance workstation, etc. Configured at any position of the production line.

Introduction to common sense of surface mount technology

Generally speaking, the specified temperature of SMT workshop is 25 3℃.

2. Materials and tools needed for solder paste printing: solder paste, steel plate, scraper, wiping paper, dust-free paper, cleaning agent and stirring knife.

3. The commonly used solder paste alloy composition is Sn/Pb alloy, and the alloy ratio is 63/37.

4. The main components in solder paste are divided into two parts: tin powder and flux.

5. The main function of flux in welding is to remove oxides, destroy the surface tension of molten tin and prevent reoxidation.

6. The volume ratio of tin powder particles to flux in solder paste is about 1: 1, and the weight ratio is about 9: 1.

7. The use principle of solder paste is FIFO.

8. When solder paste is used in Kaifeng, it must go through two important processes: heating and stirring.

9. The common manufacturing methods of steel plate are: etching, laser and electroforming.

Full name 10. SMT is a Surface mount (or patch) technology, which means surface adhesion (or patch) technology in Chinese.

The full name of 1 1.ESD is Electro-static discharge, which means electrostatic discharge in Chinese.

12. when making SMT equipment program, the program includes five parts, namely CB data; Tag 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 2 17C.

14. The control relative temperature and humidity of the parts drying box are as follows

15. Commonly used passive devices are: resistor, capacitor, point inductor (or diode), etc. Active devices include transistors and integrated circuits.

16. Commonly used SMT steel plates are made of stainless steel.

17. The thickness of commonly used SMT steel plates is 0. 15mm (or 0. 12mm).

18. The types of electrostatic charges include friction, separation, induction and electrostatic conduction. The effects of electrostatic charge on electronic industry are: ESD failure, electrostatic pollution; The three principles of electrostatic elimination are electrostatic neutralization, grounding and shielding.

19. English dimension length x width 0603 = 0.06 inch * 0.03 inch, metric dimension length x width 32 16 = 3.2 mm * 1.6 mm.

20. Exclude the four circuits indicated by ERB-05604-J8 1 code 8 "4 "with a resistance of 56 ohms. The capacitance ECA-0 105Y-M3 1 is c =106pf =1nf =1x10-6f.

2 1.ECN Chinese full name: engineering change notice; SWR is called "special work order" in Chinese, and it is only valid if it is countersigned by relevant departments and issued by the document center.

The specific contents of 22.5S are sorting, rectifying, sweeping, cleaning and literacy.

23. The purpose of vacuum packaging of PCB is to prevent dust and moisture.

24. The quality policy is: total quality control, implementation of the system, and provision of quality required by customers; Full participation, timely processing, in order to achieve the goal of zero defects.

25. Three-quality policy is: no acceptance, no manufacture and no outflow of defective products.

26. In the seven methods of QC, 4M 1H refers to (China) people, machines, materials, methods and environment respectively.

27. The components of solder paste include: metal powder, solvent, flux, anti-sag agent and active agent; The weight percentage of the metal powder is 85-92% and the volume percentage is 50%; The main components of metal powder are tin and lead, the ratio is 63/37, and the melting point is 183℃.

28. When using the solder paste, you must take it out of the refrigerator and preheat it. The purpose is to restore the temperature of the refrigerated solder paste to normal temperature for printing. If the temperature does not return, the defect that PCBA is easy to appear after reflow soldering is tin beads.

29. The file supply modes of the machine include: preparation mode, priority exchange mode, exchange mode and quick access mode.

30. PCB positioning methods of SMT include vacuum positioning, mechanical hole positioning, double-sided fixture positioning and board edge positioning.

3 1. A resistor with screen printing (symbol) of 272, resistance value of 2700Ω and resistance value of 4.8MΩ has symbol (screen printing) of 485.

32. Screen printing on the BGA body contains information such as manufacturer, manufacturer's material number, specification and date code/(batch number).

33.208 qfp pin spacing is 0.5mm..

34. Among the seven skills of QC, fishbone diagram emphasizes finding causality;

35.CPK refers to the process capability under the current actual situation;

36. The flux starts to volatilize in the constant temperature zone for chemical cleaning;

37. The mirror image relationship between the ideal cooling zone curve and the reflux zone curve;

38. the solder paste of sn 62 Pb 36 ag 2 is mainly used for ceramic plates;

39. Rosin-based flux can be divided into four types: R, RA, RSA and RMA.

40. The RSS curve is heating → constant temperature → reflux → cooling curve;

4 1. The PCB material we are using now is FR-4;

42. The warpage specification of PCB should not exceed 0.7% of its diagonal;

43. The template laser cutting is a method that can be reworked;

44. At present, the commonly used BGA ball diameter on the computer motherboard is 0.76 mm.

45.ABS system is in absolute coordinates;

46. The error of ceramic chip capacitance ECA-0 105Y-K3 1 is10%;

47. The material of the PCB of the computer used now is: glass fiber board;

48. The diameters of winding reels for SMT parts packaging are 13 inch and 7 inch;

49. Generally, the opening of SMT steel plate is 4um smaller than the PCB pad, which can prevent the phenomenon of poor solder balls.

50. According to PCBA inspection specification, when dihedral angle is greater than 90 degrees, it means that there is no adhesion between solder paste and wave solder;

5 1. When the humidity on the humidity display card is greater than 30% after the IC is unpacked, it means that the IC is damp and absorbs moisture;

52. The correct weight ratio and volume ratio of tin powder to flux in solder paste composition are 90%: 10% and 50%: 50% respectively;

53. The early surface mount technology originated in the military and avionics fields in the mid-1960s.

54. At present, the contents of Sn and Pb in the most commonly used solder paste for SMT are: 63Sn+37Pb；;

The feeding interval of 55.8mm ordinary paper tape tray is 4 mm.

56. In the early 1970s, the industry developed a new SMD, namely "packaged leadless chip carrier", which was often replaced by HCC.

57. The resistance of the element with symbol 272 should be 2.7K ohms;

58. 100 nf module capacity is the same as 0. 10uf;

The * * crystallizing point of 59.63Sn+37Pb is183℃;

60. The electronic components with the largest use of SMT are made of ceramics;

6 1. The highest temperature of reflow oven curve is 215c;

62. When checking the tin furnace, the temperature of the tin furnace is 245℃.

63. The opening types of steel plate are square, triangle, circle, star and extension;

64. Whether there is directionality in SMT segment exclusion;

65. At present, the viscosity time of solder paste on the market is actually only 4 hours;

66.SMT equipment generally adopts the rated air pressure of 5KG/cm2;

67.SMT parts repairman has: soldering iron, hot air extractor, tin suction gun and tweezers;

68.QC is divided into: IQC, IPQC,. FQC，OQC

69. High-speed mounter can mount resistors, capacitors, IC and transistors;

70. The characteristics of static electricity: small current, greatly influenced by humidity;

7 1. PTH on the front side and what welding method is used to interfere with double-wave welding when SMT on the back side passes through the tin furnace;

72. The commonly used detection methods of SMT are: visual detection, X-ray detection and machine vision detection.

73. The heat conduction mode of ferrochrome restoration is conduction+convection;

74. At present, the solder balls of BGA materials are mainly SN90Pb10;

75. Production methods of steel plates: laser cutting, electroforming and chemical etching;

76. The temperature of the welding furnace is determined as follows: measure the applicable temperature with a thermometer;

77. When the SMT semi-finished products of the welding furnace are exported, the welding condition is that the parts are fixed on the PCB;

78. The development of modern quality management TQC-TQA-TQM:

79.ICT test is a needle bed test;

80. For electronic components that can be tested by ICT, static testing is adopted;

8 1. Solder is characterized by its lower melting point than other metals, its physical properties meet the welding conditions, and its fluidity is better than other metals at low temperature.

82. When the process conditions of welding furnace parts change, the measurement curve should be re-measured;

83. Siemens 80F/S belongs to electronic control drive;

84. Solder paste thickness gauge uses laser to measure: solder paste degree, solder paste thickness and solder paste printing width;

85.SMT parts are supplied by vibrating feeder, disc feeder and belt feeder.

86. What mechanism does SMT equipment use: cam mechanism, side bar mechanism, screw mechanism, sliding mechanism;

87. If the visual inspection part cannot be confirmed, what operation BOM, manufacturer's confirmation and sample should be followed?

88. If the packaging method of parts is 12w8P, the size of counter Pinth must be adjusted to 8mm at a time.

89. Welding machine types: hot air welding furnace, nitrogen welding furnace, laser welding furnace and infrared welding furnace;

90. The trial-production methods of SMT parts include: assembly line production, handprint machine installation and handprint hand installation;

9 1. Commonly used logo shapes are: circle, cross, square, diamond, triangle and swastika;

92. Due to the improper setting of the reflow curve of SMT part, the preheating zone and cooling zone may lead to the breakage of parts.

93. Uneven heating at both ends of SMT parts is easy to cause: virtual welding, deviation and tombstone;

94. The cycle time of high-speed machine and general machine should be balanced as much as possible;

95. The essence of quality is to do it well the first time;

96. The mounter should stick small parts first, and then stick large parts;

97.BIOS is a basic input and output system, and its English is: Base Input/Output System；;

98.SMT parts can be divided into lead and no lead according to the presence or absence of parts;

99. There are three basic types of common automatic mounters: continuous mounters, continuous mounters and mass transfer mounters.

100.SMT process can be produced without feeder;

10 1.SMT process is board feeding system-solder paste printer-high speed machine-universal machine-reflow soldering-interface machine;

102. When the temperature and humidity sensitive component is opened, the color displayed in the circle of the humidity card is blue, and the component can be used;

103. The size specification of 20mm is not the width of the material belt;

104. Causes of short circuit caused by poor printing in the process: a. insufficient metal content of solder paste leads to collapse; B. The opening of the steel plate is too large, resulting in excessive tin content; C. poor quality of steel plate and poor tin removal; Replace the laser cutting template D. There is residual solder paste on the back, reduce the pressure of the scraper, and adopt appropriate vacuum and solvent.

105. The main engineering uses of the general reflow oven profile area: a. Preheating area; Engineering application: Solvent volatilization in solder paste. B. uniform temperature zone; Engineering purposes: flux activation and oxide removal; Evaporate excess water. C. recirculation zone; Engineering application: solder melting. D. cooling zone; Engineering application: forming alloy solder joint, connecting the pin and pad of the part into a whole;

106. In SMT process, PCB is the main cause of solder balls.

Poor design of bonding pad, poor design of steel plate opening, excessive depth or pressure of mounting parts, excessive rising slope of contour curve, collapse of solder paste and low viscosity of solder paste.