Dear friends, the third lesson of SMT common knowledge is coming, come and learn together!

81. The characteristics of solder are that the melting point is lower than other metals, the physical properties meet the welding conditions, and the fluidity at low temperature is better than other metals;

82. The measurement curve must be re-measured when the welding furnace parts are replaced and the process conditions are changed;

83. Siemens 80F/S is an electronically controlled transmission;

84. The solder paste thickness gauge uses Laser light to measure: solder paste thickness, solder paste thickness, and printed width of solder paste;

85. The feeding methods of SMT parts include vibrating feeder, disc feeder and tape feeder;

86. Which mechanisms are used in SMT equipment: cam mechanism, side rod mechanism, screw mechanism, sliding mechanism; SMT

87. If the visual inspection section cannot be confirmed, which operation BOM, manufacturer confirmation, and sample board must be followed;

88. If the packaging method of the parts is 12w8P, the Pinth size of the counter must be adjusted by 8mm each time;

89. Types of welding machines: hot air welding furnace, nitrogen welding furnace, laser welding furnace, infrared welding furnace;

90. Methods that can be used for SMT parts sample trial production: streamline production, hand-printed machine placement, hand-printed hand-mounted;

91. Commonly used MARK shapes are: circle, "ten" shape, square, rhombus, triangle, swastika;

92. Due to improper setting of Reflow Profile in the SMT section, it is the preheating zone and cooling zone that may cause microcracks of the parts;

93. Uneven heating at both ends of the SMT part is easy to cause: empty welding, deviation, tombstone;

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

95. The true meaning of quality is to do it right the first time;

96. The placement machine should paste small parts first, and then paste large parts;

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

98. SMT parts can be divided into two types: LEAD and LEADLESS according to whether there are parts or not;

99. There are three basic types of common automatic placement machines, continuous placement type, continuous placement type and mass transfer placement machine; SMT

100. It can be produced without LOADER in the SMT process;

101. The SMT process is board feeding system-solder paste printing machine-high-speed machine-universal machine-reverse flow soldering-board receiving machine;

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

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

104. Reasons for short circuit caused by poor printing in the manufacturing process: a. Insufficient metal content of solder paste, resulting in collapse b. Excessive opening of the steel plate, resulting in excessive tin content c. Poor quality of steel plate, poor tin application, change the laser cutting template d. There is solder paste on the back of the stencil, reduce the pressure of the scraper, and use appropriate VACUUM and SOLVENT

105. The main engineering purpose of each area of the general reflow furnace Profile: a. Preheating area; engineering purpose: solvent volatilization in solder paste. b. Uniform temperature zone; engineering purpose: activation of flux, removal of oxides; evaporation of excess water. c. Reflow area; engineering purpose: solder melting. d. Cooling area; engineering purpose: alloy solder joints are formed, part feet and pads are connected as one;

106. In the SMT process, the main reasons for solder balls are: poor design of PCB PAD, poor design of steel plate openings, excessive placement depth or pressure, excessive rising slope of Profile curve, collapse of solder paste, and low viscosity of solder paste .