Introduction to SMT Common Knowledge (3)

Source:Junze Electronics      Browse:      Time:2018-09-20

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

81. The soldering characteristics are that the melting point is lower than other metals, the physical properties satisfy the welding conditions, and the fluidity at lower temperatures is better than other metals;

82. Change the process conditions of the smelting furnace parts replacement process to re-measure the measurement curve;

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

84. The solder paste thickness gauge is measured by Laser: the degree of solder paste, the thickness of the solder paste, and the width of the solder paste;

85. SMT parts feeding methods include vibrating feeders, disc feeders, and tape feeders;

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

87. If the visual inspection section cannot be confirmed, it must be in accordance with the operation BOM, manufacturer confirmation, and sample plate;

88. If the part packaging method is 12w8P, the counter Pinth size must be adjusted to enter 8mm each time;

89. Types of brazing machines: hot air type brazing furnaces, nitrogen brazing furnaces, laser brazing furnaces, infrared brazing furnaces;

90. SMT parts sample trials can be used: streamlined production, hand-printed machine placement, hand-printed hand placement;

91. Commonly used MARK shapes are: round, "ten", square, diamond, triangle, 4D;

92. The SMT segment is improperly set by the Reflow Profile, and the preheating zone and cooling zone may cause micro-cracking of the parts;

93. The unevenness of heat at both ends of the SMT section is easy to cause: air welding, offset, tombstone;

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

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

96. The placement machine should first affix small parts and then attach large parts;

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

98. SMT parts can be divided into LEAD and LEADLESS according to whether the parts are available or not;

99. Common automatic placement machines have three basic types, continuous placement type, continuous placement type and large transfer type placement machine; SMT

100. No LOADER can be produced in the SMT process;

101. SMT process is the plate feeding system - solder paste printing machine - high speed machine - general machine - choke welding - closing machine;

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

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

104. Causes of short circuit caused by poor printing in the process: a. The content of solder paste metal is not enough, causing collapse b. The opening of the steel plate is too large, resulting in excessive tin content. c. The quality of the steel plate is poor, the tin is poor, and the laser cutting template is changed. d. Stencil has a solder paste on the back to reduce the blade pressure, using the appropriate VACUUM and SOLVENT

105. The main engineering purpose of each area of ​​general reflow oven profile: a. preheating zone; engineering purpose: volatilization of the flux in the solder paste. b. Average temperature zone; engineering purpose: flux activation, removal of oxides; evaporation of excess water. c. reflow zone; engineering purpose: solder melting. d. Cooling zone; engineering purpose: the formation of alloy solder joints, the joints of the parts and the pads are integrated;

106. In SMT process, the main reasons for tin bead: poor design of PCB PAD, poor design of plate opening, excessive depth of part or part pressure, too large slope of profile curve, collapse of solder paste, low viscosity of solder paste .

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