(Part 3) 110 Points the most Useful Knowledge of SMT

68. There is no directionality in the SMT section exclusion;

69. The solder paste currently on the market has only a sticky time of 4 hours;

70. SMT equipment is generally used at a rated air pressure of 5KG/cm2;

71. Front PTH, which welding method is used to spoil double-wave welding when SMT is over tin furnace;

72. Common test methods for SMT: visual inspection, X-ray inspection, machine vision inspection

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

74. At present, the main ball of BGA material is Sn90 Pb10;

75. Method for manufacturing steel plate, laser cutting, electroforming, chemical etching;

76. The temperature of the brazing furnace is as follows: The temperature is measured by the temperature measuring device;

77. The welding condition of the SMT semi-finished product of the soldering furnace is that the part is fixed on the PCB;

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

79. The ICT test is a needle bed test;

80. The ICT test can be used to test electronic parts using static testing;

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. Re-measure the measurement curve when changing the process conditions of the parts of the soldering furnace;

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;

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 test methods: streamlined production, hand-printed machine placement, hand-printed hand placement;

91. Commonly used MARK shapes are: round, “十” shape, square, diamond, triangle, “万” shape;

92. The SMT segment is improperly set by the Reflow Profile, and the pre-heating 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: empty welding, partial position, tombstone;

94. SMT parts repair tools are: soldering iron, hot air extractor, suction gun, tweezers;

95. QC is divided into: IQC, IPQC, .FQC, OQC;

96. High-speed placement machines can be mounted with resistors, capacitors, ICs, and transistors;

97. Characteristics of static electricity: small current, greatly affected by humidity;

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

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

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

101. BIOS is a basic input and output system, all in English: Base Input / Output System;

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

103. There are three basic types of common automatic placement machines, continuous placement, continuous placement and a large number of transfer placement machines;

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

105. SMT process is the delivery system – solder paste printing machine – high speed machine – universal machine – choke welding – closing machine;

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

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

108. Reasons for short circuit caused by poor printing in the process:

a. The content of solder paste metal is not enough, causing collapse

b. The stencil opening is too large, resulting in excessive tin content.

c. The quality of the steel mesh is poor, the tin is poor, and the laser is changed. Stencil has a solder paste on the back of the Stencil to reduce the blade pressure, using the appropriate VACCUM and SOLVENT

109. The main engineering purpose of each area of ​​general reflow furnace profile:

a. preheating zone; engineering purpose: volatilization of the medium in the solder paste.

b. Temperature equalization zone; engineering purpose: flux activation, removal of oxides; evaporation of excess water.

c. reflow zone; engineering purpose: solder melting.

d. Cooling zone; engineering purpose: alloy solder joints are formed, and the parts are connected to the pads;

110. In SMT process, the main reasons for tin bead are: poor design of PCB PAD, poor design of steel plate opening, excessive depth of placement or placement pressure, excessive rise of profile curve, collapse of solder paste, low viscosity of solder paste .