2023-08-31
31. The resistor whose silk screen (symbol) is 272 has a resistance value of 2700Ω, and the symbol (silk screen) of a resistor with a resistance value of 4.8MΩ is 485;
32.The silk screen on the BGA body contains information such as the manufacturer, manufacturer's material number, specification and Date code/(Lot No);
33.The pitch of 208pinQFP is 0.5mm;
34.Among the seven methods of QC, the fishbone diagram emphasizes the search for causality;
35.CPK refers to: Process Capability under Current Actual Conditions;
36.The flux starts to volatilize in the constant temperature zone for chemical cleaning;
37.Ideal cooling zone curve and reflow zone curve mirror image relationship;
38.The solder paste of Sn62Pb36Ag2 is mainly used on ceramic boards;
39.Rosin-based flux can be divided into four types: R, RA, RSA, RMA;
40.The RSS curve is heating→constant temperature→reflux→cooling curve;
41.The PCB material we are using is FR-4;
42.The PCB warpage specification does not exceed 0.7% of its diagonal;
43.Laser cutting by STENCIL can be reworked;
44.At present, the BGA ball diameter commonly used on computer motherboards is 0.76mm;
45.The ABS system is an absolute coordinate;
46.The error of ceramic chip capacitor ECA-0105Y-K31 is ±10%;
47.The PCB of the computer currently in use is made of: glass fiber board;
48.The diameter of tape and reel for SMT parts packaging is 13 inches and 7 inches;
49.The opening of the SMT general steel plate is 4um smaller than that of the PCB PAD to prevent the phenomenon of bad solder balls;
50.According to the "PCBA Inspection Specification", when the dihedral angle > 90 degrees, it means that the solder paste has no adhesion to the wave soldering body;
51.After the IC is unpacked, if the humidity on the display card is greater than 30%, it means that the IC is damp and absorbs moisture;
52.The weight ratio and volume ratio of tin powder and flux in the solder paste composition are correct 90%:10%, 50%:50%;
53.The early surface mount technology originated from 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 eutectic point is 183°C;
55.The feeding distance of the common paper tape tray with a bandwidth of 8mm is 4mm;
56.In the early 1970s, a new type of SMD appeared in the industry, which was a "sealed footless chip carrier", often replaced by LCC;
57.The resistance value of the component marked 272 should be 2.7K ohms;
58.The capacitance of 100NF components is the same as that of 0.10uf;
59. The most commonly used electronic component material for SMT is ceramics;
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