PCBA Tech - Knowledge of electronic components in mounting technology

Everyone in the industry knows that the SMT electronic components of PCBA board manufacturer is the basis of electronic products. Electronic components are the general name of electronic components and electronic devices. The common electronic components of SMT include resistance, capacitance, resistance, capacity, inductance, diode, triode, IC pin and fuse.

The common identification methods of SMT polar components and parts of PCBA board manufacturers are as follows:

Polar components need special attention in the whole PCBAa processing process, because directional component errors will lead to batch accidents and the failure of the whole PCBAa board. Therefore, it is very important for SMT technical engineers and production personnel to understand SMT polar components.

1. Polarity definition

Polarity refers to the fact that the positive and negative poles or the first pin of the component are in the same direction as the positive and negative poles or the first pin on the PCBA (printed circuit board). If the direction of the component does not match that on the PCBA circuit board, it is called reverse defect.

2. The polarity identification methods are as follows: the chip resistor has no polarity, the capacitor, the ceramic capacitor has no polarity, and the tantalum capacitor has polarity; PCBA board and device positive pole marking: 1) color band marking; 2) "+" sign; 3) Bevel mark. The aluminum electrolytic capacitor has polarity, and the part mark: the color band represents negative; PCBA board marks: the color band or "+" represents the positive electrode.

3. Inductor: there are no polarity requirements for the package of two welding ends such as chip coil, and there are polarity requirements for multi pin inductors; Part marking: dot / "1" represents polarity point; PCBA board marks: dot / circle / "*" represents polarity point.

4. Light emitting diode: SMT surface mounted LED has polarity, and the negative mark of the part: green is the negative; Negative pole marks on PCBA circuit board: 1) vertical bar, 2) color band, 3) silk screen sharp corner; 4) Silk screen "匚" box represents.

5. Diode: SMT surface mount diode with polarity at both ends. Negative pole marking of parts: 1) color band, 2) groove, 3) color marking (glass body); Negative pole marking of PCBA circuit board: 1) vertical bar marking, 2) color band marking, 3) silk screen sharp corner marking, and 4) "匚" box marking.

6. Integrated circuit: SOIC type package has polarity. Polarity indication: 1) color band, 2) symbol, 3) concave point, groove, 4) bevel; SOP or QFP type packages have polarity. Polarity indication: 1) concave point / groove indication, 2) one point is different from the other two / three points (size / shape); QFN type packages have polarity. Polarity indication: 1) one point is different from the other two points (size / shape), 2) oblique edge indication, 3) symbol indication (horizontal bar / "+" sign / dot).

7. Ball grid array: Part polarity: concave / groove mark / Dot / circle mark; PCBA plate polarity: indicated by circle / Dot / letter "1 or a" / oblique angle. The polarity point of the part corresponds to the polarity point on PCBA.

SMT resistance identification method: the color of color ring resistance generally includes 12 colors: Brown, red, orange, yellow, green, blue, purple, gray, white, black, gold and silver, of which the first ten colors represent 1 ~ 9 (black represents 0), and gold and silver represent two errors (plus or minus 5% and plus or minus 10%)

There are four color rings on the resistance of components normally leaving the PCBA factory. The first two colors represent pure numbers. For example, orange black represents the number 30 (not 30 Ω), and the third color ring represents the number of 0. For example, if the color ring is red on the third day, there are two zeros behind the number 30, and the resistance value of this resistance is 300 Ω (3K Ω); The color of the last color ring is either gold or silver. For example, if the last color ring is silver, what it represents here is that the resistance value of the resistance hovers between plus and minus 10% of 3000 Ω (the real resistance value of the resistance is any determined value within this range).

Capacitor polarity judgment and capacity identification in SMT chip processing: capacitors are mainly divided into electrolytic capacitors and chip capacitors. The shape of electrolytic capacitors is a cylinder, and its cylindrical surface is marked with its capacitance and polarity (the long foot is the positive pole and the short foot is the negative pole).

There is no polarity difference in the PCBA board element capacitance in the SMT technology workshop of PCBA chip processing plant. Its shape is usually pie shaped. The components are marked with three numbers, of which the first, second and third digits represent the capacitance value, and the third digit represents the number of 0. For example, 233 represents the capacitance value of 23000pf, i.e. 0.023 micro method.