In the mobile phone circuit, more new and unique components are used. Their identification and testing is a topic of great concern to practitioners.
The basic structure of mobile phone circuit
The basic components of mobile phone circuit mainly include resistor, capacitor, inductor, transistor and so on. These components must be installed on a chip (SMD) because of the phone's small size, full features and complex circuitry. Compared with traditional embedded components, chip components have higher mounting density and fewer wires. The distribution effect reduces parasitic capacitance and inductance, has good high frequency characteristics, and improves the ability to participate in interference signals and RF interference.
I. Resistance
Resistance elements mounted on the surface are mostly flaky, with pins located on either side of the element. Individual phones use a combination resistor with four pins connected to the external circuit and the internal circuit.
Ii. Capacitance
In cell phones, capacitors are usually yellow or light blue, and some electrolytic capacitors are red. Electrolytic capacitors are slightly larger and non-polar capacitors are particularly small. The minimum is 1mm by 2mm. Some capacitors have two characters in the middle. Most capacitors have no marked capacity. A narrow black bar on one end of the cell phone's electrolytic capacitor indicates that the terminal is positive.
Inductance and microstrip line
Inductance is a type of reactive power device often used in electronic circuits. The inductor is wrapped around an iron or magnetic core or a hollow coil. Unlike the resistors and capacitors on a cell phone board, the inductors in a cell phone circuit vary in appearance and shape, and some are large enough to be easily judged by their appearance. But some inductors have appearance, shape and resistance. Capacitors differ little in appearance and are difficult to judge.
Four, diode
The main diodes in mobile phones are as follows:
1. Common diode
Ordinary diodes work according to the one-way conductivity of the diode. There are two pins, generally black, with a white vertical line at one end, which means one end is negative.
2. Zener diode
Zener diodes, abbreviated to Zener tubes, work using the reverse breakdown properties of diodes. In the mobile phone circuit, generally used in the receiver (speaker, loudspeaker) circuit, vibrator circuit and ring circuit. In addition, Zener diodes are commonly used in mobile phone charging circuit and power circuit.
3. Varactor diode
Varactor diode is a special diode, using a special process using PN as the reverse bias voltage changes, junction capacitance is more sensitive.
4. Light-emitting diodes
Leds are mainly used as background lights and signal indicators in mobile phones. Leds are generally divided into red, green and yellow light. Leds vary in color depending on the material they are made from.
In addition, there are some special light-emitting diodes, such as infrared diodes. At present, infrared light-emitting diodes are increasingly used in mobile phones and infrared transmission.
5. Combination diode
The so-called combined diode, that is, the diode module circuit consists of several diodes. There are tripod and quadrupod combined diodes.
Five, Triode
1. Structure of triode
Transistors commonly used in mobile phone circuits are SMDS. From the perspective of circuit structure, devices can be divided into the following types:
(1) General triode
In general, a triode has three electrodes and four electrodes, which have the appearance and pins in a four-pin transistor, one being the output end of the transistor, the other two pins being connected to each other as emitters, and the other as the base.
(2) band stop transistor
A band-stopped triode consists of a triode and one or two internal resistors.
(3) Combined transistor
A combination triode is a module consisting of several triodes. Composite transistors have been widely used in mobile phone circuits.
2. Inductance and microstrip lines
Inductor is a type of reactance device often used in electronic circuits. A wire wound around an iron or magnetic core or a hollow coil is an inductor. The resistance on the cell phone plate. The difference between capacitors is that the inductance in the mobile phone circuit has a variety of appearance and shape, some inductance is very large, it is easy to judge from the appearance; But some inductors have the appearance and resistance. The capacitor is difficult to judge because of its small appearance.
Vi. Diode
The main diodes in mobile phones are as follows:
1. Common diode
The common diode uses the unidirectional conductivity of the diode, has two pins, generally black, one end has a white vertical bar, indicating that the end is negative.
2. Voltage regulator diode
Voltage regulator diodes, or regulator tubes for short, work by taking advantage of the diode's reverse breakdown characteristics. In the mobile phone circuit, it is often used in the receiver (horn). Speaker) circuit. Vibrator circuit and ring circuit. In addition, in the phone's charging circuit. Voltage regulator diodes are also widely used in power supply circuits.
3. Varactor diode
Varactor diode using a special process PN a special diode, junction capacitance changes with the reverse bias more sensitive.
4. Light-emitting diodes
Leds are mainly used in the background light and signal indicator light in mobile phones. Leds are generally red. Green light, yellow light, etc., the color of leds depends on the material they are made from.
In addition, there are some special light-emitting diodes, such as infrared diodes. At present, more and more mobile phones use infrared light-emitting diodes for infrared transmission.
5. Combination diode
The so-called combined diode, in other words, the diode module circuit consists of several diodes. The combined diode has three legs. With four legs.
Vii. Triode
1. Structure of triode
The commonly used triodes in the mobile phone circuit are SMD, which can be divided into:
(1) General triode
Generally speaking, triodes have three electrodes and four electrodes, appearance and pin arrangement. In a four-pin triode, one of the larger pins is the output of the triode, the other two are the emitter, and the rest are the base.
(2) band stop triode
A band stop triode consists of a triode and a. It consists of two internal resistors.
(3) Combined triode
A combination triode is a module consisting of several triodes. Combination transistor is widely used in mobile phone circuit.
In the face of such a large number of small components, the x-ray detection equipment of Datafun Technology can clearly detect whether there is a bridge, air welding and other problems in the pin part.
The solder joint status of electronic components in high resolution imaging on computers can be determined by X-ray, and bad welds can be determined by simple software Settings. Select the following equipment with welding problems and add X-ray electronic component inspection equipment to the production line to further improve inspection efficiency.
1. Continuous welding: The solder between adjacent spot welding is connected together
2. Air welding: the pin of the component is not wet by the solder. The welding layer is not wet with solder
3. Air welding: the insertion holes of the substrate components are all exposed, and the pin and welding layer of the components are not wet by the solder
4. Semi-welding: the pin and welding layer of the component have been wet, but the insertion hole is still partially exposed
5. Multi tin: welding contact element body or sealing end
6. Cladding welding: Too much solder leads to not seeing the element foot, even the corner of the element foot can not be seen
7. Tin beads. Tin residue: Diameter. Too long tin residue sticks to the surface of the bottom plate
8. Less tin. Thin tin: Solder is not fully wet double panel metal holes
9. Tin tip: The tin layer of the component pin head or the circuit board is pointed
10. Tin crack: There is a crack between spot welding and pin, or between welding layer and spot welding or spot welding itself
11. Eye of needle. Hollow. Pores: pinholes or holes of different sizes in spot welding
12. Welding layer warping: on the wire. The separation of the welding layer from the substrate is greater than the thickness of the welding layer
13. Copper mooring disconnect: The copper mooring is disconnected from the circuit board
14. Cold welding: Spot welding surface is not smooth, there are burrs or particles
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