Welding skills: A simple way to disassemble flat packaged integrated circuits is to take a copper wire with a diameter of 1 mm and a length of 10 cm. One end of the copper wire is bent into a small hook, and the other end is wound on a screwdriver for easy pulling. The iron head of the circuit must be tapered to avoid short circuit between the two feet of the integrated block. When removing the manifold block, put the small hook of copper wire into the manifold block and hook a pin. In the future operation, the hook of copper wire should be pressed on the circuit board as much as possible. Then the heated welding head is pressed on the pin with hook, and with the melting of solder, the other end of the copper wire is gently pulled, so that the hook of the copper wire is pulled out from between the pin of the integrated block and the circuit board, and the electric soldering iron is quickly removed. At this time, the contact between the pins of the integrated block and the circuit is broken. The pin of the integrated block only moves upward by about one millimeter, which will not cause mechanical damage to the integrated block. It takes about 10 minutes to disassemble the manifold block in this way. But the disadvantage of this method is that sometimes the copper foil on the circuit board may be pulled apart, so the force should be uniform. The temperature of the soldering iron should not be too high.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dismantling and welding skills of SMD components: 200 ~ 280℃ temperature regulating tip soldering iron should be used for disassembling and welding SMD components.

The substrates of patch resistors and capacitors are mostly ceramic materials, which are easily broken due to collision. Therefore, we should master the skills of temperature control, preheating and light touch when disassembling and welding. Temperature control means that the welding temperature should be controlled at about 200 ~ 250℃. Preheating means preheating the parts to be welded in an environment of 100℃ for 1 ~ 2 minutes to prevent the parts from being damaged due to sudden thermal expansion. Touch means that the welding head should first heat the solder joint or conductive tape of the printed board when operating, and try not to touch the components. In addition, the welding time should be controlled at about 3 seconds each time, and the circuit board should be naturally cooled at room temperature after welding. The above methods and techniques are also applicable to the welding of SMD crystal diodes and triodes.

Chip integrated circuit has many pins, narrow spacing and low hardness. If the welding temperature is not suitable, it is easy to cause faults such as solder short circuit, virtual welding or separation between printed circuit copper foil and printed board. When the SMD IC is disassembled, the temperature of the temperature regulating soldering iron can be adjusted to about 260℃. When the soldering head and the soldering suction device suck up the solder of the IC pin, gently insert the pliers with pointed ends into the bottom of the IC. While heating with a soldering iron, gently lift the IC pins one by one with pliers, so that the IC pins are gradually separated from the printed board. When lifting the integrated circuit with tweezers, it must be synchronized with the heated part of the soldering iron to prevent the circuit board from being washed out.

Before replacing a new integrated circuit, all the solder left by the original integrated circuit should be removed to ensure that the pad is flat and clean. Then clean the pins of the integrated circuit to be soldered with fine sandpaper, evenly tin-plate, align the pins of the integrated circuit to the corresponding solder points of the printed board, gently press the pins on the surface of the integrated circuit during soldering to prevent the integrated circuit from moving, operate the soldering iron with the other hand, dip a proper amount of solder in the soldering iron, and solder and fix the pins at the four corners of the integrated circuit with the circuit board, then check and confirm the model and direction of the integrated circuit again, and formally solder after it is correct, and adjust the temperature of the soldering iron to about 250℃. One hand holds the soldering iron to heat the pins of the integrated circuit, and the other hand sends the welding wire to the heating pins for welding until all the pins are heated and welded. Finally, carefully check and eliminate pin short circuit and virtual welding. After the solder joint cools naturally, use a brush dipped in absolute alcohol to clean the circuit board and solder joint again to prevent welding slag.

Before overhauling the module circuit board, it is advisable to clean the printed circuit board with a brush dipped in absolute alcohol to remove impurities such as dust and welding slag on the board, and observe whether there is virtual welding or welding slag short circuit on the original circuit board, so as to find the fault point early and save the overhaul time.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In order to fully understand the use, function and electrical characteristics of integrated circuits, it is necessary to know the model and source of integrated circuits. Like other integrated circuits, integrated circuits used for TV, audio recording and video recording are printed with model or logo on the front, so that we can know which manufacturer or company's integrated circuit is based on the prefix or logo of the model, and we can know which circuit function it belongs to according to its number. For example, the prefix AN indicates that it is a bipolar integrated circuit of Panasonic. The first two digits of the number "5620" distinguish the main functions of the circuit, while "56" indicates that it is an integrated circuit of television, 70-76 belong to audio applications, and 30-39 belong to the circuits of video recorders. For details, please refer to the IC model naming of some manufacturers. However, it should be noted that A4 100 often appears in practical applications. Which of TAA, TCA, TDA, etc? Japan's Hitachi, Sanyo, Toyo Electric, Toshiba, South Korea's Samsung, Sony's CXA, the European Union's Philips and Motorola belong to? Generally speaking, the name or trademark of the manufacturer or company will be printed on the integrated circuit with the English letters of the manufacturer omitted. For example, Sony indicates that the integrated circuit model is CXA 1034, Sanyo indicates that it is LA4 100 of Sanyo Company of Japan, and C 1350C is generally printed with NEC, indicating that the integrated circuit is produced by Japan Electric Company. Some integrated circuits don't even have letter prefixes. For example, KT-4056 miniature player with memory channel selection produced by Toshiba Company has a small flat package for its internal integrated circuits, and the front of two integrated circuits are mainly marked with 2066, JRC, 2067 and JRC. Obviously, 2066 and 2067 are abbreviations for the model. If you want to know the prefix or origin of this model, you must look for other marks on the integrated circuit, so JRC is the main clue. After verification, the models manufactured by Japan Radio Corporation are NJM2066 and NJM2067 integrated circuits. JRC is the abbreviation of Japanese Radio Corporation. The original text is New Japan Radio Co Ltd, and New is omitted and written as JRC. Please refer to the relevant content for the company abbreviation of the manufacturer's trademark. However, it should be noted that some IC models indicated in power diagrams or books and periodicals are also wrong. As usual, uPC 10 18C is misprinted as UPC10/8c or MPC 10 18C ("μ" is replaced by "u" in the site information). 2. Make a comprehensive understanding of the integrated circuit before use. Before using the integrated circuit, it is necessary to conduct a comprehensive analysis and understanding of the functions, internal structure, electrical characteristics, external packaging and circuits connected with the integrated circuit. When using integrated circuits, all electrical performance parameters shall not exceed the maximum allowable use range of integrated circuits. 3. Pay attention to the direction when installing the integrated circuit. When installing an integrated circuit on a printed circuit board, pay attention to the direction and don't make a mistake. Otherwise, the integrated circuit is likely to be burned when it is powered on. The general rule is that the pins of the integrated circuit are facing up, and there are gaps or points. "or vertical lines shall prevail, and they shall be arranged counterclockwise. If the single-column plug-in integrated circuit is straight, the front side (the side printed with the model trademark) faces itself and the pins are facing down, the pin numbering sequence is generally arranged from left to right. In addition to the above conventional pin orientation, there are some special pin orientation arrangements. It should be noted that most of them belong to single-line in-line package structure, and their pin orientation arrangements are just the opposite to the above, with the suffix "R". Such as M5 1 15 and M5 1 15RP, HA 1339A and A 1339AR, HA 1366W and ha139ar. , that is, when the side printed with the model or trademark faces itself. There are also double-row 14 pin patch heat dissipation packages, and mono audio power amplifier circuits AN7 1 14 and an71/5, which are basically the same as LA4 100 and LA4 102 packages, but the difference is that. The heat sink of LA4 100 is installed on pins 1 and 14, and its internal circuit and parameters are the same. If the 1 ~ 7 pin of the former corresponds to the 8 ~ 14 pin of LA4 100, the 8 ~ 14 pin of AN714 corresponds to the/kloc of LA4 100. When the heat sink is replaced by 180, these two pins are compatible. 4. Some empty needles should not be grounded without authorization. Some pins in internal equivalent circuits and application circuits are not marked. When you encounter an empty needle, you can't ground it without authorization. These pins are replacement or spare pins and are sometimes used as internal connections. All unused inputs of digital circuits should be connected to appropriate logic levels (Vdd or Vss) according to the actual situation, and must not be suspended, otherwise the working state of the circuit will be uncertain and the power consumption of the circuit will increase. For flip-flops (CMOS circuits), DC bias at the control terminal should also be considered. Generally, a resistor 100 kω can be connected between the control terminal and Vdd or Vss (as the case may be), and the trigger signal is connected to the pin. Only in this way can the circuit state be unique under normal circumstances, and once the trigger signal (pulse) comes, the trigger can flip normally. 5. Pay attention to the stress that pins can bear and the insulation between pins. Don't put too much pressure on the pins of the integrated circuit. Be careful when disassembling the integrated circuit to prevent damage. For high-voltage integrated circuits, there should be enough gap between power supply Vcc and ground wire and other input wires. 6. The power supply integrated circuit should pay attention to the following points (1). Before the radiator is installed, it is not allowed to be energized at will. (2) Do not weld the grounding wire to the heat sink before determining that the heat sink of the power integrated circuit should be grounded. (3) The installation of the heat sink should be smooth, and the fastening torque is generally 4 ~ 6 kg? Cm, the area of the radiator plate should be large enough. (4) There should be no dust and debris between the radiator and the integrated circuit. It is best to use silicone grease in the middle to reduce thermal resistance. After the heat sink is installed, the heat sink that needs grounding should be soldered to the grounding end of the printed circuit board with wires. 7. When the pins of the integrated circuit are powered on, the voltage applied by each pin of the integrated block should be synchronized. In principle, the voltage should be added between Vcc and ground of the integrated block. When the CMOS circuit is not connected to the power supply, the input signal must not be added to the input terminal of the CMOS circuit. If the signal source and CMOS circuit each use a set of power supply, connect the CMOS power supply first, and then connect the signal source; When shutting down, cut off the power supply of the signal source first, and then turn off the CMOS power supply. 8. It is not allowed to impact the integrated circuit with large current, which is the most likely to cause damage to the integrated circuit. Therefore, during normal use and testing, a current limiting circuit should be attached to the power supply. 9. Pay attention to the stability of the power supply. It is determined that if the power supply and the integrated circuit measuring instrument generate abnormal pulse waves when switching the power supply, it is necessary to add surge absorption circuits such as diodes in the circuit. The power supply voltage range of TTL circuit is very narrow, and it is stipulated that Class I and Class III products are 4.75-5.25 V (that is, 5 V 5%), Class II products are 4.5-5.5 V (that is, 5 V 10%), and the typical value is Vcc = 5 V. When in use, VCC shall not exceed the range. The input signal V 1 should not be higher than Vcc or lower than GND (ground potential). The power supply voltage of ECL is generally defined as VCC = OV and VEE =-5.2V 10%, which shall not exceed the standard in use. 65438+ 1 1. The integrated circuit and its leads should be far away from the pulse high voltage source. When setting the position of integrated circuit, it should be as far away from pulse high voltage and high frequency devices as possible. The lead wires and related wires connecting the integrated circuit should be as short as possible, and the inevitable long lines should be equipped with overvoltage protection circuits, especially the car recorder. When connecting CMOS circuits, the peripheral components should be as close as possible to the connected pins, and the leads should be as short as possible, so as to avoid using long parallel leads, otherwise it will easily lead to large distributed capacitance and inductance and LC oscillation. The solution is to connect a10kΩ resistor at the input. When CMOS is used in high-speed circuits, attention should be paid to the circuit structure and the design of printed circuit boards. The output lead is too long, which is easy to produce "ringing" phenomenon and cause waveform distortion. Because ECL is a high-speed digital integrated circuit, special problems such as "reflection" on signal lines and "crosstalk" between adjacent signal lines must be considered. When necessary, transmission lines (such as coaxial cables) should be used to ensure the impedance matching of transmission lines. In addition, certain shielding and isolation measures should be taken. When the working frequency exceeds 200Mz, multi-layer circuit boards should be selected to reduce the grounding impedance. 12. In order to prevent induced electromotive force from breaking down inductive loads such as relays in integrated circuits, relevant pins of integrated circuits should be connected with protection diodes to prevent overvoltage breakdown. 20W internal heating electric soldering iron should be used for welding, and the soldering iron shell should be grounded or anti-static electric soldering iron to prevent leakage damage of integrated circuits. Each welding time should be controlled within 3-5 seconds. Sometimes, for the sake of safety, the soldering iron can be unplugged first, and welding can be carried out by using the residual heat of the soldering iron. When the circuit is energized, welding is strictly prohibited. Between the gate and base of CMOS circuit, there is a layer with a thickness of only 0. L-0.2 um。 Because the input impedance of CMOS circuit is very high and the input capacitance is very small, as long as a small amount of charge is accumulated on the gate, a high voltage can be formed, which will breakdown the gate level and cause permanent damage. Because the human body can induce tens of volts of AC voltage, clothes will also generate several dry volts of static electricity when rubbing, so try not to touch the pins of CMOS circuits with your hands or body. When you don't use it for a long time, it's best to short-circuit all the pins with tin foil and wrap them up. Plastic bags are easy to generate static electricity and are not suitable for packaging integrated circuits. 13. In order to prevent exceeding the maximum temperature, the maximum temperature of the integrated circuit is 260℃, 10 second or 350℃ for 3 seconds. This means that all pins of each integrated circuit are immersed in the distance greater than 1 to 1.5mm from the plane of the package substrate at the same time, so the temperature of wave soldering and immersion soldering is generally controlled at 240℃ ~ 260℃ for about 7 seconds. ECL circuit has high speed and high power consumption. When used in a small system, the equipment should be equipped with a radiator; When used in large and medium-sized systems, air-cooled or liquid-cooled equipment should be added.