1. Integrated Circuit
Transmission gates and logic gates are combined together to form various complex CMOS circuits, such as counters, microprocessors, and memories. In the CMOS circuit, because of the complementary circuit of the N-channel tube and the P-channel tube, the power consumption of CMOS is smaller than that of NMOS, and the speed is higher than that of NMOS. It has low power consumption, a wide range of power supply voltage, and anti-interference. Features such as strong capabilities and good reliability are used in space, military, instrumentation, etc.
Considering that CMOS integrated circuits are susceptible to static electricity or electrostatic induction fields, the assembly process must take control measures. Of course, there are many measures to prevent static damage, but there are two general principles; one is to prevent and reduce the generation of static charge as far as possible; the second is to accelerate the leakage of static charge and prevent the accumulation of static charge. The specific control points are as follows:
(1) The power of the electric iron used must be below 25W, and at the same time ensure that the iron, tweezers and human body are well grounded. The operator is grounded with an anti-static wrist strap, and the soldering iron is grounded with a ground wire;
(2) The welding time is within 3s;
(3) Weld the high end of the power supply first, then the low end of the power supply, and then the input end and the output end;
(4) CMOS integrated circuits shall not be soldered and disassembled while powered on;
(5) The CMOS integrated circuit should be stored in a metal container to avoid the formation of electrostatic charges on the outer leads.
2. Isolator and Circulator
Isolators and circulators belong to microwave ferrite devices, which have the characteristics of working in the microwave frequency band, with magnetism, gold-plated microstrip line, welding corrosion and hard connection. Isolators and circulators are widely used in radar, electronic countermeasures, telemetry and remote control, and microwave measurement. Isolators and circulators are unidirectional transmission devices with unidirectional transmission performance. The unidirectional transmission performance of the isolator is shown in Figure 1. The input and output connections of the isolator and circulator usually use coaxial connectors and microstrip connections. The most commonly used coaxial connectors are L16, N and SMA. The requirements for microstrip connection are high, and the assembly is complicated. The isolator needs to be reliably installed and fixed according to the actual production situation of the microstrip circuit. The isolator microstrip ferrule and the microstrip circuit need to achieve a good match. The connection between the isolator microstrip ferrule and the microstrip circuit is generally not a problem in the L, S, and C bands. However, in the X and Ku bands, great care must be taken to ensure that the designed structural connection is reliable and the performance is intact.
Through the actual application in production, the following control points when assembling the isolator and circulator are summarized.
(1) Check whether the marked frequency band of the isolator and circulator is consistent with the circuit frequency band. Check whether the input and output directions of the isolator and circulator are the same. Care should be taken when installing and fixing.
(2) When the isolator and circulator are connected to the circuit, the inner conductor of the connector and the input and output microstrip lines of the isolator and circulator should be aligned on the horizontal and vertical surfaces, and the tightening degree should be appropriate to prevent loosening and excessive tightening.
(3) Low temperature solder should be used for the welding of isolator and circulator. Since the melting point (130 ° C) of SnPbIn low temperature solder is much lower than that of general HlSnPb37 solder (183 ° C) and the soldering time is less than 2s, the products developed after the assembly application of microstrip isolators and circulators have passed high and low temperatures and vibration The assessment of routine environmental tests meets the performance indicators of product design.
(4) Scrub the solder joints with a dry alcohol cotton ball. When scrubbing, pay special attention to the alcohol solution must not flow into the welding site and the isolator and circulator, so as not to melt the magnetic core during welding, damage the components.
(5) Isolators and circulators are magnetic devices, and should be stored as far away as possible from ferromagnetic materials (greater than 5cm).
Third, the trigger tube
Trigger tube is a key device used in high voltage products. In addition to requiring the trigger tube itself to work reliably, it must be strictly selected during use, and the quality of the assembly also directly affects the quality of the high-voltage components. After many process experiments, the following points should be controlled when assembling the trigger tube:
(1) Whether the welding part of the trigger tube is roughened depends on the specific conditions of the material of the welded part. If the material to be welded is a silver-plated layer, there is no need to roughen. Welding oil can be used for poor tin plating, but it must be cleaned with gasoline after plating.
(2) The exhaust hole of the trigger tube needs to be protected during tin plating and welding. There are two basic methods of protection: one is to put a high temperature resistant PTFE sleeve on the exhaust hole, but The welding position of the cathode lead requires that the lead be welded on the side away from the exhaust hole. Taking these two protective measures can effectively avoid the air leakage caused by the electric iron touching the exhaust hole of the trigger tube, causing damage or even scrapping.
(3) Wait for the trigger tube to cool down before cleaning. Since the shell material of the trigger tube is ceramic, if the tinplate is soldered and soldered with a 75W soldering iron, the shell temperature rises faster and it is difficult to control. If it is cleaned immediately with alcohol or gasoline, the tube shell is prone to micro cracks. To avoid the development of this situation, at present, Mectal smart soldering iron can be used for tin plating and welding. This soldering iron can automatically adjust the temperature, and the temperature adjustment response is fast, and it will not overheat. It can transfer high energy at a lower temperature. Compared with the general internal heating iron, it can better ensure the quality of tin plating and soldering. And reliability. It can also be soldered with a handheld temperature-controlled soldering iron on the PRC2000 maintenance workstation. PRC2000 is an SMT-type device that integrates assembly / maintenance, and has practical value for the completion of multiple varieties and small batches of products.
(4) Increase the special inspection of the process to effectively strengthen the quality control. In order to verify whether the performance of the trigger tube after tin plating and welding is normal, it is stipulated that after the tin plating and welding of the trigger tube, it needs to be left for a period of time (96h) to re-examine according to the technical conditions, check the self-breakdown voltage of the trigger tube, Can be installed. In this way, it plays the role of check and prevention.
4. Chip resistors
With the development of electronic technology, SMT chip components have appeared. In the process of adopting and implementing SMT, the quality and reliability of components are still key issues. Since chip components generally have no leads, this structure has low distributed capacitance and parasitic inductance, and is suitable for use in high-frequency and high-speed signal processing circuits. Among electronic products, chip resistors are one of the three basic electronic components and are the most widely used. Has the following characteristics:
(1) Small size and light weight provide a guarantee for the whole machine to be light, thin and small;
(2) Good high frequency performance and excellent electrical performance;
(3) The shape is simple and the size is standardized, which is convenient for high-speed automated production and installation;
(4) The resistor saves a pair of tinned metal wires, and saves the user pre-processing steps such as lead forming, flux dipping, and solder lining. Since it is installed close to the circuit board, the reliability is greatly improved.
Chip resistors can use any one of manual welding, reflow soldering and wave soldering. Due to the small size and small heat capacity of this type of resistor, no matter which method is used for soldering, the flux, solder paste and cleaning agent must be selected according to the product characteristics, and the welding temperature and welding time must be strictly controlled. When using manual welding, the power of the electric iron should not exceed 25W. The temperature of the iron should be regulated. The tip of the electric iron must be sharpened and the oxide layer removed to avoid affecting other components during welding. In order to prevent the chip resistor from being damaged by heat, the soldering time of the manual soldering iron does not exceed 2s. If it is not soldered within this time, the chip resistor must be cooled and then re-welded.
If the PRC2000 maintenance workbench is used for mounting, the following control points should be mastered:
(1) When applying solder paste, the position of the paste and the amount of paste applied must be controlled. Appropriate amount of spot coating makes the formed solder joints full and will not bridge. The solder paste brand used now is LR735, the needle diameter of the paste pin is 0.53mm, the area of ​​the solder paste covering the pad should be greater than 75%, but do not exceed the pad.
(2) It is required to clamp the main part of the chip resistor when mounting: the solder end of the chip resistor should occupy more than 75% of the width on the pad; the solder end of the chip resistor should not be offset from the pad, Do not stick other pads.
(3) For the 0805 chip resistors, use hot air hand tools to weld them with hot air at about 0.5mm above the welding end; for the 0805 chip resistors, clamp the two ends of the component with a clamp soldering iron, and quickly align the Click on the solder paste pad to solder.
Summary: The above mainly describes the characteristics, uses and control measures of the assembling process of the isolator, circulator, trigger tube and chip resistor. In short, in order to ensure the quality of products and improve the reliability of products, in the assembly of electronic products, the welding process of components is very important. Consideration should be given to the selection of welding methods (manual welding, wave soldering and reflow soldering) and process flow, such as the selection of welding tools and welding equipment and materials such as solder, flux and cleaning agent; control of process parameters such as welding time and temperature; Quality assurance of solder joints; provision of inspection methods, etc. For some special electronic components, we must also understand their characteristics and uses. In addition, in order to improve the reliability of the product, reliability tests must be conducted during the development and production process.
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