Soldering is a science. The principle is that the solid solder wire is heated and melted by a heated soldering iron, and then flows into the metal to be welded by the action of the flux. After cooling, a firm and reliable solder joint is formed.
When the solder is tin-lead alloy soldering surface is copper, the solder first wets the soldering surface, and with the occurrence of the wetting phenomenon, the solder gradually diffuses toward the metal copper, forming an adhesion layer between the solder and the metal copper contact surface, so that two It is firmly combined. Therefore, solder is completed by three physical and chemical processes of wetting, diffusion and metallurgical bonding.
1. Wetting: The wetting process means that the solder that has been melted flows along the fine concavities and convexities of the base metal surface by capillary force to the periphery, thereby forming an adhesion layer on the surface of the soldered base material to make the solder and the mother The atoms of the metal are close to each other and reach the distance at which the attraction of the atom acts. (shown in Figure 1).
Environmental conditions that cause wetting: The surface of the soldered base material must be clean and free of oxides or contaminants.
Image metaphor: Water droplets are formed on the lotus leaves, that is, water cannot wet the lotus. Put the water on the cotton, and the water will penetrate into the cotton, that is, the water can wet the cotton.
2. Diffusion: As the wetting progresses, the phenomenon of interdiffusion between the solder and the metal atoms of the parent metal begins to occur. Usually atoms are in a state of thermal vibration in the lattice lattice once the temperature rises. The atomic activity is intensified, so that the molten solder and the atoms in the base material cross each other through the contact surface into the lattice lattice of the other side. The moving speed and quantity of the atom are determined by the temperature and time of heating. (shown in Figure 2).
3. Metallurgical bonding: Due to the mutual diffusion of solder and base metal, an intermediate layer---metal compound is formed between the two metals. To obtain a good solder joint, a metal compound must be formed between the soldered base material and the solder. Thereby, the base material reaches a firm metallurgical bonding state. (shown in Figure 3)
Figure 3. The role of flux The flux (FLUX) comes from the Latin word for "Flow in Soldering." The main functions of the flux are:
1. Chemical Activity (Chemical AcTIvity)
To achieve a good solder joint, the solder must have a completely oxide-free surface, but once the metal is exposed to the air to form an oxide layer, the oxide layer cannot be cleaned with a conventional solvent, and the flux must be relied upon. It is chemically bonded to the oxide layer. When the flux removes the oxide layer, the surface of the cleaned object can be combined with the solder.
There are several chemical screenings for fluxes and oxides:
1. Mutual chemical interaction to form a third substance;
2. The oxide is directly stripped by the flux;
3. The above two reactions coexist.
The rosin flux removes the oxide layer, which is the first reaction. The main components of rosin are AbieTIc Acid and Isomeric diterpene acids. When the flux is heated, it reacts with copper oxide to form copper rosin. Copper abiet) is a green, transparent substance that is easily dissolved in unreacted rosin and removed with rosin. Even if it remains, it will not corrode the metal surface.
The reaction in which the oxide is exposed to hydrogen is a typical second reaction in which hydrogen reacts with oxygen to form water and reduce oxides, which is commonly used in the soldering of semiconductor parts.
Almost all organic or inorganic acids have the ability to remove oxides, but most of them cannot be used for soldering. Flux is used in addition to the function of removing oxides. Other functions are required for soldering operations. Free of consideration.
2. Thermal Stability
When the flux removes the oxide reaction, it must form a protective film to prevent the surface of the solder from being oxidized again until it contacts the solder. Therefore, the flux must be able to withstand high temperatures, and will not decompose or evaporate at the temperature of the soldering operation. If it decomposes, it will form a solvent insoluble matter, which is difficult to clean with a solvent. The pure rosin of W/W grade will decompose at around 280 Â°C. pay attention.
3. Fluxes with good activity at different temperatures not only require thermal stability, but also activity at different temperatures. The function of the flux is to remove the oxide, usually at a certain temperature, such as RA flux, unless the temperature reaches a certain level, the chloride ions will not be resolved to clean the oxide, of course, this temperature must be in the soldering operation Within the temperature range.
When the temperature is too high, it may also reduce its activity. For example, when the rosin exceeds 600 Â°F (315 Â°C), there is almost no reaction. This property can also be used to purify the flux activity to prevent corrosion, but in application. Pay special attention to the heating time and temperature to ensure the purification of the activity.
Third, the composition and structure of the solder wire We use lead SnPb (Sn63% Pb37%) solder wire and lead-free SAC (96.5% SN 3.0% AG0.5% CU) solder wire inside is hollow, this design is In order to store the flux (rosin), the flux can be uniformly added while the solder is applied. Of course, in the case of lead tin wire, there are more medium components depending on the composition ratio of SNPB, and its main uses are different: the following table:
There are also a variety of mainstream lead-free tin wire components, from the SC and SAC components:
The role of the solder wire: to achieve the electrical requirements of the component on the circuit and the fixing requirements of the component on the PCB.
Fourth, the basic structure of the soldering iron soldering iron: (1) handle, (2) heating wire, (3) soldering iron head, (4) power cord, (5) thermostat controller, (6) soldering iron cleaning rack (Figure 4 Show)
The role of soldering iron: tools used to solder electronic components, hardware wires and other metal objects.
V. Manual soldering process 1. Check before operation (1) Insert the soldering iron plug into the specified socket 3-5 minutes before going to work every day to check if the soldering iron is hot. If it is not hot, check if the socket is plugged in well. If it is not hot, report it to the administrator immediately. Do not open the soldering iron at will, or touch the soldering iron directly with your hand.
(2) The soldering iron tip that has been oxidized and rugged or hooked should be updated: 1. It can ensure good heat conduction effect; 2. Guarantee the quality of the soldered object. If you replace it with a new soldering iron tip, wipe the maintenance paint off after heating and immediately add tin care. The soldering iron should be cleaned before soldering. If the soldering iron is not used for more than 5 minutes, turn off the power. Sponges should be cleaned. Unclean sponges containing metal particles or sulfur-containing sponges can damage the tip.
(3) Check if the suction sponge has water and clean. If there is no water, please add proper amount of water. (Appropriate amount refers to the water seeping when the sponge is pressed to the normal half thickness. The specific operation is: humidity requires the sponge to be completely wetted Hold in the palm of your hand, the five fingers can be closed naturally. The sponge should be cleaned. The dirty sponge contains metal particles, or the sulfur-containing sponge will damage the tip.
(4) Whether the human body and the soldering iron are reliably grounded, and whether the human body wears an electrostatic ring.
2, the welding step soldering iron welding specific operation steps can be divided into five steps, called the five-step engineering method, in order to obtain good welding quality must be strictly as shown in Figure 5.
Welding according to the above steps is one of the keys to obtaining a good solder joint. In actual production, the most common way to violate the operation steps is that the soldering iron tip is not in contact with the soldered part first, but is in contact with the solder wire, and the molten solder is dropped on the soldered portion that is preheated. This is easy to produce solder joints, so the soldering iron tip must be in contact with the soldered part, and preheating the soldered part is an important means to prevent the formation of solder joints.
3, welding essentials (1) contact between the soldering iron head and the two welded parts (Figure 6)
Contact position: The soldering iron tip should be in contact with two soldered parts (such as solder fillets and pads) to be connected to each other at the same time. The soldering iron should be inclined at 45 degrees, and should avoid contact with only one of the soldered parts. When the heat capacity of the two welded parts is disparity, the inclination angle of the soldering iron should be properly adjusted. The smaller the inclination angle of the soldering iron and the welding surface, the larger the contact area of â€‹â€‹the welded part with the heat capacity and the soldering iron, and the heat conduction capacity is enhanced. For example, when the LCD is soldered, the tilt angle is about 30 degrees, and the tilt angle of the welding microphone, motor, and speaker can be about 40 degrees. The two parts to be welded can reach the same temperature at the same time and are considered to be ideal for heating.
Contact pressure: When the soldering iron tip is in contact with the soldered part, the pressure should be slightly applied. The heat conduction intensity is proportional to the applied pressure, but it does not cause damage to the surface of the soldered part.
(2) Method of supplying the welding wire The supply of the welding wire should have three essentials, which are time, position and quantity.
Supply time: In principle, the temperature of the soldered part reaches the melting temperature of the solder and the solder wire is immediately supplied.
Supply position: It should be between the soldering iron and the soldered part and as close as possible to the pad.
Supply quantity: The size of the soldered part and the pad should be considered. After the solder covers the pad, the solder is higher than 1/3 of the pad diameter.
(3) Welding time and temperature setting A. The temperature is determined by the actual use. It is most suitable to weld a tin point for 4 seconds. The maximum time is no more than 8 seconds. Usually, the tip is observed. When it is purple, the temperature is set too high.
B. Generally insert the electronic material, set the actual temperature of the soldering iron head to (350~370 degrees); the surface mount material (SMC) material, set the actual temperature of the soldering iron head to (330~350 degrees)
C, special materials, need to set the temperature of the soldering iron. FPC, LCD connectors, etc. use silver-containing tin wire, the temperature is generally between 290 degrees and 310 degrees.
D. Weld the large component feet, the temperature should not exceed 380 degrees, but the soldering iron power can be increased.
(4) Precautions for welding A. Before soldering, observe whether each solder joint (copper skin) is clean and oxidized.
B. When welding the goods, it is necessary to look at the welding points to avoid short circuit caused by poor welding of the line. 4. Check after operation:
(1) After using the soldering iron, the tin of the soldering iron should be wiped clean on the sponge.
(2) After work, you must remove the tin beads, tin slag, dust, etc. from the soldering iron seat, and then place the soldering iron on the soldering iron frame.
(3) Place the cleaned soldering iron in the upper right corner of the workbench.
Sixth, the evaluation of the quality of tin points:
1. Standard tin point:
(1) The tin point is curved inward (2) The tin point is to be round, smooth, pinhole-free, and free of rosin stains. (3) Wire the foot, and the length of the wire should be between 1-1.2MM.
(4) The shape of the foot of the part shows that the dispersion of tin is good.
(5) Tin will surround the entire tin position and the part feet.
2. Judgment of non-standard tin points:
(1) Virtual soldering: It seems that the soldering is actually not soldered, mainly the pads and pins are dirty or the flux and heating time are not enough.
(2) Short circuit: the foot part is short-circuited between the foot and the foot by the excess solder. The other phenomenon is caused by the improper use of the tweezers and bamboo sticks by the inspector, which causes the foot and the foot to touch the short circuit, including the residual. Tin dross shorts the foot and foot (3) Deviation: The pin is not in the specified pad area due to the misalignment of the device before soldering or the soldering error. (4) Less tin: Less tin means tin spot Too thin, can not fully cover the copper parts of the parts, affecting the connection and fixing.
(5) Multi-tin: The parts are completely covered by tin and formed into an outer arc shape, so that the shape and pad position of the parts cannot be seen. It is not possible to determine whether the parts and pads are well tinned.
(6) Wrong parts: If the specifications or types of parts are not in conformity with the operating regulations or BOM or ECN, they are wrong.
(7) Missing parts: The position of the parts should be placed, and vacancies may occur due to abnormal reasons.
(8) Tin ball and tin slag: Excess solder balls and tin slag are attached to the surface of the PCB, which may cause short pins.
(9) Polarity reversal: The polarity orientation correctness is inconsistent with the processing requirements, that is, the polarity is wrong.
3. Reasons for possible bad solder joints:
(1) Forming a solder ball, can tin not be spread over the entire pad?
The soldering iron temperature is too low, or the soldering iron tip is too small; the pad is oxidized.
(2) When you remove the soldering iron, form a tin tip?
The soldering iron is not hot enough, the flux does not melt, and the step works. The temperature of the soldering iron is too high, the flux volatilizes, and the soldering time is too long.
(3) The tin surface is not smooth and wrinkled?
The soldering iron temperature is too high and the soldering time is too long.
(4) The area of â€‹â€‹rosin is large and the tip is too flat.
(5) The tin wire is directly added from the soldering iron tip, too much tin is added, the soldering iron is oxidized, and the soldering iron is beaten.
(6) The temperature of the PCB off-layer soldering iron is too high, and the soldering iron tip hits the board.
(7) Black rosin? The temperature is too high.
The summary has been accelerated with the replacement of electronic components. The original in-line type has been changed to flat-type, and the connection cable has been replaced by FPC soft board. The resistance and capacitance of the components have passed after 1206, 0805, 0603, 0402. To the 0201 flat-panel type, the BGA package has been used with Bluetooth technology. This shows that the development of electronics has been toward miniaturization and miniaturization, and the difficulty of manual soldering has also increased. Damage to components, or cause poor soldering, so our first-line manual welding personnel must have a certain understanding of the welding principle, welding process, welding method, welding quality assessment, and electronic foundation.
22Mm Dc Planetary Gear Motor includes 22RP180 and 22RP250 DC Planetary Gear Motor. This kind of Planetary Gear Motor is mainly applied on medical devices like injection equipment, beauty instruments and massage devices.
22mm DC Planetary Gear Motor has the following characterics:
1.the 22mm Dc Planetary Gear Motor has a good performance on the noise level;
2.the planetary gearbox has a longer working life than other types gearbox;
3.the micro dc Planetary Gear motor has a small size, but the torque it could reach equal to some gearbox over 30mm
For 22mm dc planetary gear motor, there are 5 types gearbox;
For the 1 stage gearbox, we have 4, 4.75 gear ratio;
For the 2 stages gearbox, we have 16, 19, 22.5 gear ratios;
For the 3 stages gearbox, we have 64, 76, 90, 107 gear ratios;
For the 4 stages gearbox, we have 256, 304, 361, 428, 509 gear ratios;
For the 5 stages gearbox, we have 1024, 1216, 1444, 1714, 2036, 2418 gear ratios;
|Number of stages||1||2||3||4||5|
|Reduction ratio||4, 4.75||16, 19, 22.5||64, 76, 90, 107||256, 304, 361, 428, 509||1024, 1216, 1444, 1714, 2036, 2418|
|Gearbox length(L) mm||13||16.5||20||23.5||27|
22mm DC Planetary Gear Motor
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