Basic requirements and precautions for component welding

Date：2021-09-22 16:30:16 Views：2417

In electronic manufacturing, the connection of components needs to be welded. The quality of welding has a great impact on the quality of manufacturing. The welding of electronic components is divided into three categories: fusion welding, pressure welding and brazing. Now commonly used tin welding belongs to soft soldering in brazing (the melting point of solder is lower than 450 ℃),Because lead tin solder is used for welding, it is called tin welding. Fusion welding and pressure welding are generally used for high-power electronic components and equipment with special requirements. Welding is a very important link in the maintenance of electronic products. After the fault of electronic products is detected, welding is followed.

Basic requirements for component welding

(1) Welding of plug-in resistance

Accurately install the resistance into the specified position as required. Note that the insertion shall be in the order of color rings, starting from left to right and from top to bottom. It is required to install another specification after installing one specification, so as to make the resistance consistent as far as possible.

(2) Welding of patch resistance

Install the patch resistor into the specified position accurately according to the requirements. Note that the silk screen surface of the patch resistor must face upward.

(3) Welding of plug-in capacitor

Accurately install the capacitor into the specified position as required, and note that the "+" and "-" poles of the capacitor with polarity cannot be inserted incorrectly.

(4) Diode welding

After correctly identifying the positive and negative polarity, install it into the specified position as required. The welding time shall be as short as possible.

(5) Welding of plug-in triode

After correctly identifying each pin, install it into the specified position as required. The welding height of triode shall be as low as possible and the welding time shall be as short as possible.

(6) Welding of surface mount chip

During surface mount chip welding, pay attention to make the chip pins and pin heels all located on the pad, all pins are symmetrically centered, the pins are qualified if there is no offset between the pins and the pad, and the first pin of the chip must correspond to the first pin of PCB silk screen printing.

(7) Welding of indicator light, infrared transmitting tube, crystal oscillator and other sensitive devices

Pay attention to the positive and negative polarity and welding height, as well as the welding time and temperature. (the welding temperature shall be controlled at 360 ± 15 ℃, and the welding time shall be less than 3 seconds)

(8) Welding of LCD screen

After correctly identifying the insertion direction of the LCD screen, install it into the specified position as required. First locate the LCD screen, and then add tin to the remaining pins by drag welding or spot welding from the back of PCB.

(9) Welding of battery

After correctly identifying the polarity of the battery, install it into the specified position according to the polarity shown in the PCB silk screen, add an appropriate amount of tin, and pay attention to excessive solder leakage to the battery, resulting in short circuit of battery polarity and battery damage.

(10) Welding of transformer

Install the transformer into the specified position according to the requirements. As the transformer is a heavy device, pay attention to the complete wetting and tin eating of the transformer pin and pad during welding, and there shall be no false welding, false welding, package welding and other phenomena, otherwise the transformer pin is falsely welded after the vibration of the electric energy meter during production, transportation and installation.

Key points and methods of welding electronic components

Soldering components with electric soldering iron is a basic assembly process, which plays a key role in ensuring the quality of electronic products. The welding points of some components are introduced below.

1. Rosin, rosin oil or acid free flux is preferred for welding. Acid flux shall not be used, otherwise the welding place will be corroded.

2. Before welding, scrape the place to be welded with a knife to make it show metallic luster, apply flux, and then apply a layer of solder.

3. During welding, the electric soldering iron should have enough heat to ensure the welding quality and prevent false welding and long-term desoldering.

4. The soldering iron should not stay at the welding place for too long.

5. After the soldering iron leaves the welding place, the welded parts cannot be moved immediately, otherwise the parts are easy to be desoldered because the solder has not solidified.

6. It is better to twist and then tin the connected component wiring.

7. When welding transistors and other devices that are afraid of high temperature, it is best to clamp the lead out pin of the transistor with small flat nose pliers or tweezers, and grasp the time during welding.

8. It is better to use thin low-temperature welding wire for the welding of semiconductor components, and the welding time should be short.

It is worth noting that the overheating of electric soldering iron, long welding time and too much solder will cause the copper coating on the circuit board to tilt up. During welding, the temperature of the soldering iron shall not be too high and the welding time shall be as short as possible. Whether the welding quality is good or bad depends on whether the welding surface is very clean. If it is very clean and coated with flux, the welding will be very fast and firm. The welding surface can be polished with fine sandpaper and coated with flux immediately after polishing to prevent reoxidation. When welding triodes or integrated circuits, do not overheat for more than 3 seconds. After welding, use absolute alcohol to cool immediately, otherwise the overheating of PN junction will deteriorate the performance of components or even scrap them. If the microswitch is overheated, it may also cause damage, but the microswitch is much more heat-resistant than the transistor. Judge whether the microswitch is damaged. Use the ohm gear of the multimeter. Press it to be on and release it to be off.

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