DIP manual circuit board soldering steps and precautions

- Sep 18, 2019-

DIP manual circuit board soldering steps and precautions

Although the SMT patch automation equipment is now very advanced, replacing most of the manual work, due to the special characteristics of some components and the components that the machine can't identify, it still needs manual welding to complete the work, and the beautiful and accurate welding process. It is an important indicator for testing welding hands. Today, Jingbang Electronics will take a look at the steps and precautions for manual circuit board soldering.

The specific operation steps of soldering iron soldering can be divided into five steps, which is called five-step engineering method. To obtain good welding quality, it must be strictly operated.

• Prepare for welding: Prepare solder wire and soldering iron. At this time, the tip of the soldering iron should be kept clean, that is, it can be soldered with solder (commonly known as tin).

• Heating the weldment: Touch the soldering iron to the solder joint. Be careful to keep the soldering iron to heat the soldered parts, such as the leads and pads on the printed board.

Heating, secondly, let the flat part (larger part) of the tip touch the weldment with larger heat capacity, and the side or edge part of the tip is connected

A weldment with a small heat capacity to keep the weldment evenly heated.

• Melting the solder: When the weld is heated to a temperature that will melt the solder, the wire is placed at the solder joint and the solder begins to melt and wet the solder joint.

• Remove the solder: Remove the solder wire after melting a certain amount of solder.

• Remove the soldering iron: When the solder completely wets the solder joint, remove the soldering iron. Note that the direction of the soldering iron should be approximately 45°.

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.

Welding method How to contact the soldering iron tip with two soldered parts

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 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.

Welding wire supply method

The supply of welding wire should have three essentials, both time, position and quantity.

• Supply time: In principle, the temperature of the soldered part is raised to reach 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.

• Quantity of supply: The size of the soldered part and the pad should be considered. The solder can cover the pad and the solder is higher than 1/3 of the pad diameter.

Welding time and temperature settings

• The temperature is determined by the actual use. It is most suitable to solder a tin point for 4 seconds. The maximum is no more than 8 seconds. Usually, the tip is observed. When it is purple, the temperature is set too high.

• 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)

• Special materials require special soldering iron temperature. FPC, LCD connectors, etc. use silver-containing tin wire, the temperature is generally between 290 degrees and 310 degrees.

• Solder large component feet, the temperature should not exceed 380 degrees, but can increase the power of the soldering iron.

Welding precautions

• Before soldering, observe whether each solder joint (copper skin) is clean and oxidized.

• When soldering articles, look at the solder joints to avoid short circuits caused by poor soldering of the wires.

When soldering integrated circuits, we should pay attention to some matters. When soldering an integrated circuit, if the pins of the integrated circuit are gold-plated, do not use a knife to scrape it. Use a clean eraser to clean it. For CMOS integrated circuits, if the pins are short-circuited first, do not remove the short-circuit before soldering. Low melting point solder should be used, and the temperature should not be higher than 150 degrees Celsius. If there are rubber, plastic and other materials that are easy to accumulate static electricity on the workbench, integrated circuits and printed boards should not be placed on the countertop. Since integrated circuits are heat-sensitive devices, it is easy to damage the integrated circuit by strictly controlling the soldering temperature and soldering time.

And we should pay attention to such matters when soldering printed circuit boards. Generally, the internal heating type 20-35W or temperature-regulating soldering iron should be selected. The shape of the soldering iron should be conical according to the size of the printed circuit board pad. When the heating is performed, the temperature of the soldering iron should be adjusted to not more than 300 degrees Celsius. When heating, we should try to avoid leaving the tip in a place for a long time to avoid local overheating and damage to copper foil or components. Do not use the tip of the soldering iron to solder the solder pad when soldering, but use surface cleaning and pre-tinning. When soldering the metallization holes, the solder should be wetted and filled over the entire hole, not just soldered to the surface pads.

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