Manual patch and manual soldering process analysis

1. Inspection before operation
(1) 3-5 minutes before work every day, plug the electric soldering iron into the designated socket and check whether the soldering iron is hot. If it is not hot, first check whether the socket is properly plugged in. If it is properly plugged in, if it is still not hot, you should report it to the administrator immediately. Do not disassemble the soldering iron at will, and do not touch the soldering iron tip directly with your hands.
(2) The soldering iron tip that has been oxidized, uneven or hooked should be replaced: 1. It can ensure good heat conduction effect; 2. Ensure the quality of the soldered object. If a new soldering iron tip is replaced, the maintenance paint should be wiped off after heating, and tin should be added immediately for maintenance. The soldering iron should be cleaned before soldering. If the soldering iron is not used for more than 5 minutes, the power should be turned off. The sponge should be cleaned. Dirty sponges containing metal particles or sulfur sponges will damage the soldering iron tip.
(3) Check whether the solder-absorbing sponge has water and is clean. If it does not, add an appropriate amount of water (appropriate amount means that water seeps out when the sponge is pressed to half its normal thickness. The specific operation is: after the humidity requirement is that the sponge is completely wet, hold it in the palm of your hand and close your five fingers naturally). The sponge must be cleaned. Dirty sponges contain metal particles or sulfur-containing sponges, which will damage the soldering iron tip.
(4) Whether the human body and the soldering iron are reliably grounded, and whether the human body is wearing an anti-static ring.
2. Welding steps
    The specific operation steps of soldering iron welding can be divided into five steps, called the five-step engineering method. To obtain good welding quality, strict operation must be performed.
    Soldering according to the above steps is one of the keys to obtaining good solder joints. In actual production, the most common violation of the operation steps is that the soldering iron tip does not contact the workpiece first, but contacts the solder wire first. The molten solder drips on the welded part that has not been preheated. This can easily cause a cold solder joint. Therefore, the soldering iron tip must contact the workpiece. Preheating the workpiece is an important means to prevent cold solder joints.
III. Soldering Essentials
(1) Contact method between the soldering iron tip and the two welded parts
    Contact position: The soldering iron tip should contact the two welded parts to be connected (such as the solder foot and the solder pad) at the same time. The soldering iron is generally tilted at 45 degrees, and it should be avoided to contact only one of the welded parts. When the heat capacity of the two welded parts is very different, the soldering iron tilt angle should be adjusted appropriately. The smaller the tilt angle between the soldering iron and the welding surface, the larger the contact area between the welded part with larger heat capacity and the soldering iron, and the stronger the heat conduction capacity. For example, the tilt angle is about 30 degrees when soldering LCD, and the tilt angle can be about 40 degrees when soldering microphones, motors, speakers, etc. The two welded parts can reach the same temperature in the same time, which is considered to be the ideal heating state.
    Contact pressure: When the soldering iron tip contacts the welded parts, a slight pressure should be applied. The strength of heat conduction is proportional to the amount of pressure applied, but the principle is not to damage the surface of the welded parts.
(2) Supply method of solder wire
There are three essentials to supply solder wire, namely supply time, position and quantity.

Supply time: In principle, solder wire should be supplied immediately when the temperature of the workpiece reaches the melting temperature of the solder.

Supply position: It should be between the soldering iron and the workpiece and as close to the pad as possible.

Supply quantity: It depends on the size of the workpiece and the pad. After the solder covers the pad, the solder can be higher than 1/3 of the pad diameter.

(3) Welding time and temperature setting

A. The temperature is determined by actual use. It is most appropriate to solder a tin point for 4 seconds, and the maximum should not exceed 8 seconds. Observe the soldering iron tip at ordinary times. When it turns purple, the temperature is set too high.

B. For general direct-insert electronic materials, set the actual temperature of the soldering iron tip to (350~370 degrees); for surface mount materials (SMC), set the actual temperature of the soldering iron tip to (330~350 degrees)

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

D. When soldering large component legs, the temperature should not exceed 380 degrees, but the soldering iron power can be increased.

(4) Welding precautions

A. Before welding, you should observe whether each soldering point (copper skin) is smooth and oxidized.

B. When welding items, be sure to look at the welding points to avoid short circuits caused by poor circuit welding.

4. Post-operation inspection:

(1) After using the soldering iron, wipe off the remaining tin on the tip of the soldering iron with a sponge.

(2) After get off work every day, you must clean the soldering iron holder from tin beads, solder slag, dust, etc., and then place the soldering iron on the soldering iron rack.

(3) Place the cleaned soldering iron in the upper right corner of the workbench.