Qualified solder joints require firm welding, good contact, bright tin dots, smooth without burrs, moderate amount of tin, good fusion of solder and welded parts, and there should be no virtual soldering or false soldering. The appearance of qualified solder joints is shown in Figure 1.

   Figure 1 Appearance of qualified solder joints

■ Unqualified solder joint

   Unqualified solder joints include lap welding, too much solder, tipping, floating welding, voids, too much rosin, air bubbles, too little solder, copper foil warping, etc.

    Figure 2 Appearance of unqualified solder joints

    a) Overlap welding b) Too much brazing material c) Sharpened d) Floating welding e) Cavity f) Too much rosin g) There are bubbles h) Too little brazing material i) Copper foil warping

■ Repair of bad solder joints
    

Unqualified solder joints often occur during the welding process of electronic products. This requires repairing the unqualified solder joints. In principle, it is not allowed to repair by re-adding solder, and all the solder of the unqualified solder joints should be removed. The parts can be re-welded after cleaning.

After the cause of the unqualified solder joint is clear, the method of repairing while replenishing the solder wire with a rosin core can be taken.

■ Operation method to avoid unqualified solder joints

Disqualified solder joints will lead to various events, in order to avoid these phenomena

    1) Choose different types of electric iron according to the welding object

    2) The welding posture should be correct

    3) It is necessary to pay attention to this step of pre-welding treatment, and clean the components and solder wire before the welding and remove the oxides.

    4) Keep the soldering iron tip clean during the soldering process

    5) Master the welding temperature and time. When soldering, there must be enough heat and temperature. If the temperature is too low, the soldering resistance of the solder is poor, and it is easy to solidify and form a virtual solder; if the temperature is too high, the solder will flow, the solder joints are not easy to store tin, and the speed of flux decomposition is accelerated. The metal surface accelerates oxidation and causes the pads on the printed circuit board to come off. Especially when using natural rosin as the flux, the soldering temperature is too high, it is easy to oxidize and peel and produce carbonization, resulting in virtual soldering. And the temperature is too high may also cause different degrees of damage to the device. The soldering time must be appropriate, neither too long nor too short. The soldering time should be as short as possible while ensuring solder wetting.

    6) The amount of solder. The solder can not be too much or too little, too much will appear. Surfacing. And other phenomena, and unnecessarily waste energy, increase the cost of electronic products, increase welding time, and reduce work efficiency. Too little solder will cause insufficient mechanical strength of the solder joint.

    7) The soldering iron head cannot be used to apply force to the components and pads. The soldering iron head cannot be used to apply force to the components and pads during welding. Some people think that this will increase the heat transfer speed. In fact, the heat transfer speed of the soldering iron head is mainly This is achieved by increasing the contact area between the tip of the soldering iron and the weldment. Applying force to the solder joint will not only fail to achieve this effect but will bring some harm and cause damage to components and pads.

    8) The direction of the evacuation of the electric iron. It is necessary to see which evacuation method is appropriate according to the specific welding situation.

    9) The weldment should be fixed. Do not move or touch the soldered parts before the molten solder solidifies, especially when soldering the chip components. You must wait for the solder to solidify before removing the tweezers. Otherwise, the soldered parts will be displaced and the solder joint will be unqualified.

    10) Pay attention to safety during the welding process to avoid burns and electric shock.

    11) The electric soldering iron should be placed on the electric iron rack when not in use, and should be powered off when not used for a long time.

    12) Store a few more soldering irons of different powers for different occasions.