We Should Avoid Bad Welding Habits in SMT Processing
Welding is an important and indispensable link in the process of SMT. If there is any mistake in this link, it will directly cause the unqualified or even scrapped circuit PCB board.So we should pay special attention to have the appropriate welding habits, to avoid quality problems due to improper methods.Below I’ll sort out and introduce some common bad welding habits in SMT processing in order to remind you to pay attention to:
1.Random choice of Soldering Iron tip, do not consider the appropriate size.
It’s important to choose suitable size of soldering iron tip in the process of SMT processing, too small one will prolong its retention time, so that the solder flow is insufficient and lead to the emergence of cold welding spot.Too large one can cause the the joint to heat too quickly and burn the SMT components.Therefore, the choice of proper tip size should be based on these three standards: the correct length and shape; the correct heat capacity; and to maximize the contact surface but slightly less than the soldering pad.
2.Improper use of flux.
It is known that lots of workers are used to use too much flux in the SMT process, in fact, this not only can not help you have a good welding joint , but also can cause the problems of whether the foot is stable; produce corrosion easily;electronic transfer and other problems.
3.Improper welding process of heating bridge.
Hot welding Bridges in SMT is toprevent solder from forming a bridge, and improper handling can result in insufficient in cold spot or solder flow.So the correct welding habit is to put the soldering iron tip between the soldering pad and the pin, and the tin wire is close to the soldering iron tip. When the tin melts, move the tin wire to the opposite side, or put the tin wire between the soldering pad and the pin, and put the soldering iron on the tin wire, and move the tin wire to the opposite side when the tin melts.Only in this way, good solder joints can be produced to avoid the bad impact on the SMT processing.
4.Excessive welding force is applied to the pins during SMTprocessing.
Many SMT workers think that too much force can promote the solderpaste heat conduction, strengthen the soldering effect, so used to the habit of forcing down when welding.In fact, this is a bad habit, which will lead to the soldering pad warped, layered, dented, PCB white spots and other problems.So too much force is completely unnecessary in the process of welding , in order to ensure the quality, it’s just enough to let soldering tip touch with the welding pad gently .
5.Improper operation of transfer welding.
Transfer welding means that the solder flux is first added to the soldering tip, and then transferred to the joint.Improper transfer welding can damage the soldering tip, resulting in poor wetting.Therefore, the normal way of transfer welding is to place the soldering tip between the soldering pad and the pin. The tin wire is close to the soldering tip. Move the tin wire to the opposite side when the tin melts.
6.Unnecessary decorations or rework.
The biggest taboo in the SMT welding process is to modify or rework in pursuit of perfection.However, this method can’t not only make the quality more perfect, but also easily lead to the fracture of the metal layer of the SMT parts and components, and the layering of the PCB, wasting unnecessary time and even causing scrap.So do not do unnecessary modification and rework.
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