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PCBA manufacturers have two pre-processing steps, lead forming and component insertion, before the components are soldered to the printed circuit board.
1. The purpose of lead forming
Before the plug-in components are welded on the printed circuit board, their leads must be bent to adapt to the installation of the printed circuit board, which is called lead forming.
Welding wires on the printed circuit board and inserting components require lead forming processing. For axial lead components (the component leads extend in a straight line from both sides), in order to insert them on the printed circuit board, It must be bent vertically in the same direction. The two leads must be in the same horizontal plane and the two leads must be parallel. This can not only alleviate the thermal shock of the lead immersion tin, protect the components and the circuit board, but also make the installation of the components convenient. Reliable. For components with leads in the same direction (such as transistors), in order to increase the distance of heat conduction, increase the thermal resistance, and relieve the thermal expansion and contraction stress caused by the temperature change when the soldering iron is heated during soldering, it must also be treated When forming the lead, pay attention to the bending and forming at a certain distance from the root of the lead. Do not apply any stress to the root, because such components become brittle and easy to break due to heat treatment during the production process.
2. Wire forming and welding
The wire acts as a connecting wire in the PCB circuit board and can be regarded as a plug-in. Therefore, the shape and cleaning should be done before the wire is welded. Cut the wire to a suitable length according to the connection requirements. Note that the cut wire must be straight and not twisted. After the wire is stripped and tinned, use needle-nose pliers to clamp it at a distance of 20mm from the wire-finding end, and press the wire on the tip with your thumb The pliers are at a right angle. Do not turn the needle-nose pliers at this time. At this time, you need to pay attention to holding the wire with your thumb, which may cause dirt on the wire, so it is recommended to use tweezers or another pair of needle-nose pliers to bend the wire together.
Determine the pad hole that needs to be connected, insert one end of the bent wire into the side hole, test the length of the two holes to be soldered, take the wire out, and bend the other end of the wire to a right angle; you can also not insert the wire into the hole In the middle, the inserting part is bent upwards perpendicular to the jack, and the other end is aligned with the hole to be welded on the other side, and the wire is directly bent at a right angle.
After the wire is formed, insert the wire into the hole of the pad. When inserting the wire, the lead of the wire should be vertical. If the wire is too short or too long, it will cause the wire welding to fail.
After the wire is inserted, it is necessary to do the soldering work on the other side of the circuit board. If the circuit board is flipped and soldered directly, the wire may fall from the pad hole. Therefore, a certain method needs to be taken. The wire can be bent after inserting the wire Clean up, keep the wires from falling, pay attention to keep the needle-nose pliers parallel to the circuit board when bending, bend the wires at 30° to the circuit board, use the same method to bend the other side of the wire, the bending direction should be along the direction of the copper foil of the circuit board, Cannot go beyond its edge. In addition, an insulated small board can also be used. After the connecting wire leads are inserted, cover the insulated small board on the connection surface, and then flip the insulated small board and the PCB circuit board to complete the soldering. This method is desoldering on the PCB. There are obvious advantages at times.
After the connection wire is soldered, clean the connection wire and cut off the excess connection with diagonal pliers. The reserved length of the connection cannot exceed the radius of the PCB pad, and it should be as flush as possible with the top of the solder joint formed by the solder.
