Master the temperature and time of PCB soldering. When welding, have enough heat and temperature. If the temperature is too low, the solder has poor fluidity and is easy to solidify, forming a virtual solder; if the temperature is too high, the solder will flow, the solder joint is not easy to deposit tin, the flux decomposition speed is accelerated, the metal surface is accelerated to oxidize, and the printed circuit board is caused. The upper pad is peeled off. Especially when natural rosin is used as a flux, the soldering temperature is too high, and it is easily oxidized and peeled to cause charring, resulting in a virtual soldering.
First, the welding process of printed circuit boards
- Preparation before welding
First of all, you should be familiar with the assembly drawing of the printed circuit board, and according to the drawings, check whether the component model, specification and quantity meet the drawing requirements, and prepare the lead forming of the components before assembly.
2, welding sequence
The order of component soldering is: resistors, capacitors, diodes, transistors, integrated circuits, high-power tubes, and other components are small and large.
- Welding requirements for components
(1) resistor welding
According to the figure, the resistor is accurately loaded into the specified position. The mark is required to be up and the word direction is consistent. After installing the same specification, install another specification and try to make the resistance level consistent. After soldering, the excess pins on the surface of the printed circuit board will be cut off.
(2) Capacitor welding
Put the capacitor as specified in the figure, and note that there are polar capacitors whose "+" and "-" poles cannot be connected incorrectly. The marking direction on the capacitor should be easily visible. First install glass glaze capacitors, organic dielectric capacitors, ceramic capacitors, and finally electrolytic capacitors.
(3) Soldering of the diode
Diode soldering should pay attention to the following points: First, pay attention to the polarity of the anode cathode, can not be wrong; second, the model mark should be easy to see visible; third, when soldering the vertical diode, the welding time of the shortest lead can not exceed 2S.
(4) Triode welding
Note that the three lead positions of e, b, and c are correctly inserted; the soldering time is as short as possible, and the lead pins are clamped with tweezers during soldering to facilitate heat dissipation. When welding high-power triodes, if you need to install heat sinks, the contact surface should be flat, smooth and then tightened. If you need to add insulation film, don't forget to add film. Use plastic leads when the pins are to be connected to the board.
(5) Integrated circuit welding
First, check the model and pin position according to the requirements of the drawings. When soldering, first solder the two pins of the edge to position it, and then solder from top to bottom from left to right.
For capacitors, diodes, and triodes, the excess pins on the printed circuit board surface must be cut off.
Second, the method of desoldering
De-soldering is required during commissioning, repair, or replacement of components due to welding errors. Improper desoldering methods often result in damage to components, breakage of printed conductors, or loss of pads. Good desoldering technology can ensure the smooth operation of commissioning and maintenance, and avoid the increase of product failure rate due to the inability to replace the device.
Desoldering of common components:
1) Select suitable medical hollow needle for desoldering
2) Desoldering with copper braided wire
3) Desoldering with airbag suction device
4) Desoldering with special desoldering soldering iron
5) desoldering with tin soldering iron
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