Useful Tips | Why do other people's welding look like art, but mine looks like...

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Most of the circuit boards in the electronic devices currently used are automatically completed by reflow soldering, wave soldering, and welding robots, which can ensure the efficiency and quality of welding. Manual soldering is still widely used in the soldering and production of circuit boards in a small number of debugging equipment and the soldering process of special electronic devices. In order to ensure the quality of soldering and reduce the damage to the components on the circuit board due to the soldering process, the necessary soldering knowledge and hardware conditions are required.

Which of these soldering iron tips do you like best?

Welding components

You have to know that welding and being able to weld well are two different things. Good welding tools plus repeated practice are the basic elements to achieve perfect welding.

Some pinless packaged devices (QFN, BGA, WLCSP, Flip-Chip, etc.) require special equipment to complete soldering. In special cases, a handheld hot air gun can be used to solder the above devices with fewer pins, which requires very skilled soldering skills and rich soldering experience.

The knife-edge soldering iron tip has a very diverse welding function. It has a relatively sharp top and a wide blade, which makes it easy to solder small components or devices with large pins.

The most commonly used T12 soldering iron tip

Unlike soldering, the key to removing a device from a circuit board is that all the solder on the pins must melt at the same time. A common method of repairing and desoldering is to use a hot air gun to heat all the pins of the device at the same time to complete the desoldering. However, for circuit boards with dense components, a hot air gun may sometimes damage nearby components. The following animated image shows the method of desoldering using a soldering iron.

Desoldering resistors and capacitors

For desoldering of small surface mount resistors (1206, 0805, 0603, etc.), since resistors are not afraid of heat, you can use a horseshoe-shaped soldering iron to desolder directly.

Desoldering 0805 surface mount resistors using a horseshoe soldering iron

If you are desoldering a device in the middle of a very dense resistor array, the horseshoe-shaped soldering iron may touch the surrounding devices. Use an insulating transparent paper underneath, just like the antibacterial cloth on the operating table, to perform targeted cleaning of the device.

For dense resistor matrix, use insulating paper hollow protection

For LEDs that are afraid of heat, use a knife-edge soldering iron to heat both pads from the side of the device at the same time to remove the surface-mount LED.

Desoldering Surface Mount LEDs Using a Knife-Edge Soldering Iron

The knife-edge soldering iron has a wider heating surface and can quickly remove small two-pin devices such as resistors, capacitors, LEDs, etc. in open areas of the circuit board.

Use a knife-edge soldering iron to desolder surface mount resistors and capacitors

For resistors and capacitors located in the narrow area between integrated circuits, the components can be removed with the help of flux and molten tin on the surface of the soldering iron. There are two key points in this process:

Pre-apply solder to the knife-edge soldering iron;
The flux makes it easier for the solder to wet the device pins.

Use a knife-edge soldering iron to desolder the capacitors between the chips

Desoldering integrated circuits

When desoldering an integrated circuit, the main problem comes from the fact that the circuit has more pins and they are distributed more widely.

Small IC circuits can be directly removed using a horseshoe-shaped soldering iron.

Desoldering micro integrated circuits using a horseshoe soldering iron

If the horseshoe is not wide enough, use a knife-edge soldering iron with more solder to remove it.

Desoldering IC components with a knife-edge soldering iron

For SOP-8 integrated circuits, more solder needs to be applied and the heating time needs to be longer.

Use a knife-edge soldering iron + solder to desolder the SOP8 chip

After disassembly, you need to use a soldering iron to remove the excess solder.

Remove the remaining solder with a soldering iron

This method is also used for some wide-body tantalum capacitors.

Desoldering a wider tantalum capacitor using a knife-edge soldering iron

Thermal copper wire desoldering

For wider devices, simply using a soldering iron and solder is no longer enough to heat all the pins at the same time. The use of thermally conductive copper wire can help widen the soldering iron tip.

The following procedure shows the process of removing the Mini USB socket. This requires heating the pins of the USB socket from three sides.

Desoldering the Mini USB socket using thermal conductive copper wire

For this type of power MOS tube, the purpose can also be achieved by using thermally conductive copper wire.

Use thermal conductive copper wire to desolder power MOS tube

What if the device is wider? Then use more thermal conductive copper wire. Of course, in addition to the thermal conductive copper wire, it is also necessary to apply more solder.

For larger SOP chips, longer thermal conductive copper wires are used.

The disassembly process is a battle between the heating of the soldering iron and the heat dissipation of the circuit board. If the soldering iron is low power, this heating process will be very long. So using a high-power soldering iron can help shorten the disassembly process.

Use a soldering iron to heat the thermal conductive copper wire to melt the IC pin solder

Yes. With a high-power soldering iron, it is not a problem to remove any chip, no matter how big it is.

Add thermal conductive copper wire around the device, and then use solder to add a molten tin apron to the device, and finally the device will leave the circuit board obediently.

Patiently heat and finally remove the TQPF chip

Ok, now you know how to solder and desolder?

Source: WeChat public account tsinghuazhuoqing

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