Some Summary of Circuit Board Soldering

Soldering tasks

• Soldering of components with two pads, such as resistors and capacitors

• Soldering of TSOP and TQFP devices

• Soldering of QFN

• Soldering of BGA

Tools Required:

• A good temperature-adjustable soldering iron (preferably with a T12 soldering iron tip, usually a knife tip with temperature of around 320°C).

• A soldering iron stand, a sponge, soldering flux.

• Alcohol or circuit board cleaner.

• Tweezers.

Soldering of Components with Two Pads, Such as Resistors and Capacitors

This process is a little bit simple. When soldering the other side of a small-pad device, try to heat the pad with the soldering iron as much as possible, so that it will be easier to apply solder.

1. First, apply solder to one pad.

2. Then, use tweezers to hold the component and fix it on the pad with the soldering iron.

3. Finally, apply solder to the other pad.

Soldering of TSOP and TQFP Devices

Soldering these types of devices is also easy, anyway it's not so easy for the beginners. My practice is to use less solder and more flux. Make the soldering iron tip touch the pins and pads completely, and drag it from one end to the other slowly. If there isn't too much solder, it should be possible to succeed one time without any short circuits or cold joints. Of course, even I achieve it one time rarely. Usually, a few pins will be short-circuited . Just clean the soldering iron tip and touch the pins briefly to fix it.
For some short circuits that are not easy to solve, i usually apply some flux, then place the knife tip on the shorted pad (not on the pins), press the tip against the pins lightly , and move the soldering iron tip from high to low. After reaching the lowest position, lift the soldering iron tip upwards and backwards slightly. It's quite easy to solve these short circuit problems. Make sure the temperature is high enough and the solder is fully melted first.
My first piece of advice is to brush some flux on the pads, so that the flux can make good contact with both the pads and the pins. Apply solder to the pad of the first pin and place the IC properly to solder the first pin. Pay attention to soldering the first pin successfully. With a bit of fixation, you can now completely align the IC. If it can't be aligned, repeat the previous steps. After alignment, solder a diagonal pin. After confirming that there are no problems, start soldering the un-soldered parts until all are completed.

Soldering QFN

These devices are also very common, such as the A4988 and MPU6050. Actually, we can follow the soldering method for TQFP. What we need to note is that the tip of the soldering iron must be sharp enough, so that the tip of the soldering iron can touch the exposed pads on the side of the QFN and also the regular pads completely. In this case, there is no difference with soldering TQFP. It's not easy to cause short circuits and might even be easier to solder than soldering TQFP. However, these types of devices are generally quite small. So it's not easy for an ordinary soldering iron tip to touch the pads. Especially for some special boards, very little of the pad is exposed for working (maybe the SMT requires that the pads cannot be too large). There's no good solution, but using a hot air gun may be the only choice.

Soldering BGA

BGA can only be soldered with a hot air gun. Moreover, if it needs to be removed and re-soldered, tin balls need to be re-planted. I have very little experience with this, so I don't have much to say.