Soldering

When we were first learning to solder SMD components, we used many different tools and methods on the internet to make it easier for us. Some worked and some did not:

Lead-free solder

Since we buy from Taobao, the quality of lead free solder is really bad and unusable, which led to really high soldering temperatures. This was especially for SMD rework where we need to blast hot air / keep the iron on a component for some time, and the high temperatures required from lead-free solder would just destroy our ICs.

We use Mechanic’s leaded 0.6mm 63/37 solder, a fume extractor and a lot of caution.

Using flux

It works well, use it.

While we don’t use it on everything, especially for resistors and capacitors where it’s easy to solder anyways, flux is especially useful for ICs and in drag soldering. However, the fumes produced can be annoying and cause irritation, so do use a fume extractor and solder in well ventilated areas.

Don’t buy fake Amtech flux, it didn’t work well for us. We are using Mechanic’s UV80 Flux

Drag soldering

This technique is especially useful for ICs with leads close together, such as the STM32F103CBT6 we are using. Just spam flux along a row of pins, put a little solder and lightly drag the iron across the row. We don’t bother doing this for packages with larger pitch diameter like SOIC or SSOP, but it was the only way we could solder the LQFP of the STM32.

Using a microscope

We purchased a cheap $10 microscope from Taobao as we thought it would help us solder the small SMD components. However, we found that it hindered more than it helped: most of the time, the SMD packages we use are not too small to be seen. Even when they were too small to see, a microscope would not help much since the leads on those components would be so close together and so small that solder bridging happens anyways. To solder these small components, we just use flux and drag solder.

YMMV as the microscope we bought was a really cheap one with a bad mount that gets in the way of our hands, a better one may end up being very useful to you, but we have survived without one by selecting components of large enough packages and a lot of flux.