Over the years, we have fielded questions about soldering our kits from many different people. This blog post will hopefully answer some of the more common issues that affect our supporters during soldering.
There are two issues that we’ll be going over in this post:
- Soldering temperature is too high
- Improper use of flux
They’ll be addressed in order of importance.
Soldering temperature is too high
This is not the leading cause of defects for electronics assembly. However, it is the issue that leads to the highest number of irreparable soldering jobs, so we’re starting with this issue.
Soldering at temperatures that are too high causes problems because many components (such as the PixArt PMW-3360, the sensor part that’s in many of our mouse kits) are highly sensitive to temperature.
If the soldering temperature is too high, these sensitive components can become damaged, and the damage is often unfixable. Even worse, this damage often can’t be seen, so the job might look completely fine to you, but it’ll still be broken.
So, what’s a safe temperature to solder at? A good, safe starting point is usually the low end of the solder’s recommended temperature range.
For leaded solders, the low end is around 280°C / 540°F.
For lead-free solders, the low end is around 330°C / 630°F.
For the record, we use lead-free solder and our soldering irons are always set to 330°C, so it is absolutely possible to solder at these temperatures.
If you need to increase the temperature of your soldering iron significantly above the recommended temperature of your solder in order to get your joints to wet out, then there are almost certainly problems other than the temperature being too low that are affecting your soldering. The most common reason for higher required temperatures is that your solder iron’s tip has badly oxidized, causing it to transfer heat poorly.
Increasing the temperature may cause the solder to flow, but it may damage the component you’re soldering, leaving you worse off than before.
If you feel like your soldering temperature is too low, consider adding more flux (covered in the next section) before increasing the temperature. You’ll be amazed how often that fixes things.
KEY POINT: Never solder at temperatures that are significantly higher than the recommended temperature of the solder you are using.
Improper use of flux
The most common issue that we see is the improper use (or lack of) flux when soldering.
Flux is a key ingredient when soldering; it is not optional. But what is flux, anyways? And what does it do?
All of the metal pads on a printed circuit board oxidize, no matter what metal they’re made of. Oxidization is the process by which the metal on the outer layers of the pads bonds with oxygen. Metal that has oxidized does not bond well with other metals, electrically or mechanically.
Thus, the key to effective soldering is to strip away this oxide layer prior to soldering. Flux is a special chemical formula that does that. Once the oxide layer is stripped, solder will readily bond with PCB pads. If the oxide layer is still present, solder will not reliably bond with PCB pads.
Many solders include a core of flux in them that pours onto the pads as you’re soldering, which is good. However, many of these fluxes are not that effective. A common reason for this is that they’re old.
Adding additional flux makes soldering easier. In some cases, it is necessary. Without the right amount of flux, soldering effective joints is going to be a major issue.
This can often lead back to the first problem: if the solder isn’t flowing well, many soldering attempts will involve increasing the temperature. Ironically, this makes the problem worse, as higher temperatures cause the flux to boil before it can activate, and will cause pads to oxidize even more.
KEY POINT: When soldering the components of our kit, flux is not optional. Flux must be used to create clean, effective electrical and mechanical solder connections.
More soldering guidance
We always recommend the following soldering guide to our supporters:
This video covers in great detail what the soldering process actually is and how to solder effectively. It is a great resource for those new to electronics as well as seasoned veterans, and we watch it from time to time to refresh our own skills.