When it comes to solder, there are a few criteria and the choice I have made was based on my personal experience and interaction with other technical minded people. So, my list of preference would be as follows:

0.5mm solder

I am using a 30~35W soldering iron with a sharp tip. This means the heat from the tip is an issue but it allows me to work on SMD devices. The smaller diameter solder would melt faster than the normal 0.8mm or 1.0mm solder. And I buy them one reel at a time.


Although I have some flux handy, the resin core solder helps too. It is flux but in minute quantity Whatever you do, please do know there is also acid core solder, which is meant for plumbing.


I have been using this 0.5mm brand from Mekko (Asahi) for decades and I am very happy with it. But for the last few years, the price has risen dramatically.

There are various brands out there but over here on this side of the Earth, this OEM brand (above) has never failed me. There are better brands such as Hirosaki but I am happy with Mekko. I have seen and avoided those short lengths of thick 1.2mm solder housed in ‘test-tubes’. Just the rule of thumb, cheap solder will never work. If you are really serious into this, and expecting good results, you need to invest in it. OK, maybe just the soldering iron and the solder.


This topic is coming up quite frequently and for me, until a better replacement has been found, I still prefer lead solder. The lead-free solder was introduced after 2006 RoHS Directive where the European Union banned hazardous material in electronics including lead. Unfortunately, in creating alternative solutions, the lead-free solder created new issues.

The normal lead solder comprises of 60% tin and 40% lead. It has a lower melting point, flows easily and is not prone to mechanical shocks. On the other hand, lead-free solder being relatively new, has a higher working temperature, not easy to work with and has mechanical issues such as cracking as it cools.

From this video, Androkavo has kindly shown the differences between a normal lead solder (60/40) against lead-free. For a manufacturer, the time used to correct every soldering is a nightmare.

In general, metal oxidises on its surface all the time. Solder will not stick to them because of this thin layer. The solder flux helps to remove this layer and allows the solder to flow.
You will notice the obvious difference when you start to tin a piece of wire coated with the solder flux.
Without the flux, you would be heating both the tip and the component until solder starts to ‘melt’. That is a long time, which can burn the component and the PCB.

But remmember this: Always clean the flux off the PCB with IPA if you do use them. Heck just clean the boards after the soldering is done.


This is the type of solder flux I use. Over here, we call this solder flux. I used to have one with a metal container but it kinda got lost over the years.

You can call this version a ‘paste’ but I would reserve the term for another item. I can pre-dip the components for soldering, my soldering tip and also, toothpick some onto the PCB tracks. When the jar is full of holes and pockmarks, I’d run the soldering iron tip in a spiral. This would melt the resin and as it cools down, forms a level surface. It is fun but make sure you do not tip the jar nor poke a hole through the plastic jar.


I have just recently gotten these in 2020 or so. These are the solder flux mainly used for mobile phone or SMD component repairs. It comes in a syringe and has a 12-months storage life. The version I had (Amtech NC-559 ASM UV) can be seen with UV light.
I am not sure what to call them to differentiate between the jar and this but colgate (or toothpaste) is not one of them. Maybe, I’ll christian it Amtech.

The Amtech comes in a so-called standardised size which is quite big. Although the plunger looks the same as the syringe, it is quite long since I used the flux sparingly. I had to stretch my thumb and allow the notch to enter into my middle finger. After two years, the flux is still quite full.

This flux system is a great tool when you hand-solder SMD. I can deposit a nice line of flux on the solder pads and then another line of solder paste on top. Because the NC-559 is thick, it has a longer working time. This ideal for repairing a PCB track or component.

A simple test with the UV Light
And on a PCB
This way, under the UV light, I can see if the IPA has done its job cleaning the flux off the PCB or not.

The disadvantage of this flux are:

  • It is a bit too long if you are using your thumb to feed the syringe constantly
  • It is supposed to have a 12 month storage life and for Hobbyist like me, that is too short
  • I hate to clean the flux with IPA after soldering.

There are some solutions out there but they would also create more problems such as transferring of flux to their new syringe and more importantly, cost. So, like the one above, I like it but it is huge and and costly. Bear in mind, these are for solder paste dispensing but in my experience, I used flux more than the paste.