The four main factors to consider when choosing a soldering iron are:
2) type of the soldering iron
4) tip size and shape
The wattage of the soldering iron is one of the most important factor of a soldering iron. Most of soldering irons used in the electronics are in range 20 – 60 Watts. Soldering iron with wattage 50W is very common these days and it will provide sufficient heat for most of soldering projects on the circuit boards. Soldering irons with higher wattage (40W -60W) are better. It does not mean that soldering irons with higher wattage apply more heat to the solder joint- it means that soldering irons with higher wattage has more power available. Since most of soldering stations comes with knob on power station for setting iron’s temperature, it is possible to regulate amount of the heat on iron tip. On the other hand, soldering iron with low wattage (20W - 30W) can lose heat faster than it can re-heat itself - this results in bad solder joints.
Types of soldering irons
Generally, there are 4 different types of soldering irons:
-Soldering systems (rework /repair stations)
Soldering pencils are very simple (and very cheap) soldering tool that can be used only for simple do-it-yourself projects. The price of the soldering pencils is in the range $10-30. I do not recommend soldering pencil for fine soldering projects since they do not provide any control of the temperature on the iron tip. Too much heat applied during soldering can damage components and peel off tracks on the circuit board.
Soldering station consists of soldering pencil attached to a power station. The power station has controls for setting the desired temperature on the tip of soldering iron. Some of soldering stations come with electronic temperature control - that means you can very precisely set and maintain the temperature of the iron. The power station automatically keeps the iron tip at an appropriate temperature. The price of the soldering stations is in the range $ 40-150. Soldering station can cover most of soldering projects including soldering of through-hole components, and very fine surface-mount components as small as 0603 and 0805. Weller is most popular brand for soldering stations followed by Hakko. On the other hand, Aoyue soldering station is good combination of quality and price. The most popular models of soldering stations are the Weller WESD51 (read review of WESD51), Weller WES51, Hakko FX-888 and Aoyue 937.
Rework/repair systems are complex soldering systems which are mostly used in industry or in the high-volume manufacturing facilities. Soldering systems usually consists of several hand pieces including soldering iron, hot-air gun, de-soldering gun, thermo-tweezers, etc. The price of the soldering systems is in the wide range $250 - $2500. Pace is the most popular brand for these soldering systems. Popular models of rework/repair systems are Pace MBT-250 SDPT, Pace MBT-350, and Aoyue 2702.
Main part of a soldering gun is a transformer which converts 110 V AC to a lower voltage. A secondary winding of transformer has only one turn. This way the secondary of transformer produces very low voltage and several hundred amperes of current since primary of transformer is connected to 110 V AC and the secondary winding of transformer has only one turn. This high current is routed through copper tip of soldering gun and as result the tip of soldering gun is quickly heated by the high current flowing through it.
Soldering guns can be quickly and easily turned on and off and they have very short worm up time. However, I do not recommend soldering gun for fine work on circuit boards since they can generate too much heat and can therefore damage circuit board or components on it. The price of soldering guns is in the range $20-70.