The experienced electronic hobbyist and circuit builder knows that a quality solder joint results in trouble free device operation. Achieving a quality solder joint can be attained by ensuring correct soldering iron tip temperature for the type of solder being used. The most common type of solder for hobbyists is the Tin-Lead alloy with ratio of 60:40 Tin-to-Lead. This “soft” solder has great working characteristics and a well defined melting point of 183°C (361°F). Any soldering iron that is capable of raising component temperatures above that level can solder effective joints.
Lead Free Solder
However, exposure to lead has been found to have severe health consequences with damage to the brain and nervous system the most common problems. Due to the health concerns over lead contamination, the European Union in 2006 prohibited the use of Tin-Lead alloys in most cases. This has resulted in the increase in use and availability of lead-free solder alloys such as Tin-Silver-Copper or Tin-Silver-Copper-Zinc at prices comparable to Tin-Lead solder. These alloys differ from Tin-Lead alloys in that they melt at a higher temperature and at a range rather than a point so, for example, Tin-Silver-Copper alloys specify melting range of 217-221°C (422.6-429.8°F).
Measure Soldering Tip Temperature
Hobbyists who desire to switch to using to lead-free solder should measure the soldering iron tip temperature to ensure the tool will work effectively with lead-free solder. Two common temperature measuring devices are the infrared thermometer and the thermocouple. Of the two, the thermocouple is preferred because an infrared thermometer’s radiant heat detector typically measures across surfaces and cannot accurately measure the small point source of the soldering iron tip.
The principle behind a thermocouple is that when two differing conductive metals are joined and a temperature difference exists, a current is induced from which a voltage can be measured. By comparing a thermocouple’s reference voltage (typically room temperature) to the voltage of the measured heat source, an accurate temperature can be calculated. The Type K is the most common thermocouple in use today. This thermocouple is readily available and accurate enough for solder iron tip temperature measurement. Some companies such as Hakko sell dedicated soldering iron tip temperature measuring devices where one simply touches the heated solder tip to the thermocouple built into the device to obtain a temperature reading.
Type K Thermocouple
However, at hundreds of dollars, these devices may be too expensive for most hobbyists. A more cost effective way to measure your tip temperature is to use a digital voltmeter (DVM) that includes a thermocouple probe and the ability to display the temperature directly. The cost for a DVM with temperature measuring capabilities range from nine to over one hundred US dollars. Its use is simple and accurate. Simply connect the thermocouple leads to the indicated ports on the DVM, set the selector to measure temperature, and touch the thermocouple probe to your soldering iron tip when it has reached operating temperature. The DVM will indicate the temperature measured. Less expensive models typically only display the temperature in either degrees Fahrenheit or degrees Celsius, while more expensive models allow selection of which output to display.
Although considered harder to work with, using lead free solder is safe and effective if you ensure your soldering iron operates at the correct temperature by measuring with a thermocouple thermometer.