HAKKO Tech Tips – How to Maximise Lead-Free Soldering

December 31, 2021 WNIElectronics

In this edition of Hakko Tech Tips, we will be examining the impact of lead-free soldering and explore how to achieve peak performance in your soldering process. Since the use of lead in solder alloys became restricted in 2006, there has been a seismic shift to lead-free alternatives such as those containing mostly tin with small amounts of silver and copper. But where the Tin/Lead solders had a melting point of 183°C, today’s lead-free solders have melting points in the region of 220°C. Soldering at these higher temperatures has compounded any oxidation issues in the electronics industry. Lead-free solders may oxidise a soldering tip up to five times faster than if a Tin/Lead eutectic solder were used! With electronic products ever evolving towards increasing miniaturization, multi-function and high integration, there is growing demand for high reliability solder joints. Approximately 70% of failures in electronic devices originates during the packaging process and is largely due to the failure of solder joints. With the advancement of environmental awareness, lead-free solder joints have become a hot issue in recent years. So, let’s explore how to optimise lead-free soldering in more detail:

How does temperature impact on Lead-Free Solder Joints?

Lead-free solder’s melting temperature is still relatively like that of a Tin/Lead alloy. However, the inherent properties of a Lead-Free solder joint are significantly different. Due to the absence of the Lead content a Lead- Free joint will be physically stronger but much more rigidised less ductile. However, it will also possess a coarser grain structure which makes them duller in appearance but also much more likely to crack, especially when exposed to changes in temperature and vibration. One way to minimise this would be the use of thermal management materials to minimise the ambient temperature of an electronic device and ensure reliable operation under harsh end-use conditions. Alternatively use of a surface mount adhesive or underfill will provide increased physical strength rather than being solely reliant on the solder joint itself.

Why do Soldering Tips and De-Soldering Nozzles oxidize with Lead-Free solders?

Due the absence of the Lead content in Lead Free solder wires, and the higher temperatures involved, soldering tips and nozzles will always oxidize at a faster rate than with Tin/Lead solders. However, there are other contributory factors that need to be considered. Setting a high temperate for a solder tip and/or de-soldering nozzle with little regard for the characteristics of the lead-free solder being used and the assembly being soldered will inevitably speed up oxidization of the tips/nozzles and may even damage the component/PCB being soldered/de-soldered. The lowest acceptable temperature should be always used. If not, the inevitable result will be a reduced life expectancy for the soldering iron tip or nozzle. Understanding the unique characteristics of lead-free solder and maintaining soldering irons in a clean condition will provide the easiest route to preventing soldering iron tips from oxidizing and prematurely ageing.

How does lead-free solder impact on soldering tips?

In general, the melting point of lead-free solder is 34℃ to 44℃ higher than conventional Tin/Lead solder. In theory, one would assume that a soldering iron that is set to a temperature of 340℃ to use a Tin/Lead solder (Sn-Pb) would have to be set at around 380℃ to give the same results. This not strictly true!! The set temperature is more defined by the component and PCB being soldered. However, the higher the operating temperature the shorter the tip life will be due to tip oxidation/erosion and carbonization of the flux in the solder wire. Due to the absence of Lead content the use of lead-free solder can decrease tip life by 4 to 5 times compared with a Tin/Lead solder! To combat all the negatives of lead-free soldering, Hakko made their iron tips and nozzles compatible with lead-free solder by increasing the thickness of the plating, by incorporating accurate temperature control and excellent thermal recovery in your Hakko equipment, you will be able to use lead-free solder without the need for a higher set temperature.

What are the benefits of tip/nozzle cleaning?

The Hakko 599B cleaning wire greatly contributes to better removal of the black oxide seen predominantly when using lead-free solders. Furthermore, because the cleaning wire leaves a small amount of solder on the soldering tip, it also helps prevents further oxidation. There is also no cause for concern regarding any physical damage that might be caused by using the cleaning wires as they are made entirely from brass. The soldering tip is plated with iron and because this is harder than brass, cleaning with these wires will not scratch or cause any damage to the surface of the soldering tips.

How do I ensure the best performance of my tips when using lead-free solder?

Hakko equipment over the years has proven to be extremely reliable and compatible with lead-free solder. Nonetheless, if you want to fully optimise the performance of your tips and equipment, there are few common-sense guidelines that should be followed:

Always maintain solder tips and de-soldering nozzles
Turn off the power at the switch when changing solder tips. Failure to do this can cause electrical arcing in the handset, which may compromise the life of the electrical contacts inside. Unless using the soldering iron in a continuous workflow process, it is also advisable to switch the power off between applications to reduce the rate of oxidation.
Make a habit of covering the tip with new solder before placing the soldering iron into its holder during soldering work and ensure that the tip is covered with new solder at the end of a soldering shift.
For De-Soldering -cost filter or filter pipe than a vacuum pump!
Keep soldering tips clean. Hakko provide several cleaning aids to help prevent and remove oxidation from soldering iron tips.

Sustaining a daily maintenance regime in a clean, dry, and well-ventilated area will ensure that your Hakko equipment stays in tip top condition. For Soldering Stations, a periodic check of leak voltage, tip-to-ground resistance and tip temperature are advised. The reason for this is that even if the insulation resistance is measured, it will not show the safety of the device directly because the inside is insulated with a transformer. To prevent device damage and soldering failure, periodically perform these inspections either daily or weekly. Hakko’s Soldering Iron Tester, FG-101, can measure leak voltage, tip-to-ground resistance and the tip temperature (insulation resistance cannot be measured).

Do Hakko Tips require calibration – if so, how often?

It is good practice for all soldering tips to be calibrated, especially when using lead-free solders. Despite any technology to the contrary, the build-up of black oxide can insulate the heat from the soldering tip to the component/PCB. As a result, daily use of a digital thermometer such as Hakko’s FG100B is advisable. The process is also recommended when a soldering tip is changed. Hakko’s FG100B Digital Thermometer provides accurate automatic measurement of soldering iron tip temperatures and includes a new AUTO HOLD feature. With this function, the measurement will end automatically once the tip temperature is stabilized, which minimizes individual differences in measuring temperature. When not in use for three minutes, the auto shut-off feature turns the thermometer off to preserve battery life. The design of the thermometer allows for easy measurements from right- or left-handed operators and the temperature display allows the reading to display in either °C or °F.

Additionally, the FG100B features a low battery alarm as well as a burnout alarm, which signifies a sensor burnout. The product’s design allows for easy access to sensors for quick and easy replacement. There is also an optional temperature probe to measure solder pot temperatures

Is it possible to restore Hakko soldering tips/desoldering nozzles?

This is a question we get asked a lot, and the simple answer is yes. The Hakko FT-700, FT710 and FT720 tip polishers provide a fast and easy way to renew your soldering tips by keeping them clean and free from oxidation, they are also highly effective for lead-free solder. All tip polishers remove tip oxides, debris, and excess solder without damaging the tip plating, and can be used in conjunction with Hakko’s FS100 Tip Cleaner, a lead-free chemical paste.

To restore new life to your soldering iron tips, simply dip the soldering tip into the FS-100 paste to re-tin the tip, then insert the tip between the spinning brushes of the tip polisher to remove all of the molten paste. Finally, tin the tip with the solder currently being used, before placing the iron into the holder.

This quick and easy process is simple to adopt into your soldering routine to enjoy the benefits of a clean, oxidation-free tip, especially when working with lead-free alloys.

We welcome feedback from our customers and potential new customers, so please do talk to one of our team if you have any questions. Look out for next month’s Hakko Tech Tips where we will be providing more advice on how to get the best performance from your Hakko equipment.

For further information about Hakko, please visit www.hakko.co.uk.