lead free soldering
Purpose: To be able to teach kids how to solder, using lead free solder and materials with low toxicity or other health risks for safer handling.
This is not meant as a guide for professional soldering, since leaded solder is currently (2023) still unmatched in terms of both quality of solder results as well as ease of handling. Even for adult beginners I still recommend using leaded solder (if you can get your handy on any, since they have mostly been removed from the private market).
Introduction
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TL,DR; Lead-Free Soldering Quick Guide for Hobbyists
Read the more in depth explanations below for how I came up with these recommendations.
Tool Recommendations
Disclaimer: Most links I provide link to conrad.de, because of its accessibility to private customers. I do not endorse the shop and most products can be found cheaper on ebay.de or other sources.
Soldering Station
For private or hobby purposes I recommend using a soldering station that can be set to at least 450°C, ideally with enough wattage (e.g. 100W or more) to heat up the iron quickly. The working temperature should always be below 400°C, but heating up the iron quickly is essential both for an acceptable handling experience as well as minimizing high temperature exposure and oxidisation of the soldering iron tip.
Additionally at least two programmable buttons for temperature presets is very useful. I also recommend using a dry cleaning sponge (Reinigungswolle) instead of a wet sponge, since this will minimise temperature loss and temperature strain on the solder tip. Please don't use wet sponges.
Product example: Toolcraft ST-100D SE from conrad.de, max. temp 450°C, 3 programmable buttons, 100W power, dry cleaner sponge (Reinigungswolle) included. Pricing ca. 130EUR (incl. MwSt, in 2023).
Soldering Tip
Personall I prefer small flat soldering tips over the typical rounded ones. If your soldering station comes with a fine enough soldering tip, you don't need to worry about buying additional tips.
The Toolcraft ST-100D station includes a fine tip (not pre-mounted) useful for most THT soldering jobs. For SMD soldering we ordered a flat tip for our student lab.
Product example: Lötspitze Meißelform TOOLCRAFT T-0,8D Spitzen-Größe 0.8 mm Spitzen-Länge 17 mm
Other Tools
I also recommend getting at least one PCB-holder ("Dritte Hand", a simple one without a magnifying glass is sufficient) and a good light source on a flexible stand/arm. They can also be bought as a combined tool ("Lupenleuchte").
Product example: Tisch-Lupenleuchte with pcb-holder from conrad.de
Plastic cutting mats can cause ESD damage to electronic components, which is why I advice against using one to protect your table surface. The cheapest option is to use a large piece of cardboard, or if you want to go fancy use a proper soldering mat.
Product example: Soldering mat (Lötablage) from conrad.de
Depending on your application some tweezers or special PCB-holders and flat pliers can be useful too. Here's a list of equipment we use in our student lab:
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flat self-closing tweezers / flache Lötpinzette / flache Kreuzpinzette
Material Recommendations
Disclaimer: I focused on products by Stannol for my research for good products. There may be other useful products on the market.
Solder Wire
Solder wire with silver (Ag) component has a lower working temperature than without silver. The price is slightly higher but it's worth the cost.
Recommendation: Use 0.5mm diameter solder wire, useful not only for SMD but regular THT soldering.
Product example: Stannol HS10, 95.5% Sn, 3.8% Ag, 0.7% Cu (Sn95,5Ag3,8Cu0,7)
Alternatively the Stannol HF32 variant (Sn95,5Ag3,8Cu0,7) uses flux that is halogen-free and produces less smoke. It's worth noting the noticeable higher price and sticky residue it leaves behind. If health risks are a major concern and using a smoke filter is not an option, the HF32 wire can be recommended instead of HS10.
Liquid Flux
Additionally for lead free soldering using additional liquid flux ("Lötwasser") is essential for correcting mistakes or handling thicker wires. Thick wires require more time for heating up, which will burn through the flux included in the solder wire more quickly. Thus extra flux is required to be able to introduce enough heat.
I have found one liquid flux that is surprisingly low in toxicity but also works nicely with different solder wires that I tested. I recommend liquid flux with a brush included in the bottle cap.
Product example: Edsyn FL 112, VOC-free No-Clean rework flux.
How to Solder Lead Free Step by Step
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Solder Experiments and Research, Professional Guide
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