How-To: Go green with lead free solder

We covered many of [Jason Rollette]‘s personal projects in the past and are happy to welcome him as our newest Hack-A-Day contributor.

The electronics industry has shifted to lead free compliance, but most hobbyists haven’t even considered the personal impact of using lead. Today’s How-To will cover what it takes to switch from tin/lead solder to completely lead free. Our previous posts Introduction to soldering and the follow-up still apply to lead free. You may have never considered switching to lead free before, but we hope to help you make an informed decision.

The reason we are even talking about this is because of the Restriction of Hazardous Substances directive. RoHS was adopted in February 2003 by the European Union; all electronics sold there must comply. The substances restricted are: lead, mercury, cadmium, chromium VI also known as hexavalent chromium plating, and pbb, pbde flame retardants used in plastics. We will focus on lead. Solder joints must contain less than 0.1% lead to be compliant. RoHS is not currently required in the US, but California RoHS, effective September 2003, had a compliance deadline of January 2007.

Although the electronics industry has been directly targeted it only accounts for a small percentage of the lead used in manufacturing. The battery industry consumes nearly 80% of manufactured lead. Tire wheel weights also account for a larger percentage.

There are some good reasons for the hobbyist to convert to lead free solder, both personal safety and environmental. Lead poisoning can occur when lead enters the body through inhalation, ingestion or dermal contact such as direct contact to mouth, nose, eyes, and skin lesions. Even if you keep using tin/lead solder, wash your hands before and after you do anything. Most poisoning cases are from lead building up over time. The main environmental issue is lead leaching into drinking water or watersheds when disposed of improperly.

There are many different varieties of lead free solder. Two alloys seem be the most popular: SAC305 contains 96.5% tin, 3% silver, and 0.5% copper and melts at ~217C, SN100 contains 99.3% tin, 0.6% copper, and some nickel and silver and melts at ~228C. Choose whatever alloy and brand you feel is appropriate for you. Compare those alloys to traditional 63% tin and 37% lead melts that melts at ~183C. The higher melting point is part of what makes lead free harder to work with. We use SAC305 with a “no clean” flux core.

In addition to picking an alloy, you also need to decide on the diameter. We recommend for through hole .032″,.020″ and .015″ for SMT. Choosing the right diameter solder is very important to success. A finished joint viewed from the side should look like a little Hershey’s kiss, not an inflated balloon. The correct diameter solder makes this much easier to control.

A high wattage soldering iron with temperature adjustment is the best choice for precision work. Get a soldering iron with several sizes of replaceable tips for different soldering applications. Having a good iron makes soldering with lead free easier because of the higher melting point. It also helps to keep the dwell time as short as possible reducing damage to components caused by excessive heat.

Choosing the correct size tip for the job is perhaps the most important part for a new person learning to solder. Lead-free is less forgiving and the right tip will go a long way in preventing defects.

Using a tip that is too small will take longer, abuse the tip, and will not efficiently transfer heat to the joint. A small tip will seem too cold or too slow.

Using a tip that is too large will damage the circuit board, over heat and damage the parts, and burn off the flux too soon causing a bad joint.

Use tips that are designed for lead-free. Tips designed for lead free will have the longest life. The iron temperature should be set to 700-800F. Do not use pressure to compensate for lack of wetting and heat transfer; this will cause damage to the circuit board. Heat transfer is optimized by providing the best contact area.

Differences from tin/lead soldering

Tin/lead solder should not be mixed with lead free solder because it decreases the strength of the joint. Lead free parts can be used with tin/lead solder. You should try ordering all parts, ICs, resistors, caps, proto boards, etc. lead free even if you are not using lead free solder yet. This will ease the conversion for you in the future. Consumables such as flux and tip cleaner should be certified for lead free soldering. Flux will need to withstand higher temperatures and longer dwell times, and some tip cleaners have tin/lead solder in them that could contaminate the lead free solder joints.

Not all fluxes are capable of sustaining high soldering temperatures. Flux charring, called “black tip syndrome”, occurs when thermally incapable fluxes turn the tip black and make re-tinning nearly impossible. Heat transfer is severely reduced when this happens. Buying compatible flux is key.


As we’ve said many times: you’ll need to set your solder iron slightly higher temperature than you are used to. You will also notice that slightly longer dwell times are needed because of higher melting points. Wetting or spread is also a little slower when compared to tin/lead. The resulting lead free solder joints will appear slightly grainy and dull compared to shiny tin/lead.

The iron must be kept clean and fully coated with the solder alloy, otherwise at the higher temps oxidation can occur. Solder tips will need to be cleaned and tinned more frequently. Use a wet sponge for cleaning and keep your tip tinned by adding a small amount of solder. In general, all tips will have a reduced life when using lead free alloys.

Lead free solder is more prone to solder bridges (shorts). Tin whisker growth is also possible with high tin alloys, but is poorly understood.

The temperatures required make lead free soldering a different experience, but not out of reach. If you can solder with tin/lead solder, you can solder lead free. If you are having problems soldering, maybe some of the tips here will help. Remember, soldering takes practice; solder, desolder, resolder some old circuit boards from computers or consumer electronics before attempting a project. Otherwise you can’t expect a perfect outcome. Knowledge, practice and experience will provide the consistency required for excellent hand soldering results. Please share any experiences you have working lead free.

Comments

  1. Jake Milton says:

    As the comments show lead free is worthless and more dangerous.

    PS: I sell stuff too but claim its RoHS for EU buyers. Not to worried about the UN coming after me.

    • M. Geran says:

      “As the comments show . . . more dangerous”
      Sorry, casual speculation in comments on a blog do not amount to proof. Nice job lying to make a profit, though. Real classy.

      • Jake Milton says:

        I provide quality hardware that is highly respected and reliable. RoHS is NOT sufficient and I refuse to ruin my companies name or the reputation of our products to satisfy requirements set by bureaucrats not experts.

        Furthermore the health of my employees is very important to me and my company therefore I will not subject them to the increased toxicity of RoHS solder.

  2. keith says:

    I’ve been using lead free solder for over 8 years now. I realized a few years ago the 3% silver solder is the best. It flat out does not whisker. If industry is having problems with whiskers then they are opting for the slightly cheaper 99% tin solder. But I think lead free is actually easier to use once you get used to it. It definitely has a better flow to it and it certainly forms more conductive joints according to resistance tests. This is very critical when working on RF projects and it’s yielded much better results.

  3. jun csatillo says:

    oh yeah i hate lead free specially if you doing replace some part, you are taking a risk for your what you doing..becoz i am working as smt technician

  4. ben says:

    I am totally switched over to LFS. I do not have any problems with it. I works just as well as toxic solder. I suggest that people who hate environmentalist and “Dirty Hippies” are proof of the brain damage caused by lead.

  5. Thomas Mensi says:

    I use about 10,400 pounds of solder a year. The amount of dross left behind for recycling was a main reason for switching to lead free even in the eyes of the European standard for ROHS. We trade heavily in Europe so we had to change.
    Despite the price difference, we have engineered, to perfection, our wave process of application. Yes there are downfalls such as using alcohol based flux instead of the water based flux we used with lead. The disposal fee is higher as well.

  6. I built a fuzz box for a guitarist friend and it went wrong. The on/off for this particular device required the jack to be inserted, where the negative battery connection would pass through the jack plug shaft. A fault developed where removal of the jack plug wouldn’t switch of the unit, as intended. I spent a load of time trying to figure it out (I’m not the sharpest tool in the box) A tin wisker had shorted the negative to ground, keeping the unit in it’s ‘on’ state. This wouldn’t have happened with leaded solder. I will avoid using the unleaded stuff in future.

  7. Royce says:

    Hi Gemma,
    You are using the wrong kind of lead free solder friend.
    Like Darron said in his October 4, 2011 post, use the 96% tin and 3% copper and silver lead free. 99% tin has tin whisker problems. Silver doped does not have tin whisker problems.
    Hope this helps you out.

  8. Bill Mooney says:

    Sorry to push my own work, but this article on coping with lead free is still useful, I hate lead free btw- typical eu office based decision. 60/40 is magic and harmless if used with care, lets keep it!! :- “Coping with lead-Free solder” EPE magazine May 2006 http://david.alfa-romeo.eu/elektro/EPE/2004/EPE%202004-05.pdf

  9. I also ran into the tin whisker issue, it might be worth mentioning that if the board is conformal coated immediately after testing the whiskering might not occur for the normal lifetime of the product; Epoxy works well and so does polycaprolactone :-)

    I also found that more whiskers happen on high potential circuits, ie RFID and HV devices. It seems to be more likely in DC circuits where a constant air discharge is present at nA levels so Geiger counter enthusiasts take note here.

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