leaded solder touching and lead free solder -  conformal coating protection - Page 1
Forum section: electronics / projects

author: lots o tots
author_rank: Contributor
timestamp: March 29, 2018, 01:52:45 pm
content: First off,i would like to say to please respect my request, we all have options on different methods and tequnitues ,and what i am not comfortable doing will be comfortable with others.the topic is touch safe soldering that technically works. I do not like touching lead, but if there is a conformal or isolation coating, i am fine with that (in its cured state) . I want to know the best option to seperate skin contact from lead. i am only a hobbyist so i am only making very few boards for myselfleaded solder:i don't like touchnig this stuff when feeding solder or on the board when using it, however it will end up on circuit boards that i will touch countless times.i am fine with using a conformal coating provided it is touch safe after it dries.i am open to DIY options as well. many of the SDS sheets of conformal coatings refer to open time in terms of toxicity, but i am more concerned about the cured statelead free solderit has disadvantages that we all know. but the biggest issue i have with it is one of tin whiskers.from what i have read, options seem to be limited on coatings that are effective in actually preventing the whiskers. if i can find one that works, well super.options?also how common is tin whiskers (over a course of years)? will this happen on all electronics eventually, or is sorta rare.any options or thoughts presented will be appreciated. thanks.thanks-LOT

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 29, 2018, 02:09:11 pm
content: I am a couple of years out of date on this, but at my last check there were no coatings that cannot be penetrated by tin whiskers. The likelihood of a whisker penetrating two layers of coating to complete a short is very low though.Several formulations of lead free solder are claimed to have no problems with tin whiskers. I take these claims with a grain of salt, mostly because of the limited amount of history, but they at least do not have severe problems.Have you considered wearing gloves, mechanics gloves for example, when soldering? That should solve your issue with handling leaded solder and there are several types of gloves which are thin enough to provide acceptable feel and breathable enough to allow lengthy wear.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 29, 2018, 02:24:32 pm
content: Gloves and a decent fumes extractor are all you need. Especially if you're only doing this as a hobby, so probably only a small fraction of your time.Lead free solder has its issues but apart from needing more heat to reflow, you're probably not very likely to get hit by those in a hobbyist setting IMO. Tin whiskers on a hobby prototype board? Yeah.

author: DaJMasta
author_rank: Super Contributor
timestamp: March 29, 2018, 02:56:01 pm
content: What happened to just washing your hands before you touch your face or eat?Lead is not absorbed through your skin, it has to be ingested to be toxic. It also does not vaporize when you solder with it (the temperature is like 4x what we use or more). That means that unless you're like rubbing your eyes, licking your fingers, or eating a sandwich when there is lead residue on your hands, then there is effectively zero risk of any dangerous lead exposure.As mentioned, a fume extractor (or at least decent ventilation) is recommended because the flux we use does actually produce toxic fumes, but the lead itself is not so dangerous because we don't eat what we're working on. Even the RoHS rules that encouraged the move to lead free solder are specifically for keeping lead out of landfills and thus from leeching into groundwater sources, not because there was any real risk of exposure to consumers.There are good lead free options and while tin whiskers make a difference in high reliability applications and large production lines.... they still aren't all that likely to damage what you're working on because they have to form, form in the wrong direction, and then make contact/penetrate the oxide coating on another joint for them to actually become a problem. That said, I think the simpler approach to your problem is to get over the concern with touching leaded solder, because it really isn't dangerous with minimal handling precautions.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 29, 2018, 07:19:44 pm
content: Hobby folk need to avoid whiskers too. I have projects I made four decades ago that are still in use. While us hobby folk can diagnose and repair whisker damaged gear that isn't a panacea. It can take real effort to troubleshoot, and frequently the parts are difficult or impossible to source. Like the Exar chips in the device above.

author: rancor
author_rank: Contributor
timestamp: March 29, 2018, 08:13:32 pm
content: CatalinaWOW it looks like there might be coating that tin whiskers cannot penetrate but I don't think I would worry about that for hobbyists. The other point brought up by this presentation is that repentration and conductive dust problems are greatly reduced or eliminated by coating. So even if the tin whiskers can penetrate the coating they will not be able to get back into the coating as they are more likely to buckle.https://nepp.nasa.gov/whisker/reference/tech_papers/2010-Panashchenko-IPC-Tin-Whisker.pdfhttps://nepp.nasa.gov/whisker/reference/tech_papers/2012-Panashchenko-IPC-Art-of-Metal-Whisker-Appreciation.pdf- Last slide

author: helius
author_rank: Super Contributor
timestamp: March 29, 2018, 08:24:18 pm
content: Conformal coatings involve chemicals that are much more dangerous than lead solder: silicones cure by releasing methanol, and many are dissolved in aromatic solvents. Parylene is worse.

author: lots o tots
author_rank: Contributor
timestamp: March 30, 2018, 01:20:18 am
content: looking at two different options still. there doesn't seem to be an easy answer.i am leaning towards leaded since it seems there is a difficulty using both methods and a concern about the flux in lead free.Leaded:conformal coatings:when the coating cures and releases fumes, i will only be in the vicinity during application not during curing. are any of them at least bearable? are they safe to touch?i was reading on the forum that someone used automotive clear coat. i know i can touch that.there must be some good options out there.lead freewhat is the best type of lead free solder available? i have been reading that some flux fumes are far worse than ones used in leaded.are there any lead free solders whose flux fumes are at least as good as leaded or better?

author: helius
author_rank: Super Contributor
timestamp: March 30, 2018, 01:35:49 am
content: You can wear a respirator with an Organic Vapor cartridge while applying coating. Once cured the normal kinds should be safe to touch.Normal types of lead-free solder fuse at a higher temperature and fluxes need to be formulated for that. There exist lead-free alloys that do not have an elevated liquidus: Sn77.2In20Ag2.8 for example has liquidus at 187°C, only slightly higher than Sn63 at 183°C. But they are niche and hard to source.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 30, 2018, 02:25:22 am
content: The NASA studies are consistent with what I was saying, with the extension to better protection from thicker coatings. Anyone who has done much with conformal coat knows it comes with it's own set of issues. Getting into connectors. Hell on rework. But it does help on lots of issues.

author: lots o tots
author_rank: Contributor
timestamp: March 30, 2018, 03:50:29 pm
content: Leaded:I understand the proper method is to use a conformal coating, but if they all require organic resorators, then i would conisder an unorthodox method. can i use an automotoive clear coat?i will use an organic half mask resporator if need be, but keep in mind that not all curing vapours are organic, meaning the resporator only works for certain chemicals.do we know which ones are not too bad in this category in which organic resporators work?lead free:although we would like temperatures closer to 180 celcius , i can live with 227 celcius.The type of lead free i am interested is ones whose flux vapours are not worse for you than a rosin core leaded.there must be something out there?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 30, 2018, 04:02:58 pm
content: A clear coat will help against whiskers. But you will be guessing about how much they help. NASA and those in the health, aviation other mission critical industries have put a lot of effort into finding out how well various approaches work. The NASA paper referenced above showed an eleven year study on the normal conformal coating materials. And even that is not definitive in my opinion. Their results depended on the coating debonding from the board, allowing the coating to tent and prevent penetration of tin whiskers. Bond strength is highly sensitive to any number of environmental and process conditions. And Murphy's Law suggests that what you don't want will happen, so when it matters most, some weird combination of effects will result in superior bond strength and prevention of the tenting effect.All that said, the NASA studies, and logic, suggest that a simple clear coat will provide orders of magnitude reduction in tin whisker shorts. Only you can decide if that is enough.

author: lots o tots
author_rank: Contributor
timestamp: March 30, 2018, 06:22:26 pm
content: these have all been helpful answers, but i haven't quite got what i need.my concern about whiskers is not nearly as strong as the need to no reduce toxicity when handling conformal coatings or how to deal with lead. if i go lead free i will have to accept the posibliity of whiskersbut i am leaning towards leadedi am just looking for a good conformal coating that can either use an organic resporator only safely ORa DIY conformal that is acceptable.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 30, 2018, 11:17:07 pm
content: You probably can't get the answers you need.If you read your own words, you seem to have the answer, but you are not satisfied. You have said that whiskers are less of a concern to you than toxicity. And that you are deathly afraid of lead. That means the answer is lead free. Which as you say means some risk of whiskers.That risk is low. But no one can put an exact number on it. Even with or without any kind of coating. Whatever the number is, it will be dramatically reduced by using any kind of coating. The clear spray sold in rattle cans will dramatically reduce the impact of any whiskers, but not reduce the risk to zero. Even if you use the urethane in the NASA study, which would require some work on your part to use safely the risk would be extremely small but non zero. And the toxicity of the clear spray in rattle cans is not zero, but low enough that most are comfortable using them in well ventilated conditions.If you had numbers attached to your acceptable risks there is a chance that you can find the answers, but even that is unlikely, and there is no chance at all when you just say you don't like the options.I would suggest you select a lead free solder formulation based on ease of use in hand applications. I use leaded solder so cannot recommend a formulation to you, but if you search this forum you will find such recommendations. I have seen them. Then if you find you are having unexplained faults in your gear after a few months or years you can look into whether whiskers are the cause (a magnifying loupe or microscope are the tools for this). If you do find a problem in your use case you can then try a spray clear coat. Used outdoors with a breathing mask with appropriate filter cartridge for the spray you are using if toxicity of this concerns you. Don't start with the coating because coatings make troubleshooting and rework difficult and the odds are you won't have a problem. While I was the one pointing out that hobby folk can have tin whisker problems, it really doesn't affect most hobby people for a variety of reasons.