Lead free rework and desoldering  - Page 1
Forum section: electronics / beginners

author: EpLe
author_rank: Newbie
timestamp: May 18, 2014, 08:37:11 pm
content: Hi everyone,I'm currently working on modifying an old circuit board to make a much louder output that is closer to line level.To be honest, I don't have much experience in soldering besides the occasional replacing of 1/4" guitar jacks and once having to re solder a potentiometer on my alesis ion. In the past I've briefly used lead solder for those kinda things until recently deciding to switch to lead free. Not too long back I finally got my first soldering station, a hakko fx888d, and of course some SAC 305 by alpha to go along with it. The problem I'm facing is with lead free solder and the joints or pads on the pcb are lead based. I've done some reading on how it's not good to mix the two and how lead contamination makes for a weaker bond. So, I've come to the conclusion that in order to make the new connections needed I,ll soley have to use either one. I,ve already tried using the lead free solder and found out the hard way that it just wasn't right because of the mix. The heating was terrible and nothing seemed to bond even though I had properly tinned my wires and the connections points were properly heated. My question is, for rework and desoldering purposes, is it best to use lead solder for desoldering lead joints or can one use lead free iron tips along with lead free solder ? I basically just want to desolder the mixed joints I've created so that I can start over fresh using strictly one type of solder. I've searched online for answers and could not find anything. It even makes me wonder as to how some manufactures are repairing old electronics that were made using lead. Thanks for help and response in advance and for any opinions.

author: GreyWoolfe
author_rank: Unknown
timestamp: May 18, 2014, 09:12:57 pm
content: If all the joints are lead, keep with the lead just for the reasons you discovered. Unless, of course, you want to desolder every joint and resolder using lead free. If this circuit board is for your use and you aren't selling it to anyone, keep with the lead. Not knowing where you are from may make a difference. If you hare here in the US, stay with the lead. If you are in the EU, you might have to approach things differently and follow RoHS.

author: EpLe
author_rank: Newbie
timestamp: May 19, 2014, 05:46:58 am
content: Thanks, all of the joints are lead and will deffinately be using it for personal use. I live in the US and was thinking of getting some 63/37 for this project but just don't have any lead solder to work with at the moment. Sometimes I try to be too much of a perficionist and guess the main concern is trying to make reliable connections so they will last. However, if I do decide to go lead free instead, I'm still trying to figure out in general what the best procedure is to follow when replacing lead components.

author: GreyWoolfe
author_rank: Unknown
timestamp: May 19, 2014, 12:43:04 pm
content: That's not being a perfectionist. No one wants to keep redoing solder work every few years. If you want long lasting solder joints, stick with leaded solder. Take some extra precautions if you wish. Make sure to clean the board and components with IPA right before soldering so there is no oxidation. Use a good flux and solder, I use MG chemicals liquid rosin flux through a needle dispenser and AlphaMetals Reliacore 63/27 with a .020" diameter. I find it easier to solder components with the thinner solder. I have a thicker diameter solder for soldering wires and PL259 connectors on coax cable. Use the appropriate tip, Stay away from conical tips, use chisel tips and size them just slightly smaller that the solder pads you are going to solder. I have 4 or 5 different size chisel tips for my Hakko 936 plus 1 smd tip. Lead free solder joints, from what I have read, will develop "tin whiskers" as the solder seems to migrate outwards, as they age, into points that could possibly cause issues in tightly packs pcb's. If I am wrong on this, let someone set the record straight. Ultimately, since you are in the US, are keeping the circuit board for personal use and not beholden to RoHS standards, stick with lead. Just my 2 pence worth. I love the smell or rosin flux in the morning.

author: EpLe
author_rank: Newbie
timestamp: May 19, 2014, 03:14:01 pm
content: Ha, I like the smell also and appreciate your recommendation. Sounds like you have a lot more experience working with lead based and do appreciate your advice. In all aspects the lead solder would be easier to use without risk of damage to the board. I deffinately don't want to be doing resolder work every few years and would like to obtain good soldered joints. On my first attempt, I'm pretty sure I didn't get everything cleaned well enough and made a mistake by using chemical paste for retinning the tips which made it impossible to solder. The instructions were off and I wasn't sure how to use it properly. I used a t18-b tip and also have a small selection of chisel tips that may be of the correct size. If the lead free solder could be brought to a good melting point just to remove the bad joints it may be just as safe. That's the only other thing I have trouble understanding since lead free solders demand tighter control due to the higher temps. In a pure lead free hand soldering enviroment how would it be possible to do rework on an old board, given that lead is not to be used.

author: EpLe
author_rank: Newbie
timestamp: May 20, 2014, 09:15:17 pm
content: I didn't know they made 63/27 nor have I tried using that small of a diameter. Does the 63/27 flow smoother? I'm sure the smaller wire will also be easier to work with. Thank you for your help!

author: GreyWoolfe
author_rank: Unknown
timestamp: May 21, 2014, 12:19:23 am
content: That was a typo. I meant to say63/37not 63/27. I would think, in a pure lead free environment, the board probably would have been manufactured to RoHS standards and will be lead free already. Rework by hand wouldn't be an issue. I don't believe that the RoHS standard will allow for working on leaded solder so that would never become an issue. I guessing that those who live in countries that support RoHS and that have electronics from before the standard went into effect probably won't be able to get the device repaired and will end up recycling it and purchasing new. I know that if I was to work on anything RoHS compliant, I would have to have a second set of tips so neither set of tips would be contaminated. If I am wrong on this, I hope someone will shed the proper light on this thread.

author: nanofrog
author_rank: Super Contributor
timestamp: May 21, 2014, 01:18:34 am
content: Quote from: GreyWoolfe on May 21, 2014, 12:19:23 amYes.Quote from: GreyWoolfe on May 21, 2014, 12:19:23 amThere are exceptions, such as aerospace, military, and medical applications (i.e. critical systems). So there are products that still being manufactured with lead based joints.It's also still possible to get older equipment repaired, and the lead doesn't have to be removed. Even still see repair facilities that specialize in quality used audio equipment, as well as T&M gear (some even sell repaired & calibrated units on eBay).Lots of info out there on lead-free alloys, and why we genuinely ended up with them (hint: follow the $$$).

author: GreyWoolfe
author_rank: Unknown
timestamp: May 21, 2014, 12:06:15 pm
content: I can see critical systems still using lead. That would lead to separate rework stations for lead free and lead, possibly even in separate areas, to avoid cross contamination, wouldn't it? That would make the most sense to me. It's interesting that consumer electronics must be lead free but the "critical systems" get a pass. Maybe they know something the RoHS 'police' don't? Hmmmm. I would hate to see it devolve, in the EU, to the point where those with older quality audio and T/M gear have to do back ally deals with shady characters in trench coats and fedoras to get their equipment fixed

author: nanofrog
author_rank: Super Contributor
timestamp: May 21, 2014, 04:49:52 pm
content: Quote from: GreyWoolfe on May 21, 2014, 12:06:15 pmThat would depend on the size of the organization IMHO.A large manufacturer that produces both leaded and lead-free PCB's could separate to the point of each having it's own building (likely more to do with costs than cross contamination though, as building space isn't exactly cheap). On the other extreme, say a one person repair business, might at most, use separate tips for each alloy process (i.e. ever seen green rings that go on solder tips?). Does the trick, and keeps the costs relatively low. Some may even opt to rinse the tips instead.And there's a lot of middle ground, such as sharing the same building, but will have separate assembly and rework lines within it. Color can be used to highlight the two, green for lead-free and either blue or grey for lead based (if nothing more than the ESD mats in the rework areas). For a system using solder paste, either could be loaded in, making the equipment highly adaptable (also fast and low cost change-overs). For wave/jet solder process equipment, I'd expect those to be dedicated due to the difficulty removing all of the alloy from the machine (i.e. expensive).Quote from: GreyWoolfe on May 21, 2014, 12:06:15 pmIt was known that there would be problems with the lead-free alloys (real science, not the psudo BS used to "sell" it to politicians and the public), hence the exceptions being made. Even the tin whisker issue was known about (researched early on in the days of electrical soldering, which is how they ended up putting lead in it to begin with - empirical data showed just how much they needed to add in order to prevent tin whiskers from growing).