Oxidation when soldering

Discussion in 'General Electronics Chat' started by Dritech, Jul 16, 2016.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    812
    6
    Hi all,

    I am doing some experiments to check the effect on resistance after the soldering process.
    Does oxidation happen instantly after soldering? what methods can be applied to prevent oxidation after soldering? (withough applying any protective spray or something of that sort)
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    7,101
    1,635
    Oxidation will begin immediately after soldering. Metals used in typical solders aren't prone to excessive oxidation; that's why copper wires are often "tinned" with solder.
     
  3. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,535
    411
    Store the soldered item in an oxygen-free environment.
     
  4. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    2,199
    485
    Free oxygen? All the oxygen you can breathe for free?

    Sorry Blocco, just had to pierce in and be silly.

    Oxidation is the worst during soldering IF no flux is used. Nearly all solders have a flux core of some sort. Some are "No Clean", others are "Water Soluble" to name a few. "Rosin Core" is another, but this one you want to clean with some sort of flux cleaner. Depending on the exact chemistry of the flux it can be anywhere from very mildly corrosive to rather aggressive. And if you fail to clean it off it can deteriorate your work.

    When you heat and reheat solder it dries out (so to say) and can appear as if it were a cold solder joint. That's because without flux oxygen begins to oxidize the surface (where oxygen contacts the molten solder) forming solder dross. Dross is the unwanted byproduct of hot solder. The purpose of flux is to replace the oxygen in the immediate location where the solder is being applied so it doesn't oxidize. It has other purposes as well, such as cleaning the surface of the copper pad to aid in solder wetting (adhesion of the solder to the copper).

    As for storage of electronics - which the computer you're working from right now - has solder joints that were made some time ago. So no real application is necessary to prevent oxidation. However, an unprotected copper trace can become oxidized rather quickly if it comes in contact with something like the oils found on the human hand. It can tarnish - or if worse, it can corrode its way through the traces. For many years electronics were built without the aid of solder mask and conformal coating.

    Solder mask is a protective coating on the board meant to protect all the areas of the copper traces that solder is not intended to be applied to. Conformal Coating is a clear coating (spray type is most common and is applied after the board is complete) is meant to protect the board from moisture. Some conformal coatings are very good at sealing a board and in such cases the board can be submerged in water and not suffer any ill effects from contact with moisture.

    As for concerns over oxidation during storage - I wouldn't worry about it.
     
  5. SLK001

    Senior Member

    Nov 29, 2011
    1,166
    426
    If your joint is oxygen free (meaning that you did it properly), then the effects of the surface oxidation will not be detectable in your measurements.
     
  6. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    2,199
    485
    @jamesbarnhart
    I see you're a new member. Welcome. Some of us on this website are "Moderator's". I am NOT one of them. I've noticed that this is an old thread, and likely the person who posted it has gotten the information they needed back in July of 2016.

    When I look for threads to respond to I go to the top, select "Forum", and then select "General Electronics". From there you'll find a host of new posts and active threads to which you can respond. You can also select (at the top of the list) "Post New Thread" or something like that. There you can post questions you have or in search of information, guidance or otherwise a response to your post. There ARE some guidelines that need to be adhered to. Not sure where you can find those, but some subjects are not allowed. You may have your thread locked so that no further responses can be made, and sometimes content can be removed by a Moderator if it is something that may be hurtful toward others.

    I've read and agreed to the user guidelines, but that was a while ago. Basically, be courteous and don't start prohibited topics and everything will be fine.

    Again, welcome. And again, I'm NOT a Moderator.
     
    Last edited: Oct 28, 2017
    ScottWang and jamesbarnhart like this.
  7. Lyonspride

    Member

    Jan 6, 2014
    127
    19
    The defence and aerospace sectors get really funny about this stuff. I worked a time in a lab that tests all manner of things, detecting counterfeit parts, solder-ability, the effects of oxidation on soldered joints and tinned component leads, solder voids inside solder joints, intermetallic compounds in solder joints, tin whiskering, artificial ageing of components and solder joints, etc etc etc etc.

    In all honesty, I think there are a bunch of academics who know enough big words and can talk the hind legs off a donkey, that they've got the whole industry into a state of paranoia about something that really isn't that big a deal and of course it's created more overpaid jobs for people who sit behind desks drinking coffee all day.
    The same in many respects, as the way there's a whole industry of BS now grown up around selling ESD related equipment, put an ESD sticker on a pair of cheap metal tweezers and sell them for 3x the price.

    The defence and aerospace sectors use the same equipment for decades, we regularly fly on planes that are 30+ years old and exposed to the worst levels of stress you can imagine, whilst some of the defence sector stuff is from the 1960's, in these areas I can sort of understand the concern, but for the average commercial product all that's needed is to follow good practice and common sense.

    I was told NEVER to cut through a soldered joint, as this accelerates oxidation (the surface of a soldered joint is self protecting to an extent), but through my career i've seen it being done even in safety critical equipment and nobody blinks an eyelid, because they're all focused on the much more complicated stuff they've been sold the idea of by people trying to make a lot of money.
     
  8. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    2,199
    485
    @Lyonspride: I agree. There's been far more made of minor issues than needs to be. However, and I'm not one of those highly educated types, there is reason not to ignore some of these factors. ESD has killed satellites. I was witness to it one afternoon when a cart with a rusted chain was moved past a satellite under test on a conductive floor. It was traced back to that cart. And tin whiskers HAS ended the careers of many older satellites. Having worked largely in the oilfield electronics, particularly offshore rigs, a stray spark can and has sent some of these rigs to the depths in flames. Having given that - I've never seen any of my electronics go up in smoke because of whiskers or ESD. Still, it's reasonable to exercise some level of protection. I have an ESD mat on my workbench, grounded, and an approved wrist strap as well. Often I forget to put the strap on, but sometimes I remember. Whether I've experienced an ESD event (or an EOS - wont spell it out since you likely know what EOS is) - I don't know. But everything I've ever built (not a whole lot of stuff) still works. Cutting through soldered leads - baking boards before soldering - yeah, I've been there too.

    Working as a Micro-Section Technician (4 years) I watched as engineers debated baking boards to get the moisture out. So I contacted one of our suppliers and asked them to ship me three different types of boards that were defective. Asked them to put a hole in the middle of it to render it "UP" (Useless Product). I then took nine of each type and segregated them into three groups of three. Of one of the seg'd groups was subjected to soaking in water for three days. Three more were put into a baking oven for the same three days and the remaining group was left untouched (in their bags with the desiccant). At the end of the three days all 27 boards were run bare up the wave. The results were debated by the engineers who couldn't let go of "Pre-Baking" boards. The results were that the boards that were soaked in water soldered the best. The second best were the boards that were left to sit in their bags, and the worst solderability was from the boards that were baked at 250˚ F. Of the boards that were baked, there was some minor non-wetting issues due to oxidation, but nothing that would cause too many rejects. The boards that were soaked exhibited nearly perfect solderability and the boards left untouched was only slightly worse. The intent of the experiment was to accelerate the availability of boards to production, eliminating the pre-baking time from the equation. Alas, since it wasn't engineered by the engineers it was promptly ignored by them. Oh well. You can't educate the educated sometimes. They know too much to listen to us lowly technicians who work with the stuff daily.

    I agree, a lot more fuss is made than needs to be. But an ounce or protection may be worth - well, in our cases, a few dollars. But let me ask (and I certainly don't want or need an answer): Would you have sex with a new partner for the first time and not wear a condom? Why? The risk is likely very low. Why not? I think the answer would be 'Because you don't want to catch an STD or end up becoming a new parent at an inconvenient time.'

    Why protect your electronics? What's the harm?
     
  9. Lyonspride

    Member

    Jan 6, 2014
    127
    19
    The reason I mention ESD is because systems are often put in place which don't fully protect the product, but it's always done by the academics and by management, they never run this stuff past the hands on engineering types. They go to great expensive, do half a job and don't care as long as it looks good on paper.
    I've also done sectioning of components to view ESD damage under an electron microscope, so if it sounds like i'm against ESD protection, im not, i'm all for it as long as it's done properly, rather than just looking good for the customers. I've previously worked in a place where they claimed to have ESD flooring and "ESD jackets" for the staff, the customers lapped it up, but the floor was standard vinyl flooring you'd find in a kitchen and the "ESD jackets" were just cheap cotton/polyester lab coats that nobody wore unless there were customers visiting.

    From my experience PCB baking only really has benefits if the room humidity levels are high (which they should NOT be), high humidity plus cold PCBs from a cold store room, causes condensation on the PCBs, which ultimately leads to solder splatter, solder balling, exploding solder joints and other horrible things. The downside is a hot PCB evaporates a portion of the flux in the solder paste, leaving dry joints and all sorts of other problems. Of course people who've never experienced this and only read about it, have no idea whether they need to do it and arrogantly decide to solve a problem that doesn't exist, so they can pretend to be the hero of the day and suck up to management, they may even falsify some statistics to show how great their idea was.
     
  10. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    2,199
    485
    How many times have I seen that ! ! !
    Seen that too.

    I used to LOVE to poke into cabinets at suppliers establishments just to see if I could find the hidden "Out of Calibration" equipment. And when we've had visitors we'd run through the shop picking up and hiding anything we didn't want them to see. I always knew that visiting a company meant I wasn't going to find anything.

    And conductive floors - what a laugh. Shoes get dirty and don't ground. Heel straps are worse; and they often fall up over the heel. Conductive flooring (legitimate) that is not properly cleaned is a joke too. I've never been impressed with conductive flooring. I've also seen people say "I have my heel straps on so I don't need my wrist strap." Yeah, while they kick their feet up on the bench foot rest (not conductive) or put them up on the foot ring on the stool (supposedly ESD approved conductive wheels) (which get dirty and never cleaned). But if it makes them feel safe - conductive flooring - can't be beat as a placebo. Good for next to nothing. Except that poor satellite I saw go down with the passage of a cart. Of course the cart was wheeled right up to the satellite. Some tell the story having the cart 3 or more feet away. Sorry! Inverse Square Law. Double the distance away, cut down the danger by a factor of 4.

    Done lots of ESD auditing. Seen test stands you could pass ESD without even stepping on the pad. Also seen some pretty smart units that couldn't be fooled. At least not that I've ever discovered.

    Wave solder, reflow ovens - what a world. But it's been my world over 30 years.
     
  11. ScottWang

    Moderator

    Aug 23, 2012
    6,296
    973
    Thanks for your explanation, for the necropost posted on the thread already over one year, we have taken different action as just delete it, or maybe it's provide a new idea or useful for the members not for the TS, so we will let it stand as jamesbarnhart did, or maybe split it to a new thread, specially when the necropost is asking the same question for help, sometimes maybe let the new post to take over the old thread when the TS was gone for many years.
     
  12. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    2,199
    485
    @ScottWang That's why I'm not the moderator and you are. Thanks for the clarity.
     
    ScottWang likes this.
Loading...