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Thread: How Much More Reliable is Lead Solder? What are some other types?

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    Default How Much More Reliable is Lead Solder? What are some other types?

    I know it's not used anymore on PSUs, but in general how much better is good old lead-based solder compared to the stuff that is used these days? Also, I remember like a year ago or somebody maybe mentioned silver being in some solder? In general, what types of elements/molecules are in non-lead-based solder in power supplies, and are there still some better/worse types out there? Is the solder you find on a $20 PSU the same as that on a $100 unit?

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    Quote Originally Posted by turkey3_scratch View Post
    I know it's not used anymore on PSUs, but in general how much better is good old lead-based solder compared to the stuff that is used these days?
    Depends on the type of component you want to solder.

    With normal through hole and low pin count SMD components and not that much thermal stress, I doubt there's a huge difference.

    Where it really hurts is SMD components with high pin count and low pich.

    Wich means GPU; Chipset, CPU and stuff like that.
    That's (IMO) mostly because non leaded solder is on the brittle/harder side while leaded solder is on the softer side. So with many thermal cycles the solderjoints can become brittle and/or get off the package.
    That's what caused the failures in older nVidia GPUs, CPUs and chipsets. And that's why heating a BGA component can revive it, though it's only for a short period of time...

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    There's a huge variety of solders, you can just go to Wikipedia and see : https://en.wikipedia.org/wiki/Solder#Solder_alloys

    Leaded solder is better no matter how you look at it.

    Leaded solder becomes liquid at lower temperatures, for ex. most common 60/40 variety is liquid at around 180c, 63/37 solder at 183c
    Lead Free solder usually melts at higher temperature (most of them around 217c) so you have to set the soldering iron temperature at a higher temperature to solder, which means your solder iron tip will degrade faster and it oxidizes faster therefore it requires more frequent maintenance or replacing (cleaning oxidizes, retinning etc)

    When you solder, you also use fluxes, which are basically some acids which attack the surfaces you want to solder and clean them, removing the oxidizes and other crap before the actual metals (the solder and the circuit board metals) can interact and create a chemical "link"). You wouldn't have reliable solder connection with crap over the metals.

    This flux is usually inside the solder wire in a solid form, but as it's heated it sort of liquefies and falls on the surface you want to solder and does its job within that second or so until the heat from the iron tip will actually burn it off. With leaded solder and its lower temperature, the flux has more time to do its job before it's burned off, so with lead free solders they have to use much stronger, more corrosive acids in the fluxes, so that they'll do their job in much shorter time.
    These fluxes are worse for environment compared to the ones in lead based solders and they're also worse for your lungs... but I suppose in a factory, you don't care about the fumes of the burned acids in flux.

    Some other pros and cons.

    Solders can be euctetic or not.

    Euctetic solder is a solder that turns from solid to liquid and back to solid in a very narrow temperature range. For example, the 63/37 variety becomes liquid at exactly 183c give or take 1 degree Celsius. As soon as the temperature is above 183c, it's liquid. If it cools down below 183c, it's solid.
    Non euctetic solder will turn from solid to a sort of in-between state while the temperature is within some range and then become liquid when the temperature goes above some threshold. For example, 60/40 solder will start turning to that in-between state at 180c and then will take up to 188-190c to become fully liquid.

    So euctetic solder transitioning from solid to liquid so super fast makes it great to solder things in environments where there's vibrations, shocks. Basically, when the solder is in that in-between state it's super important to not move the two metals (wires, wire and circuit board, whatever), there won't be a good solder connection if the parts move when solder is in that in-between state. So for example, when soldering on a boat or on a plane where there's constant vibrations, for reliability reasons, you'd prefer to use the euctetic 63/37 solder because you'd only have to hold the wire in place a second or so until the solder snaps to solid (cooling from 184c to 182c)

    This isn't a problem in factories where power supplies are made, but it's still pointing this out.

    Leaded solder is also shiny when the solder connection is properly made. If you make a bad solder joint (if you move the wire as the solder cools down for example), the solder will be duller, less shiny.
    Lead free solder is pretty much dull no matter the composition, so you can no longer rely on the shiny-ness to have an indicator of quality
    For a beginner, this feature can be very good thing.

    One other important thing... lead in solder helps reduce solder whiskers .. basically tin (the major part of solder, pretty much 99% or higher in lead free solder) develops whiskers over time and this is bad because the whiskers can grow over time and create connections between pins of components that are close together.
    See https://nepp.nasa.gov/whisker/background/ where it's explained better than I could.

    This is one of the reasons why you'd still have leaded solder used in military, medical and some space applications.

    As for other metals in solder like Cu (copper) or Ag (silver). The Wikipedia article explains why some alloys types exist, the reasons why those metals are added

    I never bothered to learn in detail and do thorough research.

    From memory, I think copper was mostly added to extend the life of solder iron tips.
    Think of solder tips as made of thin tubes of copper pipe with the end flattened into a shape (chisel or whatever) and then a thin layer of tin added over it to prevent copper from oxidizing.

    When lead free solders started to show up, the higher temperatures would create layers of oxides much faster so the tips had to be cleaned more often, removing some small amount of that tin material from the tip in the process. Also, there were much stronger fluxes in the solder and those fluxes would also attack the solder iron tip removing some of the tin and eventually reaching the actual copper of the solder iron tip.
    So the small amount of copper of 1-2% in the solder would put reduce the amount of copper material that would be "sucked" from the tip and reduce the degradation and therefore increase the life of the solder iron tip.

    As for silver, lots of audiophiles say it improves sound quality and all that.
    But I think a big reason why it showed up in solders was because some surface mounted components (resistors, inductors, various chips) used to have their terminals plated with silver and a small amount of silver in the solder usually made soldering better and more reliable (silver in both surfaces would interact and create a stronger/more reliable connection, or something like that)

    There's other solders like the ones used by AMD to thermally link the silicon die to the metal lid, those solders have something like 50% indium, which has really low melting temperature (around 120c)... See In50Sn50 on Wikipedia.
    There's also solders which have Bismuth which lowers the melting temperature down to 100c or less - see Chipquick low temperature solders and others. They're good for desoldering temperature sensitive components (you add solder to existing solder to reduce its melting temperature) , or you sometimes see it used to solder sensitive components like leds , camera sensors etc

    As for ... Is the solder you find on a $20 PSU the same as that on a $100 unit?

    I guess it depends on the factory line that makes those power supplies.
    In power supplies they mostly use wave soldering which is different than regular manual soldering ...

    Here's some videos showing how wave soldering is done:

    [1] : https://www.youtube.com/watch?v=inHzaJIE7-4
    [2] : https://www.youtube.com/watch?v=VWH58QrprVc


    The board goes into a machine which sprays the bottom of the board with liquid flux, or a wave of liquid flux goes over the underside of the board coating it with flux. It's the foam in the first video. The board then goes through a sort of oven which gradually heats the circuit board activating that liquid flux and making it do its job for a few seconds, removing the oxides and impurities as much as possible.
    Then, the board usually goes in another machine where a wave of liquid solder (without any fluxes or anything) rolls over the underside of the circuit board and all the connections are soldered.

    The quality of the soldering won't depend as much on the actual solder used in that wave of solder but more in the flux used and how well the flux worked to prepare the surfaces and then also how warm the circuit board is and how hot the solder is and other things also matter.

    Temperatures matter more than the actual chemical composition of a lead free solder. They're pretty much all the same, with very few additives to reduce dross formation (impurities due to oxidation on the surface of the pool of liquid solder)

    With more expensive power supplies, the circuit board may have better quality (the pads may be gold plated or plated with other materials that make the pads easier to solder to), the traces may be thicker reducing losses in the traces.

    A factory may be more careful about soldering process with higher end power supplies, also with cheaper models a power supply manufacturer could outsource fabrication to third party manufacturers that may not have as good quality control (for example Superflower giving budget power supplies to RSY or other companies because their own factories are busy making higher end models)

    For cheaper models they could also use older machines which may not have as good temperature controls or as automated as newer ones, or may have smaller capacities for flux and solder requiring more often refills and then you could have varying degrees of quality between batches of power supplies (for example using two different solders the same day, when they refill the solder "bath" with different solder)

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    Well.. If you want to get into the QC aspect of things....

    Honestly, if the level of any of the metals in the solder become too high, the solder is considered impure and contaminated (often called "dross"). I've been by wave solder machines that have stack of bars next to them so they can keep adding solder to maintain low impurities because some metals "stick" to the components better than others and quickly throw off your ratios.

    Unfortunately, solder is an alloy that is more like simple syrup and nothing like salt water. The metals do not have that good of a solubility and some have a different tenacity to other elements than others that will cause your ratios to change. And since all of the metals used have different melting points, maintaining a perfect temperature is essential.

    The process of exchanging the solder is quite tedious. They have to separate the dross into separate metals by running the metal through different melting points, strain them and then sort them (they have machines to automate this, but that still doesn't make it an "easy task"). This also brings the line to complete halt, which is why it's just easier for them to keep adding to the mix instead of recycling the solder. Obviously, you can't do this forever and this also doesn't address the problem with oxidation.

    One of the things I see time and time again with the lead free solder and it's higher melting point is problems with solder temperature. If the solder temperature is too low, some solder will be thinner than others than this will cause a poor joint. Thus the term "cold solder joint". If the temperatures are too high, you can damage the components, burn the PCB, etc.

    Wave solder machines are easier to calibrate this as they work like a giant oven. You set the temperature and the machine brings the temperatures up. But an older wave solder machine is much like an old kitchen oven. Eventually, 188°C isn't really 188°C. I personally wouldn't trust a wave solder machine that's been used in three shifts for over 10 years.

    Hand soldering is where you get really random results. Not so much due to the skill of the person doing the soldering, but because of the random temperatures of the soldering irons. Unfortunately, there's ALWAYS going to be some hand soldering. Some users, reviewers, etc. may see a larger degree of hand soldering a bad thing, but in my opinion it can be the sign of a well run factory. I've seen some PCB-A facilities that just assemble, wave solder and then ship. Then, when they get to the actual PSU factory for final assembly, they have a fall out of around 5% to 15% of the units. In a good factory, they have inspectors that look at the boards through microscopes for consistent soldering, making sure every joint is complete. Without this process, you can have a functioning product.. but after going through shipping and through several heat cycles of turning off and on while in use, some solder joints can and will fail. If any questionable joints are found, it's sent to "repair". Now, use of the word "repair" can make someone cringe as if the PSU is "refurbished" or something. I've been in meetings where someone asks why the consistency varies from one lot code to another and when told it's because the factory realized they had to do more "repairs" to make the product more robust, it can cause some confusion.

    mariush nailed a lot of the same points I would have nailed. Older equipment sucks. Outsourcing PCB-A sucks. QC needs to be an entire process. From solder quality to temperature control to board inspection.

    That's really why we see a lot of hit and miss with products. We give a PSU a good score because it's a good design and performs well and the review sample received by the reviewer happened to not die. But it only takes one bad day at the factory, or one board to slip through one step of quality control and you can start seeing double digit failures on a PSU that scored a 10 for "mythic performance".
    Last edited by Jon Gerow; 10-01-2017 at 01:03 PM.

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    Quote Originally Posted by mariush View Post
    (for example using two different solders the same day, when they refill the solder "bath" with different solder)
    Not sure how/when this would ever occur. The same machine needs to have the same solder added to it throughout the day, but eventually it has to be completely emptied and refilled because, as I said, contamination and oxidation is to the point where adding more solder isn't going to help.

    The truly shitty factory would just keep reusing the solder until it gets to the point where components are no longer getting soldered to the PCB! But if the factory is that bad, I can also see them turning up the temperature to compensate until the shift is over, or whatever order they're working on is fulfilled and they can then change out the solder.

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    Here's a cool video of a guy recovering usable solder from dross. Looks like a fun job, doesn't it (no.. no it doesn't).

    https://www.youtube.com/watch?v=SxFghbXiJlI

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    Wow, lots of information! You especially mariush.

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