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I figured out I'm in need of taking flux seriously;Yes, indeed, flux is essential for soldering, but good solder has the flux already included. Lots of SMT soldering techniques do require adding extra flux though. Solder wick also contains (powdered) flux, but adding more flux often helps there too. There are lots of good (and also bad and ugly) video's on youtube about the use of (extra) flux during soldering. Go watch them to see what a good soldering process looks like. (Hint: "GreatScott" is terrible at soldering. Avoid him at all costs when it's the soldering you are interested in.)
I even have literal rosin but it doesn't seem great if I just ground it and mix it with alcohol; I have another "soldering grease" flux which appears to work (to achieve wetting) but I fear it might be unhealthy with its fumes and it might not be the best possibleRosin isn't healthy either. The only solution I know is to use filtering and/or ventilation.
so I wonder if you have suggestions on what to buy from ali (or elsewhere) that has the highest quality possible for the purpose.Quality from Ali? I wish yo lots of luck.
I figured out I'm in need of taking flux seriously; I even have literal rosin but it doesn't seem great if I just ground it and mix it with alcohol; I have another "soldering grease" flux which appears to work (to achieve wetting) but I fear it might be unhealthy with its fumes and it might not be the best possible so I wonder if you have suggestions on what to buy from ali (or elsewhere) that has the highest quality possible for the purpose.If you want to take flux seriously (which I recommend), then don't bother with Aliexpress, etc. Even if you get a good product now, you have no idea whether the next batch will be the same.
And how exactly does wetting work I wonder; I know it seems to split the solder when there is the plastic of the PCB between the different metal contacts; but why does the solder not just keep connecting to itself between those metal contacts since it has already connected to itself before flux and it seems to separate instead into different parts between the PCB contacts after adding flux?Wetting is name for the solvent action of molten solder on the metal of the components/boards. The surface tension of solder is very high, so it wants to pull back. Solder mask (the colored lacquer on PCBs) is specifically designed to make it hard for solder to bridge across it.
In general, you do not need additional flux, use cored solder which contains flux.I don't think that's the best advice, since especially with SMD work, there are situations where external flux is essential. (Even when THT was king, there were still situations where external flux was useful.)
In close to 40 years in the service industry working for a multinational manufacturer on their products, mostly through hole boards (SMD was a board swap), we never used additional flux.In general, you do not need additional flux, use cored solder which contains flux.I don't think that's the best advice, since especially with SMD work, there are situations where external flux is essential. (Even when THT was king, there were still situations where external flux was useful.)
No. The quality of the solder has nothing to do with whether it has a flux core or not. There is terrible quality flux-core solder, and there's top-quality solder with no flux core.I figured out I'm in need of taking flux seriously;Yes, indeed, flux is essential for soldering, but good solder has the flux already included.
Lots of SMT soldering techniques do require adding extra flux though.Indeed. It's essential to certain techniques. (Heck, that's even true in THT soldering, for example in mass production. It also helps in manual THT work if your components are a bit more tarnished.)
Solder wick also contains (powdered) flux, but adding more flux often helps there too.I thought it was made by coating it in liquid flux and drying it. I always assumed the powdery appearance was because of the wick getting flexed after the flux was dry, causing it to fracture.
There are lots of good (and also bad and ugly) video's on youtube about the use of (extra) flux during soldering. Go watch them to see what a good soldering process looks like. (Hint: "GreatScott" is terrible at soldering. Avoid him at all costs when it's the soldering you are interested in.)Absolutely! I love GreatScott's projects and explanations, but his soldering is awful!
Wetability is the same principle as with water.It's actually not like that at all!
If you pour a glass of water over a T-shirt it gets wet (and sometimes other nice side effects).
If you pour a glass of water over a raincoat it rolls of.
With soldering, there is always a bit of dirt and oxidized stuff on everything you want to solder.Which is why it's always a good idea to clean your boards (and to the extent possible, components) with solvent (like alcohol) to remove contaminants. Then the flux can take care of oxidation.
In practice, the solder sticks to the clean other metals, but not to the dirt and rust, and a part of the job of the flux is to remove the dirt.Solder doesn't "stick" like glue. It dissolves the substrate, creating an intermetallic layer between the substrate and the solder itself.
I think the flux also lowers the surface tension of the solder (but I'm not entirely sure). But if it does, it is (a bit) comparable to mixing in a bit of soap with the water before you pour it over the T-shirt. (Although the flux does not dissolve into the solder, so it's a mediocre analogy).I think it lowers the surface tension, but I think more in the sense that oxides (which form on the solder itself, too) have extremely high surface tension, and by eliminating the oxides, the flux allows the solder itself to contact the joint. The following users thanked this post: helius
And? Just because you never used it doesn't mean it might not have made some things easier. (It is possible to do something the wrong way for decades, after all! )In close to 40 years in the service industry working for a multinational manufacturer on their products, mostly through hole boards (SMD was a board swap), we never used additional flux.In general, you do not need additional flux, use cored solder which contains flux.I don't think that's the best advice, since especially with SMD work, there are situations where external flux is essential. (Even when THT was king, there were still situations where external flux was useful.)
Don’t forget the more flux you add, the more you end up having to clean off afterwards.Very true.
Adding flux is easy and it does no harm, it’s not easy to clean off.Depends on the flux (e.g. no-clean fluxes tend to be much harder to remove than "traditional" rosin fluxes), and how the flux was handled after application (e.g. overcooked flux is far harder to remove than flux heated briefly).
Those who say there is no need to clean flux off should look at commercial boards in new equipment, they are spotlessly clean.I don't think you can make that claim, as a blanket statement. Many boards are cleaned, and many are not. Some use carefully controlled reflow soldering processes using no-clean flux, such that the amount of flux residues is so small you don't notice with the naked eye. Some use water-soluble fluxes that are then removed in hot water. And, frankly, it's not uncommon to see boards that have been cleaned, but not spotlessly.
Indeed, despite some people's claims that rosin in alcohol makes a "great" flux, rosin without added activators is a very mild flux that is good only for parts/boards that are very clean already. It can't cut through serious oxides the way activated fluxes can.
"Soldering grease" is plumbing flux. Do not use it on electronics, as it will cause corrosion.
In metallurgy there are two states for metal surfaces: active and passive. An active surface has metal bonds exposed that can react with other substances. A passive surface has its metal bonds protected by a thin layer of non-metallic material, and will not react.Yeah pure rosin does not live to its reputation at all: I had to replace the surface-connected oled screen of a ts100 soldering iron and pure rosin-alcohol made a mess; a cheap 'soldering grease' felt almost perfect compared to it; but it triggered me to make this thread because obviously it wasn't the best material for the purpose.
The solvent action of solder is to react with an underlying metal and form bonds to it, as tooki said. This is analogous to the solvency of something like water, which surrounds and bonds to a solute like table salt to form a clear and homogeneous mixture called a solution. Solder surrounds and bonds to metals such as copper and tin to form a tightly adhering, strong joint after the solder cools. The heart of the joint is a solid solution of metal atoms from both the copper and solder mixed homogeneously, around a micron thick. This is called "wetting". If the solder doesn't form this solid solution layer, the joint is a defective "dry joint".
For the solder to react with the metal and bond to it in this way, the surface of the metal must be active. If the metal is passivated with oxides etc, the solder cannot get "close enough" to form metallic bonds. So the reason flux is used is to activate the metal surface: to dissolve and remove the oxides that form the passivating layer on the metal. The activity of flux is a measure of how strong its ability to dissolve oxides is. Pure rosin has some activity but is relatively weak. Most electronic flux has activators added in a few tenths of a percent that increase the flux's activity. The chemical properties of the activators are what determine the suitability of the flux to the application.
There is also a very important aspect which is the disposition of the activators after soldering is complete. If the activators remain in the dried flux and don't continue their chemical reaction, post-process cleaning is not necessary. If the activators continue to react, the flux must be cleaned off or corrosion will occur. Zinc chloride is an example of an activator that continues to react and so it must be cleaned off. In fact it is corrosive at such trace amounts that it should never really be used on electronics at all. Zinc chloride is the activator in plumber's flux. Other activators include halides: organic salts of fluorine, chlorine, or bromine; phosphates; citrates; imides, etc. The J-STD-004 category reveals details about what activators are present. Usually you want a ROL0 type flux if the board won't be cleaned. That means ROsin base, Low activity, less than 0.5% halides.
Some metal surfaces are very strongly protected by passive layers, such as aluminum or stainless steel. In order to solder to these metals very strong specialized activators are needed, such as orthophosphoric acid. Obviously cleaning must be meticulous after they are used.
Once you understand the purpose of flux, you also will see how it should be used: applied thinly to the component leads and the pads of the board. Never apply flux to the soldering iron!
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Choosing the best solder for your electronics project can be a bit daunting for many beginners and rather confusing even for seasoned veterans. My goal with this page is to provide some clarity for you, the hobbyist, so you can make an informed choice.
To start at the beginning: You want to use solder intended for use in electronics – not plumbing solder. In plumbing you apply the flux with a brush and the solder itself has no flux in it. This is not useful for electronics. Plumbing flux is way too acidic for electronics use and is also incredibly messy.
The purpose of flux is to clean the solder joint as the solder is applied, thereby allowing the solder to flow, resulting in a good and void-free solder joint. The flux also changes the surface tension, which increases the solder's adhesion the metal in the solder joint. The solder used for electronics has the flux embedded in it and the wisp of smoke that is emitted during the soldering process is caused by the flux boiling off. Prolonged exposure to flux fumes is a health hazard. The health risk is likely smaller for the hobbyist performing soldering on occasion. Still it is good practice to set up a small fan to blow the flux fumes away from the work area while soldering.
There are three different kinds of flux available for electronics soldering. The main difference is the difficulty involved with removing the flux.
If you would like to minimize the solder inventory in your toolbox, your best option is solder with RMA flux. Alternatively, I recommend using water-soluble flux for circuits that can be easily cleaned and no-clean flux in situations where cleaning is difficult or impossible.
Note that many PCB rework materials, such as de-soldering braid (Solder-Wick, for example) contain flux. Ensure that your various sources of flux are compatible, i.e. if you are soldering with RMA flux, make sure to use Solder-Wick with RMA flux for solder removal.
Solder wire for electronics already has flux embedded in it so it is very rare that I use any additional flux. That said, a little additional flux can be helpful for rework and manual assembly of components with a fine pin pitch such as ICs in BGA, QFN, and TQFP packages.
Flux is available in liquid and gel form but these forms tend to be pretty messy to work with. A flux pen is a better alternative as it allows dispensing of a thin film of flux where you need it: on the component and on the PCB pads. Flux pens contain liquid flux and have a fibreglass tip for dispensing it. They are very similar to paint pens – push the tip until the flux saturates the tip then 'paint' the flux where you want it.
I use a Kester #186 flux pen with RMA flux. As with the de-soldering braid, choose a flux pen with a flux that is compatible with the flux in the solder you use.
The trouble with flux residue is that it's hydrophilic, i.e. attracts water. This means any flux residue on the PCB will cause significant leakage currents on a wet day. You may have a circuit that works well in a dry climate but fails in a coastal climate. The combination of water and flux residue is also corrosive and can cause your circuits to fail over time. As noted above, the exceptions are the residues left behind by no-clean flux, which are not corrosive, and those from RMA flux which are only very mildly corrosive, thereby allowing the cleaning step to be omitted.
Flux removers come in varying degrees of aggressiveness ranging from light duty to heavy duty. The light duty flux removers tend to mostly be isopropyl or isopropanol based, whereas the heavy duty flux removers include acetone, hexane, and other rather nasty solvents. These cleaners are extremely flammable and should only be used in well-ventilated areas. I strongly advise that you read the Material Safety Data Sheet (MSDS) before using any of these flux removers. In addition to the personal safety, note that some of the flux removers dissolve plastics, so be careful.
Personally, I like Chemtronics Flux-Off No Clean Plus, which you can get from Mouser in the US. It does not ship via airmail due to flammability. It's a relatively aggressive flux remover and does tend to leave a dull residue on the PCB. This residue can be removed with a water rinse. MG Chemicals (and many others) make flux removers as well.
Any assembled board I send out to a customer will have the flux removed.
Contact us to discuss your requirements of Flux Drying Machine. Our experienced sales team can help you identify the options that best suit your needs.
There are two overarching groups of solder used in electronics: Lead-based and lead-free, the latter being dominant in electronics production today due to the environmental concerns with the disposal of electronic products.
Lead-free solder does not have the best reputation, in part due to technical issues with the soldering process. Most lead free solder alloys melt at a higher temperature (about 220-250 ºC) than tin/lead solder (about 180-190 ºC). Thus, changing from leaded to lead-free solder will require a change in soldering iron tip temperature. The typical tip temperature for leaded soldering is 320-370 ºC (600-700 ºF). For lead-free the temperature needs to be increased to 370-425 ºC (700-800 ºF). In addition to the higher tip temperature, the dwell time needs to be increased. A solder joint can be completed with lead-based solder in less than a second. Using lead-free solder, this time needs to be extended to avoid cold solder joints.
Health hazard: Leaded solder contains lead (DUH!). If ingested, lead accumulates in the fatty tissues in the body, including the myelin sheath surrounding the nerve fibres in the brain. This can lead to brain damage, in particular in infants and small children. This is mostly an issue with lead casting where the lead is heated to near its boiling point. The temperatures used in soldering are much lower. The main risk of lead exposure is from the lead that rubs off from the solder onto your fingers. Please make sure that you do not eat or drink while soldering. Wash your hands thoroughly when you are done soldering.
There are three commonly used lead-based alloys for electronic soldering:
In terms of conductivity, the three types are within a few percent of each other. The tensile strength of 62/36/2 solder is about twice that of 60/40, but whether that actually translates into mechanically stronger solder joints depends on the joint geometry.
The development of a good lead-free solder alloy has been a challenge, and some of the better alloys are only available in the form of solder paste. The first lead-free alloy introduced was the SAC305 (96.5/3/0.5 - Sn/Ag/Cu). Joints made with this alloy are dull and grainy in appearance, thus, indistinguishable from cold (failed) solder joints made with 60/40 solder. I suggest shying away from this alloy.
Some of the more user-friendly alloys of lead-free solder are:
It is not recommended to mix leaded and lead-free solder. Thus, ensure that soldering tips are used only for either leaded or lead-free solder. A tip tinned with leaded solder can be used for lead-free soldering after 4-5 thorough clean/re-tin cycles, though, it is strongly recommended that you pick one solder type for the tip and stick with it. Some R&D labs have a separate soldering bench set up for lead-free solder to avoid cross contamination.
In general, solder alloys should not be mixed. Keeping the solder chemistry clean ensures that only the alloys the solder manufacturer intended to form actually do form when the solder cools.
Choosing a diameter of solder wire that is appropriate for the task at hand can be a considerable help in the soldering work. Small diameter solder makes applying a small amount of solder much easier. This is very handy for soldering surface mounted components. For larger components, such as leaded components or connectors, using small diameter solder requires a significant length of solder to be fed to the joint, which extends soldering time and risk of overheating the components.
For work that involves surface mounted devices, I prefer 0.5 mm diameter solder. For leaded parts and connectors, I use 0.7 mm diameter solder. For most electronics work, solder in the range of 0.4 - 1.0 mm in diameter will work well. If you perform a lot of work on surface mounted devices, aim for the lower end of this range.
Yes. Really! Solder has an expiration date. For the alloys mentioned above, it is recommended that solder wire is used within three years of manufacturing. That said, I am just now finishing the roll of 0.7 mm 60/40 RMA flux core solder I started in the late ies and the solder joints I am making today perform as well as ever.
Do observe the shelf life on solder paste, however. Solder paste consists of small beads of solder suspended in flux paste. Over time, the flux will oxidize rendering it ineffective. The result is that the solder won't flow correctly and it becomes very difficult to get a good solder joint. The shelf life of solder paste is about six months. By refrigerating the solder paste, the shelf life can be extended to about a year. It should go without saying, but please don't store the solder in the fridge you use for food!
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