SMD & reflow rework flux recommendations

Hi Ron @zander,

  I am not aware of any distinction for flux between reflow and rework.

  Others may have more experience, but I use 3 different styles in total, covering both 'traditional iron' and hot air methods.

A 'shallow tub' of the resin based 'grease-like' ... for soldering iron stuff, especially for wires to connectors, etc... you probably already have that.

A liquid in a 'pen' .. pressing the fibre nib of the 'pen' releases a little of the liquid, which is almost certainly rosin dissolved in IPA. This is good for jobs like reflowing the solder on a many pin or ball that has a fractured solder joint, where it is necessary to get flux under the chip, etc. without removing it. You might never do this, so might decide to ignore it.

A syringe of usually white-ish flux .. mainly used for hot air surface mount, but a small blob is also handy for soldering with an iron, to supplement the flux in the solder.

Something like:

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Note for each of the solder and flux syringes, I bought a 'squeezer' which provides a lever alongside the syringe, which makes it easier to control the amount being squeezed out.

Something like:

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Hope this helps  you to choose what you want.

Best wishes, Dave

@davee I use this stuff its really good I use it for all the SMD stuff I do on the layout.

Cheers Phil

@davee I see the word reflow in some listings, and rework in others. There is a lot of codes and buzz words associated with these products. It is very confusing.

Do you have any more information on your squeezer addon, that looks quite useful.

@thephilnewman Do you use it for reflow or rework? What other products have you used and compared?

@zander reflow and rework is when replacing components on boards I believe, and I have not done any of that but I do use a few SMD components such as resistors and LEDS and also when installing decoders into any locomotives that I am converting. A small amount of that flux and the solder flows extremely well.

Cheers Phil

@zander this shows the stuff and a few other brands as well.

Cheers Phil

@thephilnewman Thanks, I will check the video.

Hi Ron @zander,

   Reflow usually refers to the 'industrial' board soldering process, where the components are tacked onto the board using solder paste, and then the whole board is heated. Solder paste is essentially flux and small balls of solder. Wikipedia gives a lot more detail if you want a background read, but maybe not much practical use for you (or me).

https://en.wikipedia.org/wiki/Reflow_soldering

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Rework generally suggests a repair, like replacing a chip or a connector on a mobile phone, but in practice, if you are assembling a board for the first time, probably one or two components at a time, then this is essentially the same process.

If you glance at the reflow process, you will see it involves careful temperature control, etc., whilst processing by hand is rather more empirical. If I buy an commercial product, then obviously I would expect care to be taken in its manufacture, but for hobby usage, most devices seem to survive much less careful handling.

I suspect you will see buzz words like reflow and rework used rather generally in the adverts to catch your eye  and Google's search engine .. I would beware of over-interpreting their usage.

If you haven't done much 'hot air wand' style of soldering, when you feel like 'relaxing',  have a look at a few YouTube videos on the subject .. some are rubbish of course, but most offer useful tips.

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As for the tool, I bought from AliExpress ... tracking back to the order, now shows this page, which might be slighty different, but essentially the same device

https://www.aliexpress.com/item/1005004458287347.html

Note, there are many rather similar devices on the market ... I make no claims as to whether this is the best value, etc.,  ... just that the two I have, actually work.

Note 1: With AliExpress, if the default postage will take a long time .. click on the "Shipping" word ... quite often they offer alternatives, such as AliExpress Standard Shipping for a small increase, with arrival in 2-3 weeks in UK.  Of course, you might find similar things on Amazon for 24 hour delivery ... I haven't looked.

Note 2: the long bolt for the plunger needs to be turned quite a number of turns to move it from one syringe to another. If like me, you have two (or more) syringes in use at the same time (I use 1 for solder and one for flux), then I recommend you get one for each, as it would get very tedious swapping back and forth every two minutes.

Good luck with your soldering adventures! Best wishes and take care, Dave

Hi @thephilnewman,

  Thanks for the note above about the flux and also the video just below.

  Personally, I am using the maybe fake 'Amtech' in the syringe, which seems to give a reasonable result and was fairly cheap.

For some jobs, I certainly like a syringe to be able to put just a tiny blob in the right place, rather than dollops from a tin, but then I have nevered soldered ICs the way that is shown in the video.

I might look into the tin you suggest for when the wires and joints are larger.

Best wishes, Dave

@davee I think that the terms reflow and rework are marketing terms and mean nothing. The video that @thephilnewman provided was very helpful. Unfortunatly the best one is not available in Canada so I will go with the Amtech NC-559-V2-TF for now but it is super expensive at $9.99 + $13.59 delivery for 5gm. My understanding is this stuff needs to be kept refrigerated and has a short shelf life so larger sizes are a problem.

@davee I think you are talking about something entirely different if you are placing tiny blobs of flux. For SMD soldering a paste is squeezed out over all the pins then a hot air gun does it's magic. That is solder paste which is a mix of flux plus small solder balls. The flux magic is that the solder is just attracted to the metal parts.

Hi Ron @zander,

 The term 'reflow' has a definite meaning .. but I agree, in the adverts it is being misused as marketing term. Rework has also been in use for a long time .. but only means fixing something has failed in manufacture or subsequent usage. Neither are specifically about a type of flux.

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 It depends on what I am soldering ... of course solder paste balls agregate and the surface tension forces can enable it to flow into the right places .. but it can also make a mess if there is too much, with shorts, etc. as well as the components tending to float away or tombstone.

The 'proper' way is to use a stencil that just puts paste onto the pads, and the thickness of the stencil ensures the paste is the right thickness.  In the absence of a stencil, it seems a good idea to me to try to apply it rather carefully.

I tend to use the syringe based flux, either to remelt the existing solder and in conjunction with a conventional iron and 'wire' solder, when the flux in the wire solder is not quite enough. Whilst an excess of flux isn't a major problem, it can be messy.

By the way, I have also seen the refrigeration advice, but prefer to keep my food well away from solder and flux, and I am not getting and running a 'solder' fridge for a couple of tubes of stuff ..  I have been using the same stuff for 6 months plus .. I guess it will expire some day, in which I'll get some more.

But we all have our own tricks .. so do whatever works for you.

Best wishes, Dave

@davee @thephilnewman Thanks for your input, here is what I have decided.

I can't see going to the expense of a stencil to make neater soldering jobs. A little mess is easily cleaned up with 'cleaner' and water if water-soluble materials are used. 

I used to watch this guy in NYC who did 'impossible' Apple repairs. He flooded a large part of the motherboard with a clear gel-like flux, and it all seemed to work. He is the fellow who is/was leading the charge for the 'right to repair'. 

As you say, different techniques and materials for different situations and people. As long as we make the needed electrical connections, then it's all good.

I used Dave's link and ordered a few of the 'squeezy' things in case I need one.

NOTE: I have used liquid flux for a while now. It is a plastic bottle with a small bore needle on the end. When doing headers or other large soldering jobs, it speeds up the process considerably but it is hard to control the amount of liquid so I can see the allure of the paste.

I have ordered the NC-559-V2-TF Clean-Free Tacky Flux - 5g Syringe kit and the Wonderway Sn63/Pb37 Tin Lead Solder Paste 183℃ Melting Point No-Clean Welding Soldering Tin for Electronics PCB IC Cellphone CPU LED BGA Repairing (30g)

Some top-rated products are either not available here in Canada through 'normal' channels, or if they are, the shipping costs are more than the product cost.

Hopefully, the rest of my parts will arrive soon, and I can begin experimenting again.

Thanks again.

@zander   Here are some things I do that might help you.

I've never bought a lever device for operating a syringe but I agree it is damn hard to dispense accurately.  It is because the syringe is too full.  When I get a new syringe of flux I squeeze 3/4 of it into a storage bottle.  At 1/4 full or less the syringe is easy to control with the original plunger.  Also, sometimes the flux is a little too viscous for the tip size so I bought a bag of assorted syringe tips for $2.

For another $2 you can buy a few two ounce squeeze bottles that also take syringe tips.  They are perfect for applying one drop of liquid flux exactly where it is needed.  I use liquid flux the most because it is so much faster to apply.

Liquid flux is cheap by the gallon but otherwise seems high priced.  I mix my own.  Less than $2 will buy a tin or pasteboard box of pure pine rosin, basically hardened pine sap.  I separate a chunk with a chisel and drop it into a bottle with a little 90% or better IPA.  It will completely dissolve within a day.  How much?  It doesn't matter very much.  If the rosin concentration is too high it will smoke more and leave more staining on your board, so just add an extra teaspoon of IPA.