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flux / soldering paste..

Discussion in 'General Electronics Discussion' started by Giorgos, Apr 6, 2015.

  1. Giorgos

    Giorgos

    28
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    Apr 6, 2015
    Dear friends, i have a simple question on soldering..
    I am new on soldering and i do not know what is going on with soldering pastes. Are there different kinds of it?
    When I watched this video i saw is that only the paste is needed for the soldering.
    BUT when i watched this i saw that the flux is not enough to do the soldering.
    Some other, told me that soldering paste is only to clean the top of the soldering iron...

    Please tell me what is going on, give me some advises.

    Thank you in advance!
    :cool:
     
  2. BobK

    BobK

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    Well, those are two very different soldering tasks. Paste is normally used for soldering SMT components with a reflow oven, though it can be used with a soldering iron as well. Most other soldering in electronics can be done using rosin core solder, which has the flux inside.

    Bob
     
  3. Giorgos

    Giorgos

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    1
    Apr 6, 2015
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Solder normally has flux inside. It is used to clean the part being soldered and to prevent oxides forming. It will not join the two parts together. You need solder for this, flux alone is not a solder. Flux is very good at making solder joints or for tinning wires. I often dip my bare wires into the flux then apply some solder. But normally a decent solder will have flux inside so you dont have to worry about it.
    Adam
     
  5. Giorgos

    Giorgos

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    1
    Apr 6, 2015
    That was really helpful.
    So, in case of SMD we are not talking just for flux, right?
    What is the liquid that we use to solder the processors and stuff on PCB (like the first video that i have in the first post)?
    Please give me a link to order the item, because i want to try this kind of soldering.

    Thank you for the answers :D
     
  6. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Solder paste is what is being used in the first video. You will need to Google this yourself. There are lots of different types out there. I am not going to link to one for you sorry.

    Adam
     
  7. Giorgos

    Giorgos

    28
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    Apr 6, 2015
    It is not a "googling" issue, but thank you for your time!

    As you can see, me question above is "What is the liquid that we use to solder the processors and stuff on PCB (like the first video that i have in the first post)?"

    I was asking if you could give me a name of this type of soldering paste.

    Thank you
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It's solder paste.

    It is a mix of flux and very small balls of solder.

    However, flux is sometimes (and especially on Chinese sites) called "soldering paste".
     
    Arouse1973 and BobK like this.
  9. Giorgos

    Giorgos

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    Apr 6, 2015
    That's why i was so confused..

    Thank you guys you really helped me!

    :D
     
  10. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    As @(*steve*) noted, not everything labeled as "solder paste" (especially if it originates in China) actually has solder particles in it. And those that do contain solder particles vary widely in composition. In your first video, an excellent presentation of SMT re-work using a sub-heater under the PCB to heat-condition multi-layers, and a hot-air pencil to actually melt and re-flow the solder paste, there is no mention of the paste composition. Most SMT components are originally soldered using lead-free solder to comply with Euro RoHS standards. You can re-solder with a eutectic 63% Sn-37% Pb alloy or a 60% Sn-40% Pb (nearly eutectic) alloy that melts at a lower temperature and produces IMO a better joint. The problem is finding real solder paste with the desired composition. Here is a website to get you started with a lead-free solder alloy paste you can apply from a syringe.

    Beware of the Chinese solder flux shown in your second video. Who knows what its composition is? It could be highly active but leave a corrosive deposit. Some of this stuff was made for tin-smith soldering and has been re-packaged as "electronic solder flux". Unless you can verify that it contains pure rosin flux, it is best to avoid this stuff.

    Not everything "made in China" is bad. Amtech is a multi-national firm that makes both flux and solder paste, leaded and lead-free, at factories in Asia and Europe. Here is a link to their product line. Problem is, their target customers are large PCB fabricators who use the flux and solder paste in huge quantities. It can be difficult finding an authorized distributor who will stock and sell in small quantities syringes of the Amtech product (if that is what you want) and guarantee it isn't an Asian counterfeit.

    I really envy you if you can afford to purchase the hot-air SMT re-work system shown in the first video. That's the cat's meow for SMT work! Most of us here use a pencil iron, tweezers, and a magnifying headset to solder a few pins at a time.
     
    Last edited: Apr 7, 2015
  11. Giorgos

    Giorgos

    28
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    Apr 6, 2015
    @hevans1944 thank you for those many details. You helped me to spote the difference between flux and solder paste finally. I ordered the paste that you suggested. The only thing left is to try it by myself..!

    I order most of my stuff from ebay and from chinese producers but i'm going to be more careful now..! I ordered in the past this
    http://www.ebay.com/itm/10g-New-Useful-Soldering-Solder-Paste-Flux-Cream-Welding-Paste-/231265899812?pt=LH_DefaultDomain_2&hash=item35d8859524
    item
    which is labeled as "solder paste" but as i said in the previous post, it doesn't seem to work..! So i 'll give a try with the paste that you suggest me.

    Of Course i cannot afford the cost of hot-air SMT re-work system shown in the first video!! I'm usually soldering with my low-cost soldering iron..!

    Thank you for your time! :D
     
  12. BobK

    BobK

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    Jan 5, 2010
  13. davenn

    davenn Moderator

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    Sep 5, 2009
    Presumably that's what is listed as the IC extractor in the BOM list ?
    how it's used is anyone's guess LOL
     
  14. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Maybe you loosen the screw and adjust the spacing of the prongs to be slightly less than the length of the part you are trying to remove. Tighten the screw and place the prongs on the device, allowing them to spread slightly so as to provide a "spring" grip. Now heat the part with the hot-air gun and (hopefully) lift it from the PCB when the solder melts. Or throw it away and get a vacuum pick.
     
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