is solder paste a better option?

Discussion in 'General Electronics Chat' started by chimera, Jun 30, 2011.

  1. chimera

    Thread Starter Member

    Oct 21, 2010
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    Hello. So over a few week i learned the amazing tool that is Eagle. Its got a learning curve but well worth it. I went first for through hole but because I dont own a drill press, i went for the smd layout

    I also bought a nice soldering station--it has an temp/speed adjusted soldering pencil and air soldering. Now ive been doing a lot of research on how to solder smt and most of the stuff just boils down to a few things:

    a fine soldering tip, a fine rosin core solder wire, plenty of no-clean flux, fine tweezers, magnification, tinning the copper pads before soldering/laying the compenent and finally, some practise.

    But i want to be able to use the soldering air gun attached to my new soldering station--it requires me to purchase solder paste.

    I researched on solder paste and it seems to be a little complicated--storage, shipping, usage and all that kind of information. So my question is:

    IS SOLDERING PASTE WORTH THE TROUBLE? and HOW DO I CHOOSE WHICH ONE TO BUY(they are pretty expensive). and lastly, HOW SHOULD I DETERMINE THE COMBO OF SPEED AND TEMPERATURE FOR MY AIR SOLDRING NOZZLE. (i dont want to blow or burn the heck out of the components/pcb). Please do give input. it'll def. help out a fellow engineer.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Yes paste is far preferable to solid for hot air.

    I use something like this which isn't so expensive and lasts about a year even if you don't refrigerate it.

    I haven't adjusted my machine off the original 300 degree C setting came with.

    You blow hot air on the parts (leads & board) till the solder melts, then you stop blowing on it. It's really that simple.
     
  3. chimera

    Thread Starter Member

    Oct 21, 2010
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    firstly thanks for the reply. Secondly, i shouldnt worry about burning the pc board or the components off of it?

    Ive seen a lot of vidoes on paste soldering with hot air but they all seem to be an overkill (personally). How do i determine what speed, nozzle and temp I need to work with? or is experimentation and deduction? Can you please mention the setting that you have been using?
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Temp is 300°C, and I run the air as high as I can without blowing the parts off the board, which is actually very easy to do with 0402 resistor or cap chips, or even a SOT-23. Occasionally I'll hold them down with tweezers but it is better to let them settle themselves as the solder surface tension will center parts better then your hand can. A light tap on the board will shuffle the parts dead on.

    The only defect I have noticed is solder not flowing. No burned boards, no bad parts. If something doesn't work just hit it with some more air till the solder flows.

    I agree, the videos I've seen seem to be recorded by people who don't actually DO solder and have a lot of abstract worries.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    PackratKing likes this.
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Good video, I like that tip as it holds the solder!

    Notice the parts he drag solders are already soldered in place at the corners, which is why he doesn't just drag them off with the tip.

    For very small leads with really tight spacing like those QFN's he did I will carefully do 2 end pins opposite corners to fix it in place, then have at the individual pins. You can either do "flood and wick" where you dump a ton of solder on then wick the excess off, or just hit each pin with a very fine tip and a strand of solder.

    I've had little success using paste on tight QFNs as the spacing is just too tight to control the paste and I wind up doing a modified flood & wick anyway, and going back with an iron to catch the pins that didn't connect.
     
  7. chimera

    Thread Starter Member

    Oct 21, 2010
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    great replies guys. But like i mentioned, the videos arent very helpful for the beginners. So basically put the solder paste to the pads, place the componenet on to the pads(with paste on) and then at 300C, blow air onto the components one by one, till the parts solder? Seems straight forward. What about QFN packages? Or maybe i should wait till i get the air soldering down, caz afterall, this is my first attempt at SMD layouts :)
     
  8. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Three Hundred CENTIGRADE :eek: ??? Components, PCB and all, until the solder melts ?? --- you are kidding............aren't you ??

    tsk ! [ sound of receeding foosteps and soft muttering...............]
     
    Last edited: Jul 2, 2011
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Nope, I am not kidding. Have you actually done this or are you answering from your armchair?

    What the "300" really means I do not know. I have never measured the temperature of this airflow. Yep, seems high to me too.

    But it works. Boards do not burn. Parts do not fry.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    For big QFNs with tight lead spacings I haven't had much success with hot air and actually hand solder two opposite pins by hand (to fix it in position) then solder each lead by itself, using the finest tip I have.
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Some people use the solder paste and an electric skillet/frying pan. Others use the paste and a household/kitchen toaster oven. Another trick is to use a 'dot' of super glue on the under side of the SMT component to hold it in place before and while soldering.

    Never done SMT myself just hints picked up from other forums.

    @ Chimera - Boy your a real gluten for punishment, Eagle and SMT on one project :)
     
  12. PackratKing

    Well-Known Member

    Jul 13, 2008
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    >> I do not do the volume of soldering on PCB's or anything for that matter, that would require such a technique -- smart <snip> :D

    >> 300 ° C is pretty close to 570 ° F. How long does one have to dwell on that heat level to complete the task ???

    Since heat is the prime enemy of solid-state electronics, I prefer to have an iron hot enough to do each connect in less than 1 second, and not have to worry about heat issues degrading the project at hand.
     
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