Soldering advise

Discussion in 'General Electronics Chat' started by Man_in_UK, Mar 4, 2010.

  1. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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    I am not new to soldering QFP's but I have a job coming up that does not look pleasant.

    My normal style of iron work involves using lots of solder, plenty of flux, some braid to remove the excess and a hot air pencil to finish off.

    I now have to face a HTQFP-64 and it don't look good.

    Any advise will be welcome, please.
     
  2. BMorse

    Senior Member

    Sep 26, 2009
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  3. Tobias

    Active Member

    May 19, 2008
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    Buy a hot air rework station. You will thank yourself daily. It makes soldering on parts and desoldering a piece of cake. The skillet deal is nice but slower It heats up the entire board so you have a wait time of heating up the skillet and letting the board cool down to work on it.
     
  4. BMorse

    Senior Member

    Sep 26, 2009
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    But it sure beats spending hundreds of dollars on a hot air rework station!!:D
     
  5. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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    The method of removing bridges in that guide is exactly the same way I do it now, darn.

    I had my fingers crossed that there might be a better method. The legs on the HTQFP looks so close together, not sure if will even be able to spot a bridge.
     
  6. BMorse

    Senior Member

    Sep 26, 2009
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    Yeah same way I do it also... but I managed to use the solder wick to properly solder a Pic32MX uc which is in a 100 Pin TQFP, not easy but can be done..... magnifying glass or eyeloops might also help in spotting bridges.... another method I use is pre-tin all leads on the ic and then use the hotplate technique to reflow the solder onto the pads on the PCB.

    B. Morse
     
  7. Tobias

    Active Member

    May 19, 2008
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    I guess it boils down to how much you value your time. Here is a link for one on EBAY with a buy it now price of $100. An electric skillet..say $20. So $80 difference. Each time you use the skillet its a 20 minute process..guessing. To remove or place a component with a rework is at most a minute. If you think you are worth even $20 bucks an hour, its going to pay for itself pretty quickly.

    http://cgi.ebay.com/SMD-Rework-Sold...emQQptZLH_DefaultDomain_0?hash=item3caac7558f

     
  8. BMorse

    Senior Member

    Sep 26, 2009
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    If you really want to argue about which way is better, read what the people at sparkfun have to say about hot air reflow versus hot plate reflow...

    http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=59

    quote right from them:
    and they actually used a similar device that you posted above for the testing!!:rolleyes:
    [​IMG]
    imagine that!
    B. Morse
     
  9. BMorse

    Senior Member

    Sep 26, 2009
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    but either way, whichever method is used, there is no guarantee that there would not be any solder bridges between the pins of the IC..... so the main question the op is after is still not answered, since he is looking for a better way to avoid solder bridges when working with the type of footprint he has (TQFP 64)....

    B. Morse
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    The best way I have used for solder bridge-less TQFP is the aluminum foil / plastic as as stencil and solder paste with a 30w regular iron.

    Press the chip onto a piece of aluminum foil, leads down. That will leave an imprint of the 64 pins. On a hardback book, place the foil on top. Use a sewing needle to poke holes in the foil or plastic. The plastic I use is a cover from "book report" folder. You can use it over and over.

    Once you have the stencil, place it over the pcb holes one the pads. Squirt a little solder paste on the holes and squeegee with a credit card. Peel the plastic back, place the chip. I use a pencil with eraser to hold the chip in place, slide the iron slowly across the tops of the pins. (Speed will come with experience) You will see the paste suck up to the leads. Its almost perfect every time. Once you get a good stencil, you will use almost no paste and almost no braid. If you use very little paste, there will be no bridging. It works very well. Make a stencil for each type of surface mount chip, and you will be good to go. Clear plastic for easy lining up and solder paste syringe for easy dispensing. No special hardware involved.

    I have a +90% no bridge rate with this method. When I do, it is usually from not cleaning the stencil, or sliding it instead of peeling it off.
     
  11. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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    clap clap clap, a point well spotted
     
  12. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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    RETCHED,

    I have never used a stencil before. I am not planning on removing all the components from the board so can I still use one ?
    Do I need a clear space around the work area to lay a stencil or is the material workable enough to use between small gaps ?
     
  13. retched

    AAC Fanatic!

    Dec 5, 2009
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    Sure, the stencil only has to be a touch larger than the component itself.

    These are the report covers I use for the stencils:
    [​IMG]

    The kind you put a few pages between the plastic sheets and slide on the binding clip.

    You can use the aluminum foil trick to mark the pin locations in foil then put the foil on the plastic to poke the holes. When your done, you can cut the stencil to any size or shape you like. I would put a few inch long "handle" for easy removal.

    If you are doing It that small, you want to place the plastic on the board, then squirt the paste in the holes, because you wont have much to hold while squeegeeing.

    So if you out the stencil down first, hold it still with a pencil eraser (or whatever you have on hand) and squirt the solder paste into the stencil holes, then peel the stencil back.

    For future note, place these chips first. It is much easier with a bigger stencil that you can tape town during squeegeeing
     
    Last edited: Mar 5, 2010
  14. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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    Sounds like a plan.
    Are there any companys that sell pre-made stencils ?

    I'm sure they are not too hard to make but package sizes are standard. Are they an off the shelf product in the UK ?
     
  15. BMorse

    Senior Member

    Sep 26, 2009
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  16. BMorse

    Senior Member

    Sep 26, 2009
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  17. retched

    AAC Fanatic!

    Dec 5, 2009
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    now that would be nice... I guess its time to retire my LabelFlash drive and see how well I can whip up a stencil maker. Anyone play with the label burning laser from such a drive?
     
  18. loosewire

    AAC Fanatic!

    Apr 25, 2008
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    retched,you have been holding back,smooth.
     
  19. BMorse

    Senior Member

    Sep 26, 2009
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    I am still waiting to find a suitable DVD burner (preferably a LightScribe one) so I can salvage the Laser Diode to make a Laser Engraver for my CNC,( I have a few of the drives but they are still too new to dissect!!), but I am sure if it is powerful enough I could possible cut stencils with it...


    B. Morse
     
  20. retched

    AAC Fanatic!

    Dec 5, 2009
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    Mine has the lightScribe laser.. I know what cha mean about too new to rip apart. It would be nice... If I had your CNC, It be done..

    I read an instructable where a guy made a laser cnc with a dvd writer laser and two scanners. It worked. Made good stencils to.. But he never turned the laser off. He just moves it faster than the laser can cut to move the head. With a real cnc and a decent setup, It is worth a try.

    I'll head to the technology scrap yard tomorrow and se if I can find 2 (or more) lightscribe dvd burners that have broken drawers or something for ~$5..

    If I do, Ill mail you one(or two)
     
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