SMT board design

yarisboyyarisboy Posts: 245
Moderator, Move this thread if necessary. I searched SMT and surface mount board design topics without success. I've designed, built, and produced through-hole boards now and want to make the jump to smt chips. What I'm looking for is the best instruction on low melting point solders, controlled ovens, solder pastes and so on. Did someone design a modified toaster oven for all this controlled by a BS2. I know the solder pot was done by a Parallax staffer. The oven control should be similar but would need a timer and perhaps an IR sensor pointed at the board surface. Are tweezers OK or do I need to tap my vacuum pump with a suction cup and foot switch while manipulating small parts? If I'm using tweezers do they need to be static strapped to the mat?
I've done pick and place vacuum lifts for mechanical robotic assembly, just never for electronics components.

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MOORE'S LAW: The capabilities of electronics shall double every 18 months.
cloyd's corollary: Hardware is easy, software is hard.

Comments

  • 14 Comments sorted by Date Added Votes
  • AnglinaSAnglinaS Posts: 1
    edited October 2009 Vote Up0Vote Down
    Hi,

    Can you show the pics what you came up with, looks perfectly fine board.

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    Voice t1
  • mctriviamctrivia Posts: 3,772
    edited October 2009 Vote Up0Vote Down
    I use lead free solder which is not low melting point.

    I use a regular convection toaster oven. I set the temperateure at:

    200F for 4 min
    325F for 2 min
    450F for 30 sec

    i start the timer at each of these temperatures when it reaches the temperature.

    Once done I turn off tap the door a few times to help seat components properly(surface tension will want to pull parts in to right spot) then open the door and let cool down for 10min.


    twezzers are the tool i would recommend for hand assembly. They do not need to be static strapped but it is a good idea to make sure you are.

    http://ohararp.com/ is a great place to get low cost stensils made. check out http://www.instructables.com/id/How-to-assemble-an-SMD-GPS-Device---OHARARP-LLC/ for instructions on how to use.

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  • ElectricAyeElectricAye Posts: 4,561
    edited October 2009 Vote Up0Vote Down
    mctrivia said...
    I use lead free solder which is not low melting point.....

    mctrivia,

    what brand of solder do you use, what composition, etc?

    thanks,
    Mark
  • T ChapT Chap Posts: 3,903
    edited October 2009 Vote Up0Vote Down
    www.smtsolderpaste.com/solder_paste_info.php?key=pbws

    I have used this leaded solder for years and really like it's performance. I never keep it refrigerated but it might be recommended to do so.

    www.amazon.com/Cuisinart-TOB-195-Toaster-Broiler-Stainless/dp/B000PYF768

    I use this convection oven. Set it to 150F for 3 minutes, then 500F for 3 minutes. Keep in mind that it takes a while to reach these temps, just use the 3 minute rule for each and it never fails to do a great job. I do not wait till the temp is reached to start the time, start the timer for 3, press the temp and change when the timer is done. When the total 6 minutes are up, power off and crack the door open and inch, let it cool for 10 minutes or so, do not rush it to cool.

    www.hitechstencils.com/

    Stainless is the only way to go hands down. If you are not doing any fine pitch or QFN size stuff you can get by with mylar(build a system to stretch the mylar (or Kaptan). Build a stencil printer with screen printing hinges and a movable base to place the PCBs on so you can slide the PCB around under the stencil.

    I went to great lengths to build a perfect system for temp control with 6 stages where you can monitor the temp and set times, If found that this made absolutely no difference versus the 6 minute method above. No lead will be more a headache to deal with. I have seen no lead boards have parts just fall right off when not done right.

    Tweezers are a big hassle. You'll spend more time doing the 'flip the part tills it's heads' than you will actually placing parts. Get a system with a vacuum, syringes and suction cup combo is best. Mount cut tape in a little groove and pick up from there.

    Lots of syringes and equipment here:

    www.zeph.com/zt5_dir.htm


    Commonly used syringe tips are black and white. Get the various suction cups for larger chips, stick them on the needle tips.

    www.abacomdirect.com/p-176-ezpick-smt-pick-and-place-system.aspx

    I haven't used this machine but it looks very cool for a low cost manual. I used the exact same pump and syringes he does which come from zeph.
  • mctriviamctrivia Posts: 3,772
    edited October 2009 Vote Up0Vote Down
    i agree that leaded solder is much nicer to work with then lead free but i sell world wide so I have to keep ROHS compliance.

    I use
    AMTECH SynTECH-LF
    96.5Sn/3Ag/0.5Cu

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    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
  • yarisboyyarisboy Posts: 245
    edited October 2009 Vote Up0Vote Down
    Thanks Todd,
    The air pencil video on Zef products was great. I'm going to order their 63/37 no clean paste. It's got lead in it but I harpooned a whale in my pajamas just this morning. How he got in my pajamas....................

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    MOORE'S LAW: The capabilities of electronics shall double every 18 months.
    cloyd's corollary: Hardware is easy, software is hard.
  • @yarisboy, the Nice topic started!!! I also like to see some new technique/product which can be used for this. Also, hot plates work OK, but with this, you are limited to one side of components.
  • tonyp12tonyp12 Posts: 1,931
    edited November 14 Vote Up0Vote Down
    MECHANIC Lead-free Low Temperature SMT Melt Melting Point 138C Solder Paste 60g
    https://www.ebay.com/itm/MECHANIC-Lead-free-Low-Temperature-SMT-Melt-Melting-Point-138C-Solder-Paste-60g/122484189368?epid=2142750810&hash=item1c84a068b8
    Pros:
    No lead, don't have to worry about getting some on your hands.

    Low temp, you don't risk burning parts or pcb when going over by a few deg.

    It's winter now, safe to ship by mail, but don't leave it in hot car though.






  • What is it? Some kind of bismuth/tin alloy? The eBay site is pretty stingy with details.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • tonyp12tonyp12 Posts: 1,931
    edited November 14 Vote Up0Vote Down
    One alli express stated this but could be a cut paste error:
    Alloy:Sn96.5 Ag3.0 Cu0.5

    This is another variant that uses Sn42 Bi58:
    https://www.banggood.com/Mechanic-SAC305-Sn42Bi58-Lead-Free-Low-Temperature-Soldering-Flux-Welding-Paste-p-1137784.html?cur_warehouse=CN
  • Wow, that's funny, typical banggood. "SAC305 Sn42Bi58" is the equivalent of saying "peanut butter and jelly BLT".

  • GOSH DARN IT ANDREW!

    Now all I can think about is a peanut butter and jelly BLT. With a side of SMT. :)

    http://www.theofficequotes.com/season-5/the-michael-scott-paper-company/quote_2586
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • erco wrote: »
    GOSH DARN IT ANDREW!

    Now all I can think about is a peanut butter and jelly BLT. With a side of SMT. :)

    http://www.theofficequotes.com/season-5/the-michael-scott-paper-company/quote_2586

    It will work.

    Oddly enough there is a firm called Schmartboard who makes boards prepopulated with useful shapes, and the locations are already smeared with solder. They do recommend water soluble flux. Which they do not sell. (Oh and the firm is not run as a subsidiary of KAOS expecting to trap a certain klutz.)

    I find it interesting that we are reopening a second thread who is nearly old enough to vote.
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  • erco wrote: »
    GOSH DARN IT ANDREW!

    Now all I can think about is a peanut butter and jelly BLT. With a side of SMT. :)

    http://www.theofficequotes.com/season-5/the-michael-scott-paper-company/quote_2586

    YCCH!

    Actually I find it interesting that we are restarting a discussion from seven years ago, and there's another one.

    As for SMT capable boards a firm named Schmartboard makes them already to go to have parts soldered on them. They want the user to apply a water soluble flux. Which they do not sell. Where I bought them, Micro Center by name, the firm had in stock a quantity of the stuff, oh and the name on it was Chipquick.

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