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How do I solder teensy chips? — Parallax Forums

How do I solder teensy chips?

Kirk FraserKirk Fraser Posts: 364
edited 2012-03-26 13:06 in General Discussion
I have an AS5055 chip that measures 4mm square with four leads dividing the middle 2mm on each side, smaller than I can measure. With regular surface mount devices I can usually solder directly or attach wires to each lead first. These are too small for anything I've got. I saw one strategy to put bits of solder on a printed circuit board and somehow heat the whole chip. Even that looks risky this small.

Also, if I make a tiny soldering iron by heating a small PCB drill bit red hot with a Radio Shack soldering torch, it doesn't hold the heat long and even that isn't really small enough. What do people use? Thanks.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-22 12:01
    There are a couple of different methods.

    Most of them use solder paste on the circuit board.

    Once you have the solder paste in place with the chip on top, you can heat it with a hot air rework station.

    I've also seen people use electric hot plates and toaster ovens to heat up the boards.

    I've wondered if it's posible to use conductive paint to make connections to small chips.

    My idea is to glue the chip upside down to a board and then paint a trace from the chip to point where it would be easier to make a connection.
  • TubularTubular Posts: 4,712
    edited 2012-03-22 12:05
    Kirk, just in case you haven't seen Duane's thread on these same sensors, its here

    T    he evaluation boards may be an option (or not)
  • Kirk FraserKirk Fraser Posts: 364
    edited 2012-03-22 12:15
    Duane,

    Any link on solder paste? I know about flux paste but I don't know what solder paste is.

    I hope your idea for conductive paint works! Looks good. It may require a one hair paintbrush. :-)
    Maybe one could glue wires to the sides of the chip then paint the connections and skip the board.
  • tonyp12tonyp12 Posts: 1,951
    edited 2012-03-22 12:25
    The good: it's 0.65mm pin spacing and not 0.5mm
    bad, it's QFN and it's harder to inspect a good solder job.

    Use solder paste, very very little of it.
    http://search.digikey.com/us/en/products/SMD291AX/SMD291AX-ND/1160002

    Then put it in a oven, skillet or use hot-air reflow station.
    You may have to reheat it with hot-air and press down on it.
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-03-22 12:26
    I was just checking in to buying some solder paste the other day. The stuff is expensive. Mouser (my preferred supplier) only does factory drop shipments, but it looks like MCM stocks the Chip Quik brand in singles.

    http://electronics.mcmelectronics.com/?N=&Ntt=solder+paste&x=0&y=0
  • Kirk FraserKirk Fraser Posts: 364
    edited 2012-03-22 12:35
    Tubular,

    Thanks, I'm Duane's consulting employer for this project. I was still looking around for other bits of information until it works, but it looks like he's got it handled.

    The evaluation boards are as usual way overpriced to use on a regular basis and in this case too large. I'd like something the size of these pots http://search.digikey.com/us/en/products/EVW-AE4001B14/P12426CT-ND/637165
  • Kirk FraserKirk Fraser Posts: 364
    edited 2012-03-22 12:46
    tonyp12 and RDL2004, thanks for the solder paste info.

    I assume it's more solid than paint when done, if done right. With paint you can see your work.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-22 12:50
    Kirk Fraser wrote: »
    tonyp12 and RDL2004, thanks for the solder paste info.

    I assume it's more solid than paint when done, if done right. With paint you can see your work.

    You wouldn't want to use paint on anything other than a prototype (I'm not sure it would even work for a prototype).

    Solderpaste is used on almost all surface mount production. It's usually pretty strong.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-22 12:52
    SparkFun sells small jars of solder paste. They have a little video on how to use it (I haven't watched the video yet).

    I'll find their electric skillet tutorial and post a link here.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-22 12:54
    Their solder paste tutorial has links to the skillet and toaster over tutorials.
  • Kirk FraserKirk Fraser Posts: 364
    edited 2012-03-22 15:03
    First time in a while the forum dumped my post.

    I found the Kester.com website lists distributors for their Kester Easy 256 product listed in the tutorial. I don't see any instructions on how to make the solder mask or where to get the plastic or metal films. I suppose they are same as used for silk screening. It would still take ultra tiny solder mask holes to do it that way but since that's the only way less costly than ordering a custom chip...

    BTW, somewhere I read of a possibility of running the solder paste through some print head. That would be nice.
  • tonyp12tonyp12 Posts: 1,951
    edited 2012-03-22 15:13
    To make 1-10 units you don't use a stencil.
    You just carefully smear some paste on the pad with the syringe.
    But with QFN, very little of it. I get a 75% sucess rate first time.
  • Kirk FraserKirk Fraser Posts: 364
    edited 2012-03-22 15:42
    tonyp12 wrote: »
    To make 1-10 units you don't use a stencil.
    You just carefully smear some paste on the pad with the syringe.
    But with QFN, very little of it. I get a 75% sucess rate first time.
    Ok, smear it is.

    One question, what if you cut a square hole in the PCB to just fit the 4mm chip then glue it so the leads are at the same surface as the PCB copper? Can you then smear the solder paste over the crack between chip and board to get a good visible solder joint?
  • tonyp12tonyp12 Posts: 1,951
    edited 2012-03-22 16:35
    Mid mont ICs I have never heard off, how are you gone get that tiny square hole done?

    What I like to do is to use a QFN pad that is little larger than recommended smt layout.
    As your IC does have exposed side pads (though not fully exposed) maybe the solder paste will cling to the sides.
  • Kirk FraserKirk Fraser Posts: 364
    edited 2012-03-22 16:51
    tonyp12 wrote: »
    Mid mount ICs I have never heard off, how are you gone get that tiny square hole done?
    The square hole can be done by drill or mill the center cut then using a file to clear out the corners. There exist some square drills for woodworking that could be tried - which are simply drills surrounded by a square knife framework to cut the square's corners as the bit plunges into the stock.
    tonyp12 wrote: »
    What I like to do is to use a QFN pad that is little larger than recommended smt layout.
    As your IC does have exposed side pads (though not fully exposed) maybe the solder paste will cling to the sides.
    Not sure what you mean, QFN pad? I had to double check on the sides, they are so small. If anything would stick there it would seem more likely to be some kind of tiny spot welder like they use to attach carrier wires inside chips.
  • tonyp12tonyp12 Posts: 1,951
    edited 2012-03-22 17:00
    Solder paste when heated up, crawls like mercury (or the melting part in Terminator 2)
    http://www.youtube.com/watch?v=Aq5ydeWWr4A
  • T ChapT Chap Posts: 4,223
    edited 2012-03-22 22:12
    You don't need solder paste for a one off project, and solder paste on a QFN is more trouble anyway if you do not have a nice stencil, preferably stainless. Just put down some flux, heat the pads in a rotating motion with a pencil, then use some very fine solder and coat the pads with the pencil tip. The flux will cause the solder to bead up on the pads assuming you don't overdo the solder and bridge it. If so just knock the solder of the pads with the tip. Place the part on the pads, heat it up with an air soldering tool, start with the air out a bit and gradually get closer to avoid heating the part and board too fast. You can gently tap on the board when the solder is liquid to cause the chip to settle and square itself up. Also, you can gently tap on the chip with a small screwdriver to make it sit square and insure all the pads make contact. A substitute for an air rework station is a heat gun, takes a little longer but I have gotten them to do the job. Sometimes using some method to reduce the airflow to a smaller diameter speeds things up, but also has melted heat guns in the process. You need a magnifying glass to inspect all sides. If there is a bad connection, I have used flux on the sides of the chips with a pencil to do repairs.
  • __red____red__ Posts: 470
    edited 2012-03-23 04:41
    My personal favorite solder paste is http://www.newark.com/jsp/search/productdetail.jsp?id=18K6979&Ntt=18K6979

    (SN62RA10BAS86-25G CARTRIDGE - SOLDER PASTE, 62/36/2 SN/PB/AG 179°C 25G)

    The reason being is that:
    a) It's the lowest temperature paste that I could find.
    b) It's no clean solder (which is a BIG DEAL imho if this is your first time around the block).

    I use a $30 electric skillet from target to bake my boards.
  • Wa_MoWa_Mo Posts: 17
    edited 2012-03-26 13:06
    I've been trying to familiarize myself with SMD soldering and found this

    http://www.youtube.com/watch?v=ihoX7x0RBz8

    The only thing I would do differently is to place just enough of the 'glue' at either end of the IC chip for easy removal after soldering, rather than a gob right underneath.
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