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Really small SMT: Popular packages?

Discussion in 'Electronic Design' started by Joerg, Jan 18, 2007.

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  1. Joerg

    Joerg Guest

    After getting used to 0402 and 0201 passives it seems my next design has
    to also shrink for the transistors, this time all of them. I have
    designed in things like SC-75 in the past but there is quite a
    bewildering number of choices in the "below SOT-23" category.

    What might percolate as the most popular transistor and diode size in
    "micro-SMT"?
     
  2. Tim Shoppa

    Tim Shoppa Guest

    SOT-323 had the most choice earlier in this millenium but your SC-75's
    are already smaller!

    Two-transistor arrays with built-in resistors are the real space-saving
    step but they can have substantial supply-line problems if you're
    working in medium quantities and use anything outside the most usual
    values.

    If your designs are "wide enough" there are some transistor and
    resistor and diode arrays that make great sense. Almost always I see
    these used in data or address bus situations and I think you fall
    outside that realm.

    Tim.
     
  3. DJ Delorie

    DJ Delorie Guest

    I've found there are two sub-sot23 sizes I like, which are
    approximately sot-323 and sot-523. These correspond to sc-70 and
    sc-75, and sot-523 corresponds to sot-416. The sot-323 part
    corresponds roughly to a 0.65mm pitch (i.e. the space between the two
    pins on the same side is 1.3mm); the sot-523 approx 0.5mm. Note that
    "approximate" is the relative size only; each package has specific
    details that differ from others, check the specs to be sure.

    Photos of the relative sizes can be found here:

    http://www.delorie.com/pcb/smd-challenge/mine-back.jpg

    The blue parts are 0402, the LEDs are 0603. The two transistors are
    sot-323 and sot-416. The grid is 1/16".

    Other cross references from my notes (mm is lead-lead, not pitch):

    SOT-23 1.9 mm
    mini 3P 1.9 mm
    SC-59 1.9 mm
    SOT-143 1.9 mm

    S-mini 3P 1.3 mm
    SC-70 1.3 mm
    SC-88A 1.3 mm
    SOT-323 1.3 mm

    SC-75 1.0 mm SOT-416
    SOT-523 1.0 mm
    SS-mini 3P 1.0 mm (chiplead, not gull-wing)

    SSS-mini 3P 0.8 mm (chiplead)

    Then you get into CSPs (i.e. micro-bga style).
     
  4. Joerg

    Joerg Guest

    SOT-323 is a massive boulder :)

    Those are indeed nice. Anything more than two was a disappointment so
    far. Found some nice quads wired up in an H-bridge. But they almost
    wanted a whopping $1 for these in qties. No way, I can do that for under
    10c with four discretes. What were they thinking?

    In the past I found that the sales of 6-7 transistor arrays were a bit
    of a closed market. Hard to buy and really only available from Asian
    sources. Which might be ok for designs that are produced in China, as
    long as the arrays cost 10c or less and come in TSSOP or smaller.

    BTW, what's up with Digikey? Fails a lot, saying "server is currently
    updated", then comes back after a minute or so. Is everything freezing
    up there?
     
  5. Joerg

    Joerg Guest

    Do you think SC-75 is here to stay? That would at least yield a factor
    of two improvement over SOT23, roughly.

    Nice! Looks like a bit much in solder. Try Kester 15mil and a Weller ETS
    tip. Probably I'll have to find even smaller solder soon. Plus a nice
    USB camera if there is one that can be fitted with a zoom lens (macro is
    too close to the iron). I don't like microscopes much and the 3x glasses
    in the lab aren't going to cut it anymore for 0201.


    I always wondered why they splintered up the descriptors so badly.
    Couldn't agree, I guess. Like with those dreaded EU and US differences
    in resistor sizes that can easily cause costly purchasing mistakes.
     
  6. Tim Shoppa

    Tim Shoppa Guest

    Gotta limit yourself to ULN2003-alikes :).
    They recently revamped the search engine. I see some good from the
    revamp, but it frustrates the hell out of me that every value is now
    specified to 4 or 5 significant digits! Like we'd have to tell the
    47.000 uF caps from the 47.001uF caps!

    Tim.
     
  7. DJ Delorie

    DJ Delorie Guest

    There are enough footprints in that size, and the cost is comparable.
    I think it's here to stay. IMHO the SSS-mini is still wait-and-see,
    perhaps the CSPs will supercede it.
    Those were hand soldered with Kester 20mil, with a Metcal 20mil
    conical tip. Since then I've gotten a syringe of paste, it works even
    better than wire solder - dab a bit of paste on the pad, place part,
    heat leads with iron, paste melts.
    Most of my close-ups are taken with an IntelPay QX3 microscope. The
    bigger ones are taken with a digital camera; the Canon A70 has a macro
    setting that works real well if you put a few layers of paper in front
    of the flash to reduce the glare.

    Other side: http://www.delorie.com/pcb/smd-challenge/mine-front.jpg

    Here are some other photos taken with the QX3:
    http://www.delorie.com/pcb/smd-challenge/fp-pix/

    As for actually soldering, I use a 3.75x mag visor (10 diopter) for
    the 0201's and 01005's, and a 2.5x (5 diopter) for everything else. I
    got them from Woodcraft (they're sold for scroll sawing, which I also
    use them for).
    I'm guessing it has to do with lead size, length, etc.
     
  8. Joerg

    Joerg Guest

    That would be great if SC-75 became a staple. So, might be time to
    generate the CAD models now.
    Good point. Paste is the next thing I want to try out.
    Nice job on the chips. Looks like they were done with paste.

    I don't like working with something between me and the board while I'd
    have no problem soldering while looking at a monitor in another
    direction. But I am in the minority here, most folks at clients don't
    like to do that at all.
     
  9. Boris Mohar

    Boris Mohar Guest

    They told me that they had a pipe burst and the hamster got all wet. I am
    trying to complete an order and it has been really flaky.
     
  10. DJ Delorie

    DJ Delorie Guest

    Nope. Also hand soldered.
     
  11. Joerg

    Joerg Guest

    And no mirror server? Oops.

    Pipe bursts can be bad. We just had a large retirement home evacuated
    and they said it'll take 4-6 weeks for restoration of the place.
     
  12. qrk

    qrk Guest

    I've been using SC89 6-pin parts for my dual transistors from ROHM.
    Still haven't ventured into 0201 parts yet.
     
  13. Joerg

    Joerg Guest

    On the design I am doing right now I'll be lucky if I can avoid the use
    of 01005 resistors :-(
     
  14. DJ Delorie

    DJ Delorie Guest

    Those take me about 20 minutes each to hand solder (place, inspect,
    solder, inspect, resolder, etc). We've renamed those to "quantum
    capacitors". One moment they're on the board, the next moment they're
    gone!

    I'll stick to 0201s or 0402s from now on.
     
  15. Joerg

    Joerg Guest

    Tell me about it. Much of the inspecting effort goes into ascertaining
    whether it is actually there. Or if not, where the heck it went. Before
    soldering all it takes is uncle Leroy next door to sneeze and it's gone.
    One of my clients actually thought that I'd switched to pixie dust.
     
  16. Rich Grise

    Rich Grise Guest

    .
    Everything is "freezing" all over the place these days.

    I think it's the fault of U-tube and those "get a date for free" sites.

    And blogs, of course. >:-(

    Thanks,
    Rich
     
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