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Surface mount, why are parts so small?

Discussion in 'Electronic Design' started by Raveninghorde, Apr 8, 2009.

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  1. I've been working on a sepic converter. There are some great parts
    out there in tiny packages.

    Then, for example, I find the fets need a square inch of 2oz copper
    (to achieve 78C/W), to get the heat out. And the diodes, and the sense
    resistors, and ... A square inch, I can fit another 4 inductors in
    that space.

    What is the point of making parts that small? I'm looking at a TO220
    fet now because it needs less pcb space than a superSOT-6 device.
     
  2. Eeyore

    Eeyore Guest

    Pleased to hear you bothered to work it out.

    Flavour of the month ?

    Graham
     
  3. I was an idiot. I only checked after I found the fet got hot.:(

    I'm only after 1A at 17V. But from a 10V input I squared R caught me.
    It's a 0.055R fet. But of course that rises as the fet gets hot enough
    to melt (lead free) solder.
     
  4. It's because almost all commercial boards are machine assembled these days,
    so small size is not only not a problem, it's a major benefit in apps were
    every square mm counts, and that's more common than you'd think. The
    majority of the market want small parts, so that's the direction the market
    heads.

    Dave.
     
  5. Eeyore

    Eeyore Guest

    As long as it's low power. Doing a trial exercise for a pro-audio product we
    had to be careful with resistor ratings since they could conceivably fail in
    normal use due to dissipation.

    Also, whatever they use for those SMT resistors isn't as quiet as leaded
    components.

    Graham
     
  6. How about two or three of the S6 FETs in parallel ?

    Rene
     
  7. Rich Grise

    Rich Grise Guest

    Does anyone else find it a tad irksome that leaded, pronounced "leeded",
    "having leads (wires)", is spelled the same as leaded, pronounced
    "ledded", meaning, "having lead (metal) added"?

    Thanks,
    Rich
     
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