Twitter Quiz – Answer


Contrary to the logic that bigger is better the answer from our Twitter Quiz Question is 0402 capacitor will filter and decouple noise better than 0805 size capacitor as it have less ESL (equivalent serial inductance).

You can read more what ESL different size components have.

ESL of 0805 capacitor is almost twice more than ESL of 0402 capacitor!


8 Comments (+add yours?)

  1. oggstreamer
    Oct 28, 2015 @ 08:01:52

    thanks for the quiz – i found the following link which provides a good explaination too:


  2. Nikolay Dimitrov
    Oct 29, 2015 @ 01:53:50

    This is not quite true. 0402 capacitors can’t filter LF noise due to their limited capacity (due to small size), so obviously bigger packages will work better for LF noise filtering. Also, ESL is different on 0402 capacitors from different models/vendors, and needs to be measured separately when characterizing new components. And last, there are additional parameters (like ESR, SRF) that are important when considering a specific capacitor model for decoupling role.


    • OLIMEX Ltd
      Oct 29, 2015 @ 08:09:04

      so you say 100NF 0805 capacity is bigger than 100NF 0402 😀


      • Guest
        Oct 30, 2015 @ 07:08:53

        Sure. The capacity-loss due to DC bias voltage is enormous in those tiny caps. I.e. from TDK’s commercial grade X7R-MLCCs: a 100nF/0402 has only 60-70nF at 10V while the 0805 is still above 95nF. At 50V the same 100nF/0402 has less than 15nF (you need a 220nF/0402 to get 100nF@10V).

        TDK’s Components Characteristic Viewer[1] is a nice tool to get these parameters.

        I totally agree with Nikolay, there’s much more to a capacitor than its ESL.


      • Guest
        Oct 30, 2015 @ 07:48:58

        PS: just found this:

        “For SMT capacitors, it is more accurate to call this [ESL] the connection inductance, since it depends much more on the geometry of the connection than on the internal construction of the capacitor.”

      • LinuxUser
        Oct 31, 2015 @ 18:18:42

        Actually, it could be not so untrue. Capacity of cercaps depends on voltage and other factors. Smaller caps are likely to have their dielecric exposed to stronger electric field, and that’s what actually changes its properties. As the result… well, you haven’t stated rated voltage is equal, nor you told dielectric is the same, etc :P. So I guess it is completely valid idea to assume 0402 would have lower rated voltage compared to 0805 in equal size, or overall more thin and/or different dielectric. As the result, except everything else, 0402 could probably exhibit higher loss of capacity at same voltage :).

        However, what I like about this quiz: all factors are complicated and hard to be weighted properly. Even datasheets grinding gives only rough idea of processes. And I absolutely like your quiz idea. It allows ones to learn some rather unobvious things about electronic engineering.

        But I would like to get idea how exactly you’ve tested your idea about 0402 is valid. Have you conducted some measurements? Have you checked stability of large batches with different caps? Or what? Theory should be proven by practice and I’m damn curious what it has been in this particular case. Because… because this is nearly first question where I got deep into physics and yet I had hard time to get answer due to multiple factors involved.

  3. OLIMEX Ltd
    Oct 30, 2015 @ 08:20:06

    Guest: 100nF is typical value of filtering capacitors for digital circuits, so 10-50V characteristics are not applicable in this case and at 1.0-3.3V which is the working power supply in digital world 100nF 0402 is exactly 100nF +- the specific tolerance
    sure the routing is also important and nobody deny this, it may be about 2-3 times higher than capacitor ESL with good routing and up to 10 times and more for bad routing, but we talk now just about the capacitors


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