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Are resistors that we will usually use on PCBs metal Film type?

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  • Are resistors that we will usually use on PCBs metal Film type?

    I have seen many videos from Robert and other peole in which they are designing schematic and PCBs. In these videos often there is discussion about capacitors which revolves around: tantalum, electrolytics, ceramic capacitor comparison and the different dielectrics used for cermaic capacitors themself. However, I have not yet seen any such discussion about resistors and inductors. This question is about resistors:

    Are the resistors that we will usually ever use in PCB designs with things like ICs: signal integrity, pull-up/down; OpAmps: set gain; discrete amplifiers: set gain and impedance; LEDs: limit current e.t.c, are going to be metal film resistors and never carbon carbon film, wirewound, metal oxide or metal strip resistor?

    I assume that with these different material and constructions, the frequency response will also change for the resistors.
    Last edited by gyuunyuu1989; 09-10-2023, 01:35 PM.

  • #2
    Most of the low cost SMD resistors are thick film. These are the cheapest to produce, but not the best (mainly tolerance and temperature stability)

    Carbon is for through hole resistors (or MELF). On main benefit of them is that they turn black when overloaded.
    I tried to overload a wire wound cement resistor of 5W by driving 50W through it. It was a terrible light bulb (glowing orange), but did not burn out even after 10 minutes.

    SMD to my knowledge from ok to best
    thick film
    thin film
    metal strip (just high power?)
    metal film

    In a quick glance, this page seems to sum up a lot of interesting qualities.


    • #3
      What I have learned so far is that we first start with carbon composite then came carbon film. Then came metal oxide and then came metal film. All this happened when through hole components were ubiquitous. Besides this we have some other types used often. These are wirewound for high power and metal strip (not same as metal foil) for high precision low value (milli ohm) range. There are of course other types like cement resistor among others.

      We also have nonlinear devices like thermistor and other nonlinear resistive elements in which the resistance changes with some external stimulus (light or temperature) quite a lot.

      We also have variable resistors like potentiometers.

      We also have digital version of potentiometers i.e an a device for which we can change the resistance by using digital communication bus to control it.

      But this question is just about the first type - linear fixed value resistors.

      Resistors seem simple enough but practically its not. So many materials many of which are obsolete or used on little now since better materials are available at same price. The criteria for what to use and what is better comes down to things like temperature stability, age drift, power rating, frequency response. The choice process is not simple.

      The SMD parts also come in variety of materials. Unless we need extra low value resistor or extra high power resistor or one one very flat frequency response, the metal film also called thin film, is usually what will be used everywhere and this is what makes the bulk of the resistors today.


      • #4
        The choice process is not simple
        No, for most design(er)s it is:
        - Power
        - Package size
        - Tolerance
        ​- Price
        - Stock
        Even though I have tolerance in this first list, I'd say for > 90%​ of the times it does not matter if it were 10% or 0.1%. However, I too prefer 1% for all resistors or better unless the price is much higher and I do not need it. This is also simply due to the very low price difference, it is just not worth it to go for the 5% one.

        When you need a ~10k pull-up for an IO pin to +3.3V, does power matter? Tolerance? This leaves you with package 0201, 0402, 0603 or 0805 whatever you preferred package is, price and stock. Perhaps when used in automotive you want to select AEC-Q200 too.
        Do not make it more difficult for yourself.


        • #5
          Is there any reason why you would go for carbon composite, carbon film or metal oxide resistors since these types are considered obsolete since metal film (aka thin film) came around?


          • #6
            I once heard a story (15 years ago?) about an audio device designer who got mad at the assembly company because they selected 1% resistors and not 5% as the 5% once were carbon.
            As I mentioned before, if you overload the carbon resistors, they turn black. That is the simple visual clue that (and possibly where) the overload happens.
            I also think that more easily fuse open so you could use them as an overload protection (non resettable).