5 ms·

Lead is no problem for RoHS-exempt components. If they can use these superlattice caps to replace tantalum caps, I'm all for it. Those suckers take up so much s

Lead is no problem for RoHS-exempt components. If they can use these superlattice caps to replace tantalum caps, I'm all for it. Those suckers take up so much space in small designs that you sometimes have to forego the recommended decoupling caps just to get the design to fit on the board.

lightedman 4y ago
The problem is that most electronic components are RoHS today. So getting these into other devices will mean loss of RoHS certification, and that is something a lot of companies don't want right now due to the environmental movement. Many use that as a selling/marketing point. I'm hoping for other superlattice materials to become available.
- deleted 4y ago
  [deleted]
- adammunich 4y ago
  Lead is exempt when used in ceramic capacitors
  - lightedman 4y ago
    Didn't that exemption expire some time before 2010? I know there were some time-based exemptions.
- GekkePrutser 4y ago
  But RoHS permits lead if there's no reasonable alternative. One example is lead acid batteries which contain a lot of lead. A similar exemption could be made for these I guess if they're really that promising.
jleahy 4y ago
Out of interest, why do tantalums get used so much over ceramics (or electrolytics even) for bulk decoupling? DC bias can be a pain I know, but I always thought of ceramics as cheaper / less fiery alternatives.
- nousermane 4y ago
  > why do tantalums get used so much over ceramics for bulk decoupling? higher energy density > (or electrolytics even) no risk of drying up. Also, higher energy density, especially for small parts.
- wiml 4y ago
  They were more compact than alternatives at the time, and had lower ESR. This made them especially desirable for supply decoupling in digital logic, whose random fast edges means a lot of broadband noise to shunt — you can't just design to a particular frequency range like you can with most analog circuitry. Digital was also the new expensive hotness, and putting in a tant wasn't going to be a big fraction of BOM cost. These days my understanding is that ceramics and non-tantalum electrolytics have gotten good enough to replace most tantalum uses, and between that, the expense, the slavery, the exploding, and the environmental damage, they're less common than they once were.
kennywinker 4y ago
What’s an application that needs to be super small, but doesn’t risk getting lead into people’s bloodstream and the environment? I can’t think of many…
- tbrownaw 4y ago
  Switching power supplies with power factor correction need some pretty hefty capacitors I think.
  - londons_explore 4y ago
    There are ways to do power factor and harmonic correction with far smaller capacitors. The problem boils down to wanting to take power from AC in a sin squared wave, and outputting it at a constant rate. So you need storage of the integrated difference. Therefore the energy storage required is the energy used in a quarter of a full cycle of the original AC. For a 500 watt PC power supply running on 60 Hz, the storage is 2 Joules, which at an energy density of 2 Joules/gram gives you a capacitor of about 1 gram or 0.5 cubic centimetres. Ie. The capacitor requirements for a desktop PC power supply can be as low as the size of a pea, if the design is right. Typically they're far larger for other reasons - usually to simplify the design
    - deleted 4y ago
      [deleted]

lightedman 4y ago

The problem is that most electronic components are RoHS today. So getting these into other devices will mean loss of RoHS certification, and that is something a lot of companies don't want right now due to the environmental movement. Many use that as a selling/marketing point. I'm hoping for other superlattice materials to become available.

deleted 4y ago
[deleted]
adammunich 4y ago
Lead is exempt when used in ceramic capacitors
- lightedman 4y ago
  Didn't that exemption expire some time before 2010? I know there were some time-based exemptions.
GekkePrutser 4y ago
But RoHS permits lead if there's no reasonable alternative. One example is lead acid batteries which contain a lot of lead. A similar exemption could be made for these I guess if they're really that promising.

jleahy 4y ago

Out of interest, why do tantalums get used so much over ceramics (or electrolytics even) for bulk decoupling? DC bias can be a pain I know, but I always thought of ceramics as cheaper / less fiery alternatives.

nousermane 4y ago
> why do tantalums get used so much over ceramics for bulk decoupling? higher energy density > (or electrolytics even) no risk of drying up. Also, higher energy density, especially for small parts.
wiml 4y ago
They were more compact than alternatives at the time, and had lower ESR. This made them especially desirable for supply decoupling in digital logic, whose random fast edges means a lot of broadband noise to shunt — you can't just design to a particular frequency range like you can with most analog circuitry. Digital was also the new expensive hotness, and putting in a tant wasn't going to be a big fraction of BOM cost. These days my understanding is that ceramics and non-tantalum electrolytics have gotten good enough to replace most tantalum uses, and between that, the expense, the slavery, the exploding, and the environmental damage, they're less common than they once were.

kennywinker 4y ago

What’s an application that needs to be super small, but doesn’t risk getting lead into people’s bloodstream and the environment? I can’t think of many…

tbrownaw 4y ago
Switching power supplies with power factor correction need some pretty hefty capacitors I think.
- londons_explore 4y ago
  There are ways to do power factor and harmonic correction with far smaller capacitors. The problem boils down to wanting to take power from AC in a sin squared wave, and outputting it at a constant rate. So you need storage of the integrated difference. Therefore the energy storage required is the energy used in a quarter of a full cycle of the original AC. For a 500 watt PC power supply running on 60 Hz, the storage is 2 Joules, which at an energy density of 2 Joules/gram gives you a capacitor of about 1 gram or 0.5 cubic centimetres. Ie. The capacitor requirements for a desktop PC power supply can be as low as the size of a pea, if the design is right. Typically they're far larger for other reasons - usually to simplify the design
  - deleted 4y ago
    [deleted]