General longevity study on electronic designs

For how long can a design last?

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If I build an electronic device, how long can I expect it to function?
If I buy an electronic device, how muck will it live?
What are the tips for a longer life?
What are the bottlenecks and the weak points of a device?
How can I improve my design?
What would be an efficient way to have a PCB in the context of longevity?
Can you tell me more about EMC and how this influences lifespan?
What other tests shall I perform to make sure I have a good product?

These are just a few questions I will try to answer in my project here and as the time passes by, I will keep writing here some of my thoughts regarding these problems. Hopefully, my experience and my struggles over the years can enrich some of you and help you overcome some of your problems.

If I build an electronic device, how long can I expect it to function? 

Influencing factors of an electronic design life would be:

- Temperature

- Humidity

- Light and UV rays 

- EMC pulses exposure 

- Semiconductor diffusion 

- General lifetime of the passive components ( capacitors, rechargeable batteries, etc )

                       ...content will be added for these separate topics in the instructions tab...

If I buy an electronic device, how muck will it live? 

Keeping in mind the factors I mentioned above, I made a few videos discussing these issues:

Moreover, here is what happens with exposing your device to high humidity or liquid splash:

   Looking at these videos, it beceames clear to everione that every device that you buy from the market these days has a limited lifetime. The estimated lifetime of a laptop or a mobile phone that is being used an average of 5 h/day, I would say should nout exceed around 4-5 years in ideal conditions. Eventually, the water in the air and the repetead heating of the components, will put an end to it's life. It is also true that these degrading factors, can act faster in some cases. This is why, even for good devices and for good designs, you don't get a warranty period taht is greater than 3 years. 

   Of course, there are exceptions to this rule. I know somebody who had a ceapish laptop that lasted for 7 years. The battery died as expected after about 3 years, but the laptop was still functional and the respective person was using it with a plugged in adapter. When I investigated this a little bit, I realised that the respective person, was using the laptop exclusively for studies and it was rarely watching movies. This meant that the motherboard was exposed to less thermical stress. Another factor was that person was living in a very dry environment that was rarely reaching the 50% RH limit. Nevertheless. the machine died after 7 years of usage even in these perfect conditions. So nothing is forever.

What are the tips for a longer life? 

Ok. Let’s say you bought yourself an electronic device. A mobile phone, a tablet, a new computer, a printer: anything. What would be the tips for a longer life or what can you do to preserve the product in a usable state for as long as possible. Well, here are some tips:

  • -Keep the electronic device away from heat or direct sunlight exposure. I saw some people placing their mobile phone on the radiator when they were charging it just because the power point was there and the charger’s cable was too short. This can definitely cause the li-ion battery to swell. And if it doesn’t swell up, then this definitely shortens the life of the battery. Never charge an electronic device while it is exposed to direct sunlight. This creates the same effect. So next time you are charging your tablet inside your car, don’t put it on the dash. Direct sunlight exposure can damage screens of any type. So this is another factor to be kept in mind.
  • -Keep it in a dry place. Although low humidity environment is not good for your lungs, this is very beneficial for any electronic device. This is why server rooms and HW chambers are having dehumidifiers and air conditioning installations. Maybe you cannot change the fact that you might be living on the shore of the ocean, but you can change something by choosing to operate your laptop inside the house and not on the veranda in a cool misty evening.
  • -Avoid metallic cases. Although the steel laptop cases, the metallic mobile phone ornaments and the aluminium alloy back lids are cool, you have to know that they attract condensing water in time. You keep the mobile phone in your pocket at 30⁰C and when somebody calls you, you take it out and expose it to the -2⁰C winter air walking down the street....
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  • About aging capacitors

    Marius Taciuc03/13/2019 at 23:22 0 comments

    Here I added another video about electrolytic capacitors. I was fixing an APC 800 UPS the other day and it was having bad capacitors. This was triggering an oscillating behavior. The MCU was resetting and this was preventing the entire device from being functional.

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  • 1
    Temperature aging process

       I think the most critical components that are aging  the capacitors (especially the electrolytic ones) and the rechargeable batteries. The picture below, shows a life expectancy characteristic of some average aluminium electrolytic caps. 

       Now the question is not how long before the capacitors loose most of their capacity or they go completely bad. In some cases, I saw capacitors that are loosing only 10% of their actual capacity or they are increasing their ESR with just a couple of OHMs and this causes a ripple voltage on the MCU that is greater than 300mV or 500mV and this is enough to cause the MCU to restart. This is the cause in all the cases of bad capacitors in monitors or other devices. A rule of the thumb would be to estimate that in normal condition, the capacitors are usually designed to last about ten yeas. If you expose the capacitors to a temperature that exceeds 25 Celsius degree with 15 to 20 degrees, the lifetime of the component shortens in half. 

       Of course now, the design could be more robust. For instance, If I'm designing a thing that I want to last in harsh conditions for 15 years instead of the usual 5, the thing to do is to forget about linear power supplies and to go for some Bust-Buck converters that will function at 100-150KHz and hopefully, a simple 100uF capacitor will be more than enough even after 10 years when there is nothing much left of it. 

       In what comes the lifetime of a regular Li-ion battery, or an AGM battery, the expectancy given by the manufacturer depends on the number of discharges and how deep you discharge it. 

       The manufacturers say that if you don't discharge your batteries more than 25% of their capacity, they could last for about 2000 cycles. If you have some batteries for a solar system or for a portable device and you charge them once a day, technically, you can go up to 5-6 years of usage. Now it depends on the battery and some manufacturers give better performances than others. They do say though,  that the lifetime of the battery shortens in half if you expose the battery to a temperature that is 10 degrees over the nominal 25C. This means that with a bit of luck, in normal operation, some normal batteries are destined to last for just about 3 years. 

       For these components, some chemical processes are involved and these processes are accelerated in most cases at higher temperatures. Both type of components have metallic plates and an electrolyte between them and this means that electrons and ions are moving from one plate to another. This material migration it is always happening unevenly because the materials are not perfectly homogeneous, they have impurities and they are not having perfect geometry or perfectly smooth surfaces at atomic level. The most expensive ones, are expensive because they use quality materials and better manufacturing processes. This is why in the chart above, the green line representing the better quality capacitors has a better life expectancy. In the case of the AGM batteries, because of the repeated migration of the materials back and forth between the plates, they end up having different structures or different geometries. They grow dendrites that short circuits the plates and eventually they will end up even having entire plates being depopulated of the necessary materials. We perceive this as a capacity lost when we test the battery. 

    Temperature is also influencing the life of the PCB and it can favor the semiconductor diffusion effect. This can lead to burned or broken PCB traces, broken viases and burned components like in the video below:

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