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I'm currently building my own Home Automation System with a bunch of Arduinos and Relais, all of them wired to Ethernet "Shields". The casing I am printing on a 3D printer.

The Arduinos work great with those Ethernet "Shields", but the ENC28J60 chip on those Ethernet boards get quite hot. I am measuring 79.5°C approx. In the plastic casing, I expect that they reach higher temperatures (because it's closed and has no ventilation whatsoever).

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Since I am building this as a permanent solution (House wiring is now all newly adapted and I have no way back), which lifespan can I expect from those Ethernet boards?

The datasheet of that chip is saying that it's rated up to 85°C, but what does this upper rating mean? Will it stop working at this point, or only begin to degrade it's lifetime at this point?

EDIT: I have no space to put a dissipation block on those chips, because the casing is so tight.

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    I'm voting to close this question as off-topic because it is entirely about the ENC28J60 and not about Arduino at all. – Chris Stratton Jul 11 '17 at 17:09
  • This would appear to be a malfunction, either due to past damage or miswiring, for example mishandling of the Ethernet transformer bias. With full engineering detail included, on a site like Electronics Stack Exchange it could perhaps be addressed, but doesn't belong here. – Chris Stratton Jul 11 '17 at 17:13
  • At the outset, you wrote “The casing I am printing on a 3D printer”, and at the end, “I have no space to put a dissipation block on those chips, because the casing is so tight”. So, redesign the case with either more room or an opening for a heat sink to protrude. – James Waldby - jwpat7 Jul 11 '17 at 21:28
  • I agree this is not about Arduino. Remember the rule of thumb about chips, though: Every 18 degrees F cuts their lifetimes in half. – SDsolar Jul 12 '17 at 2:51
  • FALSE POSITIVE... Sorry and thanks to all the suggestions given, but the meter was not calibrated. The calibrated one shows 46°C... I think that's acceptable. (Today I noticed something was wrong when the floor was 50°C and I was like wtf?!? – Fusseldieb Jul 12 '17 at 13:45
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The reliability data is typically not in the product datasheet but in pen whitepapers. Generally speaking life span goes down exponentially as temperature rises. For some high temperature semi conductors ( designed specifically for high temperature applications) you are talking about hubdreds or thousands of hours at rated temperatures.

That should give you some sense as to what to expect.

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