Hot components, what to be cautious about at design - Page 1
Forum section: electronics / projects

author: Miyuki
author_rank: Frequent Contributor
timestamp: May 21, 2018, 08:44:35 pm
content: Hi,Im designing some power inverter and acording to calculations it going to be very hot at full loadchokes have 130 °C temperature rise, some semiconductors also will be like 100 °C temperature above ambient (considered up to 35 °C)Components itself have still big temperature safety margin but what will do board and soldering at this temperatures ?Electrolytic capacitors must be as far as possible this is first rule.Is here any hidden dangers of this temperatures ?//edit:Cooling is passive convection, vertical wall mount, little support of chimney effect

author: nctnico
author_rank: Super Contributor
timestamp: May 21, 2018, 08:54:19 pm
content: I'd get the temperature rise down and do a re-design because this seems like a recipy for dissaster to me. I'd like the junction of power semiconductor devices at 90 deg. C max. Inductors may not even like a temperature of 130 deg. C.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 21, 2018, 09:04:12 pm
content: 130C temp rise plus 45C+ ambient equals ceramic chip caps rising over Curie point, let alone all the other problems you can expect.Unless there is something very special missing (e.g., high temp parts, for mil or downhole application?), this is a trainwreck waiting to happen...Tim

author: mariush
author_rank: Super Contributor
timestamp: May 21, 2018, 09:09:42 pm
content: I heard regular FR4 circuit board goes bad over time if the temperature is above around 100-110c for long periods of time , it carbonizes or the glue inside the fiberglass can go bad etc etc ... apparently that's why on motherboards they tend to have the over temperature threshold on VRMs at around 110c (even though they use mosfets rated for up to 150c)I would also worry about the insulation on the wires inside inductors at such high temperatures.May want to investigate if it's possible to have some kind of heatpipes or something to increase the heat dissipation or to spread it across a wider surface.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 21, 2018, 09:38:29 pm
content: You probably need to go back to the drawing board and try again. If you look at the derating curves for components at those temperatures, they can't handle much. The board will break down. Caps will fail. Resistors will drift or fail. Thermal compound will dry out. Everything will outgas. You'd be surprised at how much heat can be conducted down a heavy copper trace and right inside an electrolytic cap, reducing the life by decades.

author: jbb
author_rank: Super Contributor
timestamp: May 22, 2018, 05:02:01 am
content: I general, you can operate at elevated temperatures if you need to. It there will be a lot of design and testing.If you’re only making small quantities, maybe the engineering effort to save materials cost isn’t worth it. If you really want to run that hot, you can try it.Here’s what to look out for:- parameter shift of hot components (especially switching losses, leakage currents, on voltage drop, magnetic properties)- ageing of hot components- heat flow from hot to cold components through radiation, convesction, air flow, and conduction through legs etc.- connector and fastener failures due to creep and thermal cycling- glue and thermal compound ageing or destruction- keeping PCB temperatures down below 100 C (depends on exact PCB materials, I’m no expert)- ageing of enclosure plastics- dangerous temperatures of exahust air or outside of case- what happens when the fan failsAlso I think your ambient temp might be too low. I generally start with 50 degrees C (I.e. equipment shack in direct sunlight).

author: Miyuki
author_rank: Frequent Contributor
timestamp: May 22, 2018, 08:14:54 am
content: switching loses are calculated for Tvj 150°C, magnetic components are 200°C rated (and have "no aging" according to manufacturer)board can be keep under 100°C as all hot components have leads