Impressive heatsinking - Page 1
Forum section: electronics / general

author: ajb
author_rank: Super Contributor
timestamp: April 08, 2017, 09:38:37 pm
content: My crappy old UPS failed a while ago, and I finally got around to extricating it from the cable spaghetti under my desk to see if it's worth fixing. Inside I found one of the most impressive heatsinks I've ever seen. Shockingly, it actually seems to have been a bit undersized--you might be able to make out a bit of discoloration to the PCB below the transistor, which is actually worse than the photo makes it look. Although the UPS has lasted a few years, so I guess it met or exceeded the design goals...

author: tautech
author_rank: Super Contributor
timestamp: April 08, 2017, 09:42:59 pm
content: Quote from: ajb on April 08, 2017, 09:38:37 pmFunniest today.

author: Brumby
author_rank: Unknown
timestamp: April 09, 2017, 02:18:02 am
content: Ah ... ok.I'm almost inclined to ask "Why bother?" - but it does add some extra surface area for heat dissipation: all four edges.That is a sight I have never seen before.

author: jonovid
author_rank: Super Contributor
timestamp: April 09, 2017, 02:28:45 am
content: extra mass ?

author: Cerebus
author_rank: Super Contributor
timestamp: April 09, 2017, 02:40:08 am
content: The thing that almost dumbfounds me is that the device has a copper tab, which must have needed specifying, and then someone goes and clamps some lower thermal conductivity material to it!

author: t_ryner
author_rank: Regular Contributor
timestamp: April 09, 2017, 03:10:32 am
content: Boss- " OK guys, we need off shave off a few pennies! We don't really need that heat sink, but we need something there or else they'll be suspicious."Worker#1- "Hey boss, what if we just grind off the rest?"Boss- "An excellent idea! You should join the design team!"

author: digsys
author_rank: Unknown
timestamp: April 09, 2017, 03:30:36 am
content: Well, to be fair, it's actually better than a poke in the eye with a stick !!

author: Brumby
author_rank: Unknown
timestamp: April 09, 2017, 03:55:14 am
content: Abracadabra.

author: Cubdriver
author_rank: Unknown
timestamp: April 09, 2017, 05:01:58 am
content: Well, at least they didn't cheap out and make it undersized. It's even with the edge of the transistor!-Pat

author: Cubdriver
author_rank: Unknown
timestamp: April 09, 2017, 05:07:00 am
content: And it has the newest 'nano-fin' technology - what appear to those not in the know to be saw cut sides are actually nano fins that significantly increase the surface area as compared to smoothly finished edges, and thereby markedly increase the device's ability to radiate and cool itself. Luddites!! Embrace this new cutting edge () cooling development!-Pat

author: @rt
author_rank: Super Contributor
timestamp: April 09, 2017, 05:46:10 am
content: Did they use silicon grease?

author: VK5RC
author_rank: Unknown
timestamp: April 09, 2017, 08:40:07 am
content: Absolutely bizarre.Any signs of rework?

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 09, 2017, 08:48:34 am
content: Somebody was bored there

author: dmills
author_rank: Super Contributor
timestamp: April 09, 2017, 01:43:58 pm
content: Think thermal mass not heatsink...Very common in small UPS as the run time is short and very intermittent so you do not need to worry about steady state conditions, just about keeping the peak temperature down until the batteries go flat.That amount of metal probably quadruples the thermal mass, and will be sized to make the junction hit max temperature just after the batteries have failed, if it then takes many minutes to cool back down, well so what?Granted the machining on that ally block leaves a little to be desired.Even APC play this game with their low end stuff which is why grafting more batteries on to a small unit to extend the run time can be a bad plan.Regards, Dan.

author: madires
author_rank: Super Contributor
timestamp: April 09, 2017, 02:29:07 pm
content: That's what the procurement department got for 2.5ct that day at Shenzhen. Someone else got all the larger ones earlier.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 09, 2017, 02:32:39 pm
content: Quote from: dmills on April 09, 2017, 01:43:58 pmYes, I've seen this multiple times in circuits that are intended to only activate for a few seconds. The bit of metal makes the difference if it breaks running 2*Tnom.

author: ajb
author_rank: Super Contributor
timestamp: April 09, 2017, 03:26:11 pm
content: The thing I find most remarkable is that the board actually has a footprint for a *slightly* more substantial heatsink with a solder tab to secure it to the board. You can see the silkscreen outline behind the transistor in the photo. So at some point they decided they could shave off maybe a gram of aluminum as well as whatever it costs to swage a solderable tab onto it, but they couldn't quite get away with nothing at all, so they still wind up paying for the screw and washers and tapped hole and someone to sit there and screw them together. It's an impressively specific cost reduction, but I suppose it makes sense at their production quantities. What do you suppose this saved them per unit?This appears to be the primary switch for the battery charger, so while it's not expected to operate continuously, it would certainly be expected to run for long enough to recharge the battery after a power outage, so in terms of thermal mass we're talking tens of minutes to hours rather than seconds. There's only about a gram of aluminum here. Apparently that was good enough.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2017, 04:21:43 pm
content: they probably ran the calculations, did a test and saw ( on the open bench) the die temperature was over 170C without, and probably 140C with the little block, which is under the magic 150C rating. So the tiny block it is then, saved 2c per unit over the larger heatsink, plus you get 100 more out of the strip of aluminium extrusion, and still get to sell all the swarf as scrap metal again.Remember what the engineers did on the Apollo lunar rover, where they needed to dissipate heat in the motor controllers, but did not have the luxury of mass to add a big heatsink, or any way other than radiation to get rid of it, but during testing they had overheat problems and failed transistors. So all they did was to fill the controller box with paraffin wax, and rely on it melting to absorb the heat of the power devices, and then during the stops there was enough time to have the case radiate the heat away again, and for the wax to solidify again, helped by having a small reflective shield over the box so it did not get exposed to direct sun.Bet if you went to those rovers, put in a new battery pack, whacked all the wheels to shake the vacuum welds apart and tried them they would work, apart from the odometer, which used digital logic and which might still work.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 09, 2017, 04:30:13 pm
content: Quote from: ajb on April 09, 2017, 03:26:11 pmIt probably runs at acceptable temperature charging the battery, but has a problem in the few seconds between mains ok and switchover.During this it has to run at maximum capacity since the inverter is still on.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 09, 2017, 04:32:24 pm
content: Quote from: SeanB on April 09, 2017, 04:21:43 pmOnce anyway. Unless they built the box really well the paraffin wax might well be gone by now. Their shield was designed for the brief sun exposures in orbit and the low angle sun for the carefully selected mission times. That box has gotten really hot and pressurized and then hard frozen every lunar month for 40+ years. Who knows what might have happened.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2017, 05:17:23 pm
content: Electronics probably have mostly survived, aside from failures they found from the Suryeyor 3 sample return program.https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720019081.pdfPretty good reading there.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 09, 2017, 05:47:35 pm
content: Quote from: SeanB on April 09, 2017, 05:17:23 pmYou must have been thinking about marketing today. "Mostly survived".From the referenced document.The returned Surveyor television camera contained over 1500 resistors, capacitors, diodes, and transistors. Some of these components were tested in assembled circuits and as individualcopponents. These tests verified their general integrity after 31 months of lunar expasure. A complete description of the electronic component test program and detail results are presented inreference 1. Surprisingly few of the electronic components failed. It was known that many of the components which were found to have failed, such as the shorted tantalum capacitor in the video amplifiercircuit (described in ref. 1 ), were sensitive to cryogenic cycling.There were some components with cracked glass envelopes, which were the result of thermal stress cracks in the conformal coating. Some of these exhibited malfunction due to internal damage;others were functionally satisfactory. During development tests, this effect was identified and is a material and process problem rather than an electronic component problem.A unique failure in the returned hardware occurred in the shutter drive circuit of the television camera. A failed transistor, which acted as the shutter drive switch, caused the failure ofthe shutter solenoid, and indirectly, damage to stressed before launch by a defective test circuit, functioned satisfactorily during subsequent tests and during Surveyor 3 lunar operations. Theinitial failure probably was caused by a short induced by thermal stress during the lunar night.During the second or subsequent lunar day, a voltage spike from one of several possible sources (see ref. 1) caused the shutter to open and produced an overload on the shutter solenoid coil.The solenoid insulation charred; this reduced the resistance, causing an overload on the transistor and causing it to "open." Subsequent failure of the vidicon is discussed below.Minor shifts in characteristics were observed in some of the electronic components. For example, a platinum resistance thermometer showed a change of 0.4 percent in temperature coefficientof resistivity. However, these changes are i'nsignificant for most applications (see ref. 1).Most of the equipment I repair is was non-functional in spite of the survival of the vast majority of the components. Usually only one, or a few component failures have occurred. A power supply this morning totally non-functioning because of a single open resistor out of perhaps three dozen components. The Surveyor had "several" component failures, including a non-surprising tantalum cap after 31 months of cycling. I wouldn't place long odds on functioning after 31 years in the environment, even if the majority of the components did last.

author: Red Squirrel
author_rank: Super Contributor
timestamp: April 09, 2017, 07:18:33 pm
content: Ok now that is funny. I bet that part is actually suppose to act as a washer for larger heat sinks.

author: Galenbo
author_rank: Super Contributor
timestamp: April 09, 2017, 08:17:33 pm
content: The legal department is satisfied, they can't be sued for not having a heatsink :-)The only real practical use I can imagine is temperature stabilisation, for really-short over-nominal use.

author: vodka
author_rank: Frequent Contributor
timestamp: April 09, 2017, 08:22:37 pm
content: This be seemed to the waste's joke. There are two men that try to taught among them how saving sardines.The first man explains to other that he got a sardine and he rubbed the sardine versus bread. When the other man heared him, he cried: "SQUANDER".The second man shows to other his method: I get a sardine and i aim to sun. After i try to project the sardine's shadow about the bread.