(Solved)What's the emissivity of plastic chip package and aluminum heatsink? - Page 1
Forum section: electronics / general

author: sam1275
author_rank: Frequent Contributor
timestamp: February 02, 2017, 08:43:53 am
content: Hello.What's the emissivity for plastic chip package, and black aluminum heatsink?Thanks.

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 04:44:15 pm
content: Sam,If you Google for emissivity tables or even download a FLIR /Fluke camera instruction manual you will find a nice list of differing materials and their emissivities. As you know, getting the correct emissivity setting is important to accurate measurements.You can also determine a pretty close emissivity value for an unknown material by measuring the surface temperature with a decent contact thermonmeter and adjusting the camera emissivity until its temperature measurement of the surface tallies with the contact thermometer reading.You can also apply PVC ielectrical insulation tape to a surface and set the emissivity for that material when needing a known emissivity for measurements. PVC tape is normally listed in the emissivity tales I mentioned.An IC plastic case will likely be just an emissivity for ABS or ''rigid plastic'Remember the colour of a surface means little at renal wavelengths. A light paint can emit at the same level as a darker paint etc.The Heatsink emissivity varies massively depending upon whether ir is plain shiny, anodised, painted or oxidised. The emissivity tables show the different settings foe different aluminium surface finishes. Painted just uses the emissivity for cellulose, acrylic or enamel paint usually.Best WishesFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 04:47:59 pm
content: Sam,Here you go, a comprehensive Emissivity table for you.http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdfFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 04:53:03 pm
content: And another.........http://www.scigiene.com/pdfs/428_InfraredThermometerEmissivitytablesrev.pdfJust search for emissivity tableA plastic IC case will be 0.95.Aluminium can vary depending upon coating. It is worth comparing a thermometer measured reading with that of the camera to check you have a reasonable emissivity setting. You could do this at room temperature and when the heatsink is hot.Always remember that a thermal camera has a measurement to,erance of PLUS/ MINUS 2C or 2% plus any emissivity, reflected energy and atmospheric error. A super accurate absolute temperature tool it is not !Fraser

author: sam1275
author_rank: Frequent Contributor
timestamp: February 02, 2017, 04:56:12 pm
content: Thank you very much Fraser.I was troubleshooting a home router that auto-reboots under heavy load, I suspected heat issue, so I added a heatsink, but still not solved. So I'm pretty sure it's a software problem. (I have 2 different routers using the same SOC and same version of OpenWRT, both are affected, so there's no way for the hardware to be defected.)This is the first time I actually use my thermal camera to diagnostic electronic stuff, I start the adventure of thermal camera just because I was amazed by it's picture, from the first time saw it, that looks like a device only in sci-fi movie.

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 05:02:15 pm
content: Ahhh, for that sort of measurement any emissivity in the range 0.90 to 0.98 will usually be OK provided the heatsink is black anodised or painted. Shiny heatsink are a nightmare ! The nominal Emissivity for everyday tasks is 0.96 as such is goof enough for many measurements that do not require the best possible accuracy.Take a look at the emissivity tables though. You will a vast range of different emissivities depending upon the material and surface condition.Fraser

author: sam1275
author_rank: Frequent Contributor
timestamp: February 02, 2017, 05:10:40 pm
content: Quote from: Fraser on February 02, 2017, 05:02:15 pmYes, I actually checked that more than one time before, I just trying to make sure...I usually set the emissivity to 1, because I found it's too difficult to calibrate it, if a surface emissivity is too low that even reflect like a mirror on TIC, you have to consider the object it's reflecting...I think mine is black anodized because it show no sign of reflection through thermal camera, and it show a high temperture. The chipset package read 70C without heatsink, and about 60C with heatsink(direct reading with emissivity set to 1)

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 05:14:00 pm
content: Those are hot chips. Is there a datasheet spec for max temperature ?Fraser

author: sam1275
author_rank: Frequent Contributor
timestamp: February 02, 2017, 05:26:32 pm
content: Quote from: Fraser on February 02, 2017, 05:14:00 pmI just searched one for my RT3050:http://www.datasheetspdf.com/datasheet/download.php?id=785624It says TJmax is 125C, maybe that's why there's no heatsink on all devices using that SOC.