thermal imaging array cooling - Page 1
Forum section: electronics / general

author: ir.ukrm
author_rank: Contributor
timestamp: December 08, 2020, 04:39:11 am
content: I have a thermal imager in which the matrix has tilted away from the lens array, who knows if it was thermal paste or some kind of glue?

author: bap2703
author_rank: Regular Contributor
timestamp: December 08, 2020, 11:13:09 am
content: I am not sure what we are seeing there.Is that grey rectangle your sensor's window stripped of it's AR coating?

author: Fraser
author_rank: Super Contributor
timestamp: December 08, 2020, 11:31:20 am
content: This looks like a BAE core ?You need to consider how the core is constructed and that will tell you whether a thermally conductive paste or adhesive is required. The microbolometer was clearly pressed up against the metal lens chassis and there are mounting screws that would presumably hold the PCB’s in position. I would expect the microbolometer PCB to be held securely in position by some form of physical retainer such as a compression bracket. If such is used then the microbolometer to metal chassis interface will be either dry or will have a thin layer of non-migratory thermal paste applied (NOT Silicone based as Silicone grease migrates!) If the microbolometer has no retaining bracket then it may have been fixed to the chassis with a thermal adhesive but this is poor practice as it exposes the microbolometers fragile pins to flexing from the weight of the PCB. Relying on an adhesive is generally to be avoided.I would expect this microbolometer to have been dry mounted or just a thin Smear of NON-silicone based thermal grease to have been used. On the chassis to microbolometer interface. The microbolometer should be secured in position up against the chassis surface by a retaining ‘web’ that applies constant light pressure via springs. Such a method applies adequate pressure to the assembly but does not impose unacceptable forces on the microbolometer pins.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: December 08, 2020, 11:46:38 am
content: Well it looks like I am wrong about a retaining bracket for the microbolometerI have just checked my pictures of the BAE SCC500 that I dismantled and there is no retaining bracket on the microbolometer PCB. The microbolometer does indeed appear to have been glued to the lens chassisI am really surprised to see this on a BAE core !It would appear that you will need to source a good quality thermally conductive adhesive that is thin enough to permit a good close bond to the lens chassis but will not migrate onto the microbolometer window during the assembly process. I regret that I have no knowledge of what was originally used or a good replacement. Some research is recommended. I suggest looking at the 3M site for ideas. You will be looking for heat sink adhesives.Another option that I like is the tape used to attach heat sinks to aluminium LED PCB’s. 3M make it and it is basically thermally conductive double sided tape. It has the advantage of no migration during use (not messy) and the two parts can be separated later if required.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: December 08, 2020, 11:53:39 am
content: Some thermally conductive adhesive tapes......http://www.farnell.com/datasheets/2162773.pdfhttps://amecthermasol.co.uk/product/?cat=thermal-materials&family=thermal-adhesive-tapes&gclid=Cj0KCQiA5bz-BRD-ARIsABjT4nhW58NKHNr-EDp_Dnww8nYXuCoktxDL9ytAlBQlp5cdTUhAZdj55AgaAg2XEALw_wcBhttps://www.digikey.co.uk/en/product-highlight/3/3m/8810-thermally-conductive-adhesive-transfer-tapes?utm_adgroup=General&utm_source=google&utm_medium=cpc&utm_campaign=Dynamic%20Search_EN_Product&utm_term=&productid=&gclid=Cj0KCQiA5bz-BRD-ARIsABjT4nhPJ38-2kGxaJlGnFkLJGb4yNWvwPRShNiR5aiOM5yiOtxDeZnHqhEaAveaEALw_wcBhttps://www.mouser.co.uk/new/3m/3m-thermally-conductive-tapes/They can be expensive but eBay sellers often sell smaller quantities. You want the double sided tape and not double sided pads that are used as gap fillers.The Chinese suppliers may have a 3M equivalent at a better price.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: December 08, 2020, 12:07:40 pm
content: Further study of my BAE SC500 core pictures suggests that there MAY be screw fixings holding the microbolometer assembly to the lens chassis. See attached pictures. This is what I would have expected to see. Can you show us how your core was originally assembled with all brackets in place ?Fraser

author: Fraser
author_rank: Super Contributor
timestamp: December 08, 2020, 12:36:25 pm
content: At last I have just realised what I am looking at in your picture ! Sorry, my brain is a bit fuzzy today !OK, here is what you have .........The microbolometer would normally have a mounting bracket attached to it and this is used to secure it to the lens assembly. The mounting bracket is fixed to the microbolometer with an adhesive. The bracket is not intended to be removable so a permanent adhesive or tape is used. In your picture we can see the microbolometer mounting bracket but it is still attached to the lens chassis by its two screws ! The mounting bracket has broken away from the microbolometerSo now that I know what I am looking at, I can confirm that a suitable permanent adhesive is required to refit the microbolometer mounting bracket on the microbolometer. Does it need to be thermally conductive adhesive ? As the microbolometer contains a Peltier element based die temperature stabiliser, yes, I believe a thermally conductive adhesive or tape should be used in case the mounting bracket and metal lens chassis are part of the heat sink design.In the pictures that I showed of the SCC500 you can see the tip of the mounting brackets screw ‘arms’ secured with the black screws passing through the lens chassis.Fraser