Electronics that survive cleaning & sterilisation - Page 1
Forum section: electronics / general

author: cdwijs
author_rank: Regular Contributor
timestamp: January 29, 2016, 08:15:48 am
content: Hi All,I would like to build electronics that can survive cleaning. As I never attempted this before, I have no idea what I'm getting myself into. I think I run into the following problems:1)Heat. The cleaning process uses temperatures up to 100 ^C. I think the micro controller, transistors, resistors and the PCB itself can deal with that, as long as they don't dissipate heat themselves.2)The fluid. This is a problem, electronics cannot deal with that. Therefore I guess the circuit board has to be potted. I can imagine the potting agent causes problems, it has to be water tight, and the hole package has to be capable to withstand the hot-cold cycle. Also it has to withstand the cleaning agent.Is this possible? What potting agent should I use? What about connectors?Kind regards,Cedric

author: pickle9000
author_rank: Super Contributor
timestamp: January 29, 2016, 09:03:49 am
content: And don't forget dissipating heat generated by the circuit.

author: babysitter
author_rank: Frequent Contributor
timestamp: January 29, 2016, 09:19:24 am
content: For cleaning, you have to select materials accordingly.Does the device have to be re-sterilized or only once?You might consider ethylene oxide sterilisation which is much cooler than autoclave sterilisation, and also just has a mild vacuum.I got some electronics thru two cycles of sterilisation.Talk to your potential sterilisation partner for details.BRBabysitter.

author: Jeroen3
author_rank: Super Contributor
timestamp: January 31, 2016, 03:26:11 pm
content: 1) Read up on the datasheet of any flash memory you have. The data retention changes with temperature. And might reduce if you cycle it often. (or program after the heat)2) You can wash a lot of components. Those that do not often say so in the datasheet. Such as switches and relays that are not sealed, potentiometers and adjustable caps.Here you see them washing the pcb in a dishwasher.

author: _Andrew_
author_rank: Regular Contributor
timestamp: January 31, 2016, 04:53:41 pm
content: Depends on the extent of cleaning and sterilisation you require.Vacuum steam autoclaves for medical purposes are not nessaseraly considered a complete sterilisation process in them selves and aggressive chemical cleaning solutions in hot washing processes are often used first these days as steam will not nessaseraly deactivate prions. The whole process these days is often along the lines the item is loaded in to an automated washing process that cycles though washing, chemical disinfection, rinse then drying process which takes about an hour with temperatures culminating in excess of 100C. The system then automatically feeds the items in to a cleanroom environment where they are packaged in to autoclave bags in a sterile environment and loaded in to the vacuum autoclaves for thermal steam processing at temperatures typically around of 134C. The items then come out of the whole process in there sealed sterile packages. Plastics that can survive the cycle time of the basic vacuum steam autoclaves often can have major problems with this multiple stage process as they spend extended periods at high temperatures. The chemical cleaning process can cause havoc with mechanical assemblies that require lubrication as the chemicals will stripp any lubricant from all serfaces and then this is compounded by not being able to re-apply lubricant before going in to the autoclave because the lubricant can not be used in the clean room environment.Gas plasma is another method for sterilisation of sensitive materials. If I remember the process correctly a vacuum is formed in the chamber, then hydrogen peroxide is atomised into the chamber then the vapour cloud is excited with rf energy in to a gas plasma state. This creates UV photons and radicals that bombard the serfaces and break down organic deposits. One of the things that makes this process attractive to electronics is the 60 degree celsius cycle temperature. Coloured anodised aluminium can have problems with this process as the dyes used are often organic so the colour can fade with repeated cycles. It is still a new technology but it is finding more and more acceptance as an alternative. Research organisations making space probes / landers / rovers have been using this process in sterilisation prior to launch to help avoid contaminating there research experiments with earth born contaminants.If the device is completely sealed within a enclosure that can withstand the use if NuCidex this may be an option. This is a Peracetic acid solution. This stuff has to be used in fume hoods.Again if the the device is sealed and the enclosure can handle it Perasafe may be also an option. This is supplied as a dry powder which is then mixed with water to make an activated hydrogen peroxide solution.If the gas plasma was not exotic enough there is also irradiation.

author: wraper
author_rank: Unknown
timestamp: January 31, 2016, 05:08:27 pm
content: Quote from: blueskull on January 29, 2016, 08:25:57 amCompletely wrong. In most cases data in the FRAM do not survive high temperatures well. Only some ICs with FRAM are specified that data will survive soldering process. Others usually explicitly state it won't. As of FLASH, unless it is MLC, they are close to the EEPROM.http://www.ti.com/lit/ml/szzt014a/szzt014a.pdf

author: PedroDaGr8
author_rank: Super Contributor
timestamp: January 31, 2016, 06:05:21 pm
content: Quote from: _Andrew_ on January 31, 2016, 04:53:41 pmPlasma cleaning is a very interesting technology, but it also isn't always that compatible with aluminum alloys containing magnesium. I just watched a talk on it the other day. Apparently, it works really well at stripping the magnesium out of an alloy, especially if you are using an oxygen based plasma. There are others, like water-plasma cleaning seems to help combat this a bit. Still it was a really cool technology for cleaning very complex parts. You could strip straight oil off of the surfaces.

author: Jeroen3
author_rank: Super Contributor
timestamp: January 31, 2016, 07:12:21 pm
content: I don't know much about irradiation but a lot of things undergo that, judging from the trucks going in and out. And their website confirms it.Medical tools, foods, vitamin drinks, cosmetics and packaging, toys, documents for preservation and packaging with or without medicine.How do electronics hold up to this?

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: April 10, 2017, 02:48:43 pm
content: Quote from: Jeroen3 on January 31, 2016, 03:26:11 pmWe were talking about this PCB cleaning in another thread, but strangely it has gone.It was a note to say that this is not any ordinary dishwasher but something similar to this:https://blundell.co.uk/product/system-2000-aqueous-pcb-cleaning-machine/We use one similar, and part of the wash cycle is done at 90degC.

author: grumpydoc
author_rank: Super Contributor
timestamp: April 10, 2017, 03:09:54 pm
content: Ethylene oxide is commonly used for sterilisation.