PCB & environmental problems

[luke67]

HI! I developped an analogic filtering PCB composed by resistor, capacitors (4 of them electrolitics) and operational amplifiers. I have to put it inside an incubator whith 90% humididty, 5% CO2 and temperature 37 °C. Do you know if and how they can affect environment and vicecersa ? Do you have any scientific articles to suggest ?
THX!

 

[CocaCola]

The datasheets of the components will give you an idea on any adverse effects, but the humidity alone suggest that the PC board should be potted or sealed in an airtight box to avoid corrosion... Common household silicone (100% silicone, not the latex stuff) caulk will even work... You could even use a rubberized spray on sealer, there is one being sold in the As Seen On TV racks now, it's just a rubberized spray, give the board a few coats... And of course you can do a traditional epoxy potting but that is sometimes more hassle for the DIYer vs brushing on silicone...

 

[GreenGiant]

the temperature shouldn't affect it but the 90% humidity might cause problems, especially if you are going to be opening that chamber at temp and humidity, the temperature change down to room temp (about 23C) will cause condensation and with the high humidity it will not allow the evaporation of that water back into the chamber so this could cause shorts and corrosion.

I would recommend putting the board outside of the chamber if possible, or if not, put it in a water tight box, or if that's not possible try to cut costs and seal the boards in epoxy and if something goes wrong just toss it and get another.

 

[luke67]

I am going to sterilize this board cause thei well in contact with cells. Do you have any idea how to sterilize PCB ? THX

 

[GreenGiant]

I am going to sterilize this board cause thei well in contact with cells. Do you have any idea how to sterilize PCB ? THX

For that you should be able to use a large enough autoclave (depening on pressure and temperature, but a relatively low pressure one should be fine as most parts can handle being put through 100C +/- 10 degrees), or you can use non-corrosive chemicals like some alcohols or something (this depends on what the board is made out of though so be wary)

 

[CocaCola]

For that you should be able to use a large enough autoclave (depening on pressure and temperature, but a relatively low pressure one should be fine as most parts can handle being put through 100C +/- 10 degrees), or you can use non-corrosive chemicals like some alcohols or something (this depends on what the board is made out of though so be wary)

Autoclaves (steam and chem) push 130C or more during the normal sterilization process, many parts should be OK but you might experiences issues, especially if the sterilization is repeated numerous times...

If sterilization is going to be necessary, I highly recommend entirely potting in silicone block to protect the components from either the chemicals used for sterilization or to protect them from the high pressure steam that will get into everything and turn back to water when cooled...

Personally I would be looking to get the PCB out of the sterilized and harsh environment...

 

[luke67]

Notice that PCB have Silver Finishing and Copper 35 um on FR4 1,6 mm.
Do you think is still necessary coating ? If yes, the spray will be enough to coat 95% humidity ? I have bought this one :
http://docs-europe.electrocomponents.com/webdocs/0d82/0900766b80d82552.pdf
http://docs-europe.electrocomponents.com/webdocs/001e/0900766b8001e116.pdf
What do you think about it ?

And should I spray it only on IC components and/or passive components and/or solder parts and/or whole PCB ? THX!

 

[luke67]

Any new advices ?
THX

 

[CocaCola]

It might be enough or it might not... Oxidation is a funny thing, hard to predict exactly what the humidity will do without actually testing...

 

[luke67]

so the only solution to be SURE that pcb won't oxydate is using sylicon, right ? If yes, only solder parts or also active/passive components ? THX

 

[duke37]

Dissimilar metals in contact will have an electrochemical potential between them. If there is an electrolyte, there will be a current and corrosion will occur.

The problem is much more severe when external voltages are present which will promote rapid corrosion. This can be seen in battery connections.

The only way of stopping the corrosion is to get rid of the electrolyte, either by keeping the circuit dry or coating with a water repellant coating with a perfect seal.

I use Waxoyl which is sold for undersealing cars to prevent corrosion on electric fencer units, it can be removed with paraffin or white spirit.

 

[luke67]

should I spray it on the whole pcb or only on electrolyte parts ? Consider that the pcb will be placed in a 95% humidity room. Do you think that the spray will be enough ?

 

[luke67]

one other information : the pcb has 30 gold pins spaced 5 mm one each other. If a water drop link two of them a short circuit is made and this MUST'NT happe. Do you think that between them spray will be enough or is better use silicon in order to cover empty spaces between them and avoid drop formation ?
THX

 

[duke37]

Silicon is no good since it is a solid.

Silicone sealers come in two types, one type gives off acetic acid which will promote corrosion.

Wax will give good protection at room temperature and the acrylic up to 50C. Epoxies may be able to withstand slightly over 100C.

All metal surfaces must be coated or current will flow through the electrolyte and corrosion will occur.