RTV to attach RF coil - Page 1
Forum section: electronics / projects

author: steaky1212
author_rank: Regular Contributor
timestamp: April 28, 2014, 11:30:56 am
content: Hi,I'm looking at using an RTV silicone adhesive to attach an RFID coil (38mm diameter coil made with enamelled wire).The PCB is to be mounted vertically and may be subjected to physical shocks. I don't want to use hot melt as it lacks compliance and I have found it to fail after a year of so.There are no other electronic components or traces nearby so it is just between solder resist and and enamelled wire, so I don't know if I would need one that doesn't produce acetic acid.People have suggested using Dow Corning 3145 but it's a bit expensive for me. I've had a look at ACC silicone's AS1700 as that seems like it should be suitable.What are peoples thoughts??Thanks,StephenEDIT:Also, do I need to add any features to the PCB to improve adhesion? I cant add holes to it, as its just a single sided design. But I can add cross hatching etc.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 28, 2014, 05:33:27 pm
content: I realize you're not in the US, but there are several tubes of the Dow Corning stuff on ebay for like $15. Maybe you could contact them and ask for international shipment? Maybe 20 USD all in?http://www.ebay.com/itm/221345291087

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 28, 2014, 05:39:25 pm
content: I've used RTV one electronics before, but I've never stopped to think too much about the acid's effects.You maybe have already seen this, but this seems like a good discussion:http://yarchive.net/electr/silicone_sealant_corrosiveness.htmlSpecifically..."GE Contractor Bath/Plumbing products, GE6040 (clear) and GE6070 (white) are specifically formulated to be non-corrosive to metals."

author: calexanian
author_rank: Super Contributor
timestamp: April 28, 2014, 07:08:45 pm
content: RFID is generally low enough in frequency that regular Silastic (Silicone goop from the hardware store) used in a couple of small dabs will not really effect anything. I say just go for it with whatever you have around. Avoid filled epoxies as in the case of JB weld it is metal filled. Standard clear or white silicone is pretty standard faire in electronics. We use GE silicone II here. Also locktite PolySeal. Both seem to work as well as the fancy stuff.

author: wraper
author_rank: Unknown
timestamp: April 28, 2014, 07:40:45 pm
content: ACC SILICONES:AS1745G, AS1745T paste, higher hardness.AS1723 liquid, flows over the board and have lower hardness. They are specially made for electronics.

author: SeanB
author_rank: Super Contributor
timestamp: April 28, 2014, 07:55:26 pm
content: Anything that does not smell like vinegar will work, just use some appropriate solvent ( IPA, thinners or even ethyl alcohol 90%) to clean and degrease the surfaces before application. If you want make a thin plastic housing ( thin strip of PVC bent around and glued or heat welded to make a hoop just larger than the coil and a small amount higher than it) to use as a former to make it look neater when you fill with the silicone. That way you can fill it with the silicone and use a plastic card to wipe the top flat do it looks like a round block on the board.

author: fcb
author_rank: Super Contributor
timestamp: April 28, 2014, 08:19:22 pm
content: I've used Dow Corning 732 (available in tubes from Rapid) - never had a problem with it.

author: calexanian
author_rank: Super Contributor
timestamp: April 28, 2014, 09:35:27 pm
content: We have found that the acid really does not do that much. We have been using it in field for over 20 years and have never had a failure from it. The old wire varnish was a different matter. The new enamels and olefyn coatings don't seen to be bothered by it.

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 29, 2014, 12:12:57 pm
content: I remember years ago a colleague siliconed some components on a PC board and immediatelly placed it in a sealed optics compartment with some intricate machined gears and levers. He opened it up a couple of days later and almost every steel component had a thin layer of corrosion due to the acetic acid solvent. We switched to alchohol based silicone and no corrosion problem or vinegar smell anymore. The alchohol based silicone was a Dow Corning product but I can't remember the number.