OTC "Silasitc"? - Page 1
Forum section: electronics / beginners

author: ender4171
author_rank: Contributor
timestamp: February 04, 2019, 05:26:49 pm
content: Dave and others often talk about components being tied down with silastic. I have found the OG Dow/Corning 732 stuff, but it is pricey and not available in small quantities (way more than I would use in time without it going bad). Is there anything really special about it other than it is a neutral cure silicone? I was thinking of grabbing some GE Silicone II, which is also neutral cure and is available at any home store in small tubes. Does anyone have experience with that product, or have any recommendations for an alternative that is readily available?

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 05:32:24 pm
content: Ill give you a cookie if you make mechanical mounts for your parts rather then hosing it down in xenomorph juices

author: ender4171
author_rank: Contributor
timestamp: February 04, 2019, 05:41:42 pm
content: Maybe "hold down" was a bad choice of words. This is for vibration mitigation on things like capacitors. Hard mounts would of course be ideal, but they aren't practical for small-medium sized parts, especially when the board is densely populated. I am talking about this sort of thing:

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 05:53:06 pm
content: Quote from: coppercone2 on February 04, 2019, 05:32:24 pmPlease show your 'mechanical mounts' for PCB mounted capacitors, transistors, resistors, inductors...

author: rdl
author_rank: Super Contributor
timestamp: February 04, 2019, 07:12:26 pm
content: I'd never heard the term "silastic" until watching EEVblog. I think it just refers to a type of silicone glue that cures to a rubbery state and is non-corrosive. I'm pretty sure a lot of manufacturers just use hot glue of some kind, which is what I do.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 07:28:50 pm
content: Hot glue is used rarely and usually only in crappy devices. Usual cheap hot glue will not only melt at elevated temperatures, it will also delaminate in a few years at most. And if vibration or freezing temperature is present it may fail almost instantly. What you normally see is RTV silicone adhesive.

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 07:45:19 pm
content: Quote from: wraper on February 04, 2019, 05:53:06 pmyou can make them? what do you want me to , bend some thin aluminum bar stock and take pictures of brackets? amazing technology.here, its photoshoppedyou can also make them smallerand yea the best way to actually secure a transistor is to put a bar on it tensioned with screws from the side.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 08:06:09 pm
content: Quote from: coppercone2 on February 04, 2019, 07:45:19 pmLOL, I'd like to see such abysmal PCB where most of smallish inductors and caps are attached with that crap. FYI silicone adhesive works very well against vibration. It's especially useful for single layer PCBs where solder joints are much more prone to cracking. Also I would like to see how production engineer hires an assassin after you submit such design for assembly. Oh, and I guess people with trypophobia better to not look on that PCB ridden with mounting holes.

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 08:31:31 pm
content: your right about it being considered high quality and high repair ability. Of course they will dislike the design.It's also in the beginners forum.you know you can stamp a big piece of metal to fit over the entire PCB to sandwich everything?If you buy aluminum bar stock you can cut it with bolt cutters, bend it in a vice with a hammer and drill holes, in a few minutes.actually faster then curing shit.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 08:50:25 pm
content: Quote from: coppercone2 on February 04, 2019, 08:31:31 pmNor it will be high quality, nor it will have good repairability. It will be hell to disassemble and assemble back. On the other hand you can simply cut silicone adhesive with a knife and remove the component. Not to say your suggestion would have abysmal effect on size and weight.QuoteThe only way it would somewhat work is if you put pieces of elastic material between it and components. Pressing them down and adding mechanical stress on parts and solder joints. Also it would obstruct airflow this preventing heat dissipation. Adhesive on the other hand fixes components in their natural position after soldering and does not add any stress.IMO you don't know a tiny bit about DFM (design for manufacturability).

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 08:51:42 pm
content: its design for prototyping because its a blog and its the beginners forum.Putting two screws on something is not hell. Having to use a exacto blade is. It's ridiclous.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 04, 2019, 08:55:13 pm
content: Quote from: rdl on February 04, 2019, 07:12:26 pmPlease don't. Once had a PSU manufacter that also considered it a good idea. The stuff would just run out of the vent holes if you put it upside down..

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 08:55:20 pm
content: Quote from: coppercone2 on February 04, 2019, 08:51:42 pmAre you suggesting that if it's beginners section, suggestions should be such that no sane engineer would do that.QuotePutting 2 screws, then multiplied by many tens as minimum. And creating custom fixture for every different component.

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 08:57:58 pm
content: what no sane engineer would do is put silastic in a 1 off.chirst it would be so dirty and if you need to rework it you need to peel fucking glue off of everything.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 09:01:20 pm
content: Quote from: coppercone2 on February 04, 2019, 08:57:58 pmYou don't need to place it on prototype to begin with. It's usually used to prevent damage during transportation. And there is nothing dirty about it. What would be really insane is spending half of your time one making stupid custom fixtures instead of doing what matters.

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 09:04:34 pm
content: half your time? really? are you refining your own aluminum or something?get real. Are you drilling the holes with a sharp stick or are you trying to cut metal with a butter knife here?absolutely preposterous.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 09:07:39 pm
content: Quote from: coppercone2 on February 04, 2019, 09:04:34 pmFeels like logic falling apart when written by you. IMO you should look in the mirror.

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 09:11:29 pm
content: your telling my its going to take long to drill a few holes and bend a piece of metalyeahalf my timequarter of a cigarette break?

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 09:14:25 pm
content: Quote from: coppercone2 on February 04, 2019, 09:11:29 pmYou could solder a whole pcb faster than bending that stupid metal and drilling holes. Also you need to spend a lot of time when designing PCB just to make that those fixtures would fit. Insanity squared. Please show an example of actual PCB with this stupid crap.

author: Nerull
author_rank: Frequent Contributor
timestamp: February 04, 2019, 10:33:12 pm
content: OP never specified this was for a one-off, you seem to have made that detail up in your head.And yes, bolting capacitors to a big piece of metal is moronic. How many expensive custom machined or stamped parts are you going to put on your cheap, one-off board?

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2019, 10:46:25 pm
content: ones that you make with a hammer in 5 minutes?expensive? custom machined? your competing with glue ffs.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 10:51:59 pm
content: Quote from: coppercone2 on February 04, 2019, 10:46:25 pmAnd you call that crap better and more elegant than using silicone adhesive? I ask again, show a photo of PCB where your suggestion is actually realized. And not something like a one huge axial cap bolted down while other components are not on PCB from 70's-80's . Not just products of your imagination.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: February 04, 2019, 10:57:43 pm
content: Someone has had a bad experience with silicone...Only applied where needed it literally takes 5 seconds to sever/remove with a knife or side cutters. If you are doing rework but don't have either of those but you have metal fabrication tools and spare metal, perhaps crafting a blade from scratch would be more time efficient for you than making custom brackets

author: timelessbeing
author_rank: Frequent Contributor
timestamp: February 04, 2019, 11:08:29 pm
content: E6000 is flexible , temperature/chemical resistant and cheaphttps://www.amazon.com/E6000-237032-Craft-Adhesive-Clear/dp/B004BPHQWUMS Polymer is really good stuff, but expensive.https://www.tenaquip.com/product/loctite-teroson-ms-9399-sealant-2081733-af223Automotive gasket maker could be an inexpensive solutionhttps://www.permatex.com/products/gasketing/gasket-makers/permatex-sensor-safe-blue-rtv-silicone-gasket-maker/Exterior sealant might do the trickhttps://www.homedepot.com/p/OSI-QUAD-Advanced-Formula-10-fl-oz-001-White-Window-Door-and-Siding-Sealant-1379506/100186145

author: timelessbeing
author_rank: Frequent Contributor
timestamp: February 04, 2019, 11:14:13 pm
content: This looks like adhesive specific to your applicationhttps://www.rpelectronics.com/1035-85ml-rtv-silicon-clear-adhesive.html

author: westfw
author_rank: Super Contributor
timestamp: February 06, 2019, 07:48:41 am
content: I'd think the GE Silicone II would work OK.For somewhat more flexibility, the crafts industry sells a wide variety of two-part silicone mold-making resins.For example:https://www.amazon.com/Smooth-Silicone-Making-OOMOO-30/dp/B004BNF3TK/https://www.smooth-on.com/product-line/mold-max/

author: stj
author_rank: Super Contributor
timestamp: February 06, 2019, 02:23:39 pm
content: there is a chinese company that specialises in silicone products.705 is a specially usefull one because you can seal windows, leds etc.https://www.ebay.co.uk/itm/302814126123

author: timelessbeing
author_rank: Frequent Contributor
timestamp: February 06, 2019, 09:39:40 pm
content: There's also this stuffAvailable for cheap from the usual suspects.It's thermally conductive which is good if you need to spread the heat around. (But it cures firm like adhesive.)

author: Gary350z
author_rank: Regular Contributor
timestamp: February 07, 2019, 10:01:20 am
content: Quote from: rdl on February 04, 2019, 07:12:26 pmSilastic (a portmanteau of 'silicone' and 'plastic') is a trademark registered in 1948 by Dow Corning Corporation for flexible, inert silicone elastomer.https://en.wikipedia.org/wiki/SilasticWhere I used to work, everyone called it RTV (room temperature vulcanizing).If I recall correctly, I have heard that as it cures it gives of ammonia(?) which corrodes copper. I don't know if this is true or not.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: February 07, 2019, 10:28:07 am
content: Just to clear this up: Dave is Australian, and the term 'Silastic' is, as detailed, a trade name of Dow Corning, but is used in Australia as a generic term for any sealant goop (Viz: Hoover, Doona, Graviner etc.)BT

author: graeme.c.payne
author_rank: Newbie
timestamp: February 07, 2019, 02:46:35 pm
content: My memory is that "Silastic" was (is?) an early brand name for some silicone adhesives. (USA)For electronics, silicones are widely used for hording parts in place, vibration damping, and encapsulating parts or assemblies.For use in electronics, the silicone must NOT create any acid while curing. If it smells like vinegar at any time, don't use it! It will eventually cause corrosion. A silicone adhesive safe for electronics WILL cost more than what the home center carries, because it is a specialty product.An example of a suitable product is this, from Amazon (USA): GC ELECTRONICS 19-155 ADHESIVE, SILICONE, TUBE, 3FL.OZ.(US) (1 piece)https://www.amazon.com/dp/B004SPJN6K/ref=cm_sw_r_cp_apa_i_ZnexCb4WZPT1XSent using Tapatalk

author: LukeW
author_rank: Frequent Contributor
timestamp: February 10, 2019, 12:18:46 am
content: Generally, when choosing a material like this, these are the factors we're interested in:- Neutral-cure silicone. A lot of hardware-store 1-pack silicones are acetoxysilane based which will release acetic acid in the curing reaction, which will corrode nearby things - you don't want this, you really want a neutral-cure silicone. This is probably the most important thing, and if you can buy a neutral-cure Home Depot silicone for a couple of bucks it's probably fine.- One-pack, because it's more convenient than mixing a binary system.- RTV (room-temperature vulcanising), i.e. it chemically sets and crosslinks by itself at room temperature, going hard with the desired shore and mechanical properties.- Has some "bounce", which is the main motivation for choosing a silicone over a polyurethane.- Cheap and locally available for you in a non-bulk pack.- High dielectric strength, although if you're not using it for HV applications anything is probably fine.Personally, I like Dow Corning 738, which is available in a small tube.It's actually documented as an engineering material - it has a datasheet, and if we want to know, say, the dielectric strength, it's documented.https://www.ellsworth.com/products/by-manufacturer/dow/sealants/silicone/dow-738-electrical-sealant-silicone-white-90-ml-tube/

author: xavier60
author_rank: Super Contributor
timestamp: February 16, 2019, 09:40:14 pm
content: Quote from: ender4171 on February 04, 2019, 05:26:49 pmI have been using ThreeBond(Japan) 1530C for years. It is moisture curing and non corrosive. Because it self levels, it gives a neat result.The product isn't easily available in Australia. It is now available on ebay in retail blister pack. Be certain to read the review.https://www.ebay.com/p/2-Pcs-Tube-Tb1530c-All-Purpose-Adhesive-Glue-Clear-Extra-Strong-Wood-Elasticity/18024574076?iid=173609103986

author: djacobow
author_rank: Super Contributor
timestamp: February 17, 2019, 01:24:46 am
content: What do you guys think of zip ties for caps? Just put a few extra holes in the PCB design and feed the tie around the back. Seems like it would work nicely for elcos on their sides. Maybe with some silpat or other foam to provide tension.

author: stj
author_rank: Super Contributor
timestamp: February 17, 2019, 05:28:22 am
content: that's not new, it was common in the 70's, 80;s etc when linear psu's had bigger caps.

author: coppercone2
author_rank: Super Contributor
timestamp: February 17, 2019, 02:26:01 pm
content: Quote from: djacobow on February 17, 2019, 01:24:46 amits better then goo

author: timelessbeing
author_rank: Frequent Contributor
timestamp: February 18, 2019, 01:02:45 am
content: I think goo helps dissipate heat from caps

author: stj
author_rank: Super Contributor
timestamp: February 18, 2019, 01:29:05 am
content: Quote from: timelessbeing on February 18, 2019, 01:02:45 amso does putting ceramic caps in parallel with them to remove high frequency noise the electrolytic cant deal with.(another old trick from the 70's)

author: timelessbeing
author_rank: Frequent Contributor
timestamp: February 18, 2019, 01:36:33 am
content: I thought ripple current causes them to heat up.

author: stj
author_rank: Super Contributor
timestamp: February 18, 2019, 01:49:37 am
content: they heat because the esr is not low enough to react in time to fast ripple.these days we have low esr caps for that - back then you put several in parallel along with some ceramics.

author: jc101
author_rank: Frequent Contributor
timestamp: February 19, 2019, 02:27:37 pm
content: I use Dow Corning (now DOWSIL) 744, it was designed to be safe on electronics etc.

author: xavier60
author_rank: Super Contributor
timestamp: November 26, 2019, 11:26:05 pm
content: Quote from: xavier60 on February 16, 2019, 09:40:14 pmI have just received my first order for 2X 150g tubes from this Japanese online store.https://global.rakuten.com/en/store/marunishi-online/item/3552896/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 27, 2019, 02:21:33 am
content: Hmm, shopping between Digikey and MG Chemicals, isn't easy, but this seems a likely candidate... if pricey.https://www.digikey.com/product-detail/en/mg-chemicals/RTV162-300ML/473-1203-ND/1972157The thermal conductivity is specified, though with some kind of bastard unit that can't be written correctly. If it's what I think they mean, it's close to 0.21 W/(m K) which isn't bad as adhesives go (comparable to say, FR-4).Also RTV102 and 103 (black) I guess; cheaper.This is cheaper, but poor thermal conductivity (average as sealants go),https://www.digikey.com/product-detail/en/mg-chemicals/1035-85ML/473-1370-ND/1972170probably comparable to the Dow 738 and similar, listed above.https://www.digikey.com/product-detail/en/chip-quik-inc/NCS10W/NCS10W-ND/9836748too,Can't seem to find anything harder. These are pretty flexible (Shore A 20-30ish?). Saw one Shore D something. Would be nice to have options for more rigidity, like for glopping between electrolytic capacitors.Probably the kind of thing you need to old fashioned read catalogs or phone up the manufacturer to select products..Tim

author: xavier60
author_rank: Super Contributor
timestamp: November 27, 2019, 02:46:31 am
content: It's difficult to find common products that are flowable, transparent and non-corrosive.This product is easier to re-enter,https://www.permatex.com/products/adhesives-sealants/sealants/permatex-flowable-silicone-windshield-glass-sealer/Like with most Permatex products, the tube cap is programmed to fall apart so that one is likely to find spoiled contents the next time it is needed.