How to affix parts like electrolytics etc. on PCB? Which "Goop" to use? - Page 1
Forum section: electronics / repair

author: nightfire
author_rank: Frequent Contributor
timestamp: June 01, 2022, 11:35:44 am
content: Sorry if this topic has been discussed to death- in this case, please point me towards the threads ;-)Situation and general question: When working on some PCB, swapping things out like recapping or changing bigger components, usually these are affixed by the manufacturer with some kind of goop.In more modern ATX powersupplies I have seen some white stuff with the consistency of silicone mass, but I would suspect that it is something more specialized than that.Question here: What is used to affix components like big axial filter caps to the PCB and prevent vibration etc.?(Bonus points for stuff I can get here in germany...)

author: wraper
author_rank: Unknown
timestamp: June 01, 2022, 11:47:36 am
content: Neutral RTV silicone, preferably one intended for electronics. For small quantities it's better to buy Chinese silicones with 70x naming. Like 704. Depending on number you get different viscosity, from liquid to such that does not flow. Stuff from Western sources usually comes in large tubes and is quite expensive. Unless you use a lot of it, it will go bad way before you can spend a significant part of it.https://www.aliexpress.com/item/1005001845626018.html?gatewayAdapt=glo2idnAlso I suggest storing it in a moisture barrier bag with a large pouch of silica gel desiccant. Will prevent it from spoiling and clogging the nozzle.

author: voltsandjolts
author_rank: Unknown
timestamp: June 01, 2022, 11:54:40 am
content: Search for forum for RTV, lots of discussion...https://www.eevblog.com/forum/manufacture/which-glue-to-secure-wires-soldered-into-pth-holes/

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 01, 2022, 07:03:50 pm
content: Ok, so I'm going to say it then.In the typical electronics world we are discussing here, where is the evidence that standard RTV (acid based) actually DOES cause damage to PCB's within its otherwise expected lifetime?

author: wraper
author_rank: Unknown
timestamp: June 01, 2022, 07:11:07 pm
content: Quote from: Audiorepair on June 01, 2022, 07:03:50 pmIt causes damage because when it's curing it releases acetic acid. All you need to do is applying acetoxy RTV silicone on a bare copper, then on a next day remove the cured silicone and look on a nice green corrosion on the copper.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 01, 2022, 07:37:03 pm
content: Yes, but most PCBs we are discussing here do not have bare copper.That's not the evidence I am looking for.

author: wraper
author_rank: Unknown
timestamp: June 01, 2022, 07:43:51 pm
content: Quote from: Audiorepair on June 01, 2022, 07:37:03 pmSo you must be sure that solder resist won't pass any of that acid and that silicone won't touch any metal surfaces directly. While with first YMMV, with second it's almost impossible if you do any significant number of applications. Also why would you use something that you certainly know is corrosive when you can buy a usual neutral cure silicone for almost the same price? Not to say even if silicone does not directly touch any electronics, applying acetic acid fumes onto electronics during curing process is certainly not welcome.

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2022, 07:44:21 pm
content: I use RTV silicone caulk with no problems. Perpendicular to the leads' long axis and/or between tops of cans so they don't wiggle so bad with vibration, on bigger caps.Popular silicone sealant formulations off-gas acetic acid during cure. In open air, it's there for a 1/2-few hours i.e. on top of solder mask- so I've never seen a problem.But a PC board sealed inside a small enclosure, with poor circulation- I've seen corrosion of tin, copper etc. Potting boards I've done and not noticed any corrosion people speak of. Newer formulations are milder for odor and off-gassing.There are also silicone sealants "neutral cure" that instead off-gas alcohol during curing.LikePermatex Ultra Blue or Black RTV gasket makerand many others for automotive use where the acetic acid can damage sensors.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 01, 2022, 07:51:20 pm
content: Quote from: wraper on June 01, 2022, 07:43:51 pmOk, but that does not constitute any evidence that it actually causes damage, that seems to be hearsay.

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2022, 08:00:49 pm
content: Just put some silicone sealant on bare copper, to debunk or not.I agree in that I haven't seen bad effects - but formulations are milder nowadays and the real industrial silicone sealants like GE and DOW are much stronger than hardware store "kitchen and bath" caulk offerings.The only time I saw corrosion was applying industrial silicone sealant to an enclosure/keypad and then bolting the enclosure shut. So of course the gasses got to stay forever circulating inside and dulled the finish on PC board component leads and headers etc.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 01, 2022, 08:20:43 pm
content: So, popular opinions states that RTV is bad because it coats the board with acetic acid and eats it, and probably stays there to eat it more.Whereas, it maybe has some slight contact with the PCB at first, but mostly just outgasses til its gone?Where is the evidence?

author: BrokenYugo
author_rank: Super Contributor
timestamp: June 01, 2022, 08:31:52 pm
content: The evidence is fairly simple chemistry and the agreed upon concept that corrosion and electronics mix poorly.Plus the stuff reeks of acetic acid when curing, that alone is enough to get me to avoid it.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 01, 2022, 08:38:00 pm
content: Yet again, that does not constitute evidence.Where is what happens in the real world, not what you think will happen?

author: madires
author_rank: Super Contributor
timestamp: June 01, 2022, 08:42:28 pm
content: Quote from: nightfire on June 01, 2022, 11:35:44 amGo to the next best hardware store, look for 'Bausilikon' (construction silicone) and make sure it's 'neutralvernetzend' (neutral cure).

author: WattsThat
author_rank: Frequent Contributor
timestamp: June 01, 2022, 09:30:46 pm
content: Quote from: Audiorepair on June 01, 2022, 07:03:50 pmWhere’s your evidence that acetic acid is NOT corrosive?People presented their real world experiences. You’re under no obligation to accept what is said. Don’t agree? Then do your own research. Evidence, shemevidence…

author: nightfire
author_rank: Frequent Contributor
timestamp: June 01, 2022, 09:42:50 pm
content: Ok, to sum it up a bit, what I have read here and researched with some of the above keywords:- Basically some silicone is used- Type of silicone used should NOT be of the type that releases acetic acid whilst drying (therefore: Neutral type)- Preferrably there should also no other stuff be inside, like anti-fungus biocides that could vape over the next few months whilst operating- Due to the non-acetic emissions, the desired types of silicone are marketed as fit for automotive use "sensor friendly" (With the additional benefit of being high-temp certified)Guess I will head tomorrow to the next DIY-market and look for a small tube of the stuff- no need and want to buy a big cartouche of 310ml and the press for it...And for reference to other peoples that look for the same stuff:RTV: "Raum Temperatur Vernetzend" -> Will do the magic stuff at room temperatureThere are 3 Types of silicone:- Acetat-Systeme (Essigsäure-vernetzend bzw. sauer- oder Acetat-vernetzend)- Alkoxy-Systeme (neutral-vernetzend)- Oxim-Systeme (neutral-vernetzend)-> So basically some Alkoxy or Oxim based stuff should be used, if referenced.I am looking currently at a small tube of 80ml of Loctite 5910, that smiles at me- if I find nothing at the DIY-market tomorrow, I know what will be my companion for the next dance ;-)

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 01, 2022, 09:48:12 pm
content: Quote from: WattsThat on June 01, 2022, 09:30:46 pmNo, they HAVENT presented their real world experiences, they have just repeated what they have heard.Where is the actual evidence to support their assumptions?That acetic acid is corrosive is not the argument.That acetic acid released by application of silicon MUST therefore damage a PCB does not logically make sense, without data to show it does.

author: xavier60
author_rank: Super Contributor
timestamp: June 01, 2022, 11:16:25 pm
content: This is my other go-to sealant/adhesive,https://threebond-europe.com/products/tb1530c/I often apply it under components.Although it's silicon based, the uncured liquid product doesn't interfere much with soldering as Silastic does.

author: thm_w
author_rank: Super Contributor
timestamp: June 02, 2022, 01:39:56 am
content: Quote from: Audiorepair on June 01, 2022, 09:48:12 pmYes the whole electronics and solar industry use neutral cure silicone, solely due to hearsay.Is acetoxy cure going to immediately destroy the PCB you put it on? No its not that corrosive.Is acetic acid going to coat and sit on the board continuing to corrode it? No, it willevaporateif its not in an airtight compartment.Is it probably fine for non-critical applications, with large robust through hole parts, that won't be affected by a small amount of corrosion? Sure.Does it make sense to use it, when the cost difference is minimal, knowing that sensitive electronics and small SMD components can be very susceptible to corrosion? No.For me in Canada, a whole tube of acetoxy silicone (MONO kitchen and bath) is $10, or a tube of neutral cure (MONO Pro) is $13.From experience, acetoxy goes bad faster, and you won't realize its actually gone bad. It just will stay sticky, which is a huge pain in the ass.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: June 02, 2022, 02:09:37 am
content: Quote from: Audiorepair on June 01, 2022, 09:48:12 pmFound the anti-vaxxer.

author: Haenk
author_rank: Super Contributor
timestamp: June 02, 2022, 07:33:29 am
content: What a silly argument.You - of course - would not find corrosion caused by silicone, because it just isn't used anywhere (besides your bathroom), due to possible corrosion it can cause.The wicked thing about corrosion is, that it damages things over time. I have seen damages done by old foam or old soldering (flux) - breaking things after decades. No one ever thought about "do not use this foam, it will decompose and break things" back then. But the industry learned (a bit).

author: wraper
author_rank: Unknown
timestamp: June 02, 2022, 10:41:06 am
content: Quote from: Audiorepair on June 01, 2022, 09:48:12 pm1. I personally tested that acetoxy silicone causes severe corrosion on copper and aluminum.2. Component leads of square cross section often have exposed bare copper on their sides.3. Although I did not personally test if tin is resistant to acetic acid, tin plating is far from ideal. It's extremely thin in most cases and has pores in it. Therefore cannot provide a decent protection from corrosion.4. Leads which are solder dipped have thicker layer of tin, however alloy also contains copper. And from information I found online, acetic acid leaches copper from lead free alloys.https://bioresourcesbioprocessing.springeropen.com/articles/10.1186/s40643-017-0173-5

author: nightfire
author_rank: Frequent Contributor
timestamp: June 02, 2022, 01:31:43 pm
content: Just ordered some Loctite SI5660 (1718240 ) - will report how it plays out...https://www.henkel-adhesives.com/de/en/product/gasketing-sealants/loctite_si_5660.html

author: SeanB
author_rank: Super Contributor
timestamp: June 02, 2022, 02:26:58 pm
content: I have been having success with mirror mounting silicone, which does not degrade the thin aluminium layer in a mirror, and which is neutral cure. Bostik Mirror silicone, same price as the regular silicone at around $4 for a 90ml tube, which does go a long way with using only small amounts at a time. Does take longer to cure, in thick layers a few days, but minimal smell and it does skin over in a few hours, plus you only need small amounts anyway.

author: bill_c
author_rank: Regular Contributor
timestamp: June 03, 2022, 02:26:19 am
content: http://www.irvblog.com/foretravel%20projects/RTV-and-Electronics/I'm not going to waste time searching my pictures for the dozen or so devices that I have fixed or trashed due to RTV silicone use and the corrosion it caused.

author: David_AVD
author_rank: Super Contributor
timestamp: June 03, 2022, 02:49:31 am
content: Is neutral cure silicone really that hard to buy outside of Australia? Over here it's cheap, readily available and pretty much the default.

author: nightfire
author_rank: Frequent Contributor
timestamp: June 03, 2022, 07:50:18 am
content: Here in germany the vinegar/acetic type is quite the default, especially when you want to use that for your bathtub ;-)To make that worse, on the packaging it is mostly not clearly indicated which type of silicone is contained.

author: wraper
author_rank: Unknown
timestamp: June 03, 2022, 08:09:48 am
content: Quote from: nightfire on June 03, 2022, 07:50:18 amI see plenty of neutral silicone in hardware stores. If it is not clearly marked as neutral, you can be 95% sure it's acetoxy. Although I would use neither since last few years I buy 70x silicones from China which are intended specially for electronics and have dielectric specs. Frankly I like them better than specialized electronics stuff from ACC silicones (now CHT) which I purchased previously in large tubes. Their AS1723 was fine. But I also needed black silicone, not transparent. So I bought AS1821. I wonder how they still manage to sell it, as it's a pure junk. It's acetone cure type, and it does not harden properly if applied in thin layer, like 1mm (it's a viscous liquid). If you just smear it in <0.5mm layer, it will not cure at all and will remain a sticky goo forever. First I thought a got a bad batch. Then after a while purchased another tube from different batch and it was just as bad. You may say just apply it in thicker layer, but there always will be some thin trails left somewhere which remain a sticky mess forever. Datasheet says nothing about this. You would expect something better at this pricehttps://lv.farnell.com/acc-silicones/as1821/silicone-sealant-non-corrosive/dp/1776157?st=as18As of their AS1701 which is not flowing, I simply do not like it. It does not self level it's surface at all and has too thick consistency, therefore looks very lumpy. Also if you don not really push it onto the part, it won't attach well.

author: madires
author_rank: Super Contributor
timestamp: June 03, 2022, 11:47:42 am
content: Quote from: nightfire on June 03, 2022, 07:50:18 amSanitärsilikon (sanitary silcone, acetic) <-> Bausilikon (construction silicone, neutral cure)

author: voltsandjolts
author_rank: Unknown
timestamp: June 03, 2022, 01:02:08 pm
content: Quote from: wraper on June 03, 2022, 08:09:48 amAny more feedback on those?Not too thin/runny? Stay in a 'glob'?What's the curing time (for real, I don't trust Chinese specs)?Clear and white would be my preferred choice.

author: wraper
author_rank: Unknown
timestamp: June 03, 2022, 01:39:42 pm
content: Quote from: voltsandjolts on June 03, 2022, 01:02:08 pmIt depends on which you buy. Those are basically standard types made by various manufacturers. Same number can come in different colors. I attached info which I found in the past but 702 and 708 are missing. Aliexpress listings often have descriptions of properties.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 03, 2022, 04:32:19 pm
content: I have good experiences with AS1701, easy to apply, sticks well and doesn't droop that much. Sometimes it might be a bit stringy and because it sticks so well it's hard to cleanup, but that's application practice I guess.https://nl.farnell.com/acc-silicones/as1701-310ml/sealant-silicone-neutral-cure/dp/8497524

author: voltsandjolts
author_rank: Unknown
timestamp: June 03, 2022, 05:05:46 pm
content: Thanks wraper, that picture shows thegoopinessviscosity nicely.Seems like neutral-cure "electronics" RTV available in the UK is way more expensive than plain neutral-cure RTV.I sense some marketing BS going on there...I really don't care about dielectric properties for wire and cap glue.

author: james_s
author_rank: Super Contributor
timestamp: June 03, 2022, 05:17:15 pm
content: Quote from: Audiorepair on June 01, 2022, 08:20:43 pmI personally have never had ordinary clear RTV cause any damage, however this is one of those things where "your mileage may vary".For personal stuff I wouldn't hesitate to use it, although I would not seal something inside a box until it had fully cured. For a product I was selling or some valuable high end gear I would use the "sensor safe" stuff that isn't acidic.

author: nightfire
author_rank: Frequent Contributor
timestamp: June 03, 2022, 09:34:41 pm
content: Quote from: voltsandjolts on June 03, 2022, 05:05:46 pmLets say, this is one area where a "your mileage may vary" is ok for a personal project, or maybe some el cheapo chinese stuff where the manufacturer would not be traced and held liable in case of failure.But in high-end components, especially in sensitive areas, that may be regulated for safety reasons, a responsible company likes to produce a big papertrail including lots of factors like isolation parameters etc. to get some idea if leakage currents might be something to take into account, or in applications that involve high-frequency components if the goop affects some of the characteristics there...

author: thm_w
author_rank: Super Contributor
timestamp: June 03, 2022, 10:04:11 pm
content: Quote from: nightfire on June 03, 2022, 07:50:18 amYeah usually the package is not extremely clear, but if you read the fine print or look up the MSDS you can figure it out.One hint is if the same brand has two or three version of clear silicone, the cheapest will be the acetoxy.

author: inse
author_rank: Super Contributor
timestamp: June 04, 2022, 06:16:33 am
content: @HaenkI wonder whether the 'industry' will ever learn to skip this stupid soft touch surface finish that turns sticky after time.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: June 04, 2022, 01:55:38 pm
content: Are there any cons to using glue gun glue for components that do not get hot?A lot of Chinese made products I have encountered over the years of repairing PCs use regular glue gun glue to hold parts down.Glue gun glue dissolves in alcohol so can be released by using IPA or Meths (denatured alcohol).

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 04, 2022, 02:50:45 pm
content: Standard semi-clear Glue for glue guns will melt in an automotive enviroment.However hi-temp glue type will not and does not outgas.(At least none I have used)I usually use GOOP from ACE hardware.Jeff

author: wraper
author_rank: Unknown
timestamp: June 04, 2022, 07:03:49 pm
content: Quote from: paul_g_787 on June 04, 2022, 01:55:38 pmIt comes off after a while. Especially in cold environment. Don't expect it holding for more than a year or two. Silicone will hold basically forever with no noticeable degradation.

author: David_AVD
author_rank: Super Contributor
timestamp: June 04, 2022, 10:57:04 pm
content: I've seen hot melt glue when repairing gear over the last 25 years. Sometimes it's still holding firm, but other times it's long since let go of whatever it was supposed to be holding together.Maybe it was the exact type of hot melt glue used, the types of surfaces it was bonding to, or it could have been a residue / contamination issue that caused it to fail.The glue gone brittle / corrosive issue still seems to be a thing today in mass produced products. Maybe the manufacturers know but just don't care. Maybe they count on it to stop the item from being in service for too long (for their sales purposes).

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 04, 2022, 11:10:48 pm
content: Hot melt glue only sticks to a few things.Silicone sticks to just about everything.The corrosive/conductive glue problem is a totally separate issue, not to be confused with the above.Only the manufacturers use this stuff.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 04, 2022, 11:22:31 pm
content: Quote from: David_AVD on June 03, 2022, 02:49:31 amThat is pretty much the point I was going to make---"Roofing silicon sealant" is advertised as "neutral cure".If they are worried about corrosion damage to Zincalume, I would definitely be wary of using the other stuff on PCBs.Most people have a few old commercially made boards around, if anyone wanted to test the effects of the other stuff.

author: tooki
author_rank: Super Contributor
timestamp: June 04, 2022, 11:34:58 pm
content: Quote from: David_AVD on June 04, 2022, 10:57:04 pmQuote from: Audiorepair on June 04, 2022, 11:10:48 pmThere isn’t justonetype of hot melt glue! Household hot melt glue isn’t designed for everything, and the fairly low temperatures they use inhibit adhesion on some surfaces. There are industrial hot melt glues that use much higher temperatures, and with different formulations for different applications. Combined with proper surface preparation (the step many people neglect to do when using adhesives of any kind), they’ll hold well in the long run. (There are also industrial hot melt glues with especially low melting points for delicate substrates.)

author: james_s
author_rank: Super Contributor
timestamp: June 05, 2022, 06:23:33 pm
content: Quote from: Audiorepair on June 04, 2022, 11:10:48 pmI have to wonder why they still use that stuff, I was repairing CRT monitors 25 years ago and regularly had to scrap off adhesive that had turned brown and conductive. I still occasionally encounter that stuff in the present time.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: June 16, 2022, 03:39:07 pm
content: Quote from: wraper on June 04, 2022, 07:03:49 pmOK that is good to know!I remember when working at a local school about 10 years ago about 75% of the PC front panels were held on with hot glue. But the kids used to pull them off again so frequently I guess it never had time to degrade.

author: reboots
author_rank: Regular Contributor
timestamp: June 16, 2022, 04:55:38 pm
content: Typical hot melt glue sold for hobby or crafting purposes is not an adhesive, but a type of low-melting-point thermoplastic. The hardened "glue" has a different coefficient of thermal expansion from other materials; when applied to plastics or metals without a lot of surface texture it will tend to release after enough thermal cycling, sometimes fairly quickly. Epoxies such as J-B Weld can have the same problem when used on plastics.I only use hot glue in situations where it can flow under adjacent features for support.Seconding floobydust's recommendation forPermatex Ultra Black, if you need something you can buy from an automotive or hardware store.

author: nightfire
author_rank: Frequent Contributor
timestamp: June 16, 2022, 08:29:30 pm
content: Quote from: nightfire on June 02, 2022, 01:31:43 pmOk, so I received some small tube, and tested it on a piece of plastic bag first, before I am sure that i have finally all my capacitors at my current restauration project in order...Result: Nice smell, a bit chemical, but not very strong. Not very fluid, but due to the stickyness quite well to dose, and i guess that when affixing bigger axial caps, you should first put the goop on the pcb, then place the cap and solder.After hardening out (needs a few hours) nice and solid, firm attaching to the plastic ground. Needed some force to get pulled away.