How to affix parts like electrolytics etc. on PCB? Which "Goop" to use?

[nightfire]

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...)

[wraper]

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=glo2idn
Also 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.

[voltsandjolts]

Search for forum for RTV, lots of discussion...

https://www.eevblog.com/forum/manufacture/which-glue-to-secure-wires-soldered-into-pth-holes/

[Audiorepair]

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?

[wraper]

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?

It 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.

[Audiorepair]

Yes, but most PCBs we are discussing here do not have bare copper.

That's not the evidence I am looking for.

[wraper]

Yes, but most PCBs we are discussing here do not have bare copper.

That's not the evidence I am looking for.

So 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.

[floobydust]

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.
Like Permatex Ultra Blue or Black RTV gasket maker and many others for automotive use where the acetic acid can damage sensors.

[Audiorepair]

Yes, but most PCBs we are discussing here do not have bare copper.

That's not the evidence I am looking for.

So 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.

Ok, but that does not constitute any evidence that it actually causes damage, that seems to be hearsay.

[floobydust]

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.

[Audiorepair]

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?

[BrokenYugo]

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.

[Audiorepair]

Yet again, that does not constitute evidence.

Where is what happens in the real world, not what you think will happen?

[madires]

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...)

Go to the next best hardware store, look for 'Bausilikon' (construction silicone) and make sure it's 'neutralvernetzend' (neutral cure).

[WattsThat]

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?

Where’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…

[nightfire]

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 temperature

There 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 ;-)

[Audiorepair]

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?

Where’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…

No, 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.

[xavier60]

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.

[thm_w]

No, 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.

Yes 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 will evaporate if 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.

[Geoff-AU]

No, 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.

Found the anti-vaxxer.

[Haenk]

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).

[wraper]

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?

Where’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…

No, 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.

1. 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

[nightfire]

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

[SeanB]

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.

[bill_c]

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.