Why so many types of glues used in securing electronic components ? - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: July 08, 2015, 09:44:40 am
content: My latest purchase is a switching adjustable bench power supply 3-15 Volt 25 Amps, branded as Teleconcepts, the real manufacturer is Manson modeled SPS-8250.Its quite similar to Dave's bench psu Manson 9400 40A 3-15V (branded as Powertech) in his tear down video EEVblog #272, though mine has lower power and has different layout as Dave's uses bigger transformers/inductors.Everything works perfectly, its just I want to replace the noisy & crappy sleeve bearing 8 cm fan with much better quality fan like Sanyo Denki which I own.Inside the psu, I noticed there are so many types of glues used, and for sure they're not saving pennies like using only one type of glue for all.I guess its a good thing, but is it necessary to use different glue for different types of objects ?Like why don't they just use the white one for the big electrolytic caps ?Examples ...The white one used in inductors or capacitors, while the dirty yucky brown type at two big Capxon caps..... or the plastic case feets which is the same brown type as above for holding the Capxon caps...... or hot glue for securing the main on/off switch to the plastic front panel....... or red ones for all screws holding the pcb, and also the nuts for the two big main output banana connectors ...

author: dmills
author_rank: Super Contributor
timestamp: July 08, 2015, 10:14:35 am
content: The white stuff is a silicone which could probably have been used on the caps as well, but note that the PCB will quite possibly have been stuffed in a different plant from the one doing the final assembly, and the PCB assembly house will have its own standard glues for things like the caps.Note you need the non acid cure variety, ordinary bathroom caulk emits acidic vapours as it cures and tends to rot surrounding electronics.The red stuff on the screws is thread locking compound, a very thin liquid that sets in the absence of oxygen, the canonical ones are made by locktite but there are plenty of vendors (and differing strengths).The stuff under that cap, and also on the foot mounting looks like some kind of epoxy to me, silicone would actually have been a better choice here...Finally there seems to be some hot melt on the switch (the stuff is almost pointless), again silicone would have been a superior choice, I am thinking a 'QC' fix for a switch that was not snapping into the cutout correctly.Epoxy, silicone & thread locker, seems like a fairly standard set of electronics adhesives to me (I am ignoring the hotmelt crap).Incidentally, my response to seeing a CapXon cap in anything is to replace it with a real capacitor, because you will have to sooner rather then later anyway...Regards, Dan.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 08, 2015, 10:19:49 am
content: Is the red stuff on the screws more of a tamper detection thing?

author: mariush
author_rank: Super Contributor
timestamp: July 08, 2015, 10:21:22 am
content: The white stuff is a silicone based solution, somewhat elastic, the purpose is to prevent vibrations by holding parts fixed in place. It's not conductive so it can also act like an insulator. It's more expensive and harder to apply in thin layer (or small quantity) compared to glue.I'm not sure about how well this silicone stuff handles heat (see below, it may not be suited to go through wave soldering machine)The brownish stuff is a plain glue, it's used to glue bigger parts to the board so that when the board goes on assembly line or through a reflow oven, the parts will stay in place. Basically, boards move from point to point on a line which can introduce a bit of shaking or vibrations which can kick out large capacitors if their leads are precut.When the board goes through wave soldering machine, it's first hit by a wave of liquid or foam flux which washes the whole bottom of the board, preparing it for soldering. Then, the board goes over a wave of liquid solder which sticks to where it needs to be. The pressure of the flux wave and the solder wave (and the liquid flux vapors that happen when solder burns the flux) can shake large parts enough to pull them out of holes, hence the need for glue.See this video for a good example:The red stuff is thread locker. It's a liquid when applied which quickly turns into hard stuff that has a very high resistance to twisting. Basically, it's meant to prevent screws from unscrewing themselves due to vibrations and other things (heat/cold cycles etc). I guess it's more expensive than glue or that silicone solution, but it's designed for this purpose.The only bad stuff of these three is the regular glue, which I guess is also the cheapest. Depending on formula used, it can be bad for electronics. In the past, there was such a glue that was whitish when new but turned yellow/brown as it dried up due to heat inside devices and also became conductive. The glue then caused shorts and other problems (acts like wire with some resistance between points)

author: krish2487
author_rank: Frequent Contributor
timestamp: July 08, 2015, 12:39:24 pm
content: One reason for the "red stuff" is that it is not as glue but a QC check.During the mechanical assembly stage, the red compound is applied to mark that, that particular screw/bolt has been tightened and inspected.The little amount of threadlocker shown in the pics is not sufficient to lock any thread, if used as a glue. Also, The thread lockers are used is between threads of the nut / bolt.In the pics, the thread locker has no business being applied to a pcb mounting screw.It is not used as a glue, it is a inspection mark.

author: amyk
author_rank: Super Contributor
timestamp: July 08, 2015, 01:13:13 pm
content: That looks like an ATX power supply, although with a heatsink added to the input rectifier. Can it really do 375W continuous?

author: BravoV
author_rank: Super Contributor
timestamp: July 09, 2015, 02:27:04 am
content: Thanks a lot for the replies and insights, really appreciate it and learned something valuable here, even though its just a glue.Quote from: dmills on July 08, 2015, 10:14:35 amMy mentor which was an old tv repair man, taught me to use a nail polishfor the same purpose either locking a trimmer setting or just a seal, which looks almost identical to a genuine Locktite if its an opaque red one.Quote from: dmills on July 08, 2015, 10:14:35 amMy thought as well, maybe the switch was wiggling without that glue holding it.Quote from: dmills on July 08, 2015, 10:14:35 amYep, don't worry, the CRAPxon caps will be replaced once I found the same sized good quality Japanese low esr caps.Luckily since its a new old stock, it looks like the output caps are still in a good condition, verified n tested with a load (car's lamp) up to about 13 V at 22 Amp, and measured the voltage output ripple with a scope and still within the manufacturer's specification.As attached below photo, the three output caps pointed by red arrow will be replaced for sure, and the good part is the main output cap (the right one) is well ventilated as it stands right in front of the exhaust fan (detached in the photo), that it self will prolong it's working life.

author: BravoV
author_rank: Super Contributor
timestamp: July 09, 2015, 02:30:07 am
content: Quote from: mariush on July 08, 2015, 10:21:22 amCool video, thanks, I can imagine the big thru hole components like caps will be wiggled n juggled around if they're not secured properly before entering the solder chamber.

author: BravoV
author_rank: Super Contributor
timestamp: July 09, 2015, 02:41:34 am
content: Quote from: krish2487 on July 08, 2015, 12:39:24 pmMakes sense, thanks.Quote from: amyk on July 08, 2015, 01:13:13 pmThat heatsink is for the Power Factor Correction mosfet, yes, it does deliver n perform as specification, tested with car's lamp as load up to about 23 A, just watch Dave's tear down video EEVblog #272, its has identical quality build, its just mine has lower Amp model.https://youtu.be/bX8IIjf15qYJust google for Manson SPS-8250 service manual that has the complete circuit for this psu, though I'm not an expert of switching psu, I believe its better than an ordinary cheap PC psu, heck, sometimes those cheapies don't even have a proper PFC built in.EDIT : Service manual incl circuit ->http://www.pegasusmodels.co.uk/downloads/MAASSPS9400.pdf

author: Votality
author_rank: Contributor
timestamp: July 09, 2015, 04:31:29 am
content: Quote from: B.B.Bubby on July 08, 2015, 10:19:49 amNo its not for security its to stop them coming undone.

author: jwm_
author_rank: Frequent Contributor
timestamp: July 09, 2015, 05:48:53 am
content: Quote from: BravoV on July 09, 2015, 02:27:04 amThey have very different qualities, nail polish will harden when exposed to air, because it has a volatile compound (likely acetone) that evaporates and leaves the hard polish behind.Thread locking compound remains a liquid (of very low viscosity so it creeps into cracks) until it gets somewhere that no air can reach it while it is touching a metal and only then does it harden. so it will seep in between the threads of your screws until it gets into places air can't get then lock up tight. The reaction with the metal forms a very strong bond, usually you have to drill out screws on which permanent thread lock has been used.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 09, 2015, 05:58:21 am
content: Quote from: mariush on July 08, 2015, 10:21:22 amNo. Thread locker is applied to the THREADS, not externally on the head or nut.That application of lacquer on the head/nut is for "tamper detection".It has nothing to do with thread locking as it is quite brittle and easily broken.

author: Votality
author_rank: Contributor
timestamp: July 09, 2015, 08:54:51 am
content: Quote from: Richard Crowley on July 09, 2015, 05:58:21 amIm not sure it is, its just lazy application of a threadlocker. Its on the screws holding the pcb down. By the time the case is off and the components have been exposed it has been well and truly able to be tampered with. Its just to stop the screws coming out in shipping. They use peel off warranty stickers for tamper detection.

author: Gary.M
author_rank: Regular Contributor
timestamp: July 09, 2015, 10:19:10 am
content: It's acetone based lacquer used to vibration proof screws trimmers etc. RS sell it. It smells and act just like nail polish. Threadlocker, such as loctite, does on the threads and sets in the presence of traces of moisture I believe (in the air) not by reaction with metal.

author: amyk
author_rank: Super Contributor
timestamp: July 09, 2015, 02:10:30 pm
content: Quote from: BravoV on July 09, 2015, 02:41:34 amIt has a PFC stage at the input but after that it's a pretty standard TL494 half-bridge. No wonder it looks like a PC PSU, although it does use more different types of glues than one...

author: jwm_
author_rank: Frequent Contributor
timestamp: July 09, 2015, 07:55:31 pm
content: Quote from: Gary.M on July 09, 2015, 10:19:10 amNo, you are thinking of cyanoacrylates (super glue). thread locker sets anaerobically, without air and is triggered by electrochemical reactions with metal. It creates very strong metal/metal bonds when they are really tightly pressed against each other but doesn't bond that well to itself, so the very thin layer that leeches into the threads goes a long way and the residue doesn't seem that strong because it cured slowly in air, not bound to metal.It also has interesting viscosity properties being thixotropic. It is pretty odd stuff, sort of an accidental weird perfect trifecta for threadlocking and not much else.some quotes from the wikiQuote

author: Gary.M
author_rank: Regular Contributor
timestamp: July 09, 2015, 10:20:40 pm
content: Thanks jwm_ for that detail. :-)

author: DanielS
author_rank: Frequent Contributor
timestamp: July 10, 2015, 04:25:25 pm
content: Quote from: dmills on July 08, 2015, 10:14:35 amI have some 10-15 years old power supplies with Fuhjyyu primary side capacitors in them and have not had to replace any of those yet. Most of them have seen at least five years of 24/7 operation.On the secondary side though, I am surprised when I see Chinese-branded caps last more than two or three years.