EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Laval on April 21, 2024, 01:36:38 pm
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Hello everyone,
I got a Keithley 2015, a friend of mine who works at the university sold it to me for very cheap. I recapped the boards and replaced a couple of oxidized connectors and it work great. The smoke screen over the display is in very bad condition though. It had stickers on it and someone tried to remove them using acetone (I assume) which completely ruined the acrylic. I got a replacement part (from eBay) and I removed the old one. It is fairly easy using a simple spudger. I'm just not sure what kind of glue to buy to put the new one in place. The glue on the old part is not a hard curing glue. It's sticky and rubbery a bit like silicon. It ca be scraped off for the most part and makes little sticky balls when removed. The residue can be cleaned up with IPA or mineral spirit. Anyone know what kind of glue it could be ?
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What you describe sounds like a very soft, sticky, hot melt glue. Some synonyms are "snot glue, credit card glue, fugitive glue." The first two I have seen more commonly. Hot melts are often easily removed, but not dissolved by IPA.
Do you know the plastic type? If acrylic (or similar), I would recommend against any instant glue (cyanoacrylate, CA), even the fumeless variety. I would also recommend against anything with MEK/acetone/aromatic hydrocarbons as its solvent. A water-based glue, like carpenters glue will seem to hold, but peel strength is very low.
That leaves a neutral curing adhesive like electronic grade silicone or polyurethane. Both are hard to remove, so snot glue would be a top choice of mine to replicate your observations, but I have never done that repair. (IPA will help remove silicone but not as easily as it does with hot melts.)
EDIT: There are some so-called plastic safe CA glues, but I have no experience with them. They harden and are not like what you describe.
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Not that I am recommending super glue (cyanoacrylate) but FWIW I have used that around displays but then placed a fan nearby to draw the fumes away from the display so that the fumes don't attack the display bezel. It doesn't need a lot of air flow, just enough so that the fumes can't collect and settle around the display.
Another word of note, SG fumes can also built up on conductive surfaces and prevent them from making contact with other conductive surfaces, such as on keyboards or when two circuit boards are pressed together. It can also probably prevent IC and other sockets from making contact. Using a fan seems to prevent any problems, BUT it's probably safer to use some sort of hot melt glue or electrical grade RTV if you have a choice.
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What you describe sounds like a very soft, sticky, hot melt glue. Some synonyms are "snot glue, credit card glue, fugitive glue." The first two I have seen more commonly. Hot melts are often easily removed, but not dissolved by IPA.
Do you know the plastic type? If acrylic (or similar), I would recommend against any instant glue (cyanoacrylate, CA), even the fumeless variety. I would also recommend against anything with MEK/acetone/aromatic hydrocarbons as its solvent. A water-based glue, like carpenters glue will seem to hold, but peel strength is very low.
That leaves a neutral curing adhesive like electronic grade silicone or polyurethane. Both are hard to remove, so snot glue would be a top choice of mine to replicate your observations, but I have never done that repair. (IPA will help remove silicone but not as easily as it does with hot melts.)
EDIT: There are some so-called plastic safe CA glues, but I have no experience with them. They harden and are not like what you describe.
Yes, I don't want to use a hard glue like cyanoacrylate because I want to be able to remove it later should it need to be replaced again.
The smoke screen is made of acrylic and the front panel on which it was glued is made of ABS.
Thank you for the post, I'll look for some snot glue (that one makes me laugh :-DD) but it's a good description. I wouldn't say it is easily dissolved by IPA, there was very little residue left on the ABS panel which I removed with IPA but it doesn't work as well on the acrylic screen (not that I need to remove the glue on it, just testing).
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If you have not used IPA to remove hot melt from a hard surface, try it. It's like magic as it has just the right properties to wick under the hot melt and break the bond. I usually use 91% or 99%; some people use a lower percentage. Rather than having to pick little pieces, it comes off cleanly in big chunks.
EDIT: Also IPA is generally safe does not cause cracking on ABS.
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Hot melts will be easier to apply and faster than the alternative RTVs, but they will also work, and particularly if you have prior experience or stock on hand might be a good choice.
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I think I will make a mask that will let uncovered only a few mm exposed around the screen and apply glue with a small bristle brush then remove the mask. It's a bit convoluted but it will be safer for me. I was looking on Amazon for some glue and I found this
https://www.amazon.ca/Quick-Dry-Tacky-Glue-Dries/dp/B0BQCYQ5G4/ref=sr_1_4?sr=8-4 (https://www.amazon.ca/Quick-Dry-Tacky-Glue-Dries/dp/B0BQCYQ5G4/ref=sr_1_4?sr=8-4)
Would this be fine ?
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Would not strips of double stick tape work ?
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Always check the MSDS/SDS (attached): https://www.dick-blick.com/msds/DBH_SDS_238841104.pdf (https://www.dick-blick.com/msds/DBH_SDS_238841104.pdf)
It's just a modified PVA (polyvinyl alcohol) glue. That's the same basic adhesive as in carpenters white/yellow glue.
EDIT: The MSDS's I could find don't don't say what's in it. It could be modified PVA.
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Would not strips of double stick tape work ?
Yes, it would probably do as long as the tape isn't too thick.
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Always check the MSDS/SDS (attached): https://www.dick-blick.com/msds/DBH_SDS_238841104.pdf (https://www.dick-blick.com/msds/DBH_SDS_238841104.pdf)
It's just a modified PVA (polyvinyl alcohol) glue. That's the same basic adhesive as in carpenters white/yellow glue.
Would it be possible to remove the screen later on if necessary ?
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See my edit. It might work.
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I would not use any glue. Use a high quality, thin double-stick tape. Most likely that is what the original adhesive was, too. (If it rolls up without evidence of a backing tape, then it was the kind of tape that is comprised only of adhesive, with a plastic or wax paper carrier backing.) You apply the tape, with carrier, to the window, press it hard to stick well, trim any excess, then peel off the carrier and apply the window to the frame. I use that kind of stuff all the time in projects.
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I would not use any glue. Use a high quality, thin double-stick tape. Most likely that is what the original adhesive was, too. (If it rolls up without evidence of a backing tape, then it was the kind of tape that is comprised only of adhesive, with a plastic or wax paper carrier backing.) You apply the tape, with carrier, to the window, press it hard to stick well, trim any excess, then peel off the carrier and apply the window to the frame. I use that kind of stuff all the time in projects.
That's very interesting and it makes sense. Would you have an example or a term to help search for a product. There is so many kind of double side sticky tape.
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That's very interesting and it makes sense. Would you have an example or a term to help search for a product. There is so many kind of double side sticky tape.
That’s an understatement!
This one from 3M, 9471, is designed specifically for plastics: https://www.digikey.ch/en/products/detail/3m/9471LE-5-X60YD/8567506 (https://www.digikey.ch/en/products/detail/3m/9471LE-5-X60YD/8567506)
Without doing crazy research, it looks like it’d be suitable, though I can’t rule out the existence of a slightly more optimal model.
These tapes, the ones without a backing tape, 3M calls “adhesive transfer tapes”, and as you can see on DigiKey, they make a TON of different versions.
With that said, I’ve had good luck with whatever no-name stuff (with thin backing) I got at the art supply store 20 years ago, and with the various ones, with and without backing, at work. (One at work is, I think, 3M 465.) For most things it’s probably not that critical.
The other double-stick tape I love (but is much too thick for this application) is the 3M VHB 4910 (1.0mm thick) and 4905 (0.5mm thick), which are no-backing, clear acrylic “gel” tapes. These adhere well, but can be removed from nonporous materials without damage. I first encountered it when working at the Apple Store, where they used it for sticking all of the (extremely expensive) acrylic sign holders to the tables, as well as anything else that needed to be glued down. But when it was time to remove it, you’d just work a putty knife under it and it would let go without damaging the wood tabletops.
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3M 9088 is also excellent for such use cases
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Thank you very much for the references. It will make things easier.
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TRY 3M 467MP Adhesive Transfer Tape - sounds like what was used originally.
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With that said, I’ve had good luck with whatever no-name stuff (with thin backing) I got at the art supply store 20 years ago, and with the various ones, with and without backing, at work. (One at work is, I think, 3M 465.) For most things it’s probably not that critical.
FWIW, the one I used most recently at work (I just went digging in storage to find whatever we had) is 3M 965. It’s probably not what I’d recommend buying, since it’s optimized for high temperature and resistance to jet fuel. 😂
One of the ones optimized for plastics would likely be a better choice.
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TRY 3M 467MP Adhesive Transfer Tape - sounds like what was used originally.
Not a bad choice, but the 9471 I suggested above is better for plastic-on-plastic, as it supports more types of plastics than 467.
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https://www.3m.com/3M/en_US/bonding-and-assembly-us/double-sided-tape/thin-bonding-tape/ (https://www.3m.com/3M/en_US/bonding-and-assembly-us/double-sided-tape/thin-bonding-tape/)
That page has the overviews of the major adhesive types 3M offers for adhesive transfer tapes and double-sided tapes. There’s a PDF for each adhesive, and lists of the different products using each.