About the glue used in layer-laminated products and many modern phones/tablets - Page 1
Forum section: electronics / general

author: derGoldstein
author_rank: Regular Contributor
timestamp: July 05, 2018, 03:07:34 am
content: On EEVblog #1078 Dave did a tear-down of a super-thin calculator that was held together almost exclusively with adhesive. Was this similar to the type of adhesive used in many modern phones and tablets? The type that you can use "heat-retaining bags" to loosen?I was looking into designing some super-thin sensor boards and it seems like these adhesives are the only option if you want super-flat designs. My first question is -- is there a name for this category of adhesives? So far I've been using CA glue, but most CA glues I've used only "break" at over 350C, meaning it's a one-way process unless I want to effectively "reflow" the entire device if I want to take it apart.The other question is how do they *apply* the glue to the layers? I have to be super careful when I use CA glue for 2 reasons -- 1) it cures in seconds, and 2) it's very difficult to get just the right amount for each location. If I use too much I have to clean it off with acetone and hope it doesn't smudge. To complicate things the perimeter isn't just one large contiguous surface, it's a rectangle that goes around the perimeter of the circuit, just like tablets are held together.I've seen a glue "roller" used to apply a very thin layer of glue, which would seem to solve many of the problems, but I don't know what it's called or what its characteristics are. Another option seems to be to order super-thin double-sided tape, and either cut it to the exact shape you need, or order it pre-cut. There are a TON of "3M Double-Sided Bonding Tape" types. This seems to create its own set of problems, since you have to use tweezers and align it just right, and most types are a bit too thick.Does anyone have any experience with these adhesives and/or construction of layered designs? I'd be grateful for any tips.

author: helius
author_rank: Super Contributor
timestamp: July 05, 2018, 03:12:04 am
content: The term of art for what you are looking for is"pressure-sensitive adhesive". They are made from natural or synthetic rubbers mixed with rosin.

author: derGoldstein
author_rank: Regular Contributor
timestamp: July 07, 2018, 01:30:00 pm
content: Quote from: helius on July 05, 2018, 03:12:04 amThanks for your reply!The term "pressure-sensitive adhesive", "Adhesive Transfer Tape", and "Acrylic Adhesive tape" seem to be interchangeable in 3M documentation:https://multimedia.3m.com/mws/media/798675O/3mtm-laminating-adhesive-200mp-brochure-in-high-resolution.pdfBased on thickness, "467MP" or "7952MP" would fit. Die-cutting looks to be how you can get specific perimeter designs pre-made. However, applying them seems to require very stable hands, they're super-thin:https://www.ifixit.com/Guide/iPad+2+GSM+Front+Panel+Adhesive+Strips+Replacement/10847-- though I realize that I'm complaining that the tape is very thin after specifying I was looking for thin adhesive...However there is another way to apply them, spray:https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Pressure-Sensitive-Spray-Adhesive-72/?N=5002385+3293194112&rt=rudhttps://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Rubber-And-Vinyl-80-Spray-Adhesive/?N=5002385+3293194236&rt=rudhttps://www.amazon.com/3M-90-24-Spray-Adhesive-17-6-Ounce/dp/B0002BBV2Shttps://www.amazon.com/3M-72-Pressure-Sensitive-Adhesive/dp/B000WSIYZ8I may be able to 3d-print a stencil that I place over the surface I want to glue, the way you would if you were stencil-spraying with paint. I'd have less control over how much material is applied, and many of them seem to be designed to be applied to more porous materials, so I'm not sure how thin I could get it. However, some of them have a long open bond time, giving me time to align the next layer just right, so I don't have the CA glue problem of having to move very fast.Does anyone have any experience with these types of spray adhesives when it comes to gluing PCBs?