flexible pcb adhesive

Thread Starter

byakk0

Joined Nov 29, 2015
57
I need to glue a flexible pcb to a peice of acrylic. Is there any sort of adhesive that will permantly bond the PCB soldermask to the acrylic?
I've tried superglue(ca), uv curable glues. Nothing seems permanent. I can lift the pcb from the cured glue with ease.

(Not sure which forum is ideal for this question, also did a forum search)
 

SamR

Joined Mar 19, 2019
4,215
Liquid rubber comes to mind. Start with the standard rubber cement...
1649889973809.png
And if that doesn't work, go on up to the liquid electrical tape kind.
1649890215580.png
I'd test it on the acrylic first as it contains acetone. Or the silicone rubber kind...
 

SamR

Joined Mar 19, 2019
4,215
Yup, I keep a roll of the double-sided adhesive foam and plain double-sided tapes in my tool box. Also, some Velcro for when it needs to be removed and replaced. It comes in all kinds of shapes and sizes including rolls of it. All good stuff to have handy as it does get used up.
1649893886256.png
 

MrSalts

Joined Apr 2, 2020
1,762
Flex circuit is polyimide (Kapton) with etched copper or is it clear Polyester (PET) with printed silver ink?

Option 1
Buy a new piece of acrylic but tell your vendor you want acrylic WITHOUT UV absorbers. Try UV cure adhesive again. Most acrylic and polycarbonate sold at Hardware Stores for window repairs or picture frames is UV stabilized.

Option 2
Pass a torch over the acrylic and circuit quickly (don't heat it up, just a quick pass like you pass your finger over a candle). This will create ionization (partial oxidation) on the polymer surface that will make the adhesive work better.

Option 3
Or, wet the substrates with heptane, let dry by visual inspection (do not heat to dry completely), apply adhesive and bond the two parts. Henkel Loctite offers a superglue with a felt-tip pen filled with heptane (they call it catalyst or activator).
 

Thread Starter

byakk0

Joined Nov 29, 2015
57
thanks for the ideas. Gives me a little more to go off of.

It's a permanent bond, on the green flexboard with Kapton. (Although I could foreseeably need to do this with a silver on PET at a later date.)
I hadn't considered the UV blocking Acrylic. I'll see if I can find out if this has UV blockers. I was able to peel the layer of glue from both the acrylic and the flexboard in a thin sheet. It wasn't tacky so I thought it was cured. The adhesive is Norland Optical Adhesive #68

If I go the route of double stick tape, foam tape is too thick for this project. I hadn't considered using tape. Wonder if just a double sided scotch tape would do the trick.
 

Ya’akov

Joined Jan 27, 2019
5,694
This tape is the same sort of thing used in assembling mobile phones. It's ultrathin, unreasonably strong, and sticks to just about anything but PTFE and HDPE in my experience.
 

Thread Starter

byakk0

Joined Nov 29, 2015
57
I may have to try that. I found some 3M 467MP tape in the lab here at work so giving it a try. So far so good...
However, this flex PCB is being mounted to the outside of an acrylic tube with a 1 1/2" dia, so it needs to have an excellent bond so it doesn't start lifting. I'll let it rest for a while and see if stick well enough.
 

Reloadron

Joined Jan 15, 2015
6,593
Double-sided Scotch tape is 0.0035” thick, considerably thinner than 0.06”. Did you mean Scotch brand double-sided foam tape?
My bad and yes, the tape I linked to earlier. I have seen the foam tape is various thickness and just happen to have some here. :)

Ron
 

SamR

Joined Mar 19, 2019
4,215
What I have is thicker than the Scotch tape. Total thickness (tape + backing): 0.430 mm (0.017") Pretty good for all around use and much thinner than the Velcro or foam that I have.
1649977257110.png

I also keep some Kapton in the toolbox and have some Scotch brand for paper only. The adhesive on the Scotch brand is not as strong as on the double sided as it was designed for light duty on paper. Not sure about the double sided Scotch as I've never used it and didn't know it existed til now.
 

MrSalts

Joined Apr 2, 2020
1,762
I may have to try that. I found some 3M 467MP tape in the lab here at work so giving it a try. So far so good...
However, this flex PCB is being mounted to the outside of an acrylic tube with a 1 1/2" dia, so it needs to have an excellent bond so it doesn't start lifting. I'll let it rest for a while and see if stick well enough.
The 467MP is great stuff but it does have an expiration date (about two years after manufacturing and weakens with time. Also, it gets full strength after about 24 hours after applying to a surface. You need to apply sufficient pressure. If, you cant get good pressure on both sides (bonding two rigid parts) you can apply a piece of double sided adhesive to each part and then press the two adhesive surfaces together to get a very strong bond. Two layers of adhesive also work for non flat surfaces.
It is an "adhesive transfer tape". Only the adhesive is left after the backing is removed (there is no rigid cellophane or Kraft paper structure). This makes it a bit sticky/gummy so it is best to try not trying to handle it much. I use the 3" wide rolls and cut my shape on the roll and then peel off the tape shape and burnish to the surface (then peel the backing to expose the second side). Lift/move with an razor knife/razor blade/utility knife because it so easily sticks to your fingers and tears off the backing.
 

Thread Starter

byakk0

Joined Nov 29, 2015
57
Thanks for the explanation of the 467MP. That explains the Transfer part. sitting overnight it looks successful but time will tell. I'll try doubling it up if needed.

I adhered my test substrate with various adhesives, including the MP467, then wrapped with a strip of silicone mat, then used a bunch of rubber bands. I have used tape in the past but the silicone and rubber bands seems more effective.

The problem is, kapton/polyimide is very chemical resistant. I'm going to try an adhesion promoter and see if that helps.
 

Thread Starter

byakk0

Joined Nov 29, 2015
57
The adhesion promotor doesn't look to have been of any benefit, however it is used for something else and any chemical compatibility between it and the soldermask would have been nothing more than luck.
I also used some Testors spray model adhesive, its a kind of of contact cement. It was working intitially, but after a week it looks like the edges may be lifting. The 467MP is holding fast so far.
 

MrSalts

Joined Apr 2, 2020
1,762
The adhesion promotor doesn't look to have been of any benefit, however it is used for something else and any chemical compatibility between it and the soldermask would have been nothing more than luck.
I also used some Testors spray model adhesive, its a kind of of contact cement. It was working intitially, but after a week it looks like the edges may be lifting. The 467MP is holding fast so far.
The 467MP is used in automotive interiors for this exact application (polyimide flex circuit pigtails to various surfaces to avoid cracking of the polyimide flex from vibration and possibly damaging the copper circuit. I think you'll be fine m
 

Thread Starter

byakk0

Joined Nov 29, 2015
57
Just an update for anyone following this thread, or who stumbles on this later.
I have had the 467MP tape on the device for a month now, and showing no signs of lifting at the edges.
This is a 1" wide flexible PCB adhered to the outside of a 1 1/2" diameter clear acrylic tube.
(Additionally, I have discovered that WD40 helps to clean off the tape.)
 
Top