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Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
Sometimes I get to do fun stuff at work. This is one of those times.
Background: We use LCP (liquid crystal polymer - an aromatic polyester) in a lead frame moulding and need to get an encapsulant to stick to it. LCP is a notoriously difficult substrate to glue to - all the 'net search results said the same thing : surface treatment with plasma is the only way to get a good bond.
So after getting a price for a small commercial unit - 25,000 Euro! - I decided to hack something together in the workshop.
This is the result!
Digging around in my garage I found one of my bell jars, and my small HV AC supply (your usual Royer oscillator built around a TV flyback tranny). Work had a basic vacuum pump.
After messing about with various electrode configurations I ended up with this, to create a dielectric barrier discharge. Both electrodes are Al foil covered with 3mm acrylic. Discharge volume is roughly 50mm high, 30mm wide, and 10mm thick. There is a gas inlet at the bottom, and the part to be treated is placed above the gap at the top of the discharge volume. Vacuum is pulled from the top of the bell jar, so in operation I can bleed in gas at bottom to create a flow of ionised gas over the part being treated. In the open pic you can see the leadframe balanced on top for treatment.
The whole thing has a lovely purple glow when running - though my camera makes it look more blue.
Some quick tests have proved very effective : 10mins treatment and the glue bond is good enough that chunks of LCP are pulled out when the bond is tested to destruction. Can't get much better than that!
Registered Member #396
Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176
I realize this is an old thread, but I'm surprised no one ever commented on it. This is a really neat application of HV that I think a lot of us could use for hard to bond plastics.
2spoons, did you perform any more tests with this? How did the final product work out?
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
We built a pull tester to test bond strength properly - basically just a load cell and an air ram. Results were pretty impressive - bond strength on LCP went up by a factor of at least 5, sometimes more. The effect of the cleaning was still evident after a week - you could clean the LCP, leave it a week, and still get the same improved bond strength. In the end we didn't needed to implement this in manufacturing - we simply found a better glue chemistry (an epoxy made by Delo)
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
We built a pull tester to test bond strength properly - basically just a load cell and an air ram. Results were pretty impressive - bond strength on LCP went up by a factor of at least 5, sometimes more. The effect of the cleaning was still evident after a week - you could clean the LCP, leave it a week, and still get the same improved bond strength. In the end we didn't needed to implement this in manufacturing - we simply found a better glue chemistry (an epoxy made by Delo)
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Plasma cleaner.
