Plasma cleaner.

2Spoons, Wed Mar 06 2013, 04:35AM

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!

Next step is to run with oxygen, rather than air.