Post Curing US Composites?

[itisyeetimetoday]

I'm attempting to make circuit boards using fiberglass impregnated with epoxy resin. In order to save on material cost, I decided to use US Composites 635 Thin Epoxy Resin that I use for wet layups. Unfortunately, plating copper onto the fiberglass boards requires a bath at 60C degrees, and given the warping of the board in the bath, I'm guessing that's far beyond the glass transition temperature of the epoxy.

That being said, US Composites doesn't seem to publish post curing schedule, and after emailing a rep, they said that even with a post cure of 2 hours at 250F, the heat distortion temperature of my slow hardener is only 46-52C.

Has anyone tried post curing US Composites, and had any success with increasing the glass transition temperature and heat resistance of the epoxy?

 

[G_T]

It doesn't sound like you can achieve what you want with that epoxy system. Find another.

Gerald

 

[PayLoad]

I......feel so stupid

 

[G_T]

I'm guessing we were using terminology that you are not familiar with. I was going to point you to some sticky threads, but turns out they are no longer sticky and have gone? Too bad. Huge amount of good info in them.

Epoxy when cured is a polycrystalline solid. Due to its microcrystalline nature, it is somewhat rigid and therefore makes a good matrix material for other additives such as fabric to make composites. Composites -> mix of more than one type of material.

Warm cured epoxy up enough, and it undergoes a phase change. It goes from a polycrystalline solid to an amorphous solid. When it does so, it loses rigidity. AKA it gets rubbery. Cool it back down, and it undergoes a phase change and turns back into a polycrystalline solid.

The temperature of this phase change is the Glass Transition Temperature, often written Tg.

You generally want to be using an epoxy system that stays below its Tg in the conditions you are using it. The Tg is going to depend on the epoxy system. West Systems meant for fiberglassing wooden boats has a rather low Tg. The Tg of various systems go up from there.

Now the Tg isn't exactly a constant even in a single epoxy system. It usually depends on how you cured your epoxy. If you do an initial cure so that it "sets up" and then continue the cure at an elevated temperature, that is a post-cure heat treating cycle.

With most epoxy systems (practically everything except West Systems) this results in a higher Tg and a stronger epoxy. The new Tg is somewhere in the ballpark of 10 degrees C below the peak temperature in the post-cure heat treating cycle.

But if you go too high you make the epoxy very brittle. Higher than that, and you destroy it. How high you can go depends on the chemistry of that particular epoxy system.

The Heat Deformation Temperature is a bit lower than the Tg. It is where the solid epoxy will start to yield under pressure, where at a lower temperature it would have withstood the stress indefinitely.

Hope this helps!

Gerald

 

[jsdemar]

Why make your own copper-clad circuit board material?

 

[OverTheTop]

I would have thought a piece of FR4 single (or double) sided would be relatively inexpensive and not worth messing around with DIY. If you find a board manufacturer near you they might have some offcuts?

Alternatively somewhere like Fry's (closed now) would sell it. Digikey start around $15 for a 10"x8".

 

[cwbullet]

I have never used US Composites for that, but the good news is you have some to use on rockets. It works very well for that.

 

[tsmith1315]

I would have thought a piece of FR4 single (or double) sided would be relatively inexpensive and not worth messing around with DIY.

Perhaps an odd shape is needed? I thought about integrating traces into e-bay tubing as a distribution board for power and ejection charges. It seemed to be a solution looking for a problem.

 

[dhbarr]

Perhaps an odd shape is needed? I thought about integrating traces into e-bay tubing as a distribution board for power and ejection charges. It seemed to be a solution looking for a problem.

Even still with the readily-available amount of cylinders, rectangular tubes, etc. it's a bit hard to imagine OP needing to put traces on the outside of something that can't be easily obtained.

 

[jsdemar]

Even still with the readily-available amount of cylinders, rectangular tubes, etc. it's a bit hard to imagine OP needing to put traces on the outside of something that can't be easily obtained.

Or, Rogers and others have formable copper clad material with specified high dielectric values. Good for patch antennas wrapped onto an airframe body.

 

[rcktnut]

Sounds like a PITA trying to make one. https://www.mcmaster.com/copper-clad-boards/

 

[Handeman]

I'm attempting to make circuit boards using fiberglass impregnated with epoxy resin. In order to save on material cost, I decided to use US Composites 635 Thin Epoxy Resin that I use for wet layups. Unfortunately, plating copper onto the fiberglass boards requires a bath at 60C degrees, and given the warping of the board in the bath, I'm guessing that's far beyond the glass transition temperature of the epoxy.

That being said, US Composites doesn't seem to publish post curing schedule, and after emailing a rep, they said that even with a post cure of 2 hours at 250F, the heat distortion temperature of my slow hardener is only 46-52C.

Has anyone tried post curing US Composites, and had any success with increasing the glass transition temperature and heat resistance of the epoxy?

Why are you trying to make your own circuit boards? Isn't it much cheaper to just have the board made with the curcuits you want? Or just buy premade copper clad boards?