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Author Topic: Gluing the PCB material with epoxy  (Read 3575 times)

Offline Matt Piatkowski

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Gluing the PCB material with epoxy
« on: November 30, 2017, 07:28:42 AM »
Hello,
I could not find 1/8" PCB in my area (Toronto, Ontario, Canada) and wanted to glue two 1/2"x 2 1/2" x 1/16" thick PCB pieces with the 15 min. epoxy.
The PCB material is standard FR-4 glass-epoxy laminate, copper clad on one side only and I wanted to glue the other sides.

After roughing with #80 sandpaper and vacuuming, I degreased the surfaces with the mineral spirit and waited one hour for the spirit residue to evaporate.

Then, I glued the pieces and waited 24 hours.

Ten minutes ago I pulled the pieces apart very easily slightly bending the specimen. The epoxy was set but the in-plane shear strength and peeling strength of the connection was negligible.

Both previously glued surfaces have a thin layer of epoxy that sticks well to the base material.

Perhaps cleaning with the mineral spirit was a bad idea? Mineral spirit is used to clean epoxy and maybe its minute residue trapped in roughened surfaces affected the strength of the connection?

I know that many people use the 1/8" thick PCB material for the motor mounts glued to the fuselage sides using the epoxy resins so the strength of such connection was tested many times. There is not much bending, though, in such connection. It relies on the shear strength of epoxy between the PCB material and the fuselage front sides that are usually doublered with 1/64 or 1/32 plywood. The PCB mount is usually also framed on both sides by epoxied wooden pieces but some builders use only one side reinforcements with relatively small wood pieces.

Your comments and practical suggestions are appreciated,

Thank you,
M


 

Offline Motorman

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Re: Gluing the PCB material with epoxy
« Reply #1 on: November 30, 2017, 08:06:52 AM »
blank
« Last Edit: March 08, 2022, 09:21:13 PM by Motorman »

Online Lauri Malila

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Re: Gluing the PCB material with epoxy
« Reply #2 on: November 30, 2017, 09:36:21 AM »
I have also found glassfiber board difficult to glue. Even rough sanding is not allways enough, often I peel off one layer of laminate, it leaves a nice surface for glue to bite.
Also, you'll need an epoxy that remains somewhat flexible, for example West Systems G/Flex. You can also buy a softening agent that you mix with normal epoxy resin.
In emergency, you can just mix a little too much hardener, many epoxies remain flexible like that, especially UHU Endfest 300. L
« Last Edit: November 30, 2017, 12:58:50 PM by Lauri Malila »

Offline Matt Piatkowski

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Re: Gluing the PCB material with epoxy
« Reply #3 on: November 30, 2017, 10:10:41 AM »
Hi Motorman,
I will try again without mineral spirit and will add glass balloons to the resin.

Hi Lauri,
Yes..I also started thinking about resin that remains a bit gooey after setting. I know the "too much hardener"method and will use it on another specimen.

You wrote:" often I perl off one layer of laminate..". What is "perl"?

Thank you,
M

Offline pmackenzie

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Re: Gluing the PCB material with epoxy
« Reply #4 on: November 30, 2017, 08:15:17 PM »

You wrote:" often I perl off one layer of laminate..". What is "perl"?

Thank you,
M

I am guessing he meant to type "peel", and "r" is right next to "e" on the keyboard :)
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Offline Tim Wescott

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Re: Gluing the PCB material with epoxy
« Reply #5 on: November 30, 2017, 10:26:45 PM »
You were gluing laminate to laminate, and not copper to copper, yes?

Absent of what Lauri just said, I'd peel & sand, not use any solvent, and use the longest cure epoxy that's available at the hobby shop.  I'd expect a pretty good bond.  I may try his method if I ever feel a need.

McMaster-Carr sells FR4 as "Garolite" -- see here for details.  Dunno if this'll help you in the Great White North, but you can try.  It's a pretty common structural material.  McMaster has lots of sizes to choose from.  You can probably get it from da Bay, too.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Igor Burger

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Re: Gluing the PCB material with epoxy
« Reply #6 on: December 01, 2017, 01:23:41 AM »
It needs to remove (sand out) upper glossy surface, it is not gluable. Few scratches are not enough, must be removed completaly. The any epoxy will work well.

pictures show it, #1 not gluable, #2 scratched, but not enough, #3 still shows some glossy places, but already OK.

#4 shows finished wing joiner.


Offline Tim Wescott

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Re: Gluing the PCB material with epoxy
« Reply #7 on: December 01, 2017, 10:39:04 AM »
It needs to remove (sand out) upper glossy surface, it is not gluable. Few scratches are not enough, must be removed completaly. The any epoxy will work well.

I used to build & maintain molds for my dad's business, so I can actually speak on this topic as a has-been drip under pressure*.

When you mold plastic, you need a mold release compound (usually some sort of wax, with extra stuff in it) on the mold to keep it from sticking.  Particularly if the plastic in question is a Really Good Glue.  The mold release compound gets incorporated into the outermost layer of the part -- that's the glossy surface that Igor is talking about.  The bond will be good enough that you can't just use the part as a mold, and crappy enough that it'll break at the slightest provocation.  When I said "sand" earlier, I meant what Igor said -- sand all the glossy stuff off, until you're down to the inner material.  At that point you should be able to make a really good bond.

* expert.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Lauri Malila

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Re: Gluing the PCB material with epoxy
« Reply #8 on: December 01, 2017, 11:52:25 AM »
Of course, this is not rocket science but if you want to do it really well, it's recommended to clean/de-grease the surfaces before and after sanding. Otherwise you may just rub the leftovers of release agent/wax deeper into the material.
Acetone is good for that.
And when gluing with epoxy, raising the curing temperature to 50..70C never hurts. L

Offline Matt Piatkowski

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Re: Gluing the PCB material with epoxy
« Reply #9 on: December 01, 2017, 01:53:35 PM »
Hi Tim,
Yes, I was gluing laminate to laminate.

Everybody: tried again yesterday. 5 minutes epoxy on thoroughly sanded surfaces dusted with vacuum cleaner. No mineral spirit, no acetone.
The surfaces before smearing with epoxy were rough when inspected against the light but I did not touch them with my fingertips.

No glass balloons yet. I will use them in the next step

Not much peel strength improvement, maybe 10%.

Please see the photo showing how the connecting resin layer was split. The resin adhered to both PCB surfaces as its residue is still there. 

I will repeat the test sanding again, vaccum cleaning, using acetone and, this time, I will add the glass balloons to 5 min. epoxy. Then, I will change the epoxy to 30 minutes.

Thanks,
M







Offline Tim Wescott

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Re: Gluing the PCB material with epoxy
« Reply #10 on: December 01, 2017, 06:59:53 PM »
So, it was suggested that you use the slowest cure epoxy that you could, because it's pretty well known that 5-minute epoxy is a joke.

And you chose to use 5 minute epoxy.

Why?

Come to think of it, are you using fresh epoxy, and are you at least using a hobby brand and not whatever -er- stuff comes from the hardware store?  Because if you're using something that's been sitting around for ten years that was cheap when it was new, the FR-4 isn't the problem.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Matt Piatkowski

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Re: Gluing the PCB material with epoxy
« Reply #11 on: December 03, 2017, 06:17:21 AM »
I have tested the specimen using the 30 min. epoxy bought two months ago in the hobby store. The remaining shelf life of such epoxies is unknown and nobody can guarantee that they are "fresh", whatever "fresh" means in the 2017 year of our Lord.

The epoxy was filled with glass balloons and warmed a moment before gluing. Like I wrote before, the surfaces to be glued were prepared the best way I could in circumstances.

The peel strength was not much better than for 5 min. epoxy.
Perhaps it is not the peel strength but the transverse shear strength of the engine mount to fuselage connection that is critical?

I have to think about it and, in the meantime, I will not use the PCB material and any of the hobby stores epoxies to glue the PCB engine mounts into my model. 

Thank you,
M

 

Offline Motorman

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Re: Gluing the PCB material with epoxy
« Reply #12 on: December 03, 2017, 10:07:48 AM »
blank
« Last Edit: March 08, 2022, 09:20:35 PM by Motorman »

Offline Matt Piatkowski

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Re: Gluing the PCB material with epoxy
« Reply #13 on: December 11, 2017, 06:59:10 AM »
Hi Motorman,
I have the 0.039" carbon fiber laminate but have no idea what resin was used to manufacture it. I have never tried to glue this carbon laminate with epoxy but I will try. FR-4 material used presently for the PCB boards is manufactured with epoxy resin so, theoretically, it should bond sufficiently well with epoxy after the surface is properly prepared. Now: "sufficiently well" and " properly prepared" are unfortunately vague as I do not have the strength criteria for this connection.

The basic questions still stand:
1. What peel strength is required when two FR-4 pieces are glued together with various epoxies? Is peel strength relevant at all?
2. What transverse shear strength of epoxy connecting these pieces is required? Perhaps this strength is partially relevant too? When the motor is mounted, two layers of 1/16" PCB are squeezed by the mounting screws so they will stay together.
3. What strength is required from the motor mount connection to the fuselage sides and how to asses it? This is for sure critical.

Christoph Holterman published on this Forum the idea of bending the motor mount using 2 mm. 5xxx or 6yyy series aluminum alloy. Such "C" shape bracket is then epoxied to the fuselage front 1/64" or/and 1/32" plywood doublers that are glued to the fuselage balsa sides with epoxy. In addition, the "C" bracket can be, say, riveted to the plywood before mounting to the fuselage. Such solution creates not only strong connection but also the integral heat sink for the front mounted motors. "Igor's Style" integrated fins exposed to the ram air can be added to increase the effectiveness of cooling

Aluminum has higher density than the PCB laminate. Perhaps the weight of the AL mount is a bit higher but the "Holterman's solution" is, in my opinion, elegant and structurally clean.

Please see the attached.
Regards,
M   

Offline Howard Rush

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Re: Gluing the PCB material with epoxy
« Reply #14 on: December 11, 2017, 05:27:38 PM »
You are gluing together two pieces of copper-clad circuit board material so the copper is on the outside, then bolting the motor to the sandwich and gluing the edges to the fuselage sides?  Here's my guess as to answers to your questions:

1. What peel strength is required when two FR-4 pieces are glued together with various epoxies? Zero. Is peel strength relevant at all? No.
2. What transverse shear strength of epoxy connecting these pieces is required? I don't know what that is, but I'd say approximately zero. Perhaps a stress man will testify.   Perhaps this strength is partially relevant too?  Perhaps not.  When the motor is mounted, two layers of 1/16" PCB are squeezed by the mounting screws so they will stay together. I would think that would suffice.
3. What strength is required from the motor mount connection to the fuselage sides and how to asses it? I don't know.  Mine stay put, but I do them differently. This is for sure critical. Yep.

Two other issues that might concern you are the Tg of the epoxy connecting the motor mount to the fuselage side and resonance of the motor mount.  The copper looks like it will serve only to conduct heat from the motor to the glue, so the glue should be good for the heat.  Guys with thin mounts have experienced resonance with some materials.  I have a history of making carbon mounts that ring like bells, so I'm no help in predicting whether yours will shake. 
The Jive Combat Team
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Offline Matt Piatkowski

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Re: Gluing the PCB material with epoxy
« Reply #15 on: December 12, 2017, 09:11:21 AM »
Hi Howard,

After re-considering the problem. I agree with you on 1. and 2.
By the way: I am the aerospace stress engineer and the experience has taught me that devil is in the details.

Re: 3: how exactly do you do these connections? Details please. Of course if you are willing to share.

Please see the attached. Transverse shear is very high considering the load.

Thank you,
M   

Offline Howard Rush

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Re: Gluing the PCB material with epoxy
« Reply #16 on: December 12, 2017, 03:00:12 PM »
Ha! A stress man!  Almost half a century ago I worked in structural design.  I still bear a little post-traumatic resentment of stress men.  For example, I find it difficult to suppress a grin when the wing falls off a stress man's stunt plane or when his plane ejaculates its battery.

Here's what I did.  It's a sheet of cloth prepreg (I forget the thickness: maybe .025") on either side of 1/2" balsa.  I put pieces of carbon pushrod tube in the balsa where the motor mount bolts go.  The sandwich connects to 1/64" plywood fuselage side reinforcement.  I've done two dogs like this, and they have plenty of flights.  I haven't experienced any resonance with E-flite or Plettenberg motors, but Cobra bearings don't last very long.
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Offline pmackenzie

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Re: Gluing the PCB material with epoxy
« Reply #17 on: December 12, 2017, 05:50:50 PM »
when his plane ejaculates its battery.



I think only Steve Bannon can do that trick, at least according to the Mooch  VD~
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Offline Brent Williams

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Re: Gluing the PCB material with epoxy
« Reply #18 on: December 12, 2017, 08:23:13 PM »
Ha! A stress man!  Almost half a century ago I worked in structural design.  I still bear a little post-traumatic resentment of stress men.  For example, I find it difficult to suppress a grin when the wing falls off a stress man's stunt plane or when his plane ejaculates its battery.

Here's what I did.  It's a sheet of cloth prepreg (I forget the thickness: maybe .025") on either side of 1/2" balsa.  I put pieces of carbon pushrod tube in the balsa where the motor mount bolts go.  The sandwich connects to 1/64" plywood fuselage side reinforcement.  I've done two dogs like this, and they have plenty of flights.  I haven't experienced any resonance with E-flite or Plettenberg motors, but Cobra bearings don't last very long.

That is very nice work Howard.  I would have expected to see a front mounted design on that based on all of the previous front/rear discussions that have been posted.  Do the Plettenberg motors specify rear mount?  Have you experienced any of the rear mounted bearing wear/other issues?  The rear mount arrangement seems like it could certainly make for a more robust and rigid nose, (though I am not an engineer, structural or otherwise.)



Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Offline Howard Rush

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Re: Gluing the PCB material with epoxy
« Reply #19 on: December 12, 2017, 10:23:40 PM »
Do the Plettenberg motors specify rear mount?  Have you experienced any of the rear mounted bearing wear/other issues?

Plettenberg assumes their motors will be front-mounted.  They offer a rear mount (which I think they call a front mount) as an option.  This is their optional rear mount.  The backplate is mounted to the airplane by two wee 3mm screws.  I wouldn't have thought this would suffice, but Paul Walker got away with it for many hundreds of flights.  Plettenberg has another option for a large backplate, which I've been using lately.  It mounts with four screws.  Come to think of it, I have had some bearing trouble with a Plettenberg. The rear-mounted Cobra has been worse.
The Jive Combat Team
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Offline Howard Rush

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Re: Gluing the PCB material with epoxy
« Reply #20 on: December 13, 2017, 03:18:57 PM »
I think only Steve Bannon can do that trick, at least according to the Mooch  VD~

I don’t know if you noticed, Pat, but I still speak with a slight Nantucket accent.
The Jive Combat Team
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Offline Igor Burger

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Re: Gluing the PCB material with epoxy
« Reply #21 on: December 14, 2017, 10:46:47 AM »
Plettenberg assumes their motors will be front-mounted.  They offer a rear mount (which I think they call a front mount) as an option.  This is their optional rear mount.  The backplate is mounted to the airplane by two wee 3mm screws.  I wouldn't have thought this would suffice, but Paul Walker got away with it for many hundreds of flights.  Plettenberg has another option for a large backplate, which I've been using lately.  It mounts with four screws.  Come to think of it, I have had some bearing trouble with a Plettenberg. The rear-mounted Cobra has been worse.

I had it on 2.5mm glass fiber plate mounted on that small 2 screw ring and it dmaged wires going through that plate on its edges. So it was clear that motor is moving during flight. I reworked it to that large plate and it was ok.

2 screws will probably need much thicker plate.

Offline phil c

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Re: Gluing the PCB material with epoxy
« Reply #22 on: March 02, 2018, 02:34:54 PM »
I have tested the specimen using the 30 min. epoxy bought two months ago in the hobby store. The remaining shelf life of such epoxies is unknown and nobody can guarantee that they are "fresh", whatever "fresh" means in the 2017 year of our Lord.

The epoxy was filled with glass balloons and warmed a moment before gluing. Like I wrote before, the surfaces to be glued were prepared the best way I could in circumstances.

The peel strength was not much better than for 5 min. epoxy.
Perhaps it is not the peel strength but the transverse shear strength of the engine mount to fuselage connection that is critical?

I have to think about it and, in the meantime, I will not use the PCB material and any of the hobby stores epoxies to glue the PCB engine mounts into my model. 

Thank you,
M

 
I've laminated 1/16 and 1/32, un-cladded PC board.  The best results have been with West Systems slow cure,  2+ hours, left overnight.  The surface prep is very necessary.
You can make your own, in place with multiple layers of glass and a slow cure epoxy.  Just make sure it is clamped solidly, usually between two aluminum pieces.  The epoxy won't stick to the aluminum, and if it does a little bit of heat will break any bond.

If you are gluing to any kind of wood make sure the surface is fully saturated with glue, and heat the wood to drive out air and suck in the glue.  Otherwide the joint is only as strong as the wood it is attached to.
phil Cartier


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