Overmolding PCB 2

[marcunator]

I want to overmold a PCB.

This is really hard because the components upon the PCB need to survive the high temperatures and high injection pressure.

Any material suggestions?

[ul]
[li]SAN (Styrene Acrylonitrile)[/li]
[li]PS (Polystyrene)[/li]
[li]PETG (Glycol-modified Polyethylene terephthalate)[/li]
[li]PA12 (Polyamide 12)[/li]
[li][/li]
[/ul]

I am thinking to use one of the following materials. A TPE is also an option but I got nu experience with it.

Suggestions?

 

[marcunator]

I am simulating the part next friday with moldex3D. What functions in moldex3d will be valuable for me?

Cheers,

Marc

 

[cowski]

Overmolding a PCB is, in general, neither feasible nor desirable.

Why not hollow out the design you have, add some supports and turn it into a housing?

www.nxjournaling.com

 

[marcunator]

It is a research project and we want to explore the boundaries of injection molding. I know it will be hard.

We want to protect the PCB from:

[ul]
[li]Mechanical loads[/li]
[li]Electro static discharge[/li]
[li]Thermal loads(There are some plastics with decent thermal properties)[/li]
[li]Water[/li]
[li]Maybe a light guide[/li]

[/ul]

Its not about functionality in the first place, its more about pushing the process limits.

 

[cowski]

You have some more important issues to attend to before you worry about moldex. Let's assume the injected plastic doesn't tear any components off the board, or otherwise destroy them, during the injection process.

[ul][li]I assume the edge running around the perimeter of the part is the parting line. If so, it will need to move up to the centerline of the 3 round connectors otherwise the part will be trapped in the mold.[/li]
[li]The 3 round connectors may be distorted/destroyed by the pressure the mold exerts on them.[/li]
[li]The 3 round connectors appear to have a nut on them, which leads me to believe the bodies are threaded. Shutting off against a threaded surface will be next to impossible.[/li]
[li]The PCB will need to be supported in the mold, which will lead to portions of it being exposed.[/li]
[li]The rectangular connector in the middle of the board needs to have mold steel around it, which means the mold will have to shut off on the board face. There will need to be a support on the backside. The pressure of shutting off on the board may destroy nearby connections, traces, and/or the board itself.[/li]
[li]The resulting plastic piece has a very thick section that transitions sharply to a thinner section. This will result in warping as the piece cools. This will also result in sink marks and possibly voids.[/li]
[li]If it works, you'll end up with a part that has a near 0 chance of being recycled.[/li]
[/ul]

Also, you may want to check with approval agencies such as UL, CEC, etc to see what rules they have, if any, for such a design.

 

[marcunator]

Cowski,

Thanks for your reaction.

I modelled those issues on purpose.
because I want to check if moldex3D can spot those issues. We have a workshop this friday, and we are considering buying it.


This isnt a part we going to produce, this is just to test the moldex software.

Sorry for the confusion.

 

[cowski]

Perhaps a better test would be to take a part that you had problems with and use the moldex software to see if it correctly identifies the problems that you had. Real world use cases are always better, if you have them.

 

[btrueblood]

Consider room temperature curing compounds (epoxies, silicones, urethanes). Also this stuff

http://www.henkel.com/MA_Macromelt_Homepage-12494.htm

We overmold a particular PC board with reasonably good results (but no electrolytics which appear to be on your pc board?). Do consider a parylene coating first if moisture permeability is a concern.

 

[loki3000]

this sort of stuff (e.g. protecting IP of the electronic circuit) is usually done with epoxy. any kind of injection molding will completely destroy the circuit (the temp of the liquid plastics is near the metling point of the solder if i'm not mistaken.

 

[MacGyverS2000]

Typical solder melt ranges start around 360F... what's the melt temp of the plastics you're using, loki?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[loki3000]

my mistake.

 

[MikeHalloran]

Some plastics have to be nearly that hot in order to flow.
They also have very high viscosity, even at that temperature, so pressures in the vicinity of 9000 psi are required to make them flow through a typical mold. The heat and the stress from the mold flow will likely displace or destroy any preattached components.

That's why epoxy, or anything else that can be gravity cast, is preferred for encapsulating electronics.



Mike Halloran
Pembroke Pines, FL, USA

 

[marcunator]

I will try to overmold it with LDPE.

The pressure will be a problem, but I think with smart gate choices I can overcome that problem

 

[marcunator]

We already have low pressuremolds with macromelt, but thats quite a simple process. And were looking for a challenge

I am designing a mold as we speak, so I should have result in 1.5 months.

 

[Demon3]

If you want to overmold with a thermoplastic and want really low melting / processing temperature then you can't beat polycaprolactone, i.e.

http://www.instamorph.com/

Melts at 60C or 140F much lower than polyethylene.

Chris DeArmitt - PhD FRSC

My Plastics & Materials Consulting Site:

http://www.phantomplastics.com

Consultant to the Fortune 500

My Plastic Training Site:

http://www.plastictraining.com

Where you can buy recorded training webinars on plastics, filled plastics, impact modification and more

 

[ornerynorsk]

"were looking for a challenge" . . . .

Generally that's not the way manufacturing works. Unless you're simply doing pure research.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[marcunator]

Thanks for all your reactions guys,

Demon3 thank you for your useful suggestion, I will certainly take a look at that!

Ornerynorsk, It is research oriented. I thought mechanical engineering was about making the impossible possible??

Cheers.

Marc

 

[ornerynorsk]

Yes, I understand the research aspect toward a specific application, but good engineering entails simplification, rather than complication, of a product, where possible. Manufacturability, cost, reduction of waste, and all that happy stuff.

The research side is interesting and fun, I'll grant you that

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.