Homebrew PCBs

I found some copper clad boards on ebay that use CEM material
instead of the FR-4 that I'm familiar with.

Has anyone used CEM before?
Is it any different from FR-4?

acidblue pravi:
> I found some copper clad boards on ebay that use CEM material
> instead of the FR-4 that I'm familiar with.
>
> Has anyone used CEM before?
> Is it any different from FR-4?
>
>   
Depend's what you want!

Mechanicaly is not so good. If you use shear to cut it the edge is bad. 
On the other side the drill bit's last much longer. It's less heat 
resistant and has different dielectric constant. But if you do ordinar 
hobby project's (not for radio frequency above 100MHz) the CEM is just 
good choice.

Slavko.

>
>Mechanicaly is not so good. If you use shear to cut it the edge is bad.

heat it before cutting, with a hot gun, to get clean edges

Cristian 

[Non-text portions of this message have been removed]

On 01/09/2010 00:45, acidblue wrote:
> I found some copper clad boards on ebay that use CEM material
> instead of the FR-4 that I'm familiar with.
>
> Has anyone used CEM before?
> Is it any different from FR-4?


I've been using CEM-1 for years. It's a fibreglass-paper composite and 
is much easier to cut and drill than FR4. I buy mine (precoated) from 
Mega Electronics.

Leon
-- 
Leon Heller
G1HSM

Damn, I just bought a shear just for cutting PCB's.
Thanks for the info.

rocko pravi:
> Damn, I just bought a shear just for cutting PCB's.
> Thanks for the info.
>   
It's not so bad!
I just leave 0.5mm biger plate and sand it down with sandpaper on flat 
surface.

The only caution I would give about CEM is consider your end-use environment: CEM, if memory serves, is more susceptible to wicking water over time, internally, and between layers (in multi-layer boards) in high humidity environments, with eventual (years, but still...) corrosion of traces and connections.

Also, as a side note that might be slightly relevant and perhaps of use to someone here, in tests on Peltier modules, sealing out water vapor, epoxy was the only sealant that performed well. Silicone, surprisingly, did not...I guess it's fine for bathtubs and aquariums, but where there's heat cycling water vapor can still get through the molecular matrix.

The sealants that are used on boards are acrylic based, if I remember correctly. However, potting a board usually involves epoxy. I dunno how well acrylic performs at keeping water vapor out of CEM boards, although I would think a coating of epoxy on all surfaces would work well...the key phrase there being "all surfaces".... 

Best, Charlie

--- In Homebrew_PCBs@yahoogroups.com, Leon Heller <leon355@...> wrote:

>
> On 01/09/2010 00:45, acidblue wrote:
> > I found some copper clad boards on ebay that use CEM material
> > instead of the FR-4 that I'm familiar with.
> >
> > Has anyone used CEM before?
> > Is it any different from FR-4?
> 
> 
> I've been using CEM-1 for years. It's a fibreglass-paper composite and 
> is much easier to cut and drill than FR4. I buy mine (precoated) from 
> Mega Electronics.
> 
> Leon
> -- 
> Leon Heller
> G1HSM
>

Yes, silicone is quite porous. It will stop liquid but vapor penetrates 
it quite easily.

Les

> Also, as a side note that might be slightly relevant and perhaps of use to someone here, in tests on Peltier modules, sealing out water vapor, epoxy was the only sealant that performed well. Silicone, surprisingly, did not...I guess it's fine for bathtubs and aquariums, but where there's heat cycling water vapor can still get through the molecular matrix.
>