Hi,

I have a doubt friends, I sent some pcbs to manucfacture.

My desing was originally 2 layers, but I took a 8 layers deal for the same price and ENIG for free, so I made another 6 inner layers for ground/heatsink as soon as possible to take the deal.

But my concern is about the bottom layer (#8) and the layer #7, this pcb is for a flashlight so the layer #8 has a pad in the center for a Li-ion battery positive side and the layer #7 in the center has ground.

Do you think the prepeg between layer #8 and #7 is strong enough to prevent a Li-ion cell from a short circuit under stress?

With stress I mean, the battery is really thight inside the flashlight because it is hold by springs, and I'm worrying about the copper in the layer #8 could make contact with the layer #7 due to the pressure applied in the Vcc pad with the battery.

 

Hi,

I have a doubt friends, I sent some pcbs to manucfacture.

My desing was originally 2 layers, but I took a 8 layers deal for the same price and ENIG for free, so I made another 6 inner layers for ground/heatsink as soon as possible to take the deal.

But my concern is about the bottom layer (#8) and the layer #7, this pcb is for a flashlight so the layer #8 has a pad in the center for a Li-ion battery positive side and the layer #7 in the center has ground.

Do you think the prepeg between layer #8 and #7 is strong enough to prevent a Li-ion cell from a short circuit under stress?

With stress I mean, the battery is really thight inside the flashlight because it is hold by springs, and I'm worrying about the copper in the layer #8 could make contact with the layer #7 due to the pressure applied in the Vcc pad with the battery.

If the layers of insulation are fiberglass, it would take tremendous pressure to make one layer of copper contact its adjacent layer. How the board is mounted is much more important, to protect the circuit board from bending under the spring pressure.

 

If the layers of insulation are fiberglass, it would take tremendous pressure to make one layer of copper contact its adjacent layer. How the board is mounted is much more important, to protect the circuit board from bending under the spring pressure.

Flashlights usually have an upper ring at the edges of 1mm to hold the pcb and below they are either hold by a retaining ring of 2mm or soldered with tin/lead solder.

Usually when batteries are pretty thight the positive pole gets dented by the spring or brass button.

Do you think it is safe?

 

Flashlights usually have an upper ring at the edges of 1mm to hold the pcb and below they are either hold by a retaining ring of 2mm or soldered with tin/lead solder.

Usually when batteries are pretty thight the positive pole gets dented by the spring or brass button.

Do you think it is safe?

I don't know if it is safe because I don't know what any of the dimensions or materials are. I would recommend that you use something more suitable for the battery contact than solder or bare copper, each of which would oxidise and give you problems.

 

Hi,

I have a doubt friends, I sent some pcbs to manucfacture.

My desing was originally 2 layers, but I took a 8 layers deal for the same price and ENIG for free, so I made another 6 inner layers for ground/heatsink as soon as possible to take the deal.

But my concern is about the bottom layer (#8) and the layer #7, this pcb is for a flashlight so the layer #8 has a pad in the center for a Li-ion battery positive side and the layer #7 in the center has ground.

Do you think the prepeg between layer #8 and #7 is strong enough to prevent a Li-ion cell from a short circuit under stress?

With stress I mean, the battery is really thight inside the flashlight because it is hold by springs, and I'm worrying about the copper in the layer #8 could make contact with the layer #7 due to the pressure applied in the Vcc pad with the battery.

Pre Preg is typically similar to the stuff the pcb is mad off,
its just for want of a better description "none cured" when the board is assembled,
qed its typically a fibre matrix , normally fibre glass, "soaked" in a thick resin gunge,
the solid two layer boards are sandwiched with the pre preg, squeezed to size and cured.

Talk with the company you had the board built at for what thickness pre preg they used, and its dielectric capability.
Mechanicla wise, is tough stuff, have you tried to scrape your way through board ?
but the battery should really be fixed firm,
if it can "rattle" "move", then you could suffer mechanical failure due to the metal bending back and forward.

 

Pre Preg is typically similar to the stuff the pcb is mad off,
its just for want of a better description "none cured" when the board is assembled,
qed its typically a fibre matrix , normally fibre glass, "soaked" in a thick resin gunge,
the solid two layer boards are sandwiched with the pre preg, squeezed to size and cured.

Talk with the company you had the board built at for what thickness pre preg they used, and its dielectric capability.
Mechanicla wise, is tough stuff, have you tried to scrape your way through board ?
but the battery should really be fixed firm,
if it can "rattle" "move", then you could suffer mechanical failure due to the metal bending back and forward.

The thickness of the prepeg beetwen layer #7 and layer #8 is 0.1164mm, but I didn't know that impedance control was for choose the thickness of prepeg between layers some are 0.2104mm, 0.1164mm, and 0.0764mm, if I knew about it I would have choose 0.2104mm, so bad I did 5 orders without know.

About the batteries, the spring on the negative side keeps them pretty tight, probably I won't use them because of fear that layers #7 and #8 could short under the stress of a tight battery, 0.1164mm seems so thin compared to 0.2104mm thickness.



Thanks for you answer drjohsmith

 

re dielectric
that was not for impedance I asked, but thr amount of volts it could resist before it conducts
should not be a problem with a on board battery, unless its in the may 10's of volts, but check

 

re dielectric
that was not for impedance I asked, but thr amount of volts it could resist before it conducts
should not be a problem with a on board battery, unless its in the may 10's of volts, but check

The dielectric is 4.25 for 0.1126mm prepeg thickness according with this table, about the voltage will be just a single cell 4.2V max, what do you think is more an issue the voltage or that the layer #8 breaks the prepeg for the stress of a tight battery?