How to determine the thickness of core and prepreg used in PCB layers ?

[tennythomas]

It is said that the thickness of the PCB depends on the impedance. How to determine the thickness of core and prepreg used in PCB layers. Please guide me.

Is any application note on this available?

 

[keith1200rs]

PCB thickness

The characteristic impedance of a PCB track depends on its width, the PCB material and the distance to the ground plane. The PCB material is often FR4 so the dielectric constant is around 4.6 to 4.8. The distance to the ground plane depends on how many layers you are using and how they are made up. You need to check with your PCB supplier unless you just use two layers in which case 1.4mm to 1.5mm is fairly normal.

For calculating the impedance I use Appcad - a free download. I am sure there will be plenty of others.

Keith

 

[NIKHILRAJ]

PCB thickness

before fixing the layer stackup consult your PCB fabricator and check whether he is OK with your stackup.

 

[tennythomas]

Re: PCB thickness

Hi Keith,

Thanks for ur reply. U said that The distance to the ground plane depends on how many layers you are using and how they are made up.

But I do not know how to determine the core thickness and prepreg thickness.

For example:
The board thickness is 1.6mm.

TOP LAYER - 0.035mm
CORE -?mm
GND PLANE - 0.035mm
PREPREG - ?mm
PWR PLANE - 0.035mm
CORE - ?mm
BOTTOM LAYER - 0.035mm.

OR

TOP LAYER - 0.035mm
PREPREG -?mm
GND PLANE - 0.035mm
CORE - ?mm
PWR PLANE - 0.035mm
PREPREG - ?mm
BOTTOM LAYER - 0.035mm.

can u show me how to get the values?

Regards,
Tenny Thomas

 

[karesz]

PCB thickness

Hi Tenny,
as NIKHILRAJ wrote; you must consult your producer for available thicknesses_ the FR4 producer can deliver in 50um steps, but I think, no PCB producer can & will have all versions on stock...
Its good to see as goal ca at 0.3-0.5mm for both outer basis plates, the rest of your 1.6 mm plate thickness can you select as youlike, bitif you have i.e. high speed electronics on board: its favorable to take for these supply and corporate GND to use a thinst basis plate/material or core(i.e. only 100um with 2x cooper, its will work as a couple of 100pF bypass capacity on the right place for your supply ...
Even 1x cooper/2x cooper or no cooper on the basis plates=all these versions are possible in the PCB fabrication, typically will your vendor 1x/2x cooper + the needed prepregs (in the same 50um steps as basisplates/cores) use, but believe us: A CONSULTATION IN DETAIL IS NEEDED WITH YOUR PCB PRODUCER...
Most PCB producer have a "inhouse" stackup_it will be cheaper for you (if its a passable in sortiment) & in shorter time delivered as some extra construct...
BTW;
Cooper thicknesses can be others as 35um too, than the basis plates (or cores) are with 7.5/17/35/50/100um... cooper to order.
K.

 

[keith1200rs]

PCB thickness

As Karesz said, you need to consult your PCB supplier. They should easily be able to tell you what they can do. This is an example from my usual supplier:

https://www.pcb-pool.com/download/spezifikation/eng_cmso004_ml4.pdf

Keith

 

[janny8866]

PCB thickness

Hi Tenny,

Maybe i could help you.
Freely email me,if you have any question.
Best Regards,
Janny
HongKong Credit PCB Technology Limited
Tel: +86 (755) 86229318 Fax:+86 (755) 86229393
Mobile: +86 13418925004
Skype: xie_wenjuan MSN:xie_wenjuan@hotmail.com
E-mail: janny@creditpcb.com or jannyxie_kbc@yahoo.com.cn
Website:**broken link removed**

 

[tennythomas]

Re: PCB thickness

Thanks for ur reply.

 

[v.k mishra]

can u please give solution that how charcterstic impedance effect our pcb.........???????
and how to calculate the minimum distance between two copper trace.......????????????