Why we discuss semi flex PCB?
Most of MCPCB designers don’t know what is semi flex PCB.
Even thought semi flex PCB is not so widely as a conventional rigid PCB board, but really some special companies need a semi flex PCB.
The definition of semi flex PCB
If you have a look semi flex PCB, you may find it really don’t like a pic flexible printed circuit board.
Because it looks like a rigid PCB board.
In fact semi flex PCB is a flex-rigid PCB, typically 4 layers.
Also have other layer’s type of semi flex PCB.
And the surface is very similar to a conventional PCB, due to made entirely of FR4 PCB base material.
Compare semi flex PCB with conventional PCB board
We have mentioned that the surface of semi flex PCB is very similar conventional PCB.
But it’s really unlike flex-rigid PCBs.
As we know all flex-rigid PCBs use Polyimide to flexing the board.
In semi flex PCB process, never use Polyimide PCB material, its use a thin FR4 core with two layers of copper specially treated to flex without cracking.
How to deal the FR4 Core in semi flex PCB
In most semi flex PCB processes, use a thin FR4 core to produce.
But in some small flex PCB manufacturers, there were hard to handle an FR4 core to thin.
So they just at a depth-milled layer rather than a core.