1. In the core structure, all conductive layers of the PCB are applied to the core material.
2. The Shanghai SMT processing plant points out that in the foil structure, only the internal conductive layers are coated on the core material, while the outer conductive layers are applied to a foil-clad dielectric board.
3. All conductive layers are bonded together using a dielectric through a multilayer lamination process.
4. The core material consists of a double-sided foil-clad board from the factory.
5. Since each core has two sides, when fully utilized, the number of conductive layers in the PCB will be even.
6. Why not use foil on one side and a core structure for the other? The main reasons are the cost of the PCB and its susceptibility to bending.
7. Balanced structure to avoid bending.
8. The primary reason against designing PCBs with an odd number of layers is that they are prone to bending.
9. When the PCB cools after the multilayer circuit bonding process, differing lamination tensions between the core and foil-clad structures can cause the board to warp.
As the thickness of the circuit board increases, the risk of bending in the composite PCB board with two different structures also rises. The key to preventing PCB board bending is to adopt a balanced stack. Although a PCB board with a certain degree of bending may meet specification requirements, subsequent processing efficiency will be diminished, leading to increased costs. Special equipment and craftsmanship are required during assembly, which reduces the accuracy of component placement and can compromise quality.
Use Even-Numbered PCB
When an odd-numbered PCB board arises in the design, the following methods can be employed to achieve balanced stacking, lower production costs, and prevent PCB board bending. The methods are prioritized, as advised by PCB chip processing factories:
The first point:
Utilize a signal layer. This method is applicable when the design PCB has an even number of power layers and an odd number of signal layers. Adding this layer does not incur additional costs, but it can shorten delivery times and enhance PCB board quality.
The second point:
Add an additional power layer. This method is suitable when the design PCB has an odd number of power layers and an even number of signal layers. A straightforward approach is to insert a layer in the middle of the stack without altering other configurations. Begin by following the odd-numbered PCB board wiring, then replicate the ground layer in the center, and label the remaining layers. This maintains the electrical characteristics akin to a thickened layer of foil.
The third point:
Incorporate a blank signal layer near the center of the PCB stack. This method minimizes stacking imbalance and improves PCB board quality. Start by routing through the odd-numbered layers, then add a blank signal layer and label the remaining layers. This technique is useful in microwave circuits and mixed media (different dielectric constants) circuits.