Layer Stack-up

Layer stack-up means the arrangement of the copper layers and the insulating layers before PCB layout design, and these layers form a PCB. The consideration of layer stack-up depends on the technical capabilities of the production and the electrical performance requirements of the PCBs. For multilayer PCBs, a stacked PCB in PCB applications has many advantages. Here is an example of ten layers' stack-up.

The reason and the advantages of layer stack-up for PCBs

The multilayer PCBs are the result of the demands of miniaturization, lightweight, multiple functionalities, and high speed for modern electronics. A multilayer PCB contains at least three or more conductive layers. Interference, noise, and stray capacitance may exist if the layer arrangement is inefficient when it comes to the complex and high-density PCBs. An optimal multilayer stack-up benefits the end product greatly.

• l Poor stacking will cause EMI (electromagnetic interference) radiation to rise because reflections and ringing in the system can significantly reduce product performance and reliability due to impedance mismatches.
• l Layer stack-up allows getting more circuits on a single board through multilayer design of PCBs.
• l A well-designed layer stack-up can increase the EMC of a product.
• l An excellent layer stack-up can both minimize radiation and prevent the circuit from interference from external noise sources.
• l Carefully stacked PCB substrates can also reduce signal interference and the impedance mismatch issues.
• l Good PCB layer stack-up helps to balance the demands for cost-effective manufacturing methods with concerns about the signal integrity issues.

Some tips in PCB layer stack-up

No matter how many layers a PCB design has, the specifications of trace widths, pad spacing, copper weight, and drill sizes must in line with the PCB manufacturing capacity. And for PCB fabrication and assembly, the number of the layers, the arrangement or stack-up of the layers, and the material types are of significant effects. There are several tips for a better design of layer stack-up:

1. Determine the number of the layers

The primary consideration for PCB stack-up is determining how many layers are needed. This includes the signal type (high speed or low speed), power (a part of the circuit or for high power boards), ground layers, or planes. Do not mix the signal types on the inner layers.

2. Determine the layer arrangement

The number of layers can be predicted according to the pin density. And how to arrange the layers should follow some rules. Firstly, place the signal layer next to the internal power plane for tight coupling. Secondly, the space between the power layer and the ground layer should be minimal. Thirdly, avoid having two signal layers next to each other. Fourthly, make the stack symmetrical inward from the top and the bottom layers.

3. Determine routing and vias

The routing of the traces, the copper weight, the position of vias, and the vias' type of implement, these are the essential factors of layer stack-up.

4. Determine the material types of the layers

There are standard thickness and other properties for various circuit board materials. Therefore, the thickness of each signal layers and the thickness of the prepreg and cores need to be determined according to the electrical, mechanical, and thermal properties of different board material.

NextPCB provides multilayer PCBs with the layers from 4 to 16 layers, board thickness from 0.6 to 2.5mm, outer copper weight from 1 to 3 oz, inner copper weight from 0.5 to 1 oz. If you need more information about the default stack-up of standard PCB, or custom PCB stack-up service, or layer stack-up for PCB prototype, please contact online services, you will get answers very quickly.