Parenthood is one of life’s greatest joys. Having the opportunity to watch a child grow and learn is fascinating and rewarding, knowing that you play a vital part in the process. Perhaps the most awesome part is watching infants play while they learn the basics that form the foundation for future knowledge and skill development. The ability to grasp the basics is required before any higher level of understanding can occur. One of the essential basics is ordering or understanding where things belong within a larger group. The Towers of Hanoi game is a good way for a child to learn about ordering layers.
Layers and their order are also an important basic aspect of PCB design. For multilayer boards that employ surface mount device (SMD) packaging, determining the best order for your layers, the PCB stackup, defines how your board will be built and how your printed circuit will function. There are a number of considerations that influence your choice of stackup. Questions that must be answered include how many signal layers are needed, how many ground planes are required, how thick should the layers be, and what materials should be utilized. In order to optimize your board’s PCB layers and their arrangement, you need a good understanding of the types of PCB layers and properties.
Types of PCB Layers
The number of PCB layers in your board construction refers to the number of different layers or levels that will carry signals. The layer type denotes the type of signal that will be propagated along that layer. Each signal or PCB layer is composed of a dielectric material with a copper surface(s). Most layers have etched traces; however, the copper surface may also be a solid plane for grounding or power. Typically, the signal type can be classified as high frequency, low frequency, power or ground. Depending upon the signal type, the dielectric and copper may have different design requirements.
PCB Layer Type Design Requirements
The primary material considerations for your PCB layers are dielectric and copper. The dielectric material provides isolation between different signal types on adjacent layers. It is also a major determinant of the board’s resistivity. The surface copper of the layer defines trace current capacity, resistance, and loss. The copper weight or thickness is used to ensure that adequate current flow is possible. In close correlation with the copper weight is the trace width and length that specifies the physical space for each signal path. For high-frequency AC signals, trace matching (length and width) is important for signal integrity, while for power and ground signals, loss minimization (which corresponds with shorter traces) is important. The table below summarizes design requirements that should be considered when designing your PCB layers.
|Signal Type||Dielectric Requirements||
|High Frequency||Consistent impedance over a wide frequency range, lower thickness||Matched thickness and length for differential signal pairs|
|Power||Low thermal resistance||Thicker copper and wider traces, high thermal conductivity|
|Ground||Constant impedance over the plane||
Use ground vias if signals go from one plane to another for multilayer boards
In the table above, “None” denotes that default materials, such as standard FR4, are probably sufficient. There are many material considerations that impact your board’s performance. These are usually categorized as electrical, mechanical, thermal or chemical properties and should also be considered as you design your PCB stackup.
DFM for HDI Printed Circuit Boards
How to Optimize Your Board’s PCB Layers
Creating the best board layout for your design necessitates that you optimize your design for its manufacture by your CM and operation. This can only be accomplished by making the best selections for the stackup and the PCB layers of which it is comprised. Following the tips below will assist you in reaching these objectives.
Tips for Stackup of PCB Layers
Tip #1: Determine your board signal type(s)
The type of signals that will be present on and through your board is the most important factor for selecting your stackup and layers. For special and multi-signal processing, you will most likely need more layers as isolation and different grounds are required.
Tip #2: Determine the number and types of vias
Another determinant of your stackup requirements is your via choice. For example, if you opt for buried vias, then additional internal layers may be required.
Tip #3: Determine the number of signal layers needed
Once your signal types and vias have been determined, you can design your stackup by defining the number of layers needed and their types.
Tip #4: Determine the number of planes needed
Choose your power and ground planes such that they can be used to shield signal layers and reduce EMI.
Tips for Choosing PCB Layers
Tip #1: Define layers based on signal type
In order to determine what parameters or material characteristics are best, each layer needs to be classified based upon its function or the type of signal it will carry.
Tip #2: Choose layer dielectric and copper based on signal requirements
With your layers classified, you can select their dielectric and copper values. These selections will heavily influence each layer’s mechanical, electrical, thermal and chemical properties. However, other material properties should also be considered for the refinement of your choices based upon their significance for your PCB layer type.
|Tempo‘s Custom PCB Manufacturing Service
Optimizing your PCB layers is only possible by following a good paradigm to make the best material selections and working with a CM that is able to implement your choices. At Tempo Automation, we specialize in fast, high-quality PCB manufacturing for prototypes and low-volume production. Our capabilities include various material types and via options to meet your custom requirements.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB layers or optimizing your stackup for manufacturing, contact us.