Why Choose High Multilayer PCB Fabrication Materials?
The multilayer PCB fabrication materials used have a significant impact on its performance and cost. It’s crucial to work with a PCB manufacturer who understands these factors and can help you choose the best option for your project.
Modern consumer electronic devices like smartphones and smart watches use multilayer PCBs. They are also used in military and aerospace applications.
High-Speed Circuitry
A multilayer PCB is a double-sided printed circuit board that features more than two copper layers. These layers are separated by insulating material to produce a sandwich-like structure that is then bonded and laminated under high pressures and temperatures. Multilayer PCBs are used in many applications such as cell phone systems, power monitoring, test equipment and amplifiers. Generally, these boards feature a total of four to twelve copper layers. The insulating layer is also used to protect the copper circuitry from external heat and vibrations.
If the layers of a multilayer PCB are designed incorrectly, it can High Multilayer PCB result in overshoot, undershoot, electromagnetic interference and improper coupling of signals. These issues can be caused by stray capacitance, known as parasitics. Using the proper layout and design considerations can minimize the effects of these parasitics on signal performance.
In addition to careful design strategies, a high-speed PCB requires a high-quality substrate. The dielectric constant of the substrate material plays an important role in the speed at which a signal travels over the board. A lower dielectric constant results in faster signal propagation.
Moreover, a multilayer PCB should use specialty high-voltage prepregs that have smaller glass styles. This will reduce the number of voids that are created during the lamination process and improve the density of the inner layers. Lastly, the choice of vias should be carefully considered. The types of vias (blind, through hole, buried or via in pad) can impact manufacturing complexity and, therefore, PCB quality.
Controlled Impedance Traces
High-speed signals need a consistent impedance to transmit over long distances. If this impedance isn’t met, the signal will have trouble operating normally. The resulting problems will increase switching times, slow down the response of electronics, and cause unwanted errors. To prevent this, it’s necessary to use controlled impedance for each of the PCB signal traces.
The characteristic impedance of each trace depends on its resistance, inductive reactance, and capacitive reactance, among other factors. It is also affected by the geometry of the copper trace, which can be changed to meet the needed impedance. One way to achieve this is by changing the trace width.
It’s also important to make sure that the traces are routed correctly. For example, if the designer specifies a 0.025-inch trace and the manufacturer uses a 0.035-inch one, the resulting change in impedance will be dramatic. It’s best to specify the desired impedance in a clear manner.
It’s also important to note that if the design requires multiple differential pairs, the length of each differential pair should be closely matched. This will reduce the effects of signal speed variations on each pair and approximate the propagation delay. To do this, the designer must carefully select the appropriate serpentine traces. Additionally, it’s crucial to avoid placing components or vias between the differential pairs, as this will create a discontinuity in impedance.
Multiple Ground Planes
Multilayer PCBs have a higher number of layers of conductive copper than single-sided and double-sided circuit boards. They also have insulating layers between the different levels of copper. This allows them to be fabricated with higher performance, including lower impedance.
They are also used for high-speed digital signal lines, as well as EMI control. A common way to manage EMI is to use a ground plane on the bottom of the board. This creates a return path for current on the signal traces, reducing the loop inductance and minimizing EMI radiation. The ground plane must be as large as possible to achieve this. However, it must not be so large that it interferes with the traces that route to it.
To avoid this, designers must carefully plan the layered structure and stackup of the PCB. They should strategically arrange the layers to alternate signals and power planes, while making sure that routing traces do not run on the ground layer in areas where the signal will skip over. In such cases, a bypass capacitor should be placed in the area to make up for the missing current.
When it comes to the assembly of multilayer PCBs, it is crucial that you work with a reliable contract manufacturer. This will ensure that the final product is free from defects and has all the features required for your design. Additionally, they will be able to offer you the best materials for your project, High Multilayer PCB Supplier including FR4 and other advanced options. They can also provide the best trace widths, spacing, and alignment to meet your specifications.
Buried Vias
A PCB requires a means of connecting all layers to one another. These connections are typically achieved through drilled holes called vias. Vias are available in a range of shapes and sizes, and each type has its own benefits and applications.
One of the most popular types is buried vias, which enable PCB designers to increase routing density without increasing layer count. This allows for smaller pitch components, resulting in an overall lighter and more compact circuit board design. It also helps ensure proper signal integrity by limiting the length of signal paths.
Buried vias are a key component of high-density interconnect (HDI) PCBs used in modern cell phones and other multi-function digital electronics. They can be used in other PCB applications when necessary, such as when a design calls for high-speed connectivity or increased signal integrity.
The main advantages of buried vias are that they can be used to connect inner layers without touching the outermost layer. They are particularly useful in RF/microwave circuitry where signal loss and interference must be minimized.
The main disadvantage of buried vias is that they require a more complex manufacturing process than blind vias. This is because the buried vias must be drilled through the inner layers and then hole-plated. This increases manufacturing costs, but it is necessary when a design requires high-density interconnects.