Laying Out a High Multilayer PCB
With the electronics industry leaning toward smaller and more functional options, it is no wonder that multilayer PCBs have gained favor. These devices allow you to pack a lot more components into a single, durable device.
However, these boards require a skilled designer to handle them correctly. Various factors have to be taken into consideration such as inner layer compensation value and interlayer alignment control.
Controlled Impedance Traces
Controlled impedance is a critical factor in high-speed digital circuits. It ensures that the signals on a PCB are properly transmitted without distortion. This involves ensuring that the characteristic impedance of a conductor trace matches that of the signal head and tail components. A mismatched impedance means that the signal energy will be reflected, attenuated, delayed or lost during transmission.
This can be a serious problem for high-speed digital circuits, especially in multilayer PCBs. This is because these boards often have a mix of different impedance traces. To prevent this, the circuit designer must use appropriate tools to calculate the optimum impedance of each layer of the PCB. These tools can include SPICE-based simulators and Bode plots.
It is also important to note that the PCB fabrication materials and layer construction will have a significant impact on the calculated impedance. For this reason, it is best to work with High Multilayer PCB a PCB manufacturer that understands the needs of the customer and can provide advice on how to avoid potential issues.
It is important that the controlled impedance traces can be clearly distinguished from other traces on the board. This makes it possible for the PCB manufacturer to quickly locate them and, if necessary, adjust the trace width to achieve a particular impedance. For example, if the designer requires a 5mil trace to achieve 50 ohms, it is usually best to make this trace 5.1 or 4.9 mils wide.
Buried or Blind Vias
Both blind and buried vias require specialized drilling, plating, and lamination processes, adding to the cost of the PCB. However, they are essential in high-density circuit designs, enabling the creation of smaller and faster electronic devices. The use of these specialized vias also eliminates the need for additional components and increases the reliability of the product.
Unlike regular through-hole (TH) vias, which have a hole depth to diameter ratio of 1:1 or more, blind and buried vias have a much smaller gap and therefore have a lower impedance value. This reduces the amount of signal energy reflected off of the via, improving signal quality and transmission speed.
In addition, blind and buried vias are less susceptible to mechanical errors like drill breakouts. This is because they pass through only a precise portion of the PCB, making them less likely to impact the overall reliability of the board.
It’s important to note that buried or blind vias cannot start or end on the top side of a core layer, and they must always span an even number of copper layers. In addition, they should be plugged or filled with solder resist to prevent the copper from being exposed and causing oxidation or failure. Blind and buried vias are best used in high-speed PCBs, as they offer the highest possible signal integrity.
Layer Stackup Strategy
During the layer stackup phase, it’s important to think about your PCB design requirements in terms of what you want the board to achieve. For example, the layer structure can help you reduce electromagnetic interference (EMI), optimize signal-to-noise ratio (SNR), and manage power dissipation.
In addition, it’s a good idea to make sure that the copper layers have low loss tangent High Multilayer PCB Supplier so they can carry high-speed signals for long lengths with minimal signal attenuation. Also, you can use different ground planes to lower the overall impedance of the circuit boards.
A popular layout is the four-layer stackup, which has four copper layers separated by three insulating layers. This configuration is ideal for average to complicated electronic circuits that need a little bit of extra signal isolation. It also offers more routing options.
Other layer stackup strategies include the six-layer stackup, which has six copper layers separated by five insulating layers. This configuration is suitable for high-density circuits that require a lot of signal isolation and has the added benefit of providing more routing options.
Depending on your requirements, there are many other ways to configure your PCB’s layer stack. However, it’s always best to consult with a team of experts to ensure you have a technically sound and manufacturable build-up. You can use Sierra Circuits’ Stackup Designer to build the perfect layer stack for your circuit board.
Layout
When it comes to laying out the components of a high multilayer PCB, most of the work is the same as with single-sided or double-sided boards. However, you need to be more careful when positioning sensitive signals because they will have less space for routing channels. Also, the split planes need to be well-planned so that sensitive signals don’t cross them and ruin their return path.
The electrical connections between layers are made through metallized holes, which can be passersby or buried vias. The buried vias save space and prevent waste by intelligently sinking into the layer. The different layers are categorized into different planes such as ground, power, and signal. Once you have the design, you can then export the layout information to a gerber file that can be used by the manufacturer to fabricate the PCB.
In the past, a lot of people avoided multilayer PCBs because of their high cost. Nowadays, the technology has become mainstream, and people are willing to pay more for higher-capacity electronics. As a result, we are seeing more and more consumer electronic products using multilayer PCBs. This is mainly due to the fact that they offer more functionality in a smaller package. In addition, the use of multilayer PCBs allows for higher speed and power. With the right multilayer PCB stack-up strategy and layout, you can get the most out of this technology.