Volume and available manufacturing capabilities are two of the most important factors which affect PCB costs as well as the production of low cost yet high speed PCBs that differ when it comes to the number of layers they are using.
However, the market demand for a programmable logic with increased pin count pushes manufacturers to provide its end-users with an increased number of PCB layers which are implemented in a circuit. The more layers the boards have, the more costly the PCB fabrication is. The fabrication cost of these boards also varies depending on volumes and current market conditions.
The market nowadays chooses devices with high-speed PCB designs that have four to six available layers. However, there are pros and cons present on these types of PCBs that you should be aware of before deciding which is better for your needs.
Four-Layer High Speed PCBs
When looking for a high-speed PCB at the minimum possible cost, a four-layer board can be the best choice for you. This type of PCB is made up of a pair of two-layer hardboards which are stuck together while a pre-preg spacer is located in between.
Moreover, the pre-preg’s thickness on a four-layer PCB is not well controlled compared to the hardboard's thickness. If you want better control for impedance traces, using layers separated by hardboard as ground and signal is what is recommended.
A four-layer high-speed board has the following recommended stack-Up:
- Signal layer is the first layer
- The second layer is for power
- The third layer is for ground
- The fourth layer is a signal layer
This type of stack-up allows you to place most of the routing on the fourth layer which is also closest to the ground layer. This allows a higher component density on the first layer.
In order to provide the lowest possible impedance for power distribution, the spacing of the ground planes and power should be as close as possible.
Six-Layer High Speed PCBs
Six-layer high-speed PCBs, when compared to four-layer ones, are a lot more costly to manufacture and are also more expensive in the market. This is because it makes use of more layers which equates to a need for more resources.
Keep in mind that more layers doesn’t mean that the board is better. When it comes to PCB design, design engineers like to work on a few layers as much as possible as it equates to lower costs and less design cycle iterations.
The use of more layers is considered as a solution when too much stuff is already used on board and there is a need to unload some of them on another layer.
Nevertheless, manufacturers also make use of the additional layers as a chance to provide additional functionalities or more power for the end user. This can make a six-layer PCB also a good choice for end-users.
Through a careful analysis of what these high-speed PCBs can offer, you will be able to determine which type of board is best for you.
