typical layer count in an HDI printed circuit board
Whether your PCB is to be used in high-tech, complex electronics or in simpler items that only require simple functions, the number of layers will have a significant impact on the overall cost. Multilayer circuit boards are typically much more expensive than single- and double-layer PCBs. However, there are many factors to consider before you decide how many layers your circuit board should have.
The typical layer count in an HDI printed circuit board is between 6 and 12 layers. In fact, some boards may even have up to 14 layers, but this is not the norm. The key consideration is the types of machines and devices that will be using your circuit board and the demands they will place on its circuitry.
There are two main types of standard hdi printed circuit board: sequential lamination structures and every layer interconnect (ELIC). In the sequential structure, cores are first constructed, then laminated, and finally, drilling, plating and filling processes are carried out. The ELIC structure is more popular as it allows conductors on any layer of the stack-up to be freely interconnected through copper filled stacked microvia structures.
What is the typical layer count in an HDI printed circuit board?
HDI PCBs require very tight tolerances, especially for via hole size and line width. This means the use of advanced laser drill techniques and stringent quality control measures. It also requires working with experienced PCB manufacturers who have specialized expertise in the technology.
Another challenge with HDI PCBs is ensuring the precise positioning of each layer. This is achieved through the use of photoresist deposition and exposure that defines areas to be etched, which in turn creates the pattern of conductors on the surface of the laminate.
The type and amount of via holes is another factor that influences the cost of an HDI PCB. The most common vias are blind and buried, but there are other options, too. These include staggered vias and a variation of the conventional buried via called a via-in-pad (VIP).
There is a large range of available via styles for HDI PCBs. They vary in aspect ratio and the size of the via opening, as well as the thickness of the underlying dielectric. Laser drilled microvias typically have an aspect ratio less than 1. Achieving this is challenging, but it provides superior reliability to mechanically drilled through-hole vias.
The via-in-pad process is a relatively new method for connecting the layers of an HDI circuit board. This is a very complex and costly manufacturing technique that combines the plating of the via, one of several different fill materials and a pad, the creation of an inner layer connection, the creation of an outer layer connection and then the final etching of the circuit board. This is a very efficient process that is often utilized for HDI applications where space is limited and the highest reliability is required. The process is most commonly seen in mobile/cellular phone, tablet and laptop computers as well as military applications such as avionics and smart munitions.
