High-Density Interconnect (HDI) PCB Design Guidelines

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HDI PCBs have changed the outlook of the electronic devices we are using nowadays. Initially, PCBs were enough to add all the required functionalities in a device, but as technology advanced, so did the products. With everything being built for portability and mobile phones being able to perform the functionality of a computer, the need arises to minimize the size of existing PCBs.


PCBs created using the High-density interconnect technology are smaller in size and able to pack more components, thus eliminating the need to use multiple circuit boards for a single device.


As they are highly intricate, designing an HDI PCB requires multiple steps and thus multiple challenges. Let’s discuss the HDI PCB design guidelines in detail.


Difference between HDI PCB and Standard PCB


The major difference between HDI PCB and standard PCB is their size. HDI PCBwas designed solely for the purpose of reducing the diameter of the circuit board and increasing the connection density between vias. The HDI PCB boards are lighter and smaller as compared to the standard PCB.
Moreover, their manufacturing process is also different. HDI PCBs are created using direct laser drilling, whereas standard PCBs are created using mechanical drilling. HDI PCBs also offer faster speed, higher signal transmission, and reduced signal loss.
All in all, it becomes quite apparent how HDI PCBs are being utilized in different industriesand how their demand has increased.


Must-Have Features in an HDI PCB


When creating an HDI PCB layout to ensure you can increase the component count and keep the board size small, there are a few features you need to keep in mind, including:


• Layer count: an HDI PCB board needs to have multiple layers. Especially if you are working with high pin density components, the count can go up to 20 or more.
• Via type: if you use the standard through-hole vias, you won’t be able to minimize the size. Use vias like microvias, blind vias, or buried vias for layer connections. These vias are smaller and can work with finer pitches.
• Trace thinness: your HDI PCB board should have thin traces. This will ensure that vias make a connection in each layer and have a higher trace density.


Other things to look out for are signal density, stack-up, and via types, which we will discuss in detail below.


HDI PCB Design Guidelines


The process of manufacturing an HDI PCB is quite complex and something that can’t be summed up in words. We have created an overview of the steps, so you get the idea.
1. First, you need to determine the layer count. You can do this by using the largest BGA component.
2. Next, you need to select the materials for your HDI PCBcircuit board to build your PCB stack-up.
3. Then, depending on the device and the space you have, choose a via type that you will use to connect the layers.
4. Plan HDI PCB design guidelines based on the reliability test and the material you are working with.
Once you have a planned design guideline in hand, there are three routes you can take to create a high-density PCB: standard lamination, sequential lamination, or lamination build-up with micro via.


Lamination Technique


Among the ones mentioned above, the last one is most suited to manufacture an HDI PCB. Why? Because the standard lamination might cost less, but it is difficult to route, especially when working with multiple BGAs. Sequential lamination is sometimes used for HDI PCB design, but it has a limit of two to three layers maximum, which reduces their trace widths and number of components.


In comparison, the microvia PCB design helps achieve a high-density route with fewer layers. Especially if you have multiple large fine-pitch BGAs, the lesser layers will open up the effective use of patterns working with microvias and enablefaster routing. It is also cost-effective to produce and provides higher frequency and higher density circuit boards to keep up with the current technology.
Besides the lamination technique, you also need to choose the stack-up and via type for your HDI PCB layout.


HDI PCB Stack-up Types


Among the many types of HDI PCB layouts available, these are the most commonly used.
1. 1+n+1 PCB
This is the simplest type of HDI PCB circuit board. It has a single build-up of high-density interconnected layers and thus requires one lamination on each side of the core.
2. 2+n+2 PCB
This HDI PCB stack-up consists of two interconnected layers and allows the microvias used to be stacked or staggered, depending on the requirement. It has a slightly complex design and can increase the overall cost of the HDI printed circuit board.
3. M+n+M
As the number of layers increases from two, we use the formula M+n+M to calculate the number of layers. Other commonly used HDI PCB layouts are 3+n+3 and 4+n+4.
4. Any-Layer PCB
Another complex option is any-layer PCB. This is typically used in mobile phones and other hand-held devices. The dense layout enables PCB layers to interconnect freely with the microvias PCB.


Choosing the Right Via Type


Based on the variations of the vias, there are generally six types of HDI PCBs, such as via-in-pad, stacked and staggered vias, stacked and staggered microvias, etc. Choosing a via type depends on your product requirement and the material you are using.


Since the via holes get smaller in an HDI PCB, the best approach is to use the via-in-pad technique. This enables you to drill a hole inside the pad and reduce the size of the printed circuit board. For this method, you also need to use via fills, such as a conductive epoxy and copperplate to cover up the via.


The drilling technology and costs are other factors that you need to take into consideration when manufacturing an HDI PCB. HDI PCBs use advanced technologies such as blind/buried via and micro via PCB and are extremely complex and costly to manufacture than conventional PCBs.


If you are unsure about the materials being used and the best technique to move forward with, consult with Hemeixinpcb to get a free quote or use their expert services to design, manufacture, and assemble any type of HDI PCB and get it delivered right toyour doorstep.

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