How To Achieve A Perfect HDI

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Storm PCB offers quick turn HDI from 4 layer to 20 layers, fastest can be 4  days. 

HDI PCBs are so popular and in-demand nowadays because they follow the current technology trend of miniaturizing devices and electronic gadgets without compromising on efficiency and performance. HDI PCBs are different from traditional PCBs and can be used for high pin count and finer pitch devices. That’s why its design and manufacturing process is complex but cost-effective as less material and fewer layers are used.

If you are designing an HDI PCB for your project, check out the complete guide below and create the perfect HDI PCB.


What Is HDI PCB?


Before we move on to the fabrication process, let’s discuss what HDI PCBs are. A high-density interconnector is a type of PCB that packs more components on a smaller circuit board without affecting the performance.

The reduced layers and signal length increases the signal integrity and makes it perfect for almost all electronic gadgets such as smartphones, automobiles, defense systems, and much more.

HDI PCBs provide higher wiring density while further reducing the size of conventional circuit boards. The resulting electronic gadgets are smaller, lighter, and more efficient. The shorter signal path also increases the data transmission speed.

HDI PCB is constructed using smaller lines and spaces, micro vias, and connection pads, all of which play a crucial role in its miniaturization, as you will see when you read ahead.


How to Achieve the Perfect HDI


There are a lot of steps involved in creating the perfect HDI PCB. How to choose PCB material ?


Proper material selection is essential as it will determine the performance efficiency of your HDI PCB. Generally, materials are chosen depending on your project requirements and how the HDI PCB will be manufactured, but there are a few key questions you need to ask yourself. For example, will the material be able to withstand heat? Is it suitable for sequential lamination? What’s the dielectric constant and loss of the material?

If you are creating a high-speed data transmission device, you need a dielectric material that does well with thermal expansion, glass transition, high temperature, and more. But such materials are costlier.

Ideally, you need a material that has low loss and high speed, but since the cost will build up and complexity will increase, the most commonly used material is the FR-4 family. These materials offer average loss and speed and are ideal for analog and digital devices.


HDI Structure


HDI PCBs are designed in multiple ways. Manufacturers use the following 3 formulas to build up layers as required.


1. 1+n+1
There is only one high-density interconnection layer in this type of HDI PCB structure.

Below is example for 4 Layer and 6 layer structure with 1+N+1


2. 2+n+2
2+N+2 means the HDI PCB needs twice laser drilling, and both the upper and bottom outer layers have 2 PCB layers. Unlike 1+N+1, 2+N+2 has two cases. One is that the microvias of the two adjacent outer layers overlap, and the two microvia form a stacked via. The other case is that the microvias of the two adjacent outer layers do not overlap, and they form a staggered via. As we know, it requires extremely high precision to locate and pile up two microvias, so stacked via HDI PCBs are more expensive than staggered via HID PCBs.

There are two types for 2+n+2, one like below, we call the stackup with HDI interleaving.

Here is another type for 2+N+2, we call the stackup wtih HDI Stack

3+N+3,4+N+4, like below. if you have any HDI questions, please feel free to contact us .


3. Any Layer
In this type of HDI PCB, all the layers are HDI layers and easily connected. This is ideal for devices with higher complexity and stronger signal integrity demands such as smartphones, computer chips, etc.

The most expensive sturcture is any layer . That is you can design with vias from any layer to any layer,but too expensive.Many factories can not make such structure, no worries ,we can do here. 

 


Via Type
Next up is via type. There are a total of 8 via types used for HDI PCBs, such as blind, buried, through-hole, stack, staggered, micro via, etc. The choice between these can determine the final cost of your project and the manufacturing method and tools that will be used.

The most popular choice for HDI PCBs is micro vias. They help reduce the number of layers and size of the circuit board. Moreover, they can either be used as blind or buried vias, depending on how they are drilled and electrocuted.


An HDI PCB prototype is a simplified version of your HDI PCB that you can test and analyze. Professional HDI PCB manufacturers create prototypes to check different designs and test the performance and efficiency of each. The prototypes consist of stacked, staggered, micro via, blind, and buried vias, so you can create any combination and see which works best.

HDI PCB manufacturing methods vary depending on the HDI builds, and the common manufacturing is sequential laminating. The simplest 1+N+1 HDI PCB manufacturing is similar to multilayer PCB manufacturing. For example, a four-layer HDI PCB with a 1+2+1 structure is manufactured in this way:

  • 1. The two inner PCB layers are manufactured and laminated, and the two outer layers are manufactured.
  • 2. The two inner layers are drilled by mechanical drilling. The two outer layers are drilled by laser drilling.
  • 3. Blind vias in the inner layers are electroplated. The two outer layers are laminated with the inner layers.

For the 2+N+2 stacked via HDI PCBs, the common manufacturing method is below (take a 2+4+2 HDI PCB as an example):

  • 1. The 4 inner PCB layers are manufactured and laminated. Layer 2 and layer 7 are manufactured.
  • 2. The inner layers are drilled by mechanical drilling. Layer 2 and layer 7 are drilling by laser drilling.
  • 3. Blind vias in the inner layers are electroplated. Layer 2 and layer 7 are laminated with the inner layers.
  • 4. Microvias in layer 2 and layer 7 are electroplated.
  • 5. Layer 1 and layer 8 are manufactured. The HDI PCB manufacturer locates the places for the microvias and drills by laser drilling.
  • 6. Layer 1 and layer 8 are laminated with the finished PCB layers.

Manufacturing 2+N+2 staggered-via HDI PCBs is easier than 2+N+2 stacked-via HDI PCBs because the microvias do not require high precision for locating and stacking.

In HDI PCB manufacturing, besides sequential laminating, technologies for creating stacked vias and in-hole metallization are also in use. For the higher HDI builds, the stacked vias in the outer layers can also be directly drilled by laser. But direct laser drilling requires extremely high precision for the drilling depth, and the scrap rate is high. So direct laser drilling is seldom applied.

 

2022-06-22 10:25
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