What Is Blind Vias in PCB?

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The terms "blind via" and "buried via" are typically used in the PCB manufacturing industry. Components have improved with time, as noted in many of our posts on PCBs and other DIY blogs. Furthermore, most electronic devices now have smaller form factors. Hence, the requirement for an efficient HDI PCB design.

So, one of your top priorities when developing an HDI PCB should be the requirement to connect components to both sides of these intricately printed circuit boards. In short, to connect components to different sides of your PCB, you need blind and buried vias. So, on that note, let us take a detailed look at what blind vias are, their uses, benefits, and disadvantages.

What Are Blind Vias?

The surface layer of the PCB is connected to its inside layers through a blind via. Additionally, it should be noted that blind vias do not travel throughout the entire HDI PCB. After all, a PCB has several interior layers, and blind vias are typically used to form an electrical connection between them. This explains why blind vias are only visible in one area of an HDI PCB.

Types of Blind Vias

There are four common types of blind vias used in HDI PCB design. We will discuss all of them in detail down below:

Laser Drilled Blind Vias

These vias can be made before designing and covering the surface layer or after laminating all your PCB's layers. Remove the insulating material between the first and second layers and the copper on the surface layer using a laser. Remember to choose either Excimer or CO2-powered lasers for laser drilled blind vias.

Controlled Depth Drilled Vias

By employing the through-hole via technique, controlled-depth vias may be designed. However, you should only set your drill to puncture your HDI PCB halfway. In order for the drill to reach the second layer, a pad must also be placed.

Furthermore, it would be beneficial to ensure that there are elements beneath the percolated hole that make contact with it. Finally, you must simultaneously plate copper in the through-hole blind vias and the percolated hole for this process to be effective.

Sequential Lamination Blind Vias

This type of blind via can be created using the two-faced PCB method on a thin laminate piece. Drill, coat, and sketch the laminate first to identify the qualities that will define the second layer of your PCB. However, keep your HDI PCB's solid copper material in place to serve as the initial layer of your board.

The ideal approach would be to laminate your subassembly with the various board layers. Finally, put your product through the steps necessary to create the multilayer board's surface layers.

Photo-Defined Blind Vias

Photo-defined blind vias can be created by coating a photo-reactive resin sheet with the core. Laminated traces enhanced with submerged signal layers and planes typically make up this core. However, don't forget to cover the areas where you will make the holes in your photo-reactive sheet.

Furthermore, expose the sheet to the appropriate wavelength rays to harden the board's residues. Then, submerge the circuit board in a dying solution to remove any unwanted material from the holes. Lastly, After the scraping operation is complete, apply copper into the holes and on the surfaces to create the surface layer for your HDI PCB.

Potential Issues with Blind Vias

Listed below are a few issues related to blind vias.

  • Bubbles form when a component with a blind via is soldered onto a part of your HDI PCB. This issue can be solved by drilling the via to the pad's side or covering the hole with copper.
  • Not getting the copper deposit into the hole's bottom and sides. However, you can overcome this issue by ensuring the hole's diameter is larger than its depth.
  • Not following the standard distances between pads or traces on your HDI PCB's inner layers. It will cause problems with component mounting later on.
  • The blind via manufacture process is complex, to begin with.
  • Blind vias are expensive to manufacture due to the extra equipment involved.

Blind Via Manufacturing Process

An efficient way to enhance the density of multilayer boards, decrease the number of layers and board size, and considerably cut down on the number of plated through-holes is to use buried and blind vias. That said, most circuit boards use a combination of blind and buried vias for an efficient HDI PCB design.

These vias typically have a diameter measuring around 0.05mm for buried vias and 0.15mm for blind vias. The thin inner laminate is produced with buried holes using the same method as double-sided PCBs. On the other hand, blind vias are manufactured using a small hole CNC bed that regulates the Z-axis depth. Photo-induced holes, laser drilling, and plasma etching are used to create blind vias.

Carbon dioxide and Nd: YAG ultraviolet lasers are used for the blind via laser drilling. The 9.4 wavelength carbon dioxide drill made by Hitachi can drill 30,000 holes per minute. It can drill around three blind via holes in one pass.

That being said, the blind via manufacturing process is quite expensive and complex. So, ensure you use your HDI PCB according to your device's specifications and physical design.

Differences Between Blind and Buried Vias

Blind and buried vias created using laser drilling and machinal methods have an annular ring measurement of 90 micrometers. However, they differ in aspect ratios, maximum and minimum diameter, and via pad measurements.

Blind vias created with laser drilling have a maximum diameter of 100 micrometers, while buried vias using the same drilling method have a maximum diameter of 0.44 millimeters.

Through mechanical drilling, blind vias can have a minimum diameter of 200 micrometers, while buried vias can achieve a minimum diameter of 150 micrometers.

Similarly, blind vias created using laser drilling have an aspect ratio of 1:1. In contrast, buried vias have an aspect ratio of 1:12.

On the other hand, mechanically drilled blind vias have an aspect ratio of 1:1. In contrast, blind vias created using the same drilling method have an aspect ratio of 1:10.

Wrapping Up

Do you plan to use blind vias in your circuit board design? We urge you to incorporate them into your HDI PCB design to take advantage of their various benefits. Almost all of the information you need to know about circuit board blind vias has been uncovered in this article.

It focuses on the many types of blind vias, their uses, benefits, and drawbacks. So, consider this information and apply it the next time you design an HDI PCB for your electronic projects.

Furthermore, to uncover more information about different types of HDI PCB vias, visit Hemeixin Flex PCb  today to fulfill all your PCB design needs and requirements!

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