There are four categories of blind vias for your information, and we will discuss each of them in detail here. The diagram below shows the different types of PCB vias.
Photo-Defined Blind Via PCB
You can make a photo-defined blind by coating a photo-reactive resin sheet to a core. The core should consist of laminated traces enriched with planes and submerged signal layers. Remember to cover your photo-reactive sheet with patterns that shield the points where you will make the holes. You should also expose the sheet to wavelength rays to harden the residues on the board. After that, immerse your circuit board in a dying mixture to eliminate any unwanted substance from the holes. When you have finished the scraping process, plate copper into the holes and on the surfaces are to form the board’s surface layer.
Sequential Lamination Blind Via
You can make this type of blind vias by passing a thin laminate piece through the two-faced PCB process. First, you need to drill, coat, and sketch the laminate to outline the characteristics that will make your PCB’s second layer. Leave the solid copper material on the other PCB part to act as your board’s first layer. It would be best if you also laminated your subassembly with the different board layers. Finally, pass your product through the process of making the surface layers of a multilayer board.
Controlled Depth Drilled Vias
As illustrated in figure 1, you can make controlled-depth vias using the through-hole via approach. However, you should set your drill to pierce only halfway through the board. You also need to place a pad on the second layer so that the drill penetrates it. Besides, it would help if you were cautious to ensure there are components underneath the percolated hole, forming contact with it. Lastly, you need to coat copper in the percolated hole concurrently with plating copper in the through-hole blind vias.
Laser Drilled Blind Vias
You can create these vias after laminating all your board layers; you can create these vias before designing and coating the surface layer. Use a laser to remove the copper on the surface layer and the insulating substance between the first and second layers. Remember, you can either use the CO2 or Excimer laser.
- Blind Via PCB Aspect Ratio
You can calculate the blind via aspect ratio as shown below:
PCB Aspect ratio = PCB Thickness divided by the Diameter of the Drilled Hole.
Note that blind vias will minimize your board aspect ratio by decreasing the number of supported layers. Therefore, use blind-hole vias instead of through-hole.
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