The blind buried hole PCB design is located at the top and bottom layers, and has a relative height to connect the outer circuit layer and the inner circuit layer. Usually, the depth of holes in blind buried orifice plates has a specified ratio (the depth cannot be greater than the diameter of the hole). The drilling depth must be appropriate. If it is not suitable, electroplating holes will be difficult. Therefore, few blind buried hole PCB manufacturers choose this printing method. To achieve this blind hole manufacturing process, holes can be drilled in some of the layers that should be connected, and then pressed together. However, this blind hole manufacturing method requires more precise positioning and alignment equipment from the blind hole PCB manufacturer.
There are three different methods for manufacturing blind buried hole PCBs:
Mechanical designated depth drilling
Using traditional multi-layer board technology to produce blind buried hole PCBs until the lamination is completed. Use a drilling machine to set the Z-axis depth and drill the required depth for blind buried holes. This method is relatively simple, but there are some issues:
Drilling only one board at a time results in low production, which is not conducive to the mass production of multi-layer blind buried hole PCB manufacturers.
The levelness requirement of the drilling machine table is strict, and the drilling depth setting of each spindle needs to be the same. Otherwise, it is necessary to control the depth of each hole in the blind buried hole plate, which makes it difficult to ensure consistent blind hole depth of the blind buried hole PCB.
This method makes electroplating inside the hole very difficult when the aperture is smaller than the depth. In this case, it is difficult to achieve good electroplating inside the hole. Due to the above limitations, this method is gradually no longer used in blind hole and buried hole production.
Sequential lamination:
Taking an 8-layer PCB board as an example:
Step 1: The inner 3 layers (6-4 layers) are made using a typical 1-layer PCB with PTH, while the blind layers 2-7 and 8-XNUMX are made using a regular double-sided PCB;
Step 2: Stack all the layers together: the inner layer consists of 4 layers of PCB and 2 pieces of 2-layer PCB, so we have the XNUMX layer PCB;
Step 3: Produce an 8-layer PCB as a standard double-sided PCB, drill PTH holes, copper plating, solder mask, etc.
But if the blind buried holes are all on the same layer, they cannot be pressed together at once. As shown in the figure below, layers 1-3 and 6-8 are blind holes, while layers 3-6 are buried holes. So both the fifth and sixth layers have blind buried holes. At this point, laser drilling is needed. The steps are as follows:
Step 1: Layer 3-6 and produce copper wire and PTH as standard 2-layer PCB;
Step 2: Press the 2nd to 7th layers together, and laser drill the 2nd to 3rd, 6th, and 7-XNUMX layers to produce copper wire and electroplate through holes;
Step 3: Layering 1-8 layers and laser drilling 1-2, 7, 8-XNUMX layers to produce copper wire on the outer layer, and plating through holes.
Arbitrary lamination and drilling
This method is very popular, and now almost all blind buried hole PCB manufacturing industries around the world are using this method. Many large blind buried hole PCB manufacturers can achieve this.
This method of making blind buried hole plates is an extension of the above sequential lamination/drilling (Method B), but the difference is that it is added layer by layer from the inside to the outside of the plate. Usually, it starts from the second layer of the middle PCB and uses laser drilled blind holes to connect all additional layers. These through holes in blind buried PCB are stacked micro through holes or staggered micro through holes. Stacking through holes means that the through holes are located exactly at the top of another layer of through holes, but staggered through holes are not. This type of blind buried hole PCB is called an arbitrary layer PCB. There are three methods for drilling any layer:
Photo Definition Type
In the process of blind buried hole PCB production, a photosensitive resistor and a permanent dielectric layer are first applied to the board at the same time, then aligned with a specific position, exposed and developed with a negative film, exposing the bottom copper pad to form a bowl shaped blind hole of the blind buried hole board. Then, chemical copper and copper plating are thoroughly added to etch the outer layer of the circuit and blind hole on the blind buried hole PCB, and the outer layer of the circuit and blind hole can be etched, or conductivity can be achieved without copper plating. Copper paste or silver paste can also be filled. Of course, in the process of blind buried hole PCB production, other layers can be added using the same method.
Plasma etching:
This is a patent of a company, so they named their business name after the demonstration method.
Laser ablation:
In the HDI PCB manufacturing process, there are mainly three types: commonly used CO2 lasers, excimer lasers, and Nd: YAG lasers.
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