What are blind and buried vias?
Blind vias: When only one side of the vias is in the outer layer of the PCB, they are called blind vias.
Buried vias: When both sides of the vias are buried in the inner layer of the PCB, they are called buried vias.
How are blind and buried vias created?
The following three methods can create blind and buried vias:
Mechanical drilling with fixed depth
Sequential lamination and drilling
Any layer lamination and drilling
What is blind via manufacturing process?
Firstly, we talk about laser drill blind via holes. PCB blind via fabrication process as following:
1) finish all inner layers first;
2) laminate two out layers of prepreg and copper sheet on the ready-finished inner layers of PCB board;
3) drill the controlled depth blind via on the PCB by laser.
Please note accuracy is very important for the blind via in pad.
As for mechanical drill blind via holes, we take 4-layer PCBs with blind vias in layer 1 to layer 2 for example, the process as follows:
1) produce layers 1 and 2 as a standard 2-layer PCB, so there will be drills on layers 1 to 2;
2) laminate two core boards together so we get the 4-layer PCB, and drill the plating through holes;
3) when PCB is finished, you get PTH from layers 1 to 4 and blind vias from layers 1 to 2.
What are the benefits of using blind and buried vias?
The benefits of using blind and buried are stated below:
Reducing the size and weight of the PCB
Reducing the number of layers
Reducing costs of production of several types of PCBs since combining more functions
Improving the electromagnetic compatibility
Increasing the characteristics of electronic products
Making the design work easier and faster
What are the challenges of using blind and buried vias?
The miniaturization of the diameters of blind and buried vias places higher demands on PCB production.
Very highly experienced engineers are needed to design blind and buried vias PCBs.
It is more challenging to assemble blind and buried vias PCBs since they always have tiny pads, such as BGA pads.
What is the normal blind via aspect ratio?
In laser drill blind vias board, the normal blind via aspect ratio is 1:1.
What is buried via?
Buried vias in PCB are via holes between inner layers. We take a 6 layer blind/buried via circuit board for example: blind vias can via holes from layer 2-3, 2-4, 2-5, 3-4, 3-5 and 4-5.
Buried via vs blind via
Blind via and buried via are commonly used HDI PCBs, they always exist in high tech high density printed circuit boards the same time. But they are totally different types of vias.