Blind vias are plated through hole connections that pass from an outside layer and end on an internal layer. They do not pass all the way through the PCB like a conventional via hole. Blind vias aren’t cost effective, unless used for a technical reason such as permitting the fan out of tracking from a fine pitch foot-print. The use of blind vias just to reduce the PCB layer count will not save costs.
There are two basic ways to manufacture PCBs with blind vias. These are either by laser drilling or sequential layer build. Blind via holes may be drilled by a laser through a thin layer of insulating dielectric, usually stopping where the laser beam meets an internal copper pad. Laser drilled blind vias have limitations because the drill hole is small, its depth can be no more than its diameter to ensure adequate penetration of the copper plating chemistry. Therefore, it can commonly only penetrate through just one layer starting from the outside layer.
In the sequential build method, pairs of layers are drilled and plated before bonding. Because these pairs of layers are plated with the hole open at both ends, the plating chemistry penetrates the hole quite easily and the blind via can be designed to pass through multiple layers. By combining the appropriate sequence of bonding, drilling and plating, a wide variety of blind via constructions is possible. This depends on if the blind via can pass through an even number of layers, starting with an outside layer.
This is an example of a 4 layer PCB with blind vias between layers 1 and 2 as well as 3 and 4, together with through holes connecting all layers from 1 to 4.
We can produce a wide variety of blind via pcbs. We recommend that your proposed construction is checked for compatibility with our manufacturing process before design finalisation. Send us details and ask us to quote.