What Is Blind And Buried Via PCB?
Blind and buried via PCB came by high density and high precision electronic products requirement.
- Buried via is interior vias between top layer and bottom layer,it can not see after pressing,so don’t have to occupy the outer layer area.
- The blind via is non-drilled vias,it can be seen at one surface side but can’t be seen at another surface side.
Blind and buried via features:
- Eliminate large number of through hole design to improve routing density and package density.
- The design of interconnect structures can be diversification and complicated.
- Obviously improved the reliability of multilayer board and the electrical performance of electronic products.
There are three different ways to make the blind and buried via:
1.Mechanical fixed depth drilling
The process is traditional drilling of making multilayer PCB,set the depth of Z axis by using drilling machine after pressing.But there are several problems with this method:
a . Production efficiency is very low, only drill one panel one time.
b. Drilling machine table level requirements strict, each spindle drill depth settings to be consistent, otherwise it is difficult to control the depth of each hole
c. The hole plating is difficult, especially when via depth is bigger than via size, it is almost impossible to do hole plating.
The limitations of these processes have made this method less useful.
Taking 8 Layer PCB as an example, the blind hole can be produced simultaneously by successive pressing method. The first four sheets inner core by PTH double side way to make (or other combination; 6 Layer+ double sided, double double sided at top and bottom furface+ 4 Layer) and then pressure four sheets cores to 8 layer, produce by full hole. This process is long and cost much higher than others, so it is not common.
3.Build up Process
The extension of this method the lamination Sequential concept, a layer to the plate increases, and to drill the hole for interconnection between layers. There are mainly three kinds of way, as follows:
- Photo Defind photo via using photosensitive resistance agent, is also a permanent dielectric layer, and then according to the specific position, to do the film exposure, developing action, to expose the bottom copper pad, a bowl shaped blind hole, with copper and copper plus comprehensive chemical. After etching, the outer line is connected with the Blind Via, or without copper plating, and the copper paste or silver paste is used to complete the conduction. By the same principle, add one layer at a time.
- Laser Ablation laser hole burning laser hole burning can divided into three; a CO2 laser. One is Excimer laser, and the other is Nd:YAG laser. Some of the three laser hole burning methods are compared.
- Plasma, Etching, this is the Dyconex company’s patent, the business name is DYCOSTRATE method.
The above three commonly used layer adding method in the non machine drilling type, three blind hole process should be clear. Wet chemical pitting isn’t be introduced here.
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