Blind and buried via PCB came by high density and high precision electronic products requirement.
Blind and buried via features:
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.
2.Sequential lamination
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:
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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