PCB drilling is one of important part for PCBs, especially for the multilayer PCBs.Usually, the cost of drilling account is 30% to 40% to the total in PCB fabrication.
In terms of function, the holes can be divided into two categories, one is used for electrical connection between each layers; the other one is used to fix or position the components.
There are three types of holes in PCB design, which are blind vias, buried vias and through holes with HDI PCB design.
1) Blind via: We usually use laser drill to meet them,and the size of hole is Dia. 0.1mm,they are used to connect external layer with inner layers. Sometimes, we also drill them out by drill machines if it is possible.
2)Buried hole:As you know, they are buried in the PCBs. So they are used to connect between inner layers.
3) Through holes: They are drilled through the whole printed circuit board. Some holes we called PTH have the function of electric interconnection, some holes we called NPTH can be used as a positioning hole to assemble components. Through holes are easier to achieve in the pcb manufacturing process, so they are lower cost than blind holes and buried holes. If you want to discrease the cost of your PCBs’ cost,you would be try to avoid the blind &buried holes’ design ,only when it can’t meet the requirement of PCB design.
How to save your money from drill design? Some PCB designers usually would prefer to use small holes,Why? it will get more space for circuits layout. But they ignore one thing, the cost of drilling is the smaller the more expensive. So try to choose big holes in your design if it is possible. Another reason is that hole size is impossible to decrease unlimitedly, because it’s limited by process capability and plating. The smaller hole size will take longer drill time, and they are easier off center position while process. When the ratio between board thickness and hole size is over 8:1, it will be hard to plate hole wall with copper smoothly. For example, a standard 6 layer PCB with thickness about 63 mil, so the PCB manufacturer can provide the minimum hole diameter to 8 mil.
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