The present invention is directed to a bi-stable coupling for controlling the depth of a tool insertion, such as drilling, and similar processes. The bi-stable coupling can be used to penetrate (e.g., drill or push) through a material layer of unknown thickness without plunging the tool into the adjacent layer. In accordance with the invention, in a first state, force is applied to the tool to initiate penetration and a reactive force maintains the device in the first state during penetration and when tool penetrates the material, the reactive force is diminished enabling the device to transition to a second state in which the tool becomes retracted. In medical applications, the invention allows for drilling through bone of unknown thickness without plunging into the adjacent soft tissue.

Back drilling vias of a PCB, including: identifying a particular diameter of a particular via of multiple vias of the PCB; back drilling of the particular via with a first drill bit having a first diameter, the first diameter a first percentage greater than the particular diameter of the particular via; determining whether the first diameter of the first drill bit is a threshold percentage greater than the particular diameter of the particular via; determining that the first diameter of the first drill bit is less than the threshold percentage greater than the particular diameter of the particular via, and in response: back drilling of the particular via with a second drill bit having a second diameter, the second diameter a second percentage greater than the particular diameter of the particular via, the second diameter greater than the first diameter.