Elimination of Hole Mouth Burr in Multilayer PCB Micro-Hole by Using Micro-EDM.

The micro-hole is a key structure in multilayer printed circuit board (PCB), as it enables the effective transmission of electrical signals. At present, the most common way to machine PCB micro-holes is mechanical drilling using micro-bit. However, in the mechanical drilling of micro-holes, these holes are prone to burring at the hole mouth due to the micro-bit failing to cleanly cut through the first layer of copper foil on the PCB. Hole mouth burr can seriously affect the performance of the PCB, resulting in potential short circuiting or even ruining the PCB. To solve the above problems, this paper proposed to machine the first layer of copper foil on the PCB via micro electro-discharge machining (micro-EDM) to eliminate hole mouth burr. Compared with the mechanical drilling, micro-EDM is a form of non-contact machining, and the high temperature generated from the electric spark discharge can erode the first layer of copper foil, thus fully eliminating hole mouth burr. This paper performed a detailed study of the influence of spindle speed, machining voltage, pulse width, and pulse interval on hole mouth quality. After that, the technological parameters for eliminating hole mouth burr were obtained. Finally, under the effects of 20,000 rpm spindle speed, 26 V machining voltage, 4 μs pulse width, and 8 μs pulse interval, a micro-bit with a diameter of 200 μm was used to perform micro-EDM of the first layer of copper foil. From the machining results, it can be known that the PCB micro-hole was possessed of overall good quality, with good hole wall surface quality and almost no visible hole mouth burr.