Fast and accurate laser drilling with high speed digital scan head and smart controlling methods

In laser via-drilling industry, improving the drill job throughput while maintaining high drill hole position accuracy has always been the continuous drive. One push that has direct impact on throughput improvement is to speed up the galvanometer based laser beam scan head used in the drilling machine. The LightningTM II Plus scan head from Cambridge Technology with newly engineered galvo design has achieved step response time as fast as 225µs for 300µm via-hole pitch with a 100mm f-theta lens. This enables via-hole scanning frequency up to 4400 pps at this pitch size. Another route to improve throughput is through smart drilling control methods. In this paper, we will discuss two drilling control algorithms that Cambridge Technology has developed. The closed loop method uses real time in-position signal from the scan head before firing the laser. This method achieves fast drilling with guaranteed position accuracy. The other method is the ‘dynamic’ open loop method in which the controller uses the jump time look-up table to determine the time to wait before the next move instead of waiting for the in-position feedback signal, resulting in even higher throughput. In addition, the look-up table can be re-created on demand to compensate for the dynamic characteristics change in scan head over its lifetime. Finally, the paper will explain how flexible and accuracy laser timing control can be used to further optimize the laser drilling process.