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 our Cambridge Technology brand 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 Novanta 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.  

Introduction

Laser drilling plays an increasingly important role in processing via-holes in high density interconnection (HDI) printed circuit board (PCB) used in electronics devices like smart phones and tablet PCs [1,2,3]. It is also used extensively in making via-holes in semiconductor packaging where the silicon IC chips are mounted [1]. Table 1 summarizes the size and accuracy requirements for micro via-drilling on both HDI PCB and package substrate [4]. The smaller via-hole and increased pitch density have been required to address the need of compact and more powerful electronics devices [4]. Today there are various strategies to improve the laser drilling process to meet the requirements of higher throughput and better accuracy. The first strategy is to use a CO2 laser with high peak power and fast rise time to increase the material ablation rate to achieve fewer drilling cycles and shorter processing time. Figure 1 shows an example of high- peak/short-pulse CO2 laser compared with other types of CO2 lasers [5].   The second strategy to improve the laser drilling throughput is through the innovation in the scan head design. One of the key components used in a laser drilling machine is the galvanometer-based scan head that steers the laser beam to the intended via positions. The jump time it takes for the scan head to steer the laser beam from one via to the subsequent one constitutes a large percentage of the total processing time. High position resolution and efficient servo drive of the scan head is also key to enable high via-hole position accuracy. In this paper, we discuss the latest result on the jump time of 225 µs for a 300 µm via pitch achieved with a Lightning II Plus scan head. The third strategy is through careful management of the scan head motion and laser firing to minimize the total time required to coordinate the laser and scan head actions. We will discuss and compare two drilling control methods developed with Cambridge Technology ScanMaster Controller (SMC): the closed- loop method that requires in-position feedback signal and the ‘dynamic’ open-loop method that uses a look- up table to plan jump time for even higher throughput. The additional benefit from SMC such as flexible laser timing will also be presented. The fourth strategy for cost-effective throughput improvement that has been adopted widely in the industry is parallelization. Two scan heads are employed to run drilling job at different sections of the work station. Figure 2 shows typical configurations of dual-head drilling. Depending on how the laser is shared between the two scan heads, the dual-head configuration can be beam splitting or beam switching. Beam splitting avoids the use of an acousto-optic modulator (AOM) that results in up to 20% laser power loss and adds additional time when switching the beam between the heads. However the challenge for beam- splitting is that it requires high peak power laser since the laser power onto each scan head is divided by half. Therefore the implementation of this configuration can be limited by the laser peak power available. Most commercial drilling machines adopt the beam switching configuration.  

About Novanta

Who we are is inevitably embedded in what we do, our innovations, and the people that make it happen. Our core strength is delivering market-leading solutions for our customers.  The delivery of Novanta solutions continue to maintain deep and long-lasting customer relationships.  We do this through our global application sales force, and quality-focused manufacturing expertise. It is thanks to what we accomplished in our past and our continuous work towards innovation, that makes us who we are today. Novanta is a trusted technology partner to medical and industrial OEMs (original equipment manufacturers). Additionally, Novanta holds deep proprietary expertise in photonics, along with vision and precision motion technologies. We engineer mission-critical core components and subsystems that deliver extreme precision and performance.  This enables our customers to improve productivity, to achieve breakthrough performance, and to enhance people’s lives. Building a high-performing culture enables us to achieve our growth goals.  For Novanta, culture starts with cohesive teams that engage and align around our vision and strategy.  Those who live our values and drive performance through the Novanta Growth System.  This is a common set of tools and processes for continuous improvement. Our highly engineered component and sub-system solutions, and deep expertise in advanced photonics, vision and precision motion make us the global technology partner of choice for medical and advanced industrial OEMs. Learn more about Novanta by contacting us here. Interested in a career with Novanta? Check out our job listings here.