Corey M. Dunsky

Beam shaping applications in laser micromachining for the microelectronics industry

Laser micromachining has been a part of the manufacturing process for semiconductors and microelectronics devices for several decades. More recent applications such as the drilling of microvia holes in high-density electronic packages have recently entered broad industrial use for high-volume production. In such applications, process stability and throughput are key drivers of commercial success. Particularly in the UV, where solid-state laser power is growing rapidly but is still limited to less than 10 watts, innovations that permit the available laser power to be applied at the work surface more efficiently are of interest. Within the last two years, the use of beam shapers to create round laser spots with near-uniform irradiance at the work surface has been demonstrated. Shaping the irradiance profile has been shown to both increase process speed and improve the quality of the drilled holes, which range in diameter between 20 and 150 micrometers . This paper gives an historical overview of laser via drilling, presents the Gaussian-to-flattop beam shaping optics used in the microvia laser drills, and discusses the process results obtained.

Laser micromachining in the microelectronics industry: a historical overview

The use of lasers in microelectronics is production for trimming, ablating, drilling and general micromachining continues to grow. As one example, traditional laser trimming techniques for passive and active microelectronic circuits have been used for nearly thirty years to improve yields and/or device performance. The majority of these processes have been accomplished using the fundamental wavelengths of the Nd:YAG laser source. However, recent technological advances in microelectronics laser processing, mainly for hybrid integrated circuits (HIC), dynamic random access memories (DRAM) and printed wiring boards (PWB) have resulted in new process techniques. Several new technologies, such as alternative wavelength processing and shaped, uniform laser spots have produced better processing quality, higher reliabiltiy, and greater yields. This paper will review the past, present and future of laser micromachining in microelectronics.

Microvia formation with lasers

Laser drilling has emerged in the last five years as the most widely accepted method of creating microvias in high-density electronic interconnect and chip packaging devices. Most commercially available laser drilling tools are currently based on one of two laser types: far-IR CO2 lasers and UV solid-state lasers at 355 nm. While CO2 lasers are recognized for their high average power and drilling throughput, UV lasers are known for high precision material removal and their ability to drill the smallest vias, with diameters down to about 25 -30 micron now achievable in production. This paper presents an overview of techniques for drilling microvias with the lasers.

High-speed microvia formation with UV solid state lasers

Laser drilling has emerged in the last five years as the most widely accepted method of creating microvias in high- density electronic inter connect and chip packaging devices. Most commercially available laser drilling tools are currently based on one of two laser types: far-IR CO2 lasers and UV solid state lasers at 355 nm. While CO2 lasers are recognized for their high average power and drilling throughput, UV lasers are known for high precision material removal and their ability to drill the smallest vias, with diameters down to about 25-30 micrometers now achievable in production. This paper presents a historical overview of techniques for drilling microvias with UV solid state lasers. Blind and through via formation by percussion drilling, trepanning, spiralling, and image projection with a shaped beam are discussed. Advantages and range of applicability of each technique are summarized. Drivers of throughput scaling over the last five years are outlined and representative current-generation performance is presented.

Precision microfabrication with Q-switched CO2 lasers

This paper presents a new CO2 laser technology for precision microfabrication applications. The laser produces short (microsecond) pulses at very high pulse repetition frequencies (PRFs). In contrast, most commercial CO2-laser micromachining applications employ one of two type of CO2 lasers: RF-excited with external pulse modulation, and TEA lasers. The laser technology presented here produces pulses sharing some of the characteristics of the TEA CO2 laser, but is capable of delivering them at much higher PRFs (20-100 kHz). Microfabrication applications to date are primarily microdrilling in common electronic circuit board and IC packaging materials, including unreinforced, glass-fiber reinforced, and particle-filled epoxies. These materials are processed using pulse energies lower than those generally used by conventional CO2 laser designs, and at speeds typically 1.5 to three times as fast as achieved by conventional CO2 laser drills.