United States

For insulting layers in multi-layer printed circuit boards, Ajinomoto build-up film (ABF) is one of the most crucial component in manufacturing of high-performance electronic devices. The ongoing demand for miniaturized electronic components with advanced functionalities requires a higher power density in packaging and interconnect technology, in turn demanding for a reduction of the diameter of laser drilled microvias.&lt;br&gt;
Recently, ultrashort pulsed lasers have gained considerable attention for microdrilling owing to a negligible heat material interaction and the possibility of small focal diameters by a wavelength in the ultraviolet regime. In order to evaluate its full potential for laser microvia fabrication, we report on a comprehensive study of laser microvia percussion drilling of ABF using a high-power laser system with a wavelength of 355 nm and a laser pulse duration of 10 ps. For the optimization of the laser drilling quality, which in turn is defined by the fabricated taper and the diameter of the microvia as being evaluated by laser scanning microscopy and materialography, laser bursts containing of a number of intra-burst pulses between 1-6 at an intra-burst pulse repetition rate of 82 MHz, different number of laser pulses, laser pulse fluence and laser burst repetition rates, respectively, are varied. In addition, diffractive optical elements are used to transform the Gaussian beam into a round uniform-intensity laser spot within the focal plane of the telecentric f-theta lens to influence the drilling process.

ICALEO 2023

UV Picosecond Laser Drilling of ABF Material for Printed Circuit Boards Using Laser Burst Mode and Beam Shaping

beam shaping

laser burst

ajinomoto build-up film

laser microvia drilling

ultrashort pulsed (usp) laser

For insulting layers in multi-layer printed circuit boards, Ajinomoto build-up film (ABF) is one of the most crucial component in manufacturing of high-performance electronic devices. The ongoing demand for miniaturized electronic components with advanced functionalities requires a higher power density in packaging and interconnect technology, in turn demanding for a reduction of the diameter of laser drilled microvias. 
Recently, ultrashort pulsed lasers have gained considerable attention for microdrilling owing to a negligible heat material interaction and the possibility of small focal diameters by a wavelength in the ultraviolet regime. In order to evaluate its full potential for laser microvia fabrication, we report on a comprehensive study of laser microvia percussion drilling of ABF using a high-power laser system with a wavelength of 355 nm and a laser pulse duration of 10 ps. For the optimization of the laser drilling quality, which in turn is defined by the fabricated taper and the diameter of the microvia as being evaluated by laser scanning microscopy and materialography, laser bursts containing of a number of intra-burst pulses between 1-6 at an intra-burst pulse repetition rate of 82 MHz, different number of laser pulses, laser pulse fluence and laser burst repetition rates, respectively, are varied. In addition, diffractive optical elements are used to transform the Gaussian beam into a round uniform-intensity laser spot within the focal plane of the telecentric f-theta lens to influence the drilling process.

poster

**General Chair Welcome**

![](https://assets.underline.io/markdown_image/1/image/d6e6dddc08bf2371b9136ea9c18dc5ab.png)              

Welcome to ICALEO® 2023!
	
We were excited to host the world’s leading international conference on Lasers and Electro-Optics in Chicago. The Laser has been shown to have the potential to revolutionize solutions for major global challenges like energy usage and supply, global warming, and CO2 footprint. Even the fusion energy breakthrough is based on laser technology. The conference, with peer-reviewed scientific and technical presentations, focused on the newest results in Micro Applications, Macro Applications, Additive Manufacturing, Beam Shaping and Frontiers in Laser Applications. Additionally, the Battery-Manufacturing Track gave an overview of the process combined with the newest advances in laser application results. 

The Business Session brought the business aspect and environment of the laser to the audience and the possibility to discuss with seasoned industry leaders from around the world. 

Whether this is the first time you are hearing about ICALEO or you are a longtime attendee, you will find something of interest, new ideas, and an excellent opportunity to network with other laser specialists worldwide. 

**Klaus Löffler **  
ICALEO General Chair   
Managing Director, Precitec GmbH

**What is ICALEO?**

ICALEO® brings together the brightest minds, seasoned professionals, and pioneering researchers from around the world. With a laser-focused agenda, ICALEO offers an exceptional platform to delve into the cutting-edge advancements, diverse applications, and transformative research that define lasers and electro-optics.

Participants will be immersed in a dynamic environment that fosters collaborative learning, networking, and idea exchange. Through engaging plenary presentations, technical sessions, an industry business panel, and networking events, attendees gain insights into the forefront of laser technology. From industrial applications to medical breakthroughs, additive manufacturing to materials processing, ICALEO covers the entire spectrum of laser-related disciplines. Moreover, the event serves as a launching pad for synergistic partnerships, paving the way for professionals to forge connections that shape the future of our industry.

Join us in Chicago and be part of an unparalleled gathering that challenges the boundaries of possibility within lasers and electro-optics. As we convene to share knowledge, explore innovations, and cultivate collaborations, ICALEO stands as a pivotal force driving the evolution of this transformative technology.

**Who attended?**

ICALEO is tailor-made for professionals, researchers, academics, and enthusiasts who are deeply passionate about the world of lasers and electro-optics. If you're an industry trailblazer, an academic luminary, an aspiring expert, or a postgraduate student looking to dive into the latest developments and trends, this is an event you won't want to miss.

Industrial leaders seeking to stay ahead of the curve in their fields, engineers working on laser applications, and manufacturing experts interested in additive manufacturing and materials processing will find ICALEO to be an invaluable platform. Researchers and scientists exploring the forefront of laser technology, from fundamental principles to groundbreaking applications, will also discover a wealth of knowledge and networking opportunities.

Medical professionals investigating laser-based medical advancements, entrepreneurs seeking to innovate with lasers, educators aiming to stay updated with the latest in laser education, and policy makers shaping the industry's landscape are all essential attendees. Whether you're an established expert or a rising star, the 42nd annual ICALEO promises to offer a diverse ecosystem of expertise, connections, and knowledge sharing that caters to the laser and electro-optics communities.

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Please register for the ICALEO 2023 Conference to join the event.

ICALEO® brings together the brightest minds, seasoned professionals, and pioneering researchers from around the world. With a laser-focused agenda, ICALEO offers an exceptional platform to delve into the cutting-edge advancements, diverse applications, and transformative research that define lasers and electro-optics.

The topic of this research is the reduction of the amount of radioactive waste generated by the decommissioning of nuclear power plants. By removing the contaminated portion of the concrete surfaces prior to the dismantling, the amount of radioactive waste can be expected to be significantly reduced. There are various methods for removing concrete surfaces. In this study, laser is used since it can efficiently remove concrete surfaces while reducing the generation of by-products. The scraping efficiency of the laser was examined by varying the laser parameters and the concrete strength. The amount of the concrete removed could be significantly increased by lowering the laser irradiation speed and increasing the number of outputs. It was also found that the concrete strength has no influence on the amount of concrete removed using this method. This suggested that laser concrete removal methods can be adapted on a wide variety of concrete structures. Compared to the other removal methods reported in the previous studies, the laser removal method can remove the same amount of concrete in just half amount of time. These results indicated that using laser does not only reduce the generation of radioactive by-products, but also it is a more efficient method for removing concrete surfaces. Additionally, since its effectiveness does not depend on the concrete strength used in the structure, it might be widely applicable for various types of concrete structures.

Study of Efficient Removal Method of Concrete Surface by Fiber Laser

Silicon carbide, an emerging material with outstanding semiconducting and electrical properties, is increasingly triggering scientific and industrial interest for the development of cutting-edge high-power and high temperature electronics as well as ultrafast electronic devices. However, due to its high hardness mechanical processing is very difficult and its chemical inertness results in challenges in wet etching. Therefore, laser processing appears to be a promising approach for micromachining, cutting or drilling. 
As a result of recent developments in laser and optics technology, frequency tripled ultra-short pulsed laser systems emitting in the ultraviolet spectral region with high power and pulse energy, and at the same time high beam quality and durability, motivating new applications of laser micromachining. 
Against this background, we report on novel ultraviolet ultra-short pulsed laser processing of silicon carbide. Laser ablated cavities are evaluated with respect to their ablation rates, surface roughness and overall quality. In addition to pulse fluence variation, the influence of repetition rate and focus diameter are investigated. Besides to shaping of sophisticated geometries, functional surfaces are generated. The comparison with infrared wavelength underlines the advantages of the ultraviolet wavelength. Significant differences with respect to the measured ablation rates and roughness as well as generated micro- and nanostructures appear. While infrared ablation is dominated by a chipping mechanism above a critical threshold, higher ablation rates are observed with strong quality losses at the same time. In comparison to the infrared emission wavelength, in general, a significantly higher processing quality is achieved with the ultraviolet emission wavelength.

UV-Femtosecond-Laser Structuring of Silicon Carbide

Fused silica with its outstanding chemical and thermal stability as well as excellent optical properties is widely used in the optics, microsensors and medical technologies. However, its robustness and brittleness pose challenges on processing it with conventional methods. In turn, ultrashort pulsed lasers with their unique properties offer the possibility for its gentle machining. Recent developments in laser and optics technology have led to the availability of frequency tripled ultrashort pulsed laser systems emitting in the ultraviolet spectral region with high pulse energy and average power, while exhibiting high beam quality and durability, motivating their application in micromachining of fused silica. 
We report on ultraviolet ultrashort pulsed laser (UV) ablation of fused silica and compare the achievable machining results to the fundamental emission wavelength in the infrared (IR). The UV reveals a stable ablation efficiency at increasing fluences, while IR exhibits a decreasing trend. In addition, a significant improvement of surface quality is found by using UV laser in low and middle fluence regime as compared to IR. Specifically, a low surface roughness is found for UV with keeping a similar ablation efficiency of both wavelengths at middle fluence (about 10 J/cm2). 
Identifying and taking advantage of the improved ablation results by using UV-ultrashort pulsed laser, we finally present exemplifying and sophisticated application examples of UV ultrashort pulsed laser ablation of fused silica.

UV-Ultrashort Pulsed Laser Ablation of Fused Silica

Surface tortuosity is a measure of the complexity of the surface of a material, which is typically expressed as the ratio of the length of the surface over the shortest distance between two points on the surface. This characteristic has been considered beneficial for coating/steel stability of painted parts exposed to corrosive and humid conditions. Laser surface texturing process can modify the surface tortuosity by producing different structures on the steel surface. However, due to the versatility of the process, structures with different sizes and magnitudes can be fabricated on the surface giving a wide range of possibilities. In this context, this study aims to determine the influence of the V-shaped grooves dimensions into the resistance against corrosion creep of an organic coating applied on textured surfaces. Comparative surface tortuosity was obtained with deferent grooves dimensions at equal relation aspect and textured areas. Aspect ratio of one and sizes of 50, 100 and 200 µm were fabricated on AISI-A36 carbon steel surface. Distance between adjacent grooves was varied to achieve different textured areas in the range of 10 % to 60 %. Surface roughness Rz and surface tortuosity was characterized. Coating performance was evaluated through an accelerated corrosion test based on ISO 12944-9. Results show that lower coating delamination was obtained with V-shaped grooves with 100 µm and a textured area of 40 %. Delamination of the coating was diminished by the increase of surface tortuosity only if mechanical interlock/hooking of the coating is enhanced.

Evaluation of Surface Tortuosity on the Corrosion Resistance of Organic Coatings Using Laser Textured Surfaces

Copper is widely used in high heat flux and electrical applications due to the excellent electrical and thermal conductivity properties. Alloying elements such as chromium or nickel are added to strengthen the material especially for higher temperatures. Cu4Cr2Nb or GRCop-42 is a dispersion strengthened alloy developed by NASA for high temperature applications with high thermal and mechanical loads such as rocket engines. Additive manufacturing enables applications with complex functionalised geometries and is especially promising in the aerospace industry. In this contribution, a parametric study was carried out for GRCop-42 and the AM process laser powder bed fusion using a green laser source for two layer thicknesses of 30 and 60 μm. The density, electrical conductivity, macro hardness, microstructure and static mechanical properties were analysed. Various heat treatments in the temperature range of 400 °C and 1000 °C and time range of 30 min to 4 h were tested to increase electrical conductivity and hardness. For both layer thicknesses, dense parameter sets could be obtained with resulting relative densities above 99.8 %. The hardness and electrical conductivity could be tailored depending on the heat treatment in the range of 103 to 219 HV2 and 24 to 88 % International Annealed Copper standard. The highest ultimate tensile strength obtained was 493 MPa. An annealing temperature of 700 °C for 30 min has shown the best combination of room temperature properties such as electrical conductivity of 83.76 %IACS, UTS of 481 MPa, elongation at break at 24 % and hardness of 125 HV2.

Process Development for Laser Powder Bed Fusion of Grcop-42 Using a 515 NM Laser Source

There has been strong interest in laser direct lithography(LDL) due to flexibility of patterning based on software. However, the conventional LDL has a problem that is too slow compared to mask lithography because it depends on the scanning velocity of laser beam or stages, which causes a decrease in productivity, making it difficult to apply to manufacturing. To overcome these drawbacks, we implemented a resonant mirror based LDL, which is different from the conventional laser scanning method based on a stepper motor. The laser source of the instrument is a laser diode(LD) which has 405 nm wavelength, and the optics are designed to have a beam spot size of less than 20um in the focal plane. We applied this feature to laser scan system and have set 800Hz frequency. It can create a pattern in 1.25us for a line of about 10 mm. Compared to the conventional LDL system using the laser scanning method, the resonant mirror based LDL system has the advantages of being over 80,000 times faster in processing time. The designed LDL system capable of high-speed scanning with uniform physical characteristics is expected to meet the demand for small quantity production of diverse items as well as low operation costs.

Resonant Mirror Based Laser Direct Lithography

Laser welding using high-power laser forms a keyhole inside a molten pool to obtain a deep penetration. However, a spatter which is the scattering of a portion of the molten pool occurs causing welding defects. Therefore, it is necessary to elucidate the mechanism of spatter generation. In our previous study, it has been found the spatter generation is due to the variability of the keyhole. However, it is difficult to understand the spatter generation from keyhole observation only. In addition to the keyhole variability, real-time observation of molten pool dynamics would be understood the spatter generation mechanism. 
In this study, the longitudinal cross-section of the molten pool was directly observed using the glass transmission method to measure the temporal variation of the molten pool area in keyhole welding. A bead-on-plate welding test was conducted for the specimen with a 16 kW disk laser when the SS304 specimen butted against a glass plate was set in a vacuum chamber. The vacuum chamber was evacuated at the pressure of 10 Pa and then filled with Ar gas to the desired pressure. As the results, the average molten pool area was 17 mm2&nbsp;at 105 Pa, which generate a large amount of spatter, while, it was 29 mm2 at 10 Pa, where the spatter generation was small. Furthermore, the standard deviation of the molten pool area was 0.9 mm2 at 105&nbsp;Pa, and 0.36 mm2 at 10 Pa, it was indicated a large molten pool time variation was influenced to generate the spatter.

Elucidation of Spatter Generation Mechanism in Keyhole Welding of Stainless Steel With 16 kW Disk Laser by In-Situ Observation of Welding Dynamics

Besides applications like layering functional surfaces, laser cladding can be used for additive manufacturing and repair welding purposes called directed energy deposition (DED). DED is a more and more used technology in industry and research today. It fills the gap between high-resolution powder bed selective laser melting and high output wired arc additive manufacturing processes. 
The temperature-time-regime is important to be managed in the whole process. With increasing melt pool sizes according to heat accumulation, distortions and residual stresses get out of control. Hence, the part could be cooled between each layer. The temperature could be measured in order to derive the cooling time. However, if the part geometry is known and repeated in an industrial process, the cooling time will always remain the same. Modelling the process with a Finite Element Analysis (FEA) can also help to predict the correct cooling time. In order to achieve suitable results of the FEA Model, the Model has to be calibrated. Moreover, calculation times of FEA can be high according to the complexity and dimensions. 
In powder based additive manufacturing process FEA it is quite common to work with replacement heat sources. These Approaches cannot be transferred to DED because of the process conditions. However, some simplification in the model might lead to sufficient results. In this study we have investigated a process with 15 thermocouples and compared the results with a FEA model. The influence of the process efficiency, heat radiation and thermo-physical-properties in the FEA result is shown.

Finite Element Analysis and Calibration of a Directed Energy Deposition Process by Thermocouples

Cobalt based tungsten carbide composite material [WC-Co] is industrial applied for coating on tip of cutting tools and molds due to its high hardness and wear resistance. However, it is difficult to coat composite materials while maintaining the properties of the powder because of the different melting points of the metals. Thus, we pay attention to a Laser metal deposition (LMD) method. The LMD is one of additive manufacturing technologies in which the material powder is fed, and laser irradiated simultaneously at the processing point to melt and solidify the material powder to form layers, which can add new functions to material surface of any shape. However, conventional LMD has some problems to heat the powder ununiformly in flight, which a molten pool is required on the substrate to weld with powder and substrate, it was caused significantly thermal distortion and dilution. Thus, we have developed a multi-beam LMD system with two high intensity 200W blue diode lasers. The multi beam LMD can heat uniformly the powder in flight resulting in lower thermal distortion and dilution. Especially, using a blue laser with a shorter wavelength than the IR laser used in conventional LMD can improve the light absorption rate for WC-Co power and the steel substrate, to save an energy compared with the conventional LMD. In this study, we try to form a WC-Co coating on a steel substrate surface using the multi-beam LMD system equipped with two blue diode lasers.

Experimental Evaluation of WC-Co Alloy Layer Formation Process by Multi Beam Type Laser Metal Deposition With Blue Diode Lasers

Controlling the wetting characteristics of fluids (oil and water) on surfaces is highly desirable for a variety of industrial processes, such as painting, bonding, and lubrication applications. This can be achieved by altering the surface chemistry and/or topography of a material, which can be accomplished through a variety of techniques, including plasma treatment, chemical modification, surface coatings as well as microprocessing methods such as direct laser writing and direct laser interference patterning. 
This study summarizes recent developments in the field of functionalization of polymer surfaces, including polyethylene terephthalate (PET), polycarbonate (PC) and polytetrafluoroethylene (PTFE) using hot-embossing methods as well as direct laser fabrication approaches. 
The influence of different hot embossing parameters on the resulting texture topography was investigated. In case of the oil wettability tests (on PET), a method to characterize its spreading behavior was developed, allowing a comparison between the produced surface textures. In particular, a superoleophilicity state was reached, in which the contact angle approached zero. Furthermore, hierarchical structured surfaces showed fast wetting rates up to 1.4 mm²/s. 
Regarding water-wettability, the microstructured PET surfaces showed an increased hydrophobic state rising from 76° on the flat reference up to 120°. In case of PC, similar results are obtained, reaching 140°, whereas on PTFE surfaces a super-hydrophobic state was achieved, characterized by water contact angles over 150° and a very small hysteresis (&lt; 5°).

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UV Picosecond Laser Drilling of ABF Material for Printed Circuit Boards Using Laser Burst Mode and Beam Shaping

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Study of Efficient Removal Method of Concrete Surface by Fiber Laser