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VCSEL arrays: A novel high-power laser technology for ´digital thermal processing´

Dr. Ir. Armand Pruijmboom
Dr. Ir. Armand Pruijmboom

General Manager
Philips GmbH Photonics Aachen
Aachen, Germany

ZIP (english text and pictures)
ZIP (german text and pictures)

Members of the Project Team
  • Dr. Ir. Armand Pruijmboom, Philips GmbH Photonics Aachen, Aachen, D (Team Representative)
  • Dr. Günther Derra, Philips GmbH Photonics Aachen, Aachen, D
  • Dr. Pavel Pekarski, Philips GmbH Photonics Aachen, Aachen, D
  • Dipl.-Ing. Carsten Deppe, Philips GmbH Photonics Aachen, Aachen, D
  • Dipl.-Ing. Ralf Conrads, Philips GmbH Photonics Aachen, Aachen, D
  • B. Sc. Felix Ogiewa, Philips GmbH Photonics Aachen, Aachen, D

Areas of Application
All industries involving some form of thermal processing and all suppliers of related manufacturing equipment will benefit from the vertical-cavity surface-emitting laser (VCSEL) innovation. Specific processes are melting, drying, curing, annealing or alloying of any kind of material.

Machine manufacturers in the fields of solar cell manufacturing, silicon Rapid Thermal Annealing (RTA), carbon fiber tape laying, PET processing and high speed digital printing are interested in the new VCSEL technology. One of the first series applications of the high-power-VCSEL-array-based IMALUX direct-laser system is seamless edge banding of furniture panels. The highest benefit will be achieved in applications that require very fast changing heat patterns or specific spatial profiles. An example for the first aspect is Rapid Thermal Annealing (RTA) - a process used in semiconductor device fabrication which consists of heating a single wafer at a time in order to affect its electrical properties. An example for the second aspect is carbon-fiber tape laying used in several branches like the automotive industry.

Technological Impact
  • Improved quality for existing products by tailored digital heating
  • New technology with efficient and cost effective "digital heating" systems
  • Reduced heating process costs compared to conventional laser processes
  • Improved working conditions compared to conventional non-laser processes
  • Improved quality assurance

Abstract
Industrial manufacturing equipment for heating large areas with high throughput conventionally uses among others gas burners, hot air blowers and electrically or halogen lamp heated belt ovens. Due to their limited power density, high thermal inertia and low spatial selectivity, these heating methods can be switched on and off only slowly. Furthermore, they are inaccurate and cannot easily deposit the heat only where it is needed or do not allow to impose sophisticated spatial thermal profiles on a work piece. On the other side conventional laser technology has hardly shown any inroad into many industrial segments mainly for cost reasons. Development of high power lasers has traditionally focused on brightness. Treating large surfaces with high brightness sources requires either complex optics or scanning systems. Each one comes along with technical limitations but more importantly with a severe cost impact.

Vertical-cavity surface emitting laser-diodes (VCSEL´s) offer an innovative solution by heating only when and where it is needed in a short time with cost effective, compact and robust systems. Compared to conventional non-laser based heating technologies, VCSEL arrays offer flexibility, high efficiency and lifetime. As a solid state technology VCSEL´s fuel the trend to fully digitized manufacturing flows. The technology is bound to penetrate a large number of manufacturing processes and thereby adds a new and cost effective member to the family of high power lasers.

VCSEL´s are GaAs based micro lasers that are fabricated and tested using semiconductor wafer processing methods and assembled using standard semiconductor assembly processes and equipment. This involves lithography, wet- or reactive-ion etching and metal- and dielectric deposition. VCSEL´s can be tested and binned by probe testing on wafer level, such that after dicing, the good dice can be selected for the subsequent assembly process. Assembly involves standard semiconductor assembly processes- and equipment, for pick-and-place, die attach and wire bonding.

Single VCSELs have dimensions of a few μm and emit between 1-10 mW of near-infrared power (800-1100 nm) perpendicular to the wafer-surface. By densely packing more than 500 VCSELs per mm2, power-VCSEL array chips can emit several W/mm2. Virtually infinitely large arrays can be formed by stacking VCSEL arrays chips next to each other. The largest built system so far delivers a full 40kW of optical power. The circular far-field of the single VCSELs overlap already at a small distance from the chip surface, forming large areas of homogeneous illumination without using any optics. The generated power density is up to two orders of magnitude higher than that of conventional non-laser based heating methods. By segmenting large area arrays, spatial thermal profiles can be imposed on the work piece, by controlling the output power of the individual segments between 0 and 100% within milliseconds.

The innovative work of the Philips team consists in the development of the VCSEL array chips dedicated for high power application, the packaging and thermal management of the VCSEL arrays including comprehensive finite-element modeling, the system design by tailoring packages of various "standard building blocks" to specific industrial applications and finally the application development itself. The seamless edge banding of furniture panels is a first industrial application that was developed for IMA Klessmann GmbH Woodworking Systems. With the IMALUX direct laser system, the edge band is melted by a high-power VCSEL heating system, before it is welded to the edge of the board, forming an invisible seam with the surface laminates. The IMALUX system delivers a quality superior to that of hot-air blower, while consuming only one fourth of the power and generating significantly less noise. The cost of the compact VCSEL-system is significantly lower than that of comparable fiber-coupled edge-emitting-laser-diode-based systems. As the VCSEL innovation is based on solid-state-light-source technology, it is fundamentally "digital" and thereby instrumental to drive the "Industry 4.0" agenda of the thermal processing segments.


High-power VCSEL heating module with 12 Emitters and 4.8 kW Output Power
(Copyright: Philips GmbH)

2D-array of connected VCSEL array chips
(Copyright: Philips GmbH)

Pixelated heating module with 32 independently addressable VCSEL arrays and integrated driver electronics
(Copyright: Philips GmbH)
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