Optimized full-surface joining of laser crystal and heat sink by laser soldering
Abstract
A laser soldering process has been developed that outranges existing methods. The big advantage of disc lasers is that the laser active material can be hold to a constant temperature in radial direction. The contact between the disc laser and the heat spreader is important for the heat transfer.
Background
Powerful laser sources always require uniform and energy-efficient cooling. This is essential for laser power stability and thus also for process parameters such as cutting quality and speed which depend on a constant power output. In order to dissipate the thermal load during radiation generation from the laser-active medium, these are attached directly to a heat sink or a heat dissipating element. The heat transfer at the interface between this element and the laser medium is crucial for efficient cooling.
Problem
Currently, there are two different methods for joining the elements. For the standard soldering of the disk on CuW heat sink the results lead to a poor quality of the final product. On the other hand, gluing the disk on a diamond heat sink is expensive.
Solution
The method for laser disk and heat sink joining developed at the Universität Stuttgart (Institut für Strahlwerkzeuge / IFSW) uses a laser as energy source for the joining or soldering process. At a suitable wavelength, the radiation can penetrate both the laser disk and, if necessary, a contact pressure tool in order to melt the solder layer between the two components in a targeted manner. Using a suitable contact pressure tool, a defined radius of curvature of the laser disk can also be permanently generated during the soldering process. The advantages of this process: a comparatively low and locally limited heat input into the system and the possibility of using any material for the heat sink as long as it has a metallized layer on the contact surface that can form a chemical bond with the solder material.
As a result, it is possible to produce highly efficient disk laser systems at relatively low costs, offering convincing economic benefits.
![Schematic structure of the laser soldering process with soldering laser beam (λ ≈ 808 nm, 1), hold-down (2), contact pressure tool with a defined radius of curvature (3), laser disc (4), solder (5) and heat sink (6) [Fig: University of Stuttgart].](/fileadmin/user_upload/img/Technologieangebote/16_072_Schema.jpg "Schematic structure of the laser soldering process with soldering laser beam (λ ≈ 808 nm, 1), hold-down (2), contact pressure tool with a defined radius of curvature (3), laser disk (4), solder (5) and heat sink (6) [Fig: University of Stuttgart].")
Schematic structure of the laser soldering process with soldering laser beam (λ ≈ 808 nm, 1), hold-down (2), contact pressure tool with a defined radius of curvature (3), laser disk (4), solder (5) and heat sink (6) [Fig: University of Stuttgart].
Advantages
- Controlled laser disk curvature
- Avoidance of tension or distortion due to low, punctual heat input
- Reduced production costs
- Exact mounting based on the radius of curvature possible
- Ideal crystal temperature during operation due to optimized heat transfer
Application
Production of powerful laser sources.
The present invention fills the gap between both conventional methods by using a relatively low powerful laser, and therefore less expensive, for the soldering process.