Laser-Based Joining, Sintering, and Contacting

Semiconductor components are usually electrically interconnected. Depending on the industry, different joining technologies are used. These range from classic soldering of special connectors to wire bonding and conductive bonding. The quality of the joints is often decisive for the service life of the final product, which is usually exposed to operational thermal and mechanical stresses.

Laser processes are now established in many ways in the world of joining and offer a number of fundamental advantages. Lasers work without contact, with very low, excellently controllable heat input that can be localized as required. Dissimilar joining partners can be joined without the use of additional materials such as solder or flux, making the technology particularly sustainable and cost-effective. The precise and fast control of laser processes, especially in combination with an in-situ diagnostic procedure, makes it possible to compensate for production-related material fluctuations and thus produce joints of consistent quality.

Together with our project partners, we have been working since 2007 on laser-based micro-joining processes for bonding ultra-thin aluminum foil to different surfaces and materials. As part of these research activities, a whole “toolbox” of different joining processes has been developed and tested. This includes bonding processes on ceramics for the metallization of semiconductor wafers or other components. We are also developing micro-welding processes for bonding the foils to conductor tracks made of silver, aluminum, or copper that are only a few micrometers thick. These processes are generally used for electrical interconnection, for example in solar cells, batteries, or power electronics components. 

Our R&D Services on the Topic "Laser-Based Joining, Sintering, and Contacting" Include:

• Development of Laser-Based Micro-Joining Processes for Electronic Components, Photovoltaics, Power Electronics, and Battery Technology
• Development of Flat Bonding Processes and Ultra-Thin Metal Foils for Metallization of Semiconductor Wafers
• Simulation of Laser Joining Processes

We develop joining processes for bonding and micro-welding of extremely thin metal foils to semiconductor substrates or on conductor tracks. Our focus is on processes with scanner-guided beam deflection at beam travel speeds exceeding one meter per second. This is made possible by using extremely thin joining partners in combination with powerful lasers in the kilowatt range. We have a wide range of scanning systems and beam sources available for development in our Class 4 laboratory. As with all joining processes, the effective time of the heat plays a decisive role, which in our case can be influenced both by the beam travel speed in conjunction with the beam profile/spot size and by the pulse duration. In this complex field of research, we continue to pursue innovative approaches, for example by superimposing different lasers or by using special beam tractors or profiles.

In addition to interconnecting semiconductor components, joining processes can also be used for their surface contacting. The process was originally used for PERC solar cells and has several intrinsic advantages, such as significantly improved optical properties of the solar cells. For this reason, it is now being further developed for solar applications in space or for temperature-sensitive solar cells, such as silicon-perovskite tandem solar cells. The focus of our work is on producing a metal layer that is as homogeneous and low-stress as possible. This inexpensive manufacturing process appears to be suitable for use wherever PVD processes are currently used as standard for depositing metal layers that are only a few micrometers thick.

Understanding laser micromaterial processing processes is often crucial to achieving the best possible results. This is especially true when numerous process parameters can be modified. Joining materials is generally a thermally driven process, even if it takes place on a microsecond scale. With our specially developed LCPSim software, we can simulate the heating and phase transitions of a wide variety of layer systems for different laser beam parameters in a time-resolved manner, giving us a more detailed understanding of the actual process sequence. The software enables engineers to analyze and optimize our joining processes in real time, which increases efficiency and speed in process development.