Laser drop on demand joining as bonding method for electronics assembly and packaging with high thermal requirements

Abstract

In the scope of this work, a novel joining process was developed and investi-gated from both an application-driven and an academic point of view. The process utilises laser radiation to melt a CuSn-braze preform, which is subse-quently detached from a ceramic capillary via inert gas overpressure. After a flight phase, the braze droplet impinges on the joining interface and wets the joining partners where it forms a metallurgical bond after solidification. This process is referred to as laser drop on demand joining (LDJ). It was shown that the shear strength of the joints exceeds the strength of standard tin-based solders by a factor of two and the joints are able to withstand the tempera-tures and forces occurring during an Al-Casting process. In addition, an ana-lytic model was developed, enabling to quantify the absorptance and thermal energy losses by heat convection, conduction, and radiation, by measuring the time required to melt the preform.