Hermetical package of infrared sensors by Al/Ni self-propagating joining process

In this paper, patterned Cu and Si substrates are interconnected via solder alloys through Al/Ni self-propagating nano-film to obtain hermetical packaging for infrared detector. During the joining process, substrates which are coated with different solder layers (e.g. Sn and AuSn) are bonded under various atmospheres. By optimizing joining parameters, reliable metallurgical joints between Si/Cu and Si/Si can be achieved through self-propagating exothermic reaction process of Al/Ni multilayered nano-films. Thin IMC layers are observed at the bonding interfaces with some micro-voids being detected, but the bonding obtained is acceptable and can meet the requirements of the package of infrared sensors. Furthermore, the solder behavior and the formation of defects under different bonding conditions are compared to enable the optimization of the self-propagating joining process. To verify the reliability of self-propagating joints, the formed bonds are also evaluated in terms of IMCs formation and interfacial characteristics. In particular, the voids and potential leakage in joints are estimated through CSAM inspection. And the composition, morphology and defects in solder joints under different bonding conditions are also characterized based on the cross-sections of the joints. Finally, in comparison with traditional reflow process, the feasibility and advantages of self-propagating joining in hermetical package can articulated in the discussion.