Reactive bonding

The self-propagating exothermic reaction within the multilayer system contributes the local heat to bond the solder films.

The bonding is based on reactive nano scale multilayers providing an internal heat source.

[1] The metallic layer is usually 1 to 30 nm thick and can be arranged as horizontal or vertical nano scale material films and are a combination of a reactive and a low melting component.

[2] Based on difficulties, that occur during handling, patterning and positioning of the freestanding foils, the multilayer films are directly deposited onto the silicon substrate.

A multilayer system consists of thousands of thin single layers of the component combination that are alternately sputtered on the substrate surface.

This approach reduces the process time and complexity drastically due to the deposition omission of the thousands of single layers.

The system alloy, or an intermetallic compound, (AB) is formed from the intermixing elements (A+B) due to atomic diffusion.

[1] Besides the high interface energy, this reaction is also promoted by the low thickness and therefore the reduced diffusion path of the single metallic layers.

[2] The resulting internal heat melts the solder layers to form a bond with the multilayer system and the substrate based on diffusion.

[4] The bonding can take place in various environments, i.e. vacuum,[6] with a force providing a defined mechanical pressure[1] at room temperature.

[5] Reactive bonding approach is used to assemble MEMS components including die attachment and the hermetic sealing of micro-system packages.

Image of multilayer system as reactive layer on a silicon wafer by Fraunhofer ENAS
Schematic self-propagating reaction in a multilayer system after ignition. [ 4 ]
Schematic reactive bonding process with a reactive multilayer as heat source [ 2 ]