• Wafer bonding is a packaging technology on wafer level for the fabrication of micro electromechanical systems [MEMS], ensuring a mechanically stable and hermetically sealed encapsulation.

• Need of wafer bonding: In MEMS the package protects the sensitive internal structures from environmental influences such as temperature, moisture, high pressure and oxidizing species. The long term stability and reliability of the functional elements depends on the encapsulation process.

• The package has to fulfill the following requirements:

1) Protection against environmental influences

2) Heat dissipation

3) Integration of elements with different technologies

4) Compatibility with the surrounding periphery

5) Maintenance of energy and information follow.

• The commonly used and developed bonding methods are as follows:

1) Direct bonding

2) Surface bonding

3) Plasma activated bonding

4) Anodic bonding

5) Eutectic bonding

6) Glass frit bonding

7) Adhesive bonding

8) Thermo compression bonding

9) Reactive bonding

10) Transient liquid phase diffusion bonding.