1. Field of the Invention
The present invention relates to a method for manufacturing micro electro-mechanical systems using solder balls. More particularly, the present invention relates to a method for manufacturing micro electro-mechanical systems that achieves efficient electrical connection between an internal structure and external electronic parts, and that protects the internal structure by preventing penetration of external air into a vacuum chamber during manufacture of wafer level packaging elements such as an angular velocity sensor, an acceleration sensor, a gyroscope sensor or a pressure sensor.
2. Description of the Related Art
Fabricating micro electronic parts such as an angular velocity sensor or an acceleration sensor with silicon micro-mechanical technology is becoming very popular. Electronic parts of silicon micro-mechanical technology generally include a silicon substrate and two glass substrates bonded onto upper and lower surfaces of the silicon substrate. A structure for detecting angular velocity is formed on the silicon substrate, and the structure and silicon substrate are sealed by the two glass substrates.
A method is known in the prior art for mounting micro electronic parts onto a surface of a circuit board using such technology. In order to manufacture a compact-sized circuit board, it is essential that a mounting surface of the micro electronic parts be reduced. Therefore, a method of manufacturing a micro electronic part has been used in which a via hole penetrates through an upper glass substrate, electrically connecting a structure formed on a semiconductor substrate with an external circuit board, so that electrical signals can be irradiated from the structure through the via hole. A conductive material is filled in the via hole enabling electrical connection between the external circuit board and the structure therethrough.
However, a problem arises when the conductive material is formed in the via hole. Specifically, when the conductive material is filled into the via hole, an air bubble may be generated causing a defective connection between the structure and the circuit board and a subsequent deterioration in quality of the micro electronic parts. In order to prevent formation of a bubble, the via hole may be formed to have a larger diameter because more air bubbles are usually generated in via holes of a smaller diameter. However, in order to provide a via hole of a larger diameter, sizes of a corresponding part and a mounting surface also need to be increased.
Another problem in the conventional method occurs because the conductive material filling the via hole differs from the glass substrate in thermal expansion coefficient. Therefore, a crack may be formed in the glass substrate when the electronic parts go through a thermal change.
In order to ensure that an electrical signal is efficiently irradiated from the structure, a conductive film instead of a conductive material may be provided on an inner wall of the via hole. However, as the via hole is formed in the glass substrate by sand blasting, pieces of broken glass may be generated on the surface of the glass substrate and be bonded to the silicon substrate. Accordingly, when the glass substrate is bonded to the surface of the silicon substrate, a step-shaped portion may be formed due to the presence of the glass pieces between the silicon substrate and the via hole. As a result, connection of the conductive film may be hindered by the step-shaped portion causing a decrease in yield.
A solution proposed to the above problems includes a method of manufacturing a micro electronic part using a via hole. FIG. 1 illustrates a main component of the micro electronic part formed by the method, including a silicon substrate 10, a glass substrate 20, a via hole 30 formed through the glass substrate 20, a vacuum chamber 40, micro electronic structure 50 and a micro electronic part having a conductive film. The conductive film is provided inside the via hole 30. An internal wall of the via hole 30 connects the glass substrate 20 to the silicon substrate 10. Therefore, disconnection due to glass pieces between the glass substrate 20 and the silicon substrate 10 may be avoided, and the structure can be electrically connected to the outside through the conductive film and a signal output portion. A soldering bump 60 is provided on a surface of the glass substrate as a part of the conductive film. By bonding the soldering bump 60 to an anodic pad on an external circuit board, the structure can be electrically connected with external devices.
However, sand blasting is used to form the via hole in the proposed solution, generating pieces or chips of broken glass between the silicon substrate and a lower surface of the glass substrate. Accordingly, electrical disconnection from the silicon substrate may still occur. Additionally, electrical disconnection may also occur by the step-shape of the wall 70 of the via hole.
Further, the conductive film is formed in the via hole by sputtering at a high vacuum of less than 10−7 Torr using vapor depositing equipment, which my cause damage to an element. Accordingly, if the etching process requires more than several microns of vapor deposition for insulation between neighboring electrodes, problem may arise. Also, it is difficult to form fine pitches, and the elements may be damaged.
In addition, forming a bump is difficult because a separate under bump metalization is required. If silk screen or metal plating is used for the under bump metalization, the conductive film may be damaged or contaminated.
Furthermore, position control when assembling the micro electronic part and the external circuit board cannot be expected due to a lack of self-alignment ability.