1. Field of the Invention
The present invention relates to a pressure sensor module, and more particularly relates to a module structure that detects pressure in a diaphragm and has low fluctuation of pressure sensor characteristics, and a structure that can package the pressure sensor and application specific integrated circuit (ASIC) or another semiconductor device at high density and in a small size.
The present invention claims priority on Japanese Patent Application No. 2008-114262, filed on Apr. 24, 2008, and the contents of which are incorporated herein by reference.
2. Description of the Related Art
Pressure sensors are used in various fields such as household electric appliances, medical equipment, and vehicle parts. Semiconductor pressure sensors are increasingly being used, since they are small and highly reliable. Recently, with the aim of mounting pressure sensors in portable devices, there is a particular demand for a smaller package structure.
To realize a very small package, as disclosed in Japanese Unexamined Patent Application, First Publication No. 2007-248212, the applicant considered a surface mountable chip size package (CSP), and proposed a small pressure sensor module that can be realized by mounting a pressure sensor on a laminated substrate which an ASIC internally containing amplification and compensation circuits is buried in. FIG. 10 is a representative example of that structure. A pressure sensor 112 including a diaphragm 111 is mounted on a laminated substrate 115 in which an ASIC 114 is buried in via a bump 113. While this structure is suitable for realizing a small module in which a combination of devices such as the ASIC 114 and the pressure sensor 112 are mounted, some problems were discovered during subsequent systematic consideration.
In the conventional module structure shown in FIG. 10, since the pressure sensor 112 is mounted on a topmost face 115A of the laminated substrate 115, stress generated in the laminated substrate 115 is liable to be applied to the pressure sensor 112. Therefore, due to the stress applied from the laminated substrate 115 to the pressure sensor 112, there is some fluctuation in the output characteristics of the pressure sensor 112 before and after mounting it on the laminated substrate 115. This makes it difficult to obtain a pressure sensor module 130 having desired output characteristics.