1. Field of the Invention
Embodiments of the present invention relate generally to the field of semiconductor devices and more particularly to flip-chip imager packages.
2. Description of the Related Art
Image sensors, such as, for example, charge coupled device (CCD) image sensors or complementary metal-oxide semiconductor (CMOS) image sensors, are electronic devices used for capturing digital images by converting perceived color and brightness to electrical signals. For example, an image sensor may be a microchip with millions of small lenses each focusing light on an individual pixel of the microchip. Light that passes through the lenses and impinges on the pixels is converted to an electrical signal based on its intensity. These electrical signals are then conveyed to a circuit assembly which is coupled to the sensor. This assembly may organize and name a group of signals for storage and later conversion to an image, such as, for example, a photograph or a movie.
Because the lenses used in image sensors are susceptible to contamination, image sensors may be packaged within a housing to provide protection for the lenses and electrical connections. An exploded view of a conventional imager package 10 is illustrated in FIG. 1. In this example, formation of the imager package 10 has been accomplished by attaching a sensor die 12 to a transparent substrate 14 using flip-chip technology. A sealant (not shown) secures the sensor die 12 to the transparent substrate 14. The sensor die 12 is coupled to inner attachment pads 16 on the transparent substrate 14 via small solder balls 18. The inner attachment pads 16 are coupled to outer attachment pads 20 via conductive traces 22. Large solder balls 24 are then coupled to the outer attachment pads 20. The solder balls 24 are designed such that they may be coupled to an external package (not shown), and therefore the solder balls 24 generally have a diameter larger than the thickness of the sensor die 12 so that any device attached thereto does not directly contact the sensor die 12. Signals from the sensor die 12 may then be routed from pads on the underside of the sensor die 12 to the external package via the small solder balls 18, the inner attachment pads 16, the conductive traces 22, the outer attachment pads 20, and the solder balls 24.
According to the technique illustrated in FIG. 1, to avoid placing an external package in contact with the top surface of the sensor die 12 the solder balls 24 are typically large compared to the sensor die 12. In addition, all connections to external packages are typically situated around the periphery of the sensor die 12. This design places constraints on the size of the imager package 10 because it must be large enough to accommodate the sensor die 12 and the plurality of solder balls 24 situated around the sensor die 12.