Compact consumer devices increasingly include digital cameras. As one example, camera phones include a digital camera to capture digital images.
One technique to manufacture digital cameras for high volume consumer applications is to package an image sensor into a reflowable camera module using a Chip Scale Package. A Chip Scale Package (CSP) is a type of integrated circuit carrier. There are various definitions for CSP packages that are used in industry for current generation CSP packages, such as the package having an area no greater than about 1.2 times the size of the die and/or the ball pitch being no greater than one millimeter. An interposer may be used with a CSP package. Alternatively, in some implementations the die is directly mounted to the CSP package.
In a reflowable camera module, an image sensor die has an array of light sensitive pixels and may, for example, be implemented as a Complementary Metal Oxide Semiconductor (CMOS) image sensor. A CSP carrier forms the base of the reflowable camera module; i.e., a camera module that can be reflowed onto a printed circuit substrate using a solder reflow technique, such as reflowing a Ball Grid Array (BGA) of solder balls to form solder joints with a printed circuit board. Other conventional process steps include plating the module after reflow. Background information on reflowable camera modules utilizing a wafer-level Chip Scale Package (CSP) is described in more detail in U.S. Pat. Pub. No. 20070052827 by Hiltunen “Coated Wafer Level Camera Modules and Associated Methods,” the contents of which is hereby incorporated by reference.
Solder joint reliability is a concern in reflowable camera modules. Reflowable camera modules include optical elements and are thus comparatively large modules (in terms of height) compared to other types of CSP components. Additionally, reflowable camera modules are typically included in consumer products, such as camera phones, that are likely to be repeatedly dropped during their lifetime.
One approach in the prior art that may be applied to packaging reflowable camera modules is to use an underfill encapsulant to improve the reliability of solder joint connections. An underfill encapsulant is conventionally a polymeric material that is formed to fill the entire gap between a substrate (either a chip or an interposer) and a printed circuit board. It is important with conventional underfilling techniques that there are no voids (“bubbles”) between the substrate and the motherboard. The underfill encapsulant provides additional environmental protection to the solder joints. However, underfill encapsulation processes significantly increase manufacturing costs and hence are disfavored in many types of high volume manufacturing processes.
In light of the above-described problems the apparatus, system, and method of the present invention was developed.