Patent Application
20060180888
The invention relates generally to optical sensors. In particular, the invention relates to semiconductor packages for optical sensing.
Modern image capturing equipment such as digital cameras and imaging-enabled mobile phones are fast becoming indispensable tools for satisfying user needs for communicating through digital images and videos. Many of the image capturing equipment are based on Complementary Metal Oxide Semiconductor (CMOS) or Charge Coupled Device (CCD) technology for optical sensing and capturing images. The images are sensed and captured through image-sensing semiconductor chips such as CMOS and CCD integrated circuit (IC) chips, which are typically packaged into optical sensor packages.
Increasing demands for high manufacturability and quality of the optical sensor packages mean that there are needs for flexibility and reliable methods for packaging the image-sensing chips. Improving conventional methods of packaging the image-sensing chips is therefore desirable in order to achieve optical sensor packages with better operating performances and greater manufacturability.
A conventional method for forming optical sensor packages typically requires an image-sensing chip to be wire bonded to a ceramic substrate. The image-sensing chip is then usually hermetically sealed and covered by a glass filter to protect the image-sensing chip from moisture contamination and provide mechanical protection thereto. The requirements of the ceramic substrate and the glass filter for forming the optical sensor packages increases the dimensions thereof and are undesirable for increasing the compactability of the optical sensor packages. There is also a higher possibility of moisture contamination of the image-sensing chip when the glass filter is defective, thereby resulting in a loss of manufacturing yield and reducing reliability of the optical sensor packages.
Additionally, the conventional method for forming optical sensor packages requires sophisticated controlling means for ensuring each image-sensing chip is thoroughly hermetically sealed. This inevitably causes reduction in manufacturability of the optical sensor packages.
Another conventional method for forming optical sensor packages uses an index matching underfill, which is provided between the image-sensing chip and the glass filter for improving light transmissitivity to the image-sensing chip. Sealing of the image-sensing chip is not required. However, this method requires solder bumps for forming metallurgical bonds between the image-sensing chip and the substrate and is not suitable for other image-sensing chips requiring wire bonding interconnection, especially wire bonding interconnection with fine pitch. This method inherently limits the flexibility of manufacturing optical sensor packages.
Additionally, this method uses an interposer or flexible printed circuit having a center opening in which high accuracy is required in defining the center opening. This undesirably increases the complexity of the method. The use of solder bumps reduces accuracy in positioning the image-sensing chip relative to the glass filter, thereby resulting in a less controllable method for forming the optical sensor packages.
There is therefore a need for an optical sensor package having greater flexibility and controllability in manufacturing thereof.
Embodiments of the invention disclosed herein provide improved controllability relating to manufacturing of optical sensor packages. Additionally, the embodiments have greater flexibility in manufacturing the optical sensor packages.
Therefore, in accordance with one aspect of the invention, a semiconductor package for optical sensing is disclosed. The semiconductor package comprises a substrate for transmitting radiation and an integrated circuit chip for sensing the radiation. A plurality of connectors for electrical transmission is disposed on the substrate and a plurality of pillars for facilitating electrical communication between the plurality of connectors and the integrated circuit chip, wherein each of the plurality of pillars is disposed between at least one of the plurality of connectors and the integrated circuit chip.
In accordance with another aspect of the invention, a method for forming a semiconductor package for optical sensing is disclosed. The method comprising the steps of providing a substrate for receiving radiation; disposing a plurality of connectors on the substrate for electrical transmission; providing an integrated circuit chip for sensing the radiation; and connecting the integrated circuit chip to the plurality of connectors on the substrate with a plurality of pillars, wherein each of the plurality of pillars is disposed between at least one of the plurality of connectors and the integrated circuit chip.
Embodiments of the invention are described hereinafter with reference to the drawings, in which:
With reference to the drawings, a semiconductor package according to embodiments of the invention having improved controllability and greater manufacturability relating to manufacturing thereof is disclosed.
Various conventional methods for improving quality and manufacturability of optical sensor packages are disclosed herein. The conventional methods face difficulties with the manufacturing yield of packaging image-sensing chips due to a need for the image-sensing chips to be hermetically sealed. Other conventional methods have limitations in the flexibility of manufacturing optical sensor packages.
For purposes of brevity and clarity, the description of the invention is limited hereinafter to applications related to packaging of CMOS and CCD image-sensing chips. This however does not preclude embodiments of the invention from other applications, such as heat sensing chips or other chips for sensing electromagnetic radiation, which require similar packaging methods as the method for packaging the CMOS and CCD image-sensing chips. The functional and operational principles on which the embodiments of the invention are based remain the same throughout the various embodiments.
Embodiments of the invention are described in greater detail hereinafter for a semiconductor package 100 for optical sensing and method of manufacture thereof. In the detailed description and illustrations provided in FIGS. 1 to 5 of the drawings, like elements are identified with like reference numerals.
With reference to
Additionally, the substrate 102 is preferably capable of filtering infrared (IR) radiation for reducing thermal energy transmitting therethrough. A suitable material for the substrate 102 is IR filtering glass. Alternatively, the substrate 102 is made of glass coated with a layer of IR filtering material. The substrate 102 is preferably but not limited to having a square configuration.
The plurality of connectors 104 is preferably arranged around a central portion 106 of the substrate 102. Each end of the plurality of connectors 104 substantially distal to the central portion 106 and proximal to the periphery of the substrate 102 is preferably formed into a pad 108. The pad 108 is preferably formed in conjunction with the plurality of connectors 104 and is preferably but not limited to a circular configuration and electroplated with at least an additional layer of the conductive material, such as Cu with or without surface finishes, for better metallurgical bonding.
A layer of dielectric material 110, such as a coverlay, being formed on the substrate 102 is shown in
With reference to
As shown in
The pillar 118 preferably extends from the integrated circuit chip 114 and erects substantially upright therefrom. Additionally, the pillar 118 preferably has uniform longitudinal cross-sectional area and is preferably made of conductive materials such as Cu and gold (Au).
A predetermined amount of solder 120 is preferably deposited on one end of the pillar 118 for facilitating bonding of the pillar 118 to the corresponding conductor 104. The solder 120 preferably comprises material such as 63% lead (Pb)/37% Tin (Sn) eutectic composition alloy and pure Sn, as known to a person skilled in the art. The solder 120 is subsequently reflowed for bonding of the pillar 118 to the corresponding conductor 104. The reflowing process is controllable by the amount of solder 120 deposited on the pillar 118. The pillar 118 is preferably not reflowable during the reflowing of the solder 120.
The displacement D between the light sensitive area 116 of the integrated circuit chip 114 and the substrate 102 is an important parameter affecting image quality. It is therefore desirable to achieve high precision for establishing the displacement D. The use of pillars 118 for connecting the integrated circuit chip 114 to the plurality of connectors 104 allows more precision and consistency in establishing the displacement D between the integrated circuit chip 114 and the substrate 102. This advantageously reduces the possibility of focusing error due to imprecision and inconsistency of establishing the displacement D.
Additionally, the semiconductor package 100 of
In a second embodiment of the invention, additional pads (not shown) are formed on the substrate 102 together with the plurality of connectors 104. Corresponding pillars 118 are bonded to the additional pads for improving precision of the displacement D between the integrated circuit chip 114 and the substrate 102 and the positioning of the integrated circuit chip 114 relative to the substrate 102.
The additional pads are alternatively used as fiducial points for advantageously allowing more accurate placement of camera lenses 124 with respect to the substrate 102. The pillars 118 can also be formed on the opposite side of the substrate 102 as alternative alignment structures for the placement of the camera lenses 124. Layers of connector 104 and solder 120 are preferably disposed between the pillars 118 and the opposite side of the substrate 102, as shown in
Solder balls 122 are attached to the pads at the periphery of the substrate 102 for bonding the semiconductor package 100 to an external circuitry (not shown), such a printed circuit board (PCB).
In the various embodiments of the invention, the layout of the plurality of connectors 104 and pads 108 are determined by the requirements of designing the semiconductor package 100.
In the foregoing manner, a semiconductor package for optical sensing is disclosed. Although only a number of embodiments of the invention are disclosed, it becomes apparent to one skilled in the art in view of this disclosure that numerous changes and/or modification can be made without departing from the scope and spirit of the invention. For example, although the semiconductor package is formed with a square or polygonic substrate in the forgoing embodiments, the semiconductor package may be efficiently performed if the substrate is of other polygonal or circular shape for receiving the visible light.
