Conventionally, to obtain an image sensor package, a sensor chip is mounted to a chip carrier and electrically connected to the chip carrier via the bonding wires, then the top surface of the sensor chip is covered by a glass such that image light can be captured by the sensor chip. Thereafter, such an image sensor-type package is integrated to an external device such as a printed circuit board for further being applied in various kinds of electronic products such as digital cameras, digital videos, optical mouse, mobile phones and so on.
Referring to FIG. 1, a sensor-type semiconductor package disclosed by U.S. Pat. No. 6,060,340 is shown. A dam lattice 13 is prepared and attached to a substrate 11 by an adhesive 16. The dam lattice 13 has a wall-shaped structure that encloses a space 14 for receiving a sensor chip 10 and the bonding wires 12 therein, where the sensor chip 10 is electrically connected to the substrate 11 by the bonding wires 12. A glass 15 is attached to the dam lattice 13 for covering the space 14, thereby isolating the sensor chip 10 and the bonding wires 12 from external atmosphere and meanwhile allowing the light to pass through and reach the sensor chip 10 for activating the sensor chip 10. However, the adhesive 16 has a high moisture absorption property. When the adhesive 16 that has absorbed moisture experiences a high temperature environment, a popcorn phenomenon as well as delamination of the dam lattice from the substrate can occur, thereby the package reliability is reduced.
Referring to FIGS. 2A and 2B, another sensor-type semiconductor package as disclosed by U.S. Pat. No. 6,262,479 or U.S. Pat. No. 6,590,269 is shown, wherein sensor-type semiconductor packages do not need to use the mentioned adhesive for attaching the dam lattice. As shown in FIG. 2A, a molding process is performed for forming a dam lattice 23 on a substrate 21. A mold having an upper mold 27 and a lower mold 28 is employed. The upper mold 27 has mold cavities 270, and a protruding portion 271 is formed between the mold cavities 270. The substrate 21 is disposed between the upper mold 27 and the lower mold 28 with the protruding portion 271 contacting the substrate 21 so as to cover the predefined areas for mounting chip and bonding wires of the substrate 21. Subsequently, a resin compound, such as an epoxy resin, is injected into the mold cavities 270 so as to form a dam lattice 23 on the substrate 21. After the upper mold 27 and the lower mold 28 are removed, the predefined areas for mounting chip and bonding wires of the substrate 21 are exposed. As shown in FIG. 2B, a sensor chip 20 and the bonding wires 22 are disposed on the exposed area of the substrate 21 surrounded by the dam lattice 23. Finally, a glass 25 is attached to the dam lattice 23. Thereby, a sensor-type semiconductor package is obtained.
However, the above-described semiconductor package has several drawbacks. For example, the clamping force between the protruding portion and the substrate is difficult to control. If the protruding portion cannot be stably contacted with the substrate, the resin compound can easily overflow to the area between the protruding portion and the substrate, thereby causing contamination of the areas for mounting chip and bonding wires. On the other hand, if the protruding portion is tightly pressed against the substrate, the substrate can be damaged. Further, the fabrication cost for the mold having the protruding portion is high, and the mold needs to be changed according to different size of the predefined area of the substrate, thereby greatly increasing the fabrication cost and fabrication complexity.
Accordingly, U.S. Pat. No. 5,950,074 discloses a sensor-type semiconductor package that coats an adhesive having fluidity on the substrate for forming the dam lattice. Then, a glass can be attached to the dam lattice and cover the sensor chip and bonding wires.
However, a common problem exists in the above-described techniques. That is, as spaces need to be reserved for the dam lattice in the above-described semiconductor packages, it limits the packages size being further miniaturized.
Referring to FIG. 3, U.S. Pat. No. 5,962,810 discloses a sensor-type semiconductor package with reduced size. As shown in FIG. 3, a sensor chip 30 is attached to a substrate 31 and electrically connected to the substrate 31 via the bonding wires 32. A fluid adhesive 33 is coated on the bonding wires 32 for serving as a dam lattice, which completely covering the bonding wires 32. Thereafter, a transparent adhesive 35 is coated on the sensor chip 30 for obtaining a sensor-type semiconductor package with reduced size. However, such a method has high fabrication cost and poor product reliability, thus limiting its application in the industry.
Further referring to FIG. 4, according to U.S. Pat. No. 5,534,725, a glass 45 is attached to a sensor chip 40. During encapsulating the sensor chip 40, the glass 45 is abutted against the top of the upper mold of a packaging mold (not shown) so that after the mold is removed, the formed encapsulant 44 can encapsulate the sensor chip 40 with the glass 45 exposed from the encapsulant 44. However, because the glass 45 is directly abutted against the top of the upper mold, the upper and low mold clamping pressure is directly stressed on the glass 45, which can cause cracking of the glass 45 and further damage the sensor chip 40 below the glass 45. In addition, if a gap is existed between the upper mold and the glass, overflow of encapsulant can occur and thus surface of the glass 45 is contaminated.
Therefore, there is a need to develop a sensor-type semiconductor package and fabrication method thereof that can overcome the above drawbacks.