The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Exemplary embodiments of the present invention will now be described more fully with reference to the accompanying drawings. These embodiments may, however, be realized in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to one skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Like reference numerals in the drawings denote like elements, and thus descriptions thereof will not be repeated.
Referring to
A first soldering flux 13 may be formed on the ball pad 11 by dotting the first soldering flux 13 on the ball pad 11. The first soldering flux 13 removes an oxide film on a surface of a metal exposed to a conductive material such as solder, prevents re-oxidation of the metal as the metal is exposed to melted conductive material (e.g., melted solder) and decreases surface tension of the melted conductive material, thereby improving spreading and wettability of a subsequently formed conductive ball on the ball pad 11. Flux is conventionally provided as a resin-based flux or a rosin-based flux. However, the first soldering flux 13 used in the present embodiment is an epoxy-based flux that has a relatively high modulus of elasticity compared to the modulus of elasticity of rosin-based fluxes. The modulus of elasticity at room temperature of the epoxy-based flux may range from about 6 GPa to about 10 Gpa. In some embodiments, the modulus of elasticity at room temperature of the epoxy-based flux may be about 7 GPa or more. The epoxy-based flux may further include a filler to improve the modulus of elasticity of the first soldering flux 13. In some embodiments, the filler of the epoxy-based flux may comprise silica, silicon carbide, alumina, or the like or combinations thereof.
Referring to
Referring to
Due to the relatively high modulus of elasticity of the first soldering flux 13, the conductive ball 15 can be reliably fixed to the device substrate 10 even when the device substrate 10 is thermally deformed. Therefore, cracks in a solder joint between the conductive ball 15 and the device substrate 10, i.e., the ball pad 11, can be substantially prevented. Moreover, a glass transition temperature of the first soldering flux 13 may be higher than a maximum temperature of a thermal shock test performed to test the resultant mounting structure or semiconductor device. For example, when a thermal shock test is performed in a range of 0-125° C., the glass transition temperature of the first soldering flux 13 may be set to be higher than 125° C. Thus, the first soldering flux 13 has a higher modulus of elasticity during the thermal shock test so that cracks occurring in the solder joint between the conductive ball 15 and the ball pad 11 can be prevented.
Referring to
Thereafter, a second soldering flux 23 is dotted and formed on the terminal pad 21. The second soldering flux 23 may be an epoxy-based flux whose modulus of elasticity is relatively high and similar to (or substantially the same as) that of the first soldering flux 13. Furthermore, the second soldering flux 23 may include a filler as described above with respect to the first soldering flux 13.
Referring to
Because of the relatively high modulus of elasticity of the second soldering flux 23, the conductive ball 15 can be reliably fixed onto the circuit substrate 20 even when the circuit substrate 20 is thermally deformed due to temperature variations. Thus, cracks in the solder joint between the conductive ball 15 and the circuit substrate 20, i.e. the terminal pad 21, can be prevented.
Subsequently, an underfill resin layer 35 may be formed to bury the conductive ball 15 and the first and second soldering fluxes 13 and 23 between the circuit substrate 20 and the device substrate 10. As such, a mounting structure of the semiconductor device is completed. In some embodiments, the underfill resin layer 35 firmly bonds the device substrate 10 and the circuit substrate 20. In some embodiments, the underfill resin layer 35 prevents the ball pad 11, the terminal pad 21 and the conductive ball 15 from eroding due to external humidity.
The modulus of elasticity of the underfill resin layer 35 may be lower than that of any of the first and second soldering fluxes 13 and 23. Thus, if at least one of the device substrate 10 and the circuit substrate 20 is deformed due to temperature variations, the underfill resin layer 35 can absorb the deformation. Accordingly, the underfill resin layer 35 is not released from the device substrate 10 and the circuit substrate 20 and the ball pad 11, the terminal pad 21 and the conductive ball 15 can be protected from external humidity, etc. Also, the first and second soldering fluxes 13 and 23 have a higher modulus of elasticity than that of the underfill resin layer 35, so that cracks occurring in the solder joint between the conductive ball 15 and the ball pad 11 and/or the terminal pad 21 can be prevented even when the device substrate 10 and/or the circuit substrate 20 are deformed due to temperature variations. In these embodiments, the first and second soldering fluxes 13 and 23 may be composed of the epoxy-based flux having a relatively high modulus of elasticity. It will be appreciated, however, that the first and second soldering fluxes 13 and 23 may be composed of any suitable material having a relatively high modulus of elasticity other than the aforementioned epoxy-based flux.
The modulus of elasticity of the underfill resin layer 35 at room temperature may range from about 1 GPa to 5 GPa. In some embodiments, the modulus of elasticity of the underfill resin layer 35 at room temperature may be about 4 GPa or less. Additionally, the glass transition temperature Tg of the underfill resin layer 35 may be lower than the maximum temperature of a temperature range of a thermal shock test performed to test the resultant mounting structure or semiconductor device. For example, when the thermal shock test is performed in the temperature range of 0° C.-125° C., the glass transition temperature Tg of the underfill resin layer 35 may be less than the maximum temperature of the temperature range of the thermal shock test of 125° C. Therefore, the underfill resin layer 35 may have a sufficient elasticity within the temperature range of the thermal shock test to absorb the deformation of at least one of the device substrate 10 and the circuit substrate 20.
In some embodiments, the underfill resin layer 35 may comprise a material such as polyimide resin, polyurethane resin, silicon resin, or the like or combinations thereof.
The underfill resin layer 35 may be formed by filling underfill resin between the device substrate 10 and the circuit substrate 20 using a capillary, after the device substrate 10 is connected to the circuit substrate 20 via the conductive ball 15. However, the method of forming the underfill resin layer 35 is not limited thereto and may be performed by forming the underfill resin layer 35 on the device substrate 10 having the conductive ball 15, disposing the device substrate 10 having the underfill resin layer 35 and the conductive ball 15 on the circuit substrate 20, and connecting the conductive ball 15 onto the circuit substrate 20.
Meanwhile, the naming of the mounting structure of the semiconductor device differs according to the kind of the device substrate 10 and the circuit substrate 20. More specifically, when the device substrate 10 is a semiconductor chip, the mounting structure of the semiconductor device may be referred to as a flip chip package. If the device substrate 10 is a circuit board mounted with another semiconductor chip, the mounting structure of the semiconductor device may be referred to as a BGA package. Also, when the device substrate 10 is a circuit board mounted with a semiconductor chip, and the circuit substrate 20 is a circuit board mounted with another semiconductor chip, the mounting structure of the semiconductor device may be referred to as a package on package (POP).
According to the embodiments exemplarily described above, a conductive ball may be connected to a ball pad using epoxy-based flux so that crack generation can be prevented from occurring in a solder joint between the conductive ball and the ball pad even when the device substrate is thermally deformed due to temperature variations. Furthermore, the conductive ball may be connected to a terminal pad using the epoxy-based resin flux, thereby preventing crack generation in the solder joint between the conductive ball and the terminal pad even when the circuit substrate is deformed due to temperature variations. Further, an underfill resin layer having a modulus of elasticity less than that of the flux may be provided so as to absorb any deformation that may be generated when the at least one of a device substrate and the circuit substrate is deformed due to temperature variations. Therefore, the underfill resin layer can be prevented from being released from at least one of the device substrate and the circuit substrate to thereby protect the ball pad, the terminal pad and the conductive ball from external humidity, etc.
While the embodiments of the present invention have been particularly shown and described, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
Number | Date | Country | Kind |
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2006-0078917 | Aug 2006 | KR | national |