The present invention relates generally to the field of semiconductor devices and, more particularly, to a semiconductor chip package having a thermal interface material (TIM).
Semiconductor chip packages that comprise a flip chip die, a heat spreader, and a thermal interface material between the back of the die and the heat spreader, are well known. The thermal interface material plays a critical function of transferring heat generated by the die to the heat spreader, which then spreads this heat to other elements such as heat sinks, etc. Heat removal becomes a challenge however, as the die power consumption, die size, and heat density increases with every new generation of microprocessors. Thermal interface materials are used to effectively dissipate heat and reduce thermal resistance of the semiconductor chip packages.
The thermal interface material can be a thermal grease type material or a rigid type material (such as epoxy or solder). The thermal grease type has a thermal conductivity of about 1 to 6 W/mk. Epoxy has a thermal conductivity of about 10 to 25 W/mk while solder has a thermal conductivity of about 25 to 80 W/mk.
In a conventional semiconductor package, the thermal interface material is arranged between the back of the die and the heat spreader. In this arrangement, damage may occur depending of the type of thermal interface material used. For example, thermomechanical stresses may arise due to differences in the coefficients of thermal expansion (CTE) between the heat spreader, the die, and the thermal interface material. These CTE differences are commonly referred to as a “CTE” mismatch.“
The rigid type thermal interface material, such as solder, has a good heat emissive capacity, but is not capable of sufficiently absorbing the thermomechanical stresses between the heat spreader and the die. As a result, cracks may occur in the rigid type thermal interface material itself or in the die.
The preferred thermal interface material in use is the grease type thermal interface material, although it exhibits lower heat emissive capacity. The thermal grease type thermal interface material does a good job of absorbing thermomechanical stresses between the heat spreader and the die. However, greases exhibit degradation of thermal performance during temperature cycling. It is observed that in some packages greases migrate out from between the interfaces under cyclical stresses encountered during temperature cycling. This phenomenon is known as “pump out.”
For these reasons and other reasons that will become apparent upon reading the following detailed description, there is a need for an improved thermal interface material for use in semiconductor chip packages having good heat emissive capacity and improved structure for absorbing thermomechanical stresses.
The present invention is directed to a semiconductor package having a sealing membrane for a thermal interface material. In one embodiment, the semiconductor package comprises a semiconductor die, a heat spreader, and a sealed membrane for containing a thermal interface material (TIM) therein, the sealed membrane is located between the die and the heat spreader for transmitting heat generated from the die to the heat spreader.
The features, aspects, and advantages of the present invention will become more fully apparent from the following detailed description, appended claims, and accompanying drawings in which:
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, one having an ordinary skill in the art will recognize that the invention can be practiced without these specific details. In some instances, well-known structures and processes have not been described in detail to avoid unnecessarily obscuring the present invention.
Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
Referring to
Thermal interface material 8 performs a critical function of transferring heat generated by a die to a heat spreader which then spreads this heat to a heat sink. Thermal interface material 8 may have a modulus of elasticity in the range of about 1 to 500 MPA and be any type of thermally conductive material capable of being delivered to sealing membrane 2. Thermal interface material 8 may be, for example, a thermal grease, gel, polymer, or one of several epoxies.
Referring now to
A second set of solder balls 60 may be secured to contact pads (not shown) on the lower surface of first substrate 20. The combination of the first substrate 20 and the second set of solder balls 60 on the lower surface thereof are commonly known as and referred to as a ball grid array. Second set of solder balls 60 may also be secured to contact pads (not shown) on a second substrate 70, which may be a printed wire board (also sometimes called a printed circuit board) or may be a multilayer module known to those skilled in the art.
The FCBGA package 10 may also include a heat spreader 80 and one or more stiffeners 90 for preventing excess warpage of the FCBGA package 10. Heat spreader 80 is mounted on top of chip 30 and counter-balances the forces exerted by the thermal expansion mismatches between at least the chip 30 and the first substrate 20. The heat spreader 80 and the stiffeners 90 may be formed integrally or employed as discrete elements, and may substantially comprise materials having relatively high coefficients of thermal expansion. In one embodiment, the heat spreader 80 comprises copper tungsten, aluminum silicon carbide, aluminum, stainless steel, copper, nickel and/or nickel-plated copper. In one embodiment, the stiffener 90 comprises copper, copper carbon, copper tungsten, aluminum silicon carbide, aluminum, stainless steel, nickel and/or nickel-plated copper. Other materials may be implemented accordingly to meet the design requirements of a particular application and the heat spreader 80 and the stiffener 90 may comprise other materials having high coefficients of thermal expansion as is known to those skilled in the art. However, in one embodiment, heat spreader 80, stiffener 90 may have substantially equal coefficients of thermal expansion, due to substantial similarities of the materials selected for each element.
Further illustrated in
In one embodiment, heat spreader 80 has substantially similar dimensions as first substrate 20, although in other embodiments heat spreader 80 may be substantially smaller than first substrate 20. In either case, heat spreader 80 may be sized to substantially cover and enclose first substrate 20 in conjunction with the stiffeners 90. Accordingly, heat spreader 80 and stiffeners 90 may define a cavity 110 within which chip 30 is coupled to the first substrate 20. In one embodiment, the cavity 110 may be substantially filled with a thermo-set epoxy or other underfill material 50 by means known to those skilled in the art.
Also shown in
Sealing membrane 2 may comprise one or more layers and is so dimensioned as to be insertable through the space between the chip 30 and the heat spreader 80. Sealing membrane 2 comprises a flexible yet high heat transferring material and in one embodiment, sealing membrane 2 comprises silicon rubber. However, one skilled in the art will understand that sealing membrane 2 may comprise of any material having substantial flexibility, high heat emissive capacity yet maintain dimensional stability. In one embodiment, sealing membrane 2 may have a bulk thermal conductivity of 0.1 to 0.3 W/mk and have a flexural modulus less than about 1000 MPa.
Sealing membrane 2 may have a shape comprising of, for example, a rectangle, square, circle, rhombus, ellipse, or polygon but it is understood by those skilled in the art that the shape is dependent on at least the size and shape of the chip 30. The larger the chip is, the larger the sealing membrane size must be to adequately dissipate heat and withstand the package warpage and/or the fabrication process. Other shapes and configurations may be implemented accordingly to meet the design criteria of a particular application. Although
The thermal interface material for use in the sealing membrane 2 may be, for example, a thermal grease, gel, polymer, or one of several epoxies. In one embodiment, the thermal interface material comprises a conductive material such as aluminum, copper, carbon compound, aluminum compound, silver, or combinations thereof
Aspects of the present invention may be used in other semiconductor packaging, such as multiple chip module (MCM).
In the preceding detailed description, the present invention is described with reference to specifically exemplary embodiments thereof It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the present invention, as set forth in the claims. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the present invention is capable of using various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.