Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Encapsulating
Reexamination Certificate
2003-01-28
2004-08-03
Zarneke, David A. (Department: 2827)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Encapsulating
C438S124000, C438S126000
Reexamination Certificate
active
06770514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hermetically packaged semiconductor devices and, more particularly, to semiconductor devices including stereolithographically fabricated hermetic packages. The present invention also relates to the use of stereolithography to fabricate hermetic packages on semiconductor device assemblies or on semiconductor dice.
Semiconductor Device Packages
2. Background of Related Art
Solid-state electronic devices, such as semiconductor dice, which are also referred to as semiconductor devices, are typically manufactured on substrates of semiconductor material, such as silicon, germanium, gallium arsenide, or indium phosphide. Circuitry is formed on one surface of a substrate with input and output pads being formed on an active surface of the semiconductor dice of the substrate to facilitate electrical connection with other electronic devices.
Semiconductor devices are often packaged to protect the semiconductor dice from mechanical damage, external contamination, and moisture. Typical types of semiconductor device packages include plastic encapsulated packages, quasi-hermetic cavity type packages, and fully hermetic cavity type packages.
When plastic packages are used, the plastic of the package contacts metal elements of the semiconductor device. Typically, these plastic-metal interfaces do not seal sufficiently to prevent exposure of the die to moisture or to soluble ions. When brought into contact with a semiconductor die, these soluble ions act as electrolytes and, thus, cause corrosive failure of the semiconductor die. In addition, the extensive use of precious metals coupled with base metals in semiconductor dice provides direct current (dc) galvanic potentials for electrochemical corrosion reactions and dendrite growth, thereby affecting the performance and life of the encapsulated semiconductor chip. Thus, while plastic encapsulation of semiconductor devices is the most common form of packaging, semiconductor dice in plastic packages are still vulnerable to electrochemical processes.
As a result of the problems associated with the plastic encapsulation of semiconductor devices, it is sometimes desirable to hermetically package semiconductor dice to prevent external moisture and chemicals from contacting the same. Hermetic packages for semiconductor chips are generally formed from metal or ceramic material. Typically, conventional hermetic packages include a lid or a cap to seal a semiconductor device mounted on a suitable substrate. When a semiconductor device includes a die connected to a lead frame, the leads of the lead frame also need to be hermetically sealed. In metal packages, the individual leads are sealed into the metal platform by separated glass seals. In ceramic packages, the leads extend through the ceramic and are sealed thereby.
Several types of ceramic packages are used to hermetically seal semiconductor chips. Exemplary ceramic hermetic packages include ceramic dual-in-line packages, hard glass packages, side-brazed dual-in-line packages, bottom-brazed or top-brazed chip carriers, pin-grid arrays, or other multilayer ceramic packages. Some of these types of packages are described in U.S. Pat. Nos. 4,769,345, 4,821,151, 4,866,571, 4,967,260, 5,014,159, and 5,323,051. Typically, these packages include a base with a receptacle formed therein to receive a semiconductor device and a lid that is disposable over the receptacle.
In sealing these hermetic packages, the material of one or both of the lid and the base typically must be heated to a temperature that will facilitate sealing of the lid over the receptacle of the base and, thus, hermetic sealing of the semiconductor device within the receptacle. These hermetic packages are, however, somewhat undesirable due to the high temperatures (e.g., at least about 400° C. to about 500° C.) and lengthy sealing times (e.g., as much as about one or two hours) that are required to obtain a hermetic seal as the lid of a hermetic package is sealed over the receptacle of the hermetic package. Such high temperatures for prolonged periods of time can cause oxidation of the leads of a semiconductor device or cracking of the passivation layer over the active surface of a semiconductor device, both of which can cause the semiconductor device to fail.
Moreover, as conventional hermetic packages are typically fabricated separately from the semiconductor device assembly disposed therein, conventional hermetic packages are relatively bulky and can occupy undesirably large amounts of the real estate on a carrier substrate to which the packaged semiconductor device is connected.
U.S. Pat. No. 5,958,100 (hereinafter “the '100 Patent”), which is assigned to the assignee of the present invention, discloses a relatively small, substantially hermetic package that is fabricated on semiconductor dice at the wafer stage. The material of the hermetic package, which is referred to as a thermoplastic glass, is a glass with a lower melting temperature than the glass and ceramic materials typically used as hermetic packages. Nonetheless, the packaged semiconductor devices of the '100 Patent are somewhat bulky. Moreover, despite the lower process temperatures of the materials used to fabricate the hermetic packages of the '100 Patent, packaging temperatures may be as high as about 350° C. As the '100 Patent teaches a method of molding the hermetic package directly onto a semiconductor device assembly by use of known molding equipment, the semiconductor device may be exposed to these molding temperatures for several minutes, until the thermoplastic glass cools.
Less bulky hermetic packages are disclosed in U.S. Pat. Nos. 5,682,065 and 5,903,044, both of which have been assigned to the assignee of the present invention. Each of these patents discloses a method of fully hermetically packaging semiconductor dice at the wafer scale. Thus, the hermetic package disclosed in these patents takes up much less space than that occupied by conventional hermetic packages. The hermetic package of these patents is somewhat undesirable, however, in that the conventional hermetic packaging materials used to form such a package have very high process temperatures (e.g., up to about 600° C.). Thus, the semiconductor dice can be damaged during packaging.
Thus, a hermetic packaging method is needed to fabricate a compact, substantially hermetic package wherein the temperature to which a semiconductor device is exposed during the packaging process is reduced, as is the amount of time the semiconductor device is exposed to the increased temperature.
Stereolithography
In the past decade, a manufacturing technique termed “stereolithography,” also known as “layered manufacturing,” has evolved to a degree where it is employed in many industries.
Essentially, stereolithography as conventionally practiced involves utilizing a computer to generate a three-dimensional (3-D) mathematical simulation or model of an object to be fabricated, such generation usually effected with 3-D computer-aided design (CAD) software. The model or simulation is mathematically separated or “sliced” into a large number of relatively thin, parallel, usually vertically superimposed layers, each layer having defined boundaries and other features associated with the model (and thus the actual object to be fabricated) at the level of that layer within the exterior boundaries of the object. A complete assembly or stack of all of the layers defines the entire object, and surface resolution of the object is, in part, dependent upon the thickness of the layers.
The mathematical simulation or model is then employed to generate an actual object by building the object, layer by superimposed layer. A wide variety of approaches to stereolithography by different companies has resulted in techniques for fabrication of objects from both metallic and nonmetallic materials. Regardless of the material employed to fabricate an object, stereolithographic techniques usually involve disposition of a layer of unconsolidated o
TraskBritt
Zarneke David A.
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