Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-06-08
2003-01-14
Ghyka, Alexander G. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S613000
Reexamination Certificate
active
06506671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to semiconductor devices having rings disposed about the peripheries of the contact pads thereof and, more specifically, to the use of stereolithography to fabricate such rings around the contact pads either before or after securing solder balls to the contact pads. Particularly, the present invention pertains to rings disposed about the peripheries of the contact pads of a semiconductor device component for enhancing the reliability of solder balls secured to the contact pads. The present invention also relates to semiconductor device components including such rings.
2. State of the Art
Reliability of Solder Balls Used to Connect a Semiconductor Device Face-Down to a Higher Level Substrate
Some types of semiconductor devices, such as flip-chip type semiconductor dice, including ball grid array (BGA) packages, and chip-scale packages (CSPs), can be connected to higher level substrates by orienting these semiconductor devices face down over the higher level substrate. The contact pads of such semiconductor devices are typically connected directly to corresponding contact pads of the higher level substrate by solder balls.
Examples of solders that are known in the art to be useful in connecting semiconductor devices face down to higher level substrates include, but are not limited to, lead-tin (Pb/Sn) solder and silver-nickel (Ag/Ni) solder. For example, 63/37 type Pb/Sn solder bumps (i.e., solder having about 63% by weight lead and about 37% by weight tin) and 95/5 type Pb/Sn solder bumps (i.e., solder having about 95% by weight lead and about 5% by weight tin) have been used in flip-chip, ball grid array, and chip-scale packaging type attachments.
Assemblies that include semiconductor devices connected face down to higher level substrates using solder balls are subjected to thermal cycling during subsequent processing, testing thereof, and in normal use. As these assemblies undergo thermal cycling, the solder balls thereof are also exposed to wide ranges of temperatures, causing the solder balls to expand when heated and contract when cooled. Such expansion and contraction is especially problematic at the interface between a solder ball and the underlying contact pad. Expansion and contraction of solder balls can also occur at the interface between a solder ball and the contact pad of a higher level substrate to which, for example, a die is secured. Repeated variations in temperatures can cause solder fatigue, which can reduce the strength of the solder balls, cause the solder balls to crack and fail, and diminish the reliability of the solder balls as mechanical and electrical connection elements.
In an attempt to increase the reliability with which solder balls connect semiconductor devices face down to higher level substrates, resins have been applied to semiconductor devices to form rings around the bases of the solder balls protruding from the semiconductor devices. These resinous supports laterally contact the bases of the solder balls to enhance the reliability thereof. The resinous supports are applied to a semiconductor device after solder balls have been secured to the contact pads of the semiconductor device and before the semiconductor device is connected face down to a higher level substrate. As those of skill in the art are aware, however, the shapes of solder balls can change when bonded to the contact pads of a substrate, particularly after reflow thereof. If the shapes of the solder balls change, the solder balls can fail to maintain contact with the resinous supports, which could thereby fail to protect or enhance the reliability of the solder balls.
The inventor is not aware of any art that discloses a method that can be used to fabricate support rings around the contact pads of a semiconductor device before, as well as after, solder balls are secured to the contact pads.
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 or unfixed material corresponding to each layer within the object boundaries. This is followed by selective consolidation or fixation of the material to at least a partially consolidated, or semisolid, state in those areas of a given layer corresponding to portions of the object, the consolidated or fixed material also at that time being substantially concurrently bonded to a lower layer of the object to be fabricated. The unconsolidated material employed to build an object may be supplied in particulate or liquid form and the material itself may be consolidated or fixed or a separate binder material may be employed to bond material particles to one another and to those of a previously formed layer. In some instances, thin sheets of material may be superimposed to build an object, each sheet being fixed to a next lower sheet and unwanted portions of each sheet removed, a stack of such sheets defining the completed object. When particulate materials are employed, resolution of object surfaces is highly dependent upon particle size. When a liquid is employed, surface resolution is highly dependent upon the minimum surface area of the liquid which can be fixed and the minimum thickness of a layer that can be generated. Of course, in either case, resolution and accuracy of object reproduction from the CAD file is also dependent upon the ability of the apparatus used to fix the material to precisely track the mathematical instructions indicating solid areas and boundaries for each layer of material. Toward that end, and depending upon the layer being fixed, various fixation approaches have been employed, including particle bombardment (electron beams), disposing a binder or other fixative (such as by ink-jet printing techniques), or irradiation using heat or specific wavelength ranges.
An early application of stereolithography was to enable rapid fabrication of molds and prototypes of objects from CAD files. Thus, either male or female forms on which mold material might be disposed might be rapidly generated. Prototypes of objects might be built to verify the accuracy of the CAD file defining the object and to detect any design deficiencies and possible fabrication problems before a design was committed to large-scale production.
In more recent years, stereolithography has been employed to develop and refine object designs in relatively inexpensive materials and has also been used to fabricate small quantities of objects where the cost of conventional fabrication techniques is prohibitive for the same, such as in the case of plastic objects conventionally formed by injection molding. It is also known to employ stereolithography in the custom fabrication of products generally built
Ghyka Alexander G.
TraskBritt
LandOfFree
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