Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – On insulating carrier other than a printed circuit board
Reexamination Certificate
2002-03-27
2003-02-25
Booth, Richard (Department: 2812)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
On insulating carrier other than a printed circuit board
C257S688000, C257S738000
Reexamination Certificate
active
06525408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to semiconductor devices having collars disposed about the peripheries of the contact pads thereof and, more specifically, to the use of stereolithography to fabricate such collars around the contact pads prior to securing conductive structures to the contact pads. Particularly, the present invention pertains to collars disposed about the peripheries of the contact pads of a semiconductor device component for enhancing the reliability of conductive structures secured to the contact pads. The present invention also relates to semiconductor device components including such collars.
Reliability of Conductive Structures Used to Connect a Semiconductor Device Face down to a Higher Level Substrate
2. State of the Art
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 or other discrete conductive elements.
Examples of materials 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, tin-silver (Sn/Ag) solder, tin-silver-nickel (Sn/Ag/Ni) solder, copper gold, and conductive polymers. For example, 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.
When 95/5 type Pb/Sn solder bumps are employed as conductive structures to form a direct connection between a contact pad of a semiconductor device and a contact pad of a higher level substrate, a quantity of solder paste, such as 63/37 type Pb/Sn solder, can be applied to the contact pad of the higher level substrate to facilitate bonding of the solder bump thereto. As the 95/5 type Pb/Sn solder and the 63/37 type Pb/Sn solder are heated to bond the solder bump to a contact pad of the higher level substrate, the 95/5 type Pb/Sn solder, which has a higher melting temperature than the 63/37 type Pb/Sn solder, softens when the 63/37 type Pb/Sn solder is reflowed. When the 95/5 type Pb/Sn solder softens, the gravitational or compressive forces holding the semiconductor device in position over the higher level substrate can cause the softened 95/5 type Pb/Sn solder bump to flatten, pushing the solder laterally outward onto portions of the surface of the semiconductor device that surround the contact pad to which the solder bump is secured and, in the case of fine pitch or spacing of balls, into the solder of an adjacent ball.
Assemblies that include semiconductor devices connected face down to higher level substrates using solder balls are subjected to thermal cycling during subsequent processing, burn-in, 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. Repeated variations in temperatures can cause solder fatigue, which can reduce the strength of the solder balls, cause the solder balls to fail, and diminish the reliability of the solder balls. The high temperatures to which solder balls are exposed during burn-in and thermal cycling can also soften and alter the conformations of the conductive structures.
The use of other conductive structures, which have more desirable shapes, such as pillars, or columns, and mushroom-type shapes, and consume less conductive material than solder balls, to connect semiconductor devices face down to higher level substrates has been limited since taller and thinner conductive structures may not retain their shapes upon being bonded to the contact pads of a higher level substrate or in thermal cycling of the semiconductor device assembly.
The likelihood that a solder ball will be damaged by thermal cycling is particularly high when the solder ball spreads over and contacts the surface of the semiconductor device or the higher level substrate. Flattened solder balls and solder balls that contact regions of the surface of a semiconductor device that surround the contact pads thereof are particularly susceptible to the types of damage that can be caused by thermal cycling of the semiconductor device.
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 collars 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 of the solder balls. 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 use of solder balls in connecting a semiconductor device face down to higher level substrates is also somewhat undesirable from the standpoint that, due to their generally spherical shapes, solder balls consume a great deal of area, or “real estate”, on a semiconductor device. Thus, solder balls can limit the spacing between the adjacent contact pads of a semiconductor device and, thus, the pitch of the contact pads on the semiconductor device.
Moreover, when solder balls are reflowed, a phenomenon referred to as “outgassing” occurs, which can damage a semiconductor device proximate to the solder balls.
The inventors are not aware of any art that discloses peripheral collars that may be disposed individually around the contact pads of a semiconductor device so as to, at least in part, define the shapes of conductive structures to be bonded to the contact pads or to facilitate bonding of a conductive structure to a bond pad without completely reflowing the material of the conductive structures. Moreover, the inventors are not aware of methods that can be used to fabricate collars around either bare contact pads or contact pads having conductive structures protruding therefrom.
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 nonme
Ahmad Syed Sajid
Akram Salman
Booth Richard
Lindsay Jr. Walter L.
TraskBritt
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