Methods of underfilling and encapsulating semiconductor assemblies with materials having selected properties using stereolithography
Methods of forming semiconductor packages include immersing a semiconductor device assembly in a liquid photopolymerizable resin including a plurality of discrete particles dispersed therethrough, and selectively at least partially curing portions of the resin adjacent at least one semiconductor die of the semiconductor device assembly. In some embodiments, the semiconductor device assembly may be immersed in a second liquid photopolymerizable resin having at least one physical property differing from the first liquid photopolymerizable resin, and the second liquid photopolymerizable resin may be selectively at least partially cured. Furthermore, the semiconductor die may have an active surface including an array of optically interactive semiconductor devices, and portions of the liquid photopolymerizable resin surrounding a periphery of the array may be selectively at least partially cured to form a substantially opaque support structure.
This application is a divisional of application Ser. No. 10/867,257, filed Jun. 14, 2004, pending.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to the underfilling and encapsulation of semiconductor devices on a carrier substrate. More specifically, the present invention relates to a method of fabricating a semiconductor assembly, wherein the underfill and encapsulation materials may exhibit differing material properties and are formed using stereolithography.
2. State of the Art
Flip-chip style packaging for semiconductor dice is becoming ever more popular. In a flip-chip package, an array or pattern of external conductive elements such as solder bumps, or conductive or conductor-filled epoxy pillars, protrude from the active surface of the semiconductor die for use in mechanically and electrically connecting the semiconductor die to the patterned ends of conductive traces of higher level packaging, such as a carrier substrate.
There is typically a substantial mismatch in the coefficient of thermal expansion (CTE) between the material of the semiconductor die and that of the carrier substrate, such as a printed circuit board or interposer, bearing the conductive traces to which the external conductive elements of the die are bonded. Due to this substantial CTE mismatch, significant stresses develop between the semiconductor die and carrier substrate during normal thermal cycling. Without a strong mechanical attachment of the semiconductor die to the substrate, the die may debond from the carrier substrate, or one or more of the external conductive elements may fracture or release from its corresponding conductive trace. In addition, the small spacing or pitch of the external conductive elements creates a significant potential for shorting between adjacent conductive elements or conductive elements and adjacent carrier substrate traces due to the presence of a dust particle or condensed moisture between the semiconductor die and the carrier substrate. Therefore, when a flip-chip type of electronic device, such as a semiconductor die, is conductively attached to a carrier substrate, underfilling the space between the device and substrate with an electrically insulative material is very desirable to enhance the mechanical bond between the die and the carrier substrate and to dielectrically isolate adjacent electrical connections between the die and the carrier substrate.
In the past, underfilling has been achieved using a dielectric, polymeric material that is heated to a temperature sufficient for it to flow. A vacuum source is typically used to draw the heated, viscous, dielectric material to fill the region between the substrate and the semiconductor die. However, effecting adequate removal of air, water vapor, and moisture from between the substrate and the semiconductor die has always been a problem associated with the conventional underfill process. A more controlled and precise manufacturing technique termed “stereolithography,” also known as “layered manufacturing,” has been employed recently to form the underfill and encapsulation region in semiconductor packages.
A representative patent disclosing forming the underfill and encapsulation structures of semiconductor device assemblies using stereolithography, assigned to the current assignee of the present application, is U.S. Pat. No. 6,537,482 to Farnworth (hereinafter “the '482 Farnworth Patent”), the disclosure of which is herein incorporated by reference. As shown in
While the '482 Farnworth Patent provides a useful method for encapsulating and underfilling a semiconductor die to form a semiconductor package, it is limited to forming the underfill and encapsulation regions from a photopolymerizable material having uniform material properties and formed from conventional photopolymerizable materials. Therefore, it is desirable to develop a method that enables varying the photopolymerizable material used to form the underfill and encapsulation regions of the semiconductor package. Furthermore, it would be desirable to tailor the material properties of the photopolymerizable material used to form the underfill and encapsulation structures in specific regions to reduce the thermal stresses experienced by the semiconductor package in service and enable protection of the semiconductor package from external elements.
BRIEF SUMMARY OF THE INVENTIONThe present invention, in a number of embodiments, includes underfill and encapsulation structures using a variety of photopolymerizable materials exhibiting differing material properties to package semiconductor devices and assemblies. Methods for fabricating the semiconductor packages employing stereolithography are also disclosed.
In a broad exemplary embodiment, a semiconductor device assembly includes at least one semiconductor die having a back side and an active surface including a plurality of discrete conductive elements projecting therefrom. The discrete conductive elements of the at least one semiconductor die are in electrical communication with a plurality of conductive traces of a carrier substrate. At least a portion of the semiconductor device assembly may be covered with a cured photopolymer material, wherein the cured photopolymer material includes a polymerized matrix having a plurality of discrete particles dispersed therethrough.
In an exemplary embodiment, the discrete particles of the cured photopolymer material may be formed from a material such as, for example, boron nitride, which enables efficient heat transfer from the semiconductor device assembly. The cured photopolymer material may form an underfill structure between the at least one semiconductor die and the carrier substrate. In another exemplary embodiment, the cured photopolymer material may further sealingly enclose the at least one semiconductor die.
In another exemplary embodiment, a first cured photopolymer material may underfill the region between the at least one semiconductor die and the carrier substrate and cover at least portions of the lateral sides of the semiconductor die. A second cured photopolymer material that includes a polymerized matrix having a plurality of discrete particles dispersed therethrough formed from a material such as, for example, boron nitride, may cover the backside of the at least one semiconductor die to form a contiguous structure with the first cured photopolymer material. In another exemplary embodiment, the second cured photopolymer material may exhibit an electrical conductivity greater than that of the first polymerized material forming the underfill structure. The second cured photopolymer material may include a plurality of conductive particles formed from elemental metals or alloys to at least partially surround the at least one semiconductor die and improve electrostatic discharge protection and radio frequency shielding.
In yet another exemplary embodiment, the underfill structure that fills the region between the at least one semiconductor die and the carrier substrate may be formed from at least two layers of cured photopolymer materials. This underfill structure exhibits a coefficient of thermal expansion (CTE) gradient that decreases in a direction from the carrier substrate to the opposing face of the semiconductor die. By tailoring the CTE of each layer of cured photopolymer material, the thermal stresses caused by the CTE difference between carrier substrate and the at least one semiconductor die may be reduced. Additional photopolymer materials may be used to at least partially enclose the at least one semiconductor die.
In yet another exemplary embodiment, a semiconductor package for packaging an array of optically interactive semiconductor devices is disclosed. An array of optically interactive semiconductor devices may be surrounded by a substantially opaque support structure formed from a first cured photopolymer material. In another exemplary embodiment, a second cured photopolymer material covers the array of optically interactive semiconductor devices to protect the array.
These features, advantages, and alternative aspects of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGSIn the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:
The present invention, in a number of embodiments, employs stereolithography processing to form the packaging for semiconductor devices and semiconductor assemblies. In accordance with the present invention, liquid photopolymerizable resins exhibiting different material properties when cured maybe used to form various regions of underfill and encapsulation structures to tailor the material properties thereof for specific applications.
The semiconductor packages of the present invention may be formed using stereolithography systems known in the art. One such system is disclosed in the aforementioned '482 Farnworth Patent. The reader is directed to the disclosure of the '482 Farnworth Patent for specific details; however, the general aspects of the stereolithography system will be elaborated below in the description of
The semiconductor assembly 40 supported by platform 120 may be immersed into the reservoir 104 of liquid photopolymer resin 60 covering the semiconductor device assembly 40 with a precise amount of liquid photopolymer 60. While still submerged and positioned to be substantially horizontal, the layer of liquid photopolymer covering the semiconductor assembly 40 may then be irradiated by the beam 112 to cure or partially cure at least a portion of it. The individual stereolithographic acts required to form the underfill and encapsulation structures of the present invention are discussed in more detail below with respect to
The semiconductor packages of the present invention may use polymerized materials formed by modifying a variety of commercially available liquid photopolymer resins 60. Suitable photopolymers for use in practicing the present invention include, without limitation, ACCURA® SI 40 H
The liquid photopolymer resin 60 is responsive to light in the UV wavelength range such that it at least partially cures or polymerizes upon exposure to UV wavelength light to form a semisolid structure. The liquid photopolymer resin 60 may also be cured by other means, such as elevated temperature, to become a fully cured polymeric structure. Furthermore, with regard to the liquid photopolymer resins 60 that include filler constituents, as the volume percent of the filler constituent is increased in the liquid photopolymer 60, the thickness that may be partially cured using UV light to a semisolid state decreases. A thickness of about 18×10−3 inches may be partially cured to a semisolid state if the liquid photopolymer resin 60 does not posses any filler constituent. A thickness of about 4.5×10−3 inches may be partially cured to a semisolid state if the liquid photopolymer resin 60 possesses about 50 volume percent filler constituent.
An exemplary semiconductor device assembly 40 formed in accordance with the present invention is shown in
In
As shown in
Referring to
An exemplary method for forming the underfill structure 50 and encapsulation structure 48 is described with reference to
As illustrated in
Referring to
The underfill structure 50 and the encapsulation structures 48A and 48B of the embodiment shown in
Referring to
The underfill structure 50 and the encapsulation structures 49A and 49B of the embodiment shown in
Referring to
Referring to
Referring to
An IR filter 210 is necessary to filter IR radiation from being received by the array 6 if cover 204 does not absorb IR radiation. As shown in
The package for the optically interactive semiconductor device may be formed using stereolithography methods similar to those used in the previous embodiments. The semiconductor die 20 may be immersed in the liquid photopolymer resin 60 to the desired depth. The liquid photopolymer resin 60 may be scanned by laser 108 to cure or at least partially cure a portion thereof to form cover 204 that covers the array 6. Cover 204 may be formed, if needed, by multiple iterative steps to build up cover 204 from multiple layers. The liquid photopolymer resin 60 may then be changed to another and the semiconductor die 20 re-immersed therein. The liquid photopolymer resin 60 is scanned by laser 108 to cure or at least partially cure a portion thereof to surround the periphery of array 6 with a support structure 206A. If needed, the above process may be repeated to form support structure 206B that is contiguous with support structure 206A and additional support structures 206C-206n. It should be understood, that support structure 206 may be formed prior to or subsequent to forming cover 204. Lenses 208a-208n, IR filter 210, or both may then be fixed to support structure 206 using an adhesive or other suitable technique.
Although the foregoing description contains many specifics, these are not to be construed as limiting the scope of the present invention, but merely as providing certain exemplary embodiments. Similarly, other embodiments of the invention may be devised that do not depart from the spirit or scope of the present invention. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims, are encompassed by the present invention.
Claims
1. A method of forming a semiconductor package, comprising:
- providing a carrier substrate bearing a plurality of conductive traces;
- securing at least one semiconductor die having lateral sides, a back side, and an active surface including a plurality of discrete conductive elements projecting therefrom by the plurality of discrete conductive elements to the conductive traces of the carrier substrate to form a semiconductor device assembly;
- immersing the semiconductor device assembly in a first liquid photopolymerizable resin including a plurality of discrete particles dispersed therethrough; and
- selectively at least partially curing portions of the first liquid photopolymerizable resin adjacent the at least one semiconductor die.
2. The method according to claim 1, further comprising at least partially curing portions of the first liquid photopolymerizable resin to form an underfill structure that substantially fills a volume between the at least one semiconductor die and the carrier substrate.
3. The method according to claim 2, further comprising submerging the semiconductor assembly to a depth wherein the first liquid photopolymerizable resin overlies the at least one semiconductor die and at least partially curing the first liquid photopolymerizable resin to fully enclose the at least one semiconductor die.
4. The method according to claim 3, further comprising selecting the discrete particles to comprise boron nitride.
5. The method according to claim 1, further comprising:
- immersing the semiconductor device assembly in a second liquid photopolymerizable resin prior to immersion in and selectively at least partially curing portions of the first liquid photopolymerizable resin;
- at least partially curing the second liquid photopolymerizable resin within a volume between the at least one semiconductor die and the carrier substrate and a lateral periphery surrounding the at least one semiconductor die to form an underfill structure; and
- at least partially curing portions of the first liquid photopolymerizable resin to form a cover structure that covers the back side of the at least one semiconductor die and is contiguous with the underfill structure.
6. The method according to claim 5, further comprising selecting the discrete particles to comprise boron nitride.
7. The method according to claim 5, further comprising immersing the semiconductor device assembly in a third liquid photopolymerizable resin and at least partially curing portions of the third liquid photopolymerizable resin to at least partially enclose the at least one semiconductor die, the underfill structure, and the cover structure.
8. The method according to claim 7, further comprising selecting the third liquid photopolymerizable resin to include a plurality of discrete particles comprising an elemental metal or an alloy.
9. The method according to claim 1, further comprising:
- immersing the semiconductor device assembly in a second liquid photopolymerizable resin prior to immersion in and selectively at least partially curing portions of the first liquid photopolymerizable resin;
- at least partially curing the second liquid photopolymerizable resin within a volume between the at least one semiconductor die and the carrier substrate and a lateral periphery surrounding the at least one semiconductor die to form an underfill structure; and
- at least partially curing portions of the first liquid photopolymerizable resin to surround a lateral periphery of the at least one semiconductor die and be contiguous with the underfill structure.
10. The method according to claim 9, further comprising selecting the discrete particles to comprise an elemental metal or an alloy.
11. The method according to claim 1, further comprising:
- wherein the selectively at least partially curing portions of the first liquid photopolymerizable resin comprises forming a first layer thereof on the carrier substrate located in a region between the carrier substrate and the at least one semiconductor die;
- immersing the semiconductor device assembly in at least one additional liquid photopolymerizable resin including a plurality of discrete particles to cause the at least one additional liquid photopolymerizable resin to fill a volume between the at least one semiconductor die and the first layer; and
- selectively at least partially curing portions of the at least one additional liquid photopolymerizable resin to form a second layer contiguous with the first layer.
12. The method according to claim 11, further comprising formulating the at least one additional liquid photopolymerizable resin including a plurality of discrete particles to cause the second layer to have a coefficient of thermal expansion less than that of the first layer.
13. The method according to claim 12, further comprising selecting the discrete particles to comprise boron nitride or a silicate.
14. A method of forming a semiconductor package comprising:
- providing a carrier substrate having a plurality of conductive traces;
- immersing the carrier substrate in a first liquid photopolymerizable resin to cover the carrier substrate with a layer thereof, the first liquid photopolymerizable resin having a first coefficient of thermal expansion in a cured state;
- selectively at least partially curing the layer of the first liquid photopolymerizable resin to form a first layer exposing at least a portion of the plurality of the conductive traces through a plurality of apertures;
- depositing a conductive material in the plurality of apertures;
- securing at least one semiconductor die including a plurality of discrete conductive elements to the carrier substrate to form a semiconductor device assembly, the plurality of discrete conductive elements in electrical communication with the plurality of conductive traces of the carrier substrate;
- immersing the semiconductor device assembly in a second liquid photopolymerizable resin, the second liquid photopolymerizable resin having a second coefficient of thermal expansion in a cured state less than the first coefficient of thermal expansion; and
- selectively at least partially curing the second liquid photopolymerizable resin to form a second layer that fills at least a portion of a region between the first layer and the at least one semiconductor die and substantially seals the at least one semiconductor die.
15. The method according to claim 14, further comprising, prior to depositing the conductive material in the plurality of apertures, forming one or more additional layers from a cured photopolymer material, wherein the one or more additional layers and the first layer exhibit a gradient in coefficient of thermal expansion that decreases in a direction from the first layer toward the one or more additional layers.
16. The method according to claim 14, further comprising curing the first layer and the second layer to form a unitary structure.
17. The method according to claim 15, further comprising curing the first layer, the second layer, and the one or more additional layers to form a unitary structure.
18. The method according to claim 14, further comprising selecting the second layer to have a concentration of discrete particles that is greater than a concentration of discrete particles of the first layer.
19. The method according to claim 18, further comprising selecting the discrete particles to comprise boron nitride or a silicate.
20. A method of forming a semiconductor package, comprising:
- providing at least one semiconductor die having an active surface including an array of optically interactive semiconductor devices;
- immersing the at least one semiconductor die in a first liquid photopolymerizable resin; and selectively at least partially curing portions of the first liquid photopolymerizable resin surrounding a periphery of the array to form a substantially opaque support structure.
21. The method according to claim 20, further comprising:
- immersing the at least one semiconductor die in a second liquid photopolymerizable resin; and
- selectively at least partially curing portions of the second liquid photopolymerizable resin covering the array.
22. The method according to claim 21, further comprising fixing at least one lens to the support structure over the array.
23. The method according to claim 20, further comprising fixing at least one lens to the support structure.
24. The method according to claim 23, further comprising disposing an infrared filter between the at least one lens and the active surface.
25. The method according to claim 20, further comprising formulating the first liquid photopolymerizable resin to include a plurality of discrete particles.
Type: Application
Filed: Sep 5, 2006
Publication Date: Jan 25, 2007
Inventors: David Hembree (Boise, ID), Warren Farnworth (Nampa, ID)
Application Number: 11/516,099
International Classification: H01L 21/00 (20060101);