U.S. patent application number 10/328558 was filed with the patent office on 2003-05-29 for collar positionable about a periphery of a contact pad and around a conductive structure secured to the contact pad, semiconductor device components including same, and methods for fabricating same.
Invention is credited to Ahmad, Syed Sajid, Akram, Salman.
Application Number | 20030098499 10/328558 |
Document ID | / |
Family ID | 24362188 |
Filed Date | 2003-05-29 |
United States Patent
Application |
20030098499 |
Kind Code |
A1 |
Akram, Salman ; et
al. |
May 29, 2003 |
Collar positionable about a periphery of a contact pad and around a
conductive structure secured to the contact pad, semiconductor
device components including same, and methods for fabricating
same
Abstract
Dielectric collars are configured to be positioned laterally
around contact pads of a semiconductor device or another substrate.
Substrates on which the collars are positioned and that include
contact pads that are exposed through the collars are also
disclosed, as are methods for fabricating the collars and
for-positioning the collars on substrates. The collars may be
positioned laterally adjacent to the contact pads of a substrate
before or after conductive structures are secured to the contact
pads. When the conductive structures are electrically connected to
contact pads of another semiconductor device component, the collars
prevent the material of the conductive structures from contacting
regions of the surface of the substrate or other semiconductor
device component that surround the contact pads. The collars may be
preformed structures that are assembled with the substrate, or they
may be formed on the substrate. A stereolithographic method of
fabricating the collars is disclosed.
Inventors: |
Akram, Salman; (Boise,
ID) ; Ahmad, Syed Sajid; (Boise, ID) |
Correspondence
Address: |
TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
24362188 |
Appl. No.: |
10/328558 |
Filed: |
December 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10328558 |
Dec 23, 2002 |
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10107969 |
Mar 27, 2002 |
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6525408 |
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10107969 |
Mar 27, 2002 |
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09590418 |
Jun 8, 2000 |
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Current U.S.
Class: |
257/668 ;
257/E21.508; 257/E21.511 |
Current CPC
Class: |
H01L 2924/01033
20130101; H05K 3/3436 20130101; Y02P 80/30 20151101; H01L 2224/0401
20130101; H01L 2224/81801 20130101; H01L 2924/01029 20130101; H01L
21/44 20130101; H05K 2201/10977 20130101; H01L 2224/81136 20130101;
H01L 2224/16 20130101; H01L 2924/01006 20130101; H01L 2224/75
20130101; H01L 2924/014 20130101; Y02P 70/50 20151101; H01L
2924/01079 20130101; H01L 2224/13023 20130101; H01L 24/742
20130101; H01L 24/16 20130101; H01L 2224/06131 20130101; H01L
2224/1148 20130101; H01L 2924/01005 20130101; H01L 2224/10126
20130101; H01L 2924/01082 20130101; H01L 2924/0105 20130101; H01L
2224/0615 20130101; H01L 2924/12042 20130101; H01L 2224/05572
20130101; H01L 2924/0002 20130101; H01L 24/11 20130101; H01L
2924/01039 20130101; H01L 24/81 20130101; H01L 2224/1319 20130101;
H01L 2924/351 20130101; H01L 24/12 20130101; H01L 2224/1191
20130101; H01L 2224/13099 20130101; H01L 24/75 20130101; B33Y 10/00
20141201; B33Y 80/00 20141201; H01L 2924/01047 20130101; H01L
2224/05572 20130101; H01L 2924/00014 20130101; H01L 2924/0002
20130101; H01L 2224/05552 20130101; H01L 2924/351 20130101; H01L
2924/00 20130101; H01L 2924/12042 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
257/668 |
International
Class: |
H01L 023/495 |
Claims
What is claimed is:
1. A semiconductor device component, comprising: a substrate having
contact pads exposed at a surface thereof; and at least one collar
at least partially surrounding at least one contact pad of said
contact pads, said at least one collar protruding from said surface
so as to laterally contain material of at least a base portion of a
conductive structure securable to said at least one contact
pad.
2. The semiconductor device of claim 1, wherein said at least one
collar comprises a dielectric material.
3. The semiconductor device of claim 1, wherein said at least one
collar comprises a photopolymer.
4. The semiconductor device of claim 3, wherein at least a portion
of said photopolymer is at least semisolid.
5. The semiconductor device of claim 3, wherein said at least one
collar comprises a plurality of superimposed, contiguous, mutually
adhered layers.
6. The semiconductor device of claim 1, wherein said substrate
comprises a semiconductor wafer including a plurality of
semiconductor dice.
7. The semiconductor device of claim 1, wherein said substrate
comprises a semiconductor die.
8. The semiconductor device of claim 7, wherein each said at least
one contact pad comprises a bond pad.
9. The semiconductor device of claim 1, wherein said substrate
comprises at least one chip-scale package.
10. The semiconductor device of claim 1, wherein said substrate
comprises a carrier substrate.
11. The semiconductor device of claim 1, wherein said at least one
collar includes an aperture and is configured to contact at least a
portion of a surface of a conductive structure securable to said at
least one contact pad and located within said aperture.
12. The semiconductor device of claim 11, wherein said aperture is
configured to define a shape of at least a portion of said
conductive structure.
13. The semiconductor device of claim 1, further comprising a
conductive structure secured to said at least one contact pad.
14. The semiconductor device of claim 11, wherein said conductive
structure has at least one of a pillar configuration, a
mushroom-like configuration, and a non-semi-spherical
configuration.
15. The semiconductor device of claim 1, wherein said at least one
collar is configured to at least partially align a preformed
conductive structure with said at least one contact pad.
16. A semiconductor device component, comprising: at least one
contact; and a structure laterally surrounding at least a portion
of said at least one contact, said structure including: a plurality
of at least partially superimposed, mutually adhered, contiguous
material layers; and a receptacle extending through each of said
plurality of at least partially superimposed, mutually adhered,
contiguous material layers.
17. The semiconductor device of claim 16, wherein said structure is
configured to prevent a discrete conductive structure on said at
least one contact from extending laterally beyond an outer
periphery of said plurality of at least partially superimposed,
mutually adhered, contiguous material layers.
18. The semiconductor device of claim 16, wherein a surface of said
receptacle is configured to contact at least the portion of the
discrete conductive structure.
19. The semiconductor device of claim 18, wherein said surface is
configured to form a shape of at least the portion of the discrete
conductive structure.
20. The semiconductor device of claim 16, wherein each of said
plurality of at least partially superimposed, mutually adhered,
contiguous material layers comprises photopolymer.
21. The semiconductor device of claim 17, wherein said structure is
configured to facilitate alignment of the discrete conductive
structure with at least said portion of said at least one contact.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Serial No.
10/107,969, filed Mar. 27, 2002, pending, which is a divisional of
application Ser. No. 09/590,418, filed Jun. 8, 2000, pending.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] 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
[0004] 2. State of the Art
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] Moreover, when solder balls are reflowed, a phenomenon
referred to as "outgassing" occurs, which can damage a
semiconductor device proximate to the solder balls.
[0014] 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
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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 in small quantities or where a product design is
rendered only once. Finally, it has been appreciated in some
industries that stereolithography provides a capability to
fabricate products, such as those including closed interior
chambers or convoluted passageways, which cannot be fabricated
satisfactorily using conventional manufacturing techniques. It has
also been recognized in some industries that a stereolithographic
object or component may be formed or built around another,
pre-existing object or component to create a larger product.
[0020] However, to the inventors' knowledge, stereolithography has
yet to be applied to mass production of articles in volumes of
thousands or millions, or employed to produce, augment or enhance
products including other, pre-existing components in large
quantities, where minute component sizes are involved, and where
extremely high resolution and a high degree of reproducibility of
results is required. In particular, the inventor is not aware of
the use of stereolithography to fabricate peripheral collars around
the contact pads of semiconductor devices, such as flip-chip type
semiconductor devices or ball grid array packages. Furthermore,
conventional stereolithography apparatus and methods fail to
address the difficulties of precisely locating and orienting a
number of pre-existing components for stereolithographic
application of material thereto without the use of mechanical
alignment techniques or to otherwise assuring precise, repeatable
placement of components.
BRIEF SUMMARY OF THE INVENTION
[0021] The present invention includes a dielectric collar that
surrounds the periphery of a contact pad of a semiconductor device,
semiconductor device components including such collars, and methods
for fabricating the collars. The present invention also includes
forming conductive structures of desired configurations with the
collars, as well as other methods for using the collars of the
present invention.
[0022] A collar incorporating teachings of the present invention
surrounds the periphery of a contact pad exposed at the surface of
a semiconductor device component, such as a semiconductor die, a
chip-scale package substrate, or a carrier substrate. The collar
protrudes from the surface of the semiconductor device component.
If the collar is fabricated before a conductive structure is
secured to the contact pad, at least a portion of the surrounded
contact pad is exposed through an aperture defined by the collar.
The aperture of the collar may be configured to impart at least a
base portion of a conductive structure to be bonded or otherwise
secured to the contact pad with a desired shape and dimensions.
[0023] Conductive structures of any useful configuration can be
used with or defined by the collar of the present invention.
Exemplary configurations of conductive structures that can be used
with or defined by the collar include, but are not limited to,
balls, bumps, pillars or columns, mushroom shapes, or other shapes.
These conductive structures can be fabricated from solders, metals,
metal alloys, conductor filled epoxies, conductive epoxies, and
other conductive materials that are suitable for use with
semiconductor devices.
[0024] As the collar of the present invention facilitates the use
of conductive structures having shapes other than that of a solder
ball, alternatively shaped, thinner conductive structures can be
spaced more closely, facilitating a decrease in the possible pitch
of contact pads on a semiconductor device component. In addition,
some alternatively configured conductive structures, such as
pillars and mushrooms, require less material than balls.
[0025] Since the collar protrudes from the surface of the
semiconductor device component, when a conductive structure is
bonded or otherwise secured to the contact pad exposed through the
collar, the collar laterally surrounds at least a portion of the
conductive structure. Accordingly, when a conductive structure is
formed on or secured to a contact pad, or during bonding of the
conductive structure to the contact pad of another device or
substrate, the contact pad collar of the present invention
laterally contains at least a base portion of a conductive
structure extending therethrough and prevents the material of the
conductive structure from contacting and wetting portions of the
surface of the semiconductor device component adjacent to the
contact pad.
[0026] The collar is preferably configured to contact a conductive
structure extending therethrough so as to laterally support and
protect at least the contacted portion of the conductive structure
during thermal cycling of the semiconductor device, such as in the
repeated use thereof.
[0027] In addition, use of collars according to the present
invention, which may be of substantial height or protrusion from a
substrate so as to encompass the conductive structures at or
approaching their heights, may eliminate the need for an insulative
underfill conventionally applied between a die and a higher level
substrate.
[0028] Another significant advantage of the collars of the present
invention is the containment of the conductive material of the
conductive structures, in the manner of a dam, during connection of
a semiconductor device face down upon a higher level substrate,
thus preventing contamination or wetting of the passivation layer
surrounding the contact pads.
[0029] According to another aspect, the present invention includes
a method for fabricating the collar. In a preferred embodiment of
the method, a computer-controlled, 3-D CAD-initiated process known
as "stereolithography" or "layered manufacturing" is used to
fabricate the collar. When stereolithographic processes are
employed, each collar is formed as either a single layer or a
series of superimposed, contiguous, mutually adhered layers of
material.
[0030] The stereolithographic method of fabricating the collars of
the present invention preferably includes the use of a machine
vision system to locate the semiconductor devices or other
substrates on which the collars are to be fabricated, as well as
the features or other components on or associated with the
semiconductor devices or other substrates (e.g., solder bumps,
contact pads, conductor traces, etc.). The use of a machine vision
system directs the alignment of a stereolithography system with
each semiconductor device or other substrate for material
disposition purposes. Accordingly, the semiconductor devices or
other substrates need not be precisely mechanically aligned with
any component of the stereolithography system to practice the
stereolithographic embodiment of the method of the present
invention.
[0031] In a preferred embodiment, the collars to be fabricated upon
or positioned upon and secured to a semiconductor device component
in accordance with the invention are fabricated using precisely
focused electromagnetic radiation in the form of an ultraviolet
(UV) wavelength laser under control of a computer and responsive to
input from a machine vision system, such as a pattern recognition
system, to fix or cure selected regions of a layer of a liquid
photopolymer material disposed on the semiconductor device or other
substrate.
[0032] The collars of the present invention may be fabricated
around the contact pads of the semiconductor device component
either before or after conductive structures are bonded or
otherwise secured to the contact pads, although it is preferred
that the collars be fabricated before securing the conductive
structures to the contact pads.
[0033] Other features and advantages of the present invention will
become apparent to those of skill in the art through consideration
of the ensuing description, the accompanying drawings, and the
appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0034] The accompanying drawings illustrate exemplary embodiments
of the invention, wherein some dimensions may be exaggerated for
the sake of clarity, and wherein:
[0035] FIG. 1 is an enlarged perspective view of a semiconductor
device having collars positioned around the exposed contact pads
thereof;
[0036] FIG. 2 is a cross-section taken along line 2-2 of FIG. 1,
depicting the apertures of the collars;
[0037] FIG. 3 is a cross-sectional view illustrating the face down
connection of the semiconductor device of FIGS. 1 and 2 to a higher
level substrate;
[0038] FIG. 4 is an enlarged perspective view of another
semiconductor device having collars positioned around the contact
pads thereof, each collar laterally surrounding a portion of a
conductive structure bonded to the surrounded contact pad;
[0039] FIG. 5 is a cross-section taken along line 5-5 of FIG. 4,
depicting conductive structures extending through and laterally
supported by the collars;
[0040] FIG. 6 is a cross-sectional view illustrating the face down
connection of the semiconductor device of FIGS. 4 and 5 to a higher
level substrate;
[0041] FIG. 7 is a cross-sectional view illustrating a collar
protruding the substantial distance of pillar-shaped conductive
structure extending therethrough;
[0042] FIG. 8 is a perspective view of a portion of a wafer having
a plurality of semiconductor devices thereon, depicting collars
being fabricated around each of the contact pads of the
semiconductor devices at the wafer level;
[0043] FIG. 9 is a schematic representation of an exemplary
stereolithography apparatus that can be employed in the method of
the present invention to fabricate the collars of the present
invention; and
[0044] FIG. 10 is a partial cross-sectional side view of a
semiconductor device disposed on a platform of a stereolithographic
apparatus for the formation of collars around the contact pads of
the semiconductor device.
DETAILED DESCRIPTION OF THE INVENTION
Collars
[0045] With reference to FIGS. 1 and 2, a semiconductor device 10
having contact pads 12 on a surface 14 thereof is illustrated.
Semiconductor device 10 can be a semiconductor die, a chip-scale
package, a ball grid array package, a carrier substrate, or any
other type of semiconductor device component having contact pads to
which conductive structures, such as balls, bumps, or pillars, can
be attached.
[0046] As illustrated, a collar 50 surrounds the periphery of each
contact pad 12. Each collar 50 has a aperture 52, through which at
least a portion of the surrounded contact pad 12 is exposed. Each
collar 50 protrudes from surface 14 of semiconductor device 10 so
as to laterally surround at least a portion of a conductive
structure to be bonded or otherwise secured to bond pad 12 and to
prevent the material of a conductive structure from contacting
portions of surface 14 adjacent to contact pad 12.
[0047] Referring now to FIG. 3, semiconductor device 10 is shown in
a face down orientation over a higher level substrate 30. Substrate
30 has contact pads 32, or terminals, exposed at a surface 34
thereof. Contact pads 32 are preferably arranged so as to align
with corresponding ones of contact pads 12 upon positioning
semiconductor device 10 face down over substrate 30. Each contact
pad 12 of semiconductor device 10 is electrically connected to its
corresponding contact pad 32 of substrate 30 by way of a conductive
structure 20, such as a bump, ball, or pillar, formed from a
conductive material, such as a solder, other metal or metal alloy,
a conductor filled epoxy, or a conductive epoxy.
[0048] As will be explained in greater detail below, collars 50 are
at least partially fabricated prior to connecting conductive
structures 20 to contact pads 12. As depicted in FIG. 3, a base
portion 22 of each conductive structure 20, which is bonded or
otherwise secured to the contact pad 12 exposed through aperture 52
of collar 50, has a shape that is complementary to the
configuration of aperture 52. Thus, each collar 50 contacts the
conductive structure 20 that extends through aperture 52. Base
portion 22 of each conductive structure 20 can have a shape that is
defined by aperture 52 or that is configured complementarily to
aperture 52. Accordingly, collars 50 and the apertures 52 thereof
can be configured to impart desired shapes and dimensions to
conductive structures 20 or at least base portion 22 thereof.
[0049] Alternatively, conductive structures 20 can have base
portions 22 that are not shaped complementarily to apertures 52 or
that extend through apertures 52 without contacting collars 50.
[0050] With continued reference to FIG. 3, semiconductor device 10
is connected face down to a higher level substrate 30, such as a
carrier substrate. Conductive structures 20 connect contact pads 12
of semiconductor device 10 to corresponding contact pads 32 exposed
at surface 34 of substrate 30. As conductive structures 30 are
being bonded or otherwise secured to contact pads 32, collar 50
prevents material of conductive structures 20 from contacting
regions of surface 14 adjacent to contact pads 12. Moreover,
collars 50 contact conductive structures 20 so as to laterally
support and protect at least the contacted portions of conductive
structures 20.
[0051] FIGS. 4 and 5 illustrate another semiconductor device 10,
which has conductive structures 20', shown as solder bumps,
protruding from each of the contact pads 12 on the surface 14
thereof. The portion of each conductive structure 20' adjacent
surface 14 and the periphery of each bond pad 12 is laterally
surrounded by another embodiment of collar 50', which protrudes
from surface 14.
[0052] As shown in FIG. 5, conductive structure 20' extends through
an aperture 52' of collar 50' to contact pad 12. Collar 50'
contacts the sides of the portion of conductive structure 20'
extending through aperture 52'. FIG. 5 also depicts portions of
collar 50' located beneath conductive structure 20'. These portions
of collar 50' are referred to herein as "shadowed" areas 54'.
[0053] Turning now to FIG. 6, semiconductor device 10 is depicted
as being invertedly disposed over and connected to a higher level
substrate 30. Conductive structures 20' connect each contact pad 12
of semiconductor device 10 to a corresponding contact pad 32
exposed at a surface 34 of substrate 30. As depicted, collars 50'
prevent material of conductive structures 20' from contacting
surface 14 of semiconductor device 10.
[0054] As shown in FIG. 7, a collar 50" can also protrude from
surface 14 substantially the same distance as a pillar-shaped
conductive structure 20" secured to contact pad 12. When such a
collar 50" is fabricated around contact pad 12 before conductive
structure 20" is secured thereto, conductive structure 20" can be
formed by disposing a quantity of conductive material, such as a
solder, metal, metal alloy, conductor filled epoxy, or conductive
elastomer, into aperture 52". Alternatively, a pre-formed
conductive structure 20" can be secured to contact pad 12 and
collar 50" fabricated around conductive structure 20".
[0055] It should also be noted that conductive structures 20 (see
FIGS. 2 and 3), 20" are thinner than conductive structures 20' (see
FIGS. 4-6). Thus, conductive structures 20, 20" consume less area,
or real estate, on semiconductor device 10 than conductive
structures 20'. Accordingly, conductive structures 20, 20" are
spaced farther apart than conductive structures 20'. Furthermore,
conductive structures 20, 20" can be used with semiconductor
devices having tighter, or smaller, pitches than the pitches of
semiconductor devices with which solder balls or similar conductive
structures 20' are used. As conductive structures 20, 20" are
thinner than solder balls, such as conductive structure 20',
conductive structures 20, 20" also consume less conductive material
than conductive structures 20'.
[0056] FIG. 8 illustrates collars 50 on semiconductor devices 10,
in this case semiconductor dice, that have yet to be singulated, or
diced, from a wafer 72 or from a portion of a wafer 72. Each
semiconductor device 10 on wafer 72 is separated from adjacent
semiconductor devices 10 by a street 74 on surface 14.
[0057] While collars 50, 50', 50" are preferably substantially
simultaneously fabricated on or secured to a collection of
semiconductor devices 10, such as prior to singulating
semiconductor dice from a wafer 72, collars 50, 50', 50" can also
be fabricated on or secured to collections of individual
semiconductor devices 10 or other substrates, or to individual
semiconductor devices 10 or other substrates, such as substrate 30.
As another alternative, collars 50, 50', 50" can be substantially
simultaneously fabricated on or secured to a collection of more
than one type of semiconductor device 10 or other substrate.
[0058] Collars 50, 50', 50" can be fabricated directly on
semiconductor devices 10. Alternatively, collars 50, 50', 50" can
be fabricated separately from semiconductor devices 10, then
secured thereto as known in the art, such as by the use of a
suitable adhesive.
[0059] Collars 50, 50', 50" are preferably fabricated from a
photo-curable polymer, or "photopolymer" by stereolithographic
processes. When fabricated directly on a semiconductor device 10,
collars 50, 50', 50" can be made either before or after conductive
structures 20, 20', 20" are connected to contact pads 12 of
semiconductor device 10.
[0060] For simplicity, the ensuing description is limited to an
explanation of a method of fabricating collars 50 on a
semiconductor device 10 prior to securing conductive structures 20
to contact pads 12 of semiconductor device 10. As should be
appreciated by those of skill in the art, however, the method
described herein is also useful for fabricating collars 50', 50" on
semiconductor device 10, as well as for fabricating collars 50,
50', 50" on one or more semiconductor devices 10 or other
substrates having conductive structures 20, 20', 20" already
secured to the contact pads 12 thereof.
Stereolithography Apparatus and Methods
[0061] FIG. 9 schematically depicts various components and
operation of an exemplary stereolithography apparatus 80 to
facilitate the reader's understanding of the technology employed in
implementation of the method of the present invention, although
those of ordinary skill in the art will understand and appreciate
that apparatus of other designs and manufacture may be employed in
practicing the method of the present invention. The preferred,
basic stereolithography apparatus for implementation of the method
of the present invention, as well as operation of such apparatus,
are described in great detail in United States Patents assigned to
3D Systems, Inc., of Valencia, Calif., such patents including,
without limitation, U.S. Pat. Nos. 4,575,330; 4,929,402; 4,996,010;
4,999,143; 5,015,424; 5,058,988; 5,059,021; 5,059,359; 5,071,337;
5,076,974; 5,096,530; 5,104,592; 5,123,734; 5,130,064; 5,133,987;
5,141,680; 5,143,663; 5,164,128; 5,174,931; 5,174,943; 5,182,055;
5,182,056; 5,182,715; 5,184,307; 5,192,469; 5,192,559; 5,209,878;
5,234,636; 5,236,637; 5,238,639; 5,248,456; 5,256,340; 5,258,146;
5,267,013; 5,273,691; 5,321,622; 5,344,298; 5,345,391; 5,358,673;
5,447,822; 5,481,470; 5,495,328; 5,501,824; 5,554,336; 5,556,590;
5,569,349; 5,569,431; 5,571,471; 5,573,722; 5,609,812; 5,609,813;
5,610,824; 5,630,981; 5,637,169; 5,651,934; 5,667,820; 5,672,312;
5,676,904; 5,688,464; 5,693,144; 5,695,707; 5,711,911; 5,776,409;
5,779,967; 5,814,265; 5,850,239; 5,854,748; 5,855,718; 5,855,836;
5,885,511; 5,897,825; 5,902,537; 5,902,538; 5,904,889; 5,943,235;
and 5,945,058. The disclosure of each of the foregoing patents is
hereby incorporated herein by this reference.
[0062] With continued reference to FIG. 9 and as noted above, a 3-D
CAD drawing of an object to be fabricated in the form of a data
file is placed in the memory of a computer 82 controlling the
operation of apparatus 80 if computer 82 is not a CAD computer in
which the original object design is effected. In other words, an
object design may be effected in a first computer in an engineering
or research facility and the data files transferred via wide or
local area network, tape, disc, CD-ROM, or otherwise, as known in
the art, to computer 82 of apparatus 80 for object fabrication.
[0063] The data is preferably formatted in an STL (for
STereoLithography) file, STL being a standardized format employed
by a majority of manufacturers of stereolithography equipment.
Fortunately, the format has been adopted for use in many
solid-modeling CAD programs, so translation from another internal
geometric database format is often unnecessary. In an STL file, the
boundary surfaces of an object are defined as a mesh of
interconnected triangles.
[0064] Apparatus 80 also includes a reservoir 84 (which may
comprise a removable reservoir interchangeable with others
containing different materials) of an unconsolidated material 86 to
be employed in fabricating the intended object. In the currently
preferred embodiment, the unconsolidated material 86 is a liquid,
photo-curable polymer, or "photopolymer", that cures in response to
light in the UV wavelength range. The surface level 88 of material
86 is automatically maintained at an extremely precise, constant
magnitude by devices known in the art responsive to output of
sensors within apparatus 80 and preferably under control of
computer 82. A support platform or elevator 90, precisely
vertically movable in fine, repeatable increments in direction 116
responsive to control of computer 82, is located for movement
downward into and upward out of material 86 in reservoir 84.
[0065] An object may be fabricated directly on platform 90 or on a
substrate disposed on platform 90. When the object is to be
fabricated on a substrate disposed on platform 90, the substrate
may be positioned on platform 90 and secured thereto by way of one
or more base supports 122 (see FIG. 10). Such base supports 122 may
be fabricated before or simultaneously with the stereolithographic
fabrication of one or more objects on platform 90 or a substrate
disposed thereon. These supports 122 may support, or prevent
lateral movement of, the substrate relative to a surface 100 of
platform 90. Supports 122 may also provide a perfectly horizontal
reference plane for fabrication of one or more objects thereon, as
well as facilitate the removal of a substrate from platform 90
following the stereolithographic fabrication of one or more objects
on the substrate. Moreover, where a so-called "recoater" blade 102
is employed to form a layer of material on platform 90 or a
substrate disposed thereon, supports 122 can preclude inadvertent
contact of recoater blade 102, to be described in greater detail
below, with surface 100 of platform 90.
[0066] Apparatus 80 has a UV wavelength range laser plus associated
optics and galvanometers (collectively identified as laser 92) for
controlling the scan of laser beam 96 in the X-Y plane across
platform 90. Laser 92 has associated therewith a mirror 94 to
reflect beam 96 downwardly as beam 98 toward surface 100 of
platform 90. Beam 98 is traversed in a selected pattern in the X-Y
plane, that is to say, in a plane parallel to surface 100, by
initiation of the galvanometers under control of computer 82 to at
least partially cure, by impingement thereon, selected portions of
material 86 disposed over surface 100 to at least a partially
consolidated (e.g., semisolid) state. The use of mirror 94
lengthens the path of the laser beam, effectively doubling the
same, and provides a more vertical beam 98 than would be possible
if the laser 92 itself were mounted directly above platform surface
100, thus enhancing resolution.
[0067] Referring now to FIGS. 9 and 10, data from the STL files
resident in computer 82 is manipulated to build an object, such as
collar 50, illustrated in FIGS. 1-3 and 8, or base supports 122,
one layer at a time. Accordingly, the data mathematically
representing one or more of the objects to be fabricated are
divided into subsets, each subset representing a slice or layer of
the object. The division of data is effected by mathematically
sectioning the 3-D CAD model into at least one layer, a single
layer or a "stack" of such layers representing the object. Each
slice may be from about 0.0001 to about 0.0300 inch thick. As
mentioned previously, a thinner slice promotes higher resolution by
enabling better reproduction of fine vertical surface features of
the object or objects to be fabricated.
[0068] When one or more base supports 122 are to be
stereolithographically fabricated, supports 122 may be programmed
as a separate STL file from the other objects to be fabricated. The
primary STL file for the object or objects to be fabricated and the
STL file for base support(s) 122 are merged.
[0069] Before fabrication of a first layer for a support 122 or an
object to be fabricated is commenced, the operational parameters
for apparatus 80 are set to adjust the size (diameter if circular)
of the laser light beam used to cure material 86. In addition,
computer 82 automatically checks and, if necessary, adjusts by
means known in the art, the surface level 88 of material 86 in
reservoir 84 to maintain the same at an appropriate focal length
for laser beam 98. U.S. Pat. No. 5,174,931, referenced above and
previously incorporated herein by reference, discloses one suitable
level control system. Alternatively, the height of mirror 94 may be
adjusted responsive to a detected surface level 88 to cause the
focal point of laser beam 98 to be located precisely at the surface
of material 86 at surface level 88 if level 88 is permitted to
vary, although this approach is more complex. Platform 90 may then
be submerged in material 86 in reservoir 84 to a depth equal to the
thickness of one layer or slice of the object to be formed, and the
liquid surface level 88 is readjusted as required to accommodate
material 86 displaced by submergence of platform 90. Laser 92 is
then activated so laser beam 98 will scan unconsolidated (e.g.,
liquid or powdered) material 86 disposed over surface 100 of
platform 90 to at least partially consolidate (e.g., polymerize to
at least a semisolid state) material 86 at selected locations,
defining the boundaries of a first layer 122A of base support 122
and filling in solid portions thereof. Platform 90 is then lowered
by a distance equal to thickness of second layer 122B and laser
beam 98 scanned over selected regions of the surface of material 86
to define and fill in the second layer while simultaneously bonding
the second layer to the first. The process may then be repeated as
often as necessary, layer by layer, until base support 122 is
completed. Platform 90 is then moved relative to mirror 94 to form
any additional base supports 122 on platform 90 or a substrate
disposed thereon or to fabricate objects upon platform 90, base
support 122, or a substrate, as provided in the control software.
The number of layers required to erect support 122 or one or more
other objects to be formed depends upon the height of the object or
objects to be formed and the desired layer thickness 108, 110. The
layers of a stereolithographically fabricated structure with a
plurality of layers may have different thicknesses.
[0070] If a recoater blade 102 is employed, the process sequence is
somewhat different. In this instance, surface 100 of platform 90 is
lowered into unconsolidated (e.g., liquid) material 86 below
surface level 88 a distance greater than a thickness of a single
layer of material 86 to be cured, then raised above surface level
88 until platform 90, a substrate disposed thereon, or a structure
being formed on platform 90 or a substrate thereon is precisely one
layer's thickness below blade 102. Blade 102 then sweeps
horizontally over platform 90 or (to save time) at least over a
portion thereof on which one or more objects are to be fabricated
to remove excess material 86 and leave a film of precisely the
desired thickness. Platform 90 is then lowered so that the surface
of the film and material level 88 are coplanar and the surface of
the unconsolidated material 86 is still. Laser 92 is then initiated
to scan with laser beam 98 and define the first layer 130. The
process is repeated, layer by layer, to define each succeeding
layer 130 and simultaneously bond the same to the next lower layer
130 until all of the layers of the object or objects to be
fabricated are completed. A more detailed discussion of this
sequence and apparatus for performing the same is disclosed in U.S.
Pat. No. 5,174,931, previously incorporated herein by
reference.
[0071] As an alternative to the above approach to preparing a layer
of material 86 for scanning with laser beam 98, a layer of
unconsolidated (e.g., liquid) material 86 may be formed on surface
100 of support platform 90, on a substrate disposed on platform 90,
or on one or more objects being fabricated by lowering platform 90
to flood material 86 over surface 100, over a substrate disposed
thereon, or over the highest completed layer of the object or
objects being formed, then raising platform 90 and horizontally
traversing a so-called "meniscus" blade horizontally over platform
90 to form a layer of unconsolidated material having the desired
thickness over platform 90, the substrate, or each of the objects
being formed. Laser 92 is then initiated and a laser beam 98
scanned over the layer of unconsolidated material to define at
least the boundaries of the solid regions of the next higher layer
of the object or objects being fabricated.
[0072] Yet another alternative to layer preparation of
unconsolidated (e.g., liquid) material 86 is to merely lower
platform 90 to a depth equal to that of a layer of material 86 to
be scanned, and to then traverse a combination flood bar and
meniscus bar assembly horizontally over platform 90, a substrate
disposed on platform 90, or one or more objects being formed to
substantially concurrently flood material 86 thereover and to
define a precise layer thickness of material 86 for scanning.
[0073] All of the foregoing approaches to liquid material flooding
and layer definition and apparatus for initiation thereof are known
in the art and are not material to the practice of the present
invention, therefore, no further details relating thereto will be
provided herein.
[0074] In practicing the present invention, a commercially
available stereolithography apparatus operating generally in the
manner as that described above with respect to apparatus 80 of FIG.
9 is preferably employed, but with further additions and
modifications as hereinafter described for practicing the method of
the present invention. For example and not by way of limitation,
the SLA-250/50HR, SLA-5000 and SLA-7000 stereolithography systems,
each offered by 3D Systems, Inc., of Valencia, Calif., are suitable
for modification. Photopolymers believed to be suitable for use in
practicing the present invention include Cibatool SL 5170 and SL
5210 resins for the SLA-250/50HR system, Cibatool SL 5530 resin for
the SLA-5000 and 7000 systems, and Cibatool SL 7510 resin for the
SLA-7000 system. All of these photopolymers are available from Ciba
Specialty Chemicals Corporation.
[0075] By way of example and not limitation, the layer thickness of
material 86 to be formed, for purposes of the invention, may be on
the order of about 0.0001 to 0.0300 inch, with a high degree of
uniformity. It should be noted that different material layers may
have different heights so as to form a structure of a precise,
intended total height or to provide different material thicknesses
for different portions of the structure. The size of the laser beam
"spot" impinging on the surface of material 86 to cure the same may
be on the order of 0.001 inch to 0.008 inch. Resolution is
preferably .+-.0.0003 inch in the X-Y plane (parallel to surface
100) over at least a 0.5 inch.times.0.25 inch field from a center
point, permitting a high resolution scan effectively across a 1.0
inch.times.0.5 inch area. Of course, it is desirable to have
substantially this high a resolution across the entirety of surface
100 of platform 90 to be scanned by laser beam 98, such area being
termed the "field of exposure", and being substantially coextensive
with the vision field of a machine vision system employed in the
apparatus of the invention as explained in more detail below. The
longer and more effectively vertical the path of laser beam 96/98,
the greater the achievable resolution.
[0076] Referring again to FIG. 9, it should be noted that apparatus
80 useful in the method of the present invention includes a camera
140 which is in communication with computer 82 and preferably
located, as shown, in close proximity to optics and mirror 94
located above surface 100 of support platform 90. Camera 140 may be
any one of a number of commercially available cameras, such as
capacitive-coupled discharge (CCD) cameras available from a number
of vendors. Suitable circuitry as required for adapting the output
of camera 140 for use by computer 82 may be incorporated in a board
142 installed in computer 82, which is programmed, as known in the
art, to respond to images generated by camera 140 and processed by
board 142. Camera 140 and board 142 may together comprise a
so-called "machine vision system" and, specifically, a "pattern
recognition system" (PRS), operation of which will be described
briefly below for a better understanding of the present invention.
Alternatively, a self-contained machine vision system available
from a commercial vendor of such equipment may be employed. For
example, and without limitation, such systems are available from
Cognex Corporation of Natick, Mass. For example, the apparatus of
the Cognex BGA Inspection Package.TM. or the SMD Placement Guidance
Package.TM. may be adapted to the present invention, although it is
believed that the MVS-8000.TM. product family and the
Checkpoint.RTM. product line, the latter employed in combination
with Cognex PatMax.TM. software, may be especially suitable for use
in the present invention.
[0077] It is noted that a variety of machine vision systems are in
existence, examples of which and their various structures and uses
are described, without limitation, in U.S. Pat. Nos. 4,526,646;
4,543,659; 4,736,437; 4,899,921; 5,059,559; 5,113,565; 5,145,099;
5,238,174; 5,463,227; 5,288,698; 5,471,310; 5,506,684; 5,516,023;
5,516,026; and 5,644,245. The disclosure of each of the immediately
foregoing patents is hereby incorporated by this reference.
Stereolithographic Fabrication of the Collars
[0078] In order to facilitate fabrication of one or more collars 50
in accordance with the method of the present invention with
apparatus 80, a data file representative of the size,
configuration, thickness and surface topography of, for example, a
particular type and design of semiconductor device 10 or other
substrate upon which one or more collars 50 are to be mounted, is
placed in the memory of computer 82. Also, if it is desired that
the collars 50 be so positioned on semiconductor device 10 taking
into consideration features of a higher level substrate 30 (see
FIG. 3) to which semiconductor device 10 is to be connected, a data
file representative of substrate 30 and the features thereof may be
placed in memory.
[0079] One or more semiconductor devices 10, wafers 72 (see FIG.
8), or other substrates may be placed on surface 100 of platform 90
for fabrication of collars 50 around contact pads 12 thereof. If
one or more semiconductor devices 10, wafers 72, or other
substrates are to be held on or supported above platform 90 by
stereolithographically formed base supports 122, one or more layers
of material 86 are sequentially disposed on surface 100 and
selectively altered by use of laser 92 to form base supports
122.
[0080] Camera 140 is then activated to locate the position and
orientation of each semiconductor device 10, including those on a
wafer 72 (see FIG. 8), or other substrate upon which collars 50 are
to be fabricated. The features of each semiconductor device 10,
wafer 72, or other substrate are compared with those in the data
file residing in memory, the locational and orientational data for
each semiconductor device 10, wafer 72, or other substrate then
also being stored in memory. It should be noted that the data file
representing the design, size, shape and topography for each
semiconductor device 10 or other substrate may be used at this
juncture to detect physically defective or damaged semiconductor
devices 10 or other substrates prior to fabricating collars 50
thereon or before conducting further processing or assembly of
semiconductor device 10 or other substrates. Accordingly, such
damaged or defective semiconductor devices 10 or other substrates
can be deleted from the process of fabricating collars 50, from
further processing, or from assembly with other components. It
should also be noted that data files for more than one type (size,
thickness, configuration, surface topography) of each semiconductor
device 10 or other substrate may be placed in computer memory and
computer 82 programmed to recognize not only the locations and
orientations of each semiconductor device 10 or other substrate,
but also the type of semiconductor device 10 or other substrate at
each location upon platform 90 so that material 86 may be at least
partially consolidated by laser beam 98 in the correct pattern and
to the height required to define collars 50 in the appropriate,
desired locations on each semiconductor device 10 or other
substrate.
[0081] Continuing with reference to FIGS. 9 and 10, wafer 72 or the
one or more semiconductor devices 10 or other substrates on
platform 90 may then be submerged partially below the surface level
88 of liquid material 86 to a depth greater than the thickness of a
first layer of material 86 to be at least partially consolidated
(e.g., cured to at least a semisolid state) to form the lowest
layer 130 of each collar 50 at the appropriate location or
locations on each semiconductor device 10 or other substrate, then
raised to a depth equal to the layer thickness, surface level 88 of
material 86 being allowed to become calm. Photopolymers that are
useful as material 86 exhibit a desirable dielectric constant, are
of sufficient (i.e., semiconductor grade) purity, exhibit good
adherence to other semiconductor device materials, and have a
similar coefficient of thermal expansion (CTE) to the material of
conductive structures 20 (FIG. 3) (e.g., solder or other metal or
metal alloy, or conductive or conductor filled epoxy). Preferably,
the CTE of material 86 is sufficiently similar to that of
conductive structures 20 to prevent undue stressing thereof during
thermal cycling of semiconductor device 10 or another substrate in
testing, subsequent processing, and subsequent normal operation.
Exemplary photopolymers exhibiting these properties are believed to
include, but are not limited to, the above-referenced resins from
Ciba Specialty Chemical Company. One particular concern in
determining resin suitability is the substantial absence of mobile
ions, specifically fluorides.
[0082] Laser 92 is then activated and scanned to direct beam 98,
under control of computer 82, toward specific locations of surface
level 88 relative to each semiconductor device 10 or other
substrate to effect the aforementioned partial cure of material 86
to form a first layer 50A of each collar 50. Platform 90 is then
lowered into reservoir 84 and raised a distance equal to the
desired thickness of another layer 50B of each collar 50 and laser
92 is activated to add another layer 50B to each collar 50 under
construction. This sequence continues, layer by layer, until each
of the layers of collars 50 have been completed.
[0083] In FIG. 10, the first layer of collar 50 is identified by
numeral 50A and the second layer is identified by numeral 50B.
Likewise, the first layer of base support 122 is identified by
numeral 122A and the second layer thereof is identified by numeral
122B. As illustrated, both base support 122 and collar 50 have only
two layers. Collars 50 with any number of layers are, however,
within the scope of the present invention. The use of a large
number of layers may be employed to substantially simulate the
shape of the outer surface of a conductive structure to be
encompassed by collar 50.
[0084] Each layer 50A, 50B of collar 50 is preferably built by
first defining any internal and external object boundaries of that
layer with laser beam 98, then hatching solid areas of collar 50
located within the object boundaries with laser beam 98. An
internal boundary of a layer may comprise aperture 52, a
through-hole, a void, or a recess in collar 50, for example. If a
particular layer includes a boundary of a void in the object above
or below that layer, then laser beam 98 is scanned in a series of
closely-spaced, parallel vectors so as to develop a continuous
surface, or skin, with improved strength and resolution. The time
it takes to form each layer depends upon the geometry thereof, the
surface tension and viscosity of material 86, and the thickness of
that layer.
[0085] Alternatively, collars 50 may each be formed as a partially
cured outer skin extending above surface 14 of semiconductor device
10 and forming a dam within which unconsolidated material 86 can be
contained. This may be particularly useful where the collars 50
protrude a relatively high distance 56 from surface 14. In this
instance, support platform 90 may be submerged so that material 86
enters the area within the dam, raised above surface level 88, and
then laser beam 98 activated and scanned to at least partially cure
material 86 residing within the dam or, alternatively, to merely
cure a "skin" comprising the contact surface aperture 52, a final
cure of the material of the collars 50 being effected subsequently
by broad-source UV radiation in a chamber or by thermal cure in an
oven. In this manner, collars 50 of extremely precise dimensions
may be formed of material 86 by apparatus 80 in minimal time.
[0086] When collars 50', depicted in FIGS. 4-6, are being
fabricated on a substrate, such as semiconductor device 10, having
conductive structures 20' already secured to the contact pads 12
thereof, some of material 86 may be located in shadowed areas 54'
(see FIGS. 5 and 6) lying under portions of a conductive structure
20'. As laser beam 98 is directed substantially vertically
downwardly toward surface level 88 of material 86, material 86
located in shadowed regions 54' will not be contacted or altered by
laser beam 98. Nonetheless, the unconsolidated material 86 in
shadowed areas 54' will become trapped therein as material 86'
adjacent to, and laterally outward from, shadowed areas 54' is at
least partially consolidated as collar 50' is built up around
conductive structure 20'. Such trapped, unconsolidated material 86
will eventually cure due to the cross-linking initiated in the
outwardly adjacent photopolymer and the cure can be subsequently
accelerated as known in the art, such as by a thermal cure.
[0087] Once collars 50, or at least the outer skins thereof, have
been fabricated, platform 90 is elevated above surface level 88 of
material 86 and platform 90 is removed from apparatus 80, along
with any substrate (e.g., semiconductor device 10, wafer 72 (see
FIG. 8), or other substrate) disposed thereon and any
stereolithographically fabricated structures, such as collars 50.
Excess, unconsolidated material 86 (e.g., excess uncured liquid)
may be manually removed from platform 90, from any substrate
disposed thereon, and from collars 50. Each semiconductor device
10, wafer 72, or other substrate is removed from platform 90, such
as by cutting the substrate free of base supports 122.
Alternatively, base supports 122 may be configured to readily
release semiconductor devices 10, wafers 72, or other substrates.
As another alternative, a solvent may be employed to release base
supports 122 from platform 90. Such release and solvent materials
are known in the art. See, for example, U.S. Pat. No. 5,447,822
referenced above and previously incorporated herein by
reference.
[0088] Collars 50 and semiconductor device 10 may also be cleaned
by use of known solvents that will not substantially degrade,
deform, or damage collars 50 or a substrate to which collars 50 are
secured.
[0089] As noted previously, collars 50 may then require postcuring.
Collars 50 may have regions of unconsolidated material contained
within a boundary or skin thereof or in a shadowed area 54' (see
FIGS. 5 and 6), or material 86 may be only partially consolidated
(e.g., polymerized or cured) and exhibit only a portion (typically
40% to 60%) of its fully consolidated strength. Postcuring to
completely harden collars 50 may be effected in another apparatus
projecting UV radiation in a continuous manner over collars 50 or
by thermal completion of the initial, UV-initiated partial
cure.
[0090] It should be noted that the height, shape, or placement of
each collar 50 on each specific semiconductor device 10 or other
substrate may vary, again responsive to output of camera 140 or one
or more additional cameras 144, 146, or 148, shown in broken lines,
detecting the protrusion of unusually high (or low) preplaced
conductive structures which could affect the desired distance 56
that collars 50 will protrude from surface 14. Likewise, the
lateral extent (e.g., diameter) of each preplaced conductive
structure may be recognized and the girth of the outer boundary of
each collar 50 adjusted accordingly. In any case, laser 92 is again
activated to at least partially cure material 86 residing on each
semiconductor device 10 or other substrate to form the layer or
layers of each collar 50.
[0091] Although FIGS. 9 and 10 illustrate the stereolithographic
fabrication of collars 50 on a substrate, such as a semiconductor
device 10, a wafer 72 (FIG. 8), or another substrate, including a
plurality of semiconductor devices 10 or other substrates, collars
50 can be fabricated separately from a substrate, then secured to a
substrate, by known processes, such as by the use of a suitable
adhesive material.
[0092] The use of a stereolithographic process as exemplified above
to fabricate collars 50 is particularly advantageous since a large
number of collars 50 may be fabricated in a short time, the collar
height and position are computer controlled to be extremely
precise, wastage of unconsolidated material 86 is minimal, solder
coverage of passivation materials is avoided, and the
stereolithography method requires minimal handling of semiconductor
devices 10, wafers 72, or other substrates.
[0093] Stereolithography is also an advantageous method of
fabricating collars 50 according to the present invention since
stereolithography can be conducted at substantially ambient
temperature, the small spot size and rapid traverse of laser beam
98 resulting in negligible thermal stress upon semiconductor
devices 10, wafers 72, or other substrates, as well as on the
features thereof.
[0094] The stereolithography fabrication process may also
advantageously be conducted at the wafer level or on multiple
substrates, saving fabrication time and expense. As the
stereolithography method of the present invention recognizes
specific semiconductor devices 10 or other substrates 20,
variations between individual substrates are accommodated.
Accordingly, when the stereolithography method of the present
invention is employed, collars 50 can be simultaneously fabricated
on different types of semiconductor devices 10 or other substrates,
as well as on both semiconductor devices 10 and other
substrates.
[0095] While the present invention has been disclosed in terms of
certain preferred embodiments, those of ordinary skill in the art
will recognize and appreciate that the invention is not so limited.
Additions, deletions and modifications to the disclosed embodiments
may be effected without departing from the scope of the invention
as claimed herein. Similarly, features from one embodiment may be
combined with those of another while remaining within the scope of
the invention.
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