U.S. patent application number 11/521147 was filed with the patent office on 2008-03-20 for electronic packages with fine particle wetting and non-wetting zones.
Invention is credited to Nirupama Chakrapani, Chris Matayabas, Vijay S. Wakharkar.
Application Number | 20080067502 11/521147 |
Document ID | / |
Family ID | 39187637 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080067502 |
Kind Code |
A1 |
Chakrapani; Nirupama ; et
al. |
March 20, 2008 |
Electronic packages with fine particle wetting and non-wetting
zones
Abstract
Spreading or keep out zones may be formed in integrated circuit
packages by altering the roughness of package surfaces. The surface
roughness can be altered by applying or growing particles having a
dimension less than 500 nanometers. Hydrophilic surfaces may be
made hemi-wicking and hydrophobic surfaces may be made hemi-wicking
by particles of the same general characteristics.
Inventors: |
Chakrapani; Nirupama;
(Chandler, AZ) ; Wakharkar; Vijay S.; (Paradise
Valley, AZ) ; Matayabas; Chris; (Chandler,
AZ) |
Correspondence
Address: |
TROP PRUNER & HU, PC
1616 S. VOSS ROAD, SUITE 750
HOUSTON
TX
77057-2631
US
|
Family ID: |
39187637 |
Appl. No.: |
11/521147 |
Filed: |
September 14, 2006 |
Current U.S.
Class: |
257/40 ;
257/E21.503; 257/E51.02; 438/1 |
Current CPC
Class: |
H01L 2224/32057
20130101; H01L 21/563 20130101; H01L 2924/0104 20130101; H01L
2224/48091 20130101; H01L 2924/014 20130101; H01L 2224/48227
20130101; H01L 2924/01033 20130101; H01L 2224/16145 20130101; H01L
2924/00011 20130101; H01L 2924/14 20130101; H01L 24/16 20130101;
H01L 2924/181 20130101; H01L 2924/00014 20130101; H01L 2924/15311
20130101; H01L 2224/48463 20130101; H01L 2924/00014 20130101; H01L
23/3128 20130101; H01L 2224/32145 20130101; H01L 2924/00014
20130101; H01L 2924/01082 20130101; H01L 2924/00011 20130101; H01L
24/73 20130101; H01L 2224/73265 20130101; H01L 2224/73265 20130101;
H01L 2224/73265 20130101; H01L 2224/83051 20130101; H01L 2924/181
20130101; H01L 24/32 20130101; H01L 2924/00014 20130101; H01L
2224/27013 20130101; H01L 2224/83385 20130101; H01L 2224/32225
20130101; H01L 2224/73203 20130101; H01L 2924/01067 20130101; H01L
2924/01006 20130101; H01L 2924/15311 20130101; H01L 2224/32145
20130101; H01L 2924/00 20130101; H01L 2224/73265 20130101; H01L
2224/32225 20130101; H01L 2924/207 20130101; H01L 2924/00 20130101;
H01L 2924/00 20130101; H01L 24/48 20130101; H01L 2924/00012
20130101; H01L 2224/45099 20130101; H01L 2224/48227 20130101; H01L
2224/45015 20130101; H01L 2224/48227 20130101; H01L 2224/48227
20130101; H01L 2224/32145 20130101; H01L 2924/00014 20130101; H01L
2924/00012 20130101; H01L 2224/0401 20130101; H01L 2224/32225
20130101; H01L 2224/48227 20130101; H01L 2924/00 20130101; H01L
2924/00012 20130101; H01L 2224/0401 20130101; H01L 2224/73265
20130101; H01L 2224/48091 20130101 |
Class at
Publication: |
257/40 ; 438/1;
257/E51.02 |
International
Class: |
H01L 51/00 20060101
H01L051/00 |
Claims
1. A method comprising: forming a semiconductor integrated circuit
package surface; forming particles on said surface having a
dimension less than 500 nanometers; and applying a liquid to said
package surface.
2. The method of claim 1 including forming said particles on said
surface in two different regions such that one region is
hydrophobic and the other region is hydrophilic.
3. The method of claim 2 including forming a semiconductor
integrated package surface in the form of a package substrate.
4. The method of claim 3 including forming said particles of
substantially similar dimensions.
5. The method of claim 4 including forming said particles by
growing particles on said substrate.
6. The method of claim 1 including forming particles by depositing
the particles on the surface.
7. The method of claim 4 wherein applying a liquid includes
providing a die over said substrate, and injecting underfill
material between said die and said substrate.
8. The method of claim 7 including defining a keep out zone on said
substrate using hydrophobic particles around said die and providing
a region of hydrophilic particles between said die and said
substrate.
9. The method of claim 1 including growing rods on said substrate
to form said particles.
10. The method of claim 9 including using glancing angle deposition
techniques to grow said rods.
11. The method of claim 1 including forming said surface of an
integrated circuit die and treating said particles so that said
particles are hydrophobic in one area and hydrophilic in
another.
12. The method of claim 11 including providing a die attach to said
surface such that said hydrophobic particles reduce bleeding out of
the die attach material.
13. An integrated circuit package comprising: a package surface;
particles formed on said surface having a dimension less than 500
nanometers; and a liquid applied over said particles.
14. The package of claim 13 wherein said particles are
hydrophobic.
15. The package of claim 13 wherein said particles are
hydrophilic.
16. The package of claim 13 wherein some of those particles are
hydrophilic and some of said particles are hydrophobic.
17. The package of claim 13 wherein said liquid is underfill.
18. The package of claim 13 wherein said liquid is die attach.
19. The package of claim 13 wherein said surface is a die
surface.
20. The package of claim 13 wherein said surface is a package
substrate surface.
21. The package of claim 20 wherein hydrophilic particles are
formed on said substrate, a die positioned over said substrate,
said hydrophobic particles being formed on said substrate around
said die, the surface of said substrate under said die having
particles formed thereon that are hydrophilic and solder balls
being provided between said die and said substrate.
22. The package of claim 13 wherein said surface is a die surface
and a die attach is attached to said die surface, the region
contacting said die attach being hydrophilic and a region around
said die attach being hydrophobic.
23. An integrated circuit package comprising: a package surface
having particles on said surface having a dimension less than 500
nanometers; and said surface having a surface energy of greater
than or equal to 70 mN/m or less than or equal to 20 mN/m.
24. The package of claim 23 wherein said surface includes both
hydrophilic and hydrophobic regions.
25. The package of claim 23 wherein said surface is a die
surface.
26. The package of claim 23 wherein said surface is a substrate
surface.
27. The package of claim 23 wherein said surface is partially
covered with underfill, a die being positioned to sandwich the
underfill between said die and said surface.
28. The package of claim 23 wherein said particles are upstanding
rods.
29. The package of claim 28 wherein said rods are hydrofluoric acid
treated.
30. The package of claim 23 including a substrate and a die stacked
on said substrate, die attach being positioned between said
substrate and said die, said die attach being surrounded by a
region of said surface that is hydrophobic and said die contacting
a hydrophilic region of said surface.
Description
BACKGROUND
[0001] This relates to the fabrication of integrated circuit
packages for holding integrated circuit chips.
[0002] In some integrated circuit packages, a substrate may mount
one or more integrated circuit chips. Between the chip and the
substrate may be an underfill material. Advantageously, this
material fills up the region between the chip and the substrate,
but does not extend outwardly by an excessive amount therefrom.
Doing so may adversely affect the operation of the packaged part.
For example, when the underfill material is injected between the
integrated circuit and the substrate, it may tend to flow
outwardly, creating what is called a tongue of material that
extends out from under the integrated circuit die.
[0003] Underfilling may be done by capillary flow. In order to
achieve high throughput times, the underfill may be made with a
very low viscosity and good wettability to the substrate solder
resist. Moreover, the underfill may be dispensed at elevated
temperatures. The result of all these factors is that a tongue of
underfill is left on the underfill dispense side of the package.
The tongue effectively increases the footprint of the package.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is an enlarged, cross-sectional view of a package in
accordance with one embodiment of the present invention;
[0005] FIG. 2 is a greatly enlarged, cross-sectional view of a
portion of the upper surface of the package substrate shown in FIG.
1; and
[0006] FIG. 3 is an enlarged, cross-sectional view of another
embodiment.
DETAILED DESCRIPTION
[0007] In some applications in semiconductor integrated circuit
packaging, it is desirable to have a substrate that has regions
which are both wetting and non-wetting. It would be even more
desirable that the substrate have regions that are super wettable
and super unwettable. In other words, the same substrates may have
surface regions that are hemi-wicking and hydrophobic and
hemi-wicking and hydrophilic. As a result, underfill and other
fluxes may be closely controlled to spread out in limited regions
on the substrate.
[0008] In some embodiments of the present invention, fine particle
coatings may be applied across a substrate surface. The coatings
may, for example, be silicon nanorods which are grown on the
substrate and extend to a height of up to 500 nanometers. If the
substrate upper surface is relatively hydrophilic, then the
presence of the surface roughening nanoparticles serves to greatly
increase the hydrophilic nature of the surface in what may be
called hemi-wicking. Conversely, if the same surface is
hydrophobic, hemi-wicking occurs, nonetheless, making the surface
extremely hydrophobic.
[0009] Generally, a hydrophilic surface has a surface energy
greater than or equal to 70 mN/m. A hydrophobic surface has a
surface energy less than or equal to 20 mN/m.
[0010] Referring to FIG. 1, a substrate 12 has an integrated
circuit die 14 mounted thereon in a flip chip arrangement using
solder balls 16 to electrically and mechanically connect the die 14
to the substrate 12. The substrate 12 may have interconnections
which provide signals to the die 14 and transfer signals from the
die 14 to external devices.
[0011] The upper surface of the substrate 12 may have peripheral
regions 22 (e.g. 22a and 22b) which may be highly hydrophobic or
hemi-wicking. Conversely, the regions 24 underneath the die and to
a slight degree up from under the die may be very hydrophilic and
hemi-wicking. Thus, the underfill material 20 once injected in the
direction A, for example, using capillary forces, moves away from
the hydrophobic surfaces 22a and 22b and spreads on the hydrophilic
surfaces 24. Because the surfaces 22 and 24 are hemi-wicking, the
normal wetting and non-wetting effects are enhanced. As a result,
the tendency of the underfill 20 to form a tongue by extending
outwardly in a direction opposite to the arrow A is reduced. This
may achieve a smaller package footprint, in some cases, since
substrate surface is not consumed by an underfill tongue.
[0012] As still another example, the package 30 may include a
substrate 36 which includes interconnects 44, such as solder balls,
as shown in FIG. 3. Electrical vertical vias 38 may be found within
the substrate 36 which connect to horizontal metallizations 41 to
distribute signals between the external world coupled by the
interconnects 44 and the integrated circuit dice 32a, 32b, and 32c
within the package 30. An encapsulant 52 may encapsulate the dice
32a, 32b, and 32c.
[0013] The die 32a may be coupled by a wire bond 56 to a pad 46 on
the substrate 36. The pad 46 may be coupled by the horizontal
metallization 41 to the vertical via 38 and, ultimately, down to a
pad 43 that is coupled to an interconnect 44. In this way,
communications may be had between external components and the die
32a. Likewise, the wire bond 48 may connect to the die 32b via
contact 50. Connections to the die 32c may be provided in a variety
of different ways. The die 32c may be coupled to the die 32b by a
die attach adhesive layer 34. Likewise, the die 32b may be coupled
by a die attach adhesive layer 34 to the die 32a. However, other
techniques for securing the dice together may also be utilized.
[0014] In this case, it may be desirable to prevent the adhesive
used for the die attach 34 from bleeding out. If the die attach
bleeds out, it may foul the regions intended for wire bond
contacts. Thus, the surfaces 54 may be treated to be highly
hydrophobic and hemi-wicking. These surfaces may be provided on
both the die 32b upper surface and the die 32c upper surface.
[0015] Referring back to FIG. 2, in some embodiments of the present
invention, the fine particles 40 may be grown on the substrate 12.
The particles 40 may, for example, be nanorods, spherical
particles, or tetrapods, etc. However, other components and shapes
may be utilized. They may be made of materials including, but not
limited to, silica, alumina, zirconia, silicon, or carbon, etc.
Generally, it is desirable that these particles 40 have a height
above the surface of the substrate 12 of from 5 to 500 nanometers.
This is effective to enhance the hydrophobic or hydrophilic nature
of the resulting surface.
[0016] When it is desired to form both hydrophilic and hydrophobic
structures on the same surface, the same fine elements may be
formed. That is, particles 40 of comparable composition and size
may be formed across the surfaces that are supposed to be
ultimately hemi-wicking and hydrophobic or hemi-wicking and
hydrophilic. Then, the surfaces that are to be hydrophobic may be
exposed to a hydrofluoric acid treatment. The surfaces that will
remain hydrophilic may be masked with a suitable, removable mask
42.
[0017] Other hydrophobic treatments may also be used. For example,
fluorinated silanes are hydrophobic. They can easily be
functionalized to surfaces via alcohol groups or with plasma
treatment prior to functionalization. For example, a constituent
R.sub.3--Si--OH, together with HO-substrate solder resist yields
R.sub.3--Si--O-substrate solder resist. The constituent R may be,
but need not be limited to, an alkane, vinyl, or fluorine.
Alternatively, different treatments may be used to create a
hydrophilic surface. For example, amine terminated silanes are
hydrophilic. In addition, alkane silanes are hydrophobic. Moreover,
long chain alkanes self-assemble into monolayers, rendering very
high density silanes on the surface. Such monolayers may be
deposited by a solvent route or by vapor deposition. In addition,
hydroxyl groups on a solder resist surface can link silanols with
appropriate moieties to render them non-wetting to underfills.
Specific regions of a surface may be patterned with a silane
treatment to obtain regions that are non-wetting to underfill.
[0018] In some embodiments of the present invention, the structure
may be dipped to apply the hydrofluoric acid. The hydrofluoric acid
may be 48 to 51 percent and the exposure may be for one minute in
some embodiments of the present invention.
[0019] The growth of the particles 40 in the form of nanorods may
be done using glancing angle deposition techniques. Glancing angle
deposition involves physical vapor deposition on a substrate that
is rotated in two different directions. A glancing angle is formed
between the input vapor source and the surface on which the
nanorods are intended to be grown. In some cases, the angle may be
from 70 to 90 degrees. A deposition rate of 0.2 nMs.sup.-1 and a
rotation speed of 0.05 revs.sup.-1 may be used. An electron beam
evaporator with a quartz crystal thickness monitor may be used to
detect the film thickness.
[0020] Thus, surfaces can be selectively made highly hydrophilic or
highly hydrophobic. Hydrophobic regions may be effective keep out
zones to prevent incursion of fluxes, underfills, or encapsulants,
to mention a few examples. Conversely, the spreading of underfills
and molding compounds through narrow channels over ever-shrinking
packages may be improved by creating a hemi-wicking surface.
[0021] Nanoparticles generally have at least one of their
dimensions less than 100 nanometers. However, as used herein, a
fine particle is a particle with a size up to 500 nanometers.
Suitable shapes include, but are not limited, spheres, tetrapods,
rods, tubes, and platelets, to mention a few examples. Suitable
materials include, but are not limited to, silica, alumina,
titania, zirconia, and carbon.
[0022] Instead of growing the particles, deposited particles may be
utilized. In one embodiment, particles, such as microspheres, of at
least two different sizes are mixed and then deposited. The
particles may be secured by an adhesive coating, but other
techniques may be used as well.
[0023] References throughout this specification to "one embodiment"
or "an embodiment" mean that a particular feature, structure, or
characteristic described in connection with the embodiment is
included in at least one implementation encompassed within the
present invention. Thus, appearances of the phrase "one embodiment"
or "in an embodiment" are not necessarily referring to the same
embodiment. Furthermore, the particular features, structures, or
characteristics may be instituted in other suitable forms other
than the particular embodiment illustrated and all such forms may
be encompassed within the claims of the present application.
[0024] While the present invention has been described with respect
to a limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. It is
intended that the appended claims cover all such modifications and
variations as fall within the true spirit and scope of this present
invention.
* * * * *