U.S. patent application number 10/248882 was filed with the patent office on 2003-08-28 for lead-free bump fabrication process.
Invention is credited to Chen, Jau-Shoung, Chou, Yu-Chen, Fang, Jen-Kuang, Huang, Min-Lung, Lee, Chun-Chi, Lee, Yung-Chi, Su, Ching-Huei, tao, Su, Tong, Ho-Ming, Weng, Chao-Fu, Wu, Tsung-Hua.
Application Number | 20030162381 10/248882 |
Document ID | / |
Family ID | 27752474 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030162381 |
Kind Code |
A1 |
Tong, Ho-Ming ; et
al. |
August 28, 2003 |
LEAD-FREE BUMP FABRICATION PROCESS
Abstract
A lead-free solder bump fabrication process for producing a
plurality of lead-free solder bumps over a wafer is provided. The
lead-free solder bump fabrication process includes forming a
lead-free pre-formed solder bump over each bonding pad on the wafer
and then forming a patterned solder mask layer over the active
surface of the wafer. The openings in the solder mask layer expose
the respective lead-free pre-formed solder bumps on the wafer.
Thereafter, lead-free solder material is deposited into the
opening. The material composition of the lead-free solder material
differs from the material composition of the lead-free pre-formed
solder bump. A reflow process is conducted so that the lead-free
pre-formed solder bump fuses with the lead-free solder material to
form a lead-free solder bump. Finally, the solder mask layer is
removed.
Inventors: |
Tong, Ho-Ming; (Taipei,
TW) ; Lee, Chun-Chi; (Kaohsiung, TW) ; Fang,
Jen-Kuang; (Pingtung Hsien, TW) ; Huang,
Min-Lung; (Kaohsiung, TW) ; Chen, Jau-Shoung;
(Hsinchu Hsien, TW) ; Su, Ching-Huei; (Kaohsiung,
TW) ; Weng, Chao-Fu; (Tainan, TW) ; Lee,
Yung-Chi; (Kaohsiung, TW) ; Chou, Yu-Chen;
(Kaohsiung, TW) ; Wu, Tsung-Hua; (Kaohsiung Hsien,
TW) ; tao, Su; (Kaohsiung, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Family ID: |
27752474 |
Appl. No.: |
10/248882 |
Filed: |
February 27, 2003 |
Current U.S.
Class: |
438/614 ;
257/E21.508 |
Current CPC
Class: |
H01L 24/11 20130101;
H01L 2224/11334 20130101; H01L 2924/01013 20130101; H01L 24/05
20130101; H01L 2924/01082 20130101; H01L 2924/14 20130101; H01L
2924/01022 20130101; H01L 2224/05022 20130101; H01L 2924/01033
20130101; H01L 2224/11332 20130101; H01L 2924/01029 20130101; H01L
2924/0103 20130101; H01L 24/03 20130101; H01L 2224/1147 20130101;
H01L 2924/01046 20130101; H01L 2224/05572 20130101; H01L 2924/01047
20130101; H01L 2924/01023 20130101; H01L 2924/01024 20130101; H01L
2924/01049 20130101; H01L 2224/13099 20130101; H01L 2224/05001
20130101; H01L 2924/01012 20130101; H01L 2924/01006 20130101; H01L
2224/0508 20130101; H01L 2924/01051 20130101; H01L 2224/05027
20130101; H01L 2924/014 20130101; H01L 2924/01074 20130101; H01L
2924/01079 20130101; H01L 24/13 20130101 |
Class at
Publication: |
438/614 |
International
Class: |
H01L 021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2002 |
TW |
91103532 |
Claims
1. A lead-free solder bump fabrication process for producing at
least one lead-free solder bump on a wafer, wherein the wafer has
an active surface, a passivation layer and at least one bonding
pad, and the bonding pad is on the active surface of the wafer and
the passivation layer exposes the bonding pad, the lead-free solder
bump fabrication process comprising the steps of: forming an
under-ball-metallurgy layer over the bonding pad; forming a
lead-free pre-formed solder bump over the under-ball-metallurgy
layer; forming a patterned solder mask layer over the active
surface of the wafer, wherein the solder mask layer has at least an
opening that exposes the lead-free pre-formed solder bump;
depositing lead-free solder material into the opening, wherein the
material composition of the lead-free solder material differs from
the material composition of the lead-free pre-formed solder bump;
conducting a reflow process so that the lead-free pre-formed solder
bump and the lead-free solder material fuse together to form a
lead-free solder bump; and removing the solder mask layer.
2. The process of claim 1, wherein material forming the top-most
layer of the under-ball-metallurgy layer is selected from a group
of metals consisting of copper, gold, silver and palladium.
3. The process of claim 1, wherein the lead-free pre-formed solder
bump is fabricated using either a single metal other than lead or a
lead-free alloy of metals.
4. The process of claim 1, wherein the lead-free solder material is
fabricated using either a single metal other than lead or a
lead-free alloy of metals.
5. The process of claim 1, wherein the lead-free solder bump is
fabricated using an alloy of N metals where N is a natural number
greater than one.
6. The process of claim 1, wherein the melting point of the
lead-free pre-formed solder bump is lower than the lead-free solder
material.
7. The process of claim 1, wherein material constituting the
lead-free pre-formed solder bump is selected from a group of
metallic elements consisting of tin, gold, silver, copper,
magnesium, bismuth, antimony, indium and zinc or an alloy of the
aforementioned metals.
8. The process of claim 1, wherein the material constituting the
lead-free solder material is selected from a group of metallic
elements consisting of tin, gold, silver, copper, magnesium,
bismuth, antimony, indium and zinc or an alloy of the
aforementioned metals.
9. The process of claim 7, wherein the lead-free pre-formed solder
bump or the lead-free solder material contains tin.
10. The process of claim 1, wherein the lead-free solder material
is in either power or paste form.
11. The process of claim 1, wherein the step of forming the
patterned solder mask layer includes printing.
12. The process of claim 1, wherein the step of forming the
patterned solder mask layer includes coating a solder mask material
over the wafer globally and then forming an opening in the solder
mask material layer.
13. The process of claim 12, wherein the step of forming the
opening includes conducting a photo-via process.
14. The process of claim 1, wherein before the step of forming the
lead-free pre-formed solder bump, further includes forming an
under-ball-metallurgy layer over the bonding pad so that the
lead-free pre-formed solder bump is formed over the
under-ball-metallurgy layer.
15. A lead-free solder bump fabrication process for producing at
least one lead-free solder bump on a wafer, wherein the wafer has
an active surface and at least one lead-free pre-formed solder bump
on the active surface of the wafer, the lead-free solder bump
fabrication process comprising the steps of: forming a patterned
solder mask layer over the active surface of the wafer, wherein the
solder mask layer has at least an opening that exposes the
lead-free pre-formed solder bump; depositing lead-free solder
material into the opening, wherein the material composition of the
lead-free solder material differs from the material composition of
the lead-free pre-formed solder bump; conducting a reflow process
so that the lead-free pre-formed solder bump and the lead-free
solder material fuse together to form a lead-free solder bump; and
removing the solder mask layer.
16. The process of claim 15, wherein the lead-free pre-formed
solder bump is fabricated using either a single metal or an alloy
of metals.
17. The process of claim 15, wherein the lead-free solder material
is fabricated using either a single metal or an alloy of
metals.
18. The process of claim 15, wherein the lead-free solder bump is
fabricated using an alloy of N metals where N is a natural number
greater than one.
19. The process of claim 15, wherein material constituting the
lead-free pre-formed solder bump is selected from a group of
metallic elements consisting of tin, gold, silver, copper,
magnesium, bismuth, antimony, indium and zinc or an alloy of the
aforementioned metals.
20. The process of claim 15, wherein the material constituting the
lead-free solder material is selected from a group of metallic
elements consisting of tin, gold, silver, copper, magnesium,
bismuth, antimony, indium and zinc or an alloy of the
aforementioned metals.
21. The process of claim 15, wherein the lead-free pre-formed
solder bump or the lead-free solder material contains tin.
22. The process of claim 15, wherein the lead-free solder material
is in either powder or paste form.
23. The process of claim 15, wherein the step of forming the
patterned solder mask layer includes printing.
24. The process of claim 15, wherein the step of forming the
patterned solder mask layer includes coating a solder mask material
over the wafer globally and then forming an opening in the solder
mask material layer.
25. The process of claim 24, wherein the step of forming the
opening includes conducting a photo-via process.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of Taiwan
application serial no. 91103532, filed Feb. 27, 2002.
BACKGROUND OF INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to a bump fabrication process.
More particularly, the present invention relates to a process for
fabricating lead-free bumps over a wafer.
[0004] 2. Description of Related Art
[0005] In the fabrication of integrated circuit packages, a chip is
linked to a carrier inside a first level package in one of three
ways including wire bonding, tape automatic bonding (TAB) and flip
chip (F/C). In a tape automatic bonding or a flip chip package, the
process of linking up the chip and the carrier involves the
production of bumps on the bonding pads of the chip. In fact, the
bump serves as an electrical medium for connecting the chip and the
carrier. A variety of types of bumps have been developed such as
solder bumps, gold bumps, conductive polymer bumps and polymer
bumps. However, solder bumps are the most popular type.
[0006] A conventional method of fabricating a solder bump involves
forming an under-ball-metallurgy (UBM) layer over the bonding pad
of a wafer by evaporation, sputtering or electroplating.
Thereafter, a thick photoresist layer is formed over the wafer.
Through a plurality of openings that exposes the
under-ball-metallurgy layer, solder material is deposited into the
opening by evaporation, electroplating or printing. Finally, a
reflow process is conducted fusing the solder material together to
form a solder bump having a spherical external appearance.
[0007] Lead-tin alloy (Sn--Pb alloy) is a material having ideal
physical and conductive properties for forming solder bump aside
from forming connections between devices or circuit boards.
However, lead is an environmentally hazardous material that may
affect the health of people. Hence, the electronic industry has
been actively searching for lead-free solder alloy material to
replace conventional lead-tin alloy material.
[0008] Most lead-free alloy contains tin and (one or more) other
metallic elements. Common metallic elements other than tin to be
used inside a lead-free alloy include gold (Au), silver (Ag),
copper (Cu), magnesium (Mg), bismuth (Pi), antimony (Sb), indium
(In) and zinc (Zn). Aside from lead-free solder alloy containing
tin, lead-free solder alloy may contain no tin. In other words,
lead-free solder alloy also includes solder material that has no
traces of tin. Similarly, a lead-free solder refers to a solder
material containing no traces of lead only and may or may not
contain any tin. In a conventional lead-free solder bump
fabrication process, metallic elements in a specified ratio are
used to produce an alloy of lead-free solder material. This
lead-free solder material is deposited over a wafer and then a
reflow process is carried out to form a lead-free solder bump.
SUMMARY OF INVENTION
[0009] Accordingly, one object of the present invention is to
provide a lead-free solder bump fabrication process that includes
forming a lead-free pre-formed solder bump over a wafer, depositing
solder material on the lead-free solder bump and conducting a
reflow process to form a lead-free solder bump. Since the lead-free
pre-formed solder bump and the lead-free solder material may
contain different constituents and may be composed of a single
metal or an alloy of metals, ultimate composition of the lead-free
solder bump can be easily adjusted.
[0010] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a lead-free solder bump fabrication
process for forming a plurality of lead-free solder bumps over a
wafer. The wafer has an active surface with a passivation layer and
a plurality of bonding pads thereon. The passivation layer exposes
the bonding pads. First, an under-ball-metallurgy layer is formed
over the bonding pads. A lead-free pre-formed solder bump is formed
over each under-ball-metallurgy layer. Thereafter, a patterned
solder mask is formed over the active surface of the wafer. The
solder mask layer has a plurality of openings that exposes the
respective lead-free pre-formed solder bumps. A lead-free solder
material is deposited into the openings. The lead-free solder
material may contain constituents that differ from the lead-free
pre-formed solder bump. A reflow process is conducted so that the
lead-free pre-formed solder bump and the lead-free solder material
may fuse together to produce a lead-free solder bump. Finally, the
solder mask layer is removed.
[0011] The lead-free solder bump fabrication process according to
this invention includes forming an under-ball-metallurgy layer over
the bonding pads of a wafer and forming a lead-free pre-formed
solder bump over the under-ball-metallurgy layers. Thereafter, a
patterned solder mask layer having a plurality of openings that
exposes the lead-free pre-formed solder bumps is formed over the
wafer. Lead-free solder material is deposited into the openings
stacking on top of the lead-free pre-formed solder bump. A reflow
process is carried out so that the lead-free pre-formed solder bump
and the lead-free solder material are fused together to produce a
lead-free solder bump. Finally, the solder mask layer is removed.
Because the lead-free pre-formed solder bump and the lead-free
solder material may be fabricated using different constituents,
composition of the lead-free solder bump can be easily
adjusted.
[0012] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0014] FIGS. 1 to 6 are schematic cross-sectional views showing the
steps carried out in a lead-free solder bump fabrication process
according to a preferred embodiment of this invention.
DETAILED DESCRIPTION
[0015] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0016] FIGS. 1 to 6 are schematic cross-sectional views showing the
steps carried out in a lead-free solder bump fabrication process
according to a preferred embodiment of this invention. As shown in
FIG. 1, a wafer 10 having an active surface 12, a passivation layer
14 and a plurality of bonding pads 16 (only one is shown) is
provided. The passivation layer 14 and the bonding pads 16 are
formed on the active surface 12 of the wafer 10. The passivation
layer 14 exposes various bonding pads 16 on top of the wafer
10.
[0017] As shown in FIG. 2, an under-ball-metallic (UBM) layer 18 is
formed over each bonding pad 16. The under-ball-metallurgy layer 18
is a stack of material layers that includes an adhesion layer 18a,
a barrier layer 18b and a wetting layer 18c. The bottom-most
adhesion layer 18a is fabricated from a material such as aluminum
(Al), titanium (Ti), titanium-tungsten (TiW) alloy or chromium
(Cr). The barrier layer 18b in the middle is fabricated using a
material such as nickel (Ni), vanadium (V), chromium (Cr) or copper
(Cu). The top-most wetting layer 18c is fabricated using a material
such as copper (Cu), gold (Au), silver (Ag) or palladium (Pd).
Thereafter, a lead-free pre-formed solder bump 20 is formed over
the under-ball-metallurgy layer 18 above each bonding pad 16. Due
to a reflow treatment, the pre-formed solder bump 20 has a
hemispherical shape. The lead-free pre-formed solder bump 20 can be
fabricated using a single metal or an alloy of metals.
[0018] As shown in FIG. 3, a patterned solder mask layer 100 is
formed over the active surface 12 of the wafer 10. The solder mask
layer 100 has a plurality of openings (only one is shown) 102 for
exposing the lead-free pre-formed solder bumps 20 on the wafer 10.
A first method of forming the patterned solder mask layer 100 is to
print solder mask material directly over the wafer 10.
Alternatively, a patterned photoresist layer (not shown) is formed
over the active surface 12 of the wafer 10 before filling the
photoresist free region with solder mask material in a printing
process and then removing the patterned photoresist to expose the
patterned solder mask layer 100. A second method of forming the
patterned solder mask layer 100 includes coating a photosensitive
solder mask material over the active surface 12 of the wafer
globally and then a photo-via method is used to form openings 102
in the solder mask layer 100. The openings 102 in the solder mask
layer 100 expose the lead-free pre-formed solder bump 20 over the
wafer 10. The sidewalls of each opening 102 and the upper surface
of the lead-free pre-formed solder bump 20 together form a cavity
capable of holding some lead-free solder material 104 (as shown in
FIG. 4).
[0019] As shown in FIG. 4, lead-free solder material 104 is
deposited into the opening 102 above the lead-free pre-formed
solder bump 20 in a printing or some other process. The lead-free
solder material 104 may differ in composition to the lead-free
pre-formed solder bump 20. In addition, the lead-free solder
material 104 may contain a single metallic constituent or an alloy
of metallic constituents in solder power or solder paste form.
[0020] As shown in FIGS. 4 and 5, flux 106 is sprayed onto the
solder material 104 during a reflow process. The flux 106
facilitates the fusion between the lead-free solder material 104
and the lead-free pre-formed solder bump 20 into a lead-free solder
bump 22. To form a really spherical lead-free solder bump 22, some
flux 106 may be added and mixed with the lead-free solder material
104 prior to depositing the mixed material into the opening 102.
Thereafter, a first reflow process is carried out so that the
lead-free solder material 104 fuses with the lead-free pre-formed
solder bump 20 to form a preliminary solder bump mass 22. Since
shape of the preliminary solder bump mass 22 may not be too
spherical, flux 106 is again sprayed onto the preliminary solder
bump mass 22 and then a second reflow process is carried out to
form a highly spherical lead-free solder bump 22 as shown in FIG.
5.
[0021] As shown in FIGS. 4 and 5, a reflow process is carried out
after lead-free solder material 104 is deposited into the opening
102. The lead-free pre-formed solder bump 20 and the solder
material 104 fuse together to form a lead-free solder bump 22 as
shown in FIG. 5. Finally, as shown in FIG. 6, the solder mask layer
100 as shown in FIG. 5 is removed so that the lead-free solder bump
22 is exposed above the wafer 10.
[0022] The lead-free solder material 104 is a binary, tertiary or
quaternary alloy of the metallic elements including tin, gold,
silver, copper, magnesium, bismuth, antimony, indium and zinc.
Since various metallic elements can be combined in different
proportions, a countless variety of lead-free solder alloy material
can be fabricated. Furthermore, each material composition will
produce a lead-free alloy material having a specific physical and
electrical properties. Hence, the material constituting the
ultimately formed lead-free solder bump can be identified by a
natural number N for the number of metallic elements in the alloy.
Here, N is any natural number greater than 1. In the embodiment of
this invention, material composition of the lead-free solder bump
22 is set prior to adjusting the material composition of the
lead-free pre-formed solder bump 20 and the lead-free solder
material 104 so that the ultimately formed lead-free solder bump 22
can have the desired composition.
[0023] In summary, the steps for forming lead-free solder bumps
over a wafer according to this invention include forming lead-free
pre-formed solder bumps over the respective bonding pads on the
active surface of a wafer and then forming a patterned solder mask
layer over the wafer. The solder mask layer has a plurality of
openings that exposes the respective lead-free pre-formed solder
bumps. Thereafter, lead-free solder material is deposited into the
opening over the lead-free pre-formed solder bump. The lead-free
pre-formed solder bump and the lead-free solder material are fused
together to form a lead-free solder bump by conducting a reflow
process. Since material composition of the lead-free pre-formed
solder bump and the lead-free solder material can be adjusted
independently, a lead-free solder bump having a variety of material
composition can be obtained.
[0024] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *