U.S. patent application number 15/960463 was filed with the patent office on 2018-08-23 for hybrid low metal loading flux.
The applicant listed for this patent is INTEL CORPORATION. Invention is credited to Martha A. DUDEK, James C. MATAYABAS, JR., Michelle S. PHEN-GIVONI, Rajen S. SIDHU, Wei TAN.
Application Number | 20180236609 15/960463 |
Document ID | / |
Family ID | 48669308 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180236609 |
Kind Code |
A1 |
SIDHU; Rajen S. ; et
al. |
August 23, 2018 |
HYBRID LOW METAL LOADING FLUX
Abstract
Flux formulations and solder attachment during the fabrication
of electronic device assemblies are described. One flux formation
includes a flux component and a metal particle component, the metal
particle component being present in an amount of from 5 to 35
volume percent of the flux formulation. In one feature of certain
embodiments, the metal particle component includes solder
particles. Other embodiments are described and claimed.
Inventors: |
SIDHU; Rajen S.; (Portland,
OR) ; DUDEK; Martha A.; (Portland, OR) ;
MATAYABAS, JR.; James C.; (Gilbert, AZ) ;
PHEN-GIVONI; Michelle S.; (Chandler, AZ) ; TAN;
Wei; (Chandler, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTEL CORPORATION |
Santa Clara |
CA |
US |
|
|
Family ID: |
48669308 |
Appl. No.: |
15/960463 |
Filed: |
April 23, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13976001 |
Jun 25, 2013 |
9950393 |
|
|
PCT/US2011/067277 |
Dec 23, 2011 |
|
|
|
15960463 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2224/11334
20130101; H01L 2224/11848 20130101; H01L 2924/3511 20130101; H01L
2224/058 20130101; H01L 2224/131 20130101; H01L 2924/3841 20130101;
H01L 2224/03828 20130101; H05K 2203/046 20130101; H01L 24/05
20130101; H01L 2224/0401 20130101; H01L 2224/05844 20130101; H01L
2924/01049 20130101; H01L 2224/05811 20130101; H01L 2224/05839
20130101; H01L 2224/119 20130101; B23K 35/025 20130101; B23K 35/362
20130101; H01L 2224/05809 20130101; H01L 23/49816 20130101; H01L
24/13 20130101; H01L 2224/05817 20130101; H01L 24/03 20130101; H01L
2224/11849 20130101; H01L 2224/03829 20130101; H01L 24/11 20130101;
H01L 2924/00014 20130101; H01L 2224/03849 20130101; H01L 2224/0381
20130101; H01L 21/4853 20130101; H05K 2203/041 20130101; H05K
3/3489 20130101; H01L 23/488 20130101; H01L 2224/05794 20130101;
H01L 2224/05813 20130101; H01L 2224/058 20130101; H01L 2924/014
20130101; H01L 2224/05839 20130101; H01L 2924/00014 20130101; H01L
2224/05844 20130101; H01L 2924/00014 20130101; H01L 2224/05817
20130101; H01L 2924/01032 20130101; H01L 2224/058 20130101; H01L
2924/01105 20130101; H01L 2224/11848 20130101; H01L 2924/00012
20130101; H01L 2224/119 20130101; H01L 2224/11848 20130101; H01L
2224/11849 20130101; H01L 2224/119 20130101; H01L 2224/03828
20130101; H01L 2224/11334 20130101; H01L 2224/03849 20130101; H01L
2224/11849 20130101; H01L 2224/119 20130101; H01L 2224/03829
20130101; H01L 2224/11334 20130101; H01L 2224/03849 20130101; H01L
2224/11849 20130101; H01L 2224/131 20130101; H01L 2924/014
20130101; H01L 2224/05811 20130101; H01L 2924/01047 20130101; H01L
2924/01029 20130101; H01L 2224/05811 20130101; H01L 2924/01029
20130101; H01L 2224/05811 20130101; H01L 2924/01047 20130101; H01L
2224/05809 20130101; H01L 2924/0105 20130101; H01L 2224/05813
20130101; H01L 2924/0105 20130101; H01L 2224/05811 20130101; H01L
2924/0103 20130101; H01L 2924/01049 20130101; H01L 2924/01083
20130101; H01L 2224/05811 20130101; H01L 2924/0103 20130101 |
International
Class: |
B23K 35/02 20060101
B23K035/02; H01L 23/00 20060101 H01L023/00; B23K 35/362 20060101
B23K035/362; H05K 3/34 20060101 H05K003/34; H01L 23/488 20060101
H01L023/488 |
Claims
1.-17. (canceled)
18. A method for coupling solder balls to a substrate, comprising:
providing a substrate including a plurality of bonding pads;
positioning a flux formulation on the bonding pads, the flux
formulation comprising a flux component and a metal particle
component, the metal particle component being present in an amount
of from 5 to 35 weight percent of the flux formulation; positioning
solder balls on the flux formulation; and applying heat and bonding
the solder balls to the bonding pads.
19. The method of claim 18, wherein the flux component comprises an
acid and a solvent.
20. The method of claim 19, wherein the metal particle component
includes solder particles and pure metal particles.
21. The method of claim 20, wherein the pure metal particles are
selected from the group consisting of noble metals and rare earth
metals.
22. The method of claim 20, wherein a plurality of the pure metal
particles have a particle size in the range of 1 to 100 nm.
23. The method of claim 19, wherein the metal particle component
comprises solder particles having a particle size in the range of
up to 15 .mu.m.
24. The method of claim 18, wherein the metal particle component
comprises solder particles.
25. The method of claim 24, wherein the solder particles comprise
at least one metal and the solder particles have a melting point of
less than 250.degree. C.
26. The method of claim 19, wherein the metal particle component
comprises solder particles having a melting point less than the
solder balls.
27. An apparatus comprising: a bonding pad; a flux formulation on
the bonding pad, the flux formulation comprising a flux component
and metal particle component, the metal particle component being
present in an amount of from 5 to 35 weight percent of the flux
formulation; and a solder ball on the flux formulation; wherein the
metal particle component comprises solder particles, and wherein
the solder particles have a melting point that is less than that of
the solder ball.
28. The apparatus of claim 27, wherein the metal particle component
comprises solder particles and non-solder particles.
29. The apparatus of claim 28, wherein the non-solder particles
comprise pure metal particles having a particle size in the range
of 1 to 100 nm.
30. The apparatus of claim 28, wherein the non-solder particles
comprise Ge.
31. The apparatus of claim 28, wherein the non-solder particles
comprise rare earth metals.
32. The apparatus of claim 28, wherein the non-solder particles
comprise noble metals.
33. The apparatus of claim 27, wherein the metal particle component
is present in an amount of from 10 to 30 weight percent of the flux
formulation.
34. A method for coupling a solder ball to a substrate, comprising:
providing a substrate including a bonding pad; positioning a flux
formulation on the bonding pad, the flux formulation comprising a
flux component and a metal particle component, the metal particle
component comprising solder particles; and positioning a solder
ball on the flux formulation, the solder ball having a higher
melting point than the solder particles.
35. The method of claim 34, further comprising a first operation
comprising melting the solder particles on the bonding pad and
coalescing the solder particles on the bonding pad while the solder
ball remains unmelted, and, after the first operation, a second
operation comprising reflowing the solder ball.
36. The method of claim 34, wherein the metal particle component
comprises solder particles and non-solder particles.
37. The method of claim 34, wherein the flux formulation includes 5
to 35 weight percent metal particles.
Description
BACKGROUND
[0001] Solder balls are often placed onto substrate surfaces to
form electrical connections between, for example, a plurality of
conductive pads on a first substrate and a plurality of conductive
pads on a second substrate. The substrates being electrically
coupled together may include, for example, a semiconductor chip (a
chip is also known as a die), a package substrate such as a ball
grid array (BGA) package substrate, and a support substrate such as
a printed circuit board (PCB) substrate. The solder ball is heated
to melt (reflow) and forms a bond with the pad. Another reflow heat
treatment is typically carried out to couple the substrate to
another substrate through the solder. A flux composition is often
used to assist in the bonding of the solder ball to the pad on the
substrate. The flux may generally act to isolate the pad from the
atmosphere, and clean the pad to enhance the ability of the solder
to wet the pad during reflow. The flux may also provide an adhesive
force which acts to hold the ball to the pad on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] Embodiments are described by way of example, with reference
to the accompanying drawings, which are not drawn to scale.
[0003] FIG. 1 illustrates a micrograph of BGA pads having solder
balls positioned thereon prior to a reflow operation.
[0004] FIG. 2 illustrates a micrograph of the BGA pads and solder
balls of FIG. 1, after a reflow operation.
[0005] FIG. 3 illustrates an offset solder ball being pulled back
onto a pad, in accordance with certain embodiments.
[0006] FIG. 4 illustrates a flowchart of operations in accordance
with certain embodiments.
[0007] FIG. 5 illustrates an electronic system arrangement in which
embodiments may find application.
DETAILED DESCRIPTION
[0008] Reference below will be made to the drawings wherein like
structures may be provided with like reference designations. In
order to show the structures of various embodiments most clearly,
the drawings included herein include diagrammatic representations
of various structures. Thus, the actual appearance of the
fabricated structures may appear different while still
incorporating the claimed structures of the illustrated
embodiments. Moreover, the drawings may show only the structures
necessary to understand the illustrated embodiments. Additional
structures known in the art may not be included to maintain the
clarity of the drawings.
[0009] Positioning solder balls on a BGA (ball grid array)
substrate prior to reflow becomes more difficult as substrates
become smaller and the pitch between pads becomes smaller. In
addition, as substrates become thinner, they may display a level of
warpage that makes it difficult to hold the solder balls in place
on the surface in the proper location. Solder paste methods have
been used, where a solder paste (typically including a mixture of
about 90 weight percent solder and 10 weight percent liquid flux),
is printed onto bonding pads on a substrate. However, when warpage
is present, solder pastes may have an insufficient level of
tackiness to hold a solder ball in place prior to reflow. Flux only
methods have been used, where a liquid flux composition is sprayed
onto bonding pads on a substrate. A conventional liquid flux,
however, may not provide sufficient ball pull back to bring an
offset solder ball back onto the pad. FIG. 1 is a photomicrograph
of solder balls 10 on a portion of BGA substrate surface 20 prior
to reflow. The substrate surface 20 includes circular pads 12 onto
which the solder balls 10 are positioned. As seen in FIG. 1, in
many locations the solder balls 10 do not cover the entire pad 12
and instead are offset from the pad 12, with a portion of solder
ball 10 on the pad 12 and a portion of the solder ball 10 off of
the pad 12. The amount of solder ball 10 offset in FIG. 1 is up to
approximately 40-50 percent. At a pitch of, for example, 0.5 mm,
the use of a conventional liquid flux does not provide sufficient
pull back to enable effective self alignment of the 40-50% offset
solder balls during reflow, as illustrated in FIG. 2.
[0010] FIG. 2 illustrates the same BGA substrate surface 20 as FIG.
1, after reflow. The surface 20 shows a variety of defects
including empty pads, misplaced solder, and solder bridging
defects. Some of the pads 12 are completely covered by solder balls
10 that have properly bonded to the pads 12. However, a substantial
number of pads 12 are completely uncovered by solder balls 10.
Instead, in certain locations, the solder balls 10 have combined
and coalesced into larger solder balls 10a. In other locations,
solder balls 10b have positioned themselves between pads 12. In
still other locations the solder has broken down into smaller
regions of solder 10c.
[0011] Certain embodiments relate to flux formulations that have
suitable properties of tackiness to hold solder balls during the
ball placement operation and also display sufficient pull back
properties to enable solder ball self alignment on the pad prior to
reflow. Such embodiments act to inhibit solder bridging defects
formed due to misaligned solder balls.
[0012] Embodiments may include a flux formulation including a flux
component and a metal particle component. A variety of flux
components may be used. In certain embodiments, the flux component
includes an acid component and a solvent component. In certain
embodiments, additional flux ingredients including, but not limited
to amines, rosins, and other additives may be present. Certain
embodiments may include no clean and water soluble flux
compositions including metal particles.
[0013] In one aspect of certain embodiments, the acid component may
include a plurality of acids. Certain embodiments may include mono,
di, and tri carboxylic acids comprising between about 2 and 20
carbons. Examples of acids that may be suitable include, but are
not limited to, glycolic acid, oxalic acid, succinic acid, malonic
acid, and the like, and their combinations. Certain embodiments
include organic acids, although inorganic acids may also be used. A
wide variety of suitable solvents may be used, including, but not
limited to, alcohols, glycol ethers, hydrocarbons, water, and
combinations thereof. In another aspect of certain embodiments, the
flux may include an amine component. Suitable amines may include,
but are not limited to, butyl amine, diethylbutyl amine,
dimethylhexyl amine, and the like, and their combinations. The
activators (which may include the acid and amine components) may
include halogenated and non-halogenated activators. The activators
act to remove oxide from the metal pad to help prepare the pad
surface for forming a bond to solder.
[0014] In another aspect of certain embodiments, the flux may also
include rosin, which may be naturally occurring or synthetically
modified. In another aspect of certain embodiments, the flux may
also include additional additive ingredients, including, but not
limited to, surfactants, thickening agents, colorant, buffers, and
the like, and their combinations.
[0015] The metal particles present in embodiments may include
solder particles. The particles may be in the form of a powder. A
variety of solder materials may be used. In certain embodiments,
the solder particles are selected to have a melting point that is
less than 250.degree. C. In another aspect of certain embodiments,
the solder particles are selected to have a melting point that is
lower than that of the solder ball to be placed onto the pad for
reflow. This permits the solder particles in the flux to melt, wet
the pad, and pull back a misaligned solder ball prior to the solder
ball reflowing.
[0016] Embodiments may utilize a variety of solder particle
compositions, including, but not limited to, Sn (tin) based solders
(for example, alloys of Sn--Ag--Cu, Sn--Cu, Sn--Ag, etc.). Specific
examples of solder compositions that may be suitable in certain
embodiments include, but are not limited to, SAC305 (96.5 weight
percent tin, 3 percent silver, and 0.5 weight percent copper),
48Sn-52In (48 weight percent tin and 52 weight percent indium),
42Sn-58Bi (48 weight percent tin and 52 weight percent indium), In
(indium), 86.5Sn-5.5Zn-4.5In-3.5Bi (86.5 weight percent tin-5.5
weight percent zinc, 4.5 weight percent indium, and 3.5 weight
percent bismuth), and 91Sn-9Zn (91 weight percent tin and 9 weight
percent zinc).
[0017] In certain embodiments, the solder particles may have a
relatively small grain size, of up to 15 .mu.m. In certain
embodiments, the metal particles may include nanoparticles. The
metal particles may be present in certain embodiments in an amount
of 5 to 35 weight percent. It is believed that if the weight
percentage of the particles is above 35 weight percent, the flux
formulation may not have sufficient tackiness. It is also believed
that if the weight percentage of the particles is below 5 weight
percent, the flux formulation may not have sufficient pull back
properties to pull a misaligned solder ball back onto a pad. Other
ranges are also possible. For example, certain embodiments are
believed to have favorable tackiness and pull back properties with
a range of 10 to 30 weight percent. One embodiment utilizes about
20 weight percent of the metal particles.
[0018] In certain embodiments, the metal particles include both
solder particles and metal particles of other materials including
surface active elements. The surface active elements may be
particles of pure metals such as rare earths and noble metals. The
surface active particles may in certain embodiments be
nanoparticles having a particle size in the range of 1-100 nm.
Particular examples that may be suitable include, but are not
limited to, Ag, Au, and Ge nanoparticles. In certain embodiments,
the composition includes up to 5 weight percent of the surface
active particles. It has been found that the presence of the
surface active particles in certain embodiments can further enhance
the ability of the flux formulation to align a misplaced solder
ball on a pad prior to reflow.
[0019] In certain embodiments, flux formulations may be formed to
have a tackiness greater than about 100 gf. Such a level of
tackiness, together with the presence of 5-35 weight percent metal
particles as described above, should enable successful attachment
of solder balls to small pitch packages, for example, those with
less than 0.5 mm pitch. The combinations of certain ingredients may
be varied as known in the art, for example, to provide a water
soluble or to provide a no clean flux with a desired amount of
tackiness.
[0020] Embodiments may utilize flux formulations such as described
above during joining operations coupling a variety of components
together. Examples include, but are not limited to, a package
substrate to a board, a semiconductor chip to a package substrate,
and a capacitor to a substrate.
[0021] Certain embodiments may provide benefits relating to the
ability to pull back misaligned solder balls onto a bonding pad, as
described above. It is believed that this occurs due to the
presence of the metal particles in the formulation. FIG. 3
illustrates a solder ball 110 initially positioned on a bonding pad
112 in a manner such that the solder ball 110 is misaligned and
only partially on the bonding pad 112. A flux formulation 114 in
accordance with certain embodiments is positioned on the bonding
pad 112. The flux formulation 114 includes a plurality of metal
particles 116, 118 therein. In this embodiment, the metal particles
116 include solder particles having a melting point less than that
of the solder ball 110. By having a lower melting point, upon
exposure to heat at a temperature less than the reflow temperature
of the solder ball 110, the solder particles 116 will melt and
coalesce together. As the particles 116 positioned between the
solder ball 110 and the pad 112 coalesce together and with the
particles 116 positioned elsewhere on the bonding pad, the
misaligned solder ball 110 is pulled back onto the bonding pad 112,
as illustrated in FIG. 3. Then upon reflow, the solder ball 110 is
properly positioned on the bonding pad 112 and a strong joint
between the solder and pad is formed. With the solder ball 110
properly positioned on the bonding pad 112, the occurrence of
solder from adjacent solder balls merging together, or solder being
positioned in the locations between the bonding pads, or bonding
pads missing solder, are minimized or eliminated.
[0022] FIG. 3 illustrates metal particles 118 that are surface
active nanoparticle elements such as, for example, Ag, Au, and Ge,
and are optional in certain embodiments. It is believed that they
act to further improve the driving force for coalescing the solder
particles 116, which improves the ability of the flux formulation
to pull back misaligned solder balls. The term solder balls as used
herein may refer to solder bodies that are spherical or
non-spherical in shape.
[0023] FIG. 4 illustrates a flowchart of operations in accordance
with certain embodiments. Box 90 is providing a flux formulation
including metal particles therein. The metal particles include
solder particles. Box 92 is applying the flux formulation to a
bonding pad. The bonding pad may be any structure to which a
contact may be made. Box 94 is positioning a solder ball on the
bonding pad. Depending on factors such as, for example, the
positioning technique and the substrate flatness, the solder ball
may be only partially on the bonding pad. Box 96 is heating the
flux to a temperature sufficient to coalesce the solder particles
but lower than the reflow temperature. As the solder particles
coalesce, the solder ball will be pulled into position on the
bonding pad if it was misaligned. Box 98 is heating to a reflow
temperature of the solder ball to couple the solder ball to the
bonding pad.
[0024] In addition to benefits described above, certain embodiments
may also provide other benefits in relation to conventional solder
paste and liquid flux methods for attachment. By having a lower
metal load than solder paste methods, the presence of voids is
substantially decreased. For example, certain embodiments include
5-35 weight percent metal particles, whereas conventional solder
pastes include about 90 weight percent metal particles. Fewer voids
will mean fewer defects in the solder joint. In addition, because
certain embodiments include a higher metal load and lower amount of
liquid than conventional liquid fluxes, there will be less liquid
residue after the reflow operation. As a result, embodiments may
have a variety of advantages over conventional solder ball
attachment methods. Depending on factors such as, for example, the
size of the solder balls, the pad size, the pitch, and the warpage
of the substrate (if any), the flux formulations may be tailored to
provide enhanced properties such as tackiness, pull back, etc. For
instance, in certain embodiments, a higher metal load may provide
an enhanced pull back effect, and a lower metal load may provide an
enhance tackiness.
[0025] Assemblies including structures joined together as described
above may find application in a variety of electronic components.
FIG. 5 schematically illustrates one example of an electronic
system environment in which described embodiments may be embodied.
Other embodiments need not include all of the features specified in
FIG. 5, and may include alternative features not specified in FIG.
5.
[0026] The system 101 of FIG. 5 may include at least one central
processing unit (CPU) 103. The CPU 103, also referred to as a
microprocessor, may be a die which is attached to an integrated
circuit package substrate 105, which is then coupled to a printed
circuit board 107, which in this embodiment, may be a motherboard.
The package substrate 105 that is coupled to the board 107 is an
example of an electronic device assembly that may be formed in
accordance with embodiments such as described above, with a flux
such as described above used in the ball attachment operation for
attaching solder balls to the package substrate 105. A variety of
other system components, including, but not limited to, the CPU,
memory and other components discussed below, may also include the
use of flux formed in accordance with the embodiments described
above to couple solder balls to a substrate.
[0027] The system 101 may further include memory 109 and one or
more controllers 111a, 111b . . . 111n, which are also disposed on
the motherboard 107. The motherboard 107 may be a single layer or
multi-layered board which has a plurality of conductive lines that
provide communication between the circuits in the package 105 and
other components mounted to the board 107. Alternatively, one or
more of the CPU 103, memory 109 and controllers 111a, 111b . . .
111n may be disposed on other cards such as daughter cards or
expansion cards. The CPU 103, memory 109 and controllers 111a, 111b
. . . 111n may each be seated in individual sockets or may be
connected directly to a printed circuit board. A display 115 may
also be included.
[0028] Any suitable operating system and various applications
execute on the CPU 103 and reside in the memory 109. The content
residing in memory 109 may be cached in accordance with known
caching techniques. Programs and data in memory 109 may be swapped
into storage 113 as part of memory management operations. The
system 101 may comprise any suitable computing device, including,
but not limited to, a mainframe, server, personal computer,
workstation, laptop, tablet, handheld computer, handheld gaming
device, handheld entertainment device (for example, MP3 (moving
picture experts group layer-3 audio) player), PDA (personal digital
assistant), reader, telephony device (wireless or wired), network
appliance, virtualization device, storage controller, network
controller, router, etc.
[0029] The controllers 111a, 111b . . . 111n may include one or
more of a system controller, peripheral controller, memory
controller, hub controller, I/O (input/output) bus controller,
video controller, network controller, storage controller,
communications controller, etc. For example, a storage controller
can control the reading of data from and the writing of data to the
storage 113 in accordance with a storage protocol layer. The
storage protocol of the layer may be any of a number of known
storage protocols. Data being written to or read from the storage
113 may be cached in accordance with known caching techniques. A
network controller can include one or more protocol layers to send
and receive network packets to and from remote devices over a
network 117. The network 117 may comprise a Local Area Network
(LAN), the Internet, a Wide Area Network (WAN), Storage Area
Network (SAN), etc. Embodiments may be configured to transmit and
receive data over a wireless network or connection. In certain
embodiments, the network controller and various protocol layers may
employ the Ethernet protocol over unshielded twisted pair cable,
token ring protocol, Fibre Channel protocol, etc., or any other
suitable network communication protocol.
[0030] In the foregoing Detailed Description, various features are
grouped together for the purpose of streamlining the disclosure.
This method of disclosure is not to be interpreted as reflecting an
intention that the claimed embodiments of the invention require
more features than are expressly recited in each claim. Rather, as
the following claims reflect, inventive subject matter may lie in
less than all features of a single disclosed embodiment. Thus the
following claims are hereby incorporated into the Detailed
Description, with each claim standing on its own as a separate
embodiment.
[0031] While certain exemplary embodiments have been described
above and shown in the accompanying drawings, it is to be
understood that such embodiments are merely illustrative and not
restrictive, and that embodiments are not restricted to the
specific constructions and arrangements shown and described since
modifications may occur to those having ordinary skill in the
art.
* * * * *