U.S. patent application number 09/737407 was filed with the patent office on 2002-06-20 for high density electronic interconnection.
Invention is credited to Pace, Benedict G..
Application Number | 20020076910 09/737407 |
Document ID | / |
Family ID | 27389904 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020076910 |
Kind Code |
A1 |
Pace, Benedict G. |
June 20, 2002 |
High density electronic interconnection
Abstract
This is an interconnection between electronic devices and other
assemblies (e.g. printed circuits). The electronic devices are
mounted on high temperature insulating bases, such as ceramic
substrates. The insulating base has a conductive pattern to connect
the electronic device to another assembly. The conductive pattern
terminates in metal bumps capable of being connected to another
assembly (e.g. a printed circuit) by a conductive adhesive or
metallurgically by soldering, thermocompression, thermosonic or
ultrasonic bonding. The bumps are formed by applying a metal with a
melting point over 350.degree. C. to contact pads of the conductive
pattern of the insulating base, and raising the temperature of the
base above the melting point of the metal causing the molten metal
to draw back on to the contact pads forming a convex bump.
Inventors: |
Pace, Benedict G.;
(Shoreham, NY) |
Correspondence
Address: |
John F McCormack
116 Milburn Lane
Roslyn Heights
NY
11577
US
|
Family ID: |
27389904 |
Appl. No.: |
09/737407 |
Filed: |
December 15, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60170975 |
Dec 15, 1999 |
|
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60170976 |
Dec 15, 1999 |
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Current U.S.
Class: |
438/613 ;
257/E23.023; 257/E23.069; 438/108 |
Current CPC
Class: |
H01L 2924/16195
20130101; H01L 2924/01078 20130101; H01L 2224/73253 20130101; H01L
24/48 20130101; B81B 7/0077 20130101; H01L 2924/01046 20130101;
H01L 2224/48227 20130101; H01L 2224/16 20130101; H01L 23/488
20130101; H05K 3/248 20130101; H01L 2224/48091 20130101; H01L
2224/45099 20130101; H01L 2924/01025 20130101; H01L 23/49816
20130101; H01L 2924/15311 20130101; H05K 3/4007 20130101; H01L
2924/09701 20130101; H01L 2224/05599 20130101; H01L 2224/85399
20130101; H01L 2924/16315 20130101; H01L 2924/00014 20130101; H01L
2924/01079 20130101; H05K 1/092 20130101; H01L 21/4853 20130101;
H01L 2924/01004 20130101; H01L 2224/16225 20130101; H01L 2924/15151
20130101; H01L 2924/14 20130101; H01L 2224/48091 20130101; H01L
2924/00014 20130101; H01L 2224/85399 20130101; H01L 2924/00014
20130101; H01L 2224/05599 20130101; H01L 2924/00014 20130101; H01L
2924/00014 20130101; H01L 2224/45015 20130101; H01L 2924/207
20130101; H01L 2924/00014 20130101; H01L 2224/45099 20130101; H01L
2924/14 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
438/613 ;
438/108 |
International
Class: |
H01L 021/44 |
Claims
I claim:
1. A method for manufacturing bumped conductors for electrically
connecting one or more conductors on a first surface to one or more
conductors on a second surface, the method comprising melting a
metal on the first surface to form metal bumps fused to the
conductors on the first surface, the bumps being capable of being
bonded to the conductors on the second surface, and the bumps being
comprised of a metal having a melting point over 350.degree. C.
2. A method according to claim 1 wherein the metal being melted to
form bumps is capable of being metallurgically bonded to the
conductors on the second surface.
3. A method according to claim 1 wherein the metal being melted to
form bumps is capable of being adhesively bonded to the conductors
on the second surface with an organic adhesive.
4. A method according to claim 1, wherein the metal to be melted to
form the bumps is selected from the group consisting of aluminum,
copper, nickel, silver, gold, and alloys and combinations of those
metals.
5. A method according to claim 1, wherein the metal to be melted to
form the bumps is strong enough to support the first surface spaced
away from the second surface during and after the bonding of the
bumps to the conductors on the second surface.
6. A method according to claim 2, wherein the metal forming the
bumps is capable of being metallurgically bonded to the conductors
on the second surface by soldering.
7. A method according to claim 2, wherein the bumps are capable of
being metallurgically bonded to the conductors on the second
surface by welding.
8. A method for manufacturing bumped conductors for electrically
connecting one or more conductors on a first surface to one or more
conductors on a second surface, the method comprising: providing
contact areas in the conductive pattern on the first surface that
are wettable by a molten metal; depositing the metal over the
contact areas; melting the metal, the molten metal forming bumps on
the contact areas, the bumps being capable of being bonded to the
conductors on the second surface, and the bumps being comprised of
a metal having a melting point over 350.degree. C.
9. The method of claim 8, wherein the metal being deposited over
the wettable contact areas includes some metal being deposited on
non-wettable areas contiguous to the wettable area, and upon
melting the metal, the molten metal draws back from the
non-wettable areas to the wettable contact areas to form the
bumps.
10. A method according to claim 8, wherein the metal being melted
to form bumps is capable of being metallurgically bonded to the
conductors on the second surface.
11. A method according to claim 8, wherein the metal being melted
to form bumps is capable of being adhesively bonded to the
conductors on the second surface with an organic adhesive.
12. In a method according to claim 8, wherein the bumps are formed
of a metal selected from the group consisting of aluminum, copper,
nickel, silver, gold, and alloys comprising these metals.
13. A method according to claim 8, wherein the metal to be melted
to form the bumps is strong enough to support the first surface
spaced away from the second surface during and after the bonding of
the bumps to the conductors on the second surface.
14. A method according to claim 10, wherein the metal forming the
bumps is capable of being metallurgically bonded to the conductors
on the second surface by soldering.
15. A method according to claim 10, wherein the bumps are capable
of being metallurgically bonded to the conductors on the second
surface by welding.
16. In a method for manufacturing an electronic package having
solderable metal bumps as a connecting means, the improvement
comprising: providing an insulating substrate having metallic pads
as a base for the package; depositing a metal on the substrate over
the metallic pads, the metal having a melting point over
350.degree. C., and below the melting point of the metal forming
the metallic pads; melting the metal so that it draws back onto the
metallic pads, forming metal bumps on the metallic pads.
17. In a method for manufacturing an electronic package having
metal bumps according to claim 16, wherein the metal is deposited
over the metallic pads in a powdered form.
18. In a method for manufacturing an electronic package having
metal bumps according to claim 17, wherein the powdered metal is
deposited by screen printing.
19. In a method for manufacturing an electronic package having
metal bumps according to claim 16, the improvement comprising:
providing the insulating substrate with metallic pads of metals
selected from the group consisting of refractory metals and the
metals of Groups 8 and 1b of the Periodic Table of Elements and
alloys and combinations of those metals; depositing a lower melting
metal selected from the group consisting of aluminum and aluminum
alloys, copper and copper alloys, silver and silver alloys, gold
and gold alloys, nickel and nickel alloys and combinations of those
metals, over the metallic pads; and melting the lower melting metal
so that it draws back onto the metallic pads, forming metal bumps
on the metallic pads.
20. In the method of manufacturing an electronic package according
to claim 19, wherein the metal of the metallic pads on the
insulating substrate are selected from the group consisting of
chromium, molybdenum, nickel, tungsten, molybdenum/manganese and
titanium/tungsten.
21. In the method of manufacturing an electronic package according
to claim 20 wherein the metal forming the bumps comprises
copper.
22. In the method of manufacturing an electronic package according
to claim 20, wherein the metal forming the bumps is selected from
the group consisting of silver, gold, silver alloys and gold
alloys.
23. In the method of manufacturing an electronic package according
to claim 22, wherein the bumps are coated with a barrier metal
capable of preventing the bumps from dissolving in molten
solder.
24. In the method of manufacturing an electronic package according
to claim 23, wherein the barrier metal is coated with a solder aid
to enhance solderability
Description
[0001] This application claims the benefit of Provisional
Application No. 60/170,975 filed Dec. 15, 1999, and also of
Provisional Application No. 60/170,976 filed Dec. 15, 1999.
FIELD OF THE INVENTION
[0002] The invention is related to electronic interconnections and
methods of forming bumped patterns for these interconnections.
BACKGROUND OF THE INVENTION
[0003] Ball grid arrays are made by coating a pad grid on the chip
package with high temperature solder, (95% Pb/5% Sn). A glass
template is provided with a hole grid corresponding to the pad
grid. The holes are filled with copper balls coated with high
temperature solder, and the high temperature solder is reflowed to
join the balls to the pad. Subsequently, the ball grid package is
attached to the next level assembly by a lower temperature solder,
e.g. 60% Sn/40% Pb. Ball grid arrays require carefull and precise
control of soldering temperatures. Replacement or repair of
packages having ball grid arrays also requires temperature control
for package removal. Many hermetic packages have covers that are
bonded to the package by sealing glass. The covers are sealed with
sealing glasses at 360-450.degree. C. Ball grid arrays for such
packages cannot be made in advance, but must be added as the last
step in making the package.
[0004] Micro-connection systems have been proposed for testing to
produce "known-gooddie" One proposed micro-connection system has
microbumps on a copper clad polyimide substrate which are to be
temporarily pressed against the die for testing purposes. A
silicone rubber sheet backing the micro bumped polyimide surface
transmits the contact pressure to the microbumps. These proposed
microbumps are not suitable for permanent connections, or for
hermetically sealed packages.
[0005] The Controlled Collapse Chip Connection (C4) is a method of
flip chip mounting of semiconductor chips. In the C4 process solder
bumps are formed on a semiconductor chip. The solder bumps are used
to connect the chip to its package, such as a single chip module
(SCM) or multichip module (MCM). In the C4 process, first a glass
passivation layer is formed on the chip with vias in the layer for
the input/output contacts, I/Os. After DC sputter cleaning of the
via holes, a thin circular pad of chromium is evaporated through a
mask. The chromium pad covers the via and forms a ring around the
via over the passivation layer sealing the via. The DC sputter
cleaning assures low contact resistance to the aluminum I/O pad of
the chip and good adhesion to the passivation layer. Next a phased
chromium and copper layer is evaporated to provide resistance to
multiple reflows in the subsequent processing. This is followed by
a pure copper layer to form a solderable metal. A thin layer of
gold is added as an oxidation protection layer for the copper. A
thick deposit (100-125 .mu.m) of high melting solder (97-95%
Pb/3-5% Sn) is evaporated through a mask onto the chip and then
heated to about 365.degree. C. in a hydrogen atmosphere to fuse the
solder into truncated spheres adhering to the pads. These solder
bumps are fused to gold plated or solder coated pads on the
interior surface of the chip package. The solder joints in the C4
design must be high enough to compensate for substrate
non-planarity. Also because solder surface tension holds up the
chip, a sufficient number of pads is required to support the weight
of the chip. This is a concern with bulky, low 1/O devices such as
memory chips or chip carriers, where multiple dummy pads must be
added to support the chip. For this reason, among others, the C4
process has been used for connecting semiconductor chips to a first
level package, but has not been successful or widely used for
connecting a package, which is substantially heavier than a chip to
a higher level assembly.
SUMMARY OF THE INVENTION
[0006] The invention comprises a novel method of forming bumped
substrates by forming the bumps and fusing them to the substrate
simultaneously in one operation.
[0007] The present invention comprises a method of manufacturing an
electronic interconnection means for interconnecting one or more
conductors on one surface to one or more conductors on another
surface. The interconnection means comprises convex metal bumps
melted onto the conductors on the first surface, and capable of
being bonded to the conductors on the second surface. The bumps
being comprised of a metal that does not melt below 350.degree. C.,
and is strong enough to hold the two surfaces a fixed distance
apart.
[0008] In one embodiment the present invention comprises an
improved method for manufacturing an electronic package having
solderable metal bumps as a connecting means to another electronic
package or a higher level assembly. The improvement comprises
providing an insulating substrate having metallic pads on the base
of the package; depositing a metal on the substrate over the
metallic pads, the metal having a melting point over 350.degree. C.
and below the melting point of the metal forming the metallic pads;
melting the metal so that it draws back onto the metallic pads, and
forms metal bumps on the metallic pads.
[0009] In another embodiment, the invention comprises a method for
manufacturing bumped conductors for electrically connecting one or
more conductors on a first surface to one or more conductors on a
second surface by providing contact areas in the conductive pattern
on the first surface that are wettable by a molten metal. Then
depositing the metal over the contact areas, and raising the
temperature of the first surface above the melting point of the
deposited metal. The metal melts, and the molten metal forms bumps
on the contact areas. The bumps being comprised of a metal having a
melting point over 350.degree. C., and the bumps formed being
capable of being bonded to the conductors on the second surface
[0010] A further embodiment of the invention is a method of making
electrical connections to electro mechanical devices by means of
metal bumps on the conductive pattern of a ceramic substrate. The
bumps both support the device and electrically connect it.
[0011] An additional embodiment of the invention is an connector to
interconnect two or more electronic packages or assemblies. The
connector comprises a planar, high temperature, insulating
substrate with an interconnecting conductive pattern. The
conductive pattern terminates in metal bumps capable of
metallurgically bonding to contact pads of another assembly.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross section view of a chip-scale package
according to the invention.
[0013] FIG. 2 is a cross section view of a flip chip package
according to the invention.
[0014] FIG. 3 is a cross section view of a multichip module with
melted metal bumps as interconnection means
[0015] FIG. 4 is a plan view of a ceramic substrate having 256 grid
arrays of the metal bumps of the invention.
[0016] FIG. 5 is a plan view of a single grid array from FIG.
4.
[0017] FIG. 6 is a side view of a connector interconnecting two
adjacent packages.
[0018] FIG. 7 is a side view of a second grid array metal bumped
connector.
DESCRIPTION OF THE INVENTION
[0019] The interconnections of the present invention are by means
of metal bumps on a high temperature insulating substrate. The
bumps are formed by melting metals onto the contact pads on the
substrate.
[0020] In the methods of this invention the conductive pattern of a
substrate or base is provided with contact pads where the metal
forming the bumps can be adhered when the metal is molten, and a
background surface of the substrate where the molten metal is
non-adherent. The contact pads can be metal pads or metallic sites
capable of being wetted by the molten metal on a non-wettable
background. The backgrounds include non-wettable metallic surfaces
such as chrome or chrome alloys having a thin, non-wettable oxide
layer, and non-wettable insulating surfaces and combinations of
non-wettable surface background materials. Wettable areas are areas
on the substrate surface where the molten metal adsorbs.
[0021] The bumps are formed by applying metal to areas of the
substrate and melting the metal to form the bumps. The metal can be
applied or deposited on the substrate by any suitable means such as
plating, vacuum deposition, sputtering and the like, or as metal
particles or powders, wires, films or foils. The metal is applied
to the contact pads and may also be applied to contiguous
background areas. The substrate is then heated to a temperature
above the melting point of the metal and the surface tension of the
molten metal draws it back from the contiguous background area
forming a bump on the contact pad. The height of the bump depends
on the volume of metal applied on the contact pad and also on the
contiguous background area. Preferably the metal that is applied on
each pad and the contiguous background area associated with it, is
separated from neighboring areas and their contiguous metal
deposits.
[0022] If the background surface is smooth, firm and non-wettable,
the surface tension of the molten metal will draw back any metal
applied to the contiguous area onto the contact pad. The surface
tension of the molten metal may not be sufficient to draw all the
metal from the contiguous areas if the contiguous background is
rough, textured, or if the surface of the background softens at the
temperature of the molten metal. In such cases it is advisable to
apply all of the metal required to form the protuberance directly
on the contact area with little or no overlap of the contiguous
background area.
[0023] In one embodiment, the invention is a method of forming
metal bumps on an electronic interconnecting substrate, the bumps
being suitable for connecting to another electronic assembly. The
bumps are formed by applying metal particles, films or foils to
metallic pads on the substrate and melting the metal particles,
film or foils to form the bumps on the metallic pads.
[0024] The invention also provides packages with bumped arrays for
forming metallurgical bonds to another assembly. The packages are
capable of being hermetically sealed.
[0025] A characteristic of the metal forming the bumps is a melting
point above the temperature at which the package will be joined to
another package or to another assembly. The conductors on the
surface having the melted metal bumps are joined to the conductors
on the second surface by metallurgically or adhesively bonding the
bumps to the contact pads on the second surface. The metallurgical
bonds can be formed by brazing, soldering, welding or the like.
Welding techniques commonly used in the electronics industry
include thermocompression bonding, ultrasonic bonding and thermal
ultrasonic bonding. Soldering is the standard procedure by which
electronic component packages are joined to other assemblies, such
as ceramic circuits or laminated glass reinforced epoxy printed
wiring boards. The soldering takes place at temperatures between
220.degree. C. (425.degree. F.) and 290.degree. C. (550.degree.
F.), so the melting point of the metals forming the bumps should be
over 350.degree. C. (650.degree. F.). The melting point of the
metal forming the bumps must be below the melting point of the
metal forming the metallic pads.
[0026] The bumps must be formed of a metal that has sufficient
strength and rigidity to support the surface and prevent collapse
when joining it to another surface or another assembly. The bumps
should be high enough to compensate for non-planarity of the
surfaces being joined, and strong enough to keep the surfaces apart
to prevent short circuits, and to permit cleaning between the two
surfaces. Preferably the bumps should support the package without
addition of dummy bumps. The metal that is melted and melted to a
substrate to form the bumps must adhere well to the metallic pads
of the substrate.
[0027] Techniques for joining the bumped substrate to contact pads
on another surface include adhesive and metallurgical bonding
techniques. Adhesive bonding uses conductive organic materials and
includes metal filled resins such as conductive epoxies, acrylics
and polyimides. Metallurgical bonding techniques include welding,
brazing, soldering, and the like. Welding techniques commonly used
in the electronics industry include thermocompression bonding,
ultrasonic bonding and thermal ultrasonic bonding. When the bumped
substrate is to be joined to contact pads on another surface by
thermocompression, ultrasonic or thermal ultrasonic techniques, the
metal of the bumps may be gold or aluminum.
[0028] When the bumped substrate is to be joined to the contact
pads on another surface by soldering, an important characteristic
of the bumps is limited solubility in solder. If the metal
dissolves in solder, the bumps may collapse. Also at soldering
temperatures the bumps should not dissolve significantly in solder
so as to weaken and/or embrittle the solder joints. If the bumps
are formed of a metal that may be dissolved in solder, the bumps
should be coated with a barrier layer such as nickel.
[0029] The bumps are formed of metals and alloys with melting
points above 350.degree. C. Preferred metals are copper and copper
alloys such as copper/nickel, beryllium/copper, brasses and
bronzes. Nickel and nickel alloys such as nickel/phosphorus alloys
also may be used. Silver and silver alloys such as copper/silver,
palladium/silver and gold and gold alloys such as gold/germanium
and gold/silver platinum/gold alloys may be used. A barrier metal
such as nickel or palladium may be used to reduce the solubility of
the bumps in solder or prevent migration of the bump metal into the
solder. To enhance the solderability of bumps coated with nickel or
other barrier metal, a solder aid such as a thin layer of gold, tin
or a flux may be applied to the barrier metal.
[0030] The substrate is preferably formed from a high temperature
insulating material. Any insulating material may be used that will
withstand the process of fusing the metal and forming the bumps on
the substrate. Especially suitable high temperature insulating
materials are ceramic and glass/ceramic compositions and silicon.
Preferred materials comprise aluminum oxide, aluminum nitride,
diamond, beryllium oxide, boron nitride, cordierite, mullite,
silicon carbide silicon nitride and glass/ceramics.
[0031] The metallic pads are formed on the high temperature
insulating material by any suitable means. On ceramic materials,
thick film, thin film, cofired ceramic circuit or copper direct
bond metallization techniques may be used. The metallic pads are
composed of metals with melting points above the melting point of
the bumps, and that will not melt, dissolve or lose adhesion to the
insulating substrate when the metals forming the bumps are melted
and fused to the pads. The metals for the metallic pads are
selected from the group consisting of the metals of Groups 8 and 1b
of the Periodic Table of Elements and the refractory metals such as
chromium, molybdenum, tungsten and titanium. Preferred metals for
the metallic pads are formed from thick film copper pastes, gold
pastes, palladium/silver pastes and platinum/silver pastes. More
preferred metals include tungsten, titanium-tungsten, chromium,
molybdenum and nickel, and most preferred are combinations of
molybdenum and manganese. A barrier material on the metallic pad,
such as nickel or palladium may be used to limit the solubility of
the metal of the bump into the metal comprising the metallic
pad.
[0032] If the high temperature insulating material is used for an
electronic package that will contain a semiconductor die, it may
have electrical connections from the die to either metallic pads on
its bottom or metallic pads on the same side as the die. The die
may be connected to the package by wire bonds, or by a flip chip
bonding. The connections to the bottom of the package may be
through the substrate of the package as metallic vias when the
package is a cofired multilayer ceramic, or by metal plugged vias
in the substrate of the package. The connections also may be
accomplished by edge metallization.
[0033] The metal or metal alloy that is melted onto the metallic
pads may be applied to the substrate as a metal powder, by printing
metal pastes, by evaporating metal onto the substrate, by applying
a metal foil to the substrate, or other means. After the metal is
applied to the substrate, it is heated to a temperature above its
melting point. When the metal melts the surface tension of the
molten metal causes the metal to draw back and ball up on the
metallic pads.
[0034] Metal pastes applied using thick film screen printing
techniques are one method of applying metal powder onto the
metallic pads of the substrate. The pastes are formulated with
metal powders dispersed in organic vehicles. E.g., a metal paste is
prepared by dispersing 50-90% by weight metal powder in an organic
resin/solvent vehicle. The metal paste is printed over each of the
metallic pads on the substrate. The paste is dried and then the
temperature ramped up to destroy the organic vehicle, leaving only
the powder. The temperature is then raised above the melting point
of the powdered metal, and the part is fired in a vacuum or an
inert or reducing atmosphere The metal melts and draws back to the
metallic pads forming rounded metal bumps.
[0035] In one embodiment, the metallic pads on the high temperature
insulating substrate are covered by an organic adhesive and metal
particles are applied to the adhesive. The adhesive is formulated
so that it will decompose completely in the firing process. After
the metal particles are applied, the substrate is heated above the
melting point of the metal, so that the surface tension of the
molten metal causes the metal to draw back and form bumps on the
metallic pads.
[0036] The metals used to form the bumps may be applied to an
insulating substrate by electroplating. The metallic pads may be
electroplated by connecting them to the cathode of an
electroplating cell. In another electroplating method, a layer of
electroless metal is formed on a ceramic substrate including the
metallic pads, and built up to a required thickness by
electroplating, e.g., copper. An etch resist is applied over the
electroplated metal, and the metal is etched to create an area of
metal in contact with each metallic pads on the substrate. After
the etch resist is removed the metal is heated to a temperature
above the its melting point. When the metal melts the surface
tension of the molten metal causes the metal to draw back, ball up
on and fuse to the metallic pads.
[0037] In an alternative procedure, a plating resist is applied to
the electroless metal layer described above, leaving exposed metal
over each of the metallic pads. Copper is electroplated on the
exposed areas. After the plating resist is removed, the underlying
layer of electroless metal separating the electroplated areas
optionally may be removed by a quick etch prior to melting the
copper to form the bumps
[0038] Metal foils, such as copper foils may be used to form the
bumps over the metallic pads on the substrate. The foils may be
laminated to the bottom of the substrate with an adhesive that
decomposes during the firing. The foils may be perforated or porous
to better vent the decomposing adhesive. Areas of metal overlapping
the metallic pads may be formed by etching. Upon melting, these
areas draw back and ball up forming bumps on the metallic pads.
Alternatively the foil could be punched forming a pattern of
islands joined by very narrow bands. The punched foil is positioned
on the substrate with each punched island overlapping a metallic
pad. When it is heated above the melting point of the foil, the
narrow bands melt and act as cleavage points as the islands draw
back to form bumps over and fuse to the metallic pads.
[0039] The height of the bumps is determined by the quantity of
metal or alloy that is melted on each metallic pad. It would be
obvious for one skilled in the art to select the volume of material
over the metallic pad in order to obtain the desired bump
height.
[0040] A package according to the invention is illustrated in FIG.
1. The package, shown in cross-section, has a base 110, a
semiconductor device 120 connected by wire bonds 130 to the
conductive pattern of the base, a frame 140, surrounding the
device, which is closed by a cover 150. The conductive pattern
includes vias connecting the top and bottom of the base. Melted
metal bumps 160 formed on the bottom of the base are suitable for
connecting the package to another assembly. The metal bumps of the
interconnection package may be soldered to a printed wiring board,
thus connecting the semiconductor device to the next level
assembly.
[0041] A "flip-connection" package having melted metal bumps for
connection to another assembly, is shown in FIG. 2. The metal bumps
260 are formed on the bottom of the ceramic base 210. The metal
bumps are connected by the conductive pattern of the ceramic base
and the flip-connections 230 to a semiconductor die 220. The
semiconductor device is enclosed by a frame 240 and cover 250. Some
methods for providing packages with flip connections are more fully
described in U.S. Pat. Nos. 5,627,406, 5,904,499 and the copending
application entitled INTERCONNECTION METHODS, filed simultaneously
with the current application, and which is incorporated herein by
reference.
[0042] FIG. 3 illustrates a multichip module package with three
electronic devices 320, 322 and 324 connected to the conductive
pattern of a ceramic base 310. The ceramic base has melted metal
bumps 360 on the bottom to serve as input/output interconnections
for the module. A frame 340 mounted on the ceramic base, and a
cover 350 is attached to the frame to enclose and protect the
devices.
[0043] FIG. 6 illustrates a connector interconnecting two
side-by-side surfaces 614 and 615. The connector is an insulating
substrate 610 with a grid array pattern 670. Metal bumps have been
formed on the grid array by melting metal and fusing it to the grid
array. The grid array pattern is interconnected by the conductive
pattern (not shown) of the insulating substrate. The metal bumps
are metallurgically bonded to the pads 690 on the conductive
patterns (not shown) of the two side-by-side surfaces 614 and
615.
[0044] FIG. 7 shows another connector having an insulating
substrate 710, with metal bumps 770 on both top and bottom
surfaces. The metal bumps are connected by the conductive pattern
of the insulating substrate. Two surfaces 714 and 715 are
interconnected by being metallurgically bonded to the metal bumps
of the connector. It would be obvious to those skilled in the art
that the conductive pattern of the connector could be a simple
through via pattern for direct interconnection of 714 and 715, or a
more complex conductive pattern to interconnect any contact pad to
any other desired contact pad.
EXAMPLE 1
[0045] Referring to FIG. 4, a 2 in..times.2 in..times.0.01 in.
thick (50 mm.times.50 mm.times.0.25 mm) alumina substrate 400 was
printed with a pattern simulating the connections of 256 chip scale
packages. The chip scale package size was 0.125 in..times.0.125 in.
(3.175 mm.times.3.175 mm), and each simulated package had 20 pad
connections 470. FIG. 5 shows an individual package with 20 pads
570. A tungsten paste, Tungsten Mix No. 3.TM. from Ceronics Inc.,
of New Jersey, was printed in 0.006 in. diameter (150 .mu.m) pads
on 0.020" (0.5 mm) centers. The paste pattern was fired in a
hydrogen atmosphere at about 3150.degree. C. forming metallic pads
0.006" (150 .mu.m) in diameter.
[0046] A copper paste was prepared by dispersing 80% by weight
copper powder in 20% by weight ethyl cellulose/terpineol vehicle.
The copper paste was printed in oversize pads, 0.018" (0.46 mm) on
0.020" centers, where each pad overlapped a tungsten pad. The
copper paste was dried, fired in a hydrogen atmosphere at a low
temperature to decompose the organic vehicle, and then fired at a
temperature above the melting point of copper. In the firing, the
temperature was ramped up over 40 minutes to 1100.degree. C.; held
at 1100.degree. C. for 30 minutes, and ramped down over a period of
30 minutes.
[0047] In the firing process the copper pads pulled back onto and
balled up on the tungsten pads forming uniformly high copper bumps
suitable for joining the alumina substrate to another electronic
package or higher level electronic assembly by soldering or other
means.
EXAMPLE 2
[0048] A 2" by 2" (50 mm.times.50 mm) alumina plate was printed
with a molybdenum/manganese (Mo/Mn) paste in a pattern of 5120
pads, 0.006" (150 .mu.m) in diameter. The pads were in 256 groups
of 20 pads each on 0.020" (0.5 mm) centers as in Example 1. The
Mo/Mn paste on the alumina was fired forming metallic pads 0.006"
in diameter. A copper paste was screen printed over the metallic
pads in a pattern of circles 0.018" (0.46 mm) on the same 0.020"
(0.5 mm) centers as the metallic pads. The copper paste on the
alumina was dried and then temperature was ramped up over 30
minutes to 1100.degree. C. and held at 1100.degree. C. for 35
minutes before slowly cooling down. The copper melted and the
surface tension of the molten copper drew the copper back to form
bumps 0.006" in diameter on the metallic pads.
[0049] The procedure was repeated with square, copper paste prints
and long, narrow, rectangular, copper paste prints over the 0.006"
diameter metallic pads. In all cases, after firing the copper drew
back and formed smooth convex bumps over the metallic pads.
[0050] Since the copper pattern overlapping one metallic pad is
preferably spaced apart from the pattern overlapping a neighboring
metallic pad, long, narrow prints are well suited for applications
where the metallic pads are so tightly spaced that one couldn't
supply a sufficient volume of material using a circular or square
pattern.
[0051] It will be obvious to those skilled in the art that the
melted metal bumps may be used to interconnect packages having a
single layer or multilayer conductive patterns. Likewise the
invention is applicable to packages containing more than one
semiconductor chip, or a package containing multiple semiconductor
circuits on a single die, wafer or section of a wafer.
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