U.S. patent application number 14/741757 was filed with the patent office on 2016-12-22 for induction heating for underfill removal and chip rework.
The applicant listed for this patent is GLOBALFOUNDRIES INC.. Invention is credited to Stephen P. Ayotte, Glen E. Richard, Timothy M. Sullivan.
Application Number | 20160372444 14/741757 |
Document ID | / |
Family ID | 57351767 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160372444 |
Kind Code |
A1 |
Ayotte; Stephen P. ; et
al. |
December 22, 2016 |
INDUCTION HEATING FOR UNDERFILL REMOVAL AND CHIP REWORK
Abstract
Underfill materials and methods for removing an underfill
material from beneath a chip in relation to removal of the chip
from a substrate. The underfill material may a plurality of
particles dispersed in a bulk matrix. The material constituting the
particles may be capable of generating heat energy when exposed to
a time-varying magnetic field. The bulk matrix of the underfill
material between the chip and a substrate may be heated with heat
energy transferred from the particles. While heated, the underfill
material is removed. The heating of the underfill material may also
be used to heat solder bumps connecting the chip with the substrate
so that the solder bumps are liquefied.
Inventors: |
Ayotte; Stephen P.;
(Bristol, VT) ; Richard; Glen E.; (Burlington,
VT) ; Sullivan; Timothy M.; (Essex Junction,
VT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES INC. |
GRAND CAYMAN |
KY |
US |
|
|
Family ID: |
57351767 |
Appl. No.: |
14/741757 |
Filed: |
June 17, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 24/98 20130101;
H01L 2224/32225 20130101; H01L 2224/81455 20130101; H01L 21/56
20130101; H01L 2224/0401 20130101; H01L 2224/1132 20130101; H01L
2224/29357 20130101; H01L 2224/73204 20130101; H01L 2224/131
20130101; H01L 24/05 20130101; H01L 24/11 20130101; H01L 2224/05124
20130101; H01L 2224/05147 20130101; H01L 2224/13111 20130101; H01L
2224/81447 20130101; H01L 2224/29387 20130101; H01L 21/563
20130101; H01L 24/32 20130101; H01L 2224/81815 20130101; C09K 5/06
20130101; H01L 2224/05624 20130101; H01L 2224/11462 20130101; H01L
2224/29499 20130101; H01L 24/81 20130101; H01L 24/83 20130101; H01L
2224/81466 20130101; H01L 2224/11334 20130101; H01L 24/13 20130101;
H01L 24/29 20130101; H01L 2224/05647 20130101; H01L 2224/2936
20130101; H01L 2224/92125 20130101; H01L 2224/83222 20130101; H01L
2224/81424 20130101; H01L 2224/29355 20130101; H01L 2224/8388
20130101; H01L 2224/29388 20130101; H01L 2224/83862 20130101; H01L
2224/2929 20130101; H01L 2224/16227 20130101; H01L 2224/13116
20130101; H01L 2224/1145 20130101; H01L 2224/83102 20130101; H01L
24/92 20130101; H01L 2224/05666 20130101; H01L 24/16 20130101; H01L
2224/05655 20130101; H01L 2224/131 20130101; H01L 2924/014
20130101; H01L 2224/81815 20130101; H01L 2924/00014 20130101; H01L
2224/11462 20130101; H01L 2924/00014 20130101; H01L 2224/1145
20130101; H01L 2924/00014 20130101; H01L 2224/1132 20130101; H01L
2924/00014 20130101; H01L 2224/11334 20130101; H01L 2924/00014
20130101; H01L 2224/83862 20130101; H01L 2924/00014 20130101; H01L
2224/13111 20130101; H01L 2924/01082 20130101; H01L 2224/13116
20130101; H01L 2924/00014 20130101; H01L 2224/05647 20130101; H01L
2924/00014 20130101; H01L 2224/05624 20130101; H01L 2924/00014
20130101; H01L 2224/05147 20130101; H01L 2924/00014 20130101; H01L
2224/05124 20130101; H01L 2924/00014 20130101; H01L 2224/05666
20130101; H01L 2924/01074 20130101; H01L 2224/81466 20130101; H01L
2924/01074 20130101; H01L 2224/81424 20130101; H01L 2924/00014
20130101; H01L 2224/81447 20130101; H01L 2924/00014 20130101; H01L
2224/81455 20130101; H01L 2924/00014 20130101; H01L 2224/05655
20130101; H01L 2924/00014 20130101; H01L 2224/2929 20130101; H01L
2924/069 20130101; H01L 2224/29387 20130101; H01L 2924/05381
20130101; H01L 2224/29387 20130101; H01L 2924/0549 20130101; H01L
2924/054 20130101; H01L 2924/01028 20130101; H01L 2924/05381
20130101; H01L 2224/29387 20130101; H01L 2924/0549 20130101; H01L
2924/0542 20130101; H01L 2924/0103 20130101; H01L 2924/05381
20130101; H01L 2224/29387 20130101; H01L 2924/0549 20130101; H01L
2924/0542 20130101; H01L 2924/01048 20130101; H01L 2924/05381
20130101; H01L 2224/29387 20130101; H01L 2924/0549 20130101; H01L
2924/0537 20130101; H01L 2924/01025 20130101; H01L 2924/05381
20130101; H01L 2224/29387 20130101; H01L 2924/0549 20130101; H01L
2924/0532 20130101; H01L 2924/01012 20130101; H01L 2924/05381
20130101; H01L 2224/2936 20130101; H01L 2924/00014 20130101; H01L
2224/29355 20130101; H01L 2924/00014 20130101; H01L 2224/29357
20130101; H01L 2924/00014 20130101; H01L 2224/29388 20130101; H01L
2924/00014 20130101; H01L 2224/29387 20130101; H01L 2924/05442
20130101; H01L 2224/73204 20130101; H01L 2224/16225 20130101; H01L
2224/32225 20130101; H01L 2924/00 20130101 |
International
Class: |
H01L 23/00 20060101
H01L023/00; C09K 5/06 20060101 C09K005/06 |
Claims
1. A method for removing an underfill material from beneath a chip,
the method comprising: heating the underfill material with
induction heating; and while the underfill material is heated,
removing the underfill material from beneath the chip.
2. The method of claim 1 wherein heating the underfill material
comprises: coupling a time-varying magnetic field with a plurality
of particles in the underfill material to heat the particles; and
transferring heat energy from the particles to a bulk matrix of the
underfill material.
3. The method of claim 2 wherein the particles are comprised of a
ferromagnetic material, and the time-varying magnetic field induces
eddy currents in the ferromagnetic material of the particles to
produce the heat energy.
4. The method of claim 2 wherein the particles are comprised of a
ferriceramic material, and the time-varying magnetic field induces
magnetic hysteresis losses in the ferriceramic material of the
particles to produce the heat energy.
5. The method of claim 2 wherein coupling the time-varying magnetic
field with the particles in the underfill material comprises:
passing an electrical current through an induction coil to generate
the time-varying magnetic field.
6. The method of claim 1 wherein the underfill material includes a
bulk matrix that is transformed from a solid phase to a liquid
phase or a semisolid state by the induction heating, and the
underfill material is removed while the underfill material is in
the liquid phase or in the semisolid state.
7. The method of claim 6 wherein a plurality of first pads on the
chip are coupled by a plurality of solder bumps with a plurality of
second pads on a substrate, and the bulk matrix of the underfill
material transforms from the solid phase to the liquid phase or the
semisolid state at a first temperature less than a second
temperature at which the solder bumps liquefy.
8. A method for reworking a chip, the method comprising: heating an
underfill material between the chip and a substrate with induction
heating; heating a plurality of solder bumps coupling a plurality
of first pads on the chip with a plurality of second pads on the
substrate; and while the underfill material and the solder bumps
are heated, removing the chip from the substrate.
9. The method of claim 8 wherein heating the underfill material
comprises: coupling a time-varying magnetic field with a plurality
of particles in the underfill material to heat the particles; and
transferring heat energy from the particles to a bulk matrix of the
underfill material.
10. The method of claim 9 wherein heating the solder bumps further
comprises: transferring the heat energy from the bulk matrix of the
underfill material to the solder bumps.
11. The method of claim 9 wherein the particles are comprised of a
ferromagnetic material, and the time-varying magnetic field induces
eddy currents in the ferromagnetic material of the particles to
produce the heat energy.
12. The method of claim 9 wherein the particles are comprised of a
ferriceramic material, and the time-varying magnetic field induces
magnetic hysteresis losses in the ferriceramic material of the
particles to produce the heat energy.
13. The method of claim 8 wherein the underfill material includes a
bulk matrix that is transformed by the induction heating from a
solid phase to a liquid phase or a semisolid state at a first
temperature, the solder bumps are liquefied by the heating at a
second temperature, and the chip is removed from the substrate
while the underfill material is in the liquid phase or in the
semisolid state and the solder bumps are liquefied.
14. The method of claim 13 wherein the first temperature less than
the second temperature.
15. The method of claim 13 wherein the first temperature is greater
than the second temperature.
16. The method of claim 9 wherein coupling the time-varying
magnetic field with the particles in the underfill material
comprises: passing an electrical current through an induction coil
to generate the time-varying magnetic field.
17-20. (canceled)
Description
BACKGROUND
[0001] The invention relates generally to semiconductor packaging
and, in particular, to underfill materials and methods for removing
an underfill material from beneath a chip in relation to removal of
the chip from a substrate.
[0002] A die or chip includes integrated circuits formed by
front-end-of-line processing using the semiconductor material of a
wafer, a local interconnect level formed by middle-of-line
processing, and stacked metallization levels of an interconnect
structure formed by back-end-of-line processing. After the wafer is
diced, each chip may be joined with a substrate using, for example,
a controlled collapse chip connection or flip chip process. In a
flip chip process, reflowed solder bumps establish mechanical and
electrical connections between pads in the top metallization level
of the interconnect structure and a complementary set of pads on
the substrate. The solder bumps can be formed on the pads of the
chip using any number of techniques, including electroplating,
evaporation, printing, and direct placement. Reflow of the solder
bumps establishes solder joints that physically and electrically
connect the chip pads with the substrate pads.
[0003] Underfill may be applied to fill open space beneath the chip
that remains between the solder joints. After curing, the underfill
may function to protect the solder joints against various adverse
environmental factors and redistribute mechanical stresses arising
from shock. The underfill may also prevent the solder joints from
shearing during thermal cycles. Coefficient of thermal expansion
(CTE) mismatch between the chip and the substrate can cause
mechanical stresses as temperature changes are experienced that can
lead to solder joint shearing and reliability issues.
[0004] Improved underfill materials and methods for removing an
underfill material from beneath a chip in relation to removal of
the chip from a substrate are needed that improve on existing
underfill materials and such removal methods.
SUMMARY
[0005] In an embodiment of the invention, a method is provided for
removing an underfill material from beneath a chip. The underfill
material is heated by induction heating. While the underfill
material is heated, the underfill material is removed from beneath
the chip.
[0006] In an embodiment of the invention, a method is provided for
reworking a chip. An underfill material between the chip and a
substrate is heated by induction heating. Solder bumps coupling a
plurality of first pads on the chip with a plurality of second pads
on the substrate are also heated. While the underfill material and
the solder bumps are heated, the chip is removed from the
substrate.
[0007] In an embodiment of the invention, an underfill material
includes a plurality of particles dispersed in a bulk matrix. A
material constituting the particles is configured to generate heat
energy by induction heating when exposed to a time-varying magnetic
field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate various
embodiments of the invention and, together with a general
description of the invention given above and the detailed
description of the embodiments given below, serve to explain the
embodiments of the invention.
[0009] FIG. 1 is a side view of a chip mounted to a substrate by an
array of solder balls and with underfill material in a space
between the chip and the substrate.
[0010] FIG. 2 is a diagrammatic view of a system in accordance with
an embodiment of the invention.
[0011] FIG. 3 is a side view similar to FIG. 1 in which the
underfill material is in the process of being removed from the
space between the chip and the substrate with the assistance of
induction heating through the operation of the system of FIG.
2.
DETAILED DESCRIPTION
[0012] With reference to FIG. 1, an assembly 10 includes a
substrate 12 and a chip 14 that is mounted to a surface 16 of the
substrate 12. The chip 14 includes a plurality of pads 18 formed in
a topmost metallization level of the interconnect structure and
solder bumps 20 that are formed on, or placed onto, the pads 18.
The solder bumps 20 are configured to be reflowed to attach the
chip 14 to the substrate 12. In particular, each solder bump 20
mechanically attaches one of the chip pads 18 with one of a
plurality of pads 22 on the substrate 12 in a rigid connection. In
additional to the mechanical attachment, the solder bumps 20 and
pads 18, 22 provide electrical pathways for transferring signals
between the integrated circuit(s) of the chip 14 and an external
device, and also provide electrical pathways for powering and
grounding the integrated circuit(s) of the chip 14.
[0013] The solder bumps 20 may be separately formed and transferred
to the chip pads 18 by a controlled collapse chip connection (C4)
technology. Alternatively, each solder bump may be formed on its
chip pad 18 by electroplating using an appropriate plating
solution, an anode, a cathode, and a direct current supplied to the
anode/cathode while in the plating solution. The solder bumps 20
may be comprised of solder having a lead-free (Pb-free)
composition, a eutectic tin/lead (Sn/Pb) composition, a high lead
(Pb) composition, etc. An assembly including the chip 14, substrate
12, and the solder bumps 20 may be heated in a reflow oven to melt
the solder in the bumps 20. Upon solidification, the solder bumps
20 have respective metallurgical bonds with the pads 18, 22.
[0014] The substrate 12 may be comprised of an organic material,
such as a polymer or plastic, and the organic material may
optionally be reinforced with, for example, glass fibers.
Alternatively, the substrate 12 may be comprised of an inorganic
material, such as a ceramic. The pads 18, 22 may be comprised
primarily of aluminum (Al) or copper (Cu), and may further include
one or more layers of other materials, such as titanium tungsten
(TiW), nickel (Ni), etc., comprising under-bump metallurgy
(UBM).
[0015] Underfill material 24 may be introduced beneath the chip 14
into the space between the chip 14 and substrate 12 that is not
occupied by the solder bumps 20. The underfill process may entail
applying the underfill material 24 as a fluid to the substrate 12
adjacent to the perimeter of the chip 14 and allowing capillary
action to draw the underfill material 24 from the perimeter into
the space between the chip 14 and the substrate 12. When hardened
by curing, the underfill material 24 forms a strongly-bonded,
cohesive mass. Among other effects, the underfill material 24
protects the solder bumps 20 against various adverse environmental
factors, redistributes mechanical stresses due to shock, and
prevents the solder joints from shearing under strain experienced
during thermal cycles due to CTE mismatch.
[0016] The underfill material 24 may comprise a bulk matrix 25
comprised of, for example, a thermoplastic material that is an
electrical insulator and non-conductive. The bulk matrix 25 of the
underfill material 24 may include one or more polymerizable
monomers, polyurethane prepolymers, block copolymers, and radial
copolymers, as well as substances like initiators, catalysts,
cross-linking agents, stabilizers, etc. After the underfill
material 24 is located beneath the chip 14, the bulk matrix 25 of
the underfill material 24 is cured and hardened. For example,
thermoplastic materials may contain polymer molecules that can be
chained or cross-linked by heat, ultraviolet light, or another type
of electromagnetic energy to form a strongly bonded and cohesive
mass.
[0017] The underfill material 24 may further include a plurality of
particles 26 that are comprised of a material that is capable of
coupling with a time-varying magnetic field to induce eddy currents
and/or magnetic hysteresis losses in the particles 26 and to
thereby cause induction heating by one or the other, or both,
mechanisms. The particles 26 are dispersed or distributed in the
bulk matrix 25 to form a composite material made from multiple
constituent materials. The particles 26 are configured to respond
by generating heat energy when exposed to a time-varying magnetic
field by induction heating due to eddy currents and/or magnetic
hysteresis losses, and with an associated temperature rise as the
heat energy is generated. The bulk matrix 25 and any filler therein
are not electrically conductive and, therefore, do not heat or
otherwise generate heat energy in response to a time-varying
magnetic field. The time variation of the magnetic field induces
eddy currents eddy currents and/or magnetic hysteresis losses by
electromagnetic induction in the material constituting the
particles 26. Due to the electrical resistance of an
electrically-conducting material, eddy currents generate heat
energy by Joule heating. The temperature of the particles 26 rises
and heat energy flows outward from the particles 26 by thermal
conduction into the surrounding cured bulk matrix 25 comprising the
underfill material 24. The heating rate of the particles 26 may be
dependent, among other factors, on the frequency of the induced
currents, the intensity of the induced currents, the specific heat
of the constituent material, the magnetic permeability of the
material, and the electrical resistance of the material to the flow
of current.
[0018] In an embodiment, the particles 26 may be comprised of a
ferriceramic material, such as a ferrimagnetic material like
hematite (Fe.sub.2O.sub.3), magnetite (Fe.sub.3O.sub.4), or a
ferrite (MFe.sub.2O.sub.4, where M is a divalent ion such as
nickel, zinc, cadmium, manganese, or magnesium). Ferriceramic
materials are electrical insulators characterized by a low
electrical conductivity, yet heat when exposed to a time-varying
magnetic field due to magnetic hysteresis losses. Alternatively, if
the end use of the assembly 10 is tolerant to the addition of
particles 26 that are electrically conductive to the underfill
material 24 such that the dielectric properties of the bulk matrix
25 are reduced, the particles 26 may be comprised of a
ferromagnetic material, such as iron, nickel, cobalt, or an alloy
of these materials, that heat when exposed to a magnetic field due
to eddy currents and/or magnetic hysteresis losses. Incidental to
the ability to heat the bulk matrix 25 of the underfill material 24
with heat energy transferred from the particles 26 when immersed in
a time-varying magnetic field, the particles 26 may function to
improve the mechanical properties of the cured underfill material
24. The particles 26 may be spherical or near spherical in shape,
and may have a diameter or a distribution of diameters in the range
of 1 micron to 10 microns. Alternatively, the particles 26 may be
characterized by other shapes and sizes so long as the particles 26
have smaller dimensions than the solder bumps 20.
[0019] Heat energy from the distributed heat sources represented by
the heated particles 26 is transferred by thermal conduction to the
surrounding bulk matrix 25 of the underfill material 24. The
transferred heat energy causes the temperature of the surrounding
bulk matrix 25 to rise from room or ambient temperature to an
elevated temperature that is greater than room or ambient
temperature. In an embodiment, the heating of the underfill
material 24 may be sufficient to produce an elevated temperature
that induces a phase transition of the cured bulk matrix 25 of the
underfill material 24 from a solid phase to a liquid phase or a
semisolid state. As used herein, a semisolid state is characterized
by a consistency and/or viscosity intermediate between the solid
phase and the liquid phase of a material, and may also result as an
outcome when the cured bulk matrix 25 is liquefied.
[0020] The induction heating of the assembly 10 is selective in
that the underfill material 24 experiences a far greater
temperature rise than ether the chip 14 or the substrate 12. A
benefit of the selective heating, among other benefits, is that the
thermal aging of the substrate 12 may be reduced in comparison with
a rework process that melts the underfill material 24 by heating
the entire assembly 10, for example, in a reflow oven or with a
forced flow of heated air. While the underfill material 24 is in
the liquid phase or the semisolid state, the underfill material 24
may be removed from the space between the chip 14 and substrate 12,
for example, by suction or by a forced flow of heated or room
temperature air. The solder bumps 20 may be liquefied in a
subsequent heating process in order to facilitate the release of
the chip 14 from the substrate 12. In this embodiment, the removal
of the underfill material 24 and the liquefaction of the solder
bumps 20 occur during the performance of different heating
processes.
[0021] In another embodiment and in addition to increasing the
temperature of the cured bulk matrix 25 of the underfill material
24, the heating of the underfill material 24 may also be sufficient
to cause the solder bumps 20 to experience a phase transition from
a solid phase to a liquid phase or a semisolid state because of an
increase in the temperature of solder bumps 20. In order to be
liquefied, the solder bumps 20 do not have to be comprised of a
specially engineered solder material because the electromagnetic
properties of the particles 26 dispersed in the bulk matrix 25
couple with the time-varying magnetic field to provide the heat
source. The chip 14 may be removed from the substrate by, for
example, a spider rework in which the substrate 12 and chip 14 are
inverted with a weight attached to the chip 14. When the solder
bumps 20 and underfill material 24 are both liquefied,
gravitational forces assist in causing the chip 14 to be released
from the substrate 12. In this embodiment, the removal of the
underfill material 24 and the liquefaction of the solder bumps 20
occur during the performance of the same heating process.
[0022] The underfill material 24 may further include small
particles of a filler material comprised of an electrical
insulator, such as glass or silica, and dispersed in the bulk
matrix 25 in addition to the particles 26. Such optional filler
particles may function to further improve the mechanical properties
of the cured underfill material 24, but do not heat when exposed to
a time-varying magnetic field.
[0023] With reference to FIGS. 2, 3 and in accordance with an
embodiment of the invention, a system 30 is shown that is
configured to use induction heating to cause the underfill material
24 to heat through the heating of the particles 26 and experience a
temperature rise. The system 30 includes a controller 32 with at
least one processor 34 including at least one hardware-based
microprocessor and a memory 36 coupled to the at least one
processor 34. The memory 36 may represent the random access memory
(RAM) devices comprising the main storage of controller 32, as well
as any supplemental levels of memory, e.g., cache memories,
non-volatile or backup memories (e.g., programmable or flash
memories), read-only memories, etc. In addition, memory 36 may be
considered to include memory storage physically located elsewhere
in the controller 32, e.g., any cache memory in a microprocessor,
as well as any storage capacity used as a virtual memory, e.g., as
stored on a mass storage device or on another computer coupled to
the controller 32.
[0024] For interfacing with a user or operator, the controller 32
may include a user interface 38 incorporating one or more user
input/output devices, e.g., a keyboard, a pointing device, a
display, a printer, etc. Otherwise, input may be received via
another computer or terminal over a network interface 40 coupled to
a communication network. The controller 32 also may be in
communication with one or more mass storage devices, which may be,
for example, internal hard disk storage devices, external hard disk
storage devices, external databases, storage area network devices,
etc.
[0025] The controller 32 typically operates under the control of an
operating system 42 and executes or otherwise relies upon various
computer software applications, components, programs, objects,
modules, engines, data structures, etc., including for example, a
heater control module 44 and a removal control module 45. The
heater control module 44 may be configured to control the operation
of a power supply 46 when its instructions are executed by the at
least one processor 34 of the controller 32 in order to power an
induction heater 48 that causes the underfill material 24 to be
heated and experience a temperature rise above its initial
temperature (e.g., room temperature). The controller 32 may include
a power supply interface 50 that couples the controller 32 with the
power supply 46. The removal control module 45 may be configured to
control the operation of a removal apparatus 60 when its
instructions are executed by the at least one processor 34 of the
controller 32 in order to operate a removal apparatus 60 that is
configured to remove the underfill material 24. The underfill
material 24 may be removed either during heating of the underfill
material 24 by the induction heater 48 or after heating of the
underfill material 24 by the induction heater 48 while the
underfill material 24 is in a condition (i.e., a liquid phase or a
semisolid state) suitable for removal. The controller 32 may
include a removal apparatus interface 56 that couples the
controller 32 with the removal apparatus 60.
[0026] Moreover, various applications, components, programs,
objects, modules, etc. may also execute on one or more processors
in another computer coupled to the controller 32 via the
communication network, e.g., in a distributed or client-server
computing environment, whereby the processing required to implement
the functions of a computer program may be allocated to multiple
computers over a network. The memory 36 may store one or more data
structures including, for example, a database 52 configured with
records 54 to store data relating to the process (e.g., control
settings for the power supply 46, control settings for the removal
apparatus, etc.).
[0027] As best shown in FIG. 3, the induction heater 48 is located
proximate to the assembly 10 at the time of use to remove the
underfill material 24 from beneath the chip 14 in connection with
reworking the chip 14. In a representative embodiment, the
induction heater 48 may comprise an induction coil 49 consisting of
multiple turns of a helically-wound conductor. The time-varying
magnetic field, as indicated diagrammatically by the field lines
58, is formed in and around the turns of the induction coil 49,
when circulating a time-varying electrical current through the
induction coil 49, consistent with the Biot-Savart law. The
strength of the magnetic field generated by the induction heater 48
varies with distance from the induction coil 49 and may be on the
order of one (1) Tesla, although other field strengths may be
applicable.
[0028] The induction coil 49 of the induction heater 48 is coupled
by, for example, a high voltage cable with the power supply 46,
which in turn is in communication with the controller 32 through
the power supply interface 50. Time-varying electrical power is
supplied from the power supply 46 to the induction coil 49 of the
induction heater 48 in response to program code executed by the at
least one processor 34, user interaction with the user interface
38, and/or other instructions or input received by the at least one
processor 34. The power supply 46 may supply high-frequency
alternating current to the induction heater 48. In one embodiment,
the alternating current may be supplied to the induction heater 48
at a high frequency, such as at a radio frequency (e.g., 13.6 MHz).
The frequency of the alternating current generating the magnetic
field and the size of the particles 26 may be varied, among other
factors, to modify the specific characteristics of the heating.
[0029] The assembly 10 can be positioned relative to the induction
heater 48 such that the underfill material 24 between the substrate
12 and chip 14 is subjected to and influenced by the time-varying
magnetic field 58 emanating from the induction coil 49. The
induction coil 49 of the induction heater 48 may be dimensioned to
receive the chip 14 inside its inner diameter. In a representative
embodiment, the induction coil 49 of the induction heater 48 may
have an inner diameter on the order of two (2) inches to three (3)
inches with four (4) to five (5) turns and may be cooled by a
cooling medium flowing through a lumen of the induction coil 49.
Contact is not required between the chip 14 and the induction coil
49.
[0030] The removal apparatus 60 of the system 30 is configured to
remove the underfill material 24, once converted to a liquid phase
or semisolid state, from beneath the chip 14. The removal apparatus
60 may be configured to direct pressured gas or air (e.g., air
jets) at, for example, one or more side edges of the chip 14 and
thereby generate a removal force to displace the liquefied
underfill material toward opposite side edges of the chip 14. The
pressured gas or air may be maintained until the space beneath the
chip 14 is effectively cleared of the underfill material 24.
Alternatively, the removal apparatus 60 may be configured to apply
suction at one or more side edges of the chip 14 and thereby
generate a removal force to displace the underfill material 24
toward those side edges. The applied suction may be maintained
until the space beneath the chip 14 is effectively cleared of the
underfill material 24.
[0031] In use and with reference to FIGS. 1-3, the assembly 10 and
the induction heater 48 are arranged such that the cured underfill
material 24 can be exposed to the time-varying magnetic field
generated by current flowing through the induction heater 48. In
one embodiment, the induction coil 49 is placed around the chip 14
to provide a surrounding arrangement. The controller 32 then
energizes (or is caused to energize) the induction heater 48 by
causing the power supply 46 to supply a time-varying electrical
current to the induction coil 49 of the induction heater 48. The
time-varying electrical current in the induction coil 49 produces a
time-varying magnetic field in the space in and about the induction
coil 49 of the induction heater 48. At any given point in space
near the chip 14, the magnetic field may be specified by a
direction and a magnitude (or strength).
[0032] The time variation of the magnetic field induces eddy
currents and/or magnetic hysteresis losses by electromagnetic
induction in the material comprising the particles 26. Due to the
electrical resistance of the material, the electrical currents
generate heat by Joule heating and the temperature of the particles
26 rises. Heat energy is transferred outward from the heated
particles 26 by thermal conduction into the surrounding cured bulk
matrix 25 comprising the underfill material 24.
[0033] The heating time and parameters for the high-frequency
alternating current supplied to the induction heater 48 are
selected to transform the cured bulk matrix 25 from the solid phase
to a liquid phase or semisolid state. Specifically, the cured bulk
matrix 25 may be heated by the transferred heat energy to a
temperature that is greater than or equal to a liquefaction point.
The specific liquefaction point is contingent, among other factors,
upon the composition of the cured bulk matrix 25. The heating time
required to liquefy the cured bulk matrix 25 may be on the order of
tens to hundreds of microseconds. During the operation of the
induction heater 48, the heating of the chip 14 and the substrate
12 may be negligible.
[0034] While the bulk matrix 25 of the underfill material 24 is
liquefied by a phase transformation from its cured solid phase to a
liquid phase or a semifluid state, the removal apparatus 60 is
operated to remove the underfill material 24 from beneath the chip
14. After the underfill material 24 is removed, still liquefied in
advance of removal, or in the process of being removed, the
controller 32 may operate the power supply 46 to discontinue the
time-varying current in the induction coil 49 of the induction
heater 48, and thereby discontinue the application of the
time-varying magnetic field. After the underfill material 24 is
removed, the chip 14 may be removed or separated from the substrate
12 in a subsequent step that involves liquefying the solder bumps
20, for example, in a reflow oven or with heated air jets.
[0035] In an alternative embodiment, the solder bumps 20 on the
chip 14 may be heated by the heat energy generated from the
particles 26 in the underfill material 24 to a temperature that is
greater than the melting point of the constituent solder material,
which liquefies the solder bumps 20. Specifically, heat energy is
transferred outward from the cured bulk matrix 25 of the underfill
material 24 by thermal conduction to the solder bumps 20. The
degree of heating may be controlled through, among other factors,
selection of the properties on the particles 26 and the strength of
the magnetic field. While the underfill material 24 and the solder
bumps 20 are both in the liquefied state, the chip 14 is separated
from the substrate 12.
[0036] The cured bulk matrix 25 of the underfill material 24 and
the solder bumps 20 each possess a given melting temperature.
Though a selection of the constituent materials, the bulk matrix 25
of the underfill material 24 may be caused to liquefy and transform
to the liquid phase or semisolid state prior to the liquefaction of
the solder bumps 20 (i.e., the melting temperature of the bulk
matrix 25 is less than the melting temperature of the solder bumps
20). Alternatively, the bulk matrix 25 of the underfill material 24
may be caused to liquefy after the liquefaction of the solder bumps
20 (i.e., the melting temperature of the bulk matrix 25 is greater
than the melting temperature of the solder bumps 20).
[0037] Removing the underfill material 24 using induction heating
may reduce the impact of the heating on the material constituting
the substrate 12. For example, the use of induction heating may
eliminate wear-out mechanisms associated with the exposure of
certain type of substrates 12, such as plastic laminates, to an
excessive number of heat cycles. These wear-out mechanisms may
limit the number of permitted reworks of the solder bumps 20.
[0038] The methods as described above are used in the fabrication
of integrated circuit chips. The resulting integrated circuit chips
can be distributed by the fabricator in raw wafer form (that is, as
a single wafer that has multiple unpackaged chips), as a bare die,
or in a packaged form. The chip may be integrated with other chips,
discrete circuit elements, and/or other signal processing devices
as part of either (a) an intermediate product, such as a
motherboard, or (b) an end product. The end product can be any
product that includes integrated circuit chips, ranging from toys
and other low-end applications to advanced computer products having
a display, a keyboard or other input device, and a central
processor.
[0039] A feature may be "connected" or "coupled" to or with another
element may be directly connected or coupled to the other element
or, instead, one or more intervening elements may be present. A
feature may be "directly connected" or "directly coupled" to
another element if intervening elements are absent. A feature may
be "indirectly connected" or "indirectly coupled" to another
element if at least one intervening element is present.
[0040] The descriptions of the various embodiments of the present
invention have been presented for purposes of illustration, but are
not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to best explain the principles of the
embodiments, the practical application or technical improvement
over technologies found in the marketplace, or to enable others of
ordinary skill in the art to understand the embodiments disclosed
herein.
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