U.S. patent application number 10/845559 was filed with the patent office on 2005-11-17 for method and system for deflashing mold compound.
This patent application is currently assigned to Texas Instruments Incorporated. Invention is credited to Said, Mohd Hanafi Mohd.
Application Number | 20050255795 10/845559 |
Document ID | / |
Family ID | 35150741 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050255795 |
Kind Code |
A1 |
Said, Mohd Hanafi Mohd |
November 17, 2005 |
METHOD AND SYSTEM FOR DEFLASHING MOLD COMPOUND
Abstract
A method and system for deflashing mold compound is provided. In
one embodiment, a method for dislodging contaminants from an
integrated circuit includes directing sublimating particles against
a surface of the integrated circuit. Contaminants disposed on the
surface of the integrated circuit are abraded with the sublimating
particles to dislodge at least a portion of the contaminants.
Inventors: |
Said, Mohd Hanafi Mohd;
(Selangor, MY) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Assignee: |
Texas Instruments
Incorporated
|
Family ID: |
35150741 |
Appl. No.: |
10/845559 |
Filed: |
May 13, 2004 |
Current U.S.
Class: |
451/40 |
Current CPC
Class: |
B24C 1/083 20130101;
H01L 21/4864 20130101; H01L 2224/05553 20130101; H01L 2224/48247
20130101; H01L 24/97 20130101; H01L 2924/181 20130101; H01L 21/4835
20130101; H01L 2224/73265 20130101; H01L 2224/48091 20130101; H01L
2924/14 20130101; H01L 21/67051 20130101; B24C 3/12 20130101; B24C
1/003 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2224/48465 20130101; H01L 2924/00014 20130101; H01L 2224/48091
20130101; H01L 2924/00012 20130101; H01L 2224/48247 20130101; H01L
2924/00 20130101; H01L 2224/48247 20130101; H01L 2924/00 20130101;
H01L 2224/48465 20130101; B24C 3/322 20130101; H01L 2224/48465
20130101; H01L 2224/48465 20130101; H01L 2224/49175 20130101; H01L
2224/48091 20130101; H01L 2924/00 20130101; H01L 2924/14 20130101;
H01L 2924/181 20130101; H01L 2224/49175 20130101; H01L 2224/49175
20130101 |
Class at
Publication: |
451/040 |
International
Class: |
B24B 001/00 |
Claims
1. A method for dislodging contaminants from an integrated circuit,
comprising: directing sublimating particles against a surface of
the integrated circuit; abrading with the sublimating particles
contaminants disposed on the surface of the integrated circuit to
dislodge at least a portion of the contaminants, and directing a
liquid stream against the surface to remove at least a portion of
the dislodged contaminants from the surface.
2. The method of claim 1, wherein the sublimating particles are
mixed with high-pressure compressed air prior to being directed
against the surface.
3. The method of claim 1, wherein the sublimating particles
comprise frozen carbon dioxide.
4. The method of claim 1, wherein the contaminants are created
during encapsulation of the integrated circuit.
5. The method of claim 4, wherein the contaminants comprise at
least one of flash, resin burr, wax residue, and smear.
6. The method of claim 1, wherein the sublimating particles are
directed against the integrated circuit at a pressure ranging from
300 to 500 kilograms per square centimeter.
7. The method of claim 1, wherein the sublimating particles are
directed by at least one nozzle, further comprising moving the
integrated circuit at a rate of between 5 and 8 meters per minute
(m/min) relative to the at least one nozzle.
8. (canceled)
9. The method of claim 1, wherein the liquid stream comprises a
water jet.
10. The method of claim 1, wherein each sublimating particle has a
shape selected from the group consisting of a bead, rice-shaped
pellet, and a snow flake.
11. The method of claim 1, wherein the sublimating particles having
a coefficient of thermal expansion disparate from the
contaminant.
12. A system for dislodging contaminants from an integrated
circuit, comprising: at least one integrated circuit including
contaminants on at least a portion of the integrated circuit; at
least one deflashing nozzle operable to receive sublimating
particles and direct the sublimating particles against at least a
portion of the contaminants; and a rinse nozzle operable to direct
a liquid stream against the at least one integrated circuit for
removing at least a portion of the dislodged contaminants.
13. The system of claim 12, wherein the deflashing nozzle is
operable to receive a mixture of sublimating particles and a
propelling fluid and direct the mixture against the integrated
circuit for dislodging contaminants from the integrated
circuit.
14. The system of claim 12, wherein the sublimating particles
comprising frozen carbon dioxide.
15. The system of claim 12, wherein the contaminants are created
during encapsulation of the integrated circuit.
16. The system of claim 15, wherein the contaminants comprise at
least one of flash, resin burr, wax residue, and smear.
17. The system of claim 12, wherein the deflashing nozzle operable
to direct the sublimating particles at a pressure ranging from 300
to 500 kilograms per square centimeter.
18. The system of claim 12, further comprising a conveyor operable
to move the at least one integrated circuit with respect to the
deflashing nozzle at a rate ranging from range 5 to 8 meters per
minute.
19. (canceled)
20. The system of claim 12, wherein the liquid stream comprises a
water jet.
21. The system of claim 12, wherein each sublimating particle has a
shape selected from the group consisting of a bead, a rice-shaped
pellet, and a snow flake.
22. A system for dislodging contaminants from an integrated
circuit, comprising: at least one integrated circuit including
flash on at least a portion of the integrated circuit; a conveyor
operable to move the at least one integrated circuit with respect
to at least one deflashing nozzle at a rate ranging from range 5 to
8 meters per minute (m/min); the at least one deflashing nozzle
operable receive a mixture of frozen carbon dioxide beads and
high-pressure compressed air and direct the mixture against the
leadframe for dislodging the flash from the integrated circuit; and
at least one rinse nozzle operable to direct a water jet against
the at least one integrated circuit for removing at least a portion
of the dislodged flash.
Description
TECHNICAL FIELD
[0001] This invention relates generally to integrated circuit
device, and more particularly to a method system for deflashing
mold compound.
BACKGROUND
[0002] Semiconductor devices are used in a wide variety of
applications. The requirement for cheaper and smaller products
initiated the development of new semiconductor packaging
technology. A popular form of semiconductor packaging technology
includes attaching semiconductor devices to a metal frame called a
leadframe. Semiconductor devices are attached to the center of the
leadframe and are often encapsulated in a material such as an epoxy
molding compound. The encapsulation of the semiconductor devices
protects the delicate electrical devices from outside elements. In
addition, semiconductor encapsulation results in more robust
components having an acceptable level of reliability, particularly
for consumer applications. However, conventional methods of
encapsulation suffer from problems such as the formation of flash
on the leadframe. Flash can impair the physical and/or electrical
connections between leadframes and printed circuit boards, which
negatively impacts the reliability of the encapsulated
components.
[0003] Conventional deflashing processes typically use chemicals,
water, or hard solids immersed in water as agents for mold flash
removal. In the case of chemical treatment, strong acid or alkaline
chemicals are used to attack the interface between the mold flash
or resin and the leadframe surface, which creates waste and/or
recycling issues. After sufficient chemical activity, a water rinse
and water jet may be used to detach the mold flash or resin from
the leadframe or substrate surface. In the case of abrasive
blasting treatment, glass or crystal beads mixed with water may
also be used to blast the mold flash's or resin's top surface that
is in contact with the blasting agent; however, this process
results in pits or dents in leadframe surfaces and/or leadframe
warping.
SUMMARY OF THE INVENTION
[0004] A method and system for deflashing mold compound is
provided. In one embodiment, a method for dislodging contaminants
from an integrated circuit includes directing sublimating particles
against a surface of the integrated circuit. Contaminants disposed
on the surface of the integrated circuit are abraded with the
sublimating particles to dislodge at least a portion of the
contaminants.
[0005] One or more embodiments of the present invention may include
some, none, or all of the following technical advantages. For
example, some embodiments may utilize dry ice to cause contaminant
with a coefficients of thermal expansion different than the
leadframe to lose adhesion from leadframe. Other technical
advantages of one embodiment of the present invention may include
reducing, minimizing, or eliminating waste treatment or recycle
issues due to the absence of strong acid or alkaline chemicals and
pits or dents in leadframe surfaces and/or leadframe warping as a
result of the relative softness of the abrading agent. Another
technical advantage of one or more embodiments of the present
invention includes the provision of a more effective process than
conventional water jet method without some or all of the
disadvantages of other prior art techniques. Still another
technical advantage of one or more embodiments of the present
invention may include effective deflashing for moisture or chemical
sensitive packages which may not be deflashed using water-based
agents or strong acid or alkaline chemicals.
[0006] Certain embodiments may provide one or more other technical
advantages, one or more of which may be readily apparent to those
skilled in the art from the figures, description, and claims
included herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a more complete understanding of the present invention
and features and advantages thereof, reference is now made to the
following description, taken in conjunction with the accompanying
drawings, in which:
[0008] FIG. 1A illustrates a fabricated semiconductor wafer;
[0009] FIG. 1B illustrates an enlarged portion of the wafer of FIG.
1A;
[0010] FIG. 2A illustrates an example leadframe assembly FIG. 2B
illustrates a cross section of leadframe assembly of FIG. 2A;
[0011] FIG. 2C illustrates a cross section of encapsulated
leadframe assembly of FIG. 2A;
[0012] FIG. 3 illustrates one embodiment of a deflashing system
according to one embodiment of the present invention; and
[0013] FIG. 4 illustrates an example method for deflashing a
leadframe.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0014] Embodiments of the present invention and its advantages are
best understood by referring to FIGS. 1 through 4 of the drawings,
like numerals being used for like and corresponding parts of the
various drawings.
[0015] The semiconductor manufacturing process is divided into two
main processes: (1) wafer fabrication and (2) wafer testing,
assembly, and packaging. The process of wafer fabrication is a
series of steps that build successive layers of materials in and on
a blank silicon wafer to form a semiconductor device, such as an
integrated circuit. Examples of these steps include oxidation,
photolithography, deposition, metallization and chemical mechanical
planarization, among others. These wafer fabrication steps are well
known in the art and are not described in further detail.
[0016] FIGS. 1A and 1B illustrate the product that typically
results from wafer fabrication. This product is a fabricated wafer
10 comprising a grid of die 20 formed in and on a blank
semiconductor wafer 12. Each die 20 comprises an individual
semiconductor device (e.g., an integrated circuit) that was formed
during the fabrication stage. Fabricated wafer 10 may contain any
number of die 20, depending on their complexity and size. Each die
20 includes a number of bond pads or bonding pads 22 that line the
edges of die 20. Bond pads 22 are conductive areas coupled to
various parts of the integrated circuit such that electrical
signals may be supplied to the circuit. Bond pads 22 may be made
from any suitable conductive material, such as metal, may have any
suitable size and shape, and may be formed on die 20 in any
suitable pattern. Die 20 are separated on fabricated wafer 10 by
scribe channels 30 (alternatively called scribe lines or saw
lines). Scribe channels 30 comprise the area between the periphery
of each die 20 (the portions of blank wafer 12 on which circuits or
other structures have not been fabricated).
[0017] After wafer 10 has been fabricated, wafer 10 is functionally
tested during which time each die 20 may be marked as accepted or
rejected depending upon the results of the testing. Wafer testing
is well known in the art and is not described in further detail.
Wafers 10 arriving from the testing stage typically either have the
reject die marked with ink dots or are accompanied by a map of the
locations of any defects in the die which may have caused the die
to be rejected. The first step in the assembly stage is to separate
the die 20 by using a precision saw to cut down scribe channels 30
(alternatively, the die may be separated by scribing). The die 20
that were marked as rejects are discarded, and the die 20 that
passed the testing stage are each attached to a frame for packaging
(typically referred to as a leadframe), as described in more detail
with respect to FIGS. 2A and 2B.
[0018] FIG. 2A illustrates an example an integrated circuit (IC),
which in certain embodiments is a leadframe assembly 100. A cross
section of leadframe assembly 100 is illustrated in FIG. 2B.
Leadframe assembly 100 includes a leadframe 110, a die 20 attached
to leadframe 110, and wires 120 electrically coupling die 20 to
leadframe 110. A leadframe, such as leadframe 110, may be made from
any appropriate conductive material, such as metal, conductive
plastic, or others. In certain embodiments, leadframe 110 may
include a die attachment area 112. During packaging, die 20 is
attached to die attachment area 112 using a gold-silicon eutectic
layer, an epoxy adhesive material, or any other appropriate method
of attaching die 20 to die attachment area 112. Once die 20 is
attached to die attachment area 112, an automatic wire bonding tool
may be used to attach wires 120 to bond pads 22 and leads 114, such
that die 20 is electrically coupled to leads 114. In certain
embodiments, wires 120 may be made from any suitable conductive
material, such as aluminum or gold, and have a diameter less than
the diameter of a human hair. For example, wires 120 may have a
diameter of approximately 25 micrometers (em). After the
appropriate electrical connections have been made between die 20
and leadframe 110, a portion of leadframe assembly 100 may be
encapsulated in a plastic or epoxy such as, for example, mold 122
illustrated in FIG. 2B.
[0019] In one embodiment, to accomplish encapsulation of leadframe
assembly 100 in mold 122, leadframe assembly 100 is mounted between
a top and bottom mold die in a transfer molding machine where the
leadframe 110, in one embodiment, is covered with tape. In this
embodiment, the tape reduces, eliminates, or minimizes flash
forming on leadframe 110. The dies may be charged with pellets of a
molding compound, for example epoxy resin to form mold 122 around
leadframe assembly 100. Epoxy resin may include one or more of the
following: fused silica, inorganic fillers, catalyst, flame
retardants, stress modifiers, adhesion promoters, and other
suitable components. Even in light of the tape applied to leadframe
110, a contaminant 124 (illustrated in FIG. 2C) may form on
leadframe 110. Contaminant 124 may comprise resin burrs, flash,
smear, wax residue, or any other contaminant. Areas of contaminant
124 are undesirable because contaminant 124 may interfere with the
connection of LEADFRAME ASSEMBLY 100 with a printed circuit board.
For example, contaminant 124 may interfere with an electrical
connection between leadframe 100 and a printed circuit board.
Accordingly, contaminant 124 may be substantially dislodged from
leadframe 110 by the system illustrated in FIG. 3.
[0020] FIG. 3 illustrates one embodiment of a deflashing system 300
for dislodging contaminants 124 from leadframes 110 and/or other
portions of LEADFRAME ASSEMBLY 100. It will be understood that
deflashing system 300 may be used to dislodge contaminants other
than flash such as, for example, resin burrs, smear, and other
contaminants, and the term "deflashing," as used herein, refers to
the removal of any such contaminants. Referring to FIG. 3,
deflashing system 300 includes conveyor 310, deflashing nozzle 312,
and rinse nozzles 314. At a high level, conveyor 310 moves
leadframe assemblies 100 relative to deflashing nozzles 312 such
that sublimating particles 316 directed by deflashing nozzle 312
abrasively dislodge contaminants 124 from leadframes 110. After
dislodgment, rinse nozzles 314 rinse away at least a portion of the
dislodged contaminants 124. During the abrasion process, leadframe
assemblies 100 are oriented such that the bottom of leadframe
assemblies 100 as illustrated in FIG. 2A are abraded with
sublimating particles 316.
[0021] Conveyor 310 moves leadframe assemblies 100 relative to
deflashing nozzles 312 and rinse nozzles 314. Conveyor 310 is
operable to move leadframe assemblies 100 at any suitable speed.
For example, conveyor 310 may move leadframe assemblies 100
relative to deflashing nozzle 312 and rinse nozzles 314 at a speed
selected from the range 5 to 8 meters per minute (m/min).
[0022] Each deflashing nozzle 312 receives sublimating particles
316 and a propelling fluid and directs sublimating particles 316
against leadframe assemblies 100. The propelling fluid provides
force to sublimating particles 316 such that sublimating particles
316 exit deflashing nozzle 312 at a sufficient pressure to
abrasively dislodge at least a portion of contaminant 124. In one
embodiment, the propelling fluid comprises high pressure air such
that sublimating particles 316 exit deflashing nozzle 312 with a
pressure of 300 to 500 kilograms per square centimeter
(kg/cm.sup.2). The propelling fluid may comprise any other suitable
fluids that provide sublimating particles 316 sufficient pressure
to abrasively dislodge at least a portion of contaminant 124.
Moreover, the resulting pressure of sublimating particles 316 may
be substantially continuous, intermittent, variable, stepped,
ramped, tapered, a combination of the foregoing, or otherwise. The
propelling fluid and sublimating particles 316 may be mixed prior
to entering deflashing nozzle 312 or, alternatively, in connection
with entering deflashing nozzle 312. In the illustrated embodiment,
deflashing nozzles 312A-D are arranged in a stationary one
dimensional array wherein the mixture of sublimating particles 316
and propelling fluid exit deflashing nozzle 312 in a substantially
conical pattern. In another embodiment, deflashing system 300 may
include a plurality of deflashing nozzles 312 in a two dimensional
or otherwise configured array that provide streams of sublimating
particles 316 for dislodging contaminants 124. Alternatively,
deflashing system 300 may comprise one or more rastering deflashing
nozzles 312 that provides at least one stream of sublimating
particles 316 that rasters over at least a portion of at least one
leadframe 110. In short, deflashing nozzle 312 directs sublimating
particles 316 against leadframes 110.
[0023] Sublimating particles 316 exit deflashing nozzle 312 and
impact leadframes 110 and contaminants 124. As used herein,
sublimating particle means a particle that sublimates from a solid
to a gas. It will be understood that when referring to sublimating
particle that this disclosure is also referring, where appropriate,
to particles that substantially sublimate. For example, sublimating
particles 316 may substantially comprise frozen carbon dioxide
(CO.sub.2). Sublimating particles 316 may comprise other suitable
particles such as for example frozen sulfur. Alternatively,
leadframes 110 may be abraded by particles comprising
non-sublimating frozen particles that are gaseous at normal
operating conditions such as, for example, frozen nitrogen. In this
alternative, deflashing system 300 operates as described except
substituting sublimating particles 316 with non-sublimating frozen
particles that are gaseous at normal operating conditions. It will
be understood that "sublimating particles" may include, where
appropriate, "non-sublimating frozen particles that are gaseous at
normal operating conditions."
[0024] Sublimating particles 316 may have uniform or varied shapes
or, alternatively, may alternate between the foregoing over time.
For example, each sublimating particle may comprise one of the
following shapes: a bead, a pellet, a rice-shaped pellet, a snow
flake, or otherwise shaped particle. Additionally, one or more of
sublimating particles 316 may be generated by shaving and/or
pulverizing a frozen block. In one embodiment, sublimating
particles 316 comprises rice-shaped pellets with a diameter in the
range of 0.05 to 0.1 inches and a length in the range of 0.10 to
0.50 inches. The temperature difference between sublimating
particles 316 and contaminants 124 may weaken the chemical and/or
physical bonds between contaminant 124 and leadframe 110. In
addition, the kinetic energy of sublimating particle may dislodge
at least a portion of contaminant 124 that may result in dislodged
contaminants on leadframe 110.
[0025] After abrasion by the sublimating particles, rinse nozzles
314 directs a liquid stream 318 against leadframes 110 for removing
at least a portion of the contaminants dislodged by particles 316.
In the illustrated embodiment, deflashing system 300 includes a
one-dimensional array of rinse nozzles 314A-D that directs a water
jet 318 against leadframes 110. In another embodiment, deflashing
system 300 may include a plurality of rinse nozzles 314 in a
two-dimensional or otherwise configured array that provide liquid
streams 318 for dislodging dislodged contaminants from leadframe
110. Alternatively, deflashing system 300 may comprise one or more
rastering rinse nozzles 314 that provides at least one liquid
stream 318 that rasters over a portion of at least one leadframe
110. The liquid may comprise deionized water. Liquid stream 318 may
exit rinse nozzle 314 at any appropriate pressure such as, for
example, in the range of 100 to 200 kilograms per square centimeter
(kg/cm.sup.2) or 1422 to 2844 pounds per square inch (psi).
Moreover, the resulting pressure of liquid stream 318 may be
substantially continuous, intermittent, variable, stepped, ramped,
tapered, a combination of the foregoing, or otherwise.
[0026] In one aspect of operation, deflashing nozzles 312 receive a
mixture of sublimating particles and propelling fluid. In one
embodiment, the mixture includes CO.sub.2 beads and high-pressure
compressed air. Each deflashing nozzle 312 directs the mixture
against an impact spot while conveyor 310 moves leadframe
assemblies 100 relative to the impact spot such that sublimating
particles 316 are swept across leadframe assemblies 100 and
contaminants 124. For example, conveyor 310 may move leadframe
assemblies 100 at a relative rate of 5 to 8 meters per minute
(m/min). The sublimating particles 316 impact leadframe assemblies
100 and contaminates 124 dislodging at least a portion of the
contaminants 124 from leadframe assemblies 100. After at least a
portion of the contaminants 124 is dislodged, conveyor 310 moves
leadframe assemblies 100 relative to the impact spot of liquid
stream 318 directed by rinse nozzles 314, substantially removing
the dislodged contaminants.
[0027] FIG. 4 is an exemplary flow diagram illustrating a method
400 for deflashing leadframes 110. Method 400 is described with
respect to deflashing system 300 of FIG. 3, but method 400 could
also be used by any other system. Moreover, system 300 may use any
other suitable technique for performing these tasks. Thus, many of
the steps in this flowchart may take place simultaneously and/or in
different orders as shown. Moreover, system 300 may use methods
with additional steps, fewer steps, and/or different steps, so long
as the methods remain appropriate.
[0028] At a high level, method 400 illustrates two processes for
removing contaminants from a leadframe: an abrasion process and a
rinse process. The abrasion process is illustrated in steps 404 to
416, and the rinse process is illustrated in steps 418 to 424.
Method 400 begins at step 402 where sublimating particles 316 are
generated as discussed in detail above. Next, at step 404,
sublimating particles 316 and propelling fluid 318 are mixed. The
mixture is received at deflashing nozzles 314 at step 406. At step
408, deflashing nozzles 314 direct the mixture against conveyer
310. Sublimating particles 316 exit deflashing nozzles 314 at step
410. Leadframes 110 are moved relative to deflashing nozzles 312 at
step 412. Contaminants 124 on leadframes 110 are impacted with
sublimating particles 316 at step 414. At least a portion of
contaminant 124 is dislodged at step 416, which may result in
dislodged contaminants on leadframes 110.
[0029] As mentioned above, steps 418-424 illustrate the rinse
process executed by deflashing system 300. At step 418, rinse
nozzles 314 direct water jets against conveyor 310. Next, at step
420, water jets 318 exit rinse nozzles 314. Leadframes 110 are
moved relative to rinse nozzles 314 at step 422. Next, at step 424,
leadframes 110 are rinsed with water jet 318 to remove dislodged
contaminants from leadframes 110 and then the method ends.
[0030] Although the present invention has been described with
several embodiments, diverse changes, substitutions, variations,
alterations, and modifications may be suggested to one skilled in
the art, and it is intended that the invention encompass all such
changes, substitutions, variations, alterations, and modifications
as fall within the spirit and scope of the appended claims.
* * * * *