U.S. patent number RE43,980 [Application Number 13/032,199] was granted by the patent office on 2013-02-05 for laser decapsulation method.
This patent grant is currently assigned to Intersil Corporation. The grantee listed for this patent is Robert K. Lowry. Invention is credited to Robert K. Lowry.
United States Patent |
RE43,980 |
Lowry |
February 5, 2013 |
Laser decapsulation method
Abstract
A decapsulation apparatus 100 has a laser 8 that removes plastic
encapsulant from a device 24. Chamber 20 is sealed. Exhaust port 9
removes debris and fumes. The device 24 is positioned and scanned
using an X, Y table 2. A hinged end 4 rotates the device to an
acute angle of incidence with respect to a laser 8. Endpoint
detector 10 senses the exposed integrated circuit and moves or
shuts down the laser 8.
Inventors: |
Lowry; Robert K. (Indialantic,
FL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lowry; Robert K. |
Indialantic |
FL |
US |
|
|
Assignee: |
Intersil Corporation
(Melbourne, FL)
|
Family
ID: |
23191632 |
Appl.
No.: |
13/032,199 |
Filed: |
February 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12435441 |
May 5, 2009 |
Re. 42193 |
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09949736 |
Jan 8, 2008 |
7166186 |
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09307896 |
Feb 10, 2011 |
6335208 |
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Reissue of: |
11616617 |
Dec 27, 2006 |
7316936 |
Jan 8, 2008 |
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Current U.S.
Class: |
438/15; 438/940;
257/E21.521 |
Current CPC
Class: |
H01L
21/56 (20130101); H01L 22/20 (20130101); B23K
26/0853 (20130101); H01L 2924/0002 (20130101); Y10S
438/94 (20130101); B23K 2101/40 (20180801); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
G01R
31/26 (20060101) |
Field of
Search: |
;438/4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2731637 |
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Sep 1996 |
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FR |
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2177965 |
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Feb 1987 |
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GB |
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63032957 |
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Feb 1988 |
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JP |
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8607492 |
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Dec 1986 |
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WO |
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0115191 |
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Mar 2001 |
|
WO |
|
Other References
Carter, George, "Laser Decapsulation of Transfer Molded Plastic
Packages for Failure Analysis", "Proceedings from the 28th
International Symposium for Testing and Failure Analysis", 2002,
Publisher: ASM International, Published in: Phoenix, AZ. cited by
applicant.
|
Primary Examiner: Smoot; Stephen W
Attorney, Agent or Firm: Fogg & Powers LLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
.[.This Application is a continuation application of U.S. patent
application Ser. No. 09/949,736, filed Sep. 10, 2001, now U.S. Pat.
No. 7,166,186; which is a divisional application of U.S. patent
application Ser. No. 09/307,896, filed May 10, 1999, now U.S. Pat.
No. 6,335,208..]. .Iadd.Notice: More than one reissue application
has been filed for the reissue of U.S. Pat. No. 7,316,936. The
reissue applications are reissue application Ser. No. 12/435,441
(Reissue U.S. Pat. No. Re. 42,193) (the parent reissue) and reissue
application Ser. No. (13/032,199) (the present continuation
reissue)..Iaddend.
.Iadd.Both reissue applications are reissues of the same U.S. Pat.
No. 7,316,936. U.S. Pat. No. 7,316,936 is a continuation of Ser.
No. 09/949,736, filed Sep. 10, 2001, now U.S. Pat. No. 7,166,186;
which is a divisional application of U.S. patent application Ser.
No. 09/307,896, filed May 10, 1999, now U.S. Pat. No.
6,335,208..Iaddend.
Claims
What is claimed is:
.[.1. A method of manufacturing integrated circuits, the method
comprising; forming encapsulated integrated circuits; and sampling
select integrated circuits to verify if the finished integrated
circuits are made to manufacturing specifications by selectively
removing portions of the encapsulation with a laser that is
suitable for breaking cross linked bonds of the encapsulant without
damaging the integrated circuits, wherein a thin layer of
encapsulant is left on at least one portion of at least one of the
sampled integrated circuits..].
.[.2. The method of claim 1, wherein selectively removing portions
of the encapsulant of the select sampled integrated circuits
further comprises: monitoring amplitude and frequency of the laser
light reflected of each selected integrated circuit; and when a
change in at least one of the amplitude and frequency is detected,
moving each selected integrated circuit..].
.[.3. The method of claim 2, wherein moving each selected
integrated circuit further comprises: advancing a stage upon which
the select integrated circuit is mounted on..].
.[.4. The method of claim 1, wherein selectively removing portions
of the encapsulant of the select sampled integrated circuits with a
laser further comprises: using a laser with wavelengths in the
infrared range that includes at least one range of 725-900 cm-1,
1150-1300 cm-1, 1400-1500 cm-1 and 1600-1750 cm-1..].
.[.5. The method of claim 1, wherein selectively removing portions
of the encapsulation of the select sampled integrated circuits with
a laser further comprises: using at least one of a YAG laser and an
infrared laser..].
.[.6. The method of claim 1, wherein selectively removing portions
of the encapsulation of the select sampled integrated circuits
further comprises: changing an angle of incident of the laser by
rotating a stage upon which the integrated circuits are
mounted..].
.[.7. The method of claim 1, further comprising: testing the thin
layer of encapsulant for contaminates..].
.[.8. The method of claim 1, wherein selectively removing portions
of the encapsulation of the select sampled integrated circuits
further comprises: removing debris caused by the removal of select
portions of encapsulate by at least one of using a flow of gas to
direct the debris away from the integrated circuits and capturing
the debris in a dust bin..].
.[.9. A method of manufacturing integrated circuits, the method
comprising: forming integrated circuits with a manufacturing
process, wherein each integrated circuit is encapsulated to protect
the integrated circuit from environmental factors; selecting
certain formed integrated circuits; placing each selected
integrated circuit on a stage in an enclosure; directing a laser
beam having a select wavelength on a select portion of the
encapsulant to remove the select portion of encapsulant, wherein
with at least one of the select integrated circuits the select
removed portion of encapsulant has a depth, the depth being less
than a thickness of the encapsulant; monitoring the laser beam
reflected off of the integrated circuit; moving the stage based at
least in part on the monitored reflected laser beam; terminating
the laser beam based at least in part on the monitored reflect
laser beam; and testing the selected integrated circuits with the
select portion of encapsulant removed to verify that the integrated
circuits are formed to manufacture specifications..].
.[.10. The method of claim 9, further comprising: exhausting debris
from the enclosure..].
.[.11. The method of claim 10, wherein exhausting debris from the
stage further comprises: directing a flow of gas to disperse the
debris away from the integrated circuit..].
.[.12. The method of claim 9, further comprising: catching debris
particles in a dust bin..].
.[.13. The method of claim 9, further comprising: testing for
contaminates in a thin layer of encapsulant left on the at least
one select integrated circuit having the select removed portion
with a depth less than the depth of the encapsulant..].
.[.14. A manufacturing method of removing encapsulant from an
integrated circuit; the method comprising: placing an integrated
circuit on a stage in an enclosure; directing a laser beam on the
encapsulation of the integrated circuit, wherein the laser beam has
a wavelength that is suitable for breaking cross linked bonds of
the encapsulant without damaging the underlying integrated circuit;
removing at least one select portion of the encapsulant with the
laser beam; and capturing debris particles in a dust bin..].
.[.15. The method of claim 14, further comprising: monitoring the
laser beam reflected off of the integrated circuit; and based at
least in part on the monitored laser beam, doing at least one of
moving the stage and terminating the laser beam..].
.[.16. The method of claim 14, further comprising: after the
removing the at least one select portion of the encapsulant,
verifying the integrated circuit is made to manufacturing
specifications..].
.[.17. The method of claim 14, further comprising: directing a flow
of gas to move the debris away from the integrated circuit..].
.[.18. The method of claim 14, further comprising: leaving a thin
layer of encapsulant at the at least one select portion, and
testing for contaminates in the thin layer of encapsulant..].
.Iadd.19. A method of manufacturing encapsulated devices, the
method comprising: forming encapsulated devices with a
manufacturing process, wherein each encapsulated device is
encapsulated to protect the encapsulated device from environmental
factors; selecting certain formed encapsulated devices; placing
each selected encapsulated device on a stage in an enclosure;
directing a laser beam having a select wavelength on a select
portion of the encapsulant to remove the select portion of
encapsulant; catching debris particles in a dust bin; and testing
the selected encapsulated devices with the select portion of
encapsulant removed to expose failed encapsulated devices without
physical or other damage, to enable direct inspection and failure
analysis procedures to determine a cause of failure..Iaddend.
.Iadd.20. A method of manufacturing encapsulated devices, the
method comprising: forming finished encapsulated devices with a
manufacturing process, wherein each finished encapsulated device is
encapsulated to protect the finished encapsulated device from
environmental factors; selecting failed finished encapsulated
devices; placing each selected, failed finished encapsulated device
on a stage in an enclosure; directing a laser beam having a select
wavelength on a select portion of the encapsulant to remove the
select portion of encapsulant; and testing the selected, failed
finished encapsulated devices with the select portion of
encapsulant removed..Iaddend.
.Iadd.21. The method of claim 20, wherein testing the selected,
failed finished encapsulated devices comprises testing the
selected, failed finished encapsulated devices to identify process
flaws..Iaddend.
.Iadd.22. The method of claim 20, wherein testing the selected,
finished failed encapsulated devices comprises testing the
selected, failed finished encapsulated devices to discover how the
device is constructed..Iaddend.
.Iadd.23. The method of claim 20, and further comprising detecting
process flaws based on said testing and correcting said process
flaws..Iaddend.
.Iadd.24. A method of manufacturing encapsulated devices, the
method comprising: forming encapsulated devices with a
manufacturing process, wherein each encapsulated device is
encapsulated to protect the encapsulated device from environmental
factors; selecting certain failed encapsulated devices; placing
each selected, failed encapsulated device on a stage in an
enclosure; directing a laser beam having a select wavelength on a
select portion of the encapsulant to remove the select portion of
encapsulant; catching debris particles in a dust bin; and testing
the selected encapsulated devices with the select portion of
encapsulant removed to expose the selected, failed encapsulated
devices without physical or other damage, to enable inspection of
the selected, failed encapsulated devices..Iaddend.
.Iadd.25. A method of removing encapsulant from an encapsulated
device, the method comprising: placing a finished encapsulated
device on a stage in an enclosure; directing a laser beam on the
encapsulation of the finished encapsulated device; and removing at
least one select portion of the encapsulant with the laser
beam..Iaddend.
Description
BACKGROUND
This invention relates generally to an apparatus and method for
removing plastic compounds that encapsulate integrated circuits and
particularly, to a laser-equipped apparatus and method for
decapsulating plastic encapsulated integrated circuits.
The vast majority of integrated circuits are packaged in plastic
resins including but not limited to biphenyl, orthocresol novolac,
and dicyclopentadienyl types. The plastic package seals the
enclosed integrated circuit from the external environment,
including moisture and dust. The resin contains fillers such as
silica or other insulating materials to enhance the physical and
mechanical properties of the package. The integrated circuits are
encapsulated using a transfer molding process. During that process
a solid charge of resin is melted and then forced under pressure
into a multi cavity mold that contains a number of integrated
circuits. One mold may contain tens or hundreds of integrated
circuits. The size of the molded integrated circuits varies in
length, width and height. As the resins cool, their molecules
cross-link into a solid resin. Some devices using the standard
dual-in-line package are several millimeters thick. Other small
outline packages are a millimeter in thickness.
There are a number of reasons for removing the plastic encapsulant
from finished Integrated circuits. One reason is to monitor the
manufacturing process. In most mass manufacturing processes,
samples of finished product are often taken and analyzed to check
whether or not the finished product is made to the manufacturing
specifications. When one or more devices fail, it is desirable to
analyze those failed devices to detect process flaws so that the
flaws can be corrected. Some devices are also reverse engineered in
order to discover how the device is constructed.
Current techniques for removing the plastic are time consuming and
environmentally unfriendly. One acid etching technique uses fuming
nitric or sulfuric acid. That technique can take several hours or
more to remove the plastic, and the spent chemicals must be
properly disposed of. In addition, these harsh chemicals come in
contact with the surface of the integrated chip being exposed,
which may chemically remove foreign substances or contaminants
residing between the top of the die and the mold compound which
will subsequently not be detected in failure analysis. Plasma
etching may be used but it is slow and also leaves undesired
residues. As such, there is a long felt and unfulfilled need for a
faster process that is environmentally friendly and less disruptive
to the top surface of the integrated circuit chip.
SUMMARY
The invention eliminates hazardous acid waste and provides a faster
decapsulation process which is less disruptive to the top-of-die
surface. The invention provides an apparatus and method for
removing plastic encapsulant using a tunable laser. A chamber has a
stage for holding the integrated circuit during decapsulation. The
stage is an X, Y table that comprises rods so that encapsulant
debris may fall between the rods. Below the stage is a dust bin for
collecting the debris. A hinge on the table lets the operator
adjust the angle of incidence of the laser beam on the surface of
the device under test.
A laser outside the chamber shines its beam through a window or
other suitable optical opening onto the surface of the device under
test. The laser beam is tunable in frequency and intensity to
suitable settings for removing the encapsulant. The laser beam is
generated by a YAG or infrared laser or any other laser suitable
for breaking the cross linked bonds of the encapsulant without
damaging the integrated circuit.
The decapsulation process is controlled by a computer that includes
a microprocessor or digital signal processor, suitable memory, an
application program for operating the apparatus and suitable
sensors. One sensor is an endpoint detector. It is focused on the
integrated circuit to detect reflected light. Where the plastic is
removed, the beam strikes the integrated circuit and the amplitude
and frequency of the reflected light changes. The endpoint detector
senses those changes. In response to a signal indicating that the
integrated circuit is exposed, the computer shuts down the laser
beam or moves the laser beam to a new location.
The apparatus has a sealed chamber. Fumes generated by
decapsulation are exhausted through a suitable fan or
blower-operated exhaust port. A cleaning gas such as nitrogen or
compressed air is directed at the surface of the integrated circuit
to remove dust and debris. The removed dust and debris are either
exhausted or fall into the dust bin.
DRAWINGS
FIG. 1 is a sectional elevation view of the invention showing the
integrated circuit oriented at a near normal angle to the laser
beam.
FIG. 2 is a further view showing the integrated circuit oriented at
an acute angle of incidence to the laser beam.
DETAILED DESCRIPTION
Turning to FIG. 1, there is shown a decapsulation apparatus 100
that comprises a chamber wall 12 that encloses and seals a chamber
20. The chamber 20 has a clean gas inlet 11 with a conduit 22 that
directs a stream of clean gas, such as nitrogen or compressed air
at a device under test (DUT), i.e., integrated circuit 24. Chamber
20 also has an exhaust port 9 for removing fumes and dust particles
from the chamber. Within the chamber is a stage 2 that is disposed
over a dust bin 3. The dust bin 3 catches dust and debris that are
generated by the laser striking the plastic resin on the DUT
24.
A laser 8 is mounted on the outside wall 12 of the chamber 20. The
laser directs a laser beam 26 toward the DUT 24. The laser 8 is any
suitable laser, such as a YAG or an infrared laser. The laser 8 has
its frequency and its intensity (power) tunable for removing
plastic encapsulant from the DUT 24 without causing damage to the
encapsulated integrated circuit. The laser beam 26 passes through
an optical opening or window (not shown) in the wall 12 of the
chamber 20. The interior of the chamber 20 is illuminated by a
suitable light 7. Operation of the laser on the DUT 24 is observed
through a microscope 5. This is also mounted on wall 12. The
microscope 5 has a shutter 6 that may be manually or automatically
operated as hereinafter described. Light reflected from the surface
of the DUT 24 is detected by endpoint detector 10. The endpoint
detector 10 senses the amplitude or frequency or both of the
reflected light. The endpoint detector is any suitable
photosensitive device that responds to changes in sensed frequency
or intensity.
The stage 2 is an X, Y positioning table. It is desirable that the
stage be made of rods or a perforated table so that dust and debris
removed from the DUT 24 falls through the stage and the stage mount
into the dust bin 3. Such X, Y positioning tables are well known in
the art. They maybe operated using piezoelectric operators, linear
magnetic motors, or lead screws. As shown in FIG. 1, the DUT 24 is
disposed at substantially a normal angle to the laser beam 26. The
stage is hinged at one end 4 so that the DUT 24 may be rotated to a
substantially vertical position as shown in FIG. 2. In its vertical
position, the laser beam 26 has an acute angle of incidence with
the surface of the DUT 24. That particular position is useful when
it is desired to leave a thin layer of encapsulant on the surface
of the integrated circuit. Leaving such a thin layer is often
desired during failure analysis to detect contaminants on the
surface of the encapsulated DUT 24.
The apparatus 100 may be manually operated or automatically
operated or may be semiautomatically operated. For automatic and
semiautomatic operation, the apparatus 100 is provided with a
controller 50. The controller 50 includes a CPU 51 which may be a
microprocessor or a digital signal processor. The CPU 51
communicates with a random access memory 53 and a read-only memory
54. Suitable operating software and application software are stored
in the RAM 53 or ROM 54. The CPU 51 controls operations of the
various components of the apparatus 100 via the control bus 30 and
the control lines 31-37 that are respectively connected to the
microscope shutter 6, laser 8, stage 2, clean gas inlet 11,
endpoint detector 10, exhaust port 9, and joy stick 40. By manual,
automatic or semiautomatic operation, the operator may selectively
operate any one of the controlled components, move the stage to its
desired X, Y position, and rotate the top platform of the stage to
its desired Z axis orientation.
The following wavelengths in the infrared range are especially
applicable: 725-900 cm-1, 1150-1300 cm-1, 1400-1500 cm-1 and
1600-1750 cm-1. These wavelength ranges were determined from IR
chemical analysis of the mold compound resins. See "Identifying
Plastic Encapsulant Materials by Pyrolysis Infrared
Spectrophotometry", R. K. Lowry, K. L. Hanley, Proceedings, 1998
Intl Symposium for Testing and Failure Analysis, November, 1998,
pp. 399-401. It is these wavelength ranges in particular where
there is significant absorption of IR energy at the molecular level
by plastic resins. An incident beam tuned for maximized power in
these energy ranges begins to promote molecular rearrangement and
ultimately decompositional breakdown of polymerized resin
molecules. Any tuned laser operating in these ranges promotes
breakdown not just by thermal heating the material (which almost
any incident laser energy with enough power could provide) but also
by chemical decomposition. This promotes breakdown in a
"material-specific" way, so that excessive heating via
straightforward but less-controllable thermal decomposition can be
avoided.
In operation, a DUT 24 is placed or otherwise mounted on the top of
the stage 2. While the embodiment shown in FIG. 1 includes only a
single device, those skilled in the art will appreciate that
multiple devices may be mounted on the stage. Either manually or
with the assistance of controller 50, the stage 2 is positioned in
an X, Y plane relative to the laser beam 26, of laser 8. Laser 8 is
under control of the controller 50. Laser 8 may be any suitable
laser that has its amplitude and frequency tuned and controlled by
controller 50. Such suitable lasers include YAG lasers, as well as
infrared lasers. It is desired to use a laser with a suitable power
and frequency for breaking the cross-linked polymeric bonds of the
plastic resin that encapsulates the DUT 24. The laser may be
operated at a relatively low level to provide a target beam that
strikes the stage and the DUT 24. The operator may then position
the stage by using a joy stick device 40 and the microscope 5. In
the preferred embodiment, the stage is moved to initially place the
laser on one of the corners of the DUT 24. Once the starting point
for the laser has been selected, then the stage moves in a raster
pattern along a first axis, steps transverse to the first axis at
least the width of the beam, and then reverses direction and
travels back along the first axis. In this manner, the beam 26
raster-scans across the DUT 24. Of course, if desired, the laser
beam 26 may be raster-scanned using optical methods, including
prisms and/or mirrors that are selectively moved to sweep the beam
across the surface of the DUT 24.
When the beam 26 is operated at its effective frequency and
intensity, the plastic encapsulant is removed from the DUT 24. The
removal process creates a cloud of debris and fumes. The fumes and
some lighter debris particles are withdrawn from the chamber 20 via
the exhaust port 9. The heavier debris particles fall through the
rods or holes in the stage 2 and are captured in the dust bin 3.
Some of the dust may settle onto the DUT 24. Clean gas 22 drives
the dust away from the DUT 24. The clean gas 22 includes any
suitable gas, such as nitrogen or air for dispersing the dust
particles away from the surface of the DUT 24. Such dispersal
permits the operator to view the DUT in process and removes
particles from the immediate path of the laser so that the
encapsulant is more effectively removed.
Decapsulation may be carried out automatically. During automatic
decapsulation, the laser is operated until the endpoint detector 10
detects a change in the amplitude and/or frequency of light
reflected from the DUT 24. When the integrated circuit is
uncovered, the reflected light changes its frequency. The intensity
of reflected light may also change. The DUT detects these changes
and provides a signal via signal and control line 35 to the
controller 50.
Controller 50 receives and sends signals on control and sensor bus
30 via an A-to-D and D-to-A converter 52. The control and sensing
signals are analog signals. Thus, it is necessary to convert the
analog signals to digital signals so that they can be understood by
the CPU 51. If the CPU 51 is a DSP, the DSP has a built-in A-to-D
and D-to-A converter.
Controller 50 receives the signal from the endpoint detector 10.
When the endpoint detector 10 signals that the integrated circuit
is uncovered, the controller 50 advances the stage to the next
position to continue removing encapsulant. As such, for a given
beam width, the laser is focused on the DUT 24 until the underlying
integrated circuit is exposed. Upon detection of the exposed
integrated circuit, the stage is moved in a continuous or stepwise
pattern to subsequent positions.
As indicated above, it is also possible to manually operate the
apparatus or to semi-automatically operate the apparatus. For
example, it is often desired to provide one or more pinholes down
to the surface of the integrated circuit. Those holes can be
provided by selectively removing encapsulant using the laser and
the endpoint detector.
Having thus described the preferred embodiment of the invention,
those skilled in the art will appreciate that further changes,
modifications, additions and omissions may be made to that
embodiment without departing from the spirit and scope of the
appended claims.
* * * * *