       NOTE: This disposition is nonprecedential.


  United States Court of Appeals
      for the Federal Circuit
                ______________________

              RAYTHEON COMPANY,
                   Appellant

                           v.

SONY CORPORATION, SAMSUNG ELECTRONICS
 CO., LTD., SAMSUNG ELECTRONICS AMERICA,
   INC., SAMSUNG SEMICONDUCTOR, INC.,
                     Appellees
              ______________________

           2017-1554, 2017-1556, 2017-1557
               ______________________

   Appeals from the United States Patent and Trade-
mark Office, Patent Trial and Appeal Board in Nos.
IPR2015-01201, IPR2016-00209, IPR2016-00962.
                ______________________

                Decided: April 2, 2018
                ______________________

   JOHN J. MOLENDA, Steptoe & Johnson, LLP, New
York, NY, argued for appellant. Also represented by
JOHN LLOYD ABRAMIC, THOMAS J. FILARSKI, Chicago, IL;
FANG BU, Washington, DC.

    MATTHEW A. SMITH, Smith Baluch LLP, Washington,
DC, argued for all appellees. Appellee Sony Corporation
also represented by ANDREW BALUCH; ROBERT LOUIS
2                  RAYTHEON COMPANY   v. SONY CORPORATION



HAILS, JR., T. CY WALKER, Baker & Hostetler LLP, Wash-
ington, DC; ZHUANJIA GU, JENNIFER SERAPHINE, JACOB
ZWEIG, Turner Boyd LLP, Redwood City, CA.

    RONALD J. PABIS, Greenberg Traurig LLP, Washing-
ton, DC, for appellees Samsung Electronics Co., Ltd.,
Samsung Electronics America, Inc., Samsung Semicon-
ductor, Inc. Also represented by MARK G. DAVIS, PATRICK
J. MCCARTHY, STEPHEN K. SHAHIDA; RICHARD A. EDLIN,
New York, NY; HEATH BRIGGS, Denver, CO.
                 ______________________

Before LOURIE, O’MALLEY, and WALLACH, Circuit Judges.
O’MALLEY, Circuit Judge.
     Raytheon Company (“Raytheon”) appeals from final
written decisions in two inter partes review (“IPR”) pro-
ceedings, in which the Patent Trial and Appeal Board
(“Board”) held all claims of U.S. Patent No. 5,591,678
(“’678 patent”) unpatentable. See Sony Corp. v. Raytheon
Co., IPR2015-01201, 2016 Pat. App. LEXIS 13452
(P.T.A.B. Nov. 30, 2016) (“1201 Decision”); Sony Corp. v.
Raytheon Co., IPR2016-00209, -00962, 2016 Pat. App.
LEXIS 13045 (P.T.A.B. Nov. 30, 2016) (“209 Decision”).
For the following reasons, we affirm.
                     I. BACKGROUND
                   A. The ’678 Patent
    Entitled “Process of Manufacturing a Microelectric
Device Using a Removable Support Substrate and Etch-
Stop,” the ’678 patent is directed to purported advances in
the manufacture of stacked semiconductors found in
everyday electronic devices. The patent expired before
the IPR proceedings at issue were initiated, and claims
priority to an application filed on January 19, 1993.
    Rather than employ a conventional “front-side” fabri-
cation process, whereby microelectronic circuits are
RAYTHEON COMPANY       v. SONY CORPORATION                           3



formed and substrates are stacked on top of a wafer, the
’678 patent employs a “back-side” process, whereby many
of the fabrication steps are performed on the bottom of the
wafer. ’678 patent, col. 2, ll. 29–37. As shown in box 24 of
Figure 1 below, a first, multi-layer substrate 40 contain-
ing circuitry 50 is attached to the bottom of a second
substrate 58, which provides mechanical support for the
wafer and circuitry. Id. col. 4, ll. 22–52; id. col. 5, ll. 15–
44.




Id. fig.1. (boxes 24, 28). Once the wafer and circuitry are
supported, the back side of the first substrate is removed.
Id. col. 5, ll. 45–51. Finally, as shown in box 28 of Figure
1, various back-side electrical connections are formed
through the remaining portion of the first substrate. Id.
col. 6, ll. 10–15, 44–49.
    This fabrication method allows electrical connections
to be made through the device rather than around the
sides thereof—making the device more compact—while
using the second substrate to protect the fragile wafer and
circuitry from damage during fabrication. Id. col. 1, l. 50
to col. 2, l. 2; id. col. 2, ll. 32–37; id. col. 2, l. 59 to col. 3, l.
14. Additional substrates may be sequentially stacked on
the back side of the resulting structure to achieve a three-
dimensional device containing an arbitrarily large num-
ber of layers. See id. col. 3, ll. 38–40; id. col. 7, ll. 14–17,
60–65.
    Dependent claim 5 is representative and recites—
through its dependence from claim 1—the method de-
scribed above using silicon-based materials:
4                   RAYTHEON COMPANY    v. SONY CORPORATION



    1. A method of fabricating a microelectronic de-
    vice, comprising the steps of:
        furnishing a first substrate having an
        etchable layer, an etch-stop layer overly-
        ing the etchable layer, and a wafer overly-
        ing the etch-stop layer;
        forming a microelectronic circuit element
        in the exposed side of the wafer of the first
        substrate opposite to the side overlying
        the etch-stop layer;
        attaching the wafer of the first substrate to
        a second substrate; and
        etching away the etchable layer of the first
        substrate down to the etch-stop layer.
    ....
    5. The method of claim 1, wherein the etchable
    layer is silicon, the etch-stop layer is silicon diox-
    ide, and the wafer is single-crystal silicon.
Id. col. 8, ll. 5–16 (emphasis added), 30–32.
                     B. The Prior Art
     Three prior art references are at issue on appeal:
(1) U.S. Patent No. 4,422,091 to Liu (“Liu”), (2) U.S.
Patent No. 5,202,754 to Bertin (“Bertin”), and
(3) Japanese Unexamined Patent Application Publication
No. 64-18248 to Morimoto (“Morimoto”).
    Liu issued in 1983 and therefore qualifies as prior art
to the ’678 patent under pre-AIA § 102(b). Liu describes a
gallium arsenide, multi-layer charge coupled device
(“CCD”) for detecting electromagnetic radiation, as well as
a method of fabrication. Liu at Abstract; id. at col. 2, 7–
18.
RAYTHEON COMPANY    v. SONY CORPORATION                     5



     Bertin issued several months after the priority date of
the ’678 patent, but was filed sixteen months prior there-
to, on September 13, 1991, and therefore nominally quali-
fies as prior art under pre-AIA § 102(e). Bertin discloses
“[a] fabrication method and resultant three-dimensional
multichip package” containing several layers of silicon-
based material. Bertin at Abstract; id. col. 1, ll. 10–15; id.
col. 1, l. 55 to col. 2, l. 31; id. col. 3, ll. 4–46.
    Finally, Morimoto published in 1989 and therefore
qualifies as prior art under pre-AIA § 102(b). Morimoto
discloses “a method for manufacturing semiconductor
devices” containing multiple layers. J.A. 115–16. 1 One of
those layers is a “supporting silicon substrate,” which
Morimoto teaches is removed during the fabrication
process. See J.A. 116 (explaining that a “two-layer active
layer structure is formed” by, among other things, bond-
ing a “supporting silicon substrate” to an insulating film,
performing additional steps, and then “removing the
supporting silicon substrate” (emphasis added)).
                   C. Procedural History
    Appellees Sony Corporation, Samsung Electronics Co.,
Ltd., Samsung Electronics America, Inc., and Samsung
Semiconductor, Inc. (collectively, “Sony”) filed a series of
IPR petitions against Raytheon’s ’678 patent, which were
consolidated into the two proceedings at issue here.
   In its final written decisions, the Board held in rele-
vant part all claims unpatentable under pre-AIA 35
U.S.C. § 103 as obvious over the prior art of record. See
209 Decision, 2016 Pat. App. LEXIS 13045, at *33–64;
1201 Decision, 2016 Pat. App. LEXIS 13452, at *43–69.
Sony appealed with respect to claims 5, 13–14, and 16–18



    1 We cite here to the certified English translation of
Morimoto included in the joint appendix. See J.A. 115–19.
6                  RAYTHEON COMPANY    v. SONY CORPORATION



only.     We have       jurisdiction   under   28   U.S.C.
§ 1295(a)(4)(A).
                     II. DISCUSSION
    Raytheon makes three principal arguments on appeal.
First, Raytheon asserts that the Board failed to address
its argument that using silicon in Liu’s devices would
render them inoperable. Second, Raytheon argues that
the Board erred in finding that it failed to antedate Ber-
tin. Third, Raytheon argues that the Board erroneously
construed the claim term “second substrate” to encompass
Morimoto’s temporary supporting substrate. As explained
below, we disagree with Raytheon’s Liu- and Bertin-based
arguments and therefore affirm the Board’s obviousness
determinations. And, as also explained below, while we
agree with Raytheon that the Board’s construction of
“second substrate” is erroneous, that issue is rendered
moot in view of our holding.
           A. The Board’s Liu-Based Findings
     The Board found appealed claims 5, 13–14, and 16–18
obvious over Liu in view of other prior art of record. See
209 Decision, 2016 Pat. App. LEXIS 13045, at *33–63.
Obviousness is a question of law based on underlying
factual findings relating to “the scope and content of the
prior art, differences between the prior art and the claims
at issue, the level of ordinary skill in the pertinent art,
and any objective indicia of non-obviousness.” Randall
Mfg. v. Rea, 733 F.3d 1355, 1362 (Fed. Cir. 2013) (citing
KSR Int’l Co. v. Teleflex Inc., 550 U.S. 398, 406 (2007)).
We review the Board’s ultimate legal determination of
obviousness de novo and its underlying factual findings
for substantial evidence. PPC Broadband, Inc. v. Corning
Optical Commc’ns RF, LLC, 815 F.3d 747, 751 (Fed. Cir.
2016). Substantial evidence is “such relevant evidence as
a reasonable mind might accept as adequate to support a
conclusion.” In re Gartside, 203 F.3d 1305, 1312 (Fed.
RAYTHEON COMPANY    v. SONY CORPORATION                      7



Cir. 2000) (quoting Consol. Edison Co. of N.Y. v. N.L.R.B.,
305 U.S. 197, 229 (1938)).
     As described above, Liu describes a multi-layer CCD
for detecting electromagnetic radiation.            While Liu
acknowledges that silicon devices are “adequate for many
applications,” it states that silicon-based devices are
unsuitable for “some specific applications,” including “star
sensors which require extremely low dark currents and
high optical responsivity.” Liu, col. 1, ll. 15–26. Liu
teaches that these objectives—which comprise just two of
Liu’s six objects of the invention—are “not likely to be
realized simultaneously” in silicon-based CCDs. Id. col. 1,
ll. 25–26; id. col. 1, l. 59 to col. 2, l. 6. Liu therefore em-
ploys gallium arsenide, rather than silicon, for its devices.
    Pointing to these passages, Raytheon argues that us-
ing silicon in Liu’s CCDs would defeat Liu’s primary
objectives of achieving low dark current and high optical
responsivity, which, in turn, would render Liu’s devices
inoperable for their intended purpose. Appellant Br. 52–
54 (citing In re Gordon, 733 F.2d 900 (Fed. Cir. 1984)).
For this reason, Raytheon argues, a skilled artisan would
not be motivated to combine Liu with secondary refer-
ences that teach using silicon in semiconductor devices.
Raytheon contends that the Board failed to address this
argument in its final written decision. We disagree.
     Raytheon’s inoperability argument is a slight varia-
tion of the argument that the Board squarely addressed.
The Board found that Liu’s statement that silicon can
hamper performance in CCDs for “some specific applica-
tions”—i.e., for star sensors—does not teach away from
using silicon in CCDs for other applications, including
microelectronics applications. See 209 Decision, 2016 Pat.
App. LEXIS 13045, at *43–45. Indeed, as the Board
noted, Liu expressly teaches that silicon in semiconductor
systems was generally known. Id. at *44 (citing Liu, col.
1, ll. 16–17; id. col. 5, ll. 9–10). And, relying in part on
8                  RAYTHEON COMPANY    v. SONY CORPORATION



Sony’s petition and expert’s declaration, the Board found
that, because “the vast majority of devices [at the time]
were made with silicon, Liu’s reference to silicon would
not have convinced anyone to avoid it except for certain
specific applications.”  Id. (internal quotation marks
omitted).
     That Liu’s claimed invention is directed primarily to
star sensor applications does not preclude a skilled arti-
san from combining Liu with silicon-based references for
different applications. “A reference must be considered
for everything that it teaches, not simply the described
invention or a preferred embodiment.” In re Applied
Materials, Inc., 692 F.3d 1289, 1298 (Fed. Cir. 2012)
(citing EWP Corp. v. Reliance Universal Inc., 755 F.2d
898, 907 (Fed. Cir. 1985)). Indeed, “[o]n the issue of
obviousness, the combined teachings of the prior art as a
whole must be considered.” EWP, 755 F.2d at 907. As
described above, Liu teaches that silicon-based devices
were known. Thus, a skilled artisan cannot be assumed
to ignore Liu merely because it is primarily directed to a
specific application that is different from the application
claimed in the patent at issue. KSR, 550 U.S. at 420–21
(“The idea that a designer hoping to make an adjustable
electronic pedal would ignore Asano because Asano was
designed to solve the constant ratio problem makes little
sense.”). In view of Liu’s teachings and the record evi-
dence, therefore, we conclude that the Board’s findings
are supported by substantial evidence.
     Even if Raytheon were correct that Liu’s high optical
responsivity and low dark current objectives would be
thwarted by using silicon in Liu’s devices for microelec-
tronics applications, those objectives comprise just two of
Liu’s six stated goals. Raytheon does not explain why the
resulting device, with just those two objectives frustrated,
would be rendered inoperable rather than merely less
efficient or less desirable. See Allied Erecting & Disman-
tling Co. v. Genesis Attachments, LLC, 825 F.3d 1373,
RAYTHEON COMPANY    v. SONY CORPORATION                     9



1381 (Fed. Cir. 2016) (“Although modification of the
movable blades may impede the quick change functionali-
ty disclosed by Caterpillar, ‘[a] given course of action often
has simultaneous advantages and disadvantages, and this
does not necessarily obviate motivation to combine.’”
(quoting Medichem, S.A. v. Rolabo, S.L., 437 F.3d 1157,
1165 (Fed. Cir. 2006)). Raytheon’s inoperability argu-
ment therefore fails on its own terms.
     Substantial evidence supports the Board’s finding
that a skilled artisan would have been motivated to use
silicon material with Liu’s CCD semiconductors in non-
star sensor applications. We therefore affirm the Board’s
determination that Liu renders appealed claims 5, 13–14,
and 16–18 of the ’678 patent obvious.
          B. The Board’s Bertin-Based Findings
    The Board also found appealed claims 5 and 13 obvi-
ous over Bertin in view of Morimoto. See 1201 Decision,
2016 Pat. App. LEXIS 13452, at *43–48. Raytheon does
not challenge the Board’s finding that Bertin and
Morimoto collectively disclose every limitation recited in
those claims, or that a skilled artisan would have been
motivated to combine the references. Instead, Raytheon
argues only that Bertin is not prior art because the inven-
tors reduced to practice the claimed subject matter before
Bertin’s filing date. Again, we disagree.
     To antedate a prior art reference, a patentee must es-
tablish that it invented the subject matter recited in the
patent claims before the reference’s priority date. That,
in turn, can be established by showing “either an earlier
reduction to practice, or an earlier conception followed by
a diligent reduction to practice.” Purdue Pharma L.P. v.
Boehringer Ingelheim GmbH, 237 F.3d 1359, 1365 (Fed.
Cir. 2001). A party seeking to establish an actual reduc-
tion to practice, as here, must satisfy a two-prong test:
(1) the party must construct an embodiment or perform a
process that satisfies every element of the claim at issue,
10                 RAYTHEON COMPANY     v. SONY CORPORATION



and (2) the embodiment or process must operate for its
intended purpose. In re Steed, 802 F.3d 1311, 1318 (Fed.
Cir. 2015); Cooper v. Goldfarb, 154 F.3d 1321, 1327 (Fed.
Cir. 1998). “The inventor must also have ‘contemporane-
ous recognition and appreciation of the invention’ repre-
sented by the claims.” Purdue, 237 F.3d at 1365–66.
     Significantly, an inventor’s testimony alone is insuffi-
cient to establish an earlier reduction to practice. Medi-
chem, 437 F.3d at 1169–71. Instead, a party seeking to
prove an actual reduction to practice must proffer evi-
dence corroborating that testimony. Id. at 1170. “Suffi-
ciency of corroboration is determined by using a ‘rule of
reason’ analysis, under which all pertinent evidence is
examined when determining the credibility of an inven-
tor’s testimony.” Id.; Cooper, 154 F.3d at 1330. Whether
a patentee reduced its invention to practice is a mixed
question of law and fact. REG Synthetic Fuels, LLC v.
Neste Oil Oyj, 841 F.3d 954, 958 (Fed. Cir. 2016); Steed,
802 F.3d at 1318–20; Cooper, 154 F.3d at 1327. We
review the Board’s legal conclusions de novo and its
underlying factual findings for substantial evidence.
REG, 841 F.3d at 958; Steed, 802 F.3d at 1318–20;
Cooper, 154 F.3d at 1327.
     Much of the parties’ briefing and supporting evidence
related to Raytheon’s reduction to practice contention are
designated confidential. Accordingly, we do not describe
these documents in detail here. For purposes of our
analysis, it is sufficient to address Raytheon’s arguments
at a high level of generality. During the IPR proceedings,
the inventors testified that they reduced to practice the
subject matter recited in the claims by the end of 1990—
more than nine months before Bertin’s September 1991
filing date—while working on a project for their employer
and original assignee, Hughes Aircraft Company.
    Raytheon relies on a March 1991 internal report to
corroborate that testimony. As the Board found, however,
RAYTHEON COMPANY    v. SONY CORPORATION                   11



the report indicates that one of the claimed steps had not
yet been completed by December 1990. The report states,
for example, that the particular structure referenced in
the report was an “intended structure,” and that a con-
stituent structure was “awaiting” a process step and
testing critical to one of the claim limitations. 2 J.A. 241–
42 (emphases added). The Board concluded that these
statements imply that Hughes expected to complete the
claimed step in the future, contrary to the inventors’
testimony. 1201 Decision, 2016 Pat. App. LEXIS 13452,
at *36–38. Based on our careful review of the report, the
inventor testimony, and the balance of the record on
appeal, we conclude that substantial evidence supports
the Board’s finding that the report contradicts the inven-
tors’ testimony and therefore cannot corroborate such
testimony.
    We reject, moreover, Raytheon’s legal arguments as to
why the Board erred. First, Raytheon argues that the
Board erred by requiring every point of the reduction to
practice be disclosed in the corroborating evidence, which
Raytheon contends is inconsistent with the rule of reason
standard. Raytheon is correct that corroborating evidence
need not disclose each and every aspect of the claimed
invention. See Cooper, 154 F.3d at 1331 (“[T]he law does
not impose an impossible standard of independence on
corroborative evidence by requiring that every point of a



    2   The report also states that Hughes “will empha-
size continuing” development related to the claimed goals
in early 1991, J.A. 242 (emphasis added), but does not
indicate that such goals were ever achieved. And, alt-
hough the report states that Hughes “completed the
design and layout of” a particular structure, it states that
Hughes only “continued development” of a relevant step
in the claimed process. J.A. 238; J.A. 241 (emphasis
added).
12                 RAYTHEON COMPANY    v. SONY CORPORATION



reduction to practice be corroborated by evidence having a
source totally independent of the inventor[.]” (internal
quotation marks omitted)); see also Fleming v. Escort Inc.,
774 F.3d 1371, 1377 (Fed. Cir. 2014). But the Board did
not require such proof here. As described above, the
Board determined that the corroborating evidence contra-
dicted the inventor’s testimony and therefore could not be
sufficiently corroborative. This conclusion is reasonable
in view of the evidence. Cf. Woodland Tr. v. Flowertree
Nursery, Inc., 148 F.3d 1368, 1371 (Fed. Cir. 1998) (ex-
plaining that, in evaluating the rule of reason, courts take
into account “contradiction or impeachment of the wit-
ness’ testimony”).
     Second, Raytheon argues that the Board erroneously
required that the corroborating evidence itself be corrobo-
rated. To support that argument, Raytheon points to
specific language in the Board’s final written decision in
which it stated that “there is no corroborating evidence
that” a particular structure described in the report was
“constructed or tested in 1990.” 1201 Decision, 2016 Pat.
App. LEXIS 13452, at *36. That statement, however,
does not fault Raytheon for failing to proffer evidence that
corroborates the corroborating evidence. Instead, it faults
Raytheon for failing to proffer evidence that sufficiently
corroborates the inventors’ testimony that they completed
all claimed steps by the end of 1990. In other words, the
Board’s statement merely declares that the report is not
itself sufficiently corroborative, and that Raytheon prof-
fered no other evidence to fill the gap. 3 Similarly, the



     3  Before the Board, Raytheon also relied on an
August 1990 invention disclosure and a November 1990
white paper. On appeal, however, Raytheon disclaims
reliance on those documents. See Appellant Br. 15 n.8;
Oral Argument at 12:28–13:35, Raytheon Co. v. Sony
Corp. (No. 2017-1554), http://oralarguments.cafc.uscourts.
RAYTHEON COMPANY   v. SONY CORPORATION                  13



Board did not require that Raytheon’s expert’s testimony
be corroborated. Rather, the Board determined that his
testimony was not credible in view of the report’s contrary
statements.
    Third, Raytheon asserts that the Board improperly re-
lied on Sony’s attorney argument interpreting the report.
This assertion has little force given the plain language of
the report, which, on its face, contradicts the inventor
testimony.
    Substantial evidence supports the Board’s findings,
and we therefore affirm the Board’s determination that
Raytheon failed to antedate Bertin, and that Bertin also
renders appealed claims 5 and 13 of the ’678 patent
obvious.
    C. The Board’s Construction of “second substrate”
             and Morimoto-Based Findings
    In view of our holding above affirming the Board’s
Liu- and Bertin-based obviousness determinations as to
claims 5, 13–14, and 16–18, we need not reach Raytheon’s
final argument regarding the Board’s Morimoto-based
obviousness determination as to those same claims. As
explained below, however, we agree with Raytheon that
the Board’s determination on that prior art reference is
predicated on an erroneous claim construction.
    The Board found appealed claims 5, 13–14, and 16–18
obvious over Morimoto, either standing alone or in view of
other prior art of record. See 1201 Decision, 2016 Pat.
App. LEXIS 13452, at *48–68. That determination was
predicated on the Board’s construction of the claimed
“second substrate” limitation. The Board noted that the
term’s plain meaning “is merely another substrate (i.e., in



gov/default.aspx?fl=2017-1554.mp3 (“[W]e limited        the
scope of the evidence that we’re relying upon.”).
14                  RAYTHEON COMPANY     v. SONY CORPORATION



addition to the claimed ‘first substrate’).” J.A. 166 (insti-
tution decision). In view of that broad meaning and the
claims’ “comprising” transition, the Board determined
that the second substrate need not remain part of the
final device, and that the claim limitation therefore
encompasses Morimoto’s temporary substrate, which is
removed during fabrication. 1201 Decision, 2016 Pat.
App. LEXIS 13452, at *10–12, 49–62.
    Raytheon argues that the Board’s construction is too
broad, and that the correct construction requires that the
second substrate remain attached to the device through-
out the fabrication process and in the final product. We
agree.
    Where, as here, an IPR involves an expired patent,
the Board gives the claims their plain meaning in accord-
ance with the standard set forth in Phillips v. AWH Corp.,
415 F.3d 1303 (Fed. Cir. 2005) (en banc). See Wasica Fin.
GmbH v. Cont’l Auto. Sys., Inc., 853 F.3d 1272, 1279–80
(Fed. Cir. 2017).
     The plain language of the ’678 patent claims states
that the wafer of the first substrate is “attach[ed] . . . to a
second substrate,” and that a portion of the first substrate
is thereafter “etch[ed] away.” ’678 patent, col. 8, ll. 13–16.
The claims say nothing about subsequently removing the
second substrate, and, in the absence of such language,
the reasonable inference is that the substrate is not
removed once attached. Further, although the claims
make clear that the first substrate is partially removed
during fabrication via etching, they do not recite similar
language with respect to the second substrate. This
omission suggests that the second substrate is not, in fact,
removed. Cf. Rodime PLC v. Seagate Tech., Inc., 174 F.3d
1294, 1305 (Fed. Cir. 1999) (“Had Rodime intended or
desired to claim thermal compensation as a function of
the positioning means in the asserted claims, it could
have done it explicitly, as in claim 11. The absence of any
RAYTHEON COMPANY     v. SONY CORPORATION                     15



such explicit language, however, shows that claims 3, 5,
and 8 do not include the function of thermal compensa-
tion.”).
    The specification amply supports this reading. First,
every embodiment described in the specification includes
the second substrate. Box 30 of Figure 1, for example,
depicts a representative embodiment, and shows the
second substrate 58 present in the “complete device”
manufactured using the claimed method:




’678 patent, fig.1 (box 30). And, although the specification
explains that additional layers may be added to the device
after the second substrate is attached, see, e.g., id. col. 6,
ll. 50–58, it never suggests that the second substrate may
be removed. This is particularly significant because the
specification emphasizes the temporary nature of other
layers within the device. See, e.g., id. col. 3, ll. 12–14
(“With the circuit element thus supported, the etchable
portion of the first substrate is removed by etching, down
to the etch-stop layer.” (emphasis added)); id. col. 5, ll. 47–
51 (describing a base layer as being “temporarily at-
tached” to the device and eventually “removed” (emphasis
added)). The specification describes, moreover, a method
of fabricating a three-dimensional device containing
multiple layers of stacked semiconductors. See id. col. 1,
ll. 45–49; id. col. 2, ll. 37–42; id. col. 7, ll. 61–65. Without
the second substrate, the device would contain just a
single wafer layer and circuitry, which the patent de-
scribes as a “two-dimensional structure.” See id. col. 1, ll.
15–23 (explaining that a device having only “an electronic
16                   RAYTHEON COMPANY      v. SONY CORPORATION



circuit on or near the top surface of a thin substrate wafer
. . . is considered a two-dimensional structure in the plane
of the substrate wafer”). These passages suggest that the
second substrate is not removed.
     Second, the specification makes clear that one of the
purposes of the second substrate is to protect the fragile
wafer during fabrication. See id. col. 1, ll. 11–13; id. col.
1, l. 58 to col. 2, l. 2; id. col. 2, l. 59 to col. 3, l. 14. This
purpose is facilitated by transferring the microelectronic
circuit elements from the first substrate to the second
substrate. See, e.g., id. col. 3, ll. 6–8 (“In the present
approach, after initial circuit element fabrication on a
first substrate structure, the electrical circuit element is
transferred to a second substrate structure.”); see also id.
col. 1, ll. 11–13; id. col. 2, ll. 59–61. In other words, the
second substrate protects the circuitry and wafer
throughout fabrication, even as subsequent layers are
added to the back side of the structure. That purpose
implies that the second substrate is not temporary, but
instead remains within the device. See id. col. 3, ll. 2–5
(explaining that, in the absence of a second substrate,
“[t]he first substrate cannot simply be removed to permit
access to the bottom side of the electrical circuit element,
as the assembly could not be handled in that very thin
form”). The claims must be read in view of the specifica-
tion’s “consistent emphasis on this fundamental feature of
the invention.” Praxair, Inc. v. ATMI, Inc., 543 F.3d 1306,
1324 (Fed. Cir. 2008).
    Third, the only passage in the specification that de-
scribes how the second substrate is attached to the wafer
states that epoxy glue is preferably used. See id. col. 5, ll.
33–38. As the patent explains, such glue, when degassed
and cured, “is resistant to chemical attack” and therefore
provides a “permanent attachment.” Id. In other words,
the epoxy glue used in the preferred embodiment ensures
that the second substrate remains permanently affixed to
the electrical device. Epoxy glue need not be used, of
RAYTHEON COMPANY     v. SONY CORPORATION                      17



course, but its reference in the specification suggests that
whatever adhesive is used must ensure that the second
substrate is permanently attached.
    Finally, the specification explains that the second
substrate may itself possess circuitry that can be electri-
cally connected to the first substrate’s circuitry. See, e.g.,
id. at Abstract; id. col. 2, ll. 24–28; id. col. 5, ll. 38–44. It
would be illogical and inefficient to add circuitry to the
second substrate and establish electrical connections
between the two substrates, only to remove the second
substrate from the device. In sum, the ’678 patent speci-
fication makes clear that the second substrate is not
removed. 4
    The Board did not consider these, or any other, pas-
sages of the specification. Instead, it focused solely on the
“comprising” transition in the claims’ preambles, finding
that the open-ended transition allows for subsequent
removal of the second substrate. 1201 Decision, 2016 Pat.
App. LEXIS 13452, at *10; J.A. 166–67 (institution deci-
sion). It is true, of course, that “the use of ‘comprising’
creates a presumption that the body of the claim is open.”
Crystal Semiconductor Corp. v. TriTech Microelecs. Int’l,
Inc., 246 F.3d 1336, 1348 (Fed. Cir. 2001); Genentech, Inc.
v. Chiron Corp., 112 F.3d 495, 501 (Fed. Cir. 1997)
(“‘Comprising’ is a term of art used in claim language
which means that the named elements are essential, but
other elements may be added and still form a construct


    4   We recognize that the claims at issue are method
claims, and that it would be improper to read apparatus
limitations pertaining to the final device into the claims.
But we do not embark down that road. Rather, our con-
struction addresses the manner in which the second
substrate is attached during the fabrication process. In
other words, we interpret the claimed “attaching . . . a
second substrate” step to require permanent attachment.
18                 RAYTHEON COMPANY    v. SONY CORPORATION



within the scope of the claim.”). But, the term “compris-
ing” does not displace, or otherwise allow one to disre-
gard, the patent specification. As we repeatedly have
emphasized, the claims must be read in view of the speci-
fication, which “is always highly relevant to the claim
construction analysis” and is “the single best guide to the
meaning of a disputed term.” Indacon, Inc. v. Facebook,
Inc., 824 F.3d 1352, 1355 (Fed. Cir. 2016) (quoting Phil-
lips, 415 F.3d at 1315). This fundamental precept is no
less true for “comprising” claims than it is for other types
of claims. See In re Suitco Surface, Inc., 603 F.3d 1255,
1260 (Fed. Cir. 2010) (stating that the Board’s construc-
tion of a claim reciting a “comprising” limitation must be
“consistent with the specification” (internal quotation
marks omitted)).
    A “comprising” transition, moreover, is “not a weasel
word with which to abrogate claim limitations” and “does
not reach into each of the . . . steps to render every word
and phrase therein open-ended.” Dippin’ Dots, Inc. v.
Mosey, 476 F.3d 1337, 1343 (Fed. Cir. 2007). Indeed, the
word “‘[c]omprising,’ while permitting additional elements
not required by a claim, does not remove the limitations
that are present.” Power Mosfet Techs., L.L.C. v. Siemens
AG, 378 F.3d 1396, 1409 (Fed. Cir. 2004) (emphases
added); cf. In re Skvorecz, 580 F.3d 1262, 1268 (Fed. Cir.
2009) (“The signal ‘comprising’ does not render a claim
anticipated by a device that contains less (rather th[a]n
more) than what is claimed.”).
    Here, the ’678 patent claims and specification clearly
impose a limitation on the claim term “second substrate,”
requiring permanent attachment throughout the fabrica-
tion process. Morimoto’s additional step of removing the
second substrate vitiates that limitation because it, in
fact, removes the substrate from the device. Accordingly,
the claims cannot be construed so broadly as to encom-
pass such removal. See In re Varma, 816 F.3d 1352, 1362
(Fed. Cir. 2016) (explaining that “comprising” claims “do[]
RAYTHEON COMPANY   v. SONY CORPORATION                  19



not cover systems whose unclaimed features make the
claim elements no longer satisfied”); Mitsubishi Chem.
Corp. v. Barr Labs., Inc., 435 F. App’x 927, 935 (Fed. Cir.
2011) (“While claim 3 is open-ended, the addition of new
compounds to the composition that would defeat the
‘pharmaceutical’ character of the overall composition
would move the composition outside the scope of the
claimed invention.”); cf. Outside the Box Innovations, LLC
v. Travel Caddy, Inc., 695 F.3d 1285, 1305 (Fed. Cir.
2012) (per curiam) (“The usage [of] ‘comprising’ means
that additional components may be present in the device,
but does not change the elements that are stated in the
claim.”).
    Thus, although our holding is not affected by the
Board’s error, its interpretation of the word “comprising”
as displacing the ’678 patent specification and vitiating
the “second substrate” limitation is improper under the
Phillips standard; indeed, it would be improper under any
standard.
                     III. CONCLUSION
   We have considered Raytheon’s remaining arguments
and find them unpersuasive. For the reasons stated
above, we affirm the Board’s ruling invalidating claims 5,
13–14, and 16–18 of the ’678 patent as obvious.
                      AFFIRMED
