Note: Descriptions are shown in the official language in which they were submitted.
1070-1~5 ~L18~77~
TITLE: IMPROVED CERAMIC CAPACITOR AI~D
METHOD OF MAKING SAME
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BACK~ROUND OF THE INVENTION
F~eld of the Inventi_
The present in~enti~n relates t~ ceramic capacitors and
more part~cularly pertains to an improved ceramic capacitOr and
- method of m~king same. ~ore particularly, this invention relates
to a novel method of effecting termination of a fired ceramic
: : c2pacitor device and to the resultant impr~ved capac itor dèvice.
The Prior Art
The mznufacture ~f ceramic capacitors is described
generally in one or more o~ the following U.S. Letters
Patent:
,:
3,00~,1S7 October 10, 1961
3,235~39 February 22, 1966
: Generally speaking such meth~d involves forming a shee~
r sheet.c of green ceramic comprising in essence cer~mic
~: p~wder material in an ~rganic binder. me sheets ~re imprinte~
by ~ilk-screening cr ~ similar prccess wlth an ink incorporat~n~
^O mètal particles recistant t~ disinte~ration ~t high ternperatures.
mult~plicity of such sheets are stacXed wi~h the lmprinted
~r electrode form~ng zrezs in p~rti~l registry. ~ne st~cXed
sheet,s are then c~t into discrete i~crem~tS alo~g se~erance
l~nes~ such that the ~ncrements expose altern~te electrode
.~ .
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12yers at opposite edge margins.
The increments are Dext treated by heating to a first
tempçrature ~or a time sufficien~ to burn off the organic binder
materials. Heatin~ is then continued &t a higher temperature
to flre the cerami~ and to cause the electrode imprinted areas
to ~orm conductive metallic electrodes between the ceram~c
layers.
The resultsnt ceramic capacit3r subcomponents must now
be terminated i e. a conductive connection must be effective
between the edges of the various electrode layers exposed at
~he opposite margins of the capacitor preform
Hereto~ore, such connections have been effected by
applying a silver containing paste to the respective margins
and heating the capacitor to cause the silver ~o si~ter whereby
~he electrodes at the respective margins are interconnected.
In some cases, conductive leads are ~oldered to the
silver terminations. More typically, particularly with
capacitor~ of small value, the capacitors are coated with a
protective insulaking coat in all areas except ~he termination
~nd are shipped for use in such condition.
Obviously, the cost of ~uch silver terminated leadless
capac~tor~ ~s substOntially increased a~ a result of the
necessi~y of employln~ ccnsiderable 2mounts G~ silver in
effec~ing ~ermination. The silver ter~na~eZ capacitors are
fur~her disadv~ntegeous, in th~t, ~Ihen ~ soldered connec~ion
i~ made to the silver termin~tion ~he silver tends to disolve
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and flow into the lead-tin ~lloy of the solder Unless such
soldering is carefully erfected, the sllver of the termination
joint may flo~ so completely into the solder as to partially
cr co~pletely lose electrical contact I~Jith the electrode
layers e
A ~urther disadvantage of conventionally terminated
ceramic capacitors is that the E ilver termination is of
little structural value in rein~orcing the capac~tor against
delamination since the sole or principle adherance of the
silver is to the electrode materials per se and not the ceramic.
In order t~ provide a degree of reinforcing effect certain of the
silver terminating pastes may embody glass frit material which
forms a partial bond to the ceramic. However, the utilization
of glas6 frit material engenders other diff~culties and
manufacturing complications including the requirement cf
~; heating the units up to a temperature sufficiently high to
~; melt the fxit component of the silver paste. The high heat
requirements of the procedure in addition to being energy
-asteful al~o increase the chances tha~ tne capacitors will be
2G 22maged in the cource of reheating. Finally, the conductivity
of the silver-,rit termination paste in inIerior to a pure
metallic conductive material.
Y OF THE ~V~TIOIY
~ ,
The present invention may be su~marized as directed to
an improved ~ethod of manufacturin~ ceramic capaci~ors and
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an improved resultant capacitor In accordance with the
tnethod of the invention a conventional chip cap~citor which
has been fired is loaded into a j~g or like m~s~ing device
which exposes only the edge margin surfaces of the capacitor
which incorporates the edge portions of ~he electrodes. The
masked capacitors are placed in a sputtering apparatus kno~
per se wherein heavy gas ions are impacted against a target
material re~ul~ing in atoms of the target material being
bombarded against ~he exposed surface of the capacitor.
Optionally, but preferably, the exposed surface of the capacitor,
prior to sputtering, is itself R.~. suptter etched i.e the
heavy gas ions are im~ cted directly against the exposed
surface ~f the capacitor. Such ~putter etching in addition to
removlng the oxides or impurities at the surface provides a
rugose or corrugated surface for the subsequent sputter applied
metallic layer.
In acc3rdance with the method more than one sputter applied
metallic layer may be deposlted on the capacitor surface in
accordance with the intended end use of tne capacitor. By way
of example a satisfactory capacitor termination may be
effected by sputter deposi~ing 8 nickel layer, an alloy of
nickel vanadium, a copper layer etc. Optionally, a chromium
layer may first be deposited t~ improve adhesion followed by
a nickel ~r nickel venadium sputter applied layer. To
facilitate subsequent soldering a very thin silver layer may
be applied over ~he nickel e.g. in ~he order of .1 micron.
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The capacitor in accordance ~ith the-invention provides
a highly des~rsble structure ln that the absence of ~ilver at
the junction with the capaci~or electrodes eliminates the
possibility that electrode contact will be lost in the course
of soldering Subs~antial cost reductions are achieved by
eliminating the use of silver terminations Additionally
; and importantly, the sputter deposited l~yer, particul2rly
lf th~ edge portion of the capacitor has been previously
sputter etched, provides a coatin~ which adheres strongly
both to the electrodes and to the intervening ceramic spaces
whereby any tendency of the capacitor to delaminate along
.
the cleavage lines defined by the ceramic-electrode inter'zces
is substantially reduced or eliminated. The mechanical
reinforcing effect of the sputter deposited terminations
enables the final insulating or incapsulating coating, if used,
to function merely as an electrical isolation rather than as
a mechanical reinforcement of the capacitor. Thus the
overall size or bulk of the capacitor may be reduced.
It is accordingly an object of the invention to provide
an improved method of fabricating 2 ceramic czpacitor and more
particularly an improved method of ~erminating a conventiena
ceram~c capacitor. A ~urther object ~f the invent~on ls the
provision o~ a novel termination me~nod for ceramic capacitors
wnich el~minates the use of s~lver or other noble metalc a~ the
interface with ~he capacitor electrodes. Still a fur~her
object of the invention is the provision of ~ method o~
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fabr~cating ceramlc capacitors which includes the step of
sputter etch~ng the electrode containing margin of the
capacitor to clea~ the same and provide an etched or pebbled
sur~ace and thereafter sputter depositing a thin film of
conductive metal which simultaneously electrically uni~es
the e~posed electrode~ and f~rms a unifying or mechanically
rigidifying influence at the capacitor margin.
A further object of ~he invention is the provision of
a ceramic capacitor having termination which are free of
silver at the interface with the electrodes. A further
object ~f the ~nvention is the provision of a capacitor of the
type described wherein the termlnation layer functions as a
mechanical reinforcement against delamination of the capacitor.
Still other and further object of the invention will appear
herein of be hereinafter pointed out in connection with the
description of the dra~ings wherein.
Fig. 7 is a vertical sectional view diagramatic in
na~ure of a ceramic capacitor prepaxatory to termination.
Fig. 2 is a vielY similar to Fig. 1 showing the capacitor
in a masking apparatus.
Fig. 3 is a diagramatic view of the masked capacitor
in ~he course of sputter deposition treatment,
Fig. ~ A, 4 B and 4 C are diagramOtic sequential views
resp~ctively of an untreated capacitor~ a capacitor which is
: sputter etched on i~s upper surface, a~d of ~ capacitor having
; ~ spu~ter deposited layer covering the sputter etched sur~ace~
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As used herein khe term sputter coating, sputter
; deposlting or spu~tering shall mean the gas ion disentegration
of a cathode target and consequent deposition of atoms removed
from the target as a layer on the capacitor marg~n having
exposed electrode edges.
The term sputter etching or sputter etched shall be
deemed to mean a procedure whereby cathode and gas ions are
directed agalnst the capacitor margins to be terminated in
an R.F. field.
Turning now to the drawings there is shown in Fig. 1
in diagramatic form a ceramic capacitor conventional in
~ ; nature and fabricated f'or instance in accordance ~ith the
: disclosures of U.S. Patent 3,235,939. The capacitor 10
: comprises a mult iplic ity of ceramic la~ers 11 defining the
dielectric components of the capacitors, the layers 11 being
~ ~
separated by intervening electrode layers 12 and 13.
As is convent~onal the electrode layers 12 and 13 extend
for less th2n the entire length of the capacitor but overlap
~J
throu~hou~ the majority of their extent. As iE apparent from
Fig. 1 the electrode layers 12 incorporate edge portions which
are exposed at the margin 14 of the capacitor 10 whereas the
electrodes 13 include edge portions exp~sed at the margin 1
o~ ~he capac~tor,
In accordance ~ith the process ol the inven~l~n a
~,~ltiplicity ~ the capacitors 10 are loaded ~nto a die or
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~ig 16 (~ig.2) the funetion ~f which is ~o shleld all of
the surfaces of the capacitor except the uppermost surface i-e,
one or ~he other of the marginal surfaces 14 or 15. As
depicted in Fig. 2 the marginal surface 14 of the capacitor
~s located uppermos~ in the mask of Jig 16~ It ~Jill
accoralngly be apprec iated that the edge port ions of the . .
electrodes 12 are exposed in an upward direckion.
Although in the diagramatic views o~ the Figs. 1
through 3 the capacitors lO have been ~epicted 25 shielded
10 by individual pockets 17 of the masking device 16, . it will be
understood khat a mutual shielding effect may be achieved by
stacking ~ multiplicity of the capacitors in side by side
relat ion O
-The shielded capacitors are next processed by sputter
etching the uppermos~ ~urface or margin 14. While the sputter
etching step is opti~nal such step is preferred, in that, ~n
addition to the usual effect ~f cleaning the exposed surface~
the sputter etching step also provides a rugose or corrugated
or pebbled impact area f~r the subsequently applied met211ic
layer. The effect of spu~ter etching is diagrama~ically
~llustrated by a c~mparison Ol Fig. ~ A (unetched) with 4
(sputter etched~.
~ he cputter etched suxface l~ is next ~putter coated
by p2S~ ing the same Deneath the target of a sputtering oevice.
Optl~nally7 but preferably, ~n in-line cputtering system such as
a sys~em identified as the SERIES ~0 SPUTTERING DE-v~CE as
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manufactured by Materials Research Corporation of
Orangeburgh~ New York is employed. An inline sputtering
system is advan~ageous in that it permits the capacitors
to be progressively advanced beneath target areas o~
dif~erent compositions whereby a layer of a first sputter
deposited material may be formed directly over the surface
14 and thereafter a second sputter deposited layer ma.y be
formed over the first layer. Illustratively, a nickel-
va~a.dium alloy layer may first be sputter deposited by
advancing the capa.citor benea.th an appropriate target
ma~erial,~he nickel or nickel-~a.nadium layer being therea~ter
thin coated with a silver layer by advancing the same beneath
a silver target member. It is also desira.ble under rertain
clrcumstances i.e. for improved adhesion~to first effect
; the deposi~on of a thin chromium layer and thereafter coat
the chromium layer by sputter deposition wlth a nickel.or
nickel-vanadium layer, such procedures being readily carried
out in an inline sputtering system by progressively advancing
the capacitors beneath suitzbly s~lec~ed targe~ materials.
The sputter depofiition is con~inued in a manner kno~
per sP un~il the ~esired layer build up is achieved. Referring
; to Fig. 4 ~ i~ will be apparent ~hat the sputter deposited
layer or layer~ 18 ~Jill define a cohesive mass of layer~ the
lowermost surface ol which is strongly adheren~ to an~ enters
~;ith~n the recesses~ interstices or pores 19 formed by the
~pu~ter etching procedure. m e layer 18 provides an effective
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electrical and mechanical. connectio~ to the electrodes 12
,
and a mechanical connection to exposed ceramic comp~nents
at the sur~ace 14. The layer 18 thus provides a termina~ion
and a mech~nical reinforcement of the edge 14 minimizing the
possibillty of cleavage of the capa.citor along the lines of
~nterface be~een the ceramic and electrodes.
It will be a.ppreciated that the etching and spu~tering
procedures described are repeated with the edge portion 15
of the ceramic exposed to the target whereby a second
termination layer 20 is formed over the edge 15.
: The termina.ted capacitor is n3~q ready for use.
Optionally~ an insula.ting c~ating may be applied over all
portions of the capacitor except the terminations.
-By way of exa.mple, and ~or purposes of compliance
with the requirements o~ the patent laws, there will now be
described the operating parameters o~ a specific embodiment
of the invention it b~ing understood that neither the
~ materials nor the specific deta.ils ~ such de~cription shall
:: be cons~dered limitative~
In accordance with the invent.ion ~ multiplicity of
chips are loca~ed ~n a f~xture with the termination ends
exposed in a upward d ~rect ion. The loa~ed f ixture is placed
in a vacuum l~ad lock which iS pumped t~ a pressure of less
than 50 X 10 ~ torr prior to introducin6 the f~xture into
the main vacuum sput~ering chamber. ~ne loaded fixture is
m~ved to aD R.F. sputter etching station wherein ~hP pressure
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is le~s than 5 X 10-6 torr. A high purity argon gas ,
is introduced lnto the et~hing chamber to achieve a pressure
of ab~ut 10 X 10-3 torr. The parts having a surface area
of approximately 311 millimeters square are sputter etched
for 30 seconds at a power level of 1.4 kilowatt. The
fixture carrying the etched capacltors is then traversed
to a ~tation wher~ a .12 micr~meter thickness film is
deposlted over the termination end~ m e film may comprise
pure nickel or an alloy containing by weight 93 ~ nickel
, ~s~ .
and ~ % vanadium~ Sputtering is effected at a power level
of 4.2 kilowatts and a scan speed of 10.2 millimeters per
second across the target area. The sputtering is preformed
in a argon gas environment at a pressure 10 X 10-3 torr.
The procedure is repeated to effect etching and coa~ing of the
opp~site termination-s-urface o~ -the-capacitors,
Where direct nickel or nickel-vanadium coatings are
eflected,coating thickness in the range offrom ~12 to 05
micrometers has been found to be optimum, Where a chr~mium
substrate ~s used for high adhesion, layer thicknesses in the
range ~f ,02 to .05 micr~meters ~ave been found preferred. As
previously no$ed s~here direct solder~ng to the terminations is
anticipated a very thin coating of silver i.e. of the magnitude
of ab~uk .1 m~cron is desirably ~dded. I~ will be ob~erved
that such quantity of silver ~s orly ~ very small fraction
~f the amount ~ypically used to terQinate a capacitor by
eonventional methods.
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~ rom the ~oregoing it will be perceived that there
is provided ln a.ccordance with the present inventiorl c new
and novel method of manufactur~ng ceramic ca.pacitors
characterized in that the termination step is effected by
sputter deposition prefera.hly follo~.~ng spu~er etching. It
sJill further be perceived that the resultant unique
capacitor may be ec~nomic~lly manufactured and ls uniquely
strong and ~ree ~rom the tendency toward ~ilver leaching
during ~oldering which is characteristic of convent~onal
silver terminated capacitors.
A~ w~l be apparent to those skilled in ~he art,
numerous changes may be effected particularly in the
selection of materials, layer thicknesses and treatment
p~rameters for el~ecting etching and coating. Accordingly~
the invention i~!,.to.;b.e.broadly constr~uedj~rithin the scope~
o, the appended claims.
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