Note: Descriptions are shown in the official language in which they were submitted.
104'~
~his i~vention relates to the ~ealing oi electrical
components.
It i~ frequently important, and sometime~ critical,
that electricsl components should be sealed ~rom the atmosphere
to prevent their contamination and deterioration. The sealing
o~ electrical components is especially important in the ~ield oi
semiconductor packaging where the microcircuitry oi a #emi-
conductor chip iæ extremely su~ceptible to iailure. The size
of the circuitry on such miniature components i8 often oi the
order oi microns and the~ are readily subJect to short or open
failure upon e~posure to the environment. In addition to
failure o~ the connective circuitry, atmospheric contamination
oi the semiconductor material itseli may drastically affect
its electrical response.
~uch components are ~requently ~ealed and protected
irom the atmosphere by iusing a glass layer over them.
Alternatively, a metal cap may be used, ior example, by
soldering the cap over the substrate upon which the semicon-
ductor chip has been mounted.
These methods oi sealing electrical components to
protect them ~ro~ the envlronment requiree subJecting the
eloctrlcal dovice to considerable thermal strese, because the
solder or glae~ must be heated to its melting temperature. For
many electrical applioations where e~pensive, high deDsity
semiconductor chips are utilised, a hermetic ~eal 1~ required.
8uch seals must allow no detectable leakage when tested with a
- 2 - *
.,,. ,~
helium ~ass spectro~eter leak te~ter oi sensitlvity 1 s 10-8
scc/sec. in accordance with MII,Standard 88~. Pre~ioue method~
o~ iorming them have in g~neral in~ol~ed delicate and
e~pensive ~ealing operations, ior e~ample preciou~ ~etal
soldering or the ~u~ion oi a sealing glaaa to it~eli and to
metallic leads. Furthermore, once a component i~ protectod
fro~ the atmo~phere by such methods, it cannot be ea~ily
replaced. On tho other hand, ii changes in circuitry are
r~quired, the iabrication of an entirely neY packago i8 oiten
required.
The present invention provides a method Or sealing an
electrical co~ponent ~hich co~prises posltioning the component
on a sub~trate having means ~or electric~l~y connecting tbe
¢o~po~ent and ha~ing a ~all or walls to eurround said ¢omponent,
inJerting into an arsa deiined by said ~all(~) and over sald
componRnt a heat-recoverable seallng member having transverse
dimension~ less than said area deiinea by the nall(s), ~nd
~ar-lng said eealiGg mber to its heat stable etate 80 that
itB tran~v~reo di~eneions increas- and a seal i~ oi~ectod.
It ~11 bo approciated that more than one olectrical
coaponont ma~ bo sealod agalnst the atmoephere or an~ other
on~iro~nt by a dnglo heat-reco~erable sealing membor.
~po~ rooo~ery the sealing member may contact the
~ tB) o~ the ~ubetrato direotly and ezert a eealing pro88uro
upon thom. For tbis pUrpOBO the w~llte) may be ehap-d to
nhanoo tho ~eallng e~reot~ ror e~a~ple they may be ~or~ed ~th
_ ~ _
~O~
a lip or shoulder upon which the edge~ oi the sealing member
will ~it after recovery. Pre~erably, however, the wall~s)
comprise a ~eali~g ring in which the heat-recoverable eealing
member i6 positionea prior to recovery. Such a ring may, ~or
e~ mple? be made from a metal or a hard plastics material and
may be bonded to the substrate, for e~ample a ceramic substrate,
by kno~n technique~ ~uch as ~oldering or brazing. The sealing
ring ia preferably contoured to enhance the seal iormed upon
recovery and may, for esample, be formed with an inward bend
0 80 as to iorm a V-shapæ ~to which the edges of the sealing
member ~111 wedge upon recovery.
The seali~g member is preferably one which h~8 been
deformed irom a flat disc shape to a dish shape and which,
upon recovery, will return towards its original ilat shape.
~hen such a di3h shape ~ealing member i3 employed the iorces
e~erted upon the ~all upon reco~er~ may easily be calculated.
The forces ehould be such 80 a8 to de~orm the inner sur~ace
oi the wall(s) or the ae~l~ng ring sufii¢iently to se~l the
component, but not 80 great as to crack the wall(s) or the
sealing ring. The iorce at the edge may be calculated, ior
e~ample, by using etress-strain formulae such ae thoee given
in ~Formulas ror ~tress-Strain~ ~oark, 4th ~dition, ~cGraw
~ill, 1965, psge 303. B~ ad~usting the height and thickne~s
o~ the dish the rorces at the interface may be controlled 80 as
2~ to glve an ef~ecti~e seal ~ithout an~ danger o~ crac~lng.
The tra~verse dimensions Or the deformed di8c should
- 4 -
10~
be slightly les~ than the transver#e dimen~ions o~ the wall(s)
or the seallng ring. Thu~ ~or a wall dimension oi .500 inche~
the tran~verse dimen~ion of the di~c is preierably .495 inches.
With ~uch dimension~ the disc can easily be placed in~ide the
Rubstrate walls whil~t in it~ unrecovered ~tate, but cannot
return completely to it6 original flat iorm of tran3ver3e
dlmen~ion greater than .500 inohes, thus ensuring that a
pressure i8 e~erted at the inter~ace.
~lthough the use oi a disc shaped sealing member i~
pre~erred becau~e it i~ easy to calculate the recovery forces
generated at the interiace, it will be appreciated that the
particular size and shape oi the seal~ng member will often be
dictated by the requirod configuration o~ the ~inal article,
e.g. the electronic package. The edge forces of various other
shapes, including squaree and rectangles ma~ be calculated
appro~imately iro~ stress-strain for~ulaeO
~dditionally, the coniiguration oi the eeall~g member
~ay bo de~gned 80 as to increaee the sealing force, to aid
correot positioning oi the sealing member prior to reco~ery or,
in some cases, to iacilitate removl~l oi the sealing member at
a later stage. For e~ample, a generally disc shaped ~ealing
member ma~ bo provided ~ith a control protrusion ~hich
~acilitstes h~ndling oi the member using a suitable toolO
~he ~ost important advantages o~ the pre~ent invention
are deri ed irom the ~ealing member being heat-reco~erable,
~eat-recoverable articles, i.e. tho~e ~hich ha~e been de~or~ed
1 04 ~
from a fir~t heat-~table con~iguration to a second heat-unstable
coniiguration and which are capable o~ returning, or reco~ering,
to~ard~ aaid fir~t configuration upon the application o~ heat
alone, have ~ound man~ applications in diverse iields. Such
articles have typically been made irom polymeric materials,
especially cross-linked polymers, and have been described, ~or
e~ample, in U.S. Patents Nos. 2,027,g62 (Currie), 3,0B6,242
(Cook et al) and 3,415,287.
Quite recently, it has been discovered that such
articles can also be m~de irom certaln metals, sometimes called
~memory metals~ or ~memory allo~sn. The~e metals e~h~bit
changes in ~trength and coniigurational characteristics on
passing through a transitlon temperature, in mo~t ca~es the
transition temperature between the martensiti¢ and austenitic
states, and can be used to make heat-recoverable articles by
doiorming an arti~le made irom then whilst the metal is in it~
martensitic, low temperature, state. ~he articlo will retain
its deiormed coniiguration until it i~ ~armed above the tran-
sition temperature to the austenitic state ~hen it will reco~er
to~ards its original configurationO The derormation used to
placed the material in the heat-unstable coniiguration i8
com~only reierred to as thermally recoverable pla~tic deior~a-
tlon snd ¢an also, in certain csse~, be imparted by introdu¢~n~
strains into the article above the transition temperature~
~hereupon the article assumes the derormed coniiguration on
oooling through the transition temperature. It should be
1O~Z~l~
uDderstood that the tran~ition temperature may be a tempera-
ture range and that, a~ h~steresis usually o¢curs, the precise
temperature at which transition occur~ m~y depend on whether
the temperature is rising or ~alllng. Furthermore, the
tran~ition temperature is a function of other parameters, in-
cluding the stress applied to the material, the temperature
rising with increasing stress.
~mon~st such memory metals there may especially be
mentioned various alloys o~ titaniu~ and nickel which are
described, ~or example, in U.~. Patents ~o~. 3,174,851,
3,351,46~, 3,753,700, 3,759,552, British Pate~ts No~. 1,327,441
and 1,327,442 and N~S~ Publication SP 5110, ~55-Nitinol-The
~lloy ~ith a ~emory, etc.~ (U.S. Governme~t Printi~g Of~ice,
Washington, D.O. 1972). ~he property o~ heat reco~erabtl~ty
has not, ho~ever, been solely con~ined to such titanium,nickel
alloys. ~hu~, ~or example, various beta-brass alloys have
been demonstrated to eshibit thi~ property in, e.g. N. Nakan~ki
et al, ~cri~ta Metallur~ica 5, 433_440 (Ber&amon Prese 19 n )
snd such material~ may be doped to lower their trsnsition temp-
eratures to cryogenic regimes by kno~n techniques. ~1m~larly,
304 etai~less steels ha~e be-n aho~n to en~o~ such charaoterls-
tlce, ~. B~a i et al, id at pp. 663-68.
Both bypes o~ heat-recoverable material can be u~ed to
~or~ the sealing member u~ed i~ the process o~ the present
invention.
~or e~smple, a metal sealing member oan be de~ormod
1 04 ~
whilst in the martensitic state to such a dimension that it
fits snugly within a substrate onto which the elect~ical
component has been placed. Upon in~erting the deiormed sealing
member into the sub~trate and warming it to the austenitic
state the sealing member attempts to recover to its ori~inal
configuration e~erting a substantial iorce against the substrate
into which it has been inserted, the ~orce being suf~icient to
~eal the electrical component. ~ikewise, in the case o~ plastics
sealing members, by heating and derorming a heat-recoverable
pol~meric material to the appropriate dimension and then
quenching it at that dimension, upon heating, the plastics will
attempt to recover to its original con~iguration. By accurately
dimensioning the sealing member as well as the substrate,
sealing pressure may be accurately and reproducibly controlled
so as to seal the e]ectrical component.
In the case of metals, transition to the au~tenitic
stable state generally occurs at or below room temperature 80
the electrical components are not sub~ected to heat which may
cause thermal degradation. In the case o~ heat-reco~erable
plastics, heat reco~ery wlll generally take place at or below
300F, well below temperatures which will cause thermal
degradhtion oi solder connections or o~idation oi conductors.
~mong~t suitable metals there may be mentioned those
having transition temperatures within the range o~ irom
~135C to -196C, e~peciPlly nickel-titaniu~ alloys, ior
e~ample~ an allo~ containing 47.1 atom~ percent nlckel, 49.4
-- 8 --
104Zl~
atom percent titanium and 3.5 atom percent iron, which ~lloy
has a tran~ition temperature o~ appro~imately -125C. Such
an alloy can readily be brought into its martensitic st~te by
immer~ing it in llquid nitrogen.
~mongst suitabls polymeric material~ there may
eepecially be mentioned polgarylene plastics. 2hese are
polym~r~ consisting predom~n~ntly of aryl, e.g. phenyl or
substituted phenyl, groups ~hich may be linked, ~or example,
by direct linkages or b~ alkylene, carbonyl, sulphonyl or
ether linkages, or mixtures oi the above linkages. Preierred
polyarylenes are des~ribed in Belgian Patente Nos. 779,457;
779,458 and 779,459. T~ese materials may hav a highly
crystalline nature and, even without cross-linking, can be
deiormed at roo~ tomporature and yet still have sufricient
elastic memory to return to their orlginal configuration upon
heating, thereb~ e~erting a iorce suiricient to eirect a seal.
To ensure that the sealing member ~1l give a
completely eiiective seal it ~ill pre~erably be made rrom a
hard, non-deiormable material ~hen the substrate Nall or the
eePling ring is soit and deiormable. On the other hand, tho
~ealing m~ber ma~ bo ~de irom a soiter, d-~or~able ~Qteria
~h n tho ~ubstrste ~all i8 itseli hard and non-deiorDable. I~
all oases the material~ should be colected and tho dimensions
oi the sealing ~omber choson to en~ure that a au~iicient
pressur is e~erted upon the ~ubstrato ~al~ to cau~e tho ~oftor
materlal at tho lnter~aco to de~orm and thu~ 8eal the olectrioal
~04Zl~i
componentO Thus, for example, when a metal or hard~ non-
de~ormable plastic~ sealing member iB employed the sub~trate
wall(s) or the sealing ring will pre~erably be ~ormed irom a
soft metal, e.g. gold, nickel or tin, or a pla~tic~ material
which will yield upon recovery of the sealing member ~o as to
~orm a gas-tight seal at the inter~ace.
It will be eeen that by the present invention there i8
provided a method of sealing electrical components which i8
more reliable and less costly than the methods previously
employed. ~nother important advantage is that the electrical
component or æub~trate is not sub~ected to excessively high
temperatures, thereby permitting the use o~ a wider range of
component material~ and substrates, including plastics.
~nother important advantage is that the sealing member
can be readily removed to expose the electrical component ii
repair or replacemenb is necessary. In the previously employed
methods u8ing, ~or ezample, glas~ or solder cap~ it ~as
impossible to remove the sealing member without sub~e¢ting the
package to high temperatures. In the present invention,however,
a metal sealing member can readily be removed by immer0ing the
package in liquid nitrogen 80 as to cool the metal to its
martensitlc state. In this state the sealing member may be
deiormed and removed. ~lternatively the metal sealing member
could be remo~ed by crushing it ~hilst in the austenitic ~tate.
Plaatic sealing members can be removed by heating them to a
temperature at which they ca~ be de~ormed and romoved ~rom tho
-- 10 --
104Zll~
package. In all casea removal i~ racilitated by the provision
of a protru~ion on the soaling member, as described above.
It will be appreciated that one oi the moqt important
applicationq oi the present invention le in the iield o~
electronics, especiall~ in the manufacture Or electronic
packages. ~ccordingly, the ~ubstrate 18 pre~erably one whlch
is suitable ior the mounting of electronic components, belng
made, io~ eYample, ~rom an inorganic in~ulative material ~uch
as a ceramic or a glass or an organic in~ulative material such
as a poly~eric material. The neceasary means ior electrical
connection may be metalllzed on said substrate by conventional
methods or may be diacrete wires provided on or within said
substrate.
Various ~orms o~ the present invention will now be
described, by way o~ esample only, with rePerence to the
accompanying drawings, in whichs
~igure l is a top vie~ o~ an electronic pac~age
suitable ior use in the present invention;
Figure 2 is a section through said package a~ter an
eloctrical component has been ~ealed bherein
in accordance with the present lnvention;
~lgure ~ 18 an enlarged view taken ~rom Pigure 2
ohowing more clearly the lnteriace bet~een
the aealing member and the substrate ~
~igure~ 4 to 6 repreaent dii~erent sealing membere
~or use in the present invention, beiore and
after doformation;
lO,~
~igure 7 iq a section show~ng a ~ubetrate provided
with a sealing ring in acoordance with
the pre~ent in~ention; and
Figure 8 i~ a sectional ~iew illustrating a method
o~ deiorming and in~erting the sealing
member in one operation.
Referring now to ~igures 1 and 2 the electronic
package l comprises sultable substrate 2 metallized ~ith
electrical conductors 4 to pro~ide input/output means ~or an
electrical component 6 shown in Figure 20 &b~trate 2 may be
made o~ any insulative material, including inorganic ineulators
~e.g. ceramics ~nd gla88) or organic insulators (e.g. epo y
resins, phenolic resins, melamine resins, nylon, polyesters,
Teilon (~rade Mark), polyimide~ and polyarylenee)O When
organic insulator3 are used as the aubstrate material, rein-
foroing agents such as glass iibre or microspheree are desirable
to impart the required rigidit~ to the electronic packag~ 1.
~ metallized die attach pad 8 i~ utilized ior receiving
the component 6 to be attached and electrically connected. The
die attach pad 8 le generally metallized with a noble metal
such ae gold. ~imilarly conductore 4 may have a top layer o~
gold, beneath which may be less e~pensive metal~ euch as copper.
Preierably, the metal conductors 4 are depoLqited onto the
subetrate 2 by meanH oi ~nown techn~ques such ae sputtering>
vapour deposition or electroplating. Eowever, discrete wiring
~a ~ aleo be u~ed in the electronic packages ueed in the
lO~
pre~ent inYention. The electrical conductors 4 are then
connected to a second level packaging (not shown) vla conductor~
10. The substrate 2 may be oi the multi-layer variety 80 that
the conductor~ 10 are sandwiched there between. 3uch ~ub~trates
permit denser packaging since multilayer circuitry may be
utilized. Of course, a ~ingle layer substrate 2 may also be
utilized where high circuit den~ity i~ not required. As be~t
seen in Figure 2, a wall 12 i~ provided ior encompa~sing the
die attach pad 8 upon ~hich the electrical component 6 i9 to
be attachedO
~ter positioning oi the electronic component 6 over
die attach pad 8, a heat recoverable sealiDg member 14 i~
placed into the wall~ 12 and over the component 6 ~o a~ to
seal the component irom the atmosphere.
~eferring to Figure 3, wall 12 i9 provided with a
lip 18 to receive the heat recoverable ~ealing member 14. The
lip auriace at which a seal between the heat-recoverable
sealing member 14 and the wall 12 i~ formed ehould be made
~ro~ a material which will deiorm upon the esertlon oi iorce
b~ the heat-recoverable material. In the case oi a tit~n~umr
nickel metal sealing member, the lip suriace should b~ made
iro~ a material Hoiter than the titanium-nickel allo~, e.gO
gold, ~iokel or a plastics material.
8ealing member 14 ma~, ior esample, be prepared irom
a planar diac oi a nickel titaniu~ allo~ containing 4701%
nickel, 49.4% titaniu~ and 3.5% iron. This co~po~itio~ result~
~04i~
in a material with a transition temperature oi appro~imately
-125Co The di~c i~ reduced to a temperature below its
transition temperature by immer~ing it in liquid nitrogen
which exhibits a ~table temperature o~ -196C. While held at
thie reduced temperature, the di~c i~ ~ubJected to su~icient
iorce, e.g. in a prees, to cau~e thermally recoverable plastic
deiormation to take place whereby the di~c is placed in a heat-
un~table diehed configuration. ~he deiormed disc i~ held at a
temperature below it~ transition temperature, e.g. by continued
immersion in liquid nitrogen, until it i8 ready ior useO
The disc 14 is inserted into the walled ~ubstrate 2
while in the cooled ~tate, after ~hich it is allowed to war~O
This method results in little i~ any thermal stress. Ob~ioualy,
the electrical ¢omponent is not sub~ected to high temperatures
as ~as the case ~ith the prior art methods. In most instances,
the entire electronic package 1 can be cooled to liquid
nitrogen temperature during the sealing operation, although
this ie not essential.
~lternatively, member 14 may be made oi a polymer
material capable o~ being made heat-recoverable 80 as to
esert a iorce ~hen caused to recover, e.g. a polyarylene.
The coniiguration oi sealing member 14 ehould be
euch ae to iit eaeily into wPll~ 12 Nhile in the deformed state.
The use o~ round walls with a heat-recoverable member which has
been derormed rrom a rlat shape to a dish i8 particularl~
euited ior this application since the sealing pressure8 o~ tho
~ ~4 ~
wall may be readily calculated. Protrusion 16 i~ provided
on the heat-recoverable sealing member 14, ~o as to allow a
holding tool to insert and properly position the member withln
the walls 12 of the electronic package 1.
The surface con~iguration of the sealing member~ 14
may be de~igned and deformed ~o as to increase the ~ealing ~orce
or aid in insertion of the member into the substrate walls.
Figure 4a is a cross-sectional view oi a ilat disc prior to
de~ormation with Figure 4b depicting the disc a~ter deformation.
Upon warming the deiormed disc to its stable ~tate, the disc
will tend to return to the original shape, thereby e~erting a
iorce against the substrate walls.
~igures 5a and 5b depict a disc cross ~ection beiore
and after deiormation having a large control protrusion which
assists the insertion oi the disc into the walls oi the
substrate.
Figures 6a and 6b depict a ilat disc which is
de~ormed into a ~doughnut~ shape. ~his configuration result~
in a substantiall~ horizontal iorce being e~erted by the
member agalnst the substrate wall on wQrming.
~8 e~plained above, the wall may be an integral part
oi the substrate, and have the same composition as the
aubetrate. However, becauee o~ the hardness o~ inorganic
substrate~ euch ae ceramic8 or glass, it is preierable to
provide a wall having a~ lnner 8ur~ace o~ con~iderably softer
materlalO Thus, a eep~rate metallic ring may be attached to
- 15 -
1042~1~
the ceramic ~ubstrateJ the ring having that portion oi its
inner ~uriace which iB contacted by the heat-recoverable
sealing member 14 coated with a ~o~t metal quch as gold or
nickel. Of course, where the wall 12 and the substrate 2 iorm
an integral component, such as a ceramic, the inner wall ma~
still be coated with a soiter material ~uch a~q gold, nickel or
tin. When the ~ub~trate and wall are iormed irom softer,
organic inqulators, coating oi the interior suriace of the wall
with a soft material may not be necessary.
~owever, even if the interior suriace oi the ~all i8
a suitable soft material, it may ~till be desirable to provide
a sealing ring into whi¢h the sealing member can be tightly
wedged.
For e~ample, Figure 7 illustrate3 the u~e oi a eealing
ring eo that tho ~ealing member does not directly contact the
subetrate wall~. The ring 18 is preferably made oi a rigid
material such a~ ~ovar (Trade Mark) (an alloy oi ¢opper, ni¢kol
and iron having a ¢oeificient oi e~pansion similar to that oi
glas~). Preierably, the ring is coniigured with an inward bend
oo as to iorm a ~-ahape into whi¢h the sealing member, upon
re¢o~ery, will ~edge. ~nlike the straight side wall oon-
iiguratlon ehown in Figure 3, the Y configuratlon en~ures
retention oi the disc 14 and a "double seal" on two quriaces
oi the ring 18. The ring 18 may be bonded to substrate 20 on
metallized pad~ 22 b~ known techniques such as soldering or
brazing. ~he ring 18 i~ placed over the substrate ¢avity 24
- 16 -
104;~
into which the electrical component is inserted. Input/output
lead~ 26 are provided for connection with an electrical component.
Figure 8 illustrates a method of derorming the sealing
member and posi~ioning it o~er the electrical component in one
operation. An electrical component, similar to that shown in
~lgure 2, is sealed ~ia a heat-recoverable sealing member 30
which iB deiormed by punch 32 into a concave configuration.
The top w~lls Or the substrate 2 de~ine an opening the dimensions
oi which are slightl~ less than those Or the undeformed sealing
member, BO that upon insertion and operation of the punch 3 the
member 30 is de~ormed to the concave configuration shown. The
walls 36 are curved to form a lip 34 upon which the con¢a~e
sealing member 30 sits rlush. The lip 34 al~o ~er~es as a ~top
to pre~ent the sealing member 30 irom pressing and damaging
the electrical component 6.
In the case oi a metal sealing member 30, the member
iB inserted and de~ormed in its unstable m2rtensitic state~
and after in~ertion i8 allo~ed to return to its stable austenitic
state. The member 30 will attempt to return to its original
flat configuration, eserting pressure again~t the ~alls and
~ealing the electrical component 6.
In the oase o~ a plastics sealing member 30, a
heat-recoverable material is deformed during insertion, after
which lt i8 heated to cau~e it to esert pressure and seal
the electrical component 6.
- 17 -
