Note: Descriptions are shown in the official language in which they were submitted.
11[1~3~
P~IN 8~82
GELI/TJ
23-1-19q8
~ .
"Semiconductor device and method o~ enveloping
the semiconductor device".
The invention relates to semiconductor
devices comprising a semlconductor element, conductor
leads which are in electrical connection with contact
pads o:f` the semiconductor element, and an envelope
5 of syIlthetic resin ln which -the semiconductor element,
its electrical connections~ and part of the conductor
leads are aeoomodated.
~: ~ Envelopes of sy~the-tic resin : are convention- : :
` ~ :
nally used in semiconductor~ devices, such as transistors : : -
10 and integrated circuits 0 It has been general
.~ practice to: use~ as an e~veloping material a theDmosetting
resln and: to form the envelope by transfer mouldingO This
wide application~ has resul.-ted in both the properties
of :enveloping:~material and the process control
15 being generally optimized to ob tain envelopes
of` a ~ favourable quallty. Nevertheless, such an enve~
oplng~ ~te~chnlque exhlblts drawbacks .~ The rate; at
whlch devioes can be provided :wlth envelope~s is ~ :
restrlc~ted by ~ the: ~t~me ~whloh ~ls~ ~necessary t:o ~cure
20~ the thermo~sett~ng~resin:~ ~and this~ has a ~detrimental
nfluence~on the prloe~of ~the~ s~emiconductor~ ùevioer ~ :
Furthermore:, t~:e~ viscosity~ o:~ the enveloping material
lS~ low so that~ during enYeloplng measure~ have to
be~ taken to `~obt.ai.n :good; ~seallng~ the~ ~mould so as :~`
25 to prevent;~flashlng.~ Fu:Lthermore, a materl.al, for example WQX,
: is incorporated~: in the material~ o~f the envelope so that l~he
enve' ope can :be~ ~1ore readll~ de-tached f`rom the mould;
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PHN. 8682.
23-1-1978.
however, such an addition can reduce the quality of the
enveloping material.
Envelopes of thermoplastic synthetic resin
have not found acceptance in practice. The viscosity of
the liquid thermoplastic synthetic resin is comparatively
high~ so that injection moulding with this materlal can
rapidly result in damage of, for example, connection~wires
between the semiconductor element and the conductor leads.
The injection moulding process has to ~e carried out at
comparatively high pressure so as to readily fill the
mould cavity, and this pressure has to ~e maintained sub-
sequently for~a certaln p~erLod~o~ tlme~so as to~compensate
for shrlnkage~;during~solidi~fl~cati~on~of the synthetic res~in
in~the~ mould~ o~nse~quently the ~cycle time is rather long.
5;~ Furthermore,~the protection with thermoplastic synthetlc
resln~affords from ambient inf:Luences, such as contami-
nants~ln~the;envlronment~ ls not optimum.
Acoording to the invention, there lS provid~
e~d a~semiconductor~device comprising~a s~emiconductor e~le-
~
20~ ; me~t,~conductor leads which are in electrical connectionwith contact pads on the semi~conductor element~and an
e~velop~e of~synthetic resin in which the semiconductor
elemenis,~ ts electrlcal~connectlons~ and part o~the ~ ;
` conductor l~eads~arc acc~ommodated, said envelope compris-
25~ ing an inner encapsulation which protects the~semiconduc-
.tor~element~and~lts eleotrlcal~oonnectlons agalnst ambl~ent
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~:~9370~ ~
`: PHN 8682
23-1-1978
influences and a part of foamed thermoplastic
synthetic resin which is i.njection moulded around
said encapsulation and determines at least part
of the outer shape of the envelope.
:: 5 The inner encapsulation protecting against
~; ambient~in~luences can~be~provlded in a simple
manner and prevents damage~t~o~the semloonductor
element and wires~ during thè::further enveloping
with~the~ thermoplastl~c materlal. The thermoplastlo :;::~
:10~ envelope~par~t Qan bs formed by~spraylng lnto:a~
mouldl~under pressure a thermopastic ~ synthe~tic
re;sln pr~ovlded wi~th~a:foaming agent;~ln spit~e~
o~the~comparatlve~ly~hlgh vis¢oslty~of~the~ thermo~
:plastlo~syn~the~tl~c resin~ damage to the~unlt ;
5~ belng~e:nveloped,~can~be~avolded bscause this unit
is~already~encapsulated. As compared with
thermosetting~reslns, no~speolal requlrements
`ns:ed~be-~imposed~;~on ~hel~s~eàling.o~ the~mould~to pre~
:: vent flash-products~adhe~ring~to~the device envelope.
20 ~ Furthermo~e~ the~appli~cation~of~subse~quent pressure to~
he~:thermoplastio~l~synthe~t~ic:~ resin~in the mould~is not
ne~oessar~:~slnoa~the~foamin~g~ ent-ensures the~ expanslon~
of::~the~material~ s:o~ that~t~e~ outer~s~ape o~ the envelope
PHM. 8682.
23-~1978.
.
automatically corresponds to the mould cavity. The foamed
thermoplastic synthetic resin envelope thus can be pro-
vided in a very rapid process particularly i~ the mould
is cooled. The envelope of such a semiconductor device
thus can be manufactured at a comparatively low price,
can be o~ good quality and have a smooth outer shape
with accurately de~ined dimensions.
The encapsulation which protects'the semi~
conductor element and its connections against ambient
;10 ~ influences~may advantageously conslst of a thermosetting
synthetlc~resin, for example a slnter~d~powder~coatlng
of an ~epoYy~ r~esin. The protecting encapsulation can be~
provid~ed ln~a~rapid pro~cess and as w~ be descrlbed
hereinaf~er~several of~'semiconductor devices can be en-
15~ capsu~lated~simultaneously ln such a way as to both savetime~and avoid~complicat~ed~moulds;'~furthermore, by using
such a process, no materlal~need~be added to the thermo-
setting material to detach the e~capsulated product ~rom
a mo~ld~ so`'that~the~quallty;o~f~the~-encapsulatlon can~ be
20~ axtremely~good.
The~thermoplastic synth~etlc re~sin may~ad~
~antageou~sly cons~lst~of on6 0~f~the materials polypropene
and~p~olyphenylene sulphide~wi~th azo~icarbonamide as the
foaming~agent.~ In another~advantageous~form, the thermo-
25~ plastlc~-~synthetl~o resln~consists of a~poIyamide~foamed~
with a;blowlng~agent comprlslng~ no~oarbonate~as lts~
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main constituent.
According to the invention, a method of
enveloping a semiconductor device is characteri~ed
in that a semiconducbor element which is connected
01ectrically to connection conductors is provided
with an encapsulation protecting against ambient
influences~ after which the encapsulated semicon-
ductor element lS provlded in a mould having a :
cavity determining the outer shape of the envelope,
and that the mould is moved with respect to the
discharge openings of an injection moulding device, :~
n:~ in which~first a wall part of the mould shuts.
off the dlscharg~e openings~, then~a feed opening~
of the~ mould is po~s:itioned before the discharge
15 ~opening, and a mi~ture of;foamable thermoplastic ~ :
: material and a blowing agent is injected in the
mould cavit~ and futhermore a wall part of the mould
shuts off agai~ ~the discharg~ ~pening, and the ~: :
enveloped semlconductor devioe~ i5 taken~out of the ~
20:: mould after cooling the foamed:-thermoplastic material.
::
By using a matri~ which can~be~moved wlth respect
to the discharge~openings,~;a v~ery;rapid enveloping
process oan:~be obtained.~
An embodiment ~of thé lnvention will now
~be desoribed,:by way of example, wlth reference
: to the accompanyi~g diagrammatic:drawing~ in which~
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PHN 8682C
3L~3~376~
Figure 1 is a front elevation of a semiconductor de-
vice assembly without an envelope;
Figure 2 is a front elevation of the device assembly
shown in Figure 1 when provided with an encapsulation;
Figure 3 is a side elevation of the device assembly
shown in Figure 1, and
Figure 4 is a front elevation of the semiconductor
device formed from the assembly shown in Figures 2 and 3 after
providing a foamed thermoplas~tic envelope.
Figures~5 and~6 schematically and not to scale show
a number of examples o~ înjection-moulding installations partly
in cross-sectlon and partly in p1an view.
Flgures 7 through 12, Figure 8 being on the same sheet
as Figure 5 and~Figure~1~2 being on the same sheet as Figure 9,
15 ~ ln schematlc cross-sectlon~show an inJection rnoulding-installat10n,
which ;s particularly~suitable for continuously encapsulating
semiconductor devic~s with a synthetic res;n.
; Figure 1 shows a par~ of a semiconductor device having
terminals provlded by conductor leads 19 2 and~3; the conductor
~:
ZO ~ ~ 3 has a supporting~face 4 for a semi~conductor element S~ and
the lndiv;dual leads 1, Z~and~3~are~united~ln~a;~cont;nuous con-
ductor~strip,~only~part of wh;ch~is~shown~in F;gure l. The
sem;conductor;el`ement 5~is secured~to~the support 4 by means ~ -
of,~for~examp~le,~a solder~or an~electr;ca~lly conduct~lve ad~5 ~ ~ hesive. Connection~wires 6 and~7 form an electrical;con~nection
between~contact pads~on~the sem1conductor element S and ends
o~ the conductors 1 and~2.
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,7~ ~ PHN 8682
23.1.1978
This construction is usual for a transistor which
is provided with au envelope of synthetlc resin.
In a sen~iconductor device in accordance
with the present invention the envelope consis-ts
of two parts. A ~irst envelope part (Figures 2 and 3)
consists of an encapsulation 8 of a material which
protects the semiconductor element 5 against amblent
in~luences. This encapsulation 8 is provided around
the support 4, the semiconduotor element 5, the con-
nection wires 6 and 7 and the ends of the conductors2 and 3 ~acing the semiconductor element. In a
~a~ourable construction the encapsulation consists
of a thermosetting synthetic resln, ~for example an
ePo~r resin. The encapsulation may~advantageously
15~ ~ be provided by heating a conductor strlp cont~alning
several semlconductor assemblies~and providing
powder~on~the parts~to ~e covered, for~example a
powdered~mixture~o~ epoxy resin~and hardener. The
:
~ ~ powder which is only allowed to ContaGt the heated
,
~; ~20 parts to b~e covered, melts, adheres to these parts
and oures.~Thls powder oover~ing lS prefera~lr~oarried
ou~ in a whirl~sintering bath. I~ desired more than
one dipping may be~carrled out so as to gro~
the e~ncapsulation~to~the~desired~thi~ckness. ;
25~ The~second part of the envelope (~lgure~4
c~onsists~of an~envelope~part 9 of ~oamed thermoplas-
tic synthetic resin~whlch is provided by means of
injection mouldlng.~he injection moulding can
advantageously be carried out by providing~a ~her~oplastic
,
P~'~ 8682
3.1.1978
~V~3'70~:
synthetic resin with a foamiIlg agent under pressure
in a cooled mould. The method of providing the second
part of the envelope will be described in detail
hereinafter with reference to Figures 5 12.
As a r~sult of the use of the foaming
agent~ the mould cavit~ is entirel~ ~illed and the
envelope accurately assumes the shape of -the mould
cavity without requiring the applicatlon of subse-
quent pressure. The envelope can be pro~ided in a
particularly rapld productlon process, which is -
- facilitated by cooling the mould. As a result of the
comparatlvely high viscosity of the thermoplastic
synthetlc resln~no speclal requirements need be
imposed up~on the sealing of the mouid; the envelope
5~ part 8 protects the semlconductor devioe against
damage when~Ll]lng thé mould.
A~ter~;~provlding the envelope in this
manner the~conductor strip lS 6evered in kno~n
manner~to separate the conductor leads 1, 2 and
~ ~o~ the~devlce. The;resulting~d6vlc6~ls shown in
Figure~4.
The combination of the protecting encap-
sulat1on~8~and~the~cam6d~thermo~6tlc~ env610pe 9
has enab~ed 6emiccnductor device6~ to be manufactured~
5~ at a fast~rat6~and~a 1cw prioe.~Th6 env610pe may
have any desired outline.
It~has~ proved advantageou6 to u6e poly~
prcpene or po1yphenylene ~ulphide as a thermoplastic
re6ln and azodicarbonamlde as a~fcaming agent. Other
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~0 ~ 3 ~ ~ ~ PHN 8682
23.1.1978
thermoplastic synthetic resins and foaming agents,
however, may alternatively be used. For examp~e,
forming the envelope part o~ polyamide foamed wi-th
a blowing agent comprising zinc carbonate as its
main constituent has proved very ef~ective.
In the embodiment described the seml~
conductor device is a transistor. It will be obvi~
ous that the invention ma~ also be used with other
semiconductor devices, for example integrated cir-
oults, and in some~devioes a heat sink may formpart of the outline of the envelope.
.
The provision~of~the ~oamed thermoplastic
envelope~wlll be desorlbed;with ~reference to Flgures
5-12. In the diagrammaticall~ compression arrangement
iS~ ~shown in ~lgures 5~and 6,~th~e semiconductor devlce
is not yet ln the~mould. In Figure 7 the place o~
the semioonduct~or~;device ln the mould is sho~n.
In Figure 5 the reference numeral l1
denotes a sohematlcally shown~mlxlng and compression
20~ arrangem~ent for plastlos.~The constructlon thereof
will not be discussed in more detail because it
may be of the conventional type, for example an
e~xtruder devloe. Thè~compre~slon arr~ngement 11
has a discharge opening 12,~which is surrounded by
25~ a cooling plate~13~whlch is~thern1all~ lnsulated
there~rom. Underneath the discharge~openlnq~12 and
the cooling plate~13 a~guide~ay 14 is located acrass
which moulds 15;can~be moved. The moulds 15;have suoh
a height that their top sur~aoesengage~with -the cooling
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lU~3~4 PHN 8682
23.1.1978
plate 13 and the dlscharge opening 12, respectively,
whilst if necessary the cooling plate 13 or the
guideway 14 can resiliently be urged slightly
I towards each other. Each of the moulds 15 has a
¦ 5 mould cavity 17 and a feed opening 18. In the mixing
and compression arrangement a thermosetting plastic
mixed with a foaming agent is brought at a tempera~
ture a~d pressure at which this mixture is liquid.
Undern:eath the discharge opening 12,
~ ~ 10 which is continuously open, a mould 15 is slid
i ~ ~so -that at a given instant the feed opening 18
~ comes in ~ront of the discharge opening 12 and
: ~ ,
a thermoplastic material is formed into the mould
cavity 17. The mould may move continuously or may~
15~; be sbopped~brlefly if desired. After the mould 15
has ad~anced~ the discharge opening l2 is ~ut off
by the top of~the~mould 15 which severe the Plow
of plastlc. Th~e plasti~c remains pressurized and at
a high temperature in the~arrangsmsnt 11 until
j20~ the féed~opening of the next~ mould 15 is in front
o~ the discharge opening.~The filled mould is now
advanced through the guideway, the plate ~1~3 closing
; ths ~ssd~op~ening ~18 and~ ~urthsr~ oooling ths mould
j through~contaot wlth sald~mould.~During~oooling ths
th9rmopIastlc material w~ shrlnk~but; t~h~s is
j compensated~for by ths~sxpa~slon o~ ths foaming agen-t,
so that ths mould~cavlty~always remains correctly
illed. The moulds can~be~moved along the guideway
15 either continuously or discontinuously, the feed
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~ ~ 9 3 7 ~ 4 23.1.1978
opening of a mould each tlme allowing the plastic to
flow into the mould cavity through the discharge opening
- ~or some time. Because a foaming agent has been added
to the plastic, the plastic in the mould need not be
"post-compressed" until the plastic has set. This means
that a fast oycling time is obtained.
Figure 5 shows moulds 15 in which between
the feed ~opening 18 and the actual mould cavity 17
another duct is formed, so that the moulded product
still exhibits a sprue. Sometimes this is not annoying
~r even desireable. Ifsuch a sprue is undesireable,
moulds 10 may be used as shown in ~igure 6. In these
moulds the upper wal~l has been dispensed~with completely,
so that in thla case~the feed opening ia oonatltuted
by this fully open wall. This has the advantage that the
dlaoharge opening 12 communicates with the mould cavity
during substantially the entire period that the mould
is dlsposed~underneath the feed openlng. Thus, a correct
~ : :
*~ ng is now alao enaured when the moulds are rapidly
20~ ad~anced.
One~of the slde walls o* the obJect to
be formed now slides along the oooling~plate 13. It has
-~ side
been found thatlthia/wa1l neverthelesa has a very
sa*isfactory~appearance~and that owing to the foaming
aotlon the mould oavity alwaya remains correotly ~illed,
alao~durlng coollng, and~ahrlnkage ~la;~hardly peroeptible.
igures 7 through 1~2 schematically show
an apparatua for~eno;apsula-tln~g a ~tran~slator wlth a foamed
thermoplastio mater~ial,~the compresslon~and mixing de-
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~g3~7~ PHN 8682
23.1.1978
vice being omitted. This apparatus comprises a
basic section 20 (also sefe Figure 8~ in which a bore
21 for the discharge opening of the mixing and
compression devioe as well as openings 22 and 23
for cooling water supply and dralnage are formed.
Furthermore, recesses 24 are ~ormed in the basic
section 20 for the ~ixation of yokes 25 which carry
the guide ways 26 and 27 (see Figure 9). ~ ~
~ To the basic section 20 a cooling plate 28
consisting of a plurality of parts is secured
(see Fig~re 10) ln~such a way tha-t op0ning329, 3O
and 31 thereof ccrrespond to the openings 21, 22 and
, 23-
A shaft 34 which~is~provlded wlth a plate~
15~ 35 is ~jo r~alled~ln~the bas~io sect~on 20.~Thls~ plate 35carrles~an~inner~ring~of mould portions~36~, between
whioh~movable mould portions~37~are~lnterposed,
which on~their slde~which faoes the axis of the
, ~ :
shaft 34~each~ carry a gui~e wheel 38 which bears
aga~inst~the~gulde1~ay ;27 (s~ee~Flgure~
The plate 35 ~furthe~rmore~carrle6~;a rlng of~
arms 40, which are pivotabl~ connected to the plate 35
at the loaation 41~.~ Eaoh of~'the arms 4O carrles
two,mould~walls 42 be-tween whloh a mbvable mould
~ 25~ wa]l 43~;is~int0rpo~sed,~whlch lS provided with a
f ~ roller 44~which~ls~adapted t~o co~-operate with the~
guldeway~26,~ Eaoh~ ar::~ the~arms 49~furthermore com-
; prises a cam 45~whioh~ lS adap~ted~to~oo-operate wlth a
slot 46 so as~to swing out the ar~
f
~ ' In the oollar ,i1 recesses Qre formed which
:
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PHN 8682
~93~4 - 23.1.1978
accommodate the lead 52 of semiconductor devices
53 to be encapsulated which are disposed in the mould
cavity 50, the semiconduc-tor devices having the
shape as shown in Figures 2 and 3.
The operation of the present apparatus is
as follows: By a drive means coupled thereto the
shaft 44 is rotated, so that all parts connected
to said shaft are also moved. As the moulds run
between the guideways 26 and 27 the mould portions
will perform a specific cycle of movement. Starting
from position~21, 29 where the discharge opening
.
of the mixing and compression device is located,
opposite the mould cavity 50 the reproduction cycle
will be as~indicated in Figure 12.
15~ Durlng~stage I one~of the moulds communi-
oates wlth~the discharge openlng so that the mould
cavity is filled wi~th an amount of plastic.
During stage II the plastic is cooled
in that o~le of the~sldes~of the envelope slides
Zo~ along the~ooollng~pla-te 28, whioh~is cooled by a
stream o~cooling~wa~er~which is~passed through it.
Shrinkage as a result of oooling lS then compensated
for by the expans~lon of~the foaming~agent so that
the~mould~cavity~always rsmains ~ilIed and env0lopes
25 ; of ~mooth~appearanos ~are~obtained.
At~the;~beglnning of~stage III the cam 45
engages~w~;th the s~lot 46, a~ter whlch the~arm 40
pivots about polnt~41 and the~mould is opened as is
shown in ~igure 7~in the lower~position.
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~93~ ~ PI~ 8682
23.1.1978
The moulded products can now be removed
from the mould in stage IV, the arm 40 being retained
in its open position throughout this stage.
Finally, in stag0 V the mould is closed
again, after which a new cycle can start. It will
be evident from the foregoing that by means of this
machine semiconductor devices with an envelope of
thermoplastic resin can be moulded in a continuous
manner. The production rate can then be very high.
In the discharge opening of the com-
pression device no intricate valve need be mounted,
because the mould walls themselves ensure that the
discharge~opening is shut off so as to sever the
plastics flow until the next mould ari~es. As one
side o~ the mould is in ~act open, and constit~tes
the f`eed~opening~ol ~the mould, and is subsequently
slid ~past ~the cooling plate, the formation of spures
:
on the product~is completely avoided and furthermore
a very good heat transfer to the cooling plate is
; achieved~
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