Note: Descriptions are shown in the official language in which they were submitted.
The present i.nvention relates to a rnethod oE manufactu-
rlng .ll~atl-~L~ l(c~ o~.:o~ cl.:iv~ t ~ll d~ o~ 1 ol-l an
ellame:Led substrate.
A pl.ocess i.s a:l.ready knowll~ cl.i.sc:losecl in [).S. l?ateut No
3,~2~,256, iss~ c~ b~ 9~r~ lV.il~(3 1~ .LI1VC!I~ L S~ e,
wllerc~:in a :I.avel: o:f^`l~oll conduct.ing .inl; :I.oadecl with a ~)owcler o~
me~al, a1.1oy or nleta:Ll:i.c: cler:i.vat:i.vc! .i.; appli.ed oll the support,
thell heatecl in orcler to hardell the inlc, t.he ~urface oE the ink
la~er be:i.lly treatecl so as to lay t~e parL-.i.cles for.rning sa:id
powcler bare, and the support thus coated is immersedinto a bath
contaillin(3, in the form o~ particles, the conclucting metal to
be depositecl/ under conditions wh:ich are known per se anct such
that said conducting rnetal. partlcles are c1eposited 011 the
powcler parti.cles laid bare.
In the usual ways of performing this process, a glass and ;~
resin laminate is used as insulating support, the resin being
a -thermostable resin sueh as s:ilicone orpolyimide, and the ink
being also a therrno-s-table resin such as silicone or polyimide.
The use of plastic materials for the support limits how-
2G ever the opera.ting temperatures of the circuit obtained and
its resistanee to ageing. :
Moreover, it is desi.rable to be able to form printed cir-
euits, resisting or not, on supports currently used in the :
branch of electric household appliances such as on steel or
aluminium sheets r glass, etc.
According to the present invention, there is provided amethod of manufaeturing a pattern of eleetroeonductive metal
deposited on an enamel.ed substrate~ which comprises applylng an
ink composition to the enameled-substrate in accordance wi.th the
pattern, the ink composition comprising a second enamel and a
metal-eontaining powder reeeptive to eleetroless plating, the
second enamel having a melting point no greater than the soften-
ing point of the enamel of the enameled substrate and the metal-
~3~LU
containing powder being p~esen~ in an amount ~;uEicient to pro-
vide Erom 60 to 90~ by weight~o~ the ink cOMpositiOn after
balcing; baking the composi~ion; treating the baked composition
so as to expose partLc1ec ol: the meta:L containing powder; and
sllbjectil~tJ the l)aked, e~posec~ compositiorl to elc~ctroless platiny.
T~lc ~Ise o an enalnel Eor Eorminy the inlc permits usiny as
support ellamc:lled metal:Lic sheets or glasses or ~rlamelled cera-
mics. Said supports exhiblt the ac1vantaye ot having a robust-
ness, a resistance to ageing and a thermal stability which are
obviously very hiyh.
The deposit of the conductillg metal is preferably carried
out according to the so-called "electroless" chemical deposi-t
process which is not using electricity.
The proportion of powdered metal in the inlc, after baking
the enamel, is advantageously comprised between 60 and 90~ by
weight, the proportioll of enamel being -then oE 10 - 40% by weight.
A high proportion of powdered metal is in Eact necessary
for reaching a high density of the metallic particles said high
density favouring a uniform deposit oE the conducting metal.
This high proportion, and the density generally high of
the metals, lead to the fact that the outer layer of the sup-
port coating has to have a softening point of the same order
preferably slightly superior to the melting point of the ink
enamel. In fact if the coating was getting soft in a notable
manner while the ink was being baked, the powdered metal would
penetrate into the coating and cause cracks, and the electrical
insulation characteristics of the coatiny would be seriously
impaired.
As reyards the carrier, an oil which is habitually used to
this effect is employed, in a proportion such that the ink
obtained is in the form oE a fluid compound usable with
-- 2 --
.
" ~3~3~3
the sil~-screen proce~s. This proportion depends on the
specific surface of the powdered metal uqed, a high speci~lc
surface requiring a large quantity o~ oil.
The powdered metal must exhibit a relatively high resis-
tivity qo a~ not to modify the electrical characteri~tics
o~ the ~inal. prlnted circui$. On the other hand, the metal
o~ ~id powder has to be chosen such that the depo~it of
oonducting metal through the "el~ctroless" proces~ i~
carried out ~Ider the mo3t favourable conditions~ In
principle, a metal is chosen who~e electrolitlc potential E
is high relative to that of the conducting ~etalO ~owever,
one may al~o use the same metal a~ the conducting metal,
notably ln the case of nickel,
A~ examples o~ powdered metals, o~e can mention in
particular the powders of cobalt-nickel or iron, wlth
particle size comprised between 1 and 10 ym.
Preferably, partiole~ of spongy or angular shape will be
used~ since ~uc~ shape~ provide a good mutual bonding of
the particles which provides them with a better resistance
to the treatment neces~ary for laying the particles bare,
oarried out through sand blasting, brushin~ or chemical
attack. Moreover, said particle ~hapes favour the obtentio~
of a high den~ity ~hich, as has been seen, i~ advantageousc
The conducting metal chosen for making the printed
circult i9 selected of cour~e in relation with the conai-
dered applicationO I~ the circuit has to ha~e a high re-
.sistance, and is intended for u~e in heating, a hlgh re-
sistivity metal will be chosen ~uch as nickelO I~ on the
contrary a lo~ resistance circuit is required, intended
for instance fsr establi~hing connections, a lo~ con-
ductive metal will be chosen such as copper or silver.
The enamel coating applied on the support is of great
importance since, further to its stanclarcl Eunetions of pro-
teCtincJ the support alld giVinCJ it a yoocl appearanee, it has to
permit the aclh~rellce o~ t~le inli layer and provicle the eleetrical
lnsu1atioll betweell support alld prlntecl eircuit when the support
ls ikselL eoncllle~ive.
OC course, the ellamel eoatillg is chosen primarily as a
functioll of th~ support characteristics: meltin(3 point, thermal
expansion eoefEicient, resistivity, surface state, ehemical
nature.
A preferred embodiment will be deseribed hereinafter as an
example having reference the attached drawings, wherein:
Figs. 1 to 6 illustrate differell-t steps of -the method of
the present invelltioll.
The strueture and eharaeteristies of the enamel coating
will is described hereinafter in the ease where the support is
a steel (or eopper) sheet, an aluminum sheet, or a glass sheet
~or also a eeramie or a borosilieate sheet).
When the support is a normal steel sheet, a mass layer has
2n to be providecd with a very blistered strueture for easing the
removal of gas from the sheet when being baked. Said mass
being therefore little insulating, upper layers of very high
resistivity have to be provided.
On the other har.d, the linear expansion coefficients have
to decrease from the metal sheet to the eovering layer so that
the eoating be in eompression relative to the sheet.
Sueh eonditions being taken into aeeount, there will be
applied in suceession on the metal sheet, whieh has a linear
expansion eoe~icient ~, measured between 20 and 320C, of
140.10 7,
- a standard mass with a eoefficient ~= 100.10 7 and a
- 4 ~
thicl~nc-ss o~ 10 to 12 ,um,
- an insulal::in~J mass, ~irh a co~tEicien~ ~.= 85.10 7, and
a thickness o~ 40 ,um,
- an insu`l a tin~ coa t:in(3 enam~1 j wi th a coef ' ic~ en t
.
,
,. , ~ .~
..
~ : - , .:
. . ~
:
'
3~
,~= 80.10 7 and a thic]cness between 100 and 150 ~m.
If a decarburized shee-t is used, one may advan-tageously
omit -the first mass layer and apply only the insulating mass~and
the covering enamel.
The man of the art wlll have no difficul-ty in selecting,
considering the application in question, enamels having -the
hereabove characteristics. It will be only mentioned that one
can use as coa-ting enamel -the enamel sold under -the trademark
MA~OLIQUl3 by the ''Procedes ~'erro'' Colnpany, with a softening
point lylny between 600 and 650 C.
The enamel of the corresponding ink will have a melting
point of the same order, that is of abou-t 600 C.
In the case of a stainless s-teel sheet, the mass layer
becomes unnecessary, as in the case of the decarburized steel
sheet, since there is no gaz to be removed.
What has just been mentioned for steel is equally valid
in essence for copper.
The applications to consider for enamelled steel sheets
carrying a printed circuit are numerous in the household
appliances branch. Amongst Qthers coo]cers plates can be
mentioned.
When the support is aluminium, a mass layer is no more
necessary if an aluminium of the so-called ''enamelling''
- type is used.
Enamels have to be used which mel-t at a lower temperature
since the melting point of alurminium is very low. Enamels
will then be used wi-th a softening poin-t of about 460 C, the
melting point of tlle ink enamel being then of about 480 C.
The expansion coefficient~ of aluminium being oE 240.10 7,
a system will be used with two coating layers comprising a
normal enamelling layer for aluminium, with a coefficient ~ =
185,10 7, and a thickness of about 15~um, and an insula-ting enamel
~i'
layer wlth a coefficient /~ =180.10 7 and a thickness of abou-t
30 ,um, the latter beiny -the outer layer.
Aluminium exhibits a thermal conductibility higher than
that of steel, and this ma]ces it interesting in a number of
appLications.
The use of a glass sheet, of a borosilicate shee-t, or
of a caramic sheet as support creates other problems as said
materials are very insulating, very refractory and have expansion
coefficients~ whlch are very Low, i.e. 32.10 7 in the case oE
Pyrex glass (registered trade-mark) and up to 8.10 7 in the case
of ceramics.
In the case of Pyrex glass, a single layer will be used,
formed of an enamel appropria-te for Pyrex glass, wi-th a coefficient
A= 38.10 7. The evolution o~ t.he expansion coefficients is there-
fore the reverse of that which is foreseen when the support is
a metal,and it is glass which is in compression relative to the
enamel.
As regards the selective application of the ink loaded
with powdered metal onto the enamelled support, one may use the
silk-screen process directly on the support, the pervious areas
of the screen corresponding to the lay-out of the required
printed circuit.
A more advantageous process consists however in making
a transfer picture. For so.doing, a selective deposlt o~ the
loaded ink is made on a tracing paper impregnated with starch, the
deposit being carried out according to the silk-screen process.
After drying, at a temperature lower than 100 C, intended
for fixing the drawing on the tracing paper, a continuous
~,
film of varnish is appliecl above ~he ink The ink deposit is
thereby trapped sanc1wich-like between the tracing paper and
the varnish Eilln.
Ln orcler to provide trallsfer of: the inl; onto the sup-
port, the tracing paper is removed by dipping it into water,
the varnish Eilm playing thel- the role of support Eor the ink
cleposlt, ancl the ink deposit is app1ied onto the support.
The matericll is thell baked. l`he varnish clisappears during
bakiny through sublima-tion and there only remains the enamel
loaded with the powdered metal which bonds together with the
coating enamel oE the support.
This process offers the following advantages:
it provides the possibility of making deposits in areas which
are not accessible with the direct silk-screen process, for
instance at the ~ottom of a hollow support; it provides a
regular deposit on bulging or irregular surfaces and it does
away with the handling of the supports which was necessary
with the direct silk-screen process.
Moreover, the method or process can be used for applying
the enamel coating onto the support. In this case, it is
enough to apply the enamel layer or layers onto the tracing
paper and to dry tham without cooking them, then to provide
the selective ink deposit on the dry coating and to proceed
thereaEter as previously. The cookillg of the enamel load~d
wi-th metal powder is carried out at the same time as the
cooking of the enamel coating of the support, which consi-
derably simplifies the operations.
EXAMPLE
Manufacture of a heated eatlnq plate
a) Enamelling of the metal sheet ~Fig. 1)
An eating plate made of a steel sheet 1 of the enamel-
'
r5-~ - 7 -
'
1~38~
ling typet with a low carbon content and a thickness of 1,2
mm, is degreasec1 in a trichloroethylelle bath.
A first layer 2 oE 15C ~l in thickness ol-` refractory
white~ made OIA a Erit at l.00 ~ COntailillg clay as suspensio
agellt in tl-e l~roport:ion oE 4,5 ~ and sodiulm llitrate as
electrolyte in the propor~ion oE 0,3 ~ is apuliecl by sprayiny
Wittl a spray c~un according to the wet process.
The plate :i.5 clryecl at S0CC for 10 minutes and heated in
a continuous enamel baking oven at 850C for 5 minutes.
Using the same process, a layer 3 of 300 ~l in the thick-
ness of MAJOLIQUE enamel (a product of the "Procédés Ferro"
Company) containing also cla~ and sodium nitrate in the same
proportions and a metallic oxide as eolorant in the proportion
of l,5 ~ i.s appliecl accordiny ~o the same process. It is
then dried at 80C and the baking is carried out under the
same conditions as for -the first layer 2.
b) Deposit oE the drawing on the metal sheet.
A mixture is being preparecl which is composed of 80 % of
niekel prismatie particles of a size oE 2 - 5,um, and of 20 %
of enamel frit with an expansion coefEicient ~ of 70.10 7,
the mixture being kneaded with a screen-silk oil and a silk- - -
screen solvent with a boiling point of about 100C. ~A com-
pound is thereby obtained which is applied by the silk-screen
process onto a transfer pict~re blotting paper 5 r according
to the lay-out of the required circuit (Fig. 2).
The solvent is evaporated by heating at 100C and a film
6 of plas-tic material curing at 100C is applied again with
the silk-screen process on the whole surface of the paper 5
over the compound 4, and the material is then heated
between 100 and 120C for hardening the plastic film 6 (Fig.
3).
- 8 -
~3~
The paper tlIus coa~ed is dipped on to water :[.or removing
the blotting paper 5 ~rom the plastic ~ilm 6 and from the
compound 'I, and then the circuit is laid, on the side of
the compound ~, on tIle enamellecI si.de o the eatincJ plate by
expe~.ling the water stil:L tI:apped betweeIl the Eil.m 6 and the
eircui.t ~ (F.ic~. ~I).
A dryin~3 operat:i.on :is carried out at 90C for 10 m:inutes,
then a baki.Il(3 oL~erat.ioIl at ~5~ C foL 5 ~llillutes. The plastic
filrn 6 is sublimatecI anc~ the lay-out oE the circuit 4 is
integrated into the enamel 3 of the metal sheet.
c) Realization of the eircuit.
~ mechanical activation of the surface of the metal sheet
is carried out for laying bal.e the nic~el particles 4 embedded
into the enamel 3 (Fig. 5). For so doing, the metal sheet
is subjected to a micro sand blasting using the wet process
(water-blast) by utili~ing awater and silica bath containing
30 parts of silica by.weight for 100 parts of water. The
water--blast is carried out at a projection distance o~ 20 cm
and an air pressure of 3 bar.
The eating plate is then immersed into a hyclrochloric
bath foL chemical ac-tivation~ then rinsed, then dipped finally
into a chemical nickel bath of the Shipley type~ A heating
circuit 7 deposited on.an enamelled steel sheet 1-3 is
thereby obtained ~Fig. 6).
