CA1051707A

CA1051707A - Photoresist film with non-photosensitive resist layer

Info

Publication number: CA1051707A
Application number: CA211,185A
Authority: CA
Inventors: Michael Gulla; Carl W. Christensen; Michael J. Oddi
Original assignee: Shipley Co Inc
Current assignee: Shipley Co Inc
Priority date: 1973-10-25
Filing date: 1974-10-10
Publication date: 1979-04-03
Also published as: JPS5529426B2; GB1493834A; ZA746683B; NL7413916A; DE2450380A1; ES431310A1; SE7412818L; IT1025144B; ES448212A1; BR7408768D0; JPS5072704A; DE2450380C2; FR2249364A1; AU466665B2; FR2249364B1; AU7446074A; SE422631B; GB1493833A; BE821421A

Abstract

Abstract of the Disclosure A non-photosensitive resist layer is interposed between a photoresist layer and a substrate on which an image is desired to be formed. The non-photosensitive resist layer may be removable by developer for the photoresist layer, or it may require a separate developer. The properties of the non-photosensitive resist layer and the photoresist layer may comprise a two layer photosensitive element which may be laminated to a substrate, or may be applied to the substrate by liquid application.

Description

I ~S~ 37 ~ _ e Invention ¦ 1. Intr~duction ¦ This lnventlon relate~ to photore~i~t~ and more Iparticularly, to photo- ~n31tive coating~ for sub~trates such la~ clrcuit board ba~e ~aterials u~ed ln the ~roductlon Or printed ¦circuit board~ and the like.
¦ 2. Descriptlon Or the prlor art ¦ Photo~en~itiYe or light-Ren~itive re~ist~ are coating~, whi h 1 when expo~ed to actinic radiation are chemlcally changed in thelr ¦ ~olubllity characteri~tic~ toward certain solvents or developer~.
Two type~ are available, negatlve~actinK and po~itiv~-acting I resi~ts. Prior to exposure, negatlve-acting re~i~t~ are ~oluble ¦ ln-developer, but with light expo~ure, they undergo chemical ¦ change and become lnsoluble in sald dev~loper. Expo~ure 1~ done l through a film pattern and the unexpo3ed photoresi3t i8 ~electiv~l ¦ dissolved, ~oftened or washed away, leaving the desired re~i~t ¦ pattern on a ~ub~trate. Positive-actin~ resi~t~ work ln the ¦ oppo~lte manner, light expo~ure making the resi~t ~oluble in ~ I developer. The resi~t pattern that re~ain~ a~ter develop~ent l (and post-baking ln 80~e ca e~) i3 ~n~oluble and chemlcally re~ist nt ¦ to cleaning, platlng and etching ~olution~ u~d ln proce3~e~ oP th :. I natuPe.
I . ........... ..
. ~ Pro¢e~e~ lnvol~lng the ~ormation oP a coatlng o~ photo-resi~t such a~ in the ~ormatlon o~ printed ¢ircuit boards, photo-.. lithograph~ nam~plates and the like, are known. In one proces~
~or the ~or~atlon Or a prlnted clrcuit boardJ a ~tal olad ba~e sheet 18 Goated with a photore~i~t compo~ition and the photo r~ t is exposed through a po~itlve or negatlv~ or the de~ired nage. ~he ;ligh~eYpo~ed reas Or the resi~t are rendered ~oluble ,. . ' '' _y ~
., , .~ :' .
._ ___~_ l~S~7~7 by e.Yposu~e ~nd -then are washed with a developer to leave -the underlying rne-tal layer exposed. An etchant to whlch the resist is impervious may be used to etch away -the exposed metal, or selective pla-ting or other processes may be accor,lplished -to effect a layer in the desired image pattern. The remaining resist may or may not be removed as desired.
A process related to making printed circuit boards is the provision for and plating of through-holes. These holes extend between opposite surfaces of -the base sheet and are used to form an electrical connec-tion'between said surfaces. Typi-cally, they may be ca-talyzed and plated wi,th an electroless plating solution.
The surface coating of the resist necessary for the above process has in the past been applied -to surface base mat- -erial in liquid form by squeegees, rollers or wicks, dipping, - spraying or wiping, or the like, to form a layer of liquid resist on the base material. This~liquid solidifies on drying to effect the layer~ A number of drawbacks attend these liquid methods of appl~ication. For example, the resist in liquid form is frequently forced into the through-holes where it (a) may not ~, become sufficiently exposed to become soluble r or (b) may not be dissolved in a reasonable -time. In either event, the presence of a residuum of resist in the through-holesprevents copper plating therein.
Plugging of through-holes is avoided by the process oE
' United States Patent No. 3,469,982 where a resist is first ', coated as a film on a backing sheet and dried. While still on . the backing sheet, the film is ~~ 30 .j : .

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. adhered by means Or heat and/o:r pre~sure to a substrate. The backing ~heet may be transparent and the ~ilm may be expo~ed through the ~heet. Berore developlng the photore~ist, the ba~klng . sheet i3 cut to ~ize and removed by strlpping lt ~rom ~he photo- .
r~si~t layer. Though thi~ technlque ~olve~ ~ome Or the problems hereto~ore mentioned, ~uch ~ plugging of through-holes, lt 1 an extremely expensive ~olutlon to the problem because o~ the co~t Or ~abricat ing the ~ilm.

State~nent Or the Invention , ~
The present inventlon provide~ an inexpen~ive mean~ ~or overco~ing the di~icultie~ noted above by providing a non-photo~en~itive re~ist layer underneath a photore~ist layer, betwee:
the photoresi~t layer and a ~ubstrate. By non-photo~en~itive . resl~t i~ meant a layer intermediate between the ~ub~trate and a photore~i~t layer~, whioh layer 1~ a protectlve layer either alone or in combination with ~aid photoresl3t layer and i~ not itsel~
su~riciently light ~ensitive to be developed ~ollowing light e~po~ure. The non-photo~en~ltive re~lst depend3 on the develop~en o~ the la~er o~ photore~i~t which it underli~ ~or de~initlon o~
the de~ired pattern rather than on an in~ra-layeP photoch~mical reaction. Exposure o~ the photore~l~t layer ~ollow~d by develop-ment of the photore~lst and non-photosensitlve re~i~t layers ln e~ect create~ a protsctlve ~tencil over th~ sub~trat~.
Pre~erably, the non-photo~ensitive re~l~t layer i8 developable by the ~eveloper used ~or the photore~l~t layer.
While it mlght b~ expeoted tha~ the u~e o~ a developer-soluble layer undsrneath the photore~ist layer would result in llrto~ o~ the photore~i~t layer, or at lea~t seY~re undercu~ting . dur1ng development, it ha~ surpri~ingly been found that the . propertie~ o~ the nonphoto~en~ltlve re8i8t layer c~n be controlled . ~o that ~lnlmal undercutting o¢curs, even wlth non-photo~ensltive ' ~4~

. _ ~5~L7~
re~l~t layers having thicknes~s o~ 1 mll or greater. In ract, extremely ~ine resolutlon ha~ been ob~alned uaing very thin layer~ o~ photoresl~t over non~photo~ensitive resi~t layer~ whlch are in exces~ of 1 mll in thicknes~. Such reso1utlon can be optimlzed by approprlate selecl;lon o~ the material~ u~ed ln the photore~i3t and the non-photo~en~ltive re~ist layer~.
A materlal can alRo be u~ed ror the non-photosensitlve re~ist layer which i~ not removable by the photoresist developer~
in w~.lch ca~e there are two develop~ent ~teps~ one to develop the photore~ist and one to develop the non-photo ensitlve re~ist.
m e present invention provide~ numerou~ advantage~ over the photore~ist ~ystem~ previously known includlng tho~e of the ~ore~aid Uhited State~ Patent No. 3,469,982, The non-photosensl-ti~e re~i~t layer can practlcally be as thick as de~ired, but ~nly very thln photore~l~t layers are required. Since the photoresist layer by itsel~ need not po~e~ the strength and toughnesa prevlously required, only a very ~mall amount o~ the expensive light ~en~ltive material need be u~ed. Thu~ ~llm co~t i8 ~ub~tantlally reduced.
The u~e of thin photore~i t layer~ results ln much ~aster : ~xpo~ure ~peed~ ~ince expo~ure tlme 18 a ~unction o~ resist , thlckne~. Moreov~r, beca~ o~ the relatively thln re~l~t layer, development Or the expo~ed element 1~ more complete, leaving a much cleaner ~r~ace on the sub~trate, a~ ~eparation Or the photore~ist ~rom the ~ub~trate by the non-photo~en~itive resi~t layer pr~vent~ any reaction bet~een 0etal, i~ anyg o.r the ~ubstrate and the photoreæist.
In the pa~t, dy~a have been added to photoresl~t layers to ~acilltate inspectlon Or the developed layers. m ls addltion o~ dye~ has greatly ~lowed the expo~ur0 speed o~ the photoresi~t.
Wlth the pre~ent invention, the dye can be added to the non-photo-~en~ltlve re~lst layer rather than to the photoresist, thu~
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-- ~ ~ 1051707 provlding ~ast2r expo~ure ~peed~. Dye~ or pi~ments Pr~vlou~lY
used in thl~ art ar~ ~uitable. In ~actJ ~ractlcally any dye or pi~ent can be used, ~ince it no longer need~ to be ¢ompatlble with the ll~ht sen~itive materlal in the photore~i t layer.
Much higher concentratlon~ o~ dye or pigment than previou ly u~u may be employed in accordance with thi~ lnvention~
The non-photo3en~itive re~l~t layer may be chosen or .
modifled to obtain ~any propertie~ which have not been available ln photoresi3t3. The layer may have hlgher re~i~tance to etchants cleanlng solutlons and other 3ub~tance~ u~ed to treat the develope substrate sur~ace, than the photore~ist. For example~ one de~irab e ~tchant ror u~e in the prlnted circult lndustry la copp~r pyropho~phate. However, copper pyrophosphate attacks and dis~olve~ moæt diazo type photore~lst materials. Use o~ a non-photo~en~itive re~ist layer with better re~istance to copper pyropho3phate protect~ the desired surface area Or the substrate even though the outer photoreslst layer i~ di~solved~ Other propertles o~ the non-photo~en~itlve re~ist layer can be improved . by the additlon Or adhe~ion pro~oters, plastlcizers, ~lllers, etc.
I)esoription o~ th~ Prererr~d Embodlments :
. . Th~ non-photo3sn~1tiva re~lst layer, together wlth the . . photore~i3t lay~r, provide~ a photosenslklve laminate whlch i~
~trong, tough and ~l~xible, and can be ea~lly handled and ~tored ~` p~lor to dlrect a~lxation to ~ubstrate~. A3 thi~ laminake i~
~uf~iciently ~tron&~ to require no ~urther support layer3, a signlflcant ~aving~ in e~f'ort and expense ia reali~ed, not only in f ~aaterlal 1~0~1l;8, otherwi ~e lncurred for the ~upport; layer, but also due to the speed ar~ convenience afforded by dir~ot .
applicatlon Or the re3ist ~rlthout the ne~d for ~tPipping away the .
obviated layer or layer3. fmu~ thi~ lnvention ~ay be used a~ a . laminate not havln~3; additional layer~, f'or ~upport or otherwl~e, but even where such layers are u~ed, this imrention proYide~
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~_ _____ S~ 7 benefi-ts over wha~ has previo~lsly been known. For ex~mple, in some previously known "dry film" photoresist larninates, a setting period mus-t take place between the time of adherance of the lam-inate to the substrate and the time when the rele~se layer is stripped from the laminate. In the present invention, the release sheet can be conveniently removed essentially immediately a~ter the laminate is applied to the substrate, and while the laminate is still hot.
While the present speciEication deals at length with circuit board making, that use of the invention is only exernplary.
The invention also finds use in -the graphic arts, printing, the making oE labels, decals and nameplates, chemical milling, etch-ing, and in any field where a photoresist is combined with a substrate of any composition.
The non-photosensitive resist layer may be employed with either positive-working or negative-working photoresist materials. Any of the photoresist materials known in the art can be used. E~amples of suitable photoresist materials are disclosed in United States Patents Nos. 3,046,110; 3,046,118;
3,102,804; 3,130,04~ 3,174,860, 3,230,089; 3,26~,837; 3,149,983;
3,264,104; 3,288,608 and 3,427,162, and in ~osar, Light Sensi-tive Systems (1965). Preferred light-sensitive materials are diazo-type materials, both positive and negative-working diazo materials being suitable. Other suitable liyht-sensitive mat erials include CinIIamiC acid, vinylcinnomalacetophenolene poly-mers s~lch as those disclosed in United States Patent No. 2,716,-102; vinyl benzal acetophenones as disclosed in United States Patent No. 2,854,388; vinyl azidophthalate polymers of United States Patent No. 2,870,011; dichromate materials; and ~ree radical materials such as those disclosed in the Institute of Graphic Communications Monthly for August, 197~, at pp. 4-19.

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~:35~
In a pre~erred e~bodiment o~ the inventlon th~ non-photo-aensitive resi~t is soluble in at l~ast one developer ~or the photore~lst. Thu~ where the photor~st layer 1~ a photosenRitlve material ln combination with a developer-æoluble r~n, such as alkali soluble Novolac type phenol ~ormaldehyde resin, the non-photo3en~itive resist layer may be made o~ the ~ame developer-~oluble resin. Sultable material~ are well known in the artO Whlle the photoreslst layer may also contain ~aterials . whlch by themselves would not be d~veloper-soluble, ~ore pr~-ferred ls the ease where the non photosensitlve re~lst i8 ~o~ewhat less re~ovable by the developer than the photoresl~t is. Thi8 can be accomplished, ~or example, by maklng the non-photosen~iti~e re~ist layer out o~ ~aterlals which dl~fer.chemlcally ~rom the resin contained in the photore~i~t ~a~erial, or by mlxing that:
resln with other materlals which are le~s soluble or even normally lnsoluble in the developer. Acrordingly the rate o~
dissolution of the non photo~ensitive reslst layer, and thu~
the degree o~ undercutting o~ kh~ photore~l~t layer~ can be controlled. A ~lmilar re~ult oan be ~btained by ~udloiou~ly sele¢ting the developer ror the photoresist, 3uch a~ by addlng to ~aid d~veloper a materlal whlch adver~ely a~f'ecta the ~olubility v~ the non-photosensitive re~ist layer nore tha it af~eots the 301ubility of th~ photore~l st layer .
In a~ rurth~ embodlment, a two developer ~y~tem i~
used ~or the two re3i3t bJer~. The rlr~t developer may be the normal d~veloper u~ed rOr the particular photore~:LRt . layer, and the nQn-photo~en~ltive re~lst layer may be cho3en ¦ to be or modiried to b~ es~en~;ially inaoluble or only very lightly soluble ln the ~ir~t developer . Af ter th~ de3ired ~ 8~

. ~ :

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` '"1C~5~76~7 ` ' ,'' 1l areas of the photoresist layer have been dissolved by the ¦' îirst developer, the exposed areas of the non-photosensitive !l resist layer are removed~by t;he second developer, which has l! ~
!, b~en chosen or formulated so as to have the d~sired solubili~y 5 ~. ~or the non-photosensitive resist layer~ This embodiment is !
particularly useful when it is desired that the non-photo- ' sensitive resist layer have certain properties 3 such as resis- I
¦ tanc~ to etchants7 strength, etc~ which are radically dif~erent . I from or incompatible with those of the photoresist layer. For ~xample, alkaline de~elopable photoresist layers can bs used~
even where an alkaline et~hant will thereafter be used~ by . using a non-photosensitive resist laye~ which is only soluble in acid solutions or in organic solvents and thus not affected j by the alkaline developer for the photoresist. The ~on-photo- ¦
sensitive resist layer may originally have that properky7 or`
it may be modified to obtain that property, as by baking it either before or a~ter development of the photoresist.layer.
. Other desirable uses ànd properties for this embodiment o~
the invention will be readily apparent to those skilled in . the art. . . .
~terials suitable for use as the non-photosensiti~e resist la~er and suitable developers for those materials are well known in the art, Where it is desired tha~ the . non-photsensitive resist layer be soluble in aqueous developers, for example, that`layer may comprise dextrine, gum arabic~ ¦
¦! mesquite gum, water soluble salts o~ the group consisting of polyvinyl ether-maleic anhydride copolymers~ pectic acid and !¦ ' , .1 jl ' i .
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. .-. . " . ,, ¦' alginic acid9 water soluble cellulose ether, water soluble _ ¦ salts of carboxy alkyl cellulose~ water soluble salts of car- ¦
jj boxy alkyl starch9 glue, albumen, peptin~ water soluble ~, caseinate, polyvinylalcohol, polyvinyl pyrrolidone, poly-¦. acry~amide, water soluble salts of polyacrylic acid, gelatin3 ¦~ starches, ethylene oxide polymers or high molecular weight !l saccharides~ Where it is desired to utilize known organic ¦! s~lvents e.g. methyl ethyl ketone~ isopropanol, tolue~e, etc., I for developing either both resist layers or only the non- ~
p~otosensitive resist layer, suitable materials include poly- ¦
~tyrene and its copolymers such as acrylonitrile-butadiene-. skyrene (A13S~ copolymers, cel~ulose acetate, cellulose pro~ l . . pionate, ethyl cellulose, polymethyl methacrylate, polycar- ¦
... bonate~ polyamides, polyester terephthates~ polyvinyl alcohol~
regenerated cellophane, ~thylene oxide pOlymersg polyvinyl pyrrolidoneg and the like. Suitable additives to impart desired properties to the non-photosensitive resist layer are also well known in the art. If desired th~t layer may bc rendered permeable, as by inclusion of înorganic ealts, ~ as described in U. S. Patent No. 3,649,2~3~ ~
The photoresist layer and the non-pho~osensitive resist : layer may each be applieid to the substrate in liquid form, by whirl coating, roller coa~ing or other methods known in the art. Preferably, h~t~ever, the two layers are formed into 25 I an element and.that ele~ent is then adhered to t~e su~strate i with the non-photosensitive resist layer toward, the substrate.
! As~noted above~ the non-photosensitive resist layer can be 10- ~ ~, .
:, i ., '~,"~ . . ; . ~ ' ; ' ' ''' ' .. ~ ~

~ L7~ -'made s~rriciently strong, by usir~ a ~trong material or by ~ing relatively thlck layer, ~o that additional ~upport ~heets or . ~ yers are not req~ired. ~owever, addltional sheets or layer~
n be used ir rol~nd desirable ~or particl3lar circl~m~tance~. ~r, , ~ample, a release ~heet, swh a.~ a p~lyethylene terephthalate ¦,~.e-lease ~heet, ~ay b~ .applied to the photoresi~t layer ~ that the ~o~o~oten~iive ma$erial 15 protected on the ~ne slde b~y the . ~~leas0 ~,h~et and sn ~G:h~ other ~lde by the non-photosen~3iti~
. l~e~ )k~x ~itable :release ~heets are well known, ~cll~din~
~pglyethyl~ne, polyprop~rlene, -~inyl reslns, ce~ lo~ic materials"
!$~eat~d paper relea~ ~,heeks5 eto. A release sheet avallable : ~ r ~h~ mark Kim~lra fro~ Xi~berly-Claxk i~ partloul~rly ~uitabl~ O
me~hods ~ ~orming the element havin~ the photore~ist . ¦~d n~ photo~ensitlve resi~t layers are also well lu~o~ in the l~r~/~ ~ual:lyJ on~ or the materials is ~ormed i~ts a rlim, whi~h er~arter coated with a layer o~ ~he other material., ¦ - ~h~ thl~kness o~ the ~on-photo~ensitlva re~slst layer .
~d~3p~nd~ ~n ~he ~rop~tl~ ~e~lred Or it and the ~e to which lt l b~ p~ ~n~rally~ that l~yer may be betw~exl abo~J'c 0.0; and ~5) ~~ ~il thic-lco It ~s preferred ~hat lt ha~ a thickne~ o~ rrOm . . a:~)DU~ mll to abol~t 2 ~ , Llkewl~e, the thlcknes~ o~ the pho~Dr~i5t layer depends ~ the propertle~ desired Or that .
~yerl. ~ ~ted above, expenslve photoreslst ~n~terial ls saYed !~d e~po~lJre ~p~ed increa~ed by depending vPon a relatiYely th~ck, ?5 I ~tr~n~ layer 9r ~on-phot~sen~itlve r9sl~t, ror the mechanlcal ~trength ~ee~ed, and u~ing a relatl~ely thin layer o~ photoxe~ist.
~cordln~ly, a p2ererred ratio o~ the thlc~cness Or the photosen~it~ve li~ r~ t ~o the thicl.cness o~ ~he :non-photo~ensitive resl~t i~ layer i~ rrom abovt 1:1 t~ 1:20 and more pre~erably ~rom .

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11 , , ~

abo~t 1:1 to abovt 1:5. It shou:ld be noted that some gain ln resolution can be had by ~se Or 'thicker photoresi3t layersl and generally the above th~ckness rat~o can be between abol~t 1:20 and .
2001, prererably between abo~t 1:5 and 5:1, lt belng ~nderstood, however, that the advantage Or dlecreased cost i3 lost when the ~thicknes~ Or the photosensitive layer exceeds the thlcknes3 o~ the . jinon-photo~ensitlve resist layer. ~he photoresis~ layer should - i~not be so thin that when exposed it ls not i~pervlous to the ,developer ror the non-photosensitive resist~ If the developed photosenaltive reslst layer does not protect the non-photosen~lt~v reslst la~er whieh ~nderlie~ ~t, the protective ~tenoll rOr the s~b~trate will not be rormed~ ~ ~- .
. I There may be only a single layer o* non-photosensitlve re~i~t between the s~bstrate and the photoresist layer, or there .
;~ay be a p1~rallty Or s~h layers, having the`same sr di~erlng ~propertie~. For ~ome appli~atlons Lt may be de~lra~le.to have : one or ~ore non-removable laYers beneath the non-photo~ensltive r~ layers, 8.g., it may be convenlent to blnd the non-pho~o-sensitlve resist layer to the substrate wlth an adhesive lay~r.
~he invention wlll be ~urther ill~strated 1~ ~nd by ...... the rollowing lllustrative embodLments.: .
., . ., . ...... -EXAMPLE 1 ~
. ~ 25g ~olution o~ shellac ln denat~red e~hanol is whirl ~oated on a copper clad circult board base material at 78 r.p.m.
: . . . . . - . . . r .
25~or ~ive mlnute3. ~he coated s~bstrate i3 thereafter baked ror .
twenty mlnu~e~ at 80~C. A dr~d layer Or abo~ 1 mll thickne ~
obtained. The photoresi t layer is applled as a 20 per cent by weight ~olids solution o~ A2-110 Photoresist Or Shlpley Company ,-In~ This materlal comprl~e~ a maJor portlon of an alkall . 1. .
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i~ 2-. .11 . . . .
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Il soluble phenol ~maldehyde Novalac resin and an 0-quinone _ ¦~ diazide photosensitizer (comprising ab~ ut 1~3 o~ he solids~
dissolved in a predominantly Cellosolve~acetate solvent. The 1l photoresist layer is applied by ~hirl coating for ~ive minutes.l 1 The coated substrate is again b~ked for abouk 20 minukes at ~0C. The dry film thickness of the photoresist layer is about !
l/4 mil. Thereafter the coated substrate is exposed through a ~ransparency9 using a carbon arc of about 2,000 foot candles i intensity at a distance of about orle foot ~or about 6 minutes.
The substrate is then developed by immersion or swabbing with ¦ a developer such as AZ-303 Developer made by Shipley Go~, Inc., ¦ ~hich comprises an aqueous hydroxide solution. I~ immersion ¦ is employed, it is a~ected at a temperature of about 70F. for ¦ a ~ew minutes. Resolution of the de~eloped image is excellent.
I ; -¦ ; -E~ANPLE 2 ~-¦ The procedure of Example 1 is followed except that a phenol formaldehyde non-photosen~itîve resist lay~r is used9 made by mixing 25 grams of a 50% solution of Novolac phenol ¦ formaldehyde resin in toluol, ~nd 25 grams of the Cellos~olve , , acetate ~olventg and whirl coating as before~ Again~ resolu-¦ tion of the dev loped image is excellent.

. 11 ~ , .. .

2~ 1! The prodedure of Example 1 is followed except that the ~ non~photosensitive resist layer is made by mixing 25 grams ~
.~ ! . . c~ lem~ for ¦ the phenol formaldehyde sslution, 25 grams of Gantrez M55 ~a il 5% solution o~ polyvinyl methyl ether avallable from GAF Corp~, !1 and 50 grams of the Cellosolve acetate solven~ and whirl coating ! as before~ Again resvlution of khe developed image is excell~nt " li , . , ' , ' ',' , , ~ 13-~s~
EXAMPI.E 4 _ _ The procedure of Example 1 is followed except that -the non-photosensitive resist layer is rnade by Mixing 36 grams of the phenol formaldehyde resin solution, 17 grams of Gantrez M555, 0.026 grams of Modoflow (a trademark for a wetting agent avail-able from Monsanto), 3.2 grams of Lustrasol (a trademark for a 50% solution of an acrylic resin available from Reichhold Chemi-cals, Inc.), and 50 grams of the Cellosolve acetate solvent, and whirl coating as before. The resolution of the developed image is excellent.

Same as Example 1 except that non-photosensitive resist layer is made by mixing 36 grams of phenol formaldehyde resin solution, 17.6 grams Gantrez M555, 0.023 grams of Modoflow, 4.8 grams of Parlon (a trademark for a 33% solution of a chlorinated rubber resin available from Hercules, Inc.) and 72 grams of the Cellosolve acetate solvent, and whirl coating as before. The resolution of the developed image is excellent.
; EXAMPLE 6 2 a ~ This illustrates the use of the two developer embodi-~ment of the invention. ~A non-photosensitive resist is made by mixing 10 grams of Gelvatol 1-90 (a trademark for a polyvinyl ::
alcohol available from Monsanto), 190 cc of deionized water, .
~10 grams of Resloom M-75 (a trademark for a 608 solution of a methylated methanol type resin also available from Monsanto), 0~.1 grams of Catalyst AC, an amine hydrochloride catalyst also avallable from Monsanto, .:
3p ~ ~ , :
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:~CJ 5::L7~7 and 0.1 c~rams of Triton DN-65 (a trademark for a wetting ac~ent made by Rohm ~nd Haas Co.). The mix-ture is whirl coated for Eive minu-tes at 78 r.p m., and baked at 80C for twenty minutes.
During the baking the mixture reacts to become insoluble in alkaline solutions and water insensitive. AZ-ll9 Photoresist is roll coated over this layer and baked for twenty minutes at 80C. The laminate is then exposed -through a transparency as in Example 1, and developed with AZ-303 alkaline developer. At this point the photoresist in the exposed areas has been removed, but the non-photosensitive resist layer remains. The laminate is rinsed with water and developed a second time with 25~ sul-furic acid. The non-photosensitive resist layer is removed, and the resolution of the image pattern on the substrate is excellent.

The procedure of Example 6 lS followed except that the non-photosensitive rçsist layer is made by mixing 200 grams of Resloom M 75, 25 grams of AC Catalyst and 0.5 grams of Triton DN-65, and whirl coating as before. The image resolution is excellent.
~ EXAMPLE 8 Same as Example 1, except that a negative acting photoresist applied by film is used. The photoresist is avail-able from du Pont under the trademark Riston. It is believed to be comprisèd of a layer of polyethylene, a layer of photo-resist material, beIieved to be a photopolymerizable ethylene-ically unsaturated compound as described in British Patent No.
1,128,850 and a layer of polyethylene terephthalate (supplied under the trademark Mylar~. The polyethylene is stripped from the photoresist ' ~ -: : . :
: ~ .

.. . . . . . . . . . . . . . . . . . . . . . .. .. ... . . . .

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ele~ent9 which i,a, then laminated to the ~hellac-coated 9ubatrate, . ~ by mean,3 of' heated pre~sl~re rollers operated a~ about 120C with _ . ¦ a press~re o~ abol~t 10 to 12 pound~ per linear lnch at the nlp, ¦ at a rate o~ abo~t two ~eet per ~in~te" The resulting laminate l, ls thereafter exposed through a transparency and developed with !~ trichloroethylene which remove~ both the ~nexposed photoresist . i ~aterlal and the portions o~ the shellac layer beneath that . I material. The resoll~tion Or the developed lmage ~s excellent.

. I . .O EXAMPLE ~ `
¦ m i8 ill~trate~ the vse Or the non-phot~sensltive ¦ resl~t and photoresist layers in a dry rllm applieatlon.. A ~heet . ¦ o~ ~pt~cally transparent polyethylene terephthala~e ~ whirl ¦ coated with a 2Q~ solu~lon Or AZ-ll9 Photoreslst in the Cello.~olve acetate solvent ror 5 min-~tes at 78 r.p.m. me coating 1~ then . ¦ dried ~or 20 ~in~tes at 80C~ A non-photosen~itiYe re~t ~ 1 801t~tion, as ln Example 4, Or 36 grams phenol for~aldehyde resin~
; ¦ ~7 gram~ Gantrez M55, 0.026 gra~s Modoflow, 3.2 grams L~strasol ¦ and 50 grams o~ the ~ello~olve acetàte solvent, i~ whirl coated ¦ over the pho~ore~l~t layer, also ~or ~ive min~te~ a~ 78 r.p.~., ¦ and dried at abo~t 80C ror tw~nty min~-te~. The re~vlting element is lamlnatsd to a copper clad clrcuit board bas~ material ~slng r~bber covered roller~ operated at abo~t 120C with a , I press~Jre o~ abo~t 10-12 pounds per linear inch at ~he nlp~ ~t a ., . j rate Or abo~t two reet per nlnute. The photoresist layer i~
li exposed ~or a~ou.t 6 minl~te~ thro~gh a tran~parencyJ v~ing a carbon arc`o~ abo~t 2,000 ~oot candle~ lnten~i~y at a di~tance j abo~)t one rOot The polyethyle~e terephthalate .r~ lm 18 stripped away rrom the photore3ist layer and the coatln~ developed wlth . , . .
',. . -, '.
. . , 16- . -1~ , ' . .

... . . ............. .. , . . ........... , . .~.
~0517~7 -303 Developer. The ~eveloper remove3 the coating rlght do~nn !to the ba~e metal and the re301~ ion of the image ls excellent.
¦The top rilm ma~ be removed berore or a~ter exposure. It 1~ to ¦be removed before exposure, lt need not be optically transparent9 ¦,and known release ~heet~, sl~ch a~ paper baset release sheets can jbe ~ed. I
While partic~lar embodlments Or the present inventlon . .
have been shown and de~crlbed~ lt will be obvious to tho~e sk~lled in.the art that change~ and modification~ ~ay be made 'withovt departln~ fro~ this lnventlon 1n it~ broader aspect .
¦ ~here~ore, it i~ lnten~ithat the ~pec~fication be lnterpreted . ~aa illv~tratlve only, and not ln any limlting 3en~e.
I . ' '"' ' . '' `''` :- ' `. '' '. ' ' '. l - , :.' " . "" ,' "', ' . . . . . .

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, 17- . .
. . .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An element comprising a substrate, at least one non-photosensitive resist undercoat and a photosensitive resist topcoat, said photosensitive resist topcoat comprising a photo-resist material which has been selectively exposed in desired areas, and said undercoat being removable by developer for said photosensitive resist topcoat.

2. The element of claim 1 where said photoresist topcoat is a positive working photoresist and where exposed photoresist areas are removable by the developer which simult-aneously removes the undercoat.

3. The element of claim 1 where said photosensitive topcoat is a negative working photoresist and where non-exposed areas are removable by a developer which simultaneously removes the undercoat.

4. The element of claim 1, 2 or 3 wherein said undercoat has a thickness of from about 0.05 mil to about 5 mils.

5. The element of claim 1, 2 or 3 wherein said undercoat has a thickness of from about 0.2 mil to about 2 mils.

6, The element of claim 1, 2 or 3 wherein the ratios of the thickness of the photosensitive resist topcoat to the thickness of the non-photosensitive resist undercoat is between about 1:20 and 20:1.

7. The element of claim 1, 2 or 3 in which the ratio of the thickness of the photosensitive topcoat to the thickness of the non-photosensitive resist undercoat is between about 1:5 and 5:1.

8. The element of claim 1, 2 or 3 in which the ratio of the thickness of the photosensitive topcoat to the non-photosensitive resist undercoat is between about 1:1 and 1:20.

9. The element of claim 1, 2 or 3 in which the non-photosensitive resist undercoat is colored for ease in image inspection.

10. The element of claim 1 wherein said photosen-sitive resist topcoat comprises a photosensitive material and a resinous material.

11. The element of claim 10 wherein said resinous material comprises an alkali soluble novolak resin.

12. The element of claim 10 wherein said undercoat comprises the same resinous material contained in said photo-sensitive resist topcoat layer.

13. The element of claim 10 wherein said undercoat comprises a mixture of resinous materials, one of which is the same resinous material contained in said photosensitive resist topcoat layer.

14. The element of claim 10 wherein said photosen-sitive material comprises a diazo material.

15. The element of claim 14 wherein said resinous material comprises an alkali soluble novolak resin.

16. The element of claim 1, 2 or 3 wherein the sub-strate comprises a member selected from the group of non-conducting substrates and metal clad non-conducting substrates.

17. The element of claim 1 including at least one support sheet.

18. The element of claim 17 wherein said support sheet comprises a release sheet on top of the photoresist layer.

19. The element of claim 18 wherein said release sheet is polyethylene terephthalate.

20. The element of claim 1 wherein said undercoat comprises two layers of non-photosensitive material, the top layer of which is removable in the same solvent which develops the photoresist topcoat.

21. A method of selectively forming a resist image, comprising applying a non-photosensitive resist undercoat and a photosensitive resist topcoat to a substrate, selectively exposing desired areas of said photosensitive topcoat to actinic radiation, and removing portions of said topcoat and the portion of said undercoat which underlie the removed portions of said topcoat.

22. The method of claim 21 in which said portions of said topcoat are removed by means of a developer solution.

23. The method of claim 22 in which said portions of said undercoat are also removed by said developer solution.

24. The method of claim 22 in which said undercoat is less developable in said developer solution than the areas of said topcoat which are removed.

25. The method of claim 21 in which said portions of said topcoat and said undercoat are removed by contacting the surface of the coated substrate with a developer solution in which the portions of the topcoat to be removed are developable and said undercoat is not developable, and contacting said surface with a second developer in which said undercoat is developable and the topcoat is not developable.

26. The method of claim 21 in which the undercoat and topcoat are applied to said substrate by forming a laminate comprising a non-photosensitive resist layer having a photo-sensitive resist topcoat, and adhering said laminate to said substrate said other side of said non-photosensitive resist being adhered to said laminate.

27. The method of claim 26 in which said laminate is formed by forming a first layer, comprising photosensitive resist on a support film, and forming the non-photosensitive resist layer on top of said first layer.

28. The method of claim 27 in which said support film is removable after formation of the non-photosensitive resist.

29. The method of claim 21 in which the undercoat and topcoat are applied to said substrate by first forming a non-photosensitive resist layer on said substrate, and then applying said photosensitive resist topcoat on top of said non-photosensitive layer,

30. The method of claim 29 where said non-photo-sensitive resist layer on said substrate is applied as a liquid.

31. The method of claim 29 where said non-photo-sensitive resist layer is applied as a dry film.

32. The method of claim 29 where said non-photo-sensitive resist layer is applied as a liquid, substantially dried, and said photosensitive resist topcoat is applied as a liquid.

33. A flexible photosensitive transfer film com-prising a layer of a photosensitive resist material, a non-photosensitive resist undercoat adhered to the photosensitive resist layer, said undercoat being removable by a developer for said photosensitive material and a release sheet releasably adhered to said photosensitive resist layer.

34. The element of claim 33 in which the release sheet is a support film.

35. The element of claim 33 in which said photo-sensitive resist layer comprises a photosensitive material and a resinous material.

36. The element of claim 35 in which said undercoat comprises the same resinous material contained in said photo-sensitive resist layer.

37. The element of claim 35 in which said undercoat comprises the same resinous material contained in said photo-sensitive resist layer, and an additional material, which is less soluble in said developer than that resinous material.

38. The element of claim 33 in which the non-photosensitive resist undercoat comprises a material which is more easily removed by said developer than the areas of said photosensitive resist layer which are removable by said developer when selected areas of said photosensitive resist layer have been exposed to actinic radiation.

39. A method of making an etched printed circuit board, comprising applying a non-photosensitive resist under-coat and a photosensitive resist topcoat to a metal clad printed circuit base material, selectively exposing desired areas of said topcoat, developing said topcoat and removing the portions of said undercoat which underlie the removed portions of said topcoat, and the portions of the metal cladding which underlie the removed portion of said undercoat.

40. The method of claim 39 where the portions of the metal cladding which underlie the removed portions of the undercoat are not removed, but are plated with a dissimilar etch resist.