CA2108048A1 - Radiation polymerisable mixture and method for manufacture of a solder mask - Google Patents

Abstract

Abstract Radiation polymerisable mixture and method for manufacture of a folder mask A radiation polymerisable mixture is described, which is suitable for the manufacture of solder masks and which contains a) a radically polymerisable compound, b) a binder containing a carboxyl group, c) a photopolymerisation initiator, and d) a cycloaliphatic epoxy compound with at least two epoxy groups.

The mixture has better storage capability in solution and as a solid coating on a printed circuit board.

Description

Radiation polym~ le mix~t~ a~tQo~ ~or manufactur~ of a solder mask Th~ Inven~ion ~oncem~ a ra~ia~ion polymensabl~ m~ur~ whiGh i~ us~ for th~
nanufactur~ ot sol~ef masks ~nd which cont~ns, as ~s~n~ial compon~ts a) a cornpoun~ ~,vlth ~ least one t~rrninal ~thyl~ni~lly un~ur~
group which is capabl~ of ~orming a cross-link~ polym~f by radi~l Initiated additlon cha~n polynterisation, b) ~ water-insoluble, aqueou~ alkall solution~sol~bl~, polym~rlc blnd~r conta~nin~ carboxyl ~roups, c) a polymensation initiator capabl~ of activ~on by tadlaeion, or a polymer initia~or combination, and d) a compoun6i with at least ~No ej~oxy gr~ups.

Mixtures o~ this composition are known from E~-A 418 733 and dessribed in the ~arli~r ~ierman patent appli~ation P 41 42 735.1. These rnixtures cont~in, as ~poxy compounds (c~) essentially iilglycidyl ether of two or three v~lency allphatlc aicohols r~r phenols. Th~ known mixtur~s hav~ the dlsadvanta~e that cort~sion of m~tal surfQces with which they com~ into cir~ct contact is f 20 pos~ible In darnp condiUons. The storage capablllty of th~ mixtur~ In ~olution and in the ~orm of photoscnsitive coatlngs on ~ sttuo~r~d print6d clrcuit boa~d ~ Is In many cas3s unsatisfaGto~y. This n~anlf~sts itsell In that the expose~i 1~ sold~r masi< can no longer b~ reliably anci completcly deY~lopeci or that the m~talllc wi-lng patilQ can become corrode~.
~; 25 it llas now been found that these disadvanta~es are caused by ionic impurities, such as halogenide lons. It has fur~her i~een found that the ~poxy compounds u~ed until now, being rnanuf~ctured from epichlothydrin ~nd, fOt sxample, biphenol A, contain halogenide ions. By tr~r~forming epichlorhydrin ~n the presence ot bases, HCI i~ s~parated, which adheres to the trans10rmatiorl product in the forrn of chlo~lde lons.

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%~0~8 In EP-A 255 9B9 negatiYe photo-resist materials are descr~bed ~hich ~ntaln alkali- soiubie po~phenols, ~poxy compounds an~ a Ga~oni~ photoinltltator lor cross-linkin~ the epoxy ~roups. Aroma~c, aliphatic and c~doaliphalJc compounds are us~d as epoxy compounds. Cu~n~ a~cordin~ to a pat~ern is 5 substan~i~ly carried out by photo ind~ced cros~-linking of the epoxy groups but ~an also be compl~ted thetn~ally.

In EP-A 502 382 photosensitiY~ mixtures suitabl~ for manufactu~ of -~older masks ar~ de~oribecl, which contain alkali-solubl~ phenol r~sin, ~poxy resins 1~ and photo activat~ curin~ catalyst for th~ ~poxy gtoups. In this cas~ al~o, photo curing ~ncling ~ ~ pa~ern can be completed by sub~qu~nt hea~ln~.

The ob~ect of 1he inYention i6 to propose a radiatlon sensitive mi~ture ~uitabl~lS for the manufacture of solder masks, of the ~pe clescribe~ a~ve, which dlffers from the known mlxtute by ha~/ing better storage capabiiily in solution and in the sqlid state and in ~ccordance with its inten~ pu~po~e.

According to the Inv~ntion a radiation polymerisable nnixture is ptoposed which ?i 20 contains a) a compound With at least on~ terminal ~thyl~nically un~atu~ated ~roup which is capabl~ ~f formln3 ~ cross-llnked polymer by radical initiated addition chaln polymerisatlon, b) a water-lnsolubie, aqueous alkall solution-soluble, polym~rlc blnder cont~lnlng c~rboxyl groups, c) a polymerisation initiator c~pable of activation by raciiatlon. or a polymer initiator comi~ination, and :: d) a compound with at least two epo~ groups.
3~
The mixture according to the inYention is chPracterised In that the epoxy :

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30-SEP-1993 15:56 P~ITENTRNWf3LTSEURO -~4!3 611 372ili 5.03 ~ , .

2~8~)~8 compound i8 a cy~o~liph~ epo~ compound.

A~ordin~ to ~ irnrflr~nn, mo~ver~ a me~od for rr~c3~r~ of a s~Wsr ma~k is propQ~d, which is oha~ac~nsed in tha$ a s~luffQn or ~ion of a 5 n~ix~ ~ fng to one of ~ to ~ i~ appi~d to ~ ~u~:e of a s~u~rfld pnn~d ~it6 Ll;it ~aar~ and dr~l thc coa~n~ o~tainad iS Irradia~3d acca~ing to a pa:~rn w~ aG~nic ~ia~on while blard~ng the ~oldenn~ s, the non 7E~ed atR~u; Of ~he coa~ing ar~ wash~ci o~ ~ vebpe~ and t~ mas~ o~ined is h~ted at a r~ed æmpera~a.

in pnndp{e ~il compour~ which con~in a~ on~ cy¢loa ip~io rin~ and ~ tea~ o~ epoxy ~roup are sL~itaWe a~ ~rcloaiip~ p~r con~po~n~, wh~reby ~ ~pOYy, ~up8 at~ not ttlQ r~ lt ot hydsDasn chb~ ~on from a ~ In pat~c~lar, oompo~nds l~vith 9 Cornpounds ar~ pre~r~d whichcontain epD~qr groups ~n ~:ycloaliph~
that is to ~ay c~mpeun~ whi~h result from epo~ on of cycloalt(~n~s. ~n a oy~oalkyl rin~ on~ or hYo o~dr~n ringS car ~e at~ached. ThQ epoXy ~rGup~
20 ~an also bo a ccn~pcnent of an aliphalic substituent on the cyclo~l r~m~r~er, ~hat is t~ say thi9 sLIbs~tuent can be an ~p~xidlse~ alk~nyl ~up, wl~ch p~ef~y cont~ins 2 ~ 6, panicular~ pr~tera~ ~ to ~ carbon ~o~ns.

Tn~ camp~und G~ ntan one or a plur~i~y ot cyclo~kyl ~n~s~ w~h 2~ gen~r~iy ha~e 41~ R, pre~rab~ ~ to 7 and p~C~ y pr~f 3ra~Sr 5 ot ~S fi~
mem~rs, Besid~s cy¢loalipha~c and epoxy~l groL~ps. it can con~3in h~rther ~iphadc subs~h~Jtes, 8uCh as alkyl groups, ~Ikylen~ ~roups7 alkoxy ~ups and/or car~ ester ~roups. Satura~ed or ~X3n5y uns~ ~ngs ~n n~l in thQ molecules. which c~n~n 1 or ~ h~roa~ms, ~uoh 30 as Q S~ or N ~s nn~ m~mbers Su~h nngs c~ ~e sL~s~nts, aneU~d r;n~s or spir~n~ bor~s. ~he comps~und ccn~ains al leas~ 2. p~eterab~
'! ' '. ~

epoxy ~ro~ps in th~ molecul~. 210 ~ 0 4 8 Th~ ~poxy compounds are general~y ptoduce~ by ~poxi~ation, parti~lari~y with p~t-a~ids~ lor ~xarnple, perac~tio acids, trom cyclool~fin~ or 5 ~Ikenylcycloal!~anes. Th~ manu~actllre is d0soril~d for ~xampl~ in ~OLYM@~
EiNCYCLOPEDlA, Vol 6, p. 336ff.

The mi~ture preferably contains ~ fu~her curer ot addition in5tla~o~ ) tor ~poxy groups. Th~ curer is p~f~rably a nitrogen bas~, for ~xampl0 10 tnethylamine, 1.4~ bicycl~ .2.] ~ctan@ (D~bco), higher ~l~lised mono, di and triarnlnes such as for example on a allphati~ i~se, ~ncl furlh~r, aliphatlc-arom~tlc amines such as for axample ~methylanlllne. l~he tertiary, p~rUa~ y ~Ipha~ic arnlne~ preferred. Partic~larly pre~rr~d is Ji~ icyclooctane. The amount of base is ~enerally behveen 0 an~ 1.5, 15 preferably be~N~en 0.2 an~ 1.0 % by weight Genera~ly, esters of ~he ~ryi or melhacryl ~cid8 with polyvalerlt, preferably prlm~ry alcehois are useci as polymerisable csmpounds (a). The alcohol should contain at l~ast two hydroxy ~roups ~ the desired cross-linking eflect results ~rom rnultiply sa~rated compounds. At least do~bly unsaturated compounds are pref~rabl~ howev~r, 2~ monounsaturates, for example esters of monovalent alco~ols, oan ~so be contain~d in the mlxture. ~xAmples of suitable polyYalent ~cohols aro ethylone glycol, propyl~ns gly~ol, butanediol-1,4, disthylene glycol, tJi~thyl~n3 glycol, oli90propylene glycol, trim~thylolethane and trimethylpr~pane, psn~a~rythllita, dlpentaerythrite, blphenol-A-bl~hydroxyethylether. lher~ are 25 morQov~r t~ biacrylat~s anci blmcthacrylat~s ccnta~ning low~r rnolecul~r urethan~ gr~ups whlch ar~ sult~ , which result frorn trans~ormaUon of ~ mol hydroxyalkylacrylato or hydtoxymethaoryla~e with 1 mol of an aliphatic or cycloaliphatlc diisocyanate, tor e~ample 2,~,4-trimethyl-hexamethylenelsccyanate. Such monom~rs containing u~ethane groups ar~
30 dascnbed in US-A 4 088 498. Particulariy pret3rable ar~ ac~ es ~nd methacrylates, in par~cular ac~ es with high double bonding content.

30-SEP-1993 15:56 PRTENTRNWRL-rSELRO +49 61i 372ill 5.1~14 5~5 16:2~ Fi;~ D YCL~G ~ CD 21 0 8 ~ 8 ~1~1~1~ p.~

Monom~rs with 3 o~ nsa~rate~ groups ~r~ thus pr~l~rr~ In g~
~t2r~ whtch ~ll cor~tai~ ~ iea~t on~ ft~e~ hydro:~ glollp are sl~penor ~ tlhe compl~t~ stersd ~mpour~. The e~rs ot ~imet~r~lp~op~, tnrn~hylolethane, ot pe~lythri~s and dipent~r~ e are pa~ca~
5 pr~d. Tll~ mor~mer ~s oene~lly con~ned in the m~aur0 in a q~n~ o~
lû to 35, pr~ra~ fr~m 1~ to 3~ % by wei~ht wi~ 0r~ce ta ~a ~Qt~l ~nteng e~ non-vo~ ompon~
.~
Th~ potynn~tle ~indin~ is n~t s~!uble in w~ter and i~ solll~le in ~eou~
O aU¢~Une soh~tions. ~h~refore. polym3ts Yln~h l~eral G~o~yl ~r ca~ ~:~d anh~e ~roL~s are ~ib~bl~.

~inyl polymeris~ whioh can be ,9roduc~ by radica~ palymaa~on ~
pre1ef~ wla~ ccpolym~ns~e~ of ~, ,6 un8~ fbo~i~ ~r 15 sxample cr~tonic acid, Itaconic Qcid, malic add and thair anhyd~s, ac~lic ~Jinyle~ter, vinyle~r, viny~ tlcs, (me~a~rl a~id ester~ es and th~ lik@ can be considar~d as conom~ts.

2~ Par~c1~iariy prei~er~lo ate copolymers of acrylic and m~thacryllc a~d wh~ch ~: contain, as ~nomets, pa~cularly actylio or ~r e~acTylic add est~rs, ~yr~l~, ac~yli¢ or me~ac~ylic ~ e~ acrylic or n~thac~i~ ~mite or vinylheteracy~.
Allcyl esters, ~ith ptefe~ 1 t~ 10, parbcularly p~o~ra~ 1 t~ 7 ~rbon a~oms in ~ alkyl group ~ us~ as (me~h)~crylic ac.7d est~ e s~l can 25 be an o, nl or p-~l~lwl, a ~inylett~ylb~reol~ ~e a methy or a chlolsr~ol, an o, m, or p chlorstyrnl. a vinylanisol or tne lik~. The n~su~sti~ed ~ryro~
is ~neral~ pre~rred. The ~ quan~y of s~roi uni~s is in ~ tang~ ~ 30 t~
667 prelerably 45 to 60 % by ~eight; ~at o~ ~he ~m~h)a~ry~ic a~id e~
40~ pr~f~rably b~een 5 and 25 % by w~lgt~ The (meul~acryic ~id u~t~
30 sh~uld ~e of a quan~r~r such that the ac~ csunt of the pO~ymer8 iS ill the tang~ 110 to 28~, pr~Serably fr~m 1~ to 2~0. The total quar~ of .. .... . .. . .

21~8~8 polymer in the mixture is ~enerally 15 to ~0, pr~ferably 20 to 40 o/~ ~y wei~h~

Numerous ~ubstan~e~ oan be used as radi~ion ac~ivated polynl~risatlon initlators. Exa~ples are i~enzoin~, benzoin etherst mult~nuclear chinon~, such 5 ~s ~thylanth~achin~n0, acndine d~nv~tives, SuGh as ~-ph~nyl ~ in~ ~r ben~crldlne; phen~zin~ derivatives, such as 9, 10 ~imethyl~enz~a) ph2nazine; c~inoxalin or chinolin derivativ~s, ~uch a~ Z, ~-bi~4 ntethoxyphsnyl)cihinoxalin or ~-~tyrylchinolln, chinazolin c~mpounds or acfy~
phosphln~ oxide compounds. Pho~o-initiators of thls typ~ desGribeci in ~E
1D C 20 ~7 467, 20 3~ 8~1, D~-A 37 ~ 8, EP-B 11 78~ and EP-A 220 589.
In addition, for example hydrazones, mercaptan compounds, py~l}um o~
thyropyrilium salts. xan~hone, thioxanthone, benzochinofla, acetoph~none.
b~nzophenone, syner~etic mixtures with ketones orhydtoxyketones ~nd r~iox dye systems. Par~iculzrly preferable are pho~olnltlat~rs whlch hav~ photo~
15 splittable trihalo~enmethyl g~ups, wher~by in particul~r corr~sponciing compounds oi the triazine or thi3zole ~ang~ ought to be m~n~onad. Such compounds ~te descrlbed In DE~A ~7 18 2~g, 33 33 4~0 and 33 37 024~ A
preferred example is 2~(4-rnethoxystyryl)-4,6-bitrichlormethyi-s~ria~in~.

20 l he photoinitiators ~re ~enerally adcied in quantities of 0.1 to 15, pr~ferably from 0.5 to 10 % by weight with resp~ct to tne non-volatile componcnts o~ the ~ .
mlxture.

The mlxture accordlng to the invention can furth~r c~ntain a p~rticulat~ fil1er 25 (f) which is insolui~le in the coatln~ matorial anci the develoj~r, partlcul~rly a rnlneral plgmen~ Silicates or sllicic acid are suit~ as minerai plgments.
They sho~Jld be ground to a particle size so that at ieast ~0% of the particles h~v~ a diameter of 1~;um or less. In this way the solcl~r mask ratains a smooth surface. The~e silicate minerals contain prac~ically all their chemic~lly30 bona~ wate~ irl the l~rm of OH ~roups on the silicon.
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30-SEP-1993 15:57 PRTENTRNWRLTSBUR0 ~9 611 372111 5.05 i~-2~-lg33 16027 ~RQM D Y~L~ ~ CO ~210 ~ ~li37~ 3 lollowing can b~ use~, tor exarr~ silica~ ~es, tak. cp~, ~n wol~nHe, te~r, an~phi~ol~, s~rpefltin~, z~lise, pumice, ~n~ ph~no~
T~ SiQ2 c~r~n~ i5 011 U 85~ ~ ~tos~ly a~lV~ ~Bn~15~ SO~ ~h ar~
containe~ in the e~y~l struo~re acsvanta~e~usly ;~mi~urn, z~lkali ~
an~ a~ m~ds~ ~ar~ f the ~ nt i~ 9~n~11y al~ O ~o ~0, pt~e~bly 20 to ~o % by we~ght.

~he ~ur~ pr~fe~y con~ins a~ ieas~ on2 dye, ~n ma~ ~hs d~ 0~d r~ l stent:i~ rnote visi~ ~an~geou~, a ~m~ n of ~t i~ast~w~ dy~
10 is u~ed ~or ~h~s, o~ of which ch~n~es colout whsn sm~ed, andl i~
~attt~gd i~i tsmpet~es a~Oy~} 20~3C, ~Gt~ ~coming ~ufle~. Tha o~r dy~ ha8 tD witl~8~ irradiation a~ wel~ :~ t~mpe~r~ a~ove :~C
~hout chan~ing. It has to rna~ ttu3 sol~r m~sk cl~ ~ri~s~
soti~rin~ ~i aS~ ards. Suitable dy~3 for this purpos~ afe ~ui~i in CIF-A
15 311493t.
i Th~ miXn~re can. if ne~ci be. csntain a range of ~U~e~ usUai ad~fflo~ or e~ampi~ 3nhlbitt~ s for ptev~r~ing thennai polyrneris~ion cf the rnc~me~, hydro~en donors. phoEosensi~ity ~egul~or~, pigm~n~s, sofl0ne~ ~i 22 U~ixotr~pic m~terial~ ~r ctganio polymer~, such ~s pciyacrylarni~. Thixotropi~
m~rials are t~r exan pla advanta~eousiy ~sec~ In cur~ain pouring applic~ n.

Th~ mh~ure a~co~in~ t~ the in~tendon ca~ onty ~ stored for a limit~~
in its ready-~u5~ tornt b~us~ ot this the In~Fi c~mpdnQms ~rg 25 conv~ni@ntiy store~ In at le~st tHo parts as '~ c~mpon~nt eoa~t~" . Th~
n~rmal procgdLiTe iS tn~t all ~he c~pone~ns, wi~ the excsp~on of the HpOXy ~mp~und ~e rea~y in a ma~n nl~re, to wh~ch the ep~ is ~d~d sho~ly b~f~r~ use. ~lo~av~r, for ex~mple, ~e curing initif~ar c;an be k~ 8 a s~te coln~nenl~ Dyes, rniner~ solids and ~her ad~na m~Rr~s can 30 ~e kept in s~p~s mixture carnp~nen~, so U~ it na~d bs a eompon~nt sysl~m c~ Q t~ prescri~ It is ~rnportan~ ~ t~s p~

. .. . ~ .. . ... ... ..

;' 2 ~ 8 mixtureg have ~ sufficiently long s~ra~ out B to 12 months) b~for~ thg mixing process.

P~ocesslng of the mixture acco~ciin~ to ~he inveniion is don~ in a known ~y, for exa~nple In a filter application. Th~ olvecl or disp~rs~ci mix~ur~ 1~, hr example, applied to ths prirlted circuit bo~rd concerned with a squa~
through a fil~0r ne~ of 37 to 5~ mesh per cm, ~tret~hed ovef a m~tal frarn~.
:~ ~nother possibility is curtain coabn~. U~inc- a normal Gommerciai curt~in pourin~ n~achine, a continuous verlically runnin~ iiquld ~llm is pr~duced. By rneans of a conv~yor belt the printed circuit board is con~feyecl under ~is fllmand th~reby is coa~. The mixture can fnally aiso be appli~ci by spray coating, ~sdvantageously ~y an electrostatio spr~,y coatlng. In a cla~i ~in, the ~olution is ~i-sper~eci in a spray head into very fine dropletsl wshinS~h are eleS otrost~tisS~slly charged by high voltage, and dse5~;ited on the print~ circult ~oard. The mixtures Scan also be proS~sssseai in a dip drawing process and ~y roller application.

l`hse coabng mlxtur~s processed accordlng tS~ one of thsa mothosds describsS~d are treeci ot ~he solvent by dryin~ In a circui~ting air drying Scupi~oa~i arle~/ot s under an infra~red dryer. The printed circuit board thus coatsS~d is th~n exposed through a coatin~ which protects from irradiation those parts of the boarci which have tc remain free for ~he ~olderlng process.

As actlnic radiatlon, ~ whlch the mixture according to the inv~ntlon Is : ~S sensitive, any ~lectromagnetlc r~diation can be considqred, the energy ot which is sufilciont to ex~it~ a suit~le polymerisati~n iniUator. P~rticulariy I, sultable are vlsible and ultravlolet light, x~rayq, y rays and olectron ta~a~on.
Laser r~diation In the visible and uv range caSn also be ussSsd. Short wavSs visibls~ and near uv light are prefened.
The coa~ings are developed in a known manner~ Aqueous alkali solutions, for 9 2 ~ 3 ~ ~
exa~nple of alkaii phosphatesl carbonates or silica~es are ~ultable develop~rs, a~ if need be small quantities, for exaunpie up to 1a % by weigh~ could bs ~dcled to org~nic solvents or cross-iinking materials whi~h ~n b~ mixed with water.

Dev~lop~ old~r masks ar~ subjected ~o heat treatment ~efor~ the solder;ing p~s-~. In this, tor example, the carboxyl groups of the bondin~ mean~ eact with th~ multifunction~l epoxide to giv~ an in~erp~ne~ratln~ cross-link~ The Int~grating ~omponent of thiS c~ss-link is ~ examp!e ~Iso th~ mlnetai so~ici.
Ov~rall th~ ~ood mechanical, thermai and chemic~i ptoper~es ol ~ s~ld0r m~sk ~re ~ffeoted by the heat treatn~ent. This h~at tr~atm~nt Is gengraily at be~h7een 80 C and 1~0~: with appro~ma~e treatm~nt tim~s of 10 to gO
minute~. The board ready for s~lci~ring is finaily tinneci and ~ t~7en hav~
1~ electronlc componen~s inserted in a known manner.

The wiring slde of the i30atd Is th~n narmaily tr~at~d witt~7 ~ ~ul~
commer~lal flux and, fot ~xamj~le, sub3ected to wave soldering by a oomm~rclal w~ve solderer. i~nown eutectic rnixtures which can wlthstan~i 20 soldering tomperatutes ot a~out 23~ to 290C serve as soldQrin~j means. A
known mixture con~ains, for ex~rnple, 63 % by weight tin anci 37 % by wei~ht lead. ~artlcularly in methods in which double s~ded. through plated printeci dt~u7it boards are soldered by dipplng in moit~n metal baths, solde~ fnask~7 manufactured accordlng to the Irwention can be useci with success.
The mixtures according to the invention re~ult In solder r~slstant co~tings, which are dlstin~uished by their hi~h dagree of ~exibility and mechanica solldl~y in thc unexposed and expose~i states, and by ~ high d~3ree of temperature resistance in the expos~ci and post cuted stat~s. The 30 photopolymerisabl~ coatings have7 in comblnation wlth th~ prefene~
photolnitiator, a hi~h degree of photosensltlvlty and also pro~uc~ good through ~080~g ' curing or thr~ugh cross-linking in greater layer thieknes~es. Th~ ~xposecl coatings can ~iso be developeci perfectly well and cornplet~ly with aqu0~
alkali soiutions with c~atin~ thickn~sses above i OO,um. C:omp~red with mlxtures which are the same apan for the use of aroma~ic ~poxides and those 5 manufactured with ~Iycidyl groups, the mixtures ac~ordin~ to the inv~ntlon have a l~nger storage life in soluffon and as a sol3d coatin~ on a prin~ citcui~~oard.

The exposed and davelopeci GoaUngs can ~e thermally cured wl~h~ut 10 exce~siv~ innuence on the fie~bility of the mask or its adhesion to the support ~nd without changing ~h~ ;~sition and dimensions of th@ are~s uncovered by d~veloping. Th~ cur~l nlasks are resistant to atmosph~fic, therlnal and cilemicai Intluen~es for longer psrio~s. A~er exposure of the resist co~in~s a high contrast image is reta~ned in the coaUng. Solder mask~ &ontaining th~
15 mixtur~s a~cordin~ to the inv~ntion ar~ par icularly sui~a~le f~r ~ff~c~v~ly and last~ngly protecting s~nsiave electronlc wirin~ paths frorn atmosph~ri~ ~n~k.

The ~ollowing exarnples explain individual embodiments of th~ mlxhJr~
according to the Inv~ntlon. Unless otherwise indicate~, the p~rc0ntag~-~ ancl 20 ratlos of quan~t~es are in w~ight units. Parts by weight (pw) and parts by volume (pv) are in the ratio of g to ml.

i-xam~le 1 (comPa~tive ex~m~le) 25 ~:~

a) 280 pw styrol, ~ 40 pw methacrylic acld, 80 pw n-hexylmethaCrylata arld 11.5 pw 2,2 azobiisobutteric acid nitril~ were dissolved w~lile bbing stirred in 450 pw 3-methoxybutanol~ /8 of this solution was heated to 90C In a retor~ while being stined and fed throu~h ~Ivith ni~r~gen. The resulting exothermic polymerisa~on WflS maintained .

~t 90~C to a maximum of 10~C ~y e~e~nal coaling. ~ r the m~n raa~oll subslde~, within 11~2 h~uts ~he rem~ning ~ of the ~olutlor was ev~nly dosed and finaliy ~he r~action solu~ion w~s rna~ntain~d at 90 ~Ot a fu~her 12 to 14 hour~. Th~ polym~r solution w~ re~dy 70r use after cooling to room tempsrature. Th~ r~uc~ cific visc~si~y ot the p~oduct was 0.185 dl/~ (mea~ur~d fr~rn a 1%
solution in dlm0thylformamide at 25C).
b) In a oylindrical container in 1~3.9 pw 3-methoxybut~ol~1, 1n 112.~ pw pentaerythrite-triacrylat~
i28.9 pw trime~hyiolpJopan~-triaorylate 27.~ pw s-phenyla~ridine 12.4 pw neozapon ~teen 1.2 pw ot a bluq a~o dye, produced i~y couplin~ ~.4 dlnltrc~-chlo~enzoldiazonium salt with 2-methoxy-~-ace~yla~nin~N, N-dlethylanllirle and æs pw triethyl~nedlamine ~: ZO w~re dissoi~eci with a hlgh rewing, hlgh-speed sUrrer. ~uring 30 rninutes 3~6.7 pw of a silicate pigment which is a n~tural ~lome~ate of corpuscular quartz and lalninar kaolinite, was scattore~ in th~ stirred solution. It cont~3ins ov~r 80% SiO2 and about 11% Al203; about ~0 % by weight of the par~icles hav~ a grain ~ less than 5~m (sillitln~. 6~4.2 pw o~ thls susp~nsion was flnally added lo the polym~r solution descrlbeci und~r a). The oompositlon with all its componen~s was well h~mo~enised wlth th~
aid of the rnixet (1,200 turns per rnin.), wher~by care waS taken that th~ temp~r~ture of the composition did not ris~ a~ov~ 50 to 55C.
: ~ The visoous coatin~ was 3round in a turther homo~eni~tion in a .

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,~, '' ~b~s b~! mill, ~nd then filt~r~d through a 1~0~um Y2A m~sh pr~ssure ~ and dt~wn off. ll~is mixtur~ was a~ ~ar as was necessary thinn~d with n~ethoxybutanol to a solid content ot ~8.~ %
by weight an~ h~reafter de~ignated ~s cornponent ~

c) In a cylindrical container 260 pw of an ~poxid~ re~in of biph~nol A
an~ epich!orhydrine wa~ dissolved with the epoxid~ ~quival~nt wei~ht 1~n to 200 in 148 pv~ 3-methoxybuta~l ~y me~n~ o~ an arrnature stirrer. After 15 minutes rest tlm~ an obvlaus solution was produced with ~3% solid contsnt. Thi~ ~olution was her~lter designat~d as componen~ B.

d) 100 pw of component A w~s intensiv~ly mixed by means of a suita~l~ stirrer with 22.3 pw of component B. With this, the solder -i~ resist ~olution was ready fot use, that is, for applicaUon onto a print~d circuit ~oard according to one ot the ~bwe-m~ntioned methods. The solid content was 67.5%.

e) A 24 x 36cm board of epoxid~ resln/~lQss tibr~ with a circuit pattern . 20 appliecl on both sid~s of 0.2 to 1.5mm wid~ and ~0 to gO ~m ~hick copper path and feed drill holes was completely surface coat~d wilh the solution descnbe~ in b) by me~ns ol ~ ~erniautomatic p~ssur~
lllter m~chine (Alfra-Plan sQn~). A ~ull surfac~ open polyester filt~r . ~ wittl 43 rn~sh p~r cm was used to transfer th~ coatln~; the tubber sque~g~, with a hardness ot 70 Shot~ ~a~ gently ro~nded on the pf~ssur~ eclg~, and the angle ol applicaUor) was 1~. In thls w~y ~; ~ bubble and colour streak free ~oating can bQ don~ wlth a slope wvetag~ of 15 to ZO~um. The printeci circuit board t~us coat~d was lelt tor 5 minutes at roorrl temperature and subsequ~ntly dried ~or 30: 7 minutes in a circulating air drying cupboard at 80C. After coolingto room temperature~ the coated printed circuit board was exposed ; ~ ;

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~ 8 acco~dlng to a pa~rn ~hrou~n ~ foil p~ttern.

Dev~loping was in ~ conveyDr spray apparatus with 1.3% ~queous s~da solution at 30C with 1.2 bar ~pray pr~s~u~. Th~ d~velopir g tlme was 90 ~ec, th~ unexposed area~ of the ~aating w~r~ eady dev~lopeal ~ner 2/3 of th~ developing cours~

After w~shing wi~h watef~ ~he developed board was d~d in a warm air oonveyor dri~r and subse~quently temp~r~d ~n a drc~ ng ~r w~n for 1 hour at 150C. The now compl~t~ly cur~ board wa~
wav~ solder~d~ a second bo~rd, manufaatured in th~ sam~ way, was hot ~nned.

: Solde~n~ wa6 camed out in a ~vave oklerlng machine. In thl~ th~
board was conYeyecl over a foam fluxer (Alphagnllo~l FIF 12A) conn~cted in senes, pr~dned and ~onv~ye~ ov~rthe molten ~old~r, . consisting of eutscti~ l~adltin alloy. The spe~d was 1 m pe~ minute, the solder temperatute ?6~C.
, The solderin~ r~sult ~ft~r a single wav~ solder proces~ was v~ or~. To . ~ rnake the differences more clear, the proceqs was repeated thtee lim~s mo~.
~ The result~ Qre shown in tabi~ 1.
: ~
The parameters shown in tabl~ 1 hava the followin0 m~anln~:
:: 25 Ele~trolytlc corrosion (E-corro~ion):
Th~ de~ign~tion corresponds to rsgulatlon SN 57~30 orlglnatin~ Irom Si~rnens AG an~ 13 g~nerally normal ancl r~cognised in prlnt~d clrcuit board technology.
Multi-purpose test boards corrc3ponding to IPC~ ~-25 ~v~r~ ~torad for 24 days . ~: at 40C; and 92% relative h~lmidity whereby 100V direct cun~nt was applied : ~: 30 to each of tNo par~llel wirin~ paths. Corrosion is judged vi~ually and ~he :. :` ~ resul~s as8~ d as follows:
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1~ .
2~0~
~v~ry good ~g~od Os~isfactory 5 Goating appear~nce:
Visible reguiarity of the ooating regarding stn~otllr0 and colour is as5~s8ed with the naked eye.

Potlife:
tO The storage tirne at room temper~ture o~ th~ ready coating solution is given af~er whi~h a photosensitive coating i~ retained which c~n be process~d without problems. The terminal tlme is taken as the point wh~n a coa~in~ is reta~ned which tal<es twice the time to develop as is required by a freshly daveloped coating.
~5 Drying window:
P~ang~s of parameters are d~t~rmin~d for drying ~mperature and drying time, within which a usa~le result is obtained~ In this, for sufficient ~ing a temp~rature ot ~0C and A minimum d~ying time of 6 to 10 minutes, 20 dep~ndent upon the cirying temperature, is ~Ixed. Excessive dryln~ produces a product which ~annot be p~rfectly processed, in particular developed. The upper iimit is de3cribed ~y a cu~e, whicn c;oes approximately exponenti~Jly ~rom 6 minLt~s at 100C to 120 mlnutas at ~0. Th~ surfaces d0scribedi by these curv~C as well as the lower limits ol 50C and 10 minutes are 25 d~signated as ~he d~ying window anci reptesent the conditions for the comparativ~ example 1. By skewing the exponentlai cuNe towarcis harder or mor~ gonlle c~nditions tor the maximum permissible drying the cirying wlndow is chanc;ed. For each exalmple this surface is ~jiven in % with resp~ct to 100%
tor comp~ativ~ example 1. A higher percentage therefore means a ~eater 30 pn~cr~sslng ran~e.

, 21~8~8 Storage life:
Stara~e life is ~ en in hours ~or a printed circuit ~oar~, coated ~h th,e~ dned unexpos~ sold,er resiSt Coating, at room temperature. in ~his eas,~ also, the t~ermlnal time is taken as tn"~ point when h~ce the developing tilr.e is requlred Developing time:
ThR time ne~,ad for v~ free developmsnt of ,~ large unex,~sed surf~ce (break point) with a .,.3% soda solution at 2~ :: is gi~n In s~wnds.

1 0 Photossnsitivi~:
Tha number of ~,~isible cureci wedge steps in a st~dard ~tep wedje (ligh~
intensity factot p~r step ~2) at 300 rnJ/cm2 from a Fe doped nnercu,l~ v~our lamp i~ given.

15 Intiittatian on the ed~e connectors:
The numb~r of ea,ge connector~, that is, the copper ~trips 1e~,ing trom the conne~ction points, on which the solder mask is inflltrated by iea~ tin s,older is j` given as a~/Oof the toW n~ mber.
1 . I
20 Utting of the solder mask from the wiring paths:
The amount of surface of ~he wirin; paths on which the solder mask is visibly litted up from the copper in bubbles or in another way is giv~n a~ a %.
j;
Pull off test with adhesive ~ape:
:! 25 To test th~ adhesion ot the solder mask to the wiring paths on thcse places not vlsibly lifted up, atter soldering a strip ot a~hesive tap~ is pr0ssed onto ~he :, cooleci solder rnask and pulled off abrup~ly at an an~le of gao.
., ` fl It tho coating described in d) whlch iS ready ~or immediate use for nlt~r application is us~d for ano~er applicaffon process, the solids content of 67.5~ is tos high. ~f the mRsk is ap~i~d to a p~nt,e~d .

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SEP-lg93 15:57 P~ITENT~lNWl~lLrSBURO ~49 611 372111 S.06 ~2~ -~9~ 9~i:~ f~M D ~3 8. CO 2 1~ P. 7 1~

cir~ut boaJd by a ver~ l cunslll ~rou~h a ~n~imdinal ~ In a curta~n paunn~ machifle, the so~ mu~ 3~ rec~c~ by th~n~
Ymh methox~anQI ~ al~o~ 5~% bywsi~h~ ~imilar ~n~
ar~ n~6essa~y i~ th~ ma~k 3s spr3yed on~ th~ print~ c~t t~ar~
In a high vol~ge field Py means of a ro~ spr~r t~e~ t~
~hni~3 ~so r~s~ n a Yery ~ood wirin~ ~th ~h~i~ ~y d~
~k, w~kh cov~s ~e board WilhOUt pores an~ wi~ a r~lar thi~n~ss. ~rscessin~ a~rding to e) leads to th~ s~rn~ g~i ' ` res~lts ~1~ ~. Y, g an~ re comp~v~ exa~s.

In all ex~ es tt~ ~ame ~ pssi~on as in e~npi~ 1 Is pr~oe~ aH~u~
~5 th~ ep~ r~sln used in ~ exasnpl~s accordin~ to U~ Im/~n~ion ~ naF~
en q~ es oS one of lhe foll~nQ epo;cy co~npa~

1. Bi(3,4 epoxycy~loh~xylr~et~)~p~ l;
2. 3,~epxy-cyc!ohexylmet~ 3,~pDxy-cyP!ol~xanecart~b ~` 20 acid e~t~r ~. 3,4~epoxy-cyclohexy1 : 4. ~3,4~poxy~s:yc~hexyl)~a,g epo~2,4 di~
~S,~unaecane 25 Indivkh~y. in exafrlp~ to 12 ~e tollo~4inQ ep~ lr~ us~ in8 ot the ~iphenol A and epichlo~drine epaxy resin:
.
; ~QI~ 2 A~ in e~mple 1, bul with epcxy comp~ t; epQ~ equNaler~ W~t 1B7.
.~ ~ 30 , , ~, . .
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-i7 2~ 8 As ex~mple 1, ~ut with 186 pw of epoxy compound 2 in 214 pw 1-rnethoxy-prapyl~2-acet te; epoxy equivaient weight 135.

Example 4Q~
As exarnple 1, but with a novolac-glycidyl ether in th~ sam~ quan~ity as the epoxy ~Qmpound used thorein; epoxy equlvalent w~ight 195.

Ex~ np!e 5 10 ~s example 1, bu~ with 192 pw of epoxy compound 3 In ~08 pw methoxypropanol, epoxy equiv~ent weight 70.

~x~nple 6 As exarnpla 1, but wi~h 152 pw of epoxy c~n~pound 4 In 248 ~w 15 methoxybutanol; epoxy equivalent weight -33.

Examr le 7 (V) As ~xample 1, but with a mixture of pentaerythritetriac~ylate and polypropylene31ycoldiacrylate (Mw = 420) in welght ratio 1:1 instead of the ~ 0 monomer mixture used therein.
;, .~ ~ame~
A~ ~xample 7, but with 18~ pw of epoxy compound 2 in 2t4 pw 1-melhoxy-propyl-2-~cetate: epo~y equivalent weight 135.
~5 ~amE~
5 example 1, but w~th a mixture of pentaelythrltetriacrylate ancl polybutan~
1,4 cliol~iaorylate (Mu, = 400) in we;g~ ratio 15:85 5nstead of the monomer mixbure used therein.

Exam~!e 1 0 ` . ~

1~ 2~ Q~8 As exampl~ 9, but with 186 pw of ~poxy compound 2 in 214 pw 1~ thvxy-prcpyl-2-ac~tat~; epoxy equivalent wel~ht 1~.

~m~l~
As example 1, ~ut wlth a copolymer of 20 pw acrylic acid, 10 pw s~rol and 70 pw m~thylm~thacryl~t~ Instead o~ the copolyrrers of s~rol, methacrylic acid and n~hexylmethacryl~te usecl thereln.

~.2 10 As examp~ , but with 186 ~w of epoxy compoun~ 2 in 214 pw 1~rnethoxy-propyl~-ace~at~; epoxy equivalent welght 135.

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Claims (8)

1. Radiation polymerisable mixture containing a) a compound with at least one terminal ethylenically unsaturated group which is capable of forming a cross-linked polymer by radical initiated addition chain polymerisation, b) a water-insoluble, aqueous alkali solution-soluble, polymeric binder containing carboxyl groups, c) a polymerisation initiator capable of activation by radiation, or a polymer initiator combination, and d) a compound with at least two epoxy groups.

characterised in that the epoxy compound is a cycloaliphatic epoxy compound.

2. Radiation polymerisable mixture according to claim 1, characterised in that the epoxy compound (d) contains an epoxidised cycloalkene ring with 5 to 7 ring members or a cycloalkane ring with 5 to 7 ring members substituted by an epoxidised alkenyl group.

3. Radiation polymerisable mixture according to claim 1, characterised in that it contains in addition a heat activated cross-linking initiator (e) for epoxy compounds.

4. Radiation polymerisable mixture according to claim 1, characterised in that it contains in addition a fine particle mineral pigment (f).

5. Radiation polymerisable mixture according to claim 1, characterised in that the compound (a) with at least one ethylenically unsaturated group is an ester of acrylic or methacrylic acid.

6. Radiation polymerisable mixture according to claim 1, characterised in that the binder (b) containing carboxyl groups is a mixed polymerisate of acrylic or methacrylic acid.

7. Radiation polymerisable mixture according to claim 1, characterised in that it contains 10 - 35% by weight of compound (a) with ethylenically unsaturated groups, 15 - 50% by weight of binder (b) containing carboxyl groups, 0.01 - 10% by weight of polymerisation initiator (c) and 10 - 30% by weight of epoxy compound (d)

8. Method for the manufacture of a solder mask, characterised in that a solution or dispersion of a mixture according to one of claims 1 to 7 is applied to the surface of a structure printed circuit board and dried, the coating obtained is irradiated according to a pattern with actinic radiation while blanking the soldering eyes, the non-radiated areas of the coating are washed out with a developer and the mask obtained is heated at a raised temperature.