CH644882A5 - Masking compound for production of diffusion masks - Google Patents

Description

The present invention relates to a synthetic resin covering material for the production of both permanent and removable masking materials for the production of printed circuit boards. Such a mass enables a high resolution for printed circuit diagrams and is screen printable.

The mass according to the invention is used to produce

644882

Printed circuit boards with a conductor allowance of at most 0.25 to 0.1 mm.

The present invention provides a masking compound which, when hardened, changes directly from the gel-like to the solid state without liquefying in between and therefore neither runs nor flows into the holes, but retains sharp edges and contours.

The new mass also has the advantage that it provides good adhesive strength both on insulating material and metallic substrates, in particular on copper substrates, and that it withstands the heat shock that inevitably occurs during the mass soldering process.

It also enables the production of masking masks which have a smooth, glossy surface, in order to avoid undesired metal deposits when using electroless metal-depositing baths.

The masking compound also allows a mask to be formed which can serve as a removable mask in the production of printed circuits using the printing and etching process.

Finally, a further advantage is that the masking compound remains in a gel-like state until it has hardened and retains its adhesive strength on the metallic base unchanged during the hardening process, even if it is hardened over a longer period and at temperatures up to 160 ° C.

The new masking compound has improved adhesive strength, especially on metallic copper; At the same time, the cover masks produced with it have the advantage that there is no discoloration of gold coatings, as occurs in the known cover masks.

In addition to a thermosetting resin or a thermosetting resin mixture which are in solid form at temperatures up to 60 ° C. and preferably at room temperature, the compositions advantageously contain a hardener which is dissolved in a solvent and carries more than three functional groups. In its initial state, the mass is of high viscosity or is in a gel-like state and passes directly into the solid form during the curing process and without liquefaction.

In a preferred embodiment of the invention, the mixture consists of epoxy resins with an epoxy functionality of less than 10 and preferably less than 7.

If the composition according to the invention is to be used for permanent masks, it preferably consists of an epoxy resin which is dissolved in a solvent and a first hardener which contains an alicyclic amine which corrodes metallic copper; this hardener is preferably present in an amount sufficient to achieve complete hardening. In its original state, this masking compound is gel-like or a solution of very high viscosity. During the curing process, it changes directly to the solid state,

without the contours running through liquefaction of the mass. An optional second hardener consists in particular of an aromatic amine and ensures that the mask layer against cleaning agents, such as those e.g. used to remove the solvent. The mass can also contain a flux and at least one modifier and an additive for thickening the mass and another that gives it the required toughness.

So much thickener can be added that the mass has a gel-like nature; furthermore, so much organic acid is generally added that the basicity of the alicyclic amine is neutralized, but the thixotropic character is retained.

The following is an exemplary description of a mass for permanent masking masks for the production of printed scarf3

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after the additive process. The surface of a plastic plate as a carrier plate for a printed circuit is covered with the permanent covering layer. The hardened mask layer produced therefrom is resistant to the chemicals normally used in the manufacture of printed circuits and has a smooth and glossy surface. The holes at the intended conductor crossing points are either made before the mask is applied or subsequently attached using a method which leaves the mask undamaged, such as drilling or punching.

The surface is then etched with a strong oxidizing agent to improve the bond strength of the metal layer to be applied to the areas not covered by the mask. After sensitization, the carrier plate is exposed to an electroless metal-depositing bath in order to produce the corresponding metal layers on the hole walls and the conductor tracks. The finished circuit board is printed with a permanent bulk solder mask according to the present invention. The permanent solder mask layer shows a smooth and shiny surface. The hole walls and - if desired - the hole borders and the contact fingers are left free. The solder mask layer is resistant to both the thermal shock occurring during the soldering process and to cleaning agents to remove the solder residues and has a very good adhesive strength on the copper layer, even at temperatures of 160 ° C for 16 hours.

In another example, the masking compound according to the invention is to be explained as a removable mask in the production of printed circuits.

Holes are drilled in a copper-clad plastic plate and then the walls of the hole are sensitized according to known methods for metal deposition from electroless baths and electroless copper is deposited. The deposited copper layer on the surface of the plate can be easily removed by sandblasting. A removable mask from a mass according to the present invention is printed using the screen printing method. The mask corresponds to the negative circuit diagram and leaves the conductor tracks to be metallized free. Then the conductors are plated without current and provided with solder. The removable mask is removed with a solvent and the thin copper layer underneath is etched away.

Screen printing stencils consisting of a stainless steel mesh with a polyvinyl coating have proven successful in the production of printed circuits. These screen printing stencils are very robust and easy to manufacture. Of course, the steel net can also be provided with a different plastic coating. Any screen printing emulsion including so-called “transfer films” can be used, depending on the type of mask to be printed. Trans-fer films are generally understood to mean a film-like coating that is first produced on a base and then transferred to the screen. If a mask is printed on a base, any screen printing compound that cannot be removed from the mask to be printed can be used. In addition to stainless steel, nickel wire mesh with a polyester coating is also suitable as the sieve material.

According to the present invention, thermosetting resins with a high melting point and high functionality are suitable for the covering compositions according to the invention. This has the effect that the solvent volatilizes easily and the mixture changes from the gel-like state to the solid state during the hardening process, thereby preventing the contours from running.

It is assumed that the viscosity of the mass initially increases during the curing process until it changes to the solid state. The high functionality of the mass also means that the polymerization takes place very quickly, which avoids any runaway during the curing process; consequently the mask shows sharp contours.

It was found that a screen printable epoxy resin composition which has a high functionality and is dissolved in a solvent to which an organic alicyclic hardener has been added has the following properties:

1. The mask layer produced in this way has a resolution which is sufficient for a conductor spacing and conductor widths of 0.23 mm;

2. The mask layer is resistant to the chemicals used in electroless metal deposition baths;

3. The mask layer has good adhesive strength both on base materials coated with adhesion promoters and on metallic substrates;

4. And finally it resists the thermal shock that occurs during the soldering process and the cleaning agents used to remove the solder residues.

In a further embodiment of the masking compound according to the invention, it is used as a solder mask. As already mentioned, the first hardener, an alicyclic amine, has a corrosive effect on metals, in particular on copper. The thermosetting resin is solid at room temperature and does not melt until the curing temperature, which is between 60 and 200 ° C.

A simple test can determine whether a thermosetting resin meets the required conditions.

A piece of the resin to be examined between 5 and 10 g in weight is heated in an oven to 100 to 160 ° C. After removal from the oven, it is visually inspected to determine if there are any signs that the resin has melted or changed in shape. If such changes are found, the resin is unusable for the mask layers according to the invention. If, on the other hand, the resin surface remains sticky according to the procedure described above, it can be used for the resin mixtures according to the invention.

In the description of the present invention, highly functional resins are those which have more than three and less than 10 functional groups. The number of functional groups is preferably between 4 and 7. Useful thermosetting resins have been found to be those from the following groups: epoxy resins, melamines, urea derivatives, phenols, polyamide-imides, polyimides, alkyd resins (glyptals) and polyurethanes and mixtures of these Resins with an average functionality between three and seven and a melting point between 60 and 200 ° C.

Of the amino resins, melamine formaldehydes and urea formaldehydes are useful.

A usable urea-formaldehyde resin is available under the trade name “Uformite F-240M” and a melamine-formaldehyde resin under the trade name “Uformite MM55”. Other useful melamine resins include "Resimene 812" (a colorless powder), "Memac 1077" (a melamine resin with cellulose filler), "Melmac 404" (a translucent melamine resin) and "Melmac 483" (a phenol derivative of melamine resin).

Useful phenolic resins include oil soluble phenolic resins (prepolymers) to be reacted by heating such as e.g. CK-12-82 and CK-16-34 a with a Durran softening point of 82 to 99 ° C or 87 to 94 ° C and prepolymers of phenol-formaldehyde condensation products, such as. B. «Resinox P-90» and «Resinox 3700», SP 8014 and SP 6600 with a melting point of 71 or 65 ° C. SP 8014 has a specific weight of 1.25.

A useful polyamide-imide resin is "Kerimid 501" and a useful polyimide resin is "Kerimid 601".

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Usable alkyd resins (glyptals) include ethylene glycol malonic polyester such as "Plakson" and "Durez" one.

Usable polyurethane resins include prepolymers in combination with polyols such as. B. «Solithane 113» and «Polycin U56». Heat-curable epoxy resins for the purposes of the present invention preferably form 35 to 37% of the dry mask, the remainder consisting of hardeners and one or more additives which influence the specific properties of the mask.

Usable epoxy resins also include epoxy novolac and / or bisphenol resins which are solid at room temperature, have a molecular weight between 350 and 15,000 and a melting point between 60 and 200 ° C. For reasons of clarity, the following description is limited to those based on thermosetting resins Masses based on epoxy resins, which should not be interpreted as a limitation of the scope of the invention.

Particularly suitable epoxy resins have a functionality of more than 3 and include the following commercially available epoxy resins.

Table 1

Epoxy resin Medium number

Middle

Durran

the epoxy

Equivalence weight

Softening

functions of the epoxy point

EPON 1031

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220

81 ° C

ECN 163

4th

200

81 ° C

ENC1273

5

225

73 ° C

ECN 1280

4.1

230

70-80 ° C

ECN 1299

6

235

99 ° C

DEN 43

3.8

200

38 ° C

Other solid epoxy resins believed to be

that they are highly functional thermosetting resins in the sense of the invention are, for example, “Apogen 1013”, “Epi-Rez 512” with an average equivalent weight between 70 and 80 ° C; «Epi-Rez 5291» with an average equivalent weight of the epoxy groups of 310 and a Durran softening point between 90 and 95 ° C; and «Epoturf 37-171» with an average epoxy group equivalent weight of 150 and a Durran softening point between 77 and 83 ° C.

If desired, other epoxy resins with less functional groups can be added to the masking composition to avoid the brittleness of the hardened layer. Such epoxy resins include copolymers of epichlorohydrin that have a melting point between 70 and 191 ° C and a molecular weight of about 350 to 15,000. Although epichlorohydrin is the starting material for most of the major organic epoxides used to make epoxy resins, other epoxies such as e.g. B. 1,2,3,4-diepoxybutane can be used. If epichlorohydrin is the preferred starting material for the resins used according to the invention, other epihalohydrins such as e.g. Epibromohydride, quite beneficial. Likewise, epoxy resins which are derivatives of phenols other than bisphenol A can be used, e.g. the reaction product of epichlorohydrin with resorzine or with phenols made from vegetable oils, with hydroquinone, with 1,5-dihydroxynapthalene or with 2,2,5,5-te-trabis- (4-hydroxyphenyl) hexane.

Phenolic intermediates of the resol type, hydrazines and sulfonamides such. B. 2,4-toluenedisulfonamide can also be used for the production of resins useful in the context of the invention by reaction with epoxides.

Aliphatic epoxy resins can also be used for the masking composition according to the invention, including for example

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the reaction products of epichlorohydrin with glycerol, with ethylene glycol or with pentaerythritol.

Epoxy resins with less functional groups are advantageously used for the covering composition according to the invention only in small percentages of not more than 30 ° C., preferably only 10-15% of the total mass. The epoxy resins with a large number of functional groups are generally added in a percentage of between 50 and 90% and preferably 70% of the total weight of the covering composition. For this purpose, the epoxy resin is advantageously dissolved in a suitable solvent, for example in glycol ether or ester such as diethylene glycol ethyl ether , Ethylene glycol, Ethylene glycol methyl ether, Acetate of glycol ether, secondary butyl acetate, normal butyl acetate and primary amyl acetate.

As a hardener for the epoxy resins with a large number of functional groups in the inventive covering compound for metallic surfaces, e.g. primary alicyclic amines which attack the metallic surface and in particular copper are suitable as a solder mask. For this reason, such face masks have not been used for these purposes in the past. It has now been found that - contrary to the previous view - excellent adhesive strength can be achieved on copper substrates if alicyclic polyamines are used as hardeners, which were previously thought to attack metallic copper as well.

Among the alicyclic polyamines, the following have been found to be useful: methanediamine, 1,3-diaminocyclohexane, isophoronediamine, triethylenediamine and hexamethylenetetraamine. The addition of this hardener increases the heat resistance of the mask applied to metallic substrates.

The addition of gelling agents does not impair the favorable properties of the masking compound according to the invention, but rather is suitable for improving the screen printing ability and resistance of the mask. If the plates provided with the mask according to the invention are to be stored or arranged vertically for the purpose of curing or other manufacturing steps, this is generally only possible if additional thickening agents or gelling additives are added to the masking compound; otherwise the printed pattern would bleed. The thickening and gelling additives that can be added to the masking compositions according to the invention improve their screen printing ability by sealing them into a soft, gel-like state.

The soft, gel-like state can also be described as a “non-Newtonian” liquid; it is not free-flowing, but flows when using pressure, such as screen printing. If the pressure is removed, the mass returns to the non-flowable state.

It was also found that when alicyclic polyamines are used as hardeners in solder removal, the protective layer applied can be damaged. For example, methylene chloride vapor is used to remove the solder residues, or the solder is removed by scrubbing in hot water or with the aid of brushing machines.

To avoid this, an aromatic amine can be added to the mass as a further hardener. The following aromatic amines are preferably used: tris-2-ethylhexoate salt of tris (dimethylaminomethyl) phenol, diaminodiphenylsulfone, benzyldimethylamine, metaphenylenediamine and methylenedianiline. Aromatic amines are used because the hardened epoxy resin then has a structure that is stronger and more resistant to high temperatures and solvent influences, which is known per se.

The strongly basic nature of the alicyclic polyamines destroys the required thixotropic gel structure of the masking compound within 5 minutes, especially when silica airgel is used as a thickener. In order to avoid this, organic acids are added to the masking compound

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sets that can be mixed directly with the resin or with the hardener. The following organic acids have proven to be particularly suitable: a) end-carboxylated butadiene-crylonitrile polymer, and end-carboxylated butanediene polymer; b) fatty acids such as linolenic acid, oleic acid and the like; For example, dimeric or trimeric fatty acids with two or three carboxyl groups per molecule, which are produced by polymerizing a Qg fatty acid, such as, for example, “Empol 1040”, a predominantly trimeric fatty acid, with an acidity of 175-192, one can be used as fatty acids Wetting value of 192-200 which is 20% dimer and 80% trimer; «Dimac S», a dimeric acid with an acidity of 180-190, a wetting value of 192-198 and which is 8-10% monomeric, 65-69% dimeric acid and the rest of 26-30% higher polymer Acid exists; and dibasic acids such as adipic acid, glutaric acid, azelaic acid, sebacic acid and suberic acid.

End carboxylated liquid acrylonitrile rubbers with or without pendant carboxyl groups form amino salts with basic alicyclic polymers. The reaction to the salt proceeds without difficulty and very quickly and slightly exothermic, the main advantage being that the gel structure is retained. Other advantages of using carboxylated rubber are: 1) the reaction of the functional epoxy groups makes the layer more resistant; 2) The formation of carbonates is avoided or at least greatly delayed. Alicyclic polyamines absorb carbon dioxide from the air and thus turn into an unusable carbonate.

When producing the covering composition according to the invention, enough hardener should be added to form all functional groups of the epoxy resin and thus to fully harden the resin. The required amount can be calculated from the amine equivalent weight (A.E.W.) of the hardener and the epoxy equivalent weight of the epoxy resin (E.E.W.), according to the formula

A.E.W.

Weight d. Hardener = X weight of the epoxy resin

E.E.W.

Various modifiers are advantageously added to the epoxy resin solvent to improve the flowability or wetting, the screen printing ability, the toughness and, if desired, to achieve a color effect, antioxidants and agents for preventing the course of the printed mask.

Means to improve the flow properties reduce the surface tension and thus prevent the formation of ring-shaped imperfections and result in a smooth and flawless surface. The wetting agent forms a smooth, homogeneous film without the annoying craters and irregularities that usually occur when these resins are used. Useful wetting agents include alkyl acrylate polymers and silicones. The following commercial wetting agents may be mentioned, for example: “Moda-flow”, “Raybo 15” and DC 840. “Modafiow” is a high-molecular polymer which is believed to consist of a mixture of isobutyl acrylate and ethyl acrylate polymers or copolymers. "Modafiow" improves the surface properties of the mixture and causes an even distribution on the base, so that a smooth layer without ribs or bubbles is formed and a smooth, shiny surface is created after drying. These additions to the mixture are generally about 6% by weight of the total mass, preferably 4% by weight and, after use, more than 1% by weight of the covering mass.

The screen printing aids act as lubricants and facilitate the screen printing process with the masking compound. At the same time, they create a smooth surface on the printed mask layer. The screen printing aids that can be used include the epoxy resins which are liquid at room temperature, for example "The 330", "The 331", "The 332", "Epon820", "Epotuf 37-151", "Epotuf 37-134", "Epotuf37-135" , «Epotuf37-250», «Epirez508» and «Epirez510», and «Araldite 6005» and 6010. The screen printing aids are generally up to 60% by weight, preferably up to 40% by weight, and more after use than 1% by weight, preferably more than 2% by weight, in the covering composition.

Useful agents for increasing the toughness are, for example, acrylonitrile butadiene rubber and solid epoxy resins with a large epoxy equivalent weight. The rubber-containing substances to increase toughness precipitate out during curing; for example, the rubber-rich microglobulins are uniformly finely distributed in the polymer after curing. The microglobulins prevent cracking in the hardened resin. Usable agents for increasing toughness include commercially available liquid monomeric reactive rubber such as CTB, CTBN, CTBMX and ATBN. The solid epoxy resins increase toughness through greater elasticity of the crosslinking of the inherently rigid structure. Solid epoxy resins which can preferably be used and which have a solid structure at room temperature and whose epoxy equivalent weight is greater than 350 are listed in Table 2.

Table 2

resin

E.E.W.

Softening point

"The 661"

475-575

70-80 ° C

"The 667"

1000-2000

113-123 ° C

"Epon 1001"

450-550

65-74 ° C

"Araldite 7097"

1650-2000

113-123 ° C

These toughening agents are generally added to about 10% by weight of the masking compound. Preferably 7% by weight is added and the finished layer contains more than 1% by weight.

Pigments that can be used to color the masking compositions are, for example, “Cyan Green B-15-3100”, “Cyan Green Y-15-3040”, titanium dioxide (rutile) “0r-600”, “Irgazin Yellow 2GLT”, and “Monastral Red TR-79D »And« Blue BT-417 ».

Oxidation inhibitors are added to the mixture of the invention when the mask layer is exposed to temperatures above 100 ° C for extended periods of time, as they prevent excessive air oxidation of the mask at such temperatures, which would result in discoloration of the mask. This additive also prevents brittleness and lack of adhesive strength.

Suitable agents for inhibiting oxidation are thioesters such as dialkyl thiodipropionate, dilauryl thiodipropionate, distearyl thiopropionate and dimyristyl thiodipropionate; Phosphites such as tris (nonylphenol) phosphite and alkaryl phosphite; Phenols such as those substituted with fatty acids, their derivatives or substitution products, phosphetilated sterically hindered phenols and sterically hindered high molecular weight phenols, e.g. Butylated hydroxytoluene and mixtures of the compounds mentioned.

Particularly suitable agents for inhibiting oxidation are e.g. B. the mixture of a thioester with a sterically hindered phenol in a mixing ratio of 9: 1. Antioxidants are generally present in the composition in an amount of more than 1% by weight, preferably more than 3% by weight, but less than 10% by weight and preferably less than 7% by weight.

Suitable thickeners or gelling agents are e.g. Silicon dioxide aerosils with a microscopic particle size and a total surface area of 200 to 400 m2 / g such as Cab-O-sil, organic modified montmorillonites such as "Bentone 27", a trialkylarylammonium mectite and "Bentone 38", a tetraalkylammonium mectate that treated with amine

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Are bentonites; a colloidal silica anhydride such as «Ludox», a silica airgel with a microscopic particle size and a total surface area of 280 m2 / g such as "Santocel Z".

About 5% by weight of the thickening or gelling agents are present, and after use the layer contains more than 1% by weight and preferably more than 2% by weight of the weight of the solid epoxy resin of the covering composition according to the invention. When the covering compound containing a thickening or gelling agent cures, it remains in a soft, gel-like state until it is completely hardened and only then solidifies “in situ” without running, flowing or deforming.

Aerosil can also be added to the primary hardener to achieve a higher consistency and better pourability without spraying. The main advantage of such admixtures is the reduction of possible weighing errors which can occur when the primary hardener is added to the masking compound according to the invention.

For masks to be applied using the screen printing process, epoxy resins with a viscosity of between 10 and 200 Pa.s., preferably between 15 and 100 Pa.s. The Brookfield viscometer at 10 rpm with a spindle No. 7 is suitable for measuring the viscosity of the masking compound according to the invention for control purposes.

The following may be mentioned as useful additional hardeners, which also react with the functional groups of the epoxy resin in the covering composition: phenol-like resins, polyamide resins or melamine-formaldehyde resins; or in some cases also dibasic acids. Usable hardeners are, for example, amines such as methylenedianiline, diethylenetriamine or methyphenylenediamine; or amides such as Dicyandiamide. The 3- (dimethylaminomethyl) phenol salt of diethylacetic acid of a tertiary amine or 50% by weight of one of the salts described above in combination with another amine has proven to be very particularly suitable. Such hardeners allow a storage time of up to 8 hours and still quick hardening.

When producing the masking composition according to the invention for a permanent mask, the amount of hardener, as previously described on page 26, line 21, can be determined according to the formula A.E.W.

Weight d. Hardener = X weight d. Epoxy resin

E.E.W.

be determined. This formula is only applicable in practice if the equivalent weight of the hardener can easily be determined, which is e.g. B. is not the case with dicyandiamide; here the amount of hardener has to be determined experimentally.

If the masking composition according to the invention is intended for a mask which can be removed again, the addition of hardener should be kept so low that complete hardening does not take place, since, as has been found, the mask hardener is used only for a lower addition of hardener than is required for complete hardening is stable for a certain period of time. Partial curing of the mask requires more than 10% by weight, preferably 20% by weight, mostly about 30% by weight, and sometimes even 40% by weight of the amount of curing agent as required for complete curing is needed. In any event, the amount of hardener which causes partial curing is less than 80% of the amount required for complete curing, and preferably less than 50% by weight. The partially hardened mask layers can be easily removed with alkaline cleaners or solvents after use.

If the masking compound according to the invention is used as a mask for the electroplating process, the hardness can also be completely omitted if the curing temperature is selected appropriately, which is below the melting point of the epoxy resin used; nevertheless, the favorable properties of the protective layer are retained and sharp contours and a very high resolving power are achieved, so that fine printed circuit boards can be produced using this cover layer 5.

When using the masking compound according to the invention both as a removable mask and as a permanent mask, there is no bleeding or expansion of the mask layer during curing, so that the hitherto existing difficulties associated with the use of conventional resin-containing maskers, with which the manufacture is eliminated of printed circuit boards with conductors of small width and small distances due to the above Disadvantages were not possible.

The examples below, as far as known, show at least some of the most advantageous embodiments and methods according to the invention. The following are seven typical compositions of the masking compound that can be used as a permanent mask.

20 Example 1

Composition 1: For use as a permanent

Mask for the production of printed circuits using the additive technique:

25 raw materials weight (g)

70% epoxynovolac, functionality 5.4, melting point 99 ° C, dissolved in diethylene glycol ethyl ether - 643

Epoxynovolac phenol formaldehyde resin, equivalent weight of 172-179; Viscosity of 11-14 Pa.s. at 30 25 ° C (liquid screen printing aid) 20

25% copper phthalocyanine pigment in finely divided form in bisphenol A epoxy resin, epoxy equivalent weight from 180-190; Viscosity of 11-14 Pa.s. at 25 ° C for green coloring 40

35 "Modafiow" (to improve flowability) 12 end-carboxylated acrylonitrile rubber, average molecular weight 3500, carboxyl content of 2.3% by weight, functionality 1.85 and 18% by weight bonded acrylonitrile (liquid rubber to increase the 40 toughness) 25

Diethylene glycol ethyl ether 40

3- (Dimethylaminomethyl) phenol salt of diethyl sugar acid (hardener) 50

45

Composition 2: permanent mask raw materials weight (g)

Four-functional bisphenol A epoxy resin with a softening point of 80 ° C 100.0

so epoxynovoalac-phenol formaldehyde resin, epoxy equivalent weight of 172-179, viscosity of 1-2 Pa.s. at 25 ° C (liquid screen printing aid 85.0

"Modafiow" (superplasticizer) 3.4

Butyl cellosolve acetate (solvent) 20.0

55 3- (Dimethylaminomethyl) phenol salt of diethyl sugar acid (hardener) 23.8

Composition 3: permanent mask 60 raw materials weight (g)

Difunctional bisphenol A epoxy resin with a Durran softening point of approx. 75 ° C and an epoxy equivalent weight of 475-575, dissolved in diethylene glycol ethyl ether (modifier) 75 65 four-functional bisphenol A epoxy resin with a softening point of 80 ° C 25 25% copper phthalocyanine pigment distributed in bisphenol A epoxy resin, epoxy equivalent weight

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from 180-190; Viscosity of 11-14 Pa.s. at 25 ° C for green coloring 2.5 "Modafiow" (superplasticizer) 4.5 end-carboxylated acrylonitrile rubber with average molecular weight of 3500, carboxyl content, of 5 2.3% by weight functionality of 1.85 and 18% by weight

bonded acrylonitrile (liquid rubber to increase toughness) 11.3

Butyl cellosolve acetate (solvent) 35.0

3- (Dimthylaminomethyl) phenol salt of diethyl sugar 10

acid (hardener) 26.3

Composition 4: permanent mask raw materials weight (g)

Bifunctional bisphenol A epoxy resin with a softening point of about 75 ° C and an epoxy equivalent weight of 475-575, dissolved in diethylene glycol ethyl ether (modifier) 48.9 70% epoxynovolac, functionality 5.4, melting point 99 ° C, dissolved in diethylene glycol ethyl ether 227, 2 25% copper phthalocyanine pigment in finely divided form in bisphenol A epoxy resin, epoxy equivalent weight 180-190, viscosity 11-14 Pa.s. at 25 ° C as a green color 34.1 "Modafiow" (flow agent) 13.1 diethylene glycol ethyl ether (solvent) 33.0 3- (dimethylaminomethyl) phenol salt of diethyl sugar acid (hardener) 26.4 methylene dianiline (hardener) 11.3

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Composition 5: Permanent mask for electroplating raw materials weight (g) 35

Bifunctional bisphenol A epoxy resin with a softening point of approx. 75 ° C and an epoxy equivalent weight of 475-575, dissolved in diethylene glycol ethyl ether (modifier) 50 70% epoxynovolac, functionality 5.4, melting point 99 ° C, dissolved in diethylene glycol ethyl ether 60

Epoxynovolac phenol formaldehyde resin, equivalent weight 172-179, viscosity 1.4-2 Pa.s. at 25 ° C (liquid screen printing aid) 10 25% copper phthalocyanine pigment in finely divided form in bisphenol A epoxy resin, epoxy equivalent weight 180-190 and viscosity of 11-14 Pa.s. at 25 ° C for green coloring 2 "Modafiow" (flow agent) 4 diethylene glycol ethyl ether (solvent) 20 3- (dimethylaminomethyl) phenol salt of diethyl sugar acid (hardener) 2 methylene dianiline (hardener) 1

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50

Composition 6: Permanent mask raw materials weight (g)

70% bi-functional bisphenol A epoxy resin with a Durran softening point of approximately 75 ° C and an epoxy equivalent weight of 475-575, dissolved in diethylene glycol ethyl ether (agent to increase toughness) 1692

70% four-functional epoxy resin with an epoxy equivalent weight of 200-240 and a Durran softening point of 70-80 ° C, dissolved in diethylene glycol ethyl ether (an epoxy base resin) 1427 "Modafiow" (flow agent) 96 25% copper phthalocyanine pigment in finely divided form in bisphenol A-epoxy resin, epoxy equivalent

55

60

65

important 180-190, viscosity 11-14 Pa.s. at 25 ° C for green coloring 83

Aerosil with an average particle size of 0.015 µm and a total surface area of 200 nr / g (thickening and solidifying agent) 159 benzitriazole (metal deactivator) dissolved in 140 g diethylene glycol ethyl ether 218 3- (dimethylaminomethyl) phenol salt of diethyl sugar ether (hardener) 143

Composition 7: permanent mask raw materials weight (g)

70 Epoxynovolac, functionality 5.4, melting point 99 ° C, dissolved in diethylene glycol ethyl ether 1427

70% bi-functional bisphenol A epoxy resin with a Durran softening point of approximately 75 ° C and an epoxy equivalent weight of 475-575, dissolved in diethylene glycol ethyl ether (agent to increase the toughness) 1692

"Modafiow" (superplasticizer) 96

25% copper phthalocyanine pigment in finely divided form in bisphenol A epoxy resin, epoxy equivalent weight 180-190, viscosity 11-14 Pa.s. at 25 ° C for green coloring 83

Diethylene glycol ethyl ether (solvent) 140

Trialkylarylammonium smectite (solidification and thickening agent) 150 high molecular weight phenol (antioxidant) 11 20% by weight dilaurylthiodipropionatin butyl cellosolve acetate (antioxidant) 54 tertiary amine (hardener) 133

In the above compositions, "Modafiow" is a high molecular weight polymer which is believed to consist of a mixture of isobutyl acrylate and ethyl acrylate polymers or other copolymers; it is commercially available from Monsanto Chemical Company, St. Louis, Missouri, USA. “Modafiow” improves the surface properties so that a uniform, smooth surface is created and ribs and blisters are avoided. The dry mask layer has an even, smooth and shiny surface.

The following examples show some of the most advantageous embodiments of the present masking compositions, namely in their use as solder masks.

Five typical examples follow:

Composition 8: Mixture for a solder mask A. Composition of starting materials Weight (g)

50% by weight of bisfunctional bisphenol A epoxy resin with a Durran softening point of about 75 ° C. and an epoxy equivalent weight of 475-575, dissolved in diethylene glycol ethyl ether (modifier) 537 70% by weight of epoxynovolac diglycidyl ether bisphenol A resin, dissolved in diethylene glycol ethyl ether, average epoxy functionality 4.4, melting point of 99 ° C 83.4 diethylene glycol ethyl ether (solvent) 29.1

25% by weight copper phthalocyanine pigment in finely divided form in bisphenol A epoxy resin, epoxy equivalent weight 180-190, viscosity 11-14 Pa.s. at 25 ° C for green coloring 18.3

Aerosil with an average particle size of 0.15 [i, m and a total surface area of 200 m2 / g (thickener) 33.3

Polyisobutyl acrylate (superplasticizer) 4.2

liquid epoxyphenol formaldehyde resin,

9

644882

Epoxy equivalent weight 172-179, viscosity 1.4-2 Pa.s.

at 25 ° C (screen printing aid) 18.2 synthetic silica, dry white powder with a surface area of 150 m2 / g and an average

Particle size of 0.021 [im (smoothing agent) 14.5

B. First hardener (mixture), mix with A starting materials weight (g)

Methanediamine 61.0

3- (Dimethylaminomethyl) phenol salt of diethyl sugar acid 7.9

end carboxylated acrylonitrile butadiene with carboxyl side groups with an average molecular weight of 3500, a carboxyl content of 2.37% by weight, a functionality of 1.85 and 18% by weight of bound acrylonitrile 16.5

C. Additional additives can be added to A and B to give the masking compound certain properties (here, for example, to inhibit oxidation and reduce flammability):

Starting materials weight (g)

Tetrabromobisphenol-A (brominated phenol) to reduce flammability) 181.0 non-volatile phenol (antioxidant) 2.2 20% by weight dilauryl thiodipropionate dissolved in ethylene glycol butyl ether acetate (antioxidant) 11.1

Composition 9: mixture for a solder mask

A. Composition according to composition 8.

B. Mix first hardener with composition A: starting materials weight (g)

50% by weight of triethylenediamine dissolved in methyl cellosolve 127.0

end carboxylated acrylonitrile butadiene with carboxyl side groups and an average molecular weight of 3500, a carboxyl content of 2.37%, a functionality of 1.85 and 18% bound acrylonitrile 16.5

3- (Dimethylaminomethyl) phenol salt of diethyl sugar ether (second hardener) 4.6

io Aerosil with an average particle size of 0.015 µm and a total surface area of 200 m2 / g (thickener) 10.0

15

25th

Composition 10: Mixture for a solder mask A and B correspond to composition 9 with the difference that instead of 127 g of 50% by weight ° C triethylenediamine in methyl cellosolve, 65 g of N- (2-aminoethyl) piperidine are used.

Composition 11: Mixture for a solder mask A and B correspond to composition 9 with the difference that 60 g of bis- (p-aminocyclohexyl) methane are used instead of 127 g of 50% by weight of triethylenediamine in methyl cellosolve.

Composition 12: mixture for a solder mask _

A. Composition corresponds to composition 8.

B. Mix first hardener with composition A:

30 raw materials weight (g)

Methane diamine 47

dimeric acid (consisting of C36 dibasic acid with a molecular weight of approx. 565) 13

3- (Dimethylaminomethyl) phenol salt of diethyl sugar 35-acid (second hardener) 6

M

Claims (10)

644882 2 PATENT CLAIMS Improving the screen printing ability of a liquid synthetic resin that reacts with the thermosetting synthetic resin 1. Resin-containing masking material for the production of capable to form a copolymer during curing, for. B. a permanent or removable, continuous or liquid at room temperature epoxy resin, the epoxy covering mask according to a predetermined pattern for 5 equivalent weight is 225 or less. the production of printed circuit boards, characterized in that 11 ■ covering compound according to one of the claims 7 to 10, the masking compound is characterized in that at least one thermosetting resin is used to improve the flow contains a silicone or an alkyl acrylate polymer that has properties at temperatures of 60 ° C or below. is in the solid state and holds at least three functional groups. contains; and that the covering compound in the initial state is a 10 12 covering compound according to one of claims 7 to 11, liquid with a viscosity of 10 to 200 Pa.s. is or is characterized in that it contains a modifying additive to a soft gel-like state and, during the hardening process, improves the mechanical strength of the hardened layer practically completely without liquefaction in the final state, which layer consists of a liquid acrylonitrile butadiene transforms. Copolymer or from an epoxy solid at room temperature 2. masking compound according to claim 1, characterized gekenn- 15 xydharz with an epoxy equivalent weight over 350, records that the thermosetting resin or resin mixture is at room temperature in a solid state and z. B. a melamine, urea, polyamideimide, polyimide, alkyd, Polyurethane or epoxy resin or a mixture of such synthetic resins. 20 The masking and soldering masks used so far had one 3. masking compound according to claim 2, characterized gekenn- series of disadvantages. For printed circuit boards with a high conductor path, the epoxy resin has a functionality of at most dense, so far photo-dry film masks have been used, 7 and have a melting point between 60 and 200 ° C. which are very expensive. With screen printing masks that are essential 4. masking compound according to one of claims 1 to 3, are cheaper, it was previously not possible, the large resolution-characterized in that they are capable of inhibiting oxidation, which is required for high conductor densities, to contain additive, e.g. a thioester, or a phosphite. a phenol or a mixture of these. Which occur when using the known solder masks- 5. masking compound according to one of claims 1 to 4, the problems are described below in more detail in that they describe a hardener additive in one; is also pointed to the difficulties in using such an amount that is sufficient either for complete or 30 of known, permanent and removable for partial hardening and z. B. consists of an amine mask materials in detail or contains one that will be on copper surfaces. has a corrosive effect. A problem with the use of the previously known and 6. Masking compound according to claim 5, characterized in that masking masks are introduced in that these resins are characterized in that, as a second hardener additive, an aromatic 35 contains very poor adhesive strength on metallic copper sub-amine in an amount sufficient to cover the masking layers exhibit. It is generally known that copper itself, after hardening, oxidizes against cleaning agents, for example after the application of a plastic layer, which has the consequence of having an undesirable adhesive strength, such as for removing solder residues, since the mask has to be made stable, e.g. B. an amine from the group of on the loosely bonded to the copper surface oxide diamine diphenyl sulfone, benzyldimethylamine, metaphenylene di- 40 adheres. After a while the mask, amine, methylene dianiline and the tri-2-hexoate salt of tri- completely detach from the copper surface because oxygen is caused by (dimethylaminomethyl) phenol. this penetrates and oxidizes the copper surface. To do that 7. masking composition according to one of claims 1 to 6, avoid, for example, before applying the characterized in that it further contains at least one plastic mask the surface with a firmly adhering copper modification additive, the z. B. serves to cover the liquid oxide layer, e.g. to improve it by treating it with properties or suitable for screen printing to a hot alkaline hypochlorite solution, or by priori, e.g. a thickener, in particular such a complete application of a zinc or brass coating. that gives the masking compound thixotropic properties, like a practically all printed circuits, even if they are only available in Silicon dioxide aerosil, in particular one that is manufactured in submicro-small production series, is soldered by scopic particles with a total surface area of 200 to 50 immersion or solder wave processes. For circuits with Contains 400 m2 / g. high conductor density occurred here difficulties because 8. masking compound according to claim 7, characterized-firstly, the holes in such plates are very small (the fact that they still have an organic acid in a knife between 0.35 and 1 mm), and secondly contains the amount that is sufficient , the basicity of an alicyclic distance between the individual holes, at least in some amine, which is additionally present as a hardener in the mass, can be very small to 55 districts. Reduce or compensate printed circuits to such an extent that the thixotropic through-plated holes are retained on one or more properties of the masking compound before curing, surfaces a circuit diagram. Before the soldering process, a z. B. applied an acid from the group of liquid, end carboxylated solder mask in registration. This solder mask leaves Acrylonitrile rubbers with or without carboxyl side groups, the holes and their borders and all others Fatty acids, e.g. B. linolenic or oleic acid, and dibasic acid- 60 connection contact points free. Then the components are ren, in particular one that fixes at least two carboxyls by immersing them in a solder bath; This includes both groups, such as adipic acid, glutaric acid, azelaic acid, the connection contacts of the components and the connection points Sebacic acid or suberic acid. on the circuit board coated with solder. The solder mask 9. masking compound according to claim 8, characterized thereby protects the other printed circuit board areas from the solder in order to draw that the reaction product of alicyclic amine 65 prevents the occurrence of short circuits. and contains organic acid as a salt. For boards with high conductor density, very thin 10. masking compound according to one of claims 7 to 9, printing materials used. As a result, even in the case of the fact that these are used as modifiers for the application of all precautionary measures, this is no small There is a likelihood that the mask will break in some places, causing the solder to penetrate the circuit board surface and cause short circuits between the conductor lines. If thicker masks of conventional type are now used, there is a risk that the holes will be filled with the mask substance and can no longer be properly soldered. As is known, thermosetting resins are used for masking and soldering masks, these resin mixtures having low melting points and being liquid at room temperature. Such resin mixtures are useless for printing on a mask with conductor spacing of less than 0.6 mm, since they run and also those areas cover that are to be metallized or run into the holes and thus prevent the metallization of the inner walls of the hole; they are liquid from room temperature up to 60 ° C. These temperatures are reached during curing to evaporate the solvents, which is why the contours run and make a sharp image with high resolution impossible. Resin mixtures of this kind are also unusable as soldering masks because they also run during the curing process and cover those parts which are intended for soldering. Since the resins only solidify after this "bleeding" of the printed mask, i. H. the polymerization occurs, the result is blurred prints and soldering imperfections. It goes without saying, however, that a sharp image with a high resolution is required if the conductor density is high. Another disadvantage of the known masking masks is that they are not resistant to chemicals such as, for example, chromosulfuric acid and highly alkaline copper baths, such as are used to pretreat the surfaces to achieve better adhesive strength. As a further disadvantage, masking masks that have been introduced in the prior art do not have smooth, but rather very rough surfaces. Such rough surfaces can easily lead to copper or metal separating from electroless baths in places that are not pretreated for electroless metallization, which also leads to defects. The application of metal layers from electroless metal deposition baths is also referred to as “additive” technology, which is to be understood in the present description to mean that the conductor tracks, at least in part, are produced by metal deposition from electroless baths. An example of such a method is given below: A suitable insulating base is provided with holes at a distance of 2.5 mm or less. The hole walls are sensitized according to known methods for the metal deposition from electroless baths, for which purpose a known sensitizing solution of tin (II) chloride and palladium (II) chloride is used. A mask is printed using the screen printing process, leaving the areas to be coppered free. The mask is hardened and electroless metal is deposited on the uncovered areas of the plate and on the perforated walls, thus producing the circuit diagram. Another problem in the manufacture of printed circuits is the discoloration of gold plating, such as those used for connection contacts, caused by the hardener in the mask material.