Adhesive metallization of polyimide

A process for the adhesive metallization of polyimide through pretreating of the polyimide and subsequent activation, as well as chemical metallization, if necessary, followed by galvanic metal deposition, characterized in that the polyimide is pretreated with an aqueous solution of alkali hydroxide and an organic nitrogen compound such as one selected from the group consisting of N,N,N', N'-tetra-(2-hydroxypropyl)-ethylenediamine, ethylenediaminetetraacetic acid and nitrilotriacetic acid. The plastics metallized according to the present invention find use as shaped parts, preferably in the fields of electrical engineering and electronics.

BACKGROUND OF THE INVENTION 
The invention concerns a process, and an article made by the process, for 
the adhesive metallization of polyimide by pretreatment of the polyimide 
and subsequent activation as well as chemical and, if necessary, galvanic 
metal deposition. 
It is known that for the purpose of metallization of non-conducting 
articles, processes for chemical metallization should be used. 
In order to obtain sufficiently greater adhesive strength, it is necessary 
to roughen the surface of these articles mechanically or chemically. This 
occurs with many plastics, mainly by acid oxidative digestion of the 
surface, which is not, however, usable with plastics based upon polyimide. 
This is a great disadvantage since polyimide foils advantageously find use 
in the electronics field in increasing measure, instead of glass fiber 
mats impregnated with epoxide resin. Polyimide foils are given 
consideration, namely, copper coated on both sides, for multi-level 
circuits, for example so-called multilayers, since they provide 
considerably better insulation values. 
The application of the copper must generally be done by means of a suitable 
adhesive, since polyimide, in contrast to the plastics based upon epoxide 
resin, is not able to adhesively connect rolled on copper, which results 
in unfavorable working characteristics. Thus, upon boring of such 
multilayers, cavities form, which after the following metallization at the 
temperature of the adhesion process (about 250.degree. C.) can destroy the 
throughcontacting, or else adhesive residue must be removed, which of 
necessity is done by means of highly concentrated chromic acid. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to develop a process 
which makes possible an adhesive metallization of polyimide without use of 
an adhesive. 
This object is attained according to the present invention by means of a 
process which is thereby characterized in that the polyimide is pretreated 
with an aqueous solution of alkali hydroxide and an organic nitrogen 
compound. The invention also concerns the article made by the above 
process. 
Particular embodiments of the process according to the present invention 
include 
that the solution contains as alkali hydroxide, lithium hydroxide, sodium 
hydroxide and/or potassium hydroxide; 
that the solution contains 5 to 600 g/liter alkali hydroxide, preferably 50 
g/liter alkali hydroxide; 
that the solution contains as organic nitrogen compound a primary, 
secondary or tertiary amine; 
that the solution contains as the organic nitrogen compound an aliphatic or 
cycloaliphatic mono-, di- or polyamine or their hydroxy-, carboxy-, sulfo- 
and/or phosphoryl-derivatives, an aromatic mono-, di- or polyamine or 
their hydroxy-, carboxy-, sulfo- and/or phosphoryl-derivatives, a 
heterocyclic mono-, di- or polyamine or their hydroxy-, carboxy- and/or 
sulfo-derivatives, an N-containing uni- or multi-valent heterocyclic 
compound or its hydroxy-, carboxy- and/or sulfo-derivatives, which if 
necessary can be substituted preferably by the alkyl, or nitrilo group; 
that the solution contain as the organic nitrogen compound, 
N,N,N',N'-tetra-(2-hydroxypropyl)-ethylenediamine, 
ethylenediaminetetraacetic acid or nitrilotriacetic acid; 
that the solution contains 5 to 30 g/liter, preferably 20 g/liter, of an 
organic nitrogen compound; 
that the treatment be performed at temperatures from 15.degree. to 
30.degree. C., preferably 20.degree. C.; 
that the polyimide after the pretreatment is activated in customary manner, 
expediently by means of a palladium-containing activator; 
that the polyimide after the pretreatment and activation is chemically 
metallized in customary manner, preferably coppered or nickeled; and 
that the polyimide after the pretreatment and metallization is heated to 
70.degree. to 140.degree. C., preferably 130.degree. C. 
The process according to the present invention allows, in surprisingly 
advantageous manner, the production of a polyimide-metal-composite 
material, preferably a polyimide-copper-composite material, which can be 
used for shaped parts, preferably in the fields of electrical engineering 
and electronics. 
The further advantages, which are connected with the possibility of 
producing such a composite material, lie in the avoidance of all of the 
sources of error, which are present upon use of an adhesive. Moreover, the 
possibility is opened of utilizing polyimide as the last layer for the 
production of base material for the semiadditive technique, in order also 
here to be able to waive the chromic acid as treatment material. Add to 
this the substantially better electrical characteristic data which the 
construction of very more dense circuit diagrams allows, than is possible 
with the conventional adhesive mediators. 
As polyimide should be understood all plastics as are described for example 
in Ullmanns' Encyclopedia of Technical Chemistry, 1970, Supplementary 
Volume, pp. 266-268 and pp. 318-319, Urban & Schwarzenberg, Publishers, 
Munich, Berlin, Vienna. Their production can follow in known manner, for 
example, through reaction of carboxylic acid anhydrides with aromatic 
diamines. 
They involve extensively linear, highly heat-stable plastics of the general 
Formula 
##STR1## 
The polyimide is advantageously used in the form of foils for the process 
according to the present invention. 
It should be understood that not only plastics of pure polyimide can be 
treated according to the present invention, but also such which for 
example are coated on one side with other plastics. 
As organic nitrogen compounds which can be used according to the present 
invention, the following may be mentioned by way of example: 
methylamine, ethylamine, propylamine, butylamine, ethylenediamine, 
propylenediamine, isopropylenediamine, tetramethylenediamine, 
octamethylenediamine, piperidine, piperazine, pyrrolidine, benzylamine, 
diethylenediamine, ethylenediaminetetraacetic acid, 
butylenediaminetetraacetic acid, hexamethylenediaminetetraacetic acid, 
octamethylenediaminetetraacetic acid, nitrilotriacetic acid, iminodiacetic 
acid, ethylenediamine-N,N'-dipropionic acid, 
hexamethylenediamine-N,N'-dipropionic acid, 
ethylenediamine-tetra-isopropanol, ethylenediamine-tetraethanol, 
N,N,N',N'-tetra-(2-hydroxypropyl)-ethylenediamine, triethanolamine, 
ethanolamine, O-phenyldiamine, aniline, toluidine, triethylamine, 
tributylamine, N,N,N',N'-tetramethylethylenediamine, 
N,N'-dimethyl-ethylenediamine, N,N-dimethylethylenediamine, 
N-methyl-ethylenediamine, diethylamine, dibutylamine. 
imidazol, 1-methyl-imidazol, 1-propyl-imidazol, 2,4-dimethyl-imidazol, 
4-methyl-imidazol, 2-isopropyl-imidazol, 2-phenyl-imidazol, 
1-benzyl-imidazol, .beta.-imidazolopropionic acid, 1,2-dimethyl-imidazol, 
1-methyl-2-hydroxymethylimidazol, 4-sulfoimidazol, 
2-methyl-4-sulfo-imidazol, 2-(sulfophenyl)-imidazol, 
2-isopropyl-4-sulfo-imidazol, 1-n-propyl-5-sulfo-imidazol, 
1-n-propyl-4-sulfo-imidazol, 1,2-bis-(1'-imidazolyl)-ethane, 
1-(p-sulfophenyl)-imidazol, histidine, 2-(imidazolo-ethyl)-pyrridine, 
1-(2'-aminoethyl)-imidazol-hydrochloride, 
1-(3'-aminopropyl)imidazol-hydrochloride, 
1-methyl-2-carboxymethyl-imidazol, 2-(p-sulfophenyl)-4-sulfo-imidazol, 
1-methyl-2-sulfo-imidazol, 2-sulfoimidazol, 
1,2-bis-(1'-methyl-5'-imidazolyl)-ethane, 5-sulfo-benzimidazol, 
5,7-disulfobenzimidazol, 1,2-bis-(5'-sulfobenzimidazolyl-(2'))-ethane, 
1,4-bis-(5'-sulfo-benzimidazolyl-(2'))-butane, polyvinylimidazol (degree 
of polymerization=2 to 500), polyallylimidazol (degree of polymerization=2 
to 500), 3,5-dimethylpyrazole, 4-sulfopyrazole, 1-methylpyrazole, 
3-methylpyrazole, 1,3-dimethylpyrazole, 1-phenylpyrazole, 
1-carboxymethyl-pyrazole, 1-carboxyethylpyrazole, 
1-aminoethylpyrazole-hydrochloride, 1-aminopropyl-pyrazole-hydrochloride, 
3,3-dipyrazolyl, 1,3-dimethyl-5-hydroxy-pyrazole, 1-phenyl- 
3-methyl-5-hydroxy-pyrazole, 1-(p-sulfophenyl)-3-methyl-5-hydroxypyrazole, 
1-(m-sulfophenyl)-3-methyl-5-hydroxy-pyrazole, 
1-(p-aminophenyl)-3-methyl-5-hydroxy-pyrazole, 1-(p-chlorophenyl)-3 
-methyl-5-hydroxy-pyrazole, 
1-(p-sulfophenyl)-3-carboxy-5-hydroxy-pyrazole, 1,2-bis-(1'-pyrazolyl)-eth 
ane, 7-sulfo-benzpyrazole, 1-carboxyethyl-benzpyrazole, 
1,2-bis-(3'-pyrazolyl)-ethane, di-(3-pyrazolyl)-methane. 
pyridine, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 
2-hydroxypyridine, 3-hydroxypyridine, 4-hydroxypyridine, 
2,6-diaminopyridine, 2,3-diaminopyridine, 3,4-diaminopyridine, 
2-amino-methyl-pyridine, 3-aminomethyl-pyridine, 4-amino-methylpyridine, 
4-picoline, 3-picoline, 2-picoline, 2,6-lutidine, 2,4-lutidine, 
3-pyridinesulfonic acid, 2,2'-dipyridyl, 1,2-di-(2'-pyridyl), 
2,2'-dipyridylmethane, 2,2'-dipyridylamine, 
1,2-dihydroxy-1,2-di-(2'-pyridyl)-ethane, 2,2'-dipyridyl-ethylene, 
4,4'-dipyridyl-ethylene, 3-sulfo-3,3'-dipyridyl, 
1,2,-di-(4'-pyridyl)-ethane. 
2-amino-pyrimidine, 2,4,6-triamino-pyrimidine, 1,4-dimethyl-pyrimidine, 
1,5-dimethyl-pyrimidine, 4,5-dimethylpyrimidine, 4,6-dimethylpyrimidine, 
2,4-bis-(diethylamino)-pyrimidine, 3,6-bis-(dimethylamino)-pyrimidine, 
3,6-bis-(ethylamino)-pyrimidine, 2-hydroxypyrimidine, 4-hydroxypyrimidine, 
4,6-dihydroxy-pyrimidine, barbituric acid, cytosine, pyrimidine, 
bis-(2-methyl-4-pyrimidyl), 2,2'-dipyrimidyl, 4,4'-dipyrimidyl, uracil, 
5-methyl-cytosine, 2-methyl-pyrimidine, 2-ethylpyrimidine, 
2-phenyl-pyrimidine, 2-amino-6-ethyl-pyrimidine, 
2-amino-6-methyl-pyrimidine, 2-amino-5-methoxy-pyrimidine, 
2-amino-4-hydroxy-pyrimidine, 2-carboxy-pyrimidine, 
5-carboxymethyl-pyrimidine, 2-carboxymethyl-5,6-dimethyl-pyrimidine, 
2-methyl-5-carboxymethyl-pyrimidine, pyridazine, 3-methylpyridazine, 
pyrazine, 2,3,5,6-tetramethyl-pyrazine, 2,5-dimethyl-6-hydroxy-pyrazine, 
2-hydroxy-pyrazine, 2-amino-pyrazine. 
urotropine, 2,6-diamino-4-methyl-triazine-(1,3,5), 
2,6-diamino-4-ethyl-triazine-(1,3,5), 
2,6-diamino-4-propyl-triazine-(1,3,5), 
2,6-diamino-4-carboxymethyl-triazine-(1,3,5), 
2,6-diamino-4-carboxyethyl-triazine-(1,3,5), 
2,6-diamino-4-sulfopropyl-triazine-(1,3,5), melamine, cyanuric acid, 
2,4,6-tris-methylamino-triazine-(1,3,5), 
2,4,6-tris-ethylamino-triazine-(1,3,5), 
2,4,6-tris-diethylamino-triazine-(1,3,5), 
bis(4,6-diamino-2-triazinyl-(1,3,5))-methane, 
1,2-bis-(4',6'-diaminotriazinyl-(1',3',5'))-ethane, 
1,3-bis-(4',6'-diamino-2'-triazinyl-(1',3',5'))-propane, 1,2-bis-(4', 
6'-diaminotriazinyl-2'-amino)-ethane, 2,4-diamino-triazine-(1,3,5), 
2,4-diamino-6-(p-sulfophenyl)-triazine-(1,3,5), 
2,4-diamino-6-ethyl-triazine-(1,3,5), 
2,4-dihydroxy-6-methyl-triazine-(1,3,5), cyanuric acid-hydroxyethylester, 
2,4-dihydroxy-6-carboxymethyltriazine-(1,3,5), 
2-amino-4-carboxymethyl-6-n-butylaminotriazine (1,3,5), 
2-amino-4-carboxy-6-n-butylamino-triazine-(1,3,5), 
2-amino-4-carboxyethyl-6-n-butylamino-triazine-(1,3,5), 
2-amino-4-hydroxy-triazine-(1,3,5), 3-amino-triazine-(1,2,4), 3-amino-5,6 
-dimethyl-triazine-(1,2,4), 4-hydroxy-5,6-dimethyltriazine-(1,2,4), 
4-hydroxy-5-phenyl-triazine-(1,2,4), triazine-(1,2,4), 
3,3'-bis-(5,6-dimethyl-triazine)-(1,2,4), 3,5-dihydroxy-triazine-(1,2,4), 
3,5-dihydroxy-6-methyl-triazine-( 1,2,4), 
3,5-dihydroxy-6-butyl-triazine-(1,2,4), 
3,5-dihydroxy-6-phenyl-triazine-(1,2,4), 
3,5-dihydroxy-6-carboxypropyltriazine-(1,2,4). 
triazole-(1,2,4), 4-ethyl-triazole-(1,2,4), 4-methyl-triazole-(1,2,4), 
4-phenyl-triazole-(1,2,4), 3,4,5-trimethyl-triazole-(1,2,4), 
4-(p-sulfophenyl)-triazole-(1,2,4), 3-methyl-triazole-(1,2,4), 
3-ethyl-triazole-(1,2,4), 3,5-dimethyl-triazole-(1,2,4), 
3-phenyl-triazole-(1,2,4), 1-methyl-triazole-(1,2,4), 
1-ethyl-triazole-(1,2,4), 1-phenyl-triazole-(1,2,4), 
3-sulfo-triazole-(1,2,4), 3-amino-triazole-(1,2,4), 
3,5-diaminotriazole-(1,2,4), 1,2-bis-(5'-sulfo-3'-triazolyl)-ethane, 
1,2-bis-(5'-amino-3'-triazolyl)-ethane, 1,2-bis-(3'-triazolyl)ethane, 
1,2-bis-(4'-methyl-3'-triazolyl)-ethane, bis-(3-triazolyl)-methane, 
bis-(5-sulfo-3-triazolyl)-methane, bis-(5-amino-3-triazolyl)-methane, 
bis-(3-triazolyl)-methane, bis-(5-sulfo-3-triazolyl), 
bis-(5-amino-3-triazolyl), 3,3'-bis-triazolyl, 1,2-(1'-triazolyl)-ethane, 
3-(2'-aminoethyl)-triazole-(1,2,4), .beta.-(1-triazolyl)-propionic acid, 
1,4-bis-(5'-sulfo-3'-triazolyl)-butane, 
1,4-bis-(5'-amino-3'-triazolyl)-butane, 
1-(3-sulfopropyl)-triazole-(1,2,4), 1,2-bis-(4'-triazolyl)-ethane, 
1-methyl-triazole-(1,2,3), 1-ethyl-triazole-( 1,2,3), 
2-ethyl-triazole-(1,2,3), 2-propyltriazole-(1,2,3), 
1-(2'-carboxyethyl)-triazole-(1,2,3), 5-sulfobenzotriazole, 
5,7-disulfo-benzotriazole, benzotriazole, 4-methyltriazole-(1,2,3), 
4,5-dimethyltriazole-(1,2,3), 4-butyltriazole-(1,2,3), 4-phenyl-triazole( 
1,2,3), 1-(3'-amino-propyl)-triazole-(1,2,3), 
1-(2'-aminoethyl)-triazole-(1,2,3), 1,2-bis-(1'-triazolyl)-ethane. 
pyrrole, 1-methyl-pyrrole, 1-ethyl-pyrrole, 1-(2'-carboxyethyl)-pyrrole, 
2-methyl-pyrrole, 2,5-dimethyl-pyrrole, di(2-pyrrolyl)-methane, 
di(1-methyl-2-pyrrolyl)-methane, 2-ethyl-pyrrole, tryptophan. 
Polyethyleneimine, N,N-dimethyl-polyvinylamine, polyvinylimidazole, 
polyallylimidazole, polyvinylpyridine, polyvinylpyrrolidone, 
polyvinylmorpholine, polyvinylmorpholinone, polyvinyl-5-alkyl-oxazolidone, 
N-polyvinyl-N,N'-ethylene urea, soy protein albumin, 
ethylenediaminetetra-(methylphosphonic acid), hexamethylphosphontriamide. 
It should be understood that the compounds can be employed alone or also in 
mixture with one another. 
As alkali hydroxide, all customary sources find use. 
The performance of the process according to the present invention follows 
by immersing, rinsing or wetting of the polyimide articles to be 
metallized, with the solution employed according to the present invention. 
The treatment temperature and duration depend upon the quality of the 
polyimide, and amount to about 15.degree. to 30.degree. C., preferably 
20.degree. C., and about 5 to 10 minutes. 
The solution to be used according to the present invention can be prepared 
briefly before the treatment in the desired composition and concentration. 
However, also stored solutions can be used with the same results. If 
desired, water-miscible, organic solvent can be additionally added to the 
solution, such as for example alcohols or esters, which likewise belong to 
the subject of the present invention. 
The parts pretreated according to the present invention are, after the 
treatment, rinsed, expediently with water, and are then ready for the 
activation as well as chemical metallization and, if necessary, galvanic 
reinforcement. 
For this purpose the customary activators, expediently on the basis of 
palladium-containing activators, and baths, preferably chemical copper or 
nickel baths, can be used. For the galvanic reinforcement there serve 
likewise the customary baths, for example a copper bath. 
It has proven to be particularly favorable for the adhesive strength of the 
deposited metal, when the materials, after the metallization, are heated 
to 70.degree. to 140.degree. C., preferably 130.degree. C. for which about 
0.2 up to 2 hours are sufficient. 
The composite material produced according to the present invention is in 
surprising manner of previously unobtainable stability, and allows only 
upon destruction of the entire composite, rupturing, but not separating, 
which is of extraordinary technical significance. 
The novel features which are considered characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXAMPLE 1 
A polyimide foil customary in the electrical industry is treated in a 
solution of 100 g potassium hydroxide in 1 liter water for 30 minutes, and 
then rinsed. In the next step the foil is in known manner activated with 
palladium ions. After rinsing in water, reduction of the still remaining 
adsorbed palladium ions into palladium metal follows with an aqueous 1% 
dimethylaminoborane solution. Pretreated in such manner, the foil arrives 
for an objection-free metallization in a known chemical copper bath with 
formaldehyde as reducing agent. For fixing of the applied chemical copper, 
the foil is then provided with a tempering process at 100.degree. C. After 
the tempering, the extremely thin (0.5 .mu.m) copper coating is briefly 
deoxidized with 10% (volume) sulfuric acid, and then in customary manner 
reinforced in a sulfuric acid galvanic copper bath to 40 .mu.m. A testing 
of the adhesive strength reveals surprisingly good values. 
EXAMPLE 2 
A polyimide foil is treated in an aqueous solution of 100 g/liter sodium 
hydroxide and 20 g/liter 
N,N,N',N'-tetra-(2-hydroxypropyl)-ethylenediamine, whereby the treatment 
period, in comparison to Example 1, is reduced to 5 minutes. Polyimide 
foils treated in this solution are rinsed after 5 minutes exposure period, 
conventionally activated with palladium, reduced in known manner after a 
further rinsing operation with water, and the surface is chemically 
coppered. After the subsequent tempering process of 30 minutes duration at 
a temperature of 80.degree. C., in known manner the thin chemical copper 
coating is reinforced with galvanically with copper in a sulfuric acid 
electrolyte. The polyimide foil displays an outstanding stability and is 
inseparably connected with the copper. 
EXAMPLE 3 
A polyimide foil is pretreated for 5 minutes in an aqueous solution of 20 
g/liter ethylenediaminetetramethylphosphonic acid and 50 g/liter lithium 
hydroxide. Subsequently, the foil is treated in known manner with an 
alkaline, palladium-containing activator, rinsed in water, and then the 
palladium is reduced to metal in a 1% aqueous solution of 
dimethylaminoborane. After another rinsing in water, the activated foil is 
in known manner nickeled with a chemical nickel bath to about 0.2 .mu.m 
thickness, and subsequently it is tempered at 110.degree. C. for 30 
minutes. For deoxidation of the surface, the foil is then treated for 
several minutes in 10% (volume) hydrochloric acid, rinsed, and then in 
known manner reinforced in a sulfuric acid copper electrolyte with 40 
.mu.m copper. The adhesion of the nickel to the polyimide is 
extraordinary. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
metallizations differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
process for the adhesive metallization of polyimide, it is not intended to 
be limited to the details shown, since various modifications and 
structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.