Adhesive bonding and miscellaneous chemical manufacture – Surface bonding means and/or assembly means therefor – With coating means for work
Patent
1997-08-28
2000-12-12
Dixon, Merrick
Adhesive bonding and miscellaneous chemical manufacture
Surface bonding means and/or assembly means therefor
With coating means for work
156345, 428209, 427305, 4274431, 427444, B32B 3100
Patent
active
061584916
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the corrosion protection of copper or copper alloys and, in particular, to a process for the corrosion protection of copper or copper alloys to provide thermal and humidity protection.
Preflux coatings are used to protect both rigid and flexible printed circuit boards (PCBs). Various preflux coatings have been described in the prior art. Initially, benzotriazoles were used as preflux coating but at the present time the commercial preflux treatments are based upon imidazoles or benzimidazoles.
EP-A-0364132 disclosed a process for the preflux treatment of copper using an aqueous solution comprising a compound capable of generating copper or zinc ions and an imidazole having a C.sub.5-21 alkyl group at the 2-position thereof.
EP-A-0428383 discloses the use as a preflux coating of a benzimidazole compound having an alkyl group of at least 3 carbon atoms at the 2-position thereof and an organic acid.
JP-A-06002158 discloses the use as a preflux treatment agent of various 2-(phenylalkyl)-benzimidazoles, such as 2-(p-chlorobenzyl)-benzimidazole.
None of the prior art preflux coatings can be considered to be entirely satisfactory because limited thermal and/or humidity protection are given by these systems.
We have now developed a process for the preflux treatment of copper or copper alloys, in particular to protect rigid and flexible copper or copper alloy printed circuit boards, which provides improved protection and overcomes the disadvantage of the prior art processes.
Accordingly, the present invention provides a process for the corrosion protection of copper or a copper alloy which process comprises contacting the surface with an aqueous solution of at least one compound of the general formula: ##STR2## wherein X is N, Y is CR and Z is N, or X is N, Y is N and Z is N or CR, or X is CR, Y is N and Z is N, where R is a hydrogen atom or R.sup.14, and R.sup.1 is an alkyl aryl, aralkyl, halogen, trihalomethyl, amino, heterocyclic, NHR.sup.2, NR.sup.3 R.sup.4, CN, CO.sub.2 H, CO.sub.1 R.sup.5, OH or OR.sup.6 group, where each of R.sup.2 to R.sup.6 independently represents an alkyl, aryl or aralkyl group.
In the definitions of the substituent groups given above, alkyl groups preferably have from 1 to 20 carbon atoms, more preferably 1 to 6 carbon atoms; aryl groups are preferably phenyl or naphthyl groups; aralkyl groups are preferably phenyl or naphthyl groups substituted with one or more alkyl groups containing 1 to 20 carbon atoms; and heterocyclic groups are preferably furfuryl, benzotriazolyl, imidazolyl and benzimidazolyl.
The aqueous solution treatment of the present invention forms a ligand coating on the surface of the copper or copper alloy which protects the copper or copper alloy surface during storage. The ligand coating is particularly suited to the surface mounting of components thereon since it is solderable, i.e. can be removed by a suitable flux and wetted by solder, and has excellent heat resistance and long term storage stability.
Particularly preferred compounds of Formula I for use in the present invention are the triazole pyridines of the formulae: ##STR3## and purine, 6-aminopurine, 6-chloropurine, 2, 6-dichloropurine, 6-methoxypurine, 6-histaminopurine and 6-furfurylaminopurine.
The compounds of Formula I for use in the present invention are compounds which all contain four or five heterocyclic nitrogen atoms. Thus, the triazole-pyridines have one more nitrogen atom then the benzo-triazoles and the purines have two more nitrogen atoms then the corresponding benzimidazoles. The triazole pyridines and the purines generally have higher melting points than the corresponding benzotriazoles and benzimidazoles, and it is believed that this is related to the thermal stability of the complex formed at the copper or copper alloy surface. It is also believe that the extra nitrogen atoms in the compounds as compared to the prior art compounds gives rise to a greater number of sites for bonding to metal surfaces and metal ions.
The compounds of Formula (I)
Reynolds John
Soutar Andrew McIntosh
White Keith William Peter
Williams Anthony
Cookson Group PLC
Dixon Merrick
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