Process for the preliminary treatment of copper surfaces

Details Process for the preliminary treatment of copper surfaces Process for the preliminary treatment of copper surfaces

2000-09-05

2004-04-20

Talbot, Brian K. (Department: 1762)

Coating processes

With pretreatment of the base

Etching, swelling, or dissolving out part of the base

C427S327000, C148S240000, C148S270000, C134S003000

Reexamination Certificate

active

06723385

ABSTRACT:

The invention concerns a process to pretreat copper surfaces so that a tight bond can be subsequently formed between the pretreated copper surfaces and plastic substrates. The solution preferably serves to pretreat the inner layers of printed circuit boards with copper coatings to subsequently allow a tight bond between the inner layers of the printed circuit board and inner layers of the board made of resin, and to pretreat printed circuit boards with copper layers to create a tight bond between the copper layers and plastic resists.
In manufacturing printed circuit boards, various steps are carried out in which copper surfaces must be tightly bonded to an organic substrate. In some cases, the required adhesion of the formed bonds must be ensured over a long period. In other cases, a tight bond only has to exist for a short period, e.g. when the organic substrate only remains on the copper surfaces during manufacture of the printed circuit board . For example, the tight bond of dry film resists (for structuring conductor lines on printed circuit boards) to the copper surfaces only has to exist while manufacturing the printed circuit board. After the conductor line structures are formed, the resists can be removed.
The easiest way to increase the adhesion is to etch and hence roughen the copper surfaces before forming the bond. Microetching solutions are used such as sulfuric acid solutions of hydrogen peroxide or sodium peroxodisulfate.
Another procedure is described in U.S. Pat. No. 3,645,772. A pretreatment solution is used for the copper surfaces that e.g. contains 5-aminotetrazole.
Long-term stability is necessary especially when laminating multilayer printed circuit boards. Other treatments for the copper surfaces are required in this case.
When manufacturing multilayer boards, several inner layers are laminated with insulating resin layers (so-called prepregs: epoxide resin films reinforced with fiberglass nets). The inner bonds of the laminate must be retained throughout the entire life of the printed circuit board. The copper layers (preferably the conductor line structures) on the inner layers must be surface-treated. Various procedures have been developed to solve this problem.
The procedure normally used to pretreat the materials before lamination is to form an oxide layer on the copper surfaces. In this process known as the brown or black oxide process, very aggressive reaction conditions are used to form the oxide. A disadvantage of this procedure is that the oxide layer used for enhancing adhesion to the resin layer is not very resistant to acid and especially to hydrochloric treatment solutions. They are hence attacked in subsequent processes to plate the through holes in the boards, and the adhesive bond is eliminated with delamination at the attacked sites (pink ring: An externally-visible attack on the black oxide layer directly next to a hole in printed circuit boards with the discoloration of the originally black oxide layer. The pink copper coating of the inner layer is recognizable as an annular defect; wedge void: A defect (recognizable in a micrograph of a treated hole) in a printed circuit board in the form of a crack between a copper inner layer and the neighboring printed circuit board resin from the attack of acid treatment solutions on the black oxide layer).
The above-cited problem is solved by reducing the oxide layer surface before lamination. The reduced black oxide is more stable than normal black oxide against chemicals used in plating the through-holes. The additional reduction step costs a great deal, however. In addition, the chemicals used for reduction are not very resistant to oxidation from air, so that the life time of the baths and storage life of the supplementary chemicals are limited. An attempt to eliminate this problem is made in JP A 08097559 by providing the reduced copper oxide layers with a protective layer by treating them with an aqueous solution containing an aminothiazole and/or aminobenzothiazole compound. However, the problems of expensive reduction chemicals, low resistance to oxidation and the layer's sensitivity to acid are not completely eliminated.
Another option for promoting adhesion is to treat the copper surfaces with an aqueous or alcoholic solution of an azole compound. Such a procedure is e.g. presented in WO 96/19097 A1. The copper surfaces are treated with a solution that contains 0.1-20 weight percent hydrogen peroxide, an inorganic acid (e.g. sulfuric acid), an organic corrosion inhibitor (e.g. benzotrizole), and a wetting agent. The hydrogen peroxide etches the copper surface to produce microrough surfaces.
U.S. Pat. No. 4,917,758 discloses etching solutions that serve to etch copper cladding on the materials of the printed circuit board. Hydrogen peroxide, sulfuric acid and a nitrogen-containing compound (preferably amino benzoic acid, amino tetrazole or phenyl urea) are also in these solutions.
The present invention is therefore based on the problem of avoiding the disadvantages of the state of the art and finding a pretreatment process that can create a bond between the copper surfaces and plastic surfaces with excellent adhesion. The process shall be simple, easy to use, and inexpensive. In addition, the treatment solutions shall not precipitate. It is also important that treatment with the solutions produces a material bond that is not problematic (no pink ring and wedge voids) in the subsequent processes for manufacturing printed circuit boards, e.g. plating through holes in board materials. The used pretreatment solutions shall therefore be suitable for manufacturing printed circuit boards.
This problem is solved by the process found in claim 1.
The process according to the invention is for pretreating copper surfaces to allow a tight bond to be formed with plastic substrates. The substrates with the copper surfaces, e.g. copper films or resin laminates coated with copper films, are brought into contact with a first solution that contains the following components:
a. Hydrogen peroxide,
b. At least one acid, and
c. At least one nitrogen-containing, five-member heterocyclic compound that does not contain sulfur, selenium or tellurium atoms in the heterocycle.
Then the substrates with the copper surfaces are brought into contact with a second solution that has at least one adhesion-promoting compound from the group consisting of sulfinic acid, selenic acid, telluric acid, heterocyclic compounds that contain at least one sulfur, selenium and/or tellurium atom in the heterocycle, as well as sulfonium, selenonium and telluronium salts. The sulfonium, selenonium and telluronium salts are compounds of general formula
where A=S, Se or Te,
R
1
, R
2
and R
3
=alkyl, substituted alkyl, alkenyl, phenyl, substituted phenyl, benzyl, cycloalkyl, substituted cycloalkyl, where R
1
, R
2
and R
3
are the same or different, and
X−=Anion of an inorganic or organic acid or hydroxide.
Adhesion-promoting compounds are to be selected that are sufficiently soluble in the acidic, preferably sulfuric acid solution.
The problem on which the invention is based is solved by the optional uses in claims 18 and 19. The process according to the invention is useful preferably in pretreating copper-layer-coated inner layers of printed circuit boards to allow a tight bond to be formed between the inner layers of the printed circuit boards and plastic resin layers, and to pretreat printed circuit boards with copper layers so that a tight bond can be formed between the copper layers and plastics resists.
Preferred embodiments of the invention are found in the subclaims.
Preferred sulfinic acids in the second solution are adhesion-promoting compounds with chemical formula B:
with R
4
, R
5
and R
6
=hydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl or R
7
—(CO)— with R
7
=hydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl, where R
4
, R
5
and R
6
are the same or different,
and aromatic sulfinic acids.
It is preferable for the second solution to contain forma

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