JPS587077B2 - Copper foil for printed circuits and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing copper foil for printed circuits, and in particular to a method for producing copper foil for printed circuits, which has excellent anti-rust properties and also has various properties required for steel foils for printed circuits. The present invention relates to a method of manufacturing copper foil for circuits.

Steel foil for printed circuits is generally laminated and bonded to a resin base material under high temperature and pressure.

After that, an etching process is performed to form a circuit suitable for the purpose, and finally the necessary electrical elements are soldered to form circuit boards for general home appliances such as televisions and radios, or for various electronic devices including computers. A precision control circuit board is formed.

The surface of the copper foil to be bonded to the resin substrate is roughened for bonding purposes, and the other surface exposed on the laminated circuit board is smooth.

Therefore, steel foil for printed circuits is required to have various properties as described below.

First, the characteristics required for the smooth glossy side are (
1) It has a beautiful appearance, (2) It has adequate rust prevention ability and does not impair its appearance, (3) It does not discolor due to heat during lamination bonding, and (4) It wets well with solder. ,
On the other hand, it is particularly important that the rough surface side has a high peel strength before and after soldering and a suitable rust prevention ability.

Furthermore, the characteristics required for the copper foil as a whole are (1) appropriate etching treatment to avoid the etching rate being too slow, etching residue, or over-etching; (2) relative low The main reasons include that the resistance is small.

As described above, copper foil for printed circuits is required to have various and different characteristics, and the quality required for printed circuit boards is becoming increasingly strict as the field of electronic equipment advances.

Conventionally, methods for treating copper foil for printed circuits include chromate treatment using hexavalent chromium ions, organic agent treatment using a chelation reaction with copper, and coating treatment with metals less base than copper or their alloys. It's getting worse.

While these methods attempt to optimize some of the above-mentioned properties, other properties are not improved or are on the contrary worsened, and none of them are satisfactory from a comprehensive standpoint.

Specifically, chromate-treated copper foil has a beautiful appearance, but has weak rust prevention ability under high temperature and high humidity conditions, and has drawbacks in terms of solder wettability and thermal discoloration.

Although treatment with a chelating organic agent gives a beautiful appearance and good solder wettability, there are problems in terms of rust prevention and thermal discoloration, and there is also the problem of reduced peel strength when bonded to a phenolic resin substrate.

Coating treatment with a metal less base than copper is carried out in two ways: thin coating and thick coating, but in the case of thin coating, the rust prevention ability deteriorates in high temperature and humidity, and the peel strength decreases when bonded to a phenolic resin substrate. On the other hand, in the case of thick coating, the appearance of a smooth glossy surface does not have the luster of copper and takes on the color of a coated metal, and over-etching is likely to occur during etching on a rough surface.

Furthermore, thick metal-plated copper foil is sometimes subjected to heat treatment in order to improve its quality characteristics, but in this case additional equipment and labor are required, resulting in high costs.

As explained above, copper foils for printed circuits processed by conventional methods have their own drawbacks, and it is still difficult to produce steel foils for printed circuits that have various properties that are satisfactory from an overall viewpoint. There is no established treatment method for this.

In particular, it is a problem that copper foil rusts during transportation or storage, which deteriorates its appearance and causes problems in subsequent processing.For example, if the chromium oxide film formed by the chromate treatment is thickened, The more the rust prevention is improved, but the solderability is extremely deteriorated.

In view of the current state of the art, the present invention provides a method for producing a copper foil for printed circuits that has excellent anti-rust properties and also has other properties that exceed the required level. The purpose is to

For this purpose, the present inventor has developed a coating layer consisting of zinc or a mixture of zinc oxide and chromium oxide on the surface of the copper foil, whereby the effects of both substances work together to produce printed circuit steel. We have discovered scales that are provided in copper foil with various properties suitable for use as foil.

Thus, the present invention provides a copper foil for printed circuits, characterized in that at least one surface of the copper foil is provided with a coating layer of zinc or a mixture of zinc oxide and chromium oxide.

Furthermore, the present invention provides a coating layer of zinc or a mixture of zinc oxide and chromium oxide on at least one surface of the copper foil by electroplating using a plating solution containing zinc salt or zinc oxide and chromate. The present invention also provides a method for manufacturing a copper foil for printed circuits, which comprises forming a copper foil for printed circuits.

Here, at least one side means one or both sides of the copper foil.

As mentioned above, it is preferable to apply the coating treatment to both sides, but depending on the purpose, only one side may be coated.

The present invention will be explained in detail below.

The copper foil to be treated in the present invention is a rolled copper foil or an electrolytic steel foil that has been roughened on one side.

The purpose of the roughening treatment is to increase the peel strength after lamination of the surface that will be bonded to the resin base material, and is a so-called baked electrodeposition process to form a protruding copper electrodeposition layer on the surface of the copper foil. This is generally done by

Various electrolytic solution compositions, electrolytic conditions, pre-treatments, post-treatments, etc. used in the roughening treatment are already known, and their explanations will be omitted here.

In any case, the copper foil thus obtained has a smooth, shiny surface on one side and an uneven, rough surface on the other side.

According to the invention, the copper foil, which is roughened on one side, is coated on at least one side with a layer of zinc or a mixture of zinc oxide and chromium oxide.

The coating treatment consists of at least one kind of K2Cr207 t Na2Cr207 or CrO3, at least one kind of ZnO or znSO4.7H20, and NaOH.
Alternatively, electrolytic plating may be carried out using a treatment solution containing an alkali hydroxide such as KOH.

Simply immersing it in the above treatment solution to form an adhesion layer will not work.
Desired properties such as peel strength and antirust ability cannot be obtained.

The implementation conditions are shown below.

PH 7-13
Bath temperature 20~80°C Current density 0.05~5 A78
m time 5 to 30 seconds The electrolytic conditions for forming such a mixture film are extremely delicate, and the composition of the treatment solution, bath temperature, current density, and electrolysis time are interrelated and affect the properties of the formed film. Therefore, it is difficult to define the conditions unambiguously.

Furthermore, the level of acceptance on the demand side differs as to which of the various characteristics is particularly required for the processed product and to what level.

Therefore, the above-mentioned electrolytic conditions are feasible conditions for each factor, and it is necessary to select the optimum combination of condition values from among these ranges.

The point is that a dense coating containing both zinc or zinc oxide and chromium oxide and having a uniform thickness that adheres closely to the copper foil is sufficient.

The thickness of the coating increases as the current density and electrodeposition time increase, but it must be thick enough not to lose the lustrous appearance of the copper foil, but also sufficient to exhibit the desired rust prevention ability, peel strength, etc. Must be.

Generally, chromium oxide has a chromium content of 15 μg/dm'
As described above, a coating amount of zinc of 30 μi/d m″ or more is required.

The thickness may be different between the rough side and the smooth side.

The method can be carried out by continuously dipping a continuous copper foil into a water-washing treatment tank to perform electrolysis.

For example, copper foil is introduced vertically downward from the top of the treatment tank, guided vertically upward through guide rolls provided at the bottom of the tank, and, in the case of double-sided coating, is placed on the outside and center of both vertical paths. 3 sheets (for single-sided coating, 2 sheets in total on the outside of both vertical paths)
Continuous processing is possible by arranging one anode or one anode in the center.

The treated copper foil is washed with water, dried, and then wound up.

The copper foil thus obtained is made into a steel-clad laminate for printed circuits by heat-pressing it to a substrate, and after undergoing predetermined processing operations, it is used as a printed circuit board.

Several test examples will be shown below to demonstrate the effects of the present invention.

The test was conducted using electrolytic copper foil with one side roughened by electrolytic treatment for 15 seconds under the conditions shown in Tables ■ to ■. *The evaluation items in the table were conducted under the following method conditions. As an accelerated rust prevention test, the product was immersed in 10% ammonium polysulfide for 1 minute and judged visually based on the blackening of the surface in three grades: ◎, ○, and ×.

The product was left standing in a hot oven with a heat discoloration temperature of 160°C for 15 minutes, and the burnt state of the surface was observed, and it was judged on a three-grade scale of ◎, ○, and ×.

etching Soaked in 38% ferric chloride stock solution.

Measure the contact angle between solder wettability copper foil and solder using a commercially available soldergram.

As a pretreatment, it was pickled with 10% sulfuric acid, washed with water, dried, and then coated with Bryflux.

Peel strength: Copper foil is laminated and bonded to a phenolic resin board and a glass epoxy board, and the peel strength is measured.

As can be seen from the above test results, the treatment-produced film can be improved by appropriately selecting the bath temperature, liquid composition, and current density to improve rust prevention, heat discoloration resistance during soldering, etching properties, solder wettability, and peelability. It has excellent strength and can be suitable for printed circuits.

As comparative examples, Table 2 shows a case in which a zinc coating of 750 μg/d rtl was applied to both sides of a copper foil in Comparative Example 1, and a case in which a chromium oxide film was applied at 45 μg/d rtl on both sides of a copper foil in Comparative Example 2.
The test results are shown for the case where dm” was attached.

Is the present invention better than steel foil for printed circuits in terms of rust prevention, heat discoloration resistance, and peel strength? It can be seen that it is possible to manufacture a copper foil that has comprehensively excellent properties.

From Table ■, even if one of the factors listed above is at the upper or lower limit, it is possible to manufacture copper foil that is acceptable as a steel foil for printed circuits by appropriately selecting other factors. I understand that there is something.

Generally, K2Cr207, Na2Cr20 or Cr
Chromium sources such as O3 and ZnO or ZnSO4
・If the concentration of 7H20 in the treatment solution is less than 2 g/13 and 0.059/n, a good mixture film will not be formed, and on the contrary, if the concentration is so large as to exceed 10 g/II. Precipitation occurs in the treatment solution and the electrodeposit becomes coarse.

In addition, free NaOH or KOH of 10 g/l or more is required to stabilize zinc in the form of ZnO4-1, and adding 20 g/l or more of NaOH or KOH may cause precipitation of zinc in the treatment solution. Does not occur.

In order to obtain a dense electrodeposit it should not exceed 50 g/l.

The bath temperature also has a subtle effect on the properties of the product;
It can be carried out in the range of 0°C.

As the current density increases, the peel strength increases.

0. Below 0 5 A/dm2, no acceptable electrodeposit will result, while above 5 A/dm2 the electrodeposit will be rough in quality.

As explained above, according to the present invention, copper foil that has various properties required for copper foil for printed circuits, including rust prevention, can be manufactured easily and inexpensively in a continuous process, and will be produced in increasing quantities and with strict quality standards in the future. The significance of the present invention is extremely large in situations where it is necessary to manufacture copper foil for printed circuits under the following conditions.

Claims (1)

[Scope of Claims] 1. A copper foil for printed circuits, characterized in that at least one surface of the copper foil is provided with a coating layer of zinc or a mixture of zinc oxide and chromium oxide. 2 Forming a coating layer of zinc or a mixture of zinc oxide and chromium oxide on at least one surface of the copper foil by electroplating using a plating solution containing zinc salt or zinc oxide and chromate. Features: A method for producing copper foil for printed circuits.