DE1690025B2 - PRE-TREATMENT PROCESS FOR THIN INSULATING FILMS MADE OF POLYAETHYLENE TEREPHTHALATE - Google Patents

Description

The invention relates to a pretreatment method »5 for thin insulating foils made of polyethylene terephthalate <l due to the action of sulfuric acid solution, the following Treatment with hot aqueous sodium hydroxide solution and subsequent sensitization lind activation and chemical copper plating using a copper sulfate, formaldehyde, sodium lauryl sulfate, Bath containing sodium hydroxide, sodium carbonate and tartrate.

In particular, according to the invention, such insulating foils are to be pretreated which are intended for use in the technology of printed circuits and in data-processing storage technology. As is well known, there has recently been a desire to use thin insulating foils covered with copper in the form of thin layers in data processing storage technology, preferably as a carrier for ribbon cables, e.g. B. as control, word, bit and read lines for magnetic thin-film memory matrices to use. Up to now, insulating foils could be obtained laminated with copper foils. The thickness of the copper foils, from which the desired pattern was formed with the help of the photo-etching technique, is in the order of 30 to 35 μm, the thickness of the insulating foils was also between 30 and 35 μm; the total thickness of the foils has so far been relatively large. Investigations have already been made with the aim of providing thinner insulating foils with thinner copper layers. For example, attempts have been made to copper-coat thin foils by vapor deposition in a vacuum or by cathode sputtering. In this case, however, the foils must be subjected to thermal stress, and their mechanical strength is often reduced to the point of tearing. The deposited layers are also not free of tension. When copper-plating the foils from known copper-plating solutions, it has hitherto not been possible to deposit any layers on the foils that were not removed again by light rinsing with water or by wiping. Tempering the deposited copper brought about a slight improvement in the adhesive strength wedge, but the requirements are still far from being met. The tempered copper layers still adhere very poorly and are not scratch-resistant. Mechanical roughening of the foils, which would possibly improve the adhesive strength, is ruled out if they are less thick. Particular difficulties arise when the insulating films are made of polyethylene terephthalate. Polyethylene terephthalate is particularly advantageous as a carrier material due to its good chemical resistance to the solutions commonly used for etching copper. On these foils, however, I practically do not have any reasonably adhering copper layers applied at all. A number of known copper plating loaders have been investigated with which well-adhering copper layers can be achieved on thick, compact plastic slats. All of these methods fail when thin polyethylene terephthalate films are to be copper-plated. For example, baths were used which contained the following components in 1 liter of water: 14.6 g copper sulfate (crystallized), 7.5 g sodium hydroxide,
7.5 g Rochelle salt and
34.0 g formaldehyde (37%). Another bath used contains 7.8 g copper chloride per 1 1,
7.5 g sodium hydroxide,
7.5 Rochelle salt and

16.2 g formaldehyde (100% concentrated). These and a number of other baths, which, for example, when producing printed circuits according to the build-up method on circuit boards, yielding well-adhering copper layers, resulted in the foils of the type described - the foils were provided with catalytically active metal nuclei in a known manner before copper plating, for example in SnCl ₂ - Baths sensitized and then activated in PdCl ^ baths - only to a copper veil that can already be removed by water, but in no case copper layers to stick.

Pretreatment processes for polyester polymers for the purpose of metal coating are in accordance with the USA patent specification 31 42 582 already known.

Here, however, the pretreatment is carried out with a wetting agent-free sodium hydroxide solution, which, with further application, also for example from Plating 1964, Issue 11, pp. »069 to 1072, known copper bath leads to unsatisfactory layer adhesion.

The object of the present invention is therefore Development of a pretreatment process for thin insulating films made of polyethylene terephthalate, which causes a higher layer adhesion of the chemically deposited copper layer.

According to the invention, this object is achieved by a Pretreatment process solved by exposure to sulfuric acid solution, subsequent treatment with hot aqueous sodium hydroxide solution and subsequent sensitization and activation as well chemical copper plating using a copper sulfate, sodium hydroxide, and sodium carbonate Tartrate-containing bath, which is characterized in that a wetting agent-containing sodium hydroxide solution is used.

When using this pretreatment process, the thin insulating foils will adhere well Copper layers achieved. The adhesive strength is so great that, for example, with 1 mm wide copper strips, which up to a thickness of about 5 μm galvanically

strengths are, erne strength between 18 and 25 ρ required solution, which by solving little

Hch is to detach these strips from the backing. Palladium chloride and tin (II) chloride in dilute

When pulling off the copper strips, hydrochloric acid often occurs (2 parts water, 1 part concentrated salt

Tearing it up strips or even destroying the acid) is obtained.

Plastic film. 5 If necessary, before activation and

Sodium lauryl sulfate is preferably used to sensitize the insulating film with a thin layer

medium used and the proportion to be provided on 50 mg per liter of adhesive layer. This will make the

Copper plating solution set. Adhesive strength of the copper layers further improved.

According to the invention it is therefore provided that to- The adhesive is, for example, in a diluted form

Next, the thin insulating film is applied to the film in a very specific way, so that extremely thin

is pretreated. Adhesive layers are formed.

The folit! is successively in chromosulfuric acid. Invention and sodium hydroxide solution are used for copper plating of the insulating film, which dips a wetting agent according to alkaline baths, which hold a very large one; Both solutions are heated to a higher proportion of reducing agent based on the copper temperature. These solutions cause e ^; contain 15 ions. These copper plating baths change the surface of the foils, which leads to an increase in the adhesive strength of the copper to be applied by about 85 to 95 g of formaldehyde per 1 liter of solution - that is about 250 ml of the commercially available layer. Because these solutions destroy the 35 weight percent formaldehyde solution. A foil can cause the treatment only preferred copper plating solution, which can be carried out for an excellent short time. For example, * ° copper layers are delivered, has the following relationship with a one-minute treatment with the chromium-sulfurization:
acid solution and then likewise for one minute loading 12 ε CuSO -5HO
long with the hand 15 to 20gewichts _P rozentigen Na ₃₅ J potassium sodium tartrate ■ 4 H ₂ O
tnumhydroxid solution achieved very good results. iHr «-lu» l1p «aM
The chromosulfuric acid solution is preferably made from * 5 ₂ 0 g N? OH
2 parts by volume 98% sulfuric acid, 1 part by volume 15gNa, Co '
Water and 25 g of potassium dichromate per liter. ₅₀ J _{1 of} sodium lauryl sulfate and
represents. The sodium hydroxide solution must be a wetting agent _{250 m} f _formaldehyde (35 percent by weight)
tel such as sodium lauryl sulfate can be added. The proportion of the wetting agent in the is preferably 3 per liter of aqueous solution.

Caustic soda between about 300 and 600, especially after treating the insulating material for about 5 minutes

500 mg 1st foil with the copper plating solution at room temperature

After this preparatory treatment of the insulation, about 0.5 μm thick copper layers can be applied

slide with chromosulfuric acid and that can be achieved with one. This layer thickness is common

Wetting agent added sodium hydroxide solution and 35 reached when the deposited layer was uniform

briefly rinsing off this solution, the sensitization appears and no longer shows any light transmission,

tion and activation of the insulating film made- This chemically deposited copper layer can

The known SnCl ₂ - and PdCl ₂ . still be galvanically compressed and reinforced.

Find solutions to use. The order of expediency is the galvanic treatment

Baths is irrelevant here. As a sensitization 4 ° carried out in two stages by previously one

solution, a 2 percent by weight SnSl ₂ solution can contain a low cathodic current density of approx. 4 to 5 mA /

can be used, which contains 1 percent by weight HCI. cm ² and then a much higher current density i

For better wetting, this solution can have a low, for example, a cathodic current density of 40 to

rer alcohol, for example methanol, is added, 50 mA / cm ² is used.

den, for example 25 ml / l solution. After 5 minutes, a 45 becomes a familiar bath for the main copper plating

Sufficient sensitization of the insulating film is achieved. the following composition is used:

After the sensitization, the insulating film is briefly in 200 g CuSO -5HO,

Rinsed with water, for example only for 5 seconds, and 30 g H SO * (98 Vig) ',

then immersed in a palladium chloride solution. The 10gNaCl * °

Palladium chloride solution is about 0.1 percent by weight 5 <> 2 g gelatin,
acidified with 1 percent by weight HCI. she should

Also a wetting agent, for example sodium lauryl, is obtained after about 4 minutes of treatment in

sulfate. By immersing or spraying this bath a layer thickness increase of 4 to

the film with this solution for a period of 5 μπι. The first stage of galvanic treatment

Satisfactory results are achieved for about 3 minutes. 55 with low cathodic current density is preferred

For activation, for example, another way up to an increase in layer thickness of about

Noble metal salt solution, for example a gold chloride 1 μΐη carried out.

solution, can be used. As mentioned, the following examples may serve to illustrate the

Insulating film also first with the activation solution and invention,

then treated with the sensitizing solution ^6o "" soiel 1
the. It is also possible to raise awareness and

Activation in a single operation vorzu- Take an insulating film made of polyethylene terephthalate by using a solution that is 6 μm thick is stretched on a frame and catalytically attached to the copper deposition acting Me- z. B. glued. This makes the foil tall, such as palladium, gold or platinum, mechanically strengthened and manageable ^{in colloidal 6 5.} The foil, which is stretched out on the creamer, preferably together with a protective cover, is contained in chromium colloid for 1 min. Such a solution is, for example, immersed in sulfuric acid which is heated to 90 ° C. and pi ™ - colloidal stannic acid and colloidal palladium from 2 parts of H ₂ SO ₄ (98%), 1 part of water and 25 g

K ₂ Cr ₂ O _{7 is composed} per liter, then briefly soaked and immersed for 1 min in 20 weight percent sodium hydroxide solution of 9OC, which contains 500 mg sodium laury sulfate per liter. After a short soak, the film is _{dipped into an SnCl 2} solution, rinsed briefly, preferably with slightly acidic water, and then _{dipped into a 0.1 percent by weight hydrochloric acid PdCl 2} solution. For example, the SnCl ₂ solution has the following composition: 20 g SnCl ₂ and 10 g HCl per liter. Methanol can also be added to this solution. The insulating film thus provided with catalytically active Pd nuclei is now treated with a copper plating solution of the following composition (per liter of solution), if necessary after a brief intermediate rinse with water to which a wetting agent such as sodium lauryl sulfate has been added:

12 g CuSO ₄ -5 H ₂ O,
35 g Rochelle salt,
2OgNaOH,
ISgNa ₂ CO ₃ ,

50 mg sodium lauryl sulfate,
250 ml formaldehyde (35 percent by weight),
Rest water.

This solution is expediently produced shortly before use, for example by adding the required amount of formaldehyde to a solution containing the remaining components. As soon the deposited copper layer has become opaque to lichi and looks uniform, becomes the Treatment in the chemical bath interrupted. The layer thickness is now approximately 0.5 μm.

After this, the layer can be galvanically further copper-plated up to a layer thickness of about 5 or 6 μπι. These layers can then be used in a known manner by covering certain parts, For example, with the help of photoresist technology, the desired pattern can be formed.

The copper layers adhere excellently to the insulating pad. For example, the amount to be peeled off is of 1 mm wide strips with a thickness of 5.5 μm required force between 18 and 25 p. This adhesive strength can be further improved by tempering at 100 ° C., for example.

For the sake of completeness, it should be noted that the treatment of the insulating films is also continuous can be carried out in the so-called hiking pool procedure if it is ensured that that the film has the mechanical strength required for this.

Example 2

ίο A) A pretreatment bath was made according to the United States patent 3142 582 manufactured with the following composition:

38 g / l Na ₂ Cr ₂ O ₇ · 2 H ₂ O,
740 ml / 1 concentrated H ₂ SO ₁ (D: 1.84),
249 ml / 1 water.

With this bath, a film made of polyethylene terephthalate was treated for 1 min at 85 'C, which then with Rinsed water and then 1 min in an aqueous

ao solution of 150 g / l sodium hydroxide at about 90 ° C was immersed and then rinsed again with water, whereupon after previous sensitization and Activation with tin and palladium chloride solution then chemical copper plating at room temperature

»5 temperature was made from a solution containing sodium lauryl sulfate, sodium hydroxide, sodium carbonate, potassium sodium tartrate and 12 g CuSO ₄ -> H ₂ O and 90 g formaldehyde per liter.
The test of the adhesive strength (determination of the pull-off force) was carried out in accordance with the German standard DIN 53 494 and resulted in a value of 2.0 kg.

B) The experiment described under A) was repeated under otherwise identical conditions, with However, an aqueous solution of 150 g / l sodium hydroxide was used, the 500 mg sodium lauryl sulfate were added as a wetting agent.

The adhesive strength determined in accordance with DIN 53 494 was 3.1 kg.

The addition of a wetting agent to the known pretreatment bath for polyethylene terephthalate for the purpose of the subsequent chemical copper plating had an increase in the adhesive strength of the deposited metal layer from 2.0 kg to 3.1 kg, that is more than 50% result.

Claims (2)

Patent claims: 1. Pretreatment process for thin insulating films made of polyethylene terephthalate by action of sulfuric acid solution, subsequent treatment with hot aqueous sodium hydroxide solution and subsequent sensitization and activation as well as chemical copper plating under Use of a copper sulfate, formaldehyde, sodium lauryl sulfate, sodium hydroxide, sodium carbonate and tartrate-containing bath, characterized in that a wetting agent-containing Sodium hydroxide solution is used. »5 2. Pretreatment method according to claim 1, characterized in that a sodium lauryl sulfate containing sodium hydroxide solution is used. ao