JPS62114294A - Manufacture of metal pattern of insulating substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for manufacturing metal patterns, especially printed circuits, using a negative mask using an attenuation method, on an insulating substrate having holes for electrical connection. Regarding. The invention further encompasses insulating substrates, particularly printed circuits.

[Conventional technology]

In the manufacture of through-hole plated printed circuit boards (PCBS) using the attenuation method, the starting point is a laminate coated with metal foil. Insulating materials include in particular epoxide resins reinforced with glass fibers, phenolic paper, epoxy paper, polyimide, P
vC is used.

Metal foil (usually steel foil) is applied to both sides of the laminate.

Double-sided printed circuit boards are manufactured from these insulating plates coated on both sides. If several layers of conductive patterns are pressed together, thereby resulting in separation by an insulating substrate, these are called multilayer circuits (multilayer boards).

Through-hole plating on the outer surface of a two-layer or multi-layer printed circuit board and the manufacture of the printed circuit board are accomplished on the same principle. After forming holes (openings) at desired locations to connect to the individual conductive patterns (e.g. by drilling, punching, milling, etc.) and after a mechanical cleaning step of the metal thin film (e.g. by brushing),
In principle, through-hole plating and pattern plating are performed according to the following process sequence.

12 Through hole plating 1. Cleaning the printed circuit board in a cleaning aqueous solution.

2 Etching of metal thin film.

5. Activation.

4. Chemical plating, preferably chemical steel plating, and optionally.

5. Strengthening of the chemical plating layer (steel plating) if only a thin layer is deposited during step 4 above.

■ Formation of negative mask by screen printing or photoresist & brushing of board.

l For example, coating with photoresists and development of negative conductive patterns or coating with screen printing inks.

■、Pattern plating a. Cleaning.

9 Etching.

1 [L Copper plating.

11. Deposition of etching resists such as soot or lead-tin.

■ Etching of printed circuit boards 12, removal of negative masks (photoresist or screen printing ink).

15. Etching of metal (copper) not covered with etching resist.

14. Soldering and polishing, optionally reflowing (r@flowing: remelting) This method is called "metal resist method" in the technical field.

The above series of steps describes the principle of the above metal resist method. Every expert knows at what point during this process, for example a cleaning step has to be carried out, or at what point the board must be placed in a suitable device (for example a frame or a basket) so that it can be transported during manufacture. )
I am aware of what I have to put on top. After several process steps, the process is interrupted. In other words, the board can be viewed and stored for a certain amount of time.

The activation step constitutes a process in which metal nuclei are deposited on the wall of the hole to initiate subsequent chemical metal plating on the wall of the hole. Activation can be done, for example, by knee pre-soaking.

- Actual activation in a solution containing a tin-palladium paced colloid.

- for example Hl, - conditioning (promotion) in solution.

occurs in several process steps, such as

Other activation steps use copper-based colloids. This activation process is based on Yo-Rokupa patent application No. 0.04.
No. 4,878.

Activation based on metal colloids has certain disadvantages as will be discussed below.

Inorganic precious metal solutions can be substituted, for example in accordance with DE 2,116,389.

- Another possibility of producing through-hole plated printed circuit boards by the attenuation method is the so-called tenting method. In this method, the sequence of process steps is step 1 compared to the metal resist method already described above.
to 5 in principle. By selecting the operating conditions of process steps 4 and 1 or 5, the final layer thickness of copper is obtained. This is followed by the following steps: ■ Creation of the Bozitep mask with photoresist.

&a, Surface cleaning by brushing.

7.a. Coating with photoresist, development and thereby forming a positive image from the photoresist.

Melon, etching, heat immersion tin plating AA, etching, removal of Bozitep mask (photoresist).

9a, #-1t soldering is done with a mask.

IQ, A, heat immersion tin plating.

continues.

To fully press, additive and semi-additive methods for printed circuit board preparation should be mentioned. As base material, an uncoated laminate made of adhesive-coated glass fiber reinforced epoxy resin, epoxy resin paper or phenolic paper is used.

The method described above is part of the prior art and cannot be compared with other methods such as the tenting method, the additive method and the semi-additive method. For example, the metal resist method is the most widely used method for manufacturing through-hole plated printed circuit boards. This method is acceptable and economical from the standpoint of industrial practicality and completion.

Nevertheless, in its currently used form, this method has a number of drawbacks: a relatively large number of process steps. Activation, especially chemical metal deposition in the first section (through-hole plating) and reinforcement (copper plating), occurs over the entire surface of the metal film.

In these locations, where no conductive paths are provided, metal plating is generally pointless and only represents extra costs in plating, etching and flushing.

Despite some improvements recently achieved, colloidal solution-based activation systems are less stable, more sensitive to impurities, and relatively complex compared to true inorganic solutions. Due to its unique manufacturing method, it is very expensive.

In stage 4 (chemical metal plating), chemical steel baths are almost exclusively used. However, in terms of bath cost and bath maintenance, chemical nickel plating is more economical than copper plating. The cost of treating the concentrated 4 solution runoff and the wash water contained in the chemical plating baths is particularly high for weakly acidic nickel baths containing the strong complexing agents used in practice, such as EDTA. It is not as expensive as in the case of alkaline copper baths.

However, the use of chemical nickel baths has significant drawbacks; in metal resist methods, the etching solution must be used to etch the copper at a reasonable rate;
It must be used in such a way that it does not attack metal resists (such as soot or lead-tin). Slightly alkaline etching solutions are suitable for that purpose. Nickel will be attacked very slowly or not at all in these etching solutions, and etching (step 13 of Section 1) will be greatly hindered or not possible. This means that the production of conductive patterns is not possible.

The steps in sections 1 and 2 of the metal resist method include a series of various processing methods in an aqueous solution. The printed circuit board is placed on a hall goose device, such as a frame, and processed according to a circular process.

Transfers between treatment baths can be carried out quickly either manually or by automated equipment.

■The steps in the section indicate interruptions in the method. The board must be removed from the holder device (frame). Although board machining (brushing) is performed before through-hole plating, this process step must be repeated for subsequent application of photoresist or screen printing ink. After application of the negative mask. , the board is placed again, for example on a frame, and then subjected to further processing.The cleaning and etching must also be repeated.

Etching in this respect is particularly important.

This is because the coating on the surface of the still thin hole walls can be accommodated very easily. This type of corrosion is only local and therefore insidious, and so-called "out-gassing" soldering can lead to errors in the process.

In order to avoid interruptions between the steps in sections 1 and 2, a negative mask must be applied before through-hole plating of the printed circuit board. However, variations of this process involve insurmountable difficulties. If the negative mask is applied before activation, not only the walls of the waiting room but also the negative mask at the same time will be activated when using conventional activators. On activated surfaces, metal plating will be produced in a chemical plating bath. The unavoidable result, for example the overlay of a negative mask with metal, makes it impossible to create conductive patterns.

It is an object of the present invention to make available a metal resist method which largely obviates at least the existing drawbacks of the known methods.

The inventive process of the type described above is characterized by steps in the following sequence: 1. Treatment in gaseous sulfur trioxide.

λ Negative/corresponding to the conductive pattern to be manufactured
Application of masks.

5. Through-hole plating and subsequent plating of conductive patterns realized by the following process steps: activation with inorganic noble metal solutions, treatment in reducing agent solutions, chemical or chemical and electrochemical plating, whereby activation and metal plating It occurs only on the surface of the metal pattern to be manufactured.

This method has the following advantages over previously known methods: Plating occurs only at desired and convenient locations.

Metal plating, etching and draining processes are thereby saved. Through-hole plating is not only achieved by chemical copper plating. Chemical nickel plating is also used for this purpose. This process is performed in fewer steps than conventional processes.

Mechanical treatment (brushing) of the board is done only-denaturing. Cleaning and etching on the surface of the desired metal pattern prior to plating the conductive pattern can be omitted. The risk of etching associated with metal plating of the walls of holes is excluded; some of the methods are known per se, as for example with the plating of plastics. However, the advantages resulting from the combination of the successive known steps indicated above are surprising.

Treatment in gaseous sulfur trioxide is among the known methods for conditioning non-conductors for subsequent metal plating. This process is described in German Patent Application No. 2,126,781.

Chromic acid and/or chromic acid/sulfuric acid solutions are also known conditioning agents for plastics. This is sometimes preceded by a treatment in a solution containing chromic acid, which roughens or swells the plastic surface to some extent. Regarding the complete coverage of the metal during chemical plating and the adhesion strength of the metal plating on the surface of the plastic, this treatment allows a useful reaction of the plastic in solutions containing chromic acid.

A method relating specifically to the production of printed circuit boards is described in German Patent Application No. 2,105,845. Using this method, an epoxy F resin laminate is first treated in an aqueous dimethylformamide solution and then in a chromic acid/aqueous sulfuric acid bath. The board prepared in this way is activated in a solution containing a colloid based on tin-palladium. The conductive pattern is manufactured using an additive or bioadditive process.

Conditioning agents with or without swelling agents based on chromic acid are not suitable for the process of the invention. Complete plating of Ananoei is not accomplished in chemical plating baths using activators whose compositions and operating conditions can be used in the process described more fully below.

The method of treating plastic surfaces in gaseous sulfur trioxide as disclosed in DE 2,126,781 is an advantageous alternative to the method of conditioning plastic surfaces with acidic solutions containing chromic acid. It is the law.

Both methods, like other methods of glass plating,
Consists of the following steps: 1. Condition adjustment.

2. Activation using a metal salt or sensitization in a solution containing a divalent tin salt and subsequent activation in a noble metal salt solution. 5. Treatment in a reducing agent solution.

4. Chemical plating.

It is by no means clear from DE 2,126,781 that conditioning in gaseous sulfur trioxide is suitable for the production of metal patterns on insulating substrates using the depletion method. Examples 19 to 22 of the invention describe possibilities for the production of printed circuit boards according to a bioadditive or additive process.

A cyclic process according to the present invention is not mentioned or suggested in any way in this patent.

The circulation process according to the invention is described in West German Patent Publication No. 2,12
There is a fundamental difference from the method according to No. 6,781. In the process according to DE 2,126,781, the plastic is activated directly after treatment in gaseous sulfur trioxide. Although the palladium solution used for activation can certainly be used in a method such as the present invention, palladium solutions are not advantageous, as will be explained later. Activation based on treatment in tin solution followed by palladium solution is not available.

This is because the holes in the negative mask on the insulation board will be activated for subsequent deposition. It is particularly surprising that it has been found that interrupting and intermediate processing is possible before activation according to the invention.

After conditioning sensitive plastic surfaces can be dried repeatedly without difficulty, and various solutions such as photoresist developers, cleaning solutions containing wetting agents and oxidizing agent solutions can be used for etching thin metal films before the activation step. It is not obvious to experts that metals can be exposed to the effects of metals without losing their ability to usefully accept precious metals.

A strategy for using gaseous sulfur trioxide for the pretreatment of plastics is known from German Patent Publication No. 2,126,781 and is also applicable in principle to the process according to the invention. Adhering the plated metal to the wall soil of the hole is
J ring) Roughening of the medium wall is encouraged by K. Due to the already existing adhesion-friendly surface structure, greater latitude is available in the selection of processing conditions compared to the case where plastics with smooth surfaces are to be plated. For most plastics, the concentration used is 8 (J310 mf/L to 6
S03 corresponding to vapor pressure of 25℃
The concentration ranges from . The treatment time is selected from the range of 1 second to 20 minutes, preferably 10 seconds to 5 minutes.

The application of negative masks, for example with screen printing inks, photocoatings, or photoresist thin films, are known methods found in isolation and need no further explanation.

For example, after producing a negative mask before activation, the board is cleaned in an aqueous solution. Cleaning for this purpose is usually carried out in commercially available cleaning agents.

These cleaning solutions react depending on whether they are acidic or alkaline.
It contains acids such as sulfuric acid or in other cases alkalis, as well as inorganic neutral salts, various organic compounds, and especially wetting agents. It is understood that with alkali soluble photoresists only acidic and reactive cleaning agents can be used.

Some cleaning agents contain substances that strongly interfere with chemical metal plating, so-called catalyst poisons. For example, this group includes thioureas.

It will be appreciated that the use of such materials in these cleaning agents should be avoided so as not to interfere with subsequent chemical vapor deposition.

The conventional etching agents for etching gold foil (often copper foil) are based on persulfates or hydrogen peroxide.

In principle, noble metal salt solutions can be used in the method according to the invention. This is followed by reducing agent solution treatment.

An activating composition or board working with metal colloids is first sensitized with divalent soot and then activated in a precious metal salt solution on the surface of the hole in the wall and on the negative mask. Cannot be used due to simultaneous effects.

Noble metal salt solutions are easily hydrolyzed. To prevent hydrolysis, the pH value is adjusted to a value lower than K by adding acid. From the noble metal ion solution, especially an acidic solution, in which the noble metal ions are present in non-competitive form, the noble metal is plated onto the surface of the non-metal by ion exchange. West German Patent Publication No. 2
．． The ion-generating precious metal solutions used to activate nonconductors for subsequent metal plating, as described in US Pat. No. 1,26,781, have such disadvantages. With conventional plating methods for non-conductors, these drawbacks are not significant. This is because only the surface of the non-conductor is treated. In the attenuation method, non-conductors and metals (copper foil) are treated simultaneously. Metal plating is done by ion exchange.

Strategies for preventing bonding on non-noble metals are known. In the electroplating of palladium, this involves e.g. raising the pH and adding chelating agents such as e.g. ammonium salts.Apart from electrochemical baths and chemical palladium baths, this involves the application of compounds containing nitrogen atoms in the activation solution. is known from DE 1,621,207 and DE 2,116,589.

The process according to the West German patent claims that the plastic surface is first sensitized with a divalent salt solution of soot and then activated in a palladium solution containing a nitrogen atom-containing compound. The OpH value of the solution is set such that no palladium deposits on the steel, yet a reaction between the divalent soot compounds and the palladium occurs on the surface. DE 1,621,207 makes use of the fact known at the time of filing of the present invention that the bonding of palladium is prevented by adding compounds containing nitrogen atoms. By adding compounds containing nitrogen atoms, the activity of palladium ions is reduced in terms of activation. West German Patent Publication No. 1,621,2
No. 07 discovered an operating range in which activation with a palladium salt solution containing nitrogen atoms is possible after sensitization. This publication is cited as an embodiment of a known through-hole plating method with a modified activating composition. These activated compositions cannot be used in the method according to the invention because of the possibility of negative mask deposition as described above.

In the process according to DE 2,116,389, the plastic is activated in a noble metal salt solution which additionally contains nitrogen atoms and then treated with dimethylaminoborane or sodium hypophosphite for the reduction of the noble metal. and finally deposited in a chemical plating bath. West German Patent Publication No. 2,116,589
It is specifically stated in the specification that this activation is suitable for through-hole plated board production by known methods, whereby the entire surface of the copper foil is activated and chemically plated.

The functional capacity of the activation solution is determined by West German Patent Publication No. 2.116.
, 589, it depends to a large extent on the p)l value. Furthermore, there are differences between individual nitrogen-containing compounds with respect to activation. For example, it is more convenient to use 2-aminopyridine than to use ammonia or ammonium salts.

According to the example of German Patent Application No. 2,116,589, a nitrogen atom-containing compound is added to a noble metal salt and then p
Raise the H value to about 7. These solutions cannot be used in methods such as the present invention. This is because under the influence of such an activating solution in the chemical plating bath, the metal is plated not only on the wall of the hole, but also on the surface of the negative mask as shown in Example 14. It is.

Activation solutions used and/or preferred in the present invention include:
If possible, the following requirements must be met at the same time:

1. Regarding the complete plating of the walls of the holes (non-gold M), sufficient plating with precious metals must be ensured.

2. Precious metal condensation on the metal thin film (copper) must not occur at all or only to a small extent.

5. Negative masks must not be activated.

In the cited patent documents, non-conductors (plastics)
A further method is described in which sufficient activation of the metal is carried out with simultaneous prevention of adhesion of noble metals on base metals, such as copper. However, effects related to non-conductors are undesirable in the case of the present invention. This is because otherwise a negative mask (non-conductor) would be deposited.

It has been found that noble metal solutions containing basic nitrogen compounds meet all of the above conditions under certain operating conditions, such as concentration and pH value. As nitrogen-containing compounds, ammonia, primary amines, secondary amines, tertiary amines and other compounds containing basic nitrogen atoms and salts of these compounds are used. Examples include: ethylamine, butylamine, ethylenediamine, pyridine, urea, ethylhethysylamine, taurine, glycine. These compounds are used, for example, as sulphates, chlorides or nitrates.

The available concentration of nitrogen-containing compounds depends on the palladium concentration. The ratio of the molar concentration based on amino groups to the molar concentration of palladium ions should be at least 2. The pH value of the solution is between 1 and 7, preferably between 2 and 3.

It will be understood by those skilled in the art that the type of nitrogen-containing compound, the concentration of palladium and nitrogen-containing compound and the pH value will influence the usefulness of activation in the process according to the invention.

Ammonia and ammonium salts are weaker chelators for palladium ions than, for example, ethylenediamine. Bonding palladium plating on steel requires a lower concentration of ethylenediamine than when using ammonia. On the other hand, in a chemical metal plating bath,
Activation with complete coverage of the hole walls is less sensitive to higher concentrations of ammonia. Strong chelating agent (
Addition of large amounts of ethylenediamine) may reduce the effectiveness of the palladium below a usable level, thereby preventing complete coverage of the nonconductor.

Operating conditions (concentration and pH value) have an adverse effect on the usefulness of the activation solution. The most favorable operational range of activation can be found in a few trials of Nenjo.

After dissolving the palladium salt, a compound containing nitrogen atoms is added to adjust the pH value to, for example, 2 to 3. Tests are then carried out as follows, varying the conditions arbitrarily in a direction that yields the desired results: 1. Testing the condensation of palladium on thin metal films (copper).

This junction is reduced by increasing the pH value and/or by increasing the concentration of compounds containing nitrogen atoms.

2 Coating test of the hole walls in a chemical plating bath in which the drilled board is conditioned in gaseous sulfur trioxide, then cleaned, etched and activated in an available activation solution. Lower concentrations of nitrogen-containing compounds and/or higher concentrations of palladium improve results during chemical plating.

(5) Negative mask coverage test. Samples are processed as described in 2, but without the conditioning section. In principle, this test corresponds to the method described in DE 2,116,589 or DE 1,621,207.

Regarding these publications, negative results should be obtained in this respect.

Covering of non-conductors (negative mask) must not occur. This can optionally be achieved in many cases by lowering the pH value.

These tests can be performed on three samples separately or simultaneously on a drilled sample prepared in sulfur trioxide and a sample coated with a negative mask.

Examples 6 and 7 demonstrate the effect that occurred during testing.

The temperature at which the activation solution is used is not critical.

It will be appreciated that activation is performed at room temperature, but higher or lower temperatures may be tolerated.

An action time of 20 seconds to 10 minutes, preferably 1 to 3 minutes, is sufficient.

After activation, treatment is carried out in a reducing agent solution such as dimethylaminoborane. The OpH value of this solution is preferably set to be slightly acidic (eg pH=5) to eliminate attack on the alkali-soluble resist.

Chemical metal plating can be performed in a chemical copper bath or a chemical nickel bath. Alkaline chemical steel baths are not suitable when using alkali soluble resists. To make this method universally usable, preferably a weakly acidic chemical nickel bath should be used.

The chemical nickel baths used in practice in common commercial products include nickel salts, chelating agents (usually organic acids and their salts), reducing agents (usually sodium hypophosphite or aminopora/), and e.g. containing stabilizers such as sulfur or heavy metal compounds. In principle, there are no restrictions on the use of these baths. Preferably, a bath containing only an aminoborane compound or sodium hypophosphite as a reducing agent is used. These baths are 50
It can work at relatively low temperatures, up to °C. As a result, possible temperature loads on the negative mask are kept low and possible formation of air bubbles, in particular too strong elongation of the negative mask associated with flaking, is largely avoided.

Further formation of the conductive pattern is performed by conventional methods. This point is usually followed by electrolytic copper plating in an acid bath and plating of metal etching resists such as tin, lead-tin, nickel and especially gold. Chemical plating, for example in a chemical copper bath, can in principle be carried out when using an alkali-resistant negative mask, but the invention is not limited to such an example.

The comparative example is related to the above description.

Example 1 A flint circuit is fabricated from a copper coated epoxy r-sensin laminate. The sequence of processing is as follows: 1. Drilling of the board: λ Treatment in an atmosphere containing SO3 in equilibrium with 35 wt. of oleum for 20 seconds at room temperature: 5. Washing in water; 4. Drying of the board. 5. Brushing the board, coating it with a commercially available alkali-soluble photoresist film, making a negative mask; & Placing the board on the underframe; l Cleaning the board with a normal commercially available acid detergent for 5 minutes at room temperature. : a Washing in water; 2 Etching chamber @ 2 minutes in sodium persulfate solution; 1α Washing in water; 11. Activation in a solution of the following composition: Palladium as palladium nitrate 200m? / is daughter sulfuric acid 20f / is iso ammonia solution 2b? /lpH was adjusted to 2.6.

The treatment was carried out for 2 minutes at room temperature: 12-Washing in water; IA TepH in 1 f/l dimethylaminoborane solution
= 5.5 for 1 minute at room temperature; 14. Washing in water: 15. Chemical nickel plating at 45°C for 15 minutes.

The chemical nickel bath has the following composition: nickel as nickel sulfate 71/l as lactic acid
50? / Sodium hypophosphite
10r/l dimethylaminoborane 21/
Lead as acetate 0.5 mW//1 The pH of the bath adjusted with sodium hydroxide is 5.5.

1 & Washing in water; 1z Immersion in 5% sulfuric acid for 20 seconds at room temperature; 1a
Electrical steel plating in a normal commercial copper sulfate bath; layer thickness 25 μm; 19. Washing in water; Soaking in 2I:L acid; 21. Tin from a normal commercial lead-tin bath. - Tin film; 22- Washing in water and drying the board; 2! - Removal of board from white plum; 24. Removal of photoresist film and etching of remaining exposed copper film.

When the printed circuit board was optically evaluated under a binocular microscope, no defects were observed in the through-hole plating and conductor path contours.

Example 2 Four copper coated and perforated laminates made from glass fiber reinforced epoxy resin were processed as in Example 1. The conditions for treating the laminate in an atmosphere containing sulfur trioxide are as follows.

1. SO3 concentration in fuming sulfuric acid 35-chi processing time 20 seconds 2 SC2 concentration in fuming sulfuric acid 35-chi processing time
40 seconds 5 SC2 concentration in fuming sulfuric acid
42chi processing time 20 seconds 4
, SO3 concentration in fuming sulfuric acid 50 seconds Processing time 20 seconds During electrical steel plating (step 18), a 5 μm thick coating is plated.

Optical testing of the printed circuit board showed that the through-hole plating and conductive pattern plating were free of defects.

Example 3 A copper-coated PvC thin film and a copper-coated epoxy resin-impregnated paper board are treated in the same manner as in Example 2.

The production of the holes is done by punching and the negative mask is produced by screen printing colors. The conditions during treatment in gaseous sulfur trioxide are as follows.

Fuming sulfuric acid concentration for PVCK 65% S03 treatment time 10 seconds Fuming sulfuric acid concentration for epoxy resin impregnated paper 35cm S03 treatment time 20 seconds Copper plating (layer thickness 5 μm
), the through-hole plating was inspected. The results were free of defects.

Example 4 A perforated steel coated epoxy resin laminate was processed as in Example 1 above. In step 9, etching, a normal commercially available etching solution containing hydrogen peroxide as the biological material is
It was used for 2 minutes at 0°C. Through-hole plating and conductive pattern plating had no defects.

Example 5 A steel coated fiberglass reinforced epoxy resin laminate was processed as in Example 1. Various activator solutions were used in the step 11 (activation) process. Treatment with the activator solution lasted 3 minutes in each case and was carried out at room temperature. The composition of this solution is as follows: activator, solution flow 1 palladium as palladium nitrate 200 mV/L
Concentrated sulfuric acid 20y/l Viridi 7
329/lpH value
2.7 Activator, solution air 2 Palladium as palladium nitrate 200 mW/
pH value adjusted using concentrated sulfuric acid 2 oy/l ethanolamine 245//l ethanolamine 2.1 Activator, solution N[L3 Palladium as palladium nitrate 200 m? /
L concentrated sulfuric acid 209/l butylamine 50y/l pH value adjusted with butylamine 2.0 activator, solution air 4 Palladium as palladium dichloride 200 m? /L
#Sulfuric acid 1ay/ ammonium chloride 2.4y/l pH value adjusted using ammonia 2.6 activator, solution ugliness 5 Palladium as palladium nitrate 200 m”/
/ adjusted using concentrated nitric acid 40y/l ammonia pH value 2.7 upper H
No appreciable palladium condensation was observed on the copper backing during treatment in the palladium solution.

Through hole plating and negative mask condition 5μ
It was inspected after plating. The through-hole plating is defect-free and the negative mask remains uncovered.
And the contour of the conductive path was also free of defects.

Example 6 A copper-coated, perforated epoxy resin laminate was processed as in Example 1. During the step 11 process, activation with palladium and ethylamine was performed.

The palladium concentration was 200 mW/l. The amount of sulfuric acid was approximately stoichiometric, corresponding to the amount of ethylamine added. Macroscopically perceptible palladium precipitates were found on the copper foil using an ethylamine concentration of 1y, 9y/l (the pH of this solution was 2.0).

Nevertheless, the adhesion strength of the through-hole plated and electrochemically plated copper layers was not defective. When the activation pH value increased to 3.1, the condensation of palladium on the copper foil decreased obviously. The through-hole plating was free of defects. Sulfuric acid was then added to this solution and the pH value was adjusted to 3.2 using ethylamine.

The concentration of ethylamine was then 58 f/l. Again, the through-hole plating was defect-free, while there was no negative mask coverage by metal.

Example 7 In the same manner as in Example 6, an activator solution based on glycine or ethyl diamine was prepared. Unsatisfactory results were observed due to the initially selected chelating agent and palladium concentrations and the pFl value of the activator solution. concentration and p
By varying the H value, the working conditions that could be used were established. The table below shows how the conditions change and the results of the tests.

The composition of the solution is as follows.

Palladium as palladium nitrate... 4-4
．． For +S, see the table Concentrated sulfuric acid...10 Li/L chelating agent...See the table pH value arbitrarily adjusted using NaOH...See the table Example 8 Copper coating with one hole drilled in the same way as Example 1 Processed epoxy resin laminate. The chemical nickel bath composition as well as the nickel plating conditions (15th method step) were changed.

Chemical nickel bath No. 1 Chemical nickel hot air as described in Example 1 2 Nickel as nickel sulfate 6? /l malic acid 5oy7t succinic acid
10t/l dimethylaminoborane 29/lead as acetate
pH 5, 5 temperature adjusted with 0,3 rnf/L sodium hydroxide
50°C treatment time 15 minutes Chemical nickel bath volume 5 Same as chemical nickel bath N12, but thiourea (0.2 mt/!, ) f: was used instead of lead.

Using these three chemical nickel baths, defect-free through-hole plating was observed.

Example 9 This example demonstrates the use of a solvent soluble resist and a chemical copper bath.

As in Example 1, a negative mask was fabricated using a solvent-soluble photoresist in the N[L5 process step. Chemical metal plating in process step 15 was carried out in a conventional chemical steel bath such as is available commercially. The condition of the through-hole plating and negative mask was inspected after electrolytic copper plating and found to be free of defects.

Example 10 Following the method described in Example 1, 20 boards were made for soldering testing. Conditions during treatment in gaseous sulfur trioxide were varied according to Example 2. After the N124 process step, the printed circuit was subjected to reflowing. All printed circuit boards passed the soldering test without any defects.

Example 11 (Comparative) A steel-backed board with holes drilled out of an epoxy resin laminate was coated with photoresist. After creating the negative mask, conventional through-hole plating was performed. The individual processing steps were as follows: 1. Cleaning of the board in a normal commercial acid cleaner.

2. Washing in water.

& persulfate) Etching the board in IJum solution.

4. Washing in water.

5. Activation in an activation system based on palladium colloid. Therein, the individual process steps for activation were: a) Presoaking.

b) Treatment in palladium colloid.

C) Washing.

d) Facilitation.

e) Washing.

6. Chemical plating in a chemical nickel bath.

The chemical nickel feed had the same composition as described in Example 1. The through-hole plating was free of defects.

The negative mask was approximately half coated with metal. As a result, the board was found to be unusable.)7'C0 Example 12 (Comparative Example) A perforated copper-coated epoxy resin laminate was treated in an aqueous dimethylformamide solution (1:1) at room temperature for 5 minutes. Washed with water. It was then treated in a chromium/sulfuric acid-water mixture having the following composition: 10% by weight of dichromic acid, 50% by weight of sulfuric acid, 40% by weight of water.

This treatment lasted 5 minutes at room temperature. Corresponding to Example 1, the board was activated and chemically nickel plated.

Specifically, the boards were processed through a process step of 6 to N11/l as shown in Example 1.

After copper plating, it was clear that the holes were uncovered and therefore the board had not been through-hole plated.

Example 15 (Comparative) This example refers to a series of changes in method. The perforated copper-backed board was treated as follows: 1. Treatment in an SU3-containing atmosphere as described in Example 1.

2. Washing in water.

5. Activation similar to steps 11 to 14 of Example 1.

4. Board drying, interruption of continuous processing.

The subsequent production of negative chip masks was omitted.

5. Continuation of processing: cleaning, etching, step N of Example 1 [treatment in chemical nickel bath and electrochemical copper bath as in L7 to 10 and 15 to 1B.

Results: No complete through-hole plating was observed.

Example 14 (Comparative Example) Analogous to Example 5, an activated solution of 200 mf/l palladium was tested with 0.9597 t of 2-aminopyridine. Treatment in gaseous sulfur trioxide was omitted for some samples. The results are shown in the table below.

/′

Claims (18)

[Claims] (1) A method in which a substrate is provided with holes for electrical connections and a metal pattern is produced on the surface of the substrate by the attenuation method with the aid of a negative mask, comprising the steps of: gaseous sulfur trioxide; application of a negative mask corresponding to the conductive pattern to be produced, activation with an ion-generating noble metal solution, treatment in a reducing agent solution, chemistry in which metal plating is carried out only on the surface of the metal pattern to be produced. A method for producing a metal pattern, in particular a printed circuit, on an insulating substrate, characterized in that through-hole plating realized by plating or electrochemical plating and subsequent plating of a conductive pattern is carried out. (2) A process according to claim 1, in which sulfur trioxide is used during the treatment from 10 mg/l to a concentration corresponding to the vapor pressure of sulfur trioxide over 65% oleum at 25°C. (3) treatment in gaseous sulfur trioxide for 1 second to 20 minutes;
A method according to claim 1, which preferably lasts from 5 seconds to 5 minutes. (4) The method according to claim 1, wherein the negative mask is manufactured by photoresist or screen printing. (5) The method according to claim 1, wherein the activation solution contains a palladium salt. (6) A method according to claim 1, in which one or more compounds containing basic nitrogen atoms are added to the activation solution. (7) The method according to claim 6, wherein the nitrogen-based molar concentration ratio of the nitrogen atom-containing compound to the molar concentration of the palladium salt is at least 2. (8) The method according to claim 6, wherein the activation solution contains ammonium ions. (9) The method according to claim 6, wherein the activation solution contains a primary, secondary or tertiary amine. (10) The method according to claim 6, wherein the pH value of the activation solution is adjusted to 1 to 7, preferably 2 to 3. (11) The method according to claim 1, wherein the reducing agent solution contains an aminoborane compound. (12) The method according to claim 11, wherein the reducing agent solution contains dimethylaminoborane. (13) The method according to claim 1, wherein a solvent-soluble or alkali-soluble photoresist or screen printing ink is used as the negative mask. (14) The method according to claim 1, wherein a chemical nickel bath is used as the chemical plating bath. (15) The method according to claim 14, wherein the chemical plating bath contains aminoborane as a reducing agent. (16) The method according to claim 14, wherein the chemical nickel bath contains dimethylaminoborane. (17) The method according to claim 14, wherein the pH value of the chemical nickel bath is set between 5 and 7. (18) An insulating substrate in which holes for electrical connections are provided and a metal pattern is fabricated on the surface of the substrate by the attenuation method with the aid of a negative mask, the substrate being subjected to the following steps: treatment in gaseous sulfur trioxide, application of a negative mask corresponding to the conductive pattern to be produced, activation with an ion-generating noble metal solution, treatment in a reducing agent solution, the surface of the metal pattern on which metal plating is to be produced. 1. An insulating substrate characterized in that it has a metal pattern, in particular a printed circuit, made by chemical plating or electrochemical plating carried out by chisel, through-hole plating and subsequent plating of an electrically conductive pattern.