WO2000042830A1 - Method and device for producing copper foil which is coated with polymers on both sides and which is laminated onto printed circuit boards - Google Patents

Abstract

The invention relates to a method and device for producing copper foil (1) which is coated on both sides with polymers (7, 15) that can be hardened by thermal energy or radiation, and which is laminated onto printed circuit boards (28). The inventive method is characterized by the following method steps. Two, preferably 50 mu m thick metal foils (2) are bonded in the edge area using a hot-melt-type adhesive. The foil assembly (5) is coated with a conductive lacquer (7) with a thickness ranging from 5 to 20 mu m and, after having been prehardened, is dipped as a cathode into an electroplating bath (9). Said foil assembly is electroplated on both sides with copper (1) having a thickness ranging from 1 to 10 mu m. In a roller coating method, a dielectric (15) is applied with a thickness ranging from 5 to 100 mu m to both sides of the copper foil (1). After the dielectric (15) has been partially prehardened, the edges of the metal foil (2) including the areas of the coatings (lacquer/copper foil/dielectric (21)) located thereon are cut away, and two three-layered foil assemblies (26) are obtained which are comprised of copper foil (1) coated with polymers (7, 15) on both sides and which are laminated onto printed circuit boards (28) using laminator rollers (30) and a short-duration hot press (31).

Description

Process and device for producing copper foil, which is coated on both sides with polymers and which is laminated on printed circuit boards

The invention relates to a method for producing copper foil, which is coated on both sides with polymers, according to the preamble of patent claim 1, devices according to the preambles of patent claims 12 and 17 and a copper foil coated on both sides with polymers, according to the preamble of patent claim 9.

Electrolytically deposited copper foil is preferred because of its high degree of purity in electronics, especially for the production of electrical conductors.

The production of this copper foil has been described for more than thirty years by electrodeposition on a metal roller that is immersed in a copper electrolyte. Films are usually produced in thicknesses of 18 and 36 μm. It is also possible to produce thicknesses from 9 to 12 μm. Carrier foils must be used below 9 μm. Aluminum foil with a thickness of 50 μm is usually used for this. The copper foil thickness limits the progressive miniaturization because the undercutting of the conductors corresponds to the foil thickness or the conductor height. The aim of future development is therefore to produce a conductive copper layer that is as thick as 1 to 5 μm.

This is currently achieved by chemical copper deposition on oxidatively roughened circuit board surfaces provided with palladium seeds. The disadvantage of this so-called additive or semi-additive process is that chemical or physical roughening of the plastic surface to be copper-plated requires a high level of process reliability, which cannot always be guaranteed.

The removal of fillers stored in the resin matrix by means of acids also requires a filler content of more than 30% by weight in the outer layer of the dielectric. Due to sedimentation, this is not always guaranteed with sufficient certainty.

The use of palladium catalysts and copper complexing agents is also very expensive and problematic for wastewater treatment.

There is therefore a desire among printed circuit board manufacturers to use a 5 μm thick copper foil.

The published patent application P 22 42 132 describes a process for producing 5 μm copper foil. Here one side of the carrier foil is galvanized with 5 μm copper. A polymer is then applied to this film, which is preferably cured and serves as an insulating plate. With this method, a high electroplating speed is not to be expected, since only half the The circumference of the deflection rollers is used as a galvanizing or immersion section. The copper surface is not protected against particle damage after the carrier foil has been removed.

PCT / SE93 / 00786 / WO94 / 12008 describes a process for the production of printed circuit boards in which rolled copper foil or aluminum foil with a chrome layer is galvanized with copper before the galvanizing. The mechanical separation of the carrier foil and the electrolytic copper foil was thus realized.

The carrier film with a thickness of 100 to 400 μm was galvanized on both sides with 1 to 36 μm copper and pressed on both sides with epoxy resin prepreg reinforced with glass fiber. The carrier foil serves as a substitute for pressed sheets. After pressing, two laminates can be detached from the carrier film.

US Pat. No. 4,234,395 describes that the separation of the copper from the aluminum carrier is achieved by galvanizing the AL surface with zinc or indium.

The coating of copper foil with thermosetting polymers is described in US Pat. No. 5,362,534. First a first layer of a thermosetting polymer is applied and cured, then a second polymer layer is applied over this first layer, which has only been cured half. Two foils coated in this way are then pressed to form a flexible printed circuit board. A copper foil coated in this way can also be pressed onto printed circuit boards. The first hardened thermosetting polymer layer ensures a flat surface, the second semi-hardened thermosetting polymer layer ensures the filling of the conductor interstices and the contact holes with resin. The production of a double-coated copper foil is very complex. The risk of damage to the copper surface is very high. The pressing in multi-daylight presses leads to considerable dimensional instabilities.

US Pat. No. 5,837,155 describes a method and a resin formulation for coating copper foils and lamination on printed circuit boards. Here, a resin combination is used, which consists of a thermally curable epoxy resin with a melting point below 110 ° C and a resin that has double bonds. This resin combination enables the radiation-curable double bond-containing component to be crosslinked with UV rays after coating and drying. The then uncrosslinked, thermally curable epoxy resin component leads to quick bonding to the circuit board surface during hot lamination. This is pre-coated with the same resin and also partially cross-linked with UV rays after drying. When laminating with a hot roll laminator, the thermally curable components melt and bind together. The coating of the printed circuit board is particularly necessary because it is not possible to apply the insulation layer of 60 to 100 μm required for the adequate covering of the conductor and to partially crosslink it evenly with UV rays. Because the radiation intensity is greatest on the surface of the dielectric and then in the lacquer layer decreases significantly, the adhesiveness of the surface is greatly reduced and the radiation curing is further promoted here than in the interior of the dielectric. The layer thickness is also limited to 30 to 60 μm by the rollers, screen or curtain coating. This makes it necessary to coat the circuit board and the copper.

EP 0 698 232 B1 describes a two-layer coating process in which the first layer consists of largely solvent-free lacquer which is highly viscous to solid at room temperature. This varnish is applied to the circuit board surface by means of heated rollers. All components of this varnish have a softening point in the range of 20 to 25 ° C. The layer thickness of the process is up to 200 μm. The low-solvent to free lacquer is pre-crosslinked thermally or by UV rays. The melting point can thus be set to a suitable laminating temperature. All components then melt at the desired lamination temperature. The second layer consists of a high molecular weight polymer. This is applied either from solution or as a dry film resist in a small thickness of up to 20 μm. This high molecular weight polymer with a molecular weight of 2000 to 10000 can also be applied over a copper foil as a carrier foil. This copper foil is then removed by etching and the copper plating can be carried out chemically down to 5 μm using the copper treatment structure in the dielectric surface.

It is therefore the object of the present invention to make available a method and a device with which it is possible, in particular for the production of sequential multilayers, to coat one with a dielectric. 5 μm copper foil, which can be laminated onto the circuit board with the shortest possible contact time, does not require any pre-coated circuit boards and, with a layer thickness of up to 100 μm, ensures a safe filling of the conductor interstices, filling of the blind holes and contact holes and in an economical manner Production process is producible. In addition, the required etching resist should already be present on the copper foil, since this not only saves a coating process, but also achieves the maximum degree of particle freedom required for the ultra-fine conductor technology. The sensitive copper surface should also be protected against the ingress of oxygen. The copper layer should be drilled with CO2 lasers at the same time as the dielectric. The aluminum foil should be mechanically removable.

All of these and other related tasks are solved by means of a method, a film composite and devices according to independent patent claims 1, 9, 12 and 17. Particularly preferred variants of the method according to the invention and associated devices according to the invention are the subject of the corresponding dependent Process or device claims. In particular, the invention makes available a process for producing copper foil which is coated on both sides with polymers and is laminated onto printed circuit boards, which is characterized by the following process steps:

Carrier foils 2 made of aluminum, which are approximately 50 μm thick, are used as carrier foils for the electrolytic deposition of preferably copper foils 1 in the thicknesses from 1 to 10 μm. be wrapped. The carrier films 2 are optionally precoated on the coating side with an external mold release agent. Two of these carrier foils 2 unwound from the rolls are coated in the edge region by means of a heated nozzle 3 with a thermosetting melt in a width of 5 to 10 mm and connected to a foil composite 5 by means of two laminating rollers 4.

This film composite 5 is then coated by means of two roller coating units 6 with low-solvent to solvent-free lacquers 7 with a temperature of 20 to 55 ° C. in thicknesses of 5 to 20 μm. The paint 7 contains a graphite and carbon black content of 30 to 70% by weight. In a special embodiment of the method according to the invention, the lacquer 7 is soluble in solvent and in alkalis after partial curing.

The paint 7 is partially pre-cured in a downstream dryer 8. The film composite 5 is switched as a cathode with 4 A / dm-2. This film composite 5 is now guided into a galvano bath 9 with a bath liquid 10, as shown in FIG. 2, which has metallic deflection rollers 11 outside the bath liquid 10 and plastic rolls 12 inside the bath liquid 10. The length of the electroplating bath 9 and the number of deflection rollers 11 depend on the layer thickness of the copper foil 1 to be achieved and the coating speed.

A bath 13 for the oxidative roughening of the deposited copper foil 1 is arranged after the electroplating bath 9. The film composite 5 then passes through a rinsing station 14. Before coating with a dielectric 15, the film composite 5 is applied on both sides Lacquer 7 and the copper foil 1 dried by means of air nozzles 16.

The dried film composite 5 with the lacquer 7 applied on both sides and the copper foil 1 is now, as shown in FIG. 3, fed to a double-sided roll coating system which consists of two roll coating units 17. With these roller coating units 17, the low-solvent to solvent-free dielectric 15 is applied in a preferred thickness of 60 to 80 μm. Each roller coating unit 17 has a metering roller 18 and an application roller 19.

The dielectric 15 consisting of epoxy resins is heated in a tank to 20 to 55 ° C. and fed to the two roller coating units 17. The application rollers 19 are rubberized and the metering rollers 18 are surrounded with a Teflon layer, so that the warm dielectric 15 does not cool down until it is coated. The rollers are not heated.

The application of the dielectric 15 is carried out with a coating viscosity of 5 to 20 Pas. A viscosity of 200 mPas is achieved in a downstream IR circulating air dryer 20 and the coating is optimally flat. After "leveling" and drying, the film-dielectric composite 21 is cooled to room temperature in an air cooler 22, the edge is cut off with a knife 23 and wound up separately on a roll 24.

The film-dielectric composite 21 is divided on cooled rolls 25, and each composite made of Al-carrier film 2 / lacquer 7 / copper foil 1 / dielectric 15 (three-layer Foil composite 26 with carrier foil 2) is wound onto one winding station 27 each.

4 shows the lamination of printed circuit boards 28. Before the lamination, the printed circuit board 28 is preheated by means of heated rollers 29. The Al carrier foil 2 / lacquer 7 / copper foil l / dielectric 15 composite (three-layer foil composite 26 with carrier foils 2) to be laminated are unwound from the two winding stations 27 and laminated onto the printed circuit board 28 with heated laminator rollers 30. The laminated circuit board 28 is then fed to a short-cycle hot press 31 which is equipped with a pressure of 2 to 20 bar. After pressing for 10 to 60 seconds at 130 to 220 ° C., the printed circuit board 28 is removed from the mold, freed of the carrier foil 2 consisting of aluminum via two transport rollers 32 and cooled in an air cooler 33. The carrier foil 2 made of aluminum is wound up separately on rollers 34.

The process steps of gluing and duplicating the carrier foil 2 consisting of aluminum and the coating with conductive lacquer 7, the galvanic production of the copper foil 1 and the coating with dielectric 15 can be operated continuously in succession. They can also be carried out batchwise in separate production units.

The invention is illustrated by the following example: 1.Glue and duplicate the carrier foil (metal foil) 2

Aluminum rolled foil: thickness 50 μm, width 500 mm Manufacturer VAW Vereinigte Aluminumwerke

Release agent application: 1-2 μm release agent: 1% solution PAT 607 from Würtz

Edge bonding: epoxy polymer formulation C

Melt nozzle temperature: 50 ° C

2. Coating the film composite 5 with the conductive lacquer 7

Recipe A: 30.00 parts by weight of Epikote 828 EL from Shell 20.00 parts by weight HT 9490 from Ciba 24.00 parts by weight graphite from Sigri Hoechst 25.80 parts by weight of carbon black 0, 20 parts by weight of 2 ethyl- 4-methylimidazole from BASF

100.00 parts by weight 100% by weight

Coating speed: 2 m / min

Dryer length: 2 m

Dryer temperature: 180 ° C

Paint temperature: 50 ° C

Order viscosity: 20 Pas

Roll surface: R _z 10 μm

Layer thickness of the lacquer 7: 5 μm

Roll gap: 0 mm 3. Coppering the film composite 5 from aluminum carrier film 2 / conductive lacquer 7

A galvanic bath 9 is used to galvanize the film composite 5 made of aluminum carrier film 2 / lacquer 7 with a 4 μm copper layer (copper film 1). Uniplate CU from Atotech Germany is used as the bath electrolyte 10 as the copper electrolyte.

The bath liquid 10 is heated to 40 ° C. The current density is 4 A / dm-2. With a deposition speed of 1 μm / min and a coating speed of 2 m / min, a copper layer thickness of 3 to 4 μm is deposited on both sides on an immersion path of 8 m.

In a process of micro-roughening called oxidation, a surface of the deposited copper foil 1 that improves the adhesive strength to a dielectric 15 is achieved in the bath 13. For micro-roughening, 50% from Cookson Electronics is used as treatment bath Alpha Prep PC 7023 C in bath 13. The dwell time in the bath is 60 seconds. at 40 ° C.

The rinsing station 14 is then rinsed with deionized water and dried by means of air nozzles 16. 4. Coating the film composite 5 made of aluminum carrier film 2 / lacquer 7 / copper film 1

The surface of the copper foil 1 is coated with the solvent-free thermal and radiation-curable dielectric 15 by means of the roller coating units 17.

Recipe C: 16.00 parts by weight Rütapox VE 4704 Bakelite

16.00 parts by weight DEN 438 from Dow Chemical

16.00 parts by weight of HT 9490 from Ciba

48.40 parts by weight of magnesium hydroxide

2.20 parts by weight of 2-ethyl antrachinone from BASF

0.50 part by weight of 2-ethyl-4-methylimidazole, from BASF

0.90 parts by weight A 1100 Union Cabide

100.00 parts by weight 100 wt.

Coating speed 2 m / min roller temperature: 25 ° C temperature dielectric 15: 50 ° C application viscosity: 10 Pas roller gap: 180 μm

Application roller jacket: rubber coating 15 mm metering roller jacket: Teflon 5 mm dryer temperature: 150 ° C dryer length: 4 m

The properties of the coated dielectric 15 are as follows:

Layer thickness: 90 μm Softening range: 80 to 90 ° C 5. Coating the film composite 5 made of aluminum carrier film 2 / lacquer 7 / copper film 1 with the low-solvent, thermally curable dielectric 15

Recipe D: 70.00 parts by weight of resin VE 3746 80% by weight from Bakelite

28.00 parts by weight of magnesium hydroxide 1.00 parts by weight of 2-methylimidazole from BASF 1.00 parts by weight of Z 6040 from Dow Corning

100.00 parts by weight 86 wt.

Coating speed 2 m / min Roll temperature: 25 ° C Temperature dielectric 15: 25 ° C Application viscosity: 5 Pas roll gap: 180 μm

Applicator roller sheathing: rubber coating 15 mm Metering roller sheathing: Teflon 100 μm dryer temperature: 180 ° C dryer length: 4 m

The properties of the coated dielectric 15 are as follows:

Layer thickness: 60 μm Softening range: 60 to 80 ° C gel time at 170 ° C: 10 sec 6. Laminating the three-layer film composite 26 from aluminum carrier film 2 / lacquer 7 / copper film 1 / dielectric 15 on printed circuit boards 28

Circuit board temperature 28: 60 ° C. Rollers temperature 29: 60 ° C

Temperature of the laminator rollers 30: 120 ° C

Short cycle hot press 31:

Temperature: 170 ° C

Pressure: 10 bar

Pressing time: 20 sec.

Curing in a forced air oven: 30 min at 150 ° C

Adhesive strength of the copper foil 1 galvanically reinforced to 35 μm on the dielectric 15: 1.4 N / mm.

Claims

Expectations 1. A process for the production of copper foil (1) which is coated on both sides with polymers, in particular lacquers (7, 15) and which is laminated on printed circuit boards (28), characterized in that two metal foils (preferably 50 μm thick) coated on the coating side with release agent ( 2) are connected in the edge area with a hot-melt adhesive to form a film composite (5) and that this film composite (5) is coated with a conductive lacquer (7) in a thickness of 5 to 20 μm and, after precuring, as a cathode in a galvano bath (9) dipped and galvanized on both sides with a copper layer (1) of 1 to 10 μm, preferably from 3 to 5 μm, and a dielectric (15) in the thicknesses of 5 to 100 μm in each case after the oxidative micro-roughening on the copper layers (copper foil (1)) is applied in the roller coating process, and that after the drying and the partial pre-curing of the dielectric (15), the edges of the metal foils (2), including those thereon The areas of the coatings (foil-dielectric composite (21)) are cut off and two three-layer foil composites (26) are obtained on carrier foil (2), which consist of copper foils (1) coated with conductive lacquer (7) and dielectric (15) are laminated on printed circuit boards (28) for the production of sequential multilayers. 2. The method according to claim 1, characterized in that low-solvent to -free high-viscosity lacquers (7, 15) are preheated to 20 to 50 ° C and then fed to a roll coating system with unheated rolls (18, 19), the application rolls (19th ) rubberized and the metering rollers (18) are coated with plastic. 3. The method according to claim 1 or 2, characterized in that low-solvent to solvent-free paints (7, 15) with a viscosity of 5 to 20 Pas with rubberized rollers (19) in thicknesses of 5 to 100 microns at a temperature of 25 to 55 ° C on the metal foils (2) and / or the copper foil (1) are applied at a temperature of 20 to 25 ° C. 4. The method according to any one of claims 1 to 3, characterized in that solvent-free paints (7, 15) are used which have a softening point of less than 20 ° C and are thermally and by radiation curable. 5. The method according to any one of claims 1 to 4, characterized in that the applied dielectric (15) is brought to a softening range of 60 to 130 ° C by drying or by partial pre-curing. 6. The method according to any one of claims 1 to 5, characterized in that the dielectric (15) to improve the adhesion to the copper foil (1) contains an adhesion promoter, which is preferably made of y-amino-propyl-trioxisilane or from N-ß -Amino-ethyl-y-amino-propyl-trimethoxi-silane. 7. The method according to any one of claims 1 to 6, characterized in that the copper foil (1) coated with a partially pre-hardened dielectric (15) in the form of a three-layer film composite (26) on printed circuit boards (28) is laminated on, which are precoated with a partially precured dielectric. 8. The method according to any one of claims 1 to 7, characterized in that the laminate laminate (26) laminated to the surface of the printed circuit board (28) with preferably heated to 60 to 130 ° C in a short-cycle hot press (31) is cured at 130 to 220 ° C in 10 to 120 seconds. 9. Copper foil (1) coated on both sides with polymers (7, 15) according to one of claims 1 to 8, characterized in that it is in the layers of polymers (7, 15) are preferably thermally and radiation-curable epoxy polymers. 10. Both sides with polymers (7, 15) coated copper foil (1) according to one of claims 1 to 9, characterized in that as a partially pre-hardened lacquer layer (7) a dark conductive layer which is easily absorbing laser radiation and soluble in organic solvent or in alkaline media is provided with a thickness of 5 to 20 μm. 11. Copper foil (1) coated on both sides with polymers (7, 15) according to one of Claims 1 to 10, characterized in that a dielectric (15) with a melting range of 60 to 130 ° C is provided. 12. The device, in particular for carrying out the method according to one of claims 1 to 8, characterized in that in front of and behind a galvano bath (9) a roller coating unit (17) for applying polymers (7, 15) is arranged. 13. The apparatus according to claim 12, characterized in that a roll coating unit (17) is used, the rubberized, unheated application rollers (19) and plastic-coated unheated metering rollers (18). 14. The apparatus of claim 12 or 13, characterized in that for drying and partial pre-curing of the dielectric (15) an infrared radiation dryer (20) is used with countercurrent air flow, followed by an air cooler (22) and, if necessary, a UN radiation oven is. 15. Device according to one of claims 12 to 14, characterized in that heated nozzles (3) are provided for applying a preferably thermosetting melt to the edge regions of the metal foils (2) for connecting the metal foils (2) to form a film composite (5). 16. The apparatus according to claim 15, characterized in that for separating the film composite (5) into two three-layer film composites (26) with carrier film (2) knives (23) are provided for cutting off the glued edge of the film composite (21). 17. The device according to one of claims 12 to 16, characterized in that a short-cycle hot press (31) is used with a press stage, before which a with heated rollers (29) equipped film roll laminator is arranged.