DE8560011U1 - Device for producing metal-clad base material for printed circuit boards - Google Patents

Description

The innovation relates to a device for producing metal-clad base material for printed circuit boards of the type specified in the preamble of claim 1.

Metal-clad base materials for circuit boards have so far only been produced discontinuously by pressing cut-to-size laminates coated with heat-curable resin and metal foils in multi-stage presses. Such a process is complex and produces base materials with varying quality within the individual board. For this reason, there has long been a desire for devices that could enable production in a continuous process.

A step towards continuity is shown by GB-A-2 108 §

S (039) S88272-74 Tetekoperer. (CB9) 983349 Bank accounts: 3ay=i:Veremsbank München 453100 {BLZ70020270) §

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SCHWABE - SANDMAIR · MARX

427, according to which glass fiber fabric strips provided with a heat-curable resin and the metal foil to be laminated are pressed together in a press device under pressure and temperature and the base material thus obtained is cut to length. The press device has a cooling zone in the entry area to avoid an undesirable pre-reaction of the resin before pressing. The press is a cyclical device, i.e. pressing takes place intermittently in such a way that the glass fiber fabric strip and the copper foil fed into the press remain stationary during the pressing process and the pressed end product is ejected in cycles. The circuit board produced in this way therefore consists of individual sections, the dimensions of which are limited by those of the heating plate and which are connected to one another by non-pressed, i.e., unusable sections. This device also results in strong quality fluctuations within a single plate, which is a problem given the customers' demands for high, homogeneous quality of the

20 circuit boards leads to large amounts of waste.

From EP-Bl-O 036 635 a device for joining several band-shaped material layers to form a composite film is known, which has a double-belt press with rotating, heatable steel belts. On the inlet side of the double-belt press, each steel belt is assigned a protective shield that serves as thermal insulation. The two protective shields prevent the material layers from heating up above room temperature. Double-belt presses of the aforementioned type are known from the production of decorative laminates. However, dimensional stability and surface quality are by no means as important as they are for printed circuit board material, apart from the fact that the pressure and temperature

35 conditions are not comparable.

SCHWABE · SANDMAIR · MARX

DE-Cl 216 522 discloses a method and a device for producing plate-shaped material from plastic, in particular for treating the surfaces of plates made of wood, plywood, chipboard and the like, whereby synthetic resin-impregnated paper, in particular melamine resin-impregnated paper, is used as the preferred starting material for the cover layers. Neither the method nor the device are suitable for producing a metal-clad base material for high-quality circuit boards. According to a variant that was only mentioned in passing, a sheet of metal, e.g. made of copper, can also be used as the top and bottom layer, which has previously been punched in the manner required to form a specific pattern for a printed circuit. These measures are ultimately useless and cannot be implemented in practice for various reasons. During the pressing process, the resin would escape from the glass fiber fabric through the holes in a copper sheet punched in this way, harden quickly on the pressing surface of the pressing device due to the short reaction times, build up unevenness on the pressing surfaces and make the device inoperable after a short time. In addition, according to DE-C 1 216 522, the various web-shaped materials are layered on top of one another and then fed into the device together as a package, whereby three shoe-shaped narrowing transverse slots are provided for pressing, whereby the package is pressed in two defined pressure stages while simultaneously being heated. This method is only suitable for low-pressure processes, with which, for example, decorative layers can be applied to prefabricated panels. However, for the production of metal-clad base material for circuit boards with a core made of paper or glass fiber fabric, a pressing pressure of at least more than 15 bar is required, at which such a layer stack cannot be transported through the pressing device with its two stages.

SCHWABE - SANDMAIR · MARX

The innovation is based on the task of creating a device for producing metal-coated base material for circuit boards of the specified type, which continuously takes up the starting materials, namely the glass fiber fabric webs on the one hand and the metal foil to be laminated on the other hand, and processes them into a metal-coated base material for circuit boards of high homogeneous quality and in particular high dimensional stability.

This object is achieved according to the invention by the features specified in the characterising part of claim 1.

Appropriate embodiments of this device are defined by the features of claims 2 to 6.

The advantages achieved with the innovation are based primarily on the fact that the pressureless preheating of the glass fiber fabric webs impregnated with the accelerated resin enables the formation of a base material for printed circuit boards with superior properties in a continuous manner.

The arrangement of a pressure-free preheating zone for glass fiber fabric webs provided with the heat-curable resin system in front of the heatable double belt press and thus the continuous production of a qualitatively perfect metal-laminated base material web is extremely surprising, especially when you consider that a hardened, i.e. fully reacted resin is inert and no longer forms a bond, and that the preheating of the glass fiber webs further advances the hardening reaction of the accelerated, already pre-cured resin system. The extent of the surprise for the experts is particularly clear in the light of the GB-A-2 108 427 and EP-Bl-O 036 635 mentioned above and the prejudice of the experts that can be seen from this. Because according to the experts, in order to avoid

To prevent an undesirable pre-reaction, the resin should be cooled after application and before the press, i.e. the entire reaction capacity of the resin should be reserved for the creation of the bond between the individual layers during the pressing process. Even more surprising is the measure of preheating a resin that has already lost part of its reaction capacity through pre-curing and whose reaction capacity decreases at an accelerated rate as a result of the acceleration during heating. Obviously, a pre-reaction and activation of the resin for the subsequent reaction under pressure takes place in the pressure-free preheating zone by preheating the accelerated and pre-cured resin, so that a bonding process begins immediately in the press itself.

With the new device, the differences observed in a discontinuous or cyclic process between the lower-quality edge areas and the high-quality middle section of the individual panels are eliminated, so that the base material obtained is of a uniformly high quality and can be cut to length to form panels of homogeneous quality.

According to a preferred embodiment, support rollers for the pressure belts of the double belt press are provided following the inlet drum pair.

Furthermore, it has proven particularly useful if spatially separate guide devices are arranged in the area of the pressureless preheating zone for the glass fiber fabric webs on the one hand and the or each metal foil on the other. This makes it possible for the impregnated glass fiber fabric webs to be brought together before entering the double belt press and to be preheated without pressure independently of the metal foils while reducing the viscosity of the resin system, while the metal foils in this area

are not yet connected to the glass fiber webs, i.e. are spatially and physically separated from them. Viewed in the direction of transport, the joining or connection of the preheated glass fiber webs and the metal foils only takes place behind this pressure-free preheating zone. The two are then pressed together at elevated temperatures and under pressure.

In the pressure-free preheating zone, the viscosity of the heat-curable resin in the impregnated glass fiber fabric webs is reduced, which means that the resin of the individual, touching glass fiber fabric webs is brought into close contact with one another and when the pressing pressure is subsequently applied, no more interfaces between the glass fiber fabric webs or their resin layers have to be overcome. The reduction in the viscosity of the resin that occurs in the pressure-free preheating zone also enables trapped air bubbles to escape from the resin layers, which would otherwise accumulate to form larger air bubbles and could hinder the desired, homogeneous quality of the base material.

The new double belt presses preferably have independently controllable temperature ranges in the pressure-effective heating zone. A pressure-effective cooling zone can be connected to the pressure-effective heating zone.

Double belt presses that can be used in conjunction with the pressureless preheating zone are described, for example, in EP-A 0 026 396 and EP-A 0 026 401.

The resin system of the glass fibre fabric webs is, as already mentioned, already pre-cured when the latter are brought together before the preheating zone of the double belt press, generally to the B stage. Preferably, a

advanced B-stage, ie with a lower resin flow than during pre-curing for multi-stage pressing. This multi-layer structure is generally heated evenly in the pressure-free preheating zone preceding the pressure-effective zone. The reduction in viscosity, during which the resin becomes soft and plastic, evens out any existing unevenness and ensures that the layers come into close contact. The preheating temperature depends on the resin system; it is preferably between 80° and 100 ^° C. From the pressure-free preheating zone, the multi-layer structure enters the pressure-effective zone at around 100'C, where it is immediately brought together with one or two, preferably separately preheated, metal foils and is advantageously pressed at 25 to 80 bar at an increasing temperature of, for example, 150° to 210 ^° C. The base material, now made up of several layers, is then cooled, preferably under pressure, in particular while maintaining the pressing pressure, advantageously below the glass transition point of the resin, optionally further tempered and cut to length. Cooling under pressure, ie in the press, serves to stabilize the high quality of the base material achieved by the continuous process, in particular to avoid deformation.

Other key benefits of the innovation include:

- optimal utilization of cutting material, as the continuous web can be cut to any length:

- the material savings, since only two-sided trimming is necessary -;

- the energy saving, since the cooling process and thus the energy waste in the multi-stage pressing process are eliminated;

- a qualitative improvement of the laminate, especially the dimensional stability;

- Reduction of rejects due to cleaner copper foil surface - Compared to discontinuously operating devices, the so-called "Multi-level presses!, ¹ result in a significant saving in work steps, namely the cross-cutting of the prepregs to format length, the cross-cutting of the Cu foils to format length, the pre-laying of the prepreg packages, the construction of the laminate packages, the separation of the laminate packages, the elimination of the costly press plates and the elimination of the cushioning paper which can only be used once.

A device for producing metal-clad base material for printed circuit boards is explained in more detail using the embodiment shown in the accompanying drawing.

The device shown in the figure has a double belt press 1 with a pressure-effective zone 2 and a pressure-free preheating zone 3 arranged upstream of this. The pressure-effective zone 2 is divided into a longer heating area 4 adjoining the preheating zone 3 and a shorter cooling area 5 following the heating area. The heating area 4 in turn has three independently controllable temperature areas 41, 42, 43. The double belt press 1 has a heated feed-in deflection drum pair 6, 6 ¹ arranged at a greater distance from one another before the pressure-effective zone 2, a correspondingly designed feed-out deflection drum pair 7, 7 ' arranged at a smaller distance from one another after the pressure-effective zone 2 and support rollers 11, 11 ' for the pressure belts 8, δ ¹ of the double belt press 1 following the feed-in deflection roller pair. To keep the temperature constant, the preheating zone 3 is positioned opposite the zones heated by the feed deflection drums 6.

SCHWABE · SANDMAIR - MARX - 9 ·- · «,·' . · ti*

»&Lgr; *

The pressure belts 8 of the double belt press 1 are separated by a pair of heat shields 9, 9 ^1. The latter consists of a cooled sheet metal. Cooling coils, here made of copper, are used for cooling, in which the flow rate of the coolant can be controlled so that precise temperature control is possible. Instead of the cooling coils, cooling pockets with forced guidance can also be provided. The heat shields 9, 9 ¹ are arranged so that they can be moved in a horizontal direction so that the temperature-controlled preheating zone can be brought closer to or further away from the pressure-effective zone 2, ie their spatial arrangement can also be controlled.

The functional principle of the double belt press used according to the invention

is based on the fact that the j continuously moved through the press

A uniform and uniform over the width of the web of material

constant pressure is applied over time. This is done here, for example, by I

the transfer of the pressure of in-press (not shown j

placed) pressure pads on the endless steel pressure belts 8, which I

run synchronously with the web through the press and at the same time as I

Finishing agents are used. Preferably, printing ribbons with relatively

I large mass, e.g. steel strips of about 2 mm thickness, are used, which |

ensure good heat transfer. ⁽

The heating area 4 of the press 1 has a length of e.g. 3 m. The cooling area 5 has a length of 1 m in the advantageous embodiment shown. The preheating zone 3 in this case preferably has a length of 40 to 100 cm.

In front of the double belt press there are spindle unwinders 12, 13 each with two spindles 14-17 for prepregs, i.e. glass fiber fabrics provided with the resin system, and another spindle unwinder 18 with two spindles 19, 21 for copper foils. Between the spindle unwinder 18 and the double belt press 1 there are guide rollers 22, 22' for the copper foils.

In the direction of production behind the double belt press there is an edge trimming device 23 and then a cutting device 24.

SCHWABE ■ SANDMAIR · MARX

To heat the preheating zone, the feed-deflection drum pair 6, 6 ¹ , which can be heated in turn, as shown in the following drawing in an exemplary form, but also any other heat source can be used. Means for temperature control, e.g. sheets 9, 9", can be provided.

In a preferred embodiment, the double belt press can have support rollers 11, 11' for the printing belts.

The advantage of the kit is that the pressure-effective heating area is divided into different temperature ranges that can be controlled independently of one another.

In the area of the pressureless preheating zone, in a preferred embodiment, spatially controlled guide devices are provided to support the separate feeding of the glass fiber fabric web and the metal foil.

In operation, the spindle unwinders 12, 13 produce four prepreg webs, i.e. webs provided with an epoxy hardener accelerator system and

advanced B-stage pre-cured glass fiber fabrics are removed,

brought together and fed to the preheating zone 3, where the four-layer structure is heated without pressure to a temperature of about 80° to 100° C, depending on the resin system. At the same time, the two spindles 19, 21 of the spindle unwinder 18 supply copper foils, which are guided separately from the prepregs between the respective heat shield 9 or 9 ¹ and the pressure belt 8 or 8 ¹ and are brought together with the prepregs immediately before the pressure-effective zone 2. While the temperature in the preheating zone is up to 10O ⁰ C as stated, that of the feed drum is higher, so that the copper foil is heated more than the prepregs. In the three temperature ranges 41, 42, 43 of the heating area 4 of the pressure-effective zone 2, the combined individual layers are heated at a pressure of over 25 bar at a temperature of 150° to j

SCHWABE SANDMAIR · MARX -11-

pressed to the base material web at a temperature rising to about 190° C and connected by hardening of the still reactive resin. The temperature of the first temperature range 41 is lower than that of the second 42, which can be the same as that of the third 43 and is 190° to 200 ⁰ C. In the subsequent cooling area 5, the base material web is cooled under pressure. In this delicate stage, the application of pressure prevents a reduction in quality, in particular deformation of the product. The base material web now leaves the cooling area at about

schWabE-SandmaIr-MarX - 12 -

10O ⁰ C, the cooling area 5. In the subsequent edge trimming device 23, the press belts on both sides of the base material web are removed, whereupon it is cut to a desired length in the cutting device 24.

A sewing zone can be arranged between the cooling zone and the edge trimming device to stabilize the shape of the base material.

The device according to the innovation advantageously works with a dwell time in the heating area 4 that corresponds to a feed rate within the double belt press of approx. 3 m/min. The dwell time and feed rate depend on the curing temperature and the reaction rate of the epoxy resin hardener acceleration system used.

If base material is only laminated on one side, a heat-resistant release film can be wound onto the corresponding spindle instead of the copper foil and fed into the double-belt press. A siliconized aluminum foil or aluminum foil laminated with polytetrafluoroethylene can be used as a release film. The release film can be peeled off the finished base material web after it has come out of the double-wall press and reused.

Although the device according to the invention has been illustrated for the production of a 6-layer base material, it is of course also possible to produce such materials with a different number of layers.

When using the device according to the innovation for producing base material for printed circuit boards, preferably such paper or glass fiber fabric webs are used.

c!et _r which contain an accelerated resin system. Preferred accelerators are:

2-Benzoylpyridine, 3-Benzoylpyridine,

4-benzoylpyridine,

2-Benzylpyridine,

3-Benzylpyridine, 4-Benzylpyridine, 2-Benzylaminopyridine

4-Dimethylaminopyridine

2-Methoxypyridine

4-tert-butylpyridine

3-Cyanopyridine * ⁵ 2-Hydroxypyridine

6-Amino-2-pyridine

2-Aminopyridine

3-Ethylpyridine 3-Ethyl-4-Methy1pyridine 2-Phenylpyridine

2,6-Diatninopyridine

3-methylpyridine

2-(Aminomethyl]-pyridine 2-Amino-4-methylpyridine 2,4-Dimethylpyridine

A second advantageous group of accelerators are the known substituted imidazo! compounds including imidazole itself, namely:
30

N-methylimidazole 2-methylimidazole 2-phenylimidazole 4-phenylimidazole 4-methylimidazole

2-Methylbenzimidazol

5,6-Dimethylbenzimidazole i-Methyl-2-phenylbenzimidazole 1,2-Dimethylimidazole 4,5-Dipehnyliinidazole 5,2-Ethyl-4-Hethylimidazole

Carbonyldiimidazole Imidazo]

2-Undecylimidazole 1-Cyanoethyl-2-phenylimidazole 10 2-Phenylbenzimidazole.

Particularly good results are achieved with a combination of dicyandiamide or berzyldimethylamine with the above-mentioned pyridines or imidazoles. In line with the innovation, a greater acceleration is generally sought than with known resin systems, above all in order to achieve an economical throughput speed in the press.

Resin-impregnated sheets in which the resin is pre-cured, in particular to the B stage, have proven particularly effective. A more advanced B stage, ie with a lower resin flow, is preferably aimed for than in pre-curing for multi-stage pressing.

The operation of the innovative device is further illustrated by the following examples.

schvvabe-sandmair-marx - 15 -

Example 1

A glass fabric of ±λ finished type, as is usually used for tape-laminated glass fiber epoxy resin laminates for printed circuit boards, weighing 200 g/m², was impregnated with a resin solution consisting of 100 parts of a polymeric, partially brominated bisphenol A glycidyl ether with a proportion of epoxidized novolak of 1 to 15%, preferably 5 to 12%, 3.2 parts of dicyandiamide, 0.28 parts of 3-methylpyridine and 80 parts of methyl glycol. The prepreg so impregnated and dried at 165°C had a resin content of 42% and a resin flow of 10%. Seven of these prepregs were preheated to 80 ⁰ C at a temperature increasing from 150° to 195°C under a pressure of 45 bar on the device according to the invention with a double-sided 35 μm thick copper layer to form a 1.5 mm thick laminate. Testing of the laminate surprisingly showed that

SCHWABE SANDMAIR - MARX -16-

Average positive results in dimensional stability with otherwise equivalent properties to commercially available laminates.

The resulting laminate has a thickness tolerance of - 3/100 mm. In comparison, the standards for rigid laminates provide for a tolerance of t. 13/100 mm, which is also fully exploited by products from the multi-layer press.

Example 2

A glass fabric as described in Example 1 was impregnated with a resin solution consisting of 100 parts of a polymeric, partially brominated bisphenol A glycidyl ether with a proportion of epoxidized novolak of 1 to 15%, preferably 5 to 12%, 3.4 parts of dicyandiamide, 0.33 part of 4-dimethylaminopyridine and 80 parts of methyl 1-glycol. The prepreg impregnated in this way and dried at 170 ^° C had a resin content of 44% and a resin flow of 8%. Several of these prepregs were preheated to 85°C with a double-sided 35 μm copper foil layer at a temperature increasing from 155 to 200°C under a pressure of 50 bar and continuously pressed on the device according to the invention to form a 1.5 mm thick laminate. Testing of the laminate also showed that this version had values for dimensional stability that exceeded the norm, while the laminate properties were otherwise comparable to those of commercially available products.

SCHWABE · SANDMAIR ■ MARX

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Example 3

A 100 g/m glass fabric with the same intended use as described in Example 1 was impregnated with a resin mixture consisting of 100 parts of a polymeric, partially brominated bisphenol A glycidyl ether with a proportion of epoxidized novolak of 1 to 15%, preferably 5 to 12% and with an epoxy equivalent weight of between 350 and 520, 3.0 parts of dicyandiamide, 0.40 parts of 2-amino-4-niethylpyridine and 80 parts of methyl glycol, and dried at 165°C. The resin content was 44% and the resin flow 10%. Two of these prepregs were preheated to 80 ^° C with a 35 µm thick copper foil layer on one side and continuously pressed using a release film at a temperature increasing from 150°C to 150°C under a pressure of 50 bar on the device according to the invention to form a 0.2 mm thick laminate. The test gave equally good results as in Example 2.

Examples 4 to 13 years

The recipes or operating conditions of the examples j

4 to 13 are summarized in the following table.

presents. j

Example 4 5 100 7 8th 9 10 11 12 13 &Mgr;&iacgr;&Ggr;&idigr;&iacgr;&igr;&eegr;&Igr;&bgr;&Igr; I 100 JOO 6flil/million too 100 100 100 100 100 100 Epoxldbtjul &ngr;&ogr; lun( tjowlcfil )5(&Idigr;&Lgr;?0 »n/f > 4&eegr;&pgr;&Lgr;&eegr;&ogr; J6I1/1I0 J60/410 )60/<ilO J6O/5OO )6&Ogr;/5&Pgr;&Pgr; J60/WW Share npoxWderler Nauoliick in the landlord 5 5 J.J IO 10 )» 5 10 15 OicyoadI em I ti 3, J 3.) en J ₁ O 1.0 3.4 J.I >.? 3.2 3.0 _Hnthvlalvl«ol OD 00 0.1!» &EEgr;&Pgr; en &bgr;&ogr; OO B.O. 80 80 Uetnry Idlmnt hy I ami n 0.10 &ugr;, &igr;&ogr; 0.20 O.IB Curbtiny Idl imi iln/n I 0.17 0.24 . 4-Mothvl iniilHfol &ldquor; &eegr;.27 0.28 n _r 2i . ?* HothvlUldaro) 0.15 2-Hethy llieni Ie &igr; t!a/ol 0)22 0.10 .2-Phnnyllmldn/n| ₁ )O 0.21 ?-Clhyl-6.»irif»y I In jilnrnl 0,?| 0.22 0.7? Z-Afflinn-4 ·&eegr;&bgr; triy |py r idin 0.28 0.J0 4-0 litel hy I um l nnpy r I din 0.2 0.16 0.19 '«-lorllHrB!) Hutylpyridine 0.17 3-OenzylpyrJdine 200 0.25 0.15 100 Glass fabric g/m zno 200 170 200 200 100 100 48 165 6Θ; Lacklortemp. during program preparation 160 UO 44 16b 165 170 160 165 50 160 Marzgehall <lj 43 0 44 4) &Lgr;? 4&bgr; 50 9 60 HaririuO ID 9 190 fO 9 The 10 B 190 &bgr; PreOteiip, (max.) 195 190 50 195 190 190 195 195 45 190 PreO pressure in bar 40 45 1.6 50 50 45 50 45 0.25 40 Lanlnatatttrke Mm 1." 1.5 IB 1.2 OK 0.17 0.54 0.05 I 0.15 Cu-Bnlngung 55 μηγ e elntMtltig/z ■ iwolaeltlg &bgr; &zgr; !K &zgr; t &khgr; I I - &zgr; Separation quiff I &kgr; - - - - - - -

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Claims (5)

1. Device for producing metal-clad base material for printed circuit boards a) with a pressing device for pressing glass fibre fabric webs provided with a thermosetting resin and a metal foil to be laminated under pressure and temperature, and b) with a cutting device for the base material thus obtained,
characterized by the following features: c) the pressing device is a heatable double belt press (1) with a pressure-effective heating area (4) 15 formed; and d) a pressureless preheating zone (3) for the joined glass fibre fabric webs is arranged immediately in front of the double belt press (1). 2. Device according to claim 3, with an inlet drum pair (6, 6') and with an outlet drum pair (7, 7 ^' ), characterized in that support rollers (13, 31'5) for the printing belts (8, 8 ^' ) of the double belt press (1) are provided following the inlet drum pair (6, 6 ^' ). 3. Device according to one of claims 1 or ₂ , characterized in that the pressure-effective heating region (4) is followed by a pressure-effective cooling region (5). 4. Device according to one of claims 1 to 3, characterized in that the pressure-effective heating area (4) is divided into independently controllable temperature areas (41, 42, 43). 5. Device according to one of claims 1 to 4, characterized in that spatially separated guide devices (22) for the glass fiber fabric webs and the or each metal foil are arranged in the region of the pressureless preheating zone (3). 6- Device according to one of claims 1 to 5/ characterized in that the distance between the two inlet drums (6, 6') is greater than the distance between the two outlet drums (7, 7 ¹ ).