CN1004987B - Method for producing metal-clad laminates for printed circuit boards - Google Patents

Abstract

A metal-clad laminate for printed circuit boards is produced using a double belt press (1). Several sheets of laminate material, impregnated with an accelerated resin system and pre-cured, are preheated in a preheating zone (3) before being fed into the pressing zone (2) of the double belt press (1) and then fed together with the metal foil into the heating zone (4) of the pressing zone (2). In which several layers of material are pressed to form a metal-clad plate. In the cooling zone (5) of the pressing zone (2), the sheet metal-clad plate is cooled, preferably under pressure, optionally after heat treatment, trimmed and cut to the desired dimensions. The metal-clad laminated plate prepared by the method has excellent texture and uniform size.

Description

Method for producing metal-clad laminate for printed circuit board

The invention relates to a process for producing a metal-clad laminate for use as a printed circuit board according to the preamble of claim 1.

Metal clad laminates for printed circuit boards are typically manufactured using discontinuous processes. In manufacturing, a laminate cut to size impregnated with a thermosetting resin is pressed together with a metal foil on a multi-layer press. The manufacturing method has high cost, and each produced metal-clad laminated plate has uneven quality. Thus, it has long been desirable to use some continuous production process.

In uk patent application No.2,108,427, a process is disclosed which advances one step towards continuous production. The method described therein uses a press equipped with two heated plates to intermittently press in such a manner that both the fabric sheet and the copper foil fed into the press are fixed during the pressing operation and the finished pressed product is periodically fed out. The product thus produced is in a segment, the dimensions of which are defined by the dimensions of the heating plate and which are interconnected by unpressurized portions, that is to say by unusable portions. Even so, the quality of different parts on one plate is different, so that when a user needs a product with uniform quality, a large amount of product scrapping is necessarily caused.

The object underlying the invention is to propose a continuous process for producing a metal-clad laminate for printed circuit boards.

This object is achieved by the features of the characterizing part of claim 1.

The method of operation of preheating the laminate sheet coated with the thermosetting resin system under non-pressurized conditions makes it possible to use a suitable twin-belt press, and thus, it is possible to continuously produce a metal-clad laminate sheet of excellent quality. This fact is completely unexpected, especially when it comes to the fact that the resin after hardening (that is to say the resin that has finished reacting) is inert and no longer has adhesion, and that the curing reaction of the accelerated and pre-hardened resin system is further accelerated as a result of the preheating of the laminate plates. The highly unexpected sense perceived by the expert appears most clearly if viewed in light of the above-mentioned uk patent application. Because in order to avoid undesired pre-reactions, it is proposed in that application to cool the resin after its application and before the pressing operation, that is to say to preserve the total reactivity of the resin, in order to create an adhesive effect between the layers during the pressing operation. This view seems to be extremely paradoxical if the proposed method for a certain normal hardening, that is to say for an unhoaked and unhoaked resin, is considered to be the measure of the invention, namely the measure of preheating a resin which has lost part of its reactivity due to the pre-hardening and whose reactivity has been lost at a faster rate by the action of the procoagulant during heating. However, this preheating measure, while directly contradicting the one recommended in the prior art, actually makes it possible to produce the metal-clad laminates of printed circuit boards continuously. Obviously, the pre-reaction, which results from preheating the accelerated and pre-hardened resin, causes the resin to be activated in a subsequent reaction under pressure, so that the resin itself develops instantaneous adhesion in the press.

As a result of the method of the present invention, the disadvantages observed in the intermittent or batch method described above, i.e., the low quality of the edge region and the high quality of the intermediate region of each sheet, which are different in quality at the different regions, are eliminated, so that the produced metal-clad laminate sheet is high in quality and uniform, and can be cut into a certain length to produce a sheet of uniform quality.

The manner of operation of a twin-belt press is disclosed, for example, in the production of decorative plywood. However, in the production process of the present invention, there are more stringent requirements on the temperature and pressure used in the twin belt press. There are also more stringent requirements for stable consistency of the surface quality and dimensions of the product delivered from the press. For example, the types of twin belt presses suitable for use are described in European patent application Nos. 0,026,396 and 0,026,401.

The layers of thermosetting resin-based laminate are preferably fed together before the preheating zone of the twin-belt press. The resin system is here pre-hardened, usually in the B-state. The aim here is preferably to achieve a higher B-state, that is to say a lower flowability of the resin than during the pre-hardening in the multi-layer pressing process. This multilayer structure is generally heated uniformly in a preheating zone preceding the pressurizing zone. Any unevenness that may be present is leveled at this stage, since the viscosity of the resin decreases as it softens and becomes plastic. The preheating temperature used depends on the system of the resin, and the temperature is preferably 80-100 ℃. The multilayer structure is passed from the preheating zone to the pressing zone at a temperature of about 100 ℃ so that one or both of its faces is immediately bonded to one or both of the metal foils, which have been preheated, preferably individually, in advance, and is preferably pressed at a pressure of, for example, 25 to 80 bar under conditions of increasing temperature, for example, 150 to 210 ℃. The metal-clad laminate, which is now composed of several layers of material, is then cooled, preferably under pressure, by cooling under pressure, preferably to a temperature below the secondary transition temperature of the resin. If necessary, it is further heat treated and then cut to the desired size. The aim of cooling under pressure, that is to say in a press, is to ensure that the metal-clad laminate produced in this continuous manner has a high quality, in particular to prevent deformation thereof.

Some resins that are useful as fast setting thermosetting resin systems, such as epoxy, polyester and phenolic resins.

The use of an epoxy hardener-catalyst system is advantageous as a quick setting thermosetting resin system. Among the pyridine compounds, the following are suitable coagulants:

2-benzoylpyridine

3-Benzoylpyridines

4-Benzoylpyridine

2-Benzyl pyridine

3-Benzyl pyridine

4-Benzyl pyridine

2-Benzyl aminopyridine

4-Dimethylaminopyridine

2-Methoxypyridine

4-Tert-butylpyridine

3-Cyanopyridines

2-Hydroxypyridine

6-Amino-2-pyridines

2-Aminopyridine

3-Ethylpyridine

3-Ethyl-4-methylpyridine

2-Phenylpyridine

2, 6-Diaminopyridine

3-Methylpyridine

2- (Aminomethyl) -pyridine

2-Amino-4-methylpyridines

2, 4-Lutidine

A second group of coagulants which can be used are substituted imidazole compounds known per se, including imidazole itself, comprising in particular:

N-methylimidazole

2-Methylimidazole

2-Phenylimidazoles

4-Phenylimidazoles

4-Methylimidazole

2-Methylbenzimidazole

5, 6-Diphenylmethylimidazole

1-Methyl-2-phenylbenzimidazole

1, 2-Dimethylimidazole

4, 5-Diphenylimidazole

2-Ethyl-4-methylimidazole

Carbonyl diimidazoles

Imidazole

2-Undecylimidazole

1-Cyanoethyl-2-phenylimidazole

2-Phenylbenzimidazole

Very good results have been obtained by applying a method of combining dicyanodiamide or benzyldimethylamine with the above-mentioned pyridines or imidazoles. At the same time, the general object of the present invention is to achieve a higher setting acceleration than known resin systems, and in particular to achieve economically reasonable throughflow rates on such presses.

Other basic advantages of the process of the invention which are considerable are as follows:

Since the semifinished blank produced is a continuous sheet, which can be cut to the desired dimensions, the semifinished sheet product produced can be used most fully;

material saving is possible since only the two sides of the produced plate need to be trimmed;

energy savings can be achieved in that the cooling operation and the resulting energy consumption in the multi-layer press process are avoided;

-improving the quality of the laminate, in particular ensuring a constant uniformity of its dimensions;

The scrap rate is reduced since the copper foil surface is cleaner.

The invention reduces the number of processing operations compared to the discontinuous production process of the so-called multi-layer press method, and can eliminate the need for special operations such as cutting the semi-cured sheet to a predetermined length, cutting the metal foil to a predetermined length, pre-handling the semi-cured sheet stack, stacking the laminate sheet stack, separating the laminate sheet stack, eliminating expensive press plates, and eliminating the need for backing paper that can be used only once.

The invention will now be described in more detail with reference to specific embodiments of equipment (illustrated in the accompanying drawings) suitable for carrying out the method of the invention.

The apparatus shown in the figure is a twin-belt press 1 with a press zone 2 and a pressureless preheating zone 3 in front of the press zone. The pressurizing zone 2 is divided into two sub-zones, a longer heating zone 4 adjacent to the preheating zone 3 and a shorter cooling zone 5 following this heating zone 4. The heating zone 4 itself has three sub-temperature zones 41, 42 and 43 which can be controlled independently of one another. In front of the press section 2 of the twin-belt press 1 there is a pair of heated, inwardly drawn inclined cylinders 6 and 6 'which are mounted at a considerable distance from each other, and behind the press section 2 there is a pair of correspondingly designed outwardly drawn inclined cylinders 7, 7' which are mounted at a relatively short distance from each other, behind which pairs of inwardly drawn inclined cylinders there are several pairs of support rollers 11, 11 'for supporting the press belts 8 and 8' of the twin-belt press 1. In order to keep the temperature constant, the preheating zone 3 is defined by shielding heat from the press belts 8 and 8 'in the twin-belt laminator 1 with a pair of heat shielding plates 9 and 9'. The said pressure belts 8 and 8 'are heated by the inclined cylinders 6 and 6' which draw the material inwards. The pair of heat shields is composed of cooling plates. The cooling is performed by using a copper cooling coil, and the flow rate of the coolant flowing through the cooling coil can be controlled, so that the temperature can be accurately controlled. Instead of such cooling coils, it is also possible to use cooling devices with forward connecting channels. The heat shields 9 and 9' used are mounted so as to be movable in the horizontal direction so that the preheating zone with controlled temperature can be moved closer to or further away from the pressure zone 2, in other words also the spatial position of the preheating zone 3.

The principle of operation of the twin-belt press used in the present invention is based on the fact that the pressure exerted on the sheet material continuously moving through the press is uniformly distributed over the entire width of the sheet material and that the pressure does not vary with time. The reason for the uniform and constant pressure is that in a twin belt press, the pressure is transmitted through a pressure cushion (not shown) mounted on the press to closed steel press belts 8 and 8' which run synchronously with the sheet being processed through the press, and which also act as finishing machines. Preference is given to using a pressure belt of relatively large mass (for example of a thickness of approximately 2 mm) which ensures good heat transfer.

The length of the heating zone 4 of the press 1 is, for example, 3 meters, and the maximum total length of the entire twin-belt press 1 is selected to be 4 meters, that is to say the entire pressing zone length is predicted to be 4 meters. The length of the preheating zone 3 under such conditions is preferably 40 to 100 cm. In the illustrated preferred embodiment, the cooling zone 5 has a length of 1 meter.

In front of the twin-belt press, two spindle unwinders 12 and 13 are mounted, each with two spindles 14-17 for winding prepregs, which are glass fibers (textile fibers or cotton) or paper laminates coated with a resin system, and a further spindle unwinder 18 with two spindles 19 and 21 for winding metal foils. Between the spindle unwinder 18 and the twin belt press 1, foil guide wheels 22 and 22' are mounted.

Mounted behind the twin-belt press in terms of production direction is a trimming device 23 and a cutting device 24 for cutting into the desired dimensions.

During operation, four prepregs, that is to say laminates coated with a resin hardener/accelerator system and pre-hardened to the advanced B state, are drawn from spindle unwinders 12 and 13 and sent together to preheating zone 3. The four prepregs in the preheating zone 3 are heated to about 80-100 ℃ under the condition of no pressure, so that the resin system starts to act. At the same time, the metal foils are fed by the two spindles 19 and 21 on the spindle unwinder 18, guided between the specific heat shield 9 or 9 'and the pressing belt 8 or 8' in a condition separate from those prepregs, and then rapidly combined with those prepregs before the pressing zone 2. Although the preheating zone is up to 100C (this has been pointed out), the cylinder temperature fed into the machine is higher and therefore the metal foil fed into the machine is heated to a higher temperature than the prepreg. The heating zone 4 of the pressing zone 2 has three sub-temperature zones 41, 42 and 43, where several layers of raw material, which are bonded together, are pressed into a metal-clad laminate at a pressure and temperature of more than 25 bar from 150 ℃ to about 190 ℃ and are bonded together due to the hardening effect of the still reactive resin. The temperature of the first sub-temperature zone 41 is lower and the temperature of the second sub-temperature zone 42 is higher, the latter temperature may be equal to the temperature of the third sub-temperature zone, about 190-200 ℃. The metal clad laminate is cooled under pressure in a subsequent cooling zone 5. Pressurization during this complex phase prevents degradation of quality, and in particular deformation of the product. The metal clad laminate cooled to about 100C begins to leave the cooling zone 5. In a subsequent edger 23, the pressed edges are trimmed from both sides of the metal clad laminate and then cut to the desired dimensions on a subsequent cutter 24.

Between the cooling zone and the edge trimmer, a second heat treatment zone may be provided for ensuring a constant size of the base material of the metal-clad laminate.

The illustrated apparatus is preferably operated with a residence time in the heating zone 4 which corresponds to a feed rate of about 3 m/min in a twin-belt press. The residence time and the feed rate depend on the curing temperature used and the reaction rate of the resin-hardener-accelerator system.

In the production of single-sided metal-clad laminates only, instead of metal foil, a sheet of heat-resistant release foil can be used, which is wound on a corresponding spindle and fed into a twin-belt press. The separating foil used may be, for example, an aluminum foil treated with silicone or an aluminum foil coated with a polytetrafluoroethylene layer. After the formed metal clad laminate is fed from the twin belt press, the separator foil can be withdrawn from the finished board for reuse.

Although the process of the present invention is described with reference to six-layer metal clad laminates, metal clad laminates having different numbers of layers can of course also be produced.

The operating conditions described depend essentially on the resin system used and can be varied accordingly.

The method and apparatus of the present invention can be laminated not only with copper but also with other metal foils. The method and apparatus of the present invention are particularly suitable for producing metal clad laminates with composite metal foils, such as those with Cu/Al foils for high precision printed circuit boards (so-called etchability-strippable boards).

The invention will be further illustrated by the following examples:

Example 1

Finished fiberglass fabrics having a weight of 200 grams/meter ², such as those commonly used in the manufacture of copper clad fiberglass-epoxy laminates for printed circuit boards, are impregnated with a resin solution. The resin solution used consists of 100 parts of polymerized partially brominated bisphenol-A-glycidyl ether containing 1 to 15%, preferably 5 to 12%, of an epoxidized novolak, 3.2 parts of dicyanodiamide, 0.25 part of 3-methylpyridine and 80 parts of methyl glycol. The prepreg impregnated with the resin and dried at 165 ℃ contained 42% resin and 10% grease. Seven such prepregs were preheated to 80 ℃ and then pressed with the apparatus of the present invention together with two 35 micron thick copper foils in a continuous moving fashion at 45 bar pressure with a temperature increase from 150 ℃ to 195 ℃ to produce a 1.5mm thick double sided copper clad laminate. After testing this double sided copper clad laminate, it was demonstrated that this laminate unexpectedly achieved the moderately good standards described above in terms of dimensional consistency, while other properties were comparable to conventional laminates.

The tolerance of the thickness of the copper-clad laminate is + -3/100 mm. In contrast, the allowable deviation specified in the rigidity standard of the copper clad laminate is.+ -.13/100 mm, and the copper clad laminate produced by the multi-layer press has fully utilized this value.

Example 2

A glass fiber fabric such as that described in example 1 is impregnated with a resin solution. The resin solution used consists of 100 parts of a partially brominated poly bisphenol-A-glycidyl ether containing 1 to 15%, preferably 5 to 12%, of an epoxidized phenol varnish resin, 3.4 parts of dicyanodiamide, 0.33 part of 4-dimethylaminopyridine and 80 parts of methyl glycol. Prepregs impregnated in this way and dried at 170 ℃ contain 44% resin and 8% flow. Several such prepregs were preheated to 85 ℃ and then pressed in a continuous motion with two 35 micron thick copper foils using the apparatus of the present invention at a temperature increase from 155 ℃ to 200 ℃ and a pressure of 50 bar to produce a 1.5 mm thick bi-laminate. The test was conducted on the copper-clad laminate produced in this example, and as a result, it was found that the dimensional stability was equivalent to the above standard value, while the other properties of the laminate were equivalent to those of the conventional one.

Example 3

A fiberglass fabric having a weight equal to 100 grams/meter ² and the use as described in example 1 was saturated with a certain resin mixture. The resin mixture used comprises 100 parts of a partially brominated polymeric bisphenol-A-glycidyl ether containing 1 to 15%, preferably 5 to 12%, of an epoxidized novolac resin, wherein the epoxide resin equivalent weight is between 350 and 520, 3.0 parts of dicyanodiamide, 0.40 parts of 2-amino-4-methylpyridine and 80 parts of methyl glycol. And then dried at 165 ℃. The resin content was 44% and the flow fat content was 10%. After preheating two such prepregs to 80 ℃, they were pressed with the apparatus of the present invention using a separate foil together with a single-sided copper foil having a thickness of 35 μm in a continuous moving manner, and the temperature of the pressing zone was increased from 150 ℃ to 190 ℃ and the pressure was 50 bar, to produce a single-sided copper-clad laminate having a thickness of 0.2 mm. The results obtained after the test were the same as in example 2.

Examples 4 to 13

The compositions or operating conditions used in examples 4-13 are set forth in the following table.

Watch (watch)

(Follow-up table)

Claims (17)

1. A method for continuously producing metal-clad laminates for printed circuit boards, characterized in that: Laminated material sheets impregnated and pre-hardened with a setting-accelerating resin system are continuously passed through a pressure-free preheating zone to be preheated without pressure to reduce the viscosity of the resin. The preheated laminated material sheets impregnated with the above resin are then combined with at least one preheated metal foil and then sent to the pressurizing zone of a double-belt press. In this zone, the laminated material sheets and the metal foil are pressed together under pressure and gradually increasing temperature to obtain a continuous length of metal-clad laminate. The continuous metal-clad laminate is then cooled in a cooling zone, leaves the cooling zone, and then has the pressed edges on both sides cut off and finally cut into the required size. 2. The method according to claim 1, wherein the pressure in the pressurizing zone is 25 to 80 bar and the temperature is increased from about 150 to 210°C. 3. The method according to claim 1 or 2, wherein the cooling of the metal-clad laminate obtained after heating and pressurization is carried out in a cooling zone under pressure, preferably in a double-belt press. 4. The method according to claim 1, wherein said metal-clad laminate is subjected to a second heat treatment. 5. The method according to claim 1, characterized in that when a laminated base material having a metal foil on one side is produced in said continuous process, a separator foil is also fed into the side without the metal foil, and then pressurized and pulled off the base material plate after being fed out of the double-belt press. 6. A method according to any one of claims 1, 2, 4 and 5, characterized in that said laminated material sheet and said metal foil are preheated separately. 7. A method according to claim 6, characterised in that said metal foil is preheated to a higher temperature than the laminated material sheet. 8. A method according to any one of claims 1, 2, 4 and 5, characterized in that during said pressing process, said laminated material sheet and said metal foil are joined together immediately before the pressing zone of the press. 9. A method according to any one of claims 1, 2, 4 and 5, characterised in that the laminated material sheets used are impregnated with an accelerated epoxy resin hardener/catalyst system and pre-cured. 10. The method of claim 9, wherein the accelerated epoxy resin/hardener/catalyst system used in said method contains as a setting accelerator one or more compounds selected from the group consisting of substituted pyridine compounds, imidazole, substituted imidazole, dicyandiamide and benzyldimethylamine. 11. The method according to claim 10, wherein the accelerated epoxy resin/hardener/catalyst system contains an accelerator or a mixture of accelerators in an amount equivalent to 0.2 to 0.8% by weight of the solid epoxy resin. 12. An apparatus for implementing the method of claim 1, for pressing a laminate material impregnated with a thermosetting resin and a metal foil to be laminated thereon into a metal-clad laminate for use as a printed circuit board, characterized in that the press is a heatable double-belt press (1) which can continuously press the laminate material impregnated with a thermosetting resin and pre-cured with the metal foil under pressure and elevated temperature to form the metal-clad laminate; two spindle-type unwinders (12, 13) which can continuously supply prepregs, and another spindle-type unwinder (18) which can continuously supply metal foil are installed in front of the double-belt press (1); ) has a pressurized heating zone (4) and a cooling zone (5) located after the pressurized heating zone (4), and a non-pressurized preheating zone (3) is located in front of the pressurized heating zone (4); in the space near the non-pressurized preheating zone (3), laminated material sheets and metal foil guide devices are separately installed; before the pressurized heating zone (4) of the double-belt press (1), there is a pair of heated inclined cylinders 6 and 6' for inward granulation, and after the cooling zone (5), there is a pair of correspondingly designed inclined cylinders (7, 7') for outward pulling of the material, and installed behind the double-belt press (1) is a trimming device (23) and a cutting device (24) for cutting into the required size. 13. A double-belt press (1) according to claim 12, characterised in that a pair of heat shields (9, 9') are installed in the preheating zone (3) for controlling the degree of cooling. 14. Double-belt press (1) according to claim 13, characterized in that said heat shields (9, 9') are mounted so as to be displaceable in the horizontal direction. 15. Double-belt press (1) according to any one of claims 12 to 14, characterized in that the distance between the pair of cylinders (6, 6') pulling the material into the press is greater than the distance between the pair of cylinders (7, 7') pulling the material out of the press. 16. Double-belt press (1) according to any one of claims 12 to 14, characterised in that the cooling zone following the pressurised heating zone (4) is a pressurised cooling zone (5). 17. Double-belt press (1) according to claims 12 to 14, characterized in that the heating zone (4) is divided into three temperature sub-zones (41, 42, 43) which can be controlled individually.

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