DE2311919A1 - GLASS FIBER REINFORCED EPOXY LAMINATE WITH A RELATIVELY THICK EPOXY-BASED PLASTIC OVERLAY, AND PROCESS FOR THE PRODUCTION OF THIS - Google Patents

Description

DR. ING. E. HOFFMANN · DIPJL. IjPO. W. EITiE · DR. «ER. NAT. K. HOFFMANN

PATESTi-NWA! / TR D-SOOO MÖNCHEN 81 ARABEILASTRASSE 4 TELEPHONE (Οβ'ΐί) 911087

23

Perstorp AB, Perstorp / Sweden

Glass fiber reinforced epoxy laminate with a relatively thick double-sided epoxy-based plastic cover layer and process for its production

The invention relates to a method of manufacture of a glass fiber reinforced epoxy resin with relative thick layers of an epoxy plastic on both sides, for use in the manufacture of printed circuit boards with plated through holes as well as one of one or more layers of one impregnated with an epoxy resin Laminate made of fiberglass and thermally pressed for use in the manufacture of printed matter Circuits with plated through holes.

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309838/1172 original $ nspec * eo

Printed circuits are indispensable in modern electronics. They consist of an insulating base plate and electrical connections. Usually the base plate reinforced. For example, it can consist of a phenolic resin laminate reinforced with paper, which is used for simpler Circuits is used, and made of a glass fiber reinforced epoxy resin laminate that is at high technical Requirements is used.

There are two different ways of producing printed circuits on the base plate. at the first is a copper foil on top of which is impregnated with plastic Fiber material (so-called pre-impregnation) applied, whereupon under high pressure and at high temperature a pressing process takes place. Before pressing, the plastic present in the fiber material is transferred to the so-called B stage hardened. During pressing, the plastic hardens completely, which means that the fiber material also cures the plastic is connected in such a way that a laminate is formed on which the copper foil is glued. Normally the copper foil has a thickness of 35 μm. Then it will be an impression of the desired wiring on the copper sheet transferred for example by pressure or by photochemical means. The excess copper sheet is removed by etching.

With a significant number currently in production printed circuit boards, there is a circuit on both sides of the laminate. The connections between the two Pages are obtained through so-called plated through-openings. Among other things, it takes place in the manufacture of such Circuits chemically plating the inside of the drilled holes.

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reprinted circuits with plated through holes produced this first process. It is obvious that the copper foil is on both sides of a laminate for plating no through openings if the surface of the laminate can be plated chemically in the same operation as the holes. this happens in the second method of manufacturing printed circuit boards. With this procedure, the entire circuit is on the Base plate built up by chemical and / or electrolytic deposition of copper on a plastic laminate which no copper layer is applied.

A strong adhesive force is required between the copper layer and the insulating base plate. However is the adhesion between a phemically plated copper layer and a vitreous epoxy surface is poor. For this reason the surface of the epoxy laminate must be pretreated before the copper is deposited. In many processes known for this purpose, the surface is pretreated by etching, whereby a porous surface structure is obtained. Etching the entire surface of homogeneous plastic materials is easy perform. However, reinforced materials, such as glass fiber reinforced epoxy laminates, are difficult to handle as the etchant can easily spread between the fibers and the plastic material. Becomes a fiberglass material used as reinforcement, there are often some fibers close to the surface. If the etchant can come into contact with the reinforcing material during the etching, then one obtains not only do the mechanical properties of the plastic layer have less good mechanical properties, but also the electrical properties worse. For this reason there is a great need to be able to produce a glass fiber reinforced epoxy laminate.

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put, in which above the reinforcement material a so thick epoxy layer is present that the etchant does not can penetrate into the reinforcement material.

When using a conventional pressing process, it is obtained in general, an epoxy layer with a thickness of 0-5 / µm. However, it is to achieve a satisfactory Adhesive force required to etch deeper layers.

The invention is now based on the object of avoiding the aforementioned disadvantages in that the epoxy layer applied to a reinforcing material has a thickness such that that during the subsequent etching - even in deeper layers - the etchant does not interact with the glass fibers contained in the reinforcement material comes into contact with the required adhesive force being large enough.

According to the invention, this object is achieved with a method of the type described above solved in that an epoxy resin applied to one side of a provisional base plate made of a sheet of aluminum or aluminum alloy and is cured so far that its flowability is reduced in a subsequent pressing process that such a film is pressed under the action of heat on both sides of a final base plate, the epoxy-coated Surface of the provisional base plates is directed towards the final base plate, which consists of a or several layers of a glass fiber material impregnated with an epoxy resin, and that the temporary base plates after the pressing process in a suitable "manner from the finished Laminate can be removed.

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It is important that the epoxy resin on the temporary base plates is cured to the point No material flow into the during the subsequent pressing process Main part of the laminate takes place more. However, chemical groups which have not yet reacted must remain which are suitable for provide bonding of the epoxy resin in the main body of the laminate.

The thickness of the epoxy layer on the finished laminate can be changed by changing the thickness on the temporary base plate applied amount of epoxy resin can be adjusted. A suitable thickness of the epoxy layer on the temporary base plate is 10-200 µm, for example approx. 50 µm.

If necessary, an organic or inorganic filler in the form of fine particles can be mixed into the epoxy resin which is applied to the provisional base plates.

A foil made of aluminum or aluminum alloy is used as a provisional base plate. In particular, a matted foil preferred. The thickness of the temporary base plates can be changed depending on the rigidity of the foil used will. However, it is about 30 µm in thickness for aluminum foil suitable for this purpose.

The temporary base plates are removed from both sides of the finished laminate, for example by peeling off or dissolving or etching away. Of course, it is an advantage if the provisional base plate is as thin as possible when they to be removed chemically.

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The present invention will now be described in greater detail in connection with the following exemplary embodiments described. Example 1 represents a comparative test for the manufacture of a laminate in a conventional manner, while Examples 2 and 3 serve to illustrate the process according to the invention.

example 1

A glass fiber fabric was impregnated with an epoxy resin with a plastic content of 50 wt .- # and cured so far that the original epoxy equivalent of the resin increased by about 30 %, namely from 523 to 675. Four pieces pre-impregnated in this way were pressed into a laminate under the action of heat in the usual manner. The thickness of the plastic layer - measured from the laminate surface to the glass fiber bundle closest to the surface - was 0-10 μm.

Example 2

An aluminum foil, optionally matt aluminum foil,

ο with a thickness of 25 / µm was coated on both sides with 100 g / m epoxy resin. The plastic layer was cured to such an extent that the epoxy equivalent increased by about 100 % , namely from the initial value of 523 to 1040.

A glass fiber cloth was impregnated with epoxy resin content to a plastic of 50 wt -.% Impregnated and cured to the extent that the epoxy equivalent of the resin to about 30% _s namely from 523 to 675, increased.

An aluminum foil coated with epoxy resin was made of four layers of plastic on both sides

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impregnated fiberglass fabric existing base plate. The plastic coating of the foils was directed inwards towards the base plate. After pressing under The foils were etched in sodium hydroxide under the influence of heat. The thickness of those on the laminate surface Plastic layer was measured and found to be 50 + 10 µm.

Example 3

A laminate was produced according to the method described in Example 2, but the provisional base plate was coated with 150 g / m epoxy resin ^{instead of 100 g / m 2.} The thickness of the plastic layer on the finished laminate was 75 + 10 μm.

The present invention is of course not limited to the illustrated embodiments, since these can be modified in various ways within the scope of the invention.

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30 98 33/117 2

Claims (5)

P a t e η t a n s ρ r ü ehe ^ l _. 'Process air production of a glass fiber reinforced Epoxy laminate with relatively thick layers of an epoxy plastic on both sides, for use in the Manufacture of printed circuits with plated through openings, thereby g e k e η η ζ e i c h ne t, that an epoxy resin on one side of a 'foil made of aluminum or aluminum alloy "temporary Base plate is applied and cured so far that its flowability in a subsequent Pressing process is reduced that such a film under the action of heat on both sides of a final Base plate is pressed on, the epoxy-coated Surface of the provisional base plates is directed towards the final base plate, which consists of one or more layers of one impregnated with an epoxy resin There is fiberglass material, and that the provisional base plates after the pressing process in a suitable manner from finished laminate can be removed. 2. The method according to claim 1, characterized in that a provisional base plate matted aluminum foil is used. J). Method according to claim 1, characterized in that a layer of epoxy resin with a thickness of 10-200 µm, for example approx. 50 µm, is applied to the temporary base plate. 4. The method according to claim 1, characterized in that an organic or inorganic Fine particle filler mixed into the epoxy resin applied to the provisional base plate -9- 3 0 9 8 3 8/1172 5. Consists of one or more layers of a glass fiber material impregnated with an epoxy resin and under Thermally pressed laminate for use in the manufacture of printed circuit boards with clad Through openings, characterized in that it is covered on both sides with a cover layer of epoxy resin in a thickness of 10-200 μm, preferably about 50 μm, is provided. 309838/1172