It is well-known that printed electronic circuit plates are formed by stable association of heated and pressed sheets of pre-preg and of copper.

The pre-preg sheets can be of paper, fiberglass or materials of other kinds, impregnated with plastic material which may be phenolic, melamine, epoxy, polyester or of other types.

Pressure and heat is obtained by forming a pile of substantially equal packages comprising the components of said circuits separated by perfectly smooth flat plates, and placing said pile in presses provided with heating plates.

At the end of the heating cycle, which also includes final cooling, a compact and rigid product is obtained in which the single components are closely bound together.

Clearly, the presses suited to this type of production are complex and of low efficiency due to the difficulties of obtaining, by conduction, uniform temperatures among the packages making up the pile of which obviously only those at each end of the pile are in contact with the heating plates of the press.

Propagation of heat from the heating plates to the piled packages is greatly hindered by the nature of the components, for example the pre-preg, which by their very nature are poor. conductors of heat.

Over recent years use has been made of endothermic generation of heat directly from the copper laminae by electricity obtained on closing the laminae in an electric'circuit.

Two processes are employed for closing all the copper laminae contained in the pile in an electric circuit.

One process consists in substituting the copper laminae with a band wound S-wise round each package in the pile so that it is only necessary to close the electric circuit at the two ends of the pile.

Using another process the two opposite ends of each copper lamina are connected to the conductors of an electric circuit.

Clearly, both processes create problems over forming the pile of packages and in making the electrical connections, also bearing in mind the considerable voltages involved.

The advantages of endothermic hearing are therefore to some extent lessened by the greater difficulties over making up the packages and forming the electrical connections.

The disclosure here described provides endothermic heating in the packages avoiding all the complications arising with present methods, as will now be explained.

Subject of the invention is a process for producing plastic laminates with a copper lamina, for electronic circuits, including multilayer, in a cold press and with endothermic heating of a pile of packages of the components.

Endothermic heating is obtained by generating electric current in the copper laminae by induction created inside the press by a ferromagnetic core with a winding through which alternating current passes.

In one type of execution the alternating current is low-frequency.

The ferromagnetic core comprises two horizontal yokes and at least one column with electric winding connected in a closed ciricuit to the generator of alternating current.

The pile of packages is placed between the lower fixed yoke and, the upper mobile yoke to which the pressure required for pressing is applied.

The upper mobile yoke is connected to the pistons of one or more hydraulic cylinders situated on an upper fixed plate of the press.

At least when the electric winding is connected in a closed circuit to the generator of alternating current, one end face of said mobile yoke adheres to the opposite internal face of the column ensuring continuity of the ferromagnetic core.

The generator of alternating electric current is connected to a programmable electronic processor by a keyboard and display, for programming production cycles, setting the preferred temperatures to be obtained in the copper laminae, as well as pressing times, frequency and power of the electric current.

The electronic processor is provided with a control and regulation circuit that automatically controls and regulates temperatures, pressing times, frequency and power of the alternating electric current to ensure that these values are applied as programmed.

Characteristics and purposes of the disclosure will be made still clearer by the following examples of its execution illustrated by diagrammatically drawn figures.

Fig. 1 Front view of a cold press in which a pile of packages for printed circuits has been placed.

Fig. 2 Perpsective view of the package of printed circuits.

Fig. 3 Front view of the press at the start of. pressing.

The press 10 presents the base plate 20 and upper fixed plate 21.

Hydraulic cylinders 30,31 with pistons 40,41, are fixed to the upper plate 21 through which said pistons pass.

Installed on the piate 20 is the ferromagnetic core 50 comprising the column 51 and yokes 55,56.

Around the column 50 is the electric winding 60 whose ends 75,76 can be connected in a closed circuit to the generator 70 of low- frequency alternating current.

The generator 70 is connected by cables 85 to the electronic processor 80 comprising the display 81 and keyboard 82 through which the stages of the cycle, such as temperatures, timing, frequency and electric power, can be set.

At least when the electric winding round column 50 is connected in a closed, circuit to the generator of alternating current, the end face 57 of the upper mobile yoke 56 adheres to the opposing internal face 52 of said column 50 ensuring continuity of the ferromagnetic core.

The cycle starts on pressing the push button 83.

The electronic processor maintains control, from one moment to the next, over the programmed characteristics.

The mobile upper yoke 56, fixed to the pistons 40,41, constitutes that part of the press which generates the required pressure.

The pile 88, comprising a number of superimposed equal packages such as 90, is placed between the lower fixed yoke 55 and the mobile yoke 56.

As shown-in Figure 2, each package, between the separating plates 100, 101, comprises two copper laminae 102 and 103, two groups 104,105 of sheets of pre-preg, and the internal layer 106.

The low-frequency alternating current provided by the generator 70 creates, between yokes 55 and 56, electromagnetic waves 110 which, on passing through the pile 88 of packages, heat the copper laminae, like 102 and 103 ; by induction.

A special software having established, through the keyboard 82, the desired sequences of current voltage and frequency, temperatures and times, and the cycle having been started by pressing the push

button 83, the mobile yoke 56, pressed by the pistons 40,41 in the cylinders 30,31 applies the required pressure to the pile 88 of packages, its end face 57 adhering to the internal face 52 of the column 51, while the alternating electric current creates, by induction, the most suitable degree of heat in the copper laminae.

The invention offers evident advantages.

As the presses need not provide heat as well as pressure, they are much more simply constructed than are those at present used.

Heat is generated in each single package much faster and is more uniform since propagation of calories in any one package is not hindered by the sheets of pre-preg in those above or below it.

Mounting problems arising over endothermic heating where there is an S-shaped band in each package, or alternatively by closed circuit electrical connections for each copper lamina, are here avoided.

Summing up the advantages: production of printed circuits is considerably faster and cheaper than with present systems using either hot or cold presses.

As the above invention has been described and explained as an example only, not limited to this one, and to show its essential features, it is understood that numerous variations may be made to it according to industrial, commercial or other requirements, and that other systems and means may be added without thereby causing any departure from its present sphere of operation.

It is therefore understood that the application to patent comprises any equivalent application of the concepts and any equivalent product executed and/or operating in accordance with any one or more of the characteristics set forth in the following claims.