Process for making of plastic laminates each having a metal lamina on each of two opposite side surfaces, especially for printed circuits

A process for making plastic laminates, each of said plastic laminates comprising a prepreg body having an opposing side surface on each of two opposite sides of the prepreg body and a metal lamina on each of said opposing side surfaces, and each of said prepreg bodies having insulating properties and consisting of a plurality of prepreg layers and including a plastic material, said process comprising the steps of:

• a) stacking a plurality of the prepreg bodies, one over the other, so that each pair of adjacent ones of said prepreg bodies has two of said opposing side surfaces of said pair facing each other;
• b) passing a first metal band and a second metal band in a serpentine manner back and forth between said prepreg bodies with said first metal band and said second metal band spaced from each other to form a plurality of bends in both said first metal band and in said second metal band, said first and second metal band each having two opposite ends and extending continuously between said two opposite ends;
• c) arranging each of said prepreg bodies between the first metal band and the second metal band so that said first metal band contacts on only one of the two opposing side surfaces of each of said prepreg bodies and said second metal band contacts on another of said two opposing side surfaces of each of said prepreg bodies on an opposite side from the one side surface contacted by the first metal band;
• d) arranging a rigid flattening sheet provided with an electrically insulating layer covering each of two opposite sides thereof between said adjacent prepreg bodies of each of said pairs and, at the same time, between adjacent sections of said metal bands between said adjacent prepreg bodies to form a stack comprising said prepreg bodies and said rigid flattening sheets with said metal bands passing through said stack in said serpentine manner;
• e) passing an electric current through each of the metal bands from one of the opposite ends of each of said metal bands to another of the opposite ends so as to heat the first and second metal bands and thus the prepreg bodies and the rigid flattening sheets with the electrically insulating layers;
• and
• f) applying pressure to the stack of the prepreg bodies and the rigid flattening sheets with the electrically insulating layers.