Attachment of a stiff heat spreader for fabricating a cavity down plastic chip carrier

A method of attaching a stiff heat spreader element to a circuit substrate for making a cavity down plastic chip carrier, comprising:

• providing a plastic circuit substrate having a first surface and a second surface opposite said first surface, and an opening penetrating through said circuit substrate adapted to receive a chip;
• providing a first thermally conductive sheet which serves as a stiff heat spreader element having a first surface and a second surface opposite said first surface;
• providing a purality of second thermally conductive sheets, each of which has a first surface, a second surface opposite said first surface, and an opening for receiving said chip;
• said first surface of said first thermally conductive sheet being bonded to said second thermally conductive sheet with using of a first bonding sheet, being at least one layer of prepreg, placed randomly in between two adjacent thermally conductive sheet;
• after bonding, said second surface of said first conductive sheet and said first surface of one of said second thermally conductive sheets being exposed to air;
• providing a second bonding sheet, being made without a prepreg, bonding said first surface of one of said second thermally conductive sheets and said second surface of said circuit substrate.