Printed wiring boards substrate materials

The symposium and this book have enabled us to assemble the results of research by experts in polyimides and related materials, polymeric encapsulants, gels, and printed wiring board (PWB) substrates, with emphasis on the chemical aspects of these materials. 

These films have a three-layer stmctnre, with the photosensitive material sandwiched between a polyester coversheet and a polyethylene separator sheet (see Fig. 26.4). The photoresist thickness is typically 25 to 50 fim, but thinner and thicker films are used for special applications. The photoresist is apphed to the printed wiring board (PWB) substrate using lamination The polyethylene separator is removed, and the photoresist flows under the heat and pressure from the laminating rolls to adhere to the substrate. The polyester coversheet... 

Those applications were for removal of acidic flux and flux residues from various printed circuit (wire) boards (PWBs), removal of camauba wax from optic materials, removal of buffing and lapping compounds from metal substrates, and some others. These applications share at least one characteristic — that high quality, thoroughly repeatable cleaning is essential. And these applications remain highly valued. 

The thermoplastics used for MID are neither as rigid nor as strong as the glass-reinforced themosets routinely used for printed-circuit boards. The layer of metal deposited on the substrate is typically hard and compensates for the poor wirebonding properties of the soft substrate material. This is why bondability is largely independent of the polymer used. It is important to bear in mind, however, that there is a minimum thickness specification for plating (Table 5.7). The thicker the metallization, the more dependable the wire-bonding process becomes. [182]... 

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