Flexible Circuits and Tape Automated Bonding

The second method is based on the use of polyimides with lower glass transition temperatures that can be melt-processed. For example, intrinsically photosensitive preimidized polymers formed by reacting 3,3 4,4 -benzopheno-netetracarboxylic acid dianhydride (BTDA) with methyl-substituted 4,4 -methylenebisbenzeneamine (MDA), blended to epoxy resins, give high strength laminate with copper. Poly(isoimides), which exhibit good melt-flow properties before thermal isomerization to imides, are also used to make flexible circuits. In the last process copper is electroless plated on polyimide film such as Kapton 200H. 

Starting from a 35-70 mm wide blank tape (a), sprocket holes and window patterns are mechanically fabricated in the film by die punch or laser cut (b). The film is then laminated to 35 p-m thick copper foil (c). Photoresist film is deposited on copper and patterned through a mask (d), before beam leads are formed by chemical etching (e). In the final stage, the connecting pads along the periphery of the integrated circuit are bonded to copper leads (f). 

However, the write method is a relatively slow proeess in comparison to the print approach in which the complete pattern is printed in one shot through 

The polymers used to manufacture the film or tape adhesives are either thermoplastic materials including acrylic, polyester, and fully imidized polyimides or thermosetting resins based on epoxy and polyimide chemistries. The tapes are often made with partially cured (B-staged) epoxies similar to those used in the fabrication of the PCBs. Some commercially available films are also 

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