Method for Connecting Flexible Printed Circuit Board to Another Circuit Board

A method for connecting a flexible printed circuit board (FPC) to a second circuit board, comprising the steps of:

• (i) preparing a flexible printed circuit board (FPC) having connection parts assigned to end parts of a plurality of conductor wirings, and a second circuit board having connection parts assigned to corresponding end parts of a plurality of conductor wirings, to which said FPC is connected,
• (ii) disposing the connection parts of said FPC to face the connection parts of said second circuit board such that a thermosetting adhesive film is present between the connection parts of said FPC and the connection parts of said second circuit board, and
• (iii) applying heat and pressure to said connection parts and said thermosetting adhesive film, sufficiently high to thoroughly push away the adhesive film for establishing electrical contact between connection parts of circuit boards facing each other and allow for curing of the adhesive,
• wherein the ratio of conductor width (L)/conductor-to-conductor distance (S) in the conductor wiring end parts constituting the connection parts of said flexible circuit board is 0.5 or less and said thermosetting adhesive film is adjusted to have a viscosity of 500 to 20,000 Pa·s at 200° C.