FIELD OF THE INVENTION

This invention relates to a flexible circuit board, and more particularly to a layout structure of a flexible circuit board.

BACKGROUND OF THE INVENTION

In conventional flexible circuit board, such as TCP (tape on carrier) or COF (chip on film) package, a patterned circuit layer is arranged on a flexible substrate, then a chip is flip-mounted on the flexible substrate and electrically connected to the circuit layer. A fine-pitch flexible circuit board having circuit lines with highly density and narrow width is adequate for smaller-size electronic equipment. However, the different thermal expansion behavior of the flexible substrate and the circuit layer during thermal bonding of the chip to the circuit layer on the flexible substrate may cause stress concentration and damage on the circuit layer around the chip.

SUMMARY

One object of the present invention is to provide a stress release portion adjacent to a chip mounting area defined on a flexible substrate so as to protect a circuit layer around a chip from breaking caused by stress concentration.

A layout structure of flexible circuit board of the present invention includes a flexible substrate, a chip and a circuit layer. A chip mounting area and a circuit area are defined on a top surface of the flexible substrate, and the circuit area surrounds the chip mounting area having a first side and a second side. The chip is mounted on the chip mounting area of the top surface and includes a bump. The circuit layer is disposed on the top surface and includes a connection portion, a transmission portion and a stress release portion. The connection portion extends across the first side and into the chip mounting area and is electrically connected to the bump. The transmission portion is located on the circuit area and adjacent to the second side. A space of between 100 um and 800 um exists between the transmission portion and the second side of the chip mounting area. The stress release portion is located between the transmission portion and the second side of the chip mounting area and is a comb-shaped structure.

The stress release portion of the present invention is disposed between the transmission portion and the second side of the chip mounting area and used to avoid stress concentration on the second side of the chip mounting area and protect the connection portion from breaking. As a result, the manufacturing yield rate of the flexible circuit board can be improved.

