Flexible circuit board and heat spreader thereof

Description

FIELD OF THE INVENTION

This invention relates to a flexible circuit board, and more particularly to a flexible circuit board having a heat spreader.

BACKGROUND OF THE INVENTION

Small, thin and flexible circuit boards are widely used in thin mobile devices, e.g. smartphone, laptop and smart watch, but heat dissipation of the flexible circuit board is difficult owing to its small size. For this reason, a heat spreader is usually attached onto the bottom surface of the flexible circuit board for heat dissipation. With reference to FIG. 1, a conventional flexible circuit board 400 is connected to a panel 200 and a control circuit board 300, in practice, both ends of the flexible circuit board 400 are electrically connected to the panel 200 and the control circuit board 300 respectively such that signals from the control circuit board 300 are processed and delivered to control the panel 200. Moreover, the flexible circuit board 400 and a heat spreader 410 attached on the bottom surface of the flexible circuit board 400 are bent together in order to match the installation requirement. As the mobile device is getting thinner and thinner, the flexible circuit board 400 has to be bent with more radius of curvature, that may cause delamination of the heat spreader 410 having a lower bending strength away from the flexible circuit board 400 and cause overheat damages to the flexible circuit board 400.

SUMMARY

One object of the present invention is to provide a heat spreader containing more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation such that the bending strength of the heat spreader is improved significantly to prevent the delamination of the heat spreader from a flexible circuit board.

A flexible circuit board of the present invention includes a flexible substrate, an electronic component and a heat spreader. The electronic component is mounted on a top surface of the flexible substrate. The heat spreader is disposed on a bottom surface of the flexible substrate and includes a copper layer containing more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation.

A heat spreader of the present invention is configured for dissipating heat from a flexible circuit board and includes a copper layer containing more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation.

The heat spreader exhibits excellent bending strength because of the copper layer containing more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation. Consequently, delamination of the bent heat spreader from the flexible circuit board is preventable.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view diagram illustrating a conventional flexible circuit board connected with a panel and a control circuit board.

FIG. 2 is a cross-section view diagram illustrating a flexible circuit board in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a cross-section view diagram illustrating a flexible circuit board 100 of one embodiment of the present invention. The flexible circuit board 100 includes a flexible substrate 110, an electronic component 120 and a heat spreader 130, and further includes solder resist and chip underfill which are not shown in diagram owing to they are irrelevant to technical features of the present invention.

With reference to FIG. 2, the flexible substrate 110 is made of polyimide or other polymers having excellent electric insulativity, stability and chemical resistance. A patterned circuit layer 111a on a top surface 111 of the flexible substrate 110 includes fine circuit traces which are formed by etching a copper layer plated on the top surface 111. The electronic component 120 is mounted on the top surface 111 of the flexible substrate 110 and electrically connected to the patterned circuit layer 111a. In this embodiment, the electronic component 120 is a flip-chip element including a chip 121 and a plurality of bumps 122, both ends of each of bumps 122 are electrically connected to the chip 121 and the patterned circuit layer 111a respectively for signal transmission between the chip 121 and the patterned circuit layer 111a.

The heat spreader 130 is disposed on a bottom surface 112 of the flexible substrate 110. In this embodiment, the heat spreader 130 includes a copper layer 131 and an adhesive (not shown), the adhesive is located between the copper layer 131 and the flexible substrate 110 and provided to adhere the copper layer 131 on the bottom surface 112 of the flexible substrate 110. Preferably, the heat spreader 130 is located under the electronic component 120 and provided for dissipating heat from the electronic component 120.

In this embodiment, the copper layer 131 contains more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation. Film or laminate containing copper grains with (1,0,0) crystallographic orientation exhibits a good bending strength, for this reason, the copper layer 131 of the heat spreader 130 of this embodiment has a good bending strength to prevent delamination from the flexible circuit board 100. The electrical conductivity of the heat spreader 130 is not to be concerned owing to the heat spreader 130 is not electrically connected to the electronic component 120 and there is no current passing through the heat spreader 130 so the copper layer 131 of the heat spreader 130 can contain more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation.

Preferably, in light of heat-dissipation efficiency of the heat spreader 130, the copper grains with (1,0,0) crystallographic orientation in the copper layer 131 of the heat spreader 130 have a grain size greater than 5 μm and the copper layer 131 of the heat spreader 130 has a thickness between 5 μm and 50 μm such that the heat spreader 130 has both good bending strength and good heat-dissipation performance.

The heat spreader 130 exhibits good bending strength because of the copper layer 131 containing more than or equal to 50% copper grains by volume with (1,0,0) crystallographic orientation. Consequently, it is possible to prevent the heat spreader 130 from peeling from the flexible circuit board 100.

While this invention has been particularly illustrated and described in detail with respect to the preferred embodiments thereof, it will be clearly understood by those skilled in the art that is not limited to the specific features shown and described and various modified and changed in form and details may be made without departing from the scope of the claims.