Flexible printed circuit board and its manufacturing method

Abstract

A flexible circuit board, comprising: a polyimide substrate, provided with at least one through hole through, grooves are formed on opposite surfaces of the polyimide substrate; a polyimide conductive film, Formed on the opposite two surfaces of the polyimide substrate except for the groove and the inner wall of the through hole, the polyimide conductive film includes a second layer located on the inner wall of the through hole A polyimide conductive layer and a second polyimide conductive layer except the first polyimide conductive layer; two conductive circuit layers, formed on the second polyimide conductive layer away from On the surface of the polyimide substrate, each conductive circuit layer has a circuit opening corresponding to the position of the groove, wherein the through hole formed with the first polyimide conductive layer has a conductive part to The two conductive circuit layers are electrically connected; two covering films are formed on the surfaces of the two conductive circuit layers away from the polyimide substrate, and the covering films are filled into the grooves.

Description

technical field [0001] The invention relates to a flexible circuit board and a manufacturing method thereof. Background technique [0002] With the development of electronic products such as smartphones, tablet computers and wearable devices in the direction of miniaturization and multi-function, flexible circuit boards also need to meet the requirements of high density. The modified semi-additive method (MSAP) is a relatively common process for making high-density flexible circuit boards. MSAP adopts the method of laminating ultra-thin bottom copper on the surface of polyimide (PI) substrate, thinning the bottom copper to the required thickness, and then laminating the dry film, using the exposure and development technology to form an electroplated copper layer on the top of the bottom copper, and then Tear off the dry film, and then etch and remove the bottom copper located between the electroplated copper layers. [0003] However, during the etching process of the botto...

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Problems solved by technology

[0003] However, during the etching process of the bottom copper, the sidewall of the electroplated copper layer may also be etched, resulting in an increase in the line pitch and making it difficult to obtain a high-density flexible circuit board

Moreover, since the bottom copper is generally electrolytic copper, and its material is denser than that of electroplated copper, the difference in corrosion rate between the two will cause undercut at the bottom of the copper line, causing the line to be skewed

Furthermore, the surface of the PI substrate has a certain roughness, and the surface of the PI substrate usually forms a seed layer by sputtering to overcome the problem of poor adhesion between the bottom copper and the PI substrate, and the seed layer is used in subsequent It is difficult to remove during the etching process, resulting in residues and the risk of short circuits

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