Flexible circuit board and method for manufacturing same

The present disclosure relates to a flexible circuit board. The flexible circuit board includes a first conductive trace substrate and a third conductive layer, a second conductive post and a third conductive post. The first conductive trace substrate includes a first insulating layer, a first conductive layer and a second conductive layer formed two opposite surfaces of the first insulating layer. The first conductive layer includes a first signal line, the second conductive layer includes a second signal line, and the first signal line is parallel connected with the second signal line.

FIELD

The subject matter herein generally relates to printed circuit boards, and particularly to a flexible circuit board and a method for manufacturing the flexible circuit board.

BACKGROUND

Generally, flexible circuit boards are light, soft, thin, small, ductile, flexible, and supporting high wiring density. However, a serious problem of signal transmitting loss is generated in the flexible circuit boards.

DETAILED DESCRIPTION

The term “substantially” is defined to be essentially conforming to the particular dimension, shape, or other feature that the term modifies, such that the component need not be exact. For example, “substantially cylindrical” means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. The references “a plurality of” and “a number of” mean “at least two.”

FIG. 10,FIG. 11, andFIG. 12together illustrate a flexible circuit board100according to one embodiment. The flexible circuit board100comprises a first conductive substrate140, a first glue sheet25formed on one surface of the first conductive140, a second glue sheet35formed on the other surface of the first conductive140; a second insulating layer21formed on the first glue sheet25, a third insulating layer31formed on the second glue sheet35; a outer layer220formed on the second insulating layer21, a fourth copper clad layer32formed on the third insulating layer31; a first solder mask layer34formed on the outer layer220, a second solder mask layer36formed on the fourth copper clad layer32; a first electromagnetic shielding layer241and, a second electromagnetic shielding layer242.

The first conductive substrate140includes a first insulating layer12, a first conductive layer110, and a second conductive layer130formed on opposite surfaces of the first insulating layer12, and a plurality of conductive posts103. The conductive posts103extend through the first conductive layer110and the first insulating layer12and expose part of the second conductive layer130.

The first conductive layer110includes a first signal line112and a first conductive pad114located at one end of the first signal line112. The second conductive layer130includes a second signal line132and a second conductive pad134located at one end of the second signal line132. The first signal line112is in parallel electrically connected to the second signal line132via the first conductive posts103. The first signal line112and the second signal line132transmit electrical signals.

The first signal line112corresponds to the second signal line132, the first signal line112has a same length with the second signal line132, and the first conductive pad114opposites to the second conductive pad134. The number of conductive posts103is four, and the four conductive post103are evenly distributed at opposite ends of the first signal line112. The first conductive pad114is adjacent to one part of the first conductive post103, and the second conductive pad134is adjacent to the other part of the first conductive posts103.

The flexible circuit board100further includes a second conductive post213and a third conductive post215. The second conductive post211extends through the outer layer220, the second insulating layer21, and the first glue sheet25and exposes the first conductive pad114. The third blind hole215extends through the third copper clad layer220, the second insulating layer21, and the first glue sheet25, the first insulating layer12and exposes the second conductive pad134.

The outer layer220includes a first pad222and a second pad224. The first pad222and the second pad224are configured to mount electrical elements. Therefore, the first pad222is configured as a signal input end, and the second pad224is configured as a signal output end.

The first pad222surrounds the second conductive post213and the second pad224surrounds the third conductive post215. The first pad222corresponds to the first conductive114, and the second pad224corresponds to the second conductive pad134. The second conductive post213is electrically connected the first pad222and the first conductive pad114, and the third conductive post215is electrically connected the second pad224and the second conductive pad134.

The first solder mask layer34exposes the first pad222and the second pad224, and the first solder mask layer34and the second solder mask layer36are configured to protect the outer layer220and the fourth copper clad layer32.

The first electromagnetic shielding layer241and the second electromagnetic shielding layer242are arranged at edges of the flexible circuit board100. The first electromagnetic shielding layer241and the second electromagnetic shielding layer242are perpendicular to the outer layer220. Both the first electromagnetic shielding layer241and the second electromagnetic shielding layer243comprise a plurality of conductive through holes242, and the conductive through holes242are spaced apart by a same distance. The outer layer220, the first electromagnetic shielding layer241, the second electromagnetic shielding layer243and the fourth copper clad layer32together form a shield against external signals for the benefit of the first signal line112and the second signal line132.

When the flexible circuit board100is in use, the first pad222is configured as a signal input end, and the second pad224is configured as a signal output end. That is to say, the external electrical signal is input to the first pad222and then divided into a first part signal and a second part signal and these are respectively transmitted along the first signal line112and the second signal line132.

In detail, the external electrical signal enters into the flexible circuit board100, passes through the second conductive posts213, and then enters into the first signal line112. Since the first signal line112is in parallel electrically connected with the second signal line132via the first conductive posts103, the first part electrical signal continues along the first signal line112. The second part electrical signal passes into the second signal line132via the first conductive posts103adjacent to the first conductive pad114and is transmitted along the second signal line132. When the first part electrical signal of the first signal line112comes across the first conductive posts103adjacent to the second conductive pad134, the first part electrical signal passes into the second signal line132and converges with the second part electrical signal. The first part electrical signal and the second part electrical signal are together transmitted along the third conductive posts215and are outputted from the second pad224.

The first signal line112is in a parallel connection with the second signal line132via the plurality of first conductive posts103. That is to say, a total thickness of the signal line includes a thickness of the first signal line112and a thickness of the second signal line132. Signal transmission loss is reduced and the total resistance of a parallel connection of the first signal line112and the second signal line132is less than the resistance of the first signal line112. The total resistance of the parallel connection of the first signal line112and the second signal line132is less than the resistance of the second signal line132. In this way, heat generated by the first signal line112and the second signal line132of the flexible circuit board100is reduced.

FIG. 13illustrates a flowchart in accordance with a second embodiment. The example method200for manufacturing the flexible circuit board100(shown inFIG. 9andFIG. 10) is provided by way of an example, as there are a variety of ways to carry out the method. Additionally, the illustrated order of blocks is by example only, and the order of the blocks can change. Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps. The method200can begin at block201.

At block201, as shown inFIG. 1, a first flexible copper clad laminate (FCCL)10is provided, and the first flexible copper clad laminate is processed to form a first conductive substrate140.

The first flexible copper clad laminate10is a double-sided copper clad laminate and includes a first insulating layer12, a first copper clad layer11and a second copper clad layer13. The first insulating layer12includes a first surface120and a second surface122opposite to the first surface120, the first copper clad layer11is formed on the first surface120, the second copper clad layer13is formed on the second surface130. A material of the first insulating layer12is selected from the group consisting of polynaphthalene dicarboxylic acid glycol ester (PEN), polyimide (PI), or polyterephthalate (PET).

The method of processing the first flexible copper clad laminate10to form a first conductive substrate140comprises steps:

Firstly, as shown inFIG. 2andFIG. 3, the first copper clad layer11and the first insulating layer12are etched to form the blind holes101. In the embodiment, an amount of the first blind holes101is four and evenly distributed at two opposite ends of the first flexible copper clad laminate10. That is, the amount of the first conductive posts103is at least two, and the at least two conductive posts103are evenly distributed at a predetermine location of the first copper clad layer11.

Secondly, the blind holes101are filled with electric conductive material to form the first conductive posts103. Alternatively, the first conductive posts103also can be formed using an electroplating method.

Lastly, as shown inFIG. 4, the first copper clad layer11and the second copper clad layer13are processed to form the first conductive layer110and the second conductive layer130, and obtain a first conductive substrate140. In the illustrated embodiment, the first conductive layer110and the second conductive layer130are formed using a laser etch method.

The first conductive layer110includes a first signal line112and a first conductive pad114located at one end of the first signal line112. The second conductive layer130includes a second signal line132and a second conductive pad134located at one end of the second signal line132. The first signal line112and the second signal line132are configured to transmit signals. The first signal line112corresponds to the second signal line132, and a projection of the first conductive pad114on the first insulating layer12and a projection of the second conductive pad134on the first insulating layer12are located at opposite sides of the first insulating layer12. The first conductive pads114adjacent to one part of the first conductive posts103, and the second conductive pads134adjacent to the other part of the first conductive posts103. The first signal line112is electrically connected to the second signal line132via the first conductive posts103.

At block202, as shown inFIG. 5, a second flexible copper clad laminate20is provided and processed to form a outer layer220. In this step, a first glue sheet25, a second glue sheet35, and a third flexible copper clad laminate30are also provided respectively. The method to process the second flexible copper clad laminate20to form the outer layer220comprises steps:

Firstly, as shown inFIG. 6, the second flexible copper clad laminate20, the first glue sheet25, the first conductive substrate140, the second glue sheet35and the third flexible copper clad laminate30are laminated together to form a second conductive substrate210. The second flexible copper clad laminate20and the first conductive layer110are located at opposites surface of the first glue sheet25, the third flexible copper clad laminate30and the second conductive layer130are located two opposites surface of the second glue sheet35.

A structure of the second flexible copper clad laminate20is substantially same with the third flexible copper clad laminate30. In the illustrated embodiment, the second flexible copper clad laminate20includes a second insulating layer21and a third copper clad layer22formed on the second insulating layer21. The third flexible copper clad laminate30includes a third insulating layer31and a fourth copper clad layer32formed on the second insulating layer31. the first glue sheet25and the second glue sheet35are prepreg.

Secondly, as shown inFIG. 7, a second blind hole211and a third blind214are formed in the second conductive substrate210, the second blind hole211extends through from the third copper clad layer22to the first conductive pad114, and the third blind hole214extends through from the third copper clad layer22to the second conductive pad134.

Thirdly, as shown inFIG. 8, the second blind hole211and the third blind214are electroplated to form a second conductive post213and a third conductive post215.

At block203, as shown inFIG. 9, the third copper layer22is etched to form a outer layer220. The outer layer220includes a first pad222and a second pad224. The first pad222surrounds the second conductive post213. The second pad224surrounds the third conductive post215. The first pad222corresponds to the first conductive114, and the second pad224corresponds to the second conductive pad134. The second conductive post213is electrically connected the first pad222and the first conductive pad114, and the third conductive post215is electrically connected the second pad224and the second conductive pad134. In the illustrated embodiment, the first pad222is configured as a signal input end and the second pad224is configured as a signal output end.

At block204, as shown inFIG. 10, two column conductive through holes242are formed in the third conductive substrate240, the two column conductive through holes242are formed a first electromagnetic shielding layer241and a second electromagnetic shielding layer243, respectively. The conductive through holes242are distributed outsides of the first pad222and the second pad224, and the through holes242in each column are spaced apart at the same distance. The conductive through holes242extend through from the outer layer220to the fourth copper clad layer32. In an alternative embodiment, the conductive through holes242and the second conductive post213are able to form in a same step.

At block205, as shown inFIG. 12, a first solder mask layer34is formed on the outer layer220and a second solder mask layer36is formed on the fourth copper clad layer32. The first solder mask layer34exposes the first pad222and the second pad224, and the first solder mask layer34and the second solder mask layer36are configured to protect the outer layer220and the fourth copper clad layer32. The outer layer220, the first electromagnetic shielding layer241, the second electromagnetic shielding layer243and the fourth copper clad layer32together form a square shield space for the first signal line112and the second signal line132, and the flexible circuit board100is obtained.

FIG. 14andFIG. 15together illustrate a flexible circuit board300according to a third embodiment. The flexible circuit board300inFIG. 14is similar to the flexible circuit board100inFIG. 10. The difference between the flexible circuit board300and the flexible circuit board100inFIG. 10is that the flexible circuit board300further includes a fourth conductive substrate340, a fourth copper clad laminate40, a fourth conductive post217, a fifth conductive219, a third pad226, and a fourth pad228. The third pad226and the fourth pad228are formed on the outer layer220.

In detail,FIG. 14is a perspective view of the third conductive substrate which omitting the first glue sheet between the second insulating layer21and the first conductive layer110, omitting the second glue sheet33between the third insulating layer31and the second conductive layer130, and omitting a third glue sheet45and a fourth glue sheet55formed two opposite surfaces of the fourth conductive substrate340.

The fourth conductive substrate340is laminated on the third insulating layer31via the third glue sheet45, the fourth copper clad laminate40is laminated on the third conductive substrate340via the fourth glue sheet55. The fourth copper clad laminate40includes a fifth insulating layer41and a fifth copper clad layer42formed on the fifth insulating layer41. The fifth copper clad layer42is configured as a ground shield layer.

The fourth conductive substrate340is similar to the first conductive substrate140. The fourth conductive substrate340includes a fourth insulating layer341, a third conductive layer342, and a fourth conductive layer345formed on opposite surfaces of the fourth insulating layer341. The third conductive layer342includes a third linear signal line343and a third conductive pad344located at one end of the first signal line343. The fourth conductive layer345includes a fourth linear signal line346and a second conductive pad347located at one end of the fourth linear signal line346. The third linear signal line343and the fourth linear signal line346are parallel electrically connected via the sixth conductive posts and configured to transmit an electrical signal.

The fourth conductive post217extends through from the outer layer220to the third conductive layer342, and the fifth conductive post217extends through from the outer layer220to the fourth conductive layer345. The fourth conductive post217electrically connected the third pad226and the third conductive pad344, The fifth conductive post219electrically connected the fourth pad228and the third conductive pad347, and the third pad226is configured as a signal input end and the fourth pad228is configured as a signal output end. The working principle of the flexible circuit board300is similar to the flexible circuit board100, so in the illustrated embodiment, there is no need to described in detail.