TWI633821B - Flexible printed circuit board and method manufacturing same - Google Patents

Abstract

A flexible circuit board includes a first photosensitive layer, a second photosensitive layer, and a third sensor, which are attached to each other. A light layer, a third photosensitive layer is located between the first photosensitive layer and a second photosensitive layer, the first photosensitive layer includes a first wiring layer and a first via hole, the first via hole is located in the first wiring layer, and the second photosensitive layer Including a second circuit layer and a second via hole, the second via hole is located in the second circuit layer, and the third photosensitive layer includes a third via hole, and the positions of the first via hole, the second via hole, and the third via hole correspond to each other. The first via hole, the second via hole, and the third via hole are conductively connected to each other to connect the first circuit layer and the second circuit layer. The diameters of the first via hole and the second via hole are the same. And the diameter of the second via.

Description

Flexible circuit board and manufacturing method thereof

The present invention relates to the field of circuit boards and their manufacturing, in particular to a flexible circuit board and its manufacturing method.

At present, the traditional manufacturing methods of flexible circuit board circuits are mainly the subtractive method and the additive method, and the conduction between the circuit layers is conducted by laser drilling or mechanical drilling. The hole wall is metalized by electroplating. However, in the process of manufacturing flexible circuit boards by traditional methods, deviations between the circuit and the hole ring disk often occur, resulting in shortness between the wires, hole breakage, etc .; or poor ring wire disconnection caused by the hole ring gap; due to the cover film (CVL) The surface layer of the flexible circuit board (FPC) is uneven due to the filling lines between the sizing layers. No matter the subtractive method or the additive method is used to form a line, it will be convexly attached to the surface of polyimide (PI). The adhesion depends entirely on the bonding force between the lower surface of the four surfaces of the line and the PI, and the line width is increasing. The thinner, the circuit is easy to peel off from PI under a certain external force, causing short circuit and poor disconnection. After CVL bonding, the glue will fill the gap between the circuits, causing the CVL surface to be uneven, and high-density surface mount technology (SMT) The flatness requirements of flexible circuit boards are getting higher and higher, so the uneven CVL surface will definitely restrict the development of SMT towards fineness and high density.

In view of this, it is necessary to provide a method for manufacturing a flexible circuit board that overcomes the above problems.

A method for manufacturing a flexible circuit board includes the steps of providing a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer. The first photosensitive layer, the second photosensitive layer, and the third photosensitive layer are all made of photosensitive material. Making; respectively performing exposure processing on the first photosensitive layer and the second photosensitive layer to obtain a first photoresist layer, a first hole region, a second photoresist layer, and a second hole region, and the third The photosensitive layer is subjected to exposure processing to obtain a third hole region; the first photosensitive layer, the second photosensitive layer, and the third photosensitive layer are aligned and laminated to obtain a composite substrate, the first photosensitive layer and the second The photosensitive layer is located on opposite sides of the third photosensitive layer; the laminated composite substrate is subjected to development processing, a first groove and a first through hole are formed on the first photosensitive layer, and the second photosensitive layer A second groove and a second through-hole are formed on the third photosensitive layer, and a third through-hole is formed on the third photosensitive layer. Said first via hole, forming a second line on said second photosensitive layer Layer, and a second via hole, a third via hole is formed on the third photosensitive layer, the first via hole, the second via hole, and the third via hole mutually communicate with the first circuit layer and The second circuit layer.

A flexible circuit board includes a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer that are pasted on each other. The third photosensitive layer is located between the first photosensitive layer and the second photosensitive layer. The first photosensitive layer includes a first circuit layer and a first via hole, the first via hole is located in the first circuit layer, the second photosensitive layer includes a second circuit layer and a second via hole, and the first two A via hole is located in the second circuit layer, the third photosensitive layer includes a third via hole, and the first via hole, the second via hole, and the third via hole are corresponding in position, and the first via hole The second via hole and the third via hole are connected to each other to connect the first circuit layer and the second circuit layer. The diameters of the first via hole and the second via hole are the same, and the diameter of the third via hole is the same. Larger than the diameter of the first and second vias.

Compared with the prior art, the manufacturing method of the flexible circuit board provided in this embodiment has the following advantages compared with the traditional manufacturing method of the flexible circuit board: 1. Various holes in the product of the present invention can be manufactured by exposure and development without the need for a mechanical drill Hole or laser processing, effectively improve production efficiency; 2. The vias and lines in the first photosensitive layer and the second photosensitive layer are formed by exposure and development at the same time, so that the holes and lines are not offset, no need to design small holes Large pad (hole ring), that is, to achieve a non-porous ring design, higher-density wiring can be laid at the interlayer conduction; 3. the circuit layer is embedded in the substrate, the surface of the circuit board is covered with a flat surface; 4. the surface of the circuit board is flat Breakage difference, the protective cover film can use thinner materials, which reduces the product thickness; 5. The manufacturing method can overcome the migration failure caused by insufficient filling of the cover layer between the ultra-fine lines.

10‧‧‧The first photosensitive layer

11‧‧‧The first photoresist layer

12‧‧‧ first hole area

13‧‧‧first groove

14‧‧‧The first through hole

15‧‧‧First line layer

16‧‧‧first via

20‧‧‧Second photosensitive layer

21‧‧‧Second photoresist layer

22‧‧‧Second hole area

23‧‧‧Second groove

24‧‧‧Second through hole

25‧‧‧Second line layer

26‧‧‧Second via

30‧‧‧ the third photosensitive layer

32‧‧‧ third hole area

34‧‧‧Third through hole

36‧‧‧Third via

40‧‧‧ composite substrate

42‧‧‧The first copper layer

44‧‧‧Second copper layer

50‧‧‧The first cover film

52‧‧‧The first film layer

54‧‧‧The first adhesive layer

60‧‧‧Second cover film

62‧‧‧Second film layer

64‧‧‧Second glue layer

100‧‧‧ flexible circuit board

FIG. 1 is a schematic cross-sectional view of a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the photoresist layer and the hole area formed after the first photosensitive layer, the second photosensitive layer, and the third photosensitive layer are exposed in FIG. 1.

FIG. 3 is a schematic cross-sectional view of the first photosensitive layer, the second photosensitive layer, and the third photosensitive layer in FIG. 2 after being combined to form a composite substrate.

FIG. 4 is a schematic cross-sectional view of the composite substrate in FIG. 3 after being developed and solidified.

FIG. 5 is a schematic perspective view of the composite substrate in FIG. 4.

FIG. 6 is a schematic cross-sectional view of the composite substrate in FIG. 4 after electroless copper plating is performed to form a first copper layer.

FIG. 7 is a schematic cross-sectional view of the composite substrate in FIG. 6 after the second copper layer is formed after the plating process is performed.

8 is a schematic cross-sectional view of the composite substrate in FIG. 7 after being subjected to copper reduction treatment to form a flexible circuit board having a first circuit layer and a second circuit layer.

9 is a schematic cross-sectional view of the flexible circuit board in FIG. 8 after the two sides are covered with a cover film.

The method for manufacturing a flexible circuit board provided by this technical solution includes the following steps:

The first step, referring to FIG. 1, provides a first photosensitive layer 10, a second photosensitive layer 20 and a third photosensitive layer 30.

The first photosensitive layer 10, the second photosensitive layer 20, and the third photosensitive layer 30 are all made of a photosensitive material. The photosensitive material may be other photosensitive materials suitable for making flexible circuit boards, such as a photosensitive cover film (PICL), a photosensitive polyimide resin (PSPI), and the like.

In this embodiment, the thicknesses of the first photosensitive layer 10 and the second photosensitive layer 20 are the same. The thickness of the third photosensitive layer 30 is slightly larger than the thickness of the first photosensitive layer 10 and the second photosensitive layer 20.

In the second step, referring to FIG. 2, the first photosensitive layer 10, the second photosensitive layer 20, and the third photosensitive layer 30 are separately exposed.

Specifically, the first photosensitive layer 10, the second photosensitive layer 20, and the third photosensitive layer 30 are respectively exposed, so that part of the first photosensitive layer 10, the second photosensitive layer 20, and the The third photosensitive layer 30 is cured.

After the first photosensitive layer 10 is exposed, a first photoresist layer 11 and a first hole region 12 are formed. The first hole region 12 is formed in the first photoresist layer 11. After the second photosensitive layer 20 is developed, a second photoresist layer 21 and a second hole region 22 are formed. The second hole region 22 is formed in the second photoresist layer 21. After the third photosensitive layer 30 is developed, a third hole region 32 is formed. The shape of the first hole region 12 is the same as that of the second hole region 22. The shape of the third hole region 32 is larger than the shape of the first hole region 12. In this embodiment, a plurality of first hole regions 12 are formed on the first photosensitive layer 10, a plurality of second hole regions 22 are formed on the second photosensitive layer 20, and two holes are formed on the third photosensitive layer 30.个 third hole area 32. The plurality of first hole regions 12 respectively correspond to the plurality of second hole regions 22. The two third hole regions 32 correspond to the two first hole regions 12 and the two second hole regions 22 on opposite sides of the first photosensitive layer 10 and the second photosensitive layer 20, respectively.

In the third step, referring to FIG. 3, the first photosensitive layer 10, the second photosensitive layer 20, and the third photosensitive layer 30 are laminated together to form a composite substrate 40.

The third photosensitive layer 30 is located between the first photosensitive layer 10 and the second photosensitive layer 20, and the three are aligned with each other. Each third hole region 32 is aligned with a corresponding one of the first hole regions 12 and a corresponding one of the second hole regions 22. Specifically, the first photosensitive layer 10, the second photosensitive layer 20, and the third photosensitive layer 30 are each provided with a plurality of positioning holes, so as to facilitate the alignment pressing between the three.

In the fourth step, referring to FIGS. 4 and 5, a development process is performed on the laminated composite substrate 40.

After the first photoresist layer 11 is developed, a first groove 13 is formed. After the first hole region 12 is developed, a first through hole 14 is formed. The first through hole 14 is formed in the first groove 13. A second groove 23 is formed after the second photoresist layer 21 is developed. After the second hole region 22 is developed, a second through hole 24 is formed. The second through hole 24 is formed in the second groove 23. After the third hole region 32 is developed, a third through hole 34 is formed. Each of the third through-holes 34 communicates with the corresponding first through-hole 14 and the second through-hole 24 to form a first photosensitive layer 10, a second photosensitive layer 20, and a third photosensitive layer. 30 through holes.

Fifth step, referring to FIG. 6, the developed composite substrate 40 is subjected to an electroless copper plating process, so that a first copper layer 42 is formed on an exposed portion of the composite substrate 40.

The first copper layer 42 is formed on the surface of the first photosensitive layer 10, the surface of the second photosensitive layer 20, in the first groove 13, the second groove 23, the first through hole 14, and the second through hole 24. And in the third through hole 34.

The first copper layer 42 is a thin copper layer. This step prepares for the subsequent copper electroplating process, so that the composite substrate 40 is more easily electroplated with copper during the electroplating process.

In the sixth step, referring to FIG. 7, copper plating is performed on the composite substrate 40 after the first copper layer 42 is formed.

The surface of the first copper layer 42, including the first through-holes 14, the second through-holes 24 and the third through-holes 34, are filled with copper plating to form a second copper layer 44.

The second copper layer 44 fills the first groove 13. The second copper layer 44 fills the first via hole 14 to form the first via hole 16. The second copper layer 44 fills the second groove 23. The second copper layer 44 fills the second through hole 24 to form a second through hole 26. The second copper layer 44 fills the third via hole 34 to form a third via hole 36. Wherein, the third via hole 36 corresponds to the positions of the first via hole 16 and the second via hole 26, and is connected to the second copper layer 44 on both sides of the composite substrate 40.

In a seventh step, referring to FIG. 8, copper reduction is performed on the composite substrate 40 after copper plating.

The composite substrate 40 removes copper on both surfaces of the composite substrate 40 through steps such as etching, leaving only the copper in the first via 16, the second via 26, and the third via 36. The first circuit layer 15 and the second circuit layer 25 are formed on both surfaces of the composite substrate 40. At this time, the first photosensitive layer 10 and the second photosensitive layer 20 are both smooth surfaces. The surface of the first circuit layer 15 is flush with the surface of the first photosensitive layer 10, and the surface of the second circuit layer 25 is flush with the surface of the second photosensitive layer 20.

Eighth step, referring to FIG. 9, a first cover film 50 and a second cover film 60 are provided. The first cover film 50 and the second cover film 60 are laminated on both surfaces of the composite substrate. The flexible circuit board 100 is formed.

The first cover film 50 includes a first film layer 52 and a first adhesive layer 54. The first adhesive layer 54 is adhered on the surfaces of the first photosensitive layer 10 and the first circuit layer 15. The first film layer 52 is far from the first circuit layer 15.

The second cover film 60 includes a second film layer 62 and a second adhesive layer 64. The second adhesive layer 64 is adhered on the surfaces of the second photosensitive layer 20 and the second circuit layer 25. The second film layer 62 is far from the second circuit layer 25.

The first cover film and the second cover film may be made of materials such as CVL, photosensitive cover film (PICL), liquid crystal polymer (LCP), etc. Since the filling material is not involved, thin materials can be selected to make ultra-thin products.

FIG. 9 is a flexible circuit board 100 made by the method described in this embodiment.

A flexible circuit board 100 includes a first photosensitive layer 10, a second photosensitive layer 20 and a third photosensitive layer 30 which are bonded to each other. The third photosensitive layer 30 is located between the first photosensitive layer 10 and the second photosensitive layer 20. The first photosensitive layer 10 includes a first circuit layer 15 and a first via hole 16. The first via hole 16 is located in the first circuit layer 15. The second photosensitive layer 20 includes a second circuit layer 25 and a second via hole 26. The second via hole 26 is located in the second circuit layer 25. The third photosensitive layer 30 includes a third through hole 36. The third via holes 36 correspond to positions of the first via holes 16 and the second via holes 26. Each of the third via holes 36 is electrically connected to a corresponding one of the first via holes 16 and the second via hole 26. The first circuit layer 15 and the second circuit layer 25 communicate with each other through the first via hole 16, the second via hole 26, and the third via hole 36. A diameter of the first via hole 16 is the same as that of the second via hole 26. A diameter of the third via 36 is slightly larger than a diameter of the first via 16 and the second via 26.

Compared with the prior art, the manufacturing method of the flexible circuit board provided in this embodiment has the following advantages compared with the traditional manufacturing method of the flexible circuit board: 1. Various holes in the product of the present invention can be manufactured by exposure and development without the need for a mechanical drill Hole or laser processing, effectively improve production efficiency; 2. The vias and lines in the first photosensitive layer and the second photosensitive layer are formed by exposure and development at the same time, so that the holes and lines are not offset, no need to design small holes Large pad (hole ring), that is, to achieve a non-porous ring design, higher-density wiring can be laid at the interlayer conduction; 3. the circuit layer is embedded in the substrate, the surface of the circuit board is covered with a flat surface; 4. the surface of the circuit board is flat Breakage difference, the protective cover film can use thinner materials, which reduces the product thickness; 5. The manufacturing method can overcome the migration failure caused by insufficient filling of the cover layer between the ultra-fine lines.

Understandably, for those having ordinary knowledge in the art, various other corresponding changes and deformations can be made according to the technical concept of the present invention, and all these changes and deformations should belong to the protection scope of the present invention.

Claims (8)

A method for manufacturing a flexible circuit board includes the steps of providing a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer, the first photosensitive layer, the second photosensitive layer, and the third photosensitive layer. Both are made of a photosensitive material, the thickness of the first photosensitive layer and the second photosensitive layer are the same, and the thickness of the third photosensitive layer is slightly larger than the thickness of the first photosensitive layer and the second photosensitive layer; Performing exposure processing on the first photosensitive layer and the second photosensitive layer to obtain a first photoresist layer, a first hole area, a second photoresist layer, and a second hole area, and performing a third photosensitive layer A third hole region is obtained through exposure processing; the first photosensitive layer, the second photosensitive layer, and the third photosensitive layer are aligned and laminated to obtain a composite substrate, the first photosensitive layer, and the first photosensitive layer. Two photosensitive layers are located on opposite sides of the third photosensitive layer; the laminated composite substrate is subjected to development processing, a first groove and a first through hole are formed on the first photosensitive layer, and the second photosensitive layer is formed on the second photosensitive layer. A second groove and a second through hole are formed on the layer, A third through hole is formed thereon; a circuit is made on the composite substrate, a first circuit layer and a first via are formed on the first photosensitive layer, and a second circuit layer and a first via are formed on the second photosensitive layer. Two via holes, a third via hole is formed on the third photosensitive layer, and the first via hole, the second via hole, and the third via hole mutually conduct the first circuit layer and the first via layer. Two circuit layers; two cover films are provided, and the two cover films are respectively attached to the first photosensitive layer and the second photosensitive layer. The method for manufacturing a flexible circuit board according to claim 1, wherein, when the circuit substrate is fabricated, the composite substrate is first subjected to electroless copper plating on the surfaces of the first photosensitive layer and the second photosensitive layer. A first copper layer is formed in the plurality of through holes. The method for manufacturing a flexible circuit board according to claim 2, wherein the composite substrate after electroless copper plating is electroplated, and the first groove is filled with copper to form the first circuit layer, and the second The groove is filled with copper plating to form the second circuit layer. The method for manufacturing a flexible circuit board according to claim 3, wherein after the composite substrate is electroplated, the method further includes the following steps: performing a copper reduction treatment on the composite substrate to expose the first photosensitive layer and the substrate. The second photosensitive layer forms the first circuit layer and the second circuit layer. The method for manufacturing a flexible circuit board according to claim 1, wherein the cover film includes an adhesive film layer and an adhesive layer, and the adhesive layer is adhered to the first photosensitive layer and the second photosensitive layer . The method for manufacturing a flexible circuit board according to claim 1, wherein during the exposure process, the third hole region corresponds to the first and second hole regions, respectively, and the aperture of the first hole region is equal to the The pore diameter of the second hole region is larger than that of the first and second hole regions. The method for manufacturing a flexible circuit board according to claim 1, wherein the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are provided with a plurality of positioning holes for the first photosensitive layer, Positioning between the second photosensitive layer and the third photosensitive layer. A flexible circuit board includes a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer that are pasted on each other. The third photosensitive layer is located between the first photosensitive layer and the second photosensitive layer. The thickness of the first photosensitive layer and the second photosensitive layer are the same. The thickness of the third photosensitive layer is slightly larger than the thickness of the first photosensitive layer and the second photosensitive layer. The first photosensitive layer includes a first A circuit layer and a first via hole, the first via hole is located in the first circuit layer, the second photosensitive layer includes a second circuit layer and a second via hole, and the second via hole is located in the first Within the two circuit layers, the third photosensitive layer includes a third via hole, and the first via hole, the second via hole, and the third via hole are corresponding in position. The first via hole, the second via hole, and Third vias are connected to each other to connect the first circuit layer and the second circuit layer. The diameters of the first and second vias are the same, and the diameters of the third vias are larger than those of the first and second vias. The aperture of the second via, the flexible circuit board further includes two coverings The two films are attached to cover overlying the first surface of the second photosensitive layer and the photosensitive layer.