CN101516159B - Stiffening plate and stiffening flexible circuit board comprising same - Google Patents

Abstract

The invention provides a reinforcing plate, which is formed by alternate arrangement of at least one polyimide layer and at least one polyamideimide layer. Described polyamide-imide layer is made up of polyamide-imide material, and the structural general formula A of this polyamide-imide material is: Wherein Ar and Ar' are aromatic ring substituents. The invention also provides a reinforced flexible circuit board comprising the reinforcing board. The reinforced flexible circuit board is less likely to warp and has better structural stability.

Description

Reinforcement board and reinforced flexible circuit board including the reinforcement board

technical field

The invention relates to the technical field of flexible circuit boards, in particular to a reinforcing board and a reinforced flexible circuit board comprising the reinforcing board.

Background technique

With the continuous development of foldable electronic products such as folding mobile phones and slider mobile phones, flexible printed circuit boards (Flexible Printed Circuit Board, FPCB), which are light, thin, short, small and bendable, are widely used in electronic products In order to realize the electrical connection between different circuits. In order to obtain FPCB with better flexural properties, improving the flexural properties of base film materials used in FPCB has become a research hotspot. See the literature Electrical Insulation Maganize, Volume 5, Issue 1, Jan.-Feb., 1989 Papers: 15-23, "Applications of Polyimide Films to the Electrical and Electronic Industries in Japan".

In order to meet the multifunctional design requirements of foldable electronic products, the number of electronic components mounted on the surface of the FPCB has also increased accordingly. However, compared with rigid circuit boards, FPCBs with good flexural properties have low mechanical strength and low load-carrying capacity, and during use, such as when electronic devices are installed in surface mount technology (Surface Mount Technology, SMT), FPCBs are easy to Cracked or damaged, unable to carry a large mass or a large number of electronic devices, hindering the development of multifunctional foldable electronic products. At present, as shown in FIG. 1 , the industry generally presses a reinforcing sheet 110 made of polyimide (Polyimide, PI) material on the surface of a flexible substrate 130 through an adhesive layer 120 made of epoxy resin to produce Reinforced FPCB10 with higher load carrying capacity. However, the coefficient of thermal expansion (Coefficient of Thermal Expansion, CET) of PI and epoxy resin is different. When the adhesive layer 120 is heated, the expansion and contraction degrees of the two layers are different, which may easily cause warping of the reinforced FPCB 10 and increase the difficulty of subsequent surface mount electronic components.

Contents of the invention

Therefore, it is necessary to provide a reinforcing plate and a reinforced flexible circuit board including the reinforcing plate, so as to increase the mechanical strength of the flexible circuit board and prevent the flexible circuit board from warping.

A reinforcing board and a reinforced flexible circuit board comprising the reinforcing board will be described below with a plurality of embodiments.

The reinforcing plate is formed by alternate arrangement of at least one polyimide layer and at least one polyamideimide layer. Described polyamide-imide layer is made up of polyamide-imide material, and the general structural formula A of this polyamide-imide material is:

其中Ar及Ar’为芳香环取代基。

Wherein Ar and Ar' are aromatic ring substituents.

The reinforced flexible circuit board includes a flexible circuit board and a reinforcing board bonded to the flexible circuit board. The reinforcing plate is formed by alternate arrangement of at least one polyimide layer and at least one polyamideimide layer, the polyamideimide layer is composed of polyamideimide material, the polyamideimide The general structural formula A of the amine material is:

Wherein Ar and Ar' are aromatic ring substituents.

Compared with the prior art, the reinforcing plate is made of a polyamide-imide layer having a general structural formula A, because the thermal expansion coefficient of the polyamide-imide is similar to that of polyimide, that is, polyamide-imide The expansion and contraction rates of imide and polyimide are similar after being heated. Therefore, the flexible circuit board including the reinforcing plate is not easy to warp, improves the structural stability, and facilitates the operation of subsequent manufacturing processes.

Description of drawings

Fig. 1 is a sectional view of a reinforced FPCB provided in the prior art.

Fig. 2 is an enlarged partial cross-sectional view of the reinforcing plate provided by the first embodiment of the technical solution.

Fig. 3 is an enlarged partial cross-sectional view of the reinforcing plate provided by the second embodiment of the technical solution.

Fig. 4 is an enlarged partial cross-sectional view of the reinforcing plate provided by the third embodiment of the technical solution.

Fig. 5 is an enlarged partial cross-sectional view of the reinforced flexible circuit board provided by the fourth embodiment of the technical solution.

Fig. 6 is an enlarged partial cross-sectional view of the reinforced flexible circuit board provided by the fifth embodiment of the technical solution.

Detailed ways

The reinforcing plate provided by the embodiment of the technical solution and the reinforced flexible circuit board including the reinforcing plate will be further described in detail below with reference to the drawings and multiple embodiments.

Since the actual thickness of the reinforcement plate is very thin and has the same structure along the width direction, in order to clearly show the structure of the reinforcement plate, the structure of the reinforcement plate will be described in detail in conjunction with the enlarged partial section of the reinforcement plate (as shown in Figure 2 , Figure 3 and Figure 4). Similarly, the structure of the reinforced flexible circuit board (as shown in FIG. 5 and FIG. 6 ) is also illustrated with a partial cross-sectional enlarged view for easy understanding.

Please refer to FIG. 2 , the reinforcing plate 20 provided in the first embodiment of the technical solution is used for attaching to the flexible circuit board to improve the mechanical properties of the flexible circuit board. The reinforcing board 20 is formed by at least one PI layer 210 and at least one polyamideimide (PAI) layer 220 arranged alternately. The number of layers of the PI layer 210 is N, and the number of layers of the PAI layer 220 is M. According to the different design requirements of the circuit board, the values of the number of layers N of the PI layer 210 and the number of layers M of the PAI layer 220 may be equal or unequal, so the opposite two outermost sides of the reinforcement board 20 may be the PI layer 210 at the same time, or at the same time PAI layer 220 or PI layer 210 on one side and PAI layer 220 on the other. The reinforcing plate 20 has a thickness of 25 μm to 250 μm. Among them, the thickness of the PI layer 210 is 25 μm-75 μm, or the thickness of the PAI layer 220 is 25 μm-75 μm. The thickness of the PI layer 210 and the thickness of the PAI layer 220 can be determined according to the design requirements, as long as the total thickness of the reinforcing plate 20 is 25 μm-250 μm. Can.

In this embodiment, the reinforcing board 20 is a five-layer composite reinforcing board including three PI layers 210 and two PAI layers 220 , namely: N=3, M=2. The PAI layer 220 is located between two PI layers 210 and is used to bond two adjacent PI layers 210 to form the reinforcing plate 20 . The outermost side of the reinforcing plate 20 is a PI layer 210 . The outermost PI layer 210 is used for bonding with the flexible circuit board. Certainly, the number of layers of the reinforcing plate 20 including the PI layer 210 and the PAI layer 220 is not limited, and can be determined according to different design requirements, as long as N=M+1 (ie, the outermost layer is the PI layer 210 ).

The PAI layer 220 is composed of PAI material, and the general structural formula A of the PAI material is:

其中Ar及Ar’为芳香环取代基，例如

Where Ar and Ar' are aromatic ring substituents, such as

等。

wait.

The PAI can be obtained by reacting a diamine monomer with trimellitic anhydride to obtain an imide group-containing dicarboxylic acid monomer, that is, a diimide dicarboxylic acid monomer; and then performing polycondensation reaction with a diamine monomer. Of course, PAI can also be prepared by other methods, as long as the prepared PAI has the general structural formula A.

The molecular chain of the general structural formula A of the PAI material contains aromatic imide groups. The aromatic imide group also exists on the molecular chain of the PI material, so the PAI material has similar properties to the PI material. For example, good flexibility, heat resistance and chemical resistance, more importantly, the thermal expansion coefficient of PAI material is 22×10 ^-6 ~33×10 ^-6 K ^-1 , which is different from that of PI material The coefficient of thermal expansion is similar. In addition, the PAI material has good fluidity in molten state and has good cohesive force. Therefore, when the reinforcing plate 20 made by bonding the PI layer 210 with the PAI layer 220 is heated, the expansion of the PAI material and the PI material is related to The degree of shrinkage tends to be consistent, which can prevent the reinforcement board 20 from warping.

Please refer to Fig. 3, the reinforcing board 30 provided for the second embodiment of the technical solution has the same structure as the reinforcing board 20 provided in the first embodiment of the technical solution, the difference is that the number of layers of the PI layer 310 is N It is the same as that the number of layers of the PAI layer 320 is M, that is, M=N. In this embodiment, the reinforcing board 30 is a four-layer composite reinforcing board including two PI layers 310 and two PAI layers 320 , ie: M=N=2. At this time, the opposite outermost sides of the reinforcement plate 30 are the PI layer 310 on one side and the PAI layer 320 on the other side. The outermost PI layer 310 or PAI layer 320 can be used for bonding with the flexible circuit board.

Please refer to Fig. 4, the reinforcing board 40 provided for the third embodiment of the technical solution has the same structure as the reinforcing board 20 provided in the first embodiment of the technical solution, the difference is that the number of layers of the PI layer 410 is N The relationship with the number of layers of the PAI layer 420 being M is M=N+1. In this embodiment, the reinforcing board 40 includes a PI layer 410 and two PAI layers 420 bonded to opposite sides of the PI layer 410 , namely: M=2, N=1. The two opposite outermost sides of the reinforcing board 40 are PAI layers 420 at the same time. The outermost PAI layer 420 is used for bonding with the flexible circuit board.

Please refer to Figure 5, taking the flexible circuit board including the reinforcing plate 20 provided by the first embodiment of the technical solution as an example to introduce the reinforced flexible circuit board 50 provided by the fourth embodiment of the technical solution, which includes a flexible circuit plate 510 , reinforcing plate 20 and adhesive layer 520 . The flexible circuit board 510 is a single-sided or double-sided single-layer or multi-layer flexible circuit board made of a metal-clad substrate through a series of manufacturing processes, such as making lines, via holes, attaching protective films, or electroplating. layers of circuit substrates. The flexible circuit board 510 has a reinforcing surface 511 for bonding with the reinforcing board 20 .

The reinforcement board 20 is attached to the reinforcement surface 511 of the flexible circuit board 510 through the adhesive layer 520 . In this embodiment, the outermost layer of the reinforcing plate 20 is the PI layer 210 . The PI layer 210 is attached to the reinforcing surface 511 of the flexible circuit board 510 through the adhesive layer 520 .

The thickness of the adhesive layer 520 is 25 μm˜70 μm. In this embodiment, the adhesive layer 520 is composed of PAI material, and the general structural formula A of the PAI material is:

其中Ar及Ar’为芳香环取代基，例如：

Where Ar and Ar' are aromatic ring substituents, for example:

等。

wait.

PAI material has good fluidity and good cohesive force in molten state, and the thermal expansion coefficient of PAI material is 22×10 ^-6 ~33×10 ^-6 K ^-1 . Similarly, it can be seen that when the reinforced flexible circuit board 50 made by bonding the flexible circuit board 510 and the reinforcing board 20 with the adhesive layer 520 is heated, the PAI material of the adhesive layer 520 and the PI material of the reinforcing board 20 will expand. It tends to be consistent with the degree of shrinkage, which can avoid warping of the reinforced flexible circuit board 50 .

It can be understood that the reinforced flexible circuit board 50 can also be a flexible circuit board 510 including the reinforced board 30 provided in the second embodiment or the reinforced board 40 provided in the third embodiment, so as to increase the strength of the flexible circuit board 510 Mechanical strength.

Please refer to Figure 6, taking the flexible circuit board including the reinforcing plate 20 provided by the first embodiment of the technical solution as an example to introduce the reinforced flexible circuit board 60 provided by the fifth embodiment of the technical solution, its structure and reinforcement The structure of the flexible circuit board 50 is similar, the difference is that the reinforcing plate 20 is directly attached to the flexible circuit board 610 to form the reinforcing flexible circuit board 60 without using adhesive. The reinforcing surface 611 of the flexible circuit board 610 is in contact with and attached to the reinforcing plate 20 .

In this embodiment, the outermost layer of the reinforcing plate 20 is the PI layer 210 . Due to better fluidity and cohesive force in the molten state, the PI layer 210 on the outermost side of the reinforcement board 20 can act as an adhesive to bond the reinforcement board 20 and the flexible circuit board 610 .

It can be understood that the reinforced flexible circuit board 60 can also be a flexible circuit board 610 including the reinforced board 30 provided in the second embodiment or the reinforced board 40 provided in the third embodiment, so as to increase the strength of the flexible circuit board 610 Mechanical strength.

In addition, both the PAI material and the PI material are sticky, but the cohesive force of the PAI material is better than that of the PI material. Therefore, in order to ensure that the reinforced flexible circuit board 60 will not be peeled or delaminated, it is preferable to use PAI material to make the outermost layer structure.

It can be understood that those skilled in the art can make various other corresponding changes and modifications according to the technical concept of the present invention, and all these changes and modifications should belong to the protection scope of the claims of the present invention.

Claims (10)

1. A reinforcement plate, characterized in that, it is formed by alternate arrangement of at least one polyimide layer and at least one polyamide-imide layer, and the polyamide-imide layer is made of polyamide-imide Material composition, the general structural formula A of this polyamide-imide material is:

Wherein Ar and Ar' are aromatic ring substituents. 2 . The reinforcing plate according to claim 1 , wherein the thickness of the reinforcing plate is 25 μm˜250 μm. 3 . The reinforcing plate according to claim 2 , wherein the polyimide layer has a thickness of 25 μm˜75 μm. 4 . 4. The reinforcing plate according to claim 2, wherein the polyamide-imide layer has a thickness of 25 μm˜75 μm. 5 . The reinforcing plate according to claim 1 , wherein the thermal expansion coefficient of the polyamide-imide is 22×10 ^-6 ~33×10 ^-6 K ^-1 . 6. The reinforcing plate according to claim 1, wherein the number of layers of the polyimide layer is 3, and the number of layers of the polyamide-imide layer is 2; or the number of layers of the polyimide layer is 2; The number of layers of the amine layer is 2, and the number of layers of the polyamide-imide layer is 2; or the number of layers of the polyimide layer is 1, and the number of layers of the polyamide-imide layer is 2. 7. A reinforced flexible circuit board, comprising a flexible circuit board and the reinforcing board according to any one of claims 1 to 6 bonded to the flexible circuit board. 8. The reinforced flexible circuit board according to claim 7, wherein the reinforcing board is attached to the flexible circuit board through an adhesive layer, and the adhesive layer is composed of polyamide-imide material , the general structural formula A of the polyamide-imide material is:

Wherein Ar and Ar' are aromatic ring substituents. 9 . The reinforced flexible circuit board according to claim 8 , wherein the thermal expansion coefficient of the polyamide-imide of the adhesive layer is 22×10 ^-6 ~33×10 ^-6 K ^-1 . 10. The reinforced flexible circuit board according to claim 8, wherein the thickness of the adhesive layer is 25 μm˜70 μm. the

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