Asymmetric metal foil clad laminate and printed circuit board including same

Abstract

The present invention provides an asymmetric metal foil-clad laminate and a printed circuit board including the same. The asymmetric metal foil-clad laminate includes one or at least two laminated low-modulus prepregs and a metal foil coated on one side of the one or at least two laminated low-modulus prepregs, or a metal foil with different thicknesses on both sides. The low-modulus prepreg has an elastic modulus of 22 GPa or less after curing. By using a low-modulus prepreg with an elastic modulus of 22 GPa or less after curing as an insulating material for the asymmetric metal foil-clad laminate, the obtained asymmetric metal foil-clad laminate and the printed circuit board manufactured therefrom have low warpage in state A and warpage after reflow soldering, ensuring the reliability of the printed circuit board.

Description

[Technical Field]

[0001] The present invention relates to the technical field of circuit boards, and more particularly to an asymmetric metal foil clad laminate and a printed circuit board including the same. [Background technology]

[0002] Printed circuit boards are the support for electronic devices and the provider of electrical connections for electronic devices, and are widely used in various electronic devices, communication devices, computers, automobiles, household appliances, etc. With the development of electronic information technology and the multi-functionality and miniaturization of electronic products, the integrated circuit board, which is the core structure, tends to be increasingly multi-layered and multi-functional.

[0003] Metal foil-clad laminates are the substrate for manufacturing printed circuit boards. Conventional double-sided metal foil-clad laminates are coated with metal foils of the same thickness and with consistent properties. Even if the metal foils on both sides are different, there is no significant difference in thickness or properties. This is to minimize or eliminate warpage in the double-sided metal foil-clad laminate in the A state and after reflow soldering, and to ensure that the printed circuit board has good support for electronic devices.

[0004] Single-sided circuit boards require a single-sided copper-clad board. When a single-sided circuit board is required to carry a large current, the metal foil on each side of the double-sided metal foil-clad laminate must be designed to have different thicknesses. This not only meets performance and cost requirements, but also satisfies the heat dissipation requirements of the circuit under high current. However, such asymmetric metal foil structures can lead to uneven internal stresses in the asymmetric metal foil-clad laminate during processing such as lamination, solder resist application, and hot air leveling. This can lead to warpage of the laminate and printed circuit boards manufactured using the laminate, as well as problems such as poor installation of electronic devices and circuit shorts, reducing reliability.

[0005] Therefore, in order to improve the reliability of printed circuit boards manufactured using asymmetric metal foil clad laminates, it is necessary to develop asymmetric metal foil clad laminates with low warpage. Summary of the Invention

[0006] In response to the deficiencies of the prior art, the present invention provides an asymmetric metal foil-clad laminate and a printed circuit board including the same, which exhibits low warpage in state A and after reflow soldering, thereby contributing to improved safety and reliability of the printed circuit board.

[0007] To achieve this object, the present invention provides the following technical solutions.

[0008] In a first aspect, the present invention provides an asymmetric metal foil-clad laminate comprising one or at least two laminated low modulus prepregs and a metal foil coated on one side of the one or at least two laminated low modulus prepregs, or a metal foil having a different thickness on both sides.

[0009] The low modulus prepreg has an elastic modulus after curing of 22 GPa or less (for example, 22 GPa, 21.5 GPa, 21 GPa, 20.5 GPa, 20 GPa, 19.5 GPa, 19 GPa, 18.5 GPa, 18 GPa, 17.5 GPa, 17 GPa, 16.5 GPa, 16 GPa, 15.5 GPa, 15 GPa, 14 GPa, 13 GPa, 12 GPa, 11 GPa, 10 GPa, 8 GPa, 6 GPa, or 5 GPa, etc.).

[0010] Through research, the inventors discovered that by selecting a low-modulus prepreg with a post-cure elastic modulus of 22 GPa or less as the insulating material for an asymmetric metal foil clad laminate, the amount of warpage of the laminate can be kept low. If the post-cure elastic modulus of the prepreg exceeds 22 GPa, the laminate will be too rigid and have poor stress buffering ability, and will not be able to effectively buffer the stress caused by the asymmetry of the asymmetric metal foil clad laminate's structure, making the asymmetric metal foil clad laminate prone to warping.

[0011] In the present invention, when a laminate contains one low-modulus prepreg, "one or both sides of the low-modulus prepreg" refers to one or both sides of the single low-modulus prepreg. When a laminate contains at least two stacked low-modulus prepregs, "one or both sides of the low-modulus prepreg" refers to one or both sides of the stacked low-modulus prepreg composite. The thickness of the prepreg is not limited in the present invention. In the present invention, the term "asymmetric" primarily refers to a situation in which the thicknesses of the metal foil on both sides of the low-modulus prepreg are different, and only one side of the low-modulus prepreg is covered with metal foil, resulting in a single-sided board with one side covered with metal foil and the other side uncovered. It also includes a situation in which both sides are covered with metal foil of different thicknesses.

[0012] The low-modulus prepreg includes a substrate and a resin composition adhered to the substrate by immersion or coating. In the present invention, the type of resin composition is not particularly limited, and those skilled in the art can select it according to actual needs as long as the low-modulus prepreg has an elastic modulus of 22 GPa or less after curing. In the present invention, the substrate is not particularly limited, and examples include textiles, nonwoven fabrics, thick yarns, staple fibers, and fiber paper. The substrate may be made of inorganic fibers (e.g., glass fibers such as E-glass, D-glass, L-glass, M-glass, S-glass, T-glass, NE-glass, Q-glass, and quartz) or organic fibers (e.g., polyimide, polyamide, polyester, polyphenylene ether, and liquid crystal polymers), with glass fiber cloth being preferred.

[0013] The method for producing the asymmetric metal foil-clad laminate according to the present invention is not specifically limited, and it can be produced by a well-known method. As lamination conditions, general lamination conditions for metal foil-clad laminates, laminates for printed circuit boards, and multilayer boards may be used.

[0014] The following are only preferred technical solutions of the present invention, and are not intended to limit the technical solutions of the present invention. By utilizing the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] In a preferred technical solution of the present invention, the low modulus prepreg has an elastic modulus of 20 GPa or less after curing.

[0016] In a preferred technical solution of the present invention, the low modulus prepreg has an elastic modulus of 18 GPa or less after curing.

[0017] In a preferred technical solution of the present invention, the low modulus prepreg has an elastic modulus of 16 GPa or less after curing.

[0018] In a preferred technical solution of the present invention, the low-modulus prepreg has a post-cure elastic modulus of 5 GPa or more. If the post-cure elastic modulus of the prepreg is too low, the laminate's rigidity will be too low, and if the external force is too large, the asymmetric metal foil clad laminate may deform, resulting in poor support for the electronic device on the printed circuit board. Furthermore, if the modulus is too low, it will cause operational difficulties in the manufacture of printed circuit boards. An appropriate modulus must be selected according to application needs to avoid significant deformation of the asymmetric metal foil clad laminate or printed circuit board when bent during use.

[0019] In a preferred technical solution of the present invention, the XY-CTE (coefficient of thermal expansion in the in-plane direction) of the low modulus prepreg after curing is 18 ppm / °C or less, and may be, for example, 18 ppm / °C, 17.5 ppm / °C, 17 ppm / °C, 16.5 ppm / °C, 16 ppm / °C, 15.5 ppm / °C, 15 ppm / °C, 14.5 ppm / °C, 14 ppm / °C, 13.5 ppm / °C, 13 ppm / °C, 12.5 ppm / °C, 12 ppm / °C, 11.5 ppm / °C, 11 ppm / °C, 10 ppm / °C, 9 ppm / °C, 8 ppm / °C, 7 ppm / °C, 6 ppm / °C, 5 ppm / °C, 3 ppm / °C, or 1.5 ppm / °C.

[0020] In a preferred technical solution of the present invention, the XY-CTE of the low modulus prepreg after curing is 16 ppm / °C or less.

[0021] In a preferred technical solution of the present invention, the XY-CTE of the low modulus prepreg after curing is 14 ppm / °C or less.

[0022] In the present invention, if the XY-CTE of the low modulus prepreg after curing is too high, above 18 ppm / °C, the laminate will deform significantly when heated and subjected to stress, resulting in increased warpage of the asymmetric metal foil clad laminate and printed circuit boards manufactured therefrom, and reduced reliability. By using a low modulus prepreg after curing with an XY-CTE of 18 ppm / °C or less, the amount of deformation that occurs during use of the asymmetric metal foil clad laminate and printed circuit boards manufactured therefrom is insufficient to affect their normal use, ensuring low warpage and good reliability.

[0023] In the present invention, the type of the metal foil is not particularly limited, and can be selected from metal foils used as materials for printed circuit boards.

[0024] In the present invention, the thickness of the metal foil is not particularly limited, and can be selected from metal foils of any thickness that are used as materials for printed circuit boards.

[0025] As a preferred technical solution of the present invention, when the asymmetric metal foil clad laminate is one in which metal foil is coated on one side, the thickness of the metal foil coating one side of the low modulus prepreg is 1.5 to 700 μm, and may be, for example, 1.5 μm, 3 μm, 5 μm, 9 μm, 12 μm, 18 μm, 35 μm, 70 μm, 80 μm, 90 μm, 105 μm, 120 μm, 140 μm, 175 μm, 200 μm, 210 μm, 245 μm, 280 μm, 300 μm, 315 μm, 350 μm, 385 μm, 400 μm, 420 μm, 490 μm, 525 μm, or 700 μm.

[0026] In a preferred technical solution of the present invention, when metal foil is coated on both sides of the one or at least two laminated low modulus prepregs, the difference in thickness of the metal foils on both sides is 5 μm or more, for example, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, 52 μm, 55 μm, 58 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 110 μm , 130 μm, 150 μm, 170 μm, 190 μm, 200 μm, 210 μm, 230 μm, 250 μm, 270 μm, 290 μm, 300 μm, 310 μm, 330 μm, 350 μm, 370 μm, 390 μm, 400 μm, or 410 μm, and is preferably 10 μm or more, more preferably 18 μm or more, and even more preferably 35 μm or more. If the difference in thickness of the metal foil on both sides is 5 μm or more, the metal foil-clad laminate will warp, but by using the low-modulus prepreg of the present invention, warping can be effectively improved or even completely eliminated. The greater the difference in thickness of the metal foil on both sides, the greater the difference in internal stress due to structural asymmetry, making the metal foil-clad laminate more susceptible to warping. However, it is clear that the low-modulus prepreg of the present invention plays a significant role in improving and even completely eliminating warping compared to conventional prepregs.

[0027] As a preferred technical solution of the present invention, from the viewpoint of signal transmission loss and the ability to process thin circuits, when metal foil is coated on both sides of the one or at least two laminated low modulus prepregs, it is preferable that the thickness of the metal foil coated on one side of the one or at least two laminated low modulus prepregs is 35 μm or less (for example, it may be 35 μm, 33 μm, 30 μm, 28 μm, 25 μm, 22 μm, 20 μm, 18 μm, 15 μm, 12 μm, 9 μm, 6 μm, 5 μm, 3 μm, or 1.5 μm, etc.). From the viewpoint of current conduction and heat dissipation capability, the thickness of the metal foil covering the other side of the one or at least two laminated low-modulus prepregs is 70 μm or more (for example, 70 μm, 80 μm, 90 μm, 105 μm, 120 μm, 140 μm, 175 μm, 200 μm, 210 μm, 245 μm, 280 μm, 300 μm, 315 μm, 350 μm, 385 μm, 400 μm, 420 μm, 490 μm, 525 μm, or 700 μm). From the viewpoint of processability of the metal foil-clad laminate and the printed circuit board, the thickness of the metal foil covering the other side of the one or at least two laminated low-modulus prepregs is more preferably 70 to 420 μm. Furthermore, when the current conduction and heat dissipation capabilities, and the processability of the metal foil-clad laminate and printed circuit board are taken into consideration comprehensively, it is more preferable that the thickness of the metal foil covering the other side of the one or at least two laminated low-modulus prepregs is 140 to 420 μm.

[0028] As a preferred technical solution of the present invention, the T gis 150°C or higher, and may be, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 290°C, or 300°C, and is preferably 170°C or higher, more preferably 200°C or higher, even more preferably 230°C or higher, and most preferably 250°C or higher.

[0029] The T after curing of the low modulus prepreg of the present invention g The choice for is related to the operating temperature of the asymmetric metal foil clad laminate and the printed circuit board manufactured therefrom. g If the temperature is above 150°C, the prepreg after curing will be rubber-like, and the deformation of the asymmetric metal foil clad laminate and the printed circuit board manufactured therefrom after stress will increase, affecting their reliability. Since the operating temperature of the asymmetric metal foil clad laminate and the printed circuit board manufactured therefrom is usually above 150°C, the T g is 150°C or higher, preferably 170°C or higher, more preferably 200°C or higher, even more preferably 230°C or higher, and most preferably 250°C or higher, in order to improve the modulus retention of the cured prepreg at high temperatures.

[0030] In a second aspect, the present invention provides a printed circuit board comprising at least one asymmetric metal foil clad laminate according to the first aspect.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] In the present invention, by adjusting the elastic modulus of the prepreg after curing to 22 GPa or less, the resulting asymmetric metal foil-clad laminate has a low amount of warpage, thereby ensuring the reliability of the manufactured printed circuit board. DETAILED DESCRIPTION OF THE INVENTION

[0033] The technical solution of the present invention will be further described below by means of specific embodiments. Those skilled in the art should understand that the above examples are only for understanding the present invention and should not be considered as specifically limiting the present invention.

[0034] The specifications of the prepreg used in the examples of the present invention are as follows. Prepreg A: Elastic modulus after curing is 17 GPa, XY-CTE is 13 ppm / ℃, T g is 270℃. Prepreg B: Elastic modulus after curing is 21 GPa, XY-CTE is 10 ppm / ℃, T g is 270℃. Prepreg C: Elastic modulus after curing is 10 GPa, XY-CTE is 10 ppm / ℃, T g is 170℃. Prepreg D: Elastic modulus after curing is 18GPa, XY-CTE is 20ppm / ℃, T g is 150℃. Prepreg E: Elastic modulus after curing is 17GPa, XY-CTE is 20ppm / ℃, T g is 270℃. Prepreg F: Elastic modulus after curing is 28GPa, XY-CTE is 10ppm / ℃, T g is 270℃. Prepreg G: Elastic modulus after curing is 23GPa, XY-CTE is 15ppm / ℃, T g is 270℃. Prepreg H: Elastic modulus after curing is 28GPa, XY-CTE is 20ppm / ℃, T g is 270℃. Prepreg I: Elastic modulus after curing is 17 GPa, XY-CTE is 15 ppm / ℃, T g is 270℃.

[0035] In the present invention, the thickness of the prepreg and the thickness of the glass fiber cloth are not limited. For ease of comparison, the thickness of each of the above-mentioned prepregs is uniformly selected to be 125 μm.

[0036] The test method for the performance of the cured prepreg is as follows.

[0037] Sample preparation: 12 μm copper foil was coated on both sides of eight laminated prepregs and one prepreg, respectively, and then placed in a hot press for curing at a temperature of 200°C and a pressure of 30 kg / cm. 2 The prepreg was fully cured by curing for 90 minutes under the conditions of

[0043] . After etching the copper foil, laminates with thicknesses of 1.0 mm and 0.125 mm were obtained.

[0038] Copper foil thickness test method: Based on GB / T 29847-2013 Test method 6.3 for copper foil for printed circuit boards.

[0039] Elastic modulus test method: A laminated plate with a length of 76.2 mm, a width of 25.4 mm, and a thickness of 1.0 mm was prepared as a sample. Measurements were carried out using a material testing machine. The span was 25.4 mm, and the test speed was 0.76 mm / min. The maximum bending strength was converted using a formula to obtain the elastic modulus as the bending modulus (unit: GPa).

[0040] XY-CTE test method: A laminated board measuring 60 mm in length, 4 mm in width, and 0.125 mm in thickness was used as the sample. The glass fiber weft was oriented in the X direction, and the glass fiber warp was oriented in the Y direction. The sample was oven-dried at 105°C for 1 hour and then cooled to room temperature in a dryer. Measurements were performed using thermomechanical analysis (TMA). The sample was heated from room temperature to 260°C at a rate of 10°C / min, and then heated twice. After the first heating cycle, the sample was cooled to room temperature. The sample was then reinserted into the oven and heated for a second time. The in-plane thermal expansion coefficient was measured after the second heating cycle, from 50°C to 130°C (unit: ppm / °C).

[0041] Glass transition temperature (T g Test method: A laminated plate measuring 60 mm in length, 10 mm in width, and 1.0 mm in thickness was used as the sample. Measurements were performed using a dynamic thermomechanical analyzer (DMA) at a heating rate of 10°C / min. The transition peak temperature of tan δ was reported as the result (unit: °C).

[0042] The specifications of the copper foil used in the examples of the present invention are as follows: Copper foil A: Thickness 12 μm Copper foil B: thickness 35μm Copper foil C: thickness 105μm Copper foil D: thickness 210μm

[0043] Examples 1 to 11 and Comparative Examples 1 to 4

[0044] Examples 1 to 11 and Comparative Examples 1 to 4 provide asymmetric metal foil-clad laminates each comprising the low modulus prepreg and a metal foil covering one side of the low modulus prepreg or a metal foil having different thicknesses on both sides, and the manufacturing method thereof is as follows.

[0045] Two copper foils with different thicknesses were coated on both sides of the prepreg, or one copper foil was coated on one side of the prepreg, and then the prepreg was placed in a hot press at a temperature of 200°C and a pressure of 30 kg / cm. 2 The prepreg was cured completely under the above conditions for 90 minutes to obtain an asymmetric metal foil clad laminate.

[0046] The types of prepreg and copper foil are shown in Tables 1 and 2.

[0047] The warpage of the asymmetric metal foil-clad laminates according to the above-mentioned Examples 1 to 11 and Comparative Examples 1 to 4 was measured.

[0048] The types of warpage of asymmetric metal foil clad laminates are classified as bow warpage and twist warpage, the definitions and test methods of which are based on the IPC-TM-650 standard.

[0049] Bowing refers to deformation of the sheet material that resembles a cylinder or a curved sphere. For rectangular copper clad sheets, the four corners are flush.

[0050] The bow test method involves placing the sample on the test platform with the convex side facing upwards and measuring the maximum vertical distance between the sample and the platform.

[0051] Warpage is a deformation of a rectangular plate in a direction parallel to the diagonal, with one corner not contained in the plane of the other three corners.

[0052] The torsional warpage test method involves placing a sample on a test platform, bringing any three corners into contact with the platform, and measuring the maximum vertical distance between the platform and any corner not in contact with the platform.

[0053] The A-state warpage refers to the A-state warpage that is the maximum bowing or twist obtained by directly testing the sample without any treatment.

[0054] The warpage after reflow soldering refers to the maximum bow or twist warpage obtained by testing a sample after reflow soldering (the reflow soldering parameters are set to heat from 30°C to 260°C, and then cool from 260°C to 30°C at a rate of 3°C / min).

[0055] The size of the asymmetric metal foil clad laminate sample was 250 mm (radial direction) x 300 mm (lateral direction).

[0056] The test results described above are shown in Tables 1, 2 and 3. [Table 1] [Table 2] [Table 3]

[0057] As can be seen from the test results in Tables 1 and 2, asymmetric metal foil-clad laminates using low-modulus prepregs with a post-curing elastic modulus of 22 GPa or less have low warpage, with the warpage in state A and after reflow soldering both being 5 mm or less.

[0058] As can be seen from the test data in Table 3, when the post-curing modulus of the prepreg was too high (Comparative Examples 1 to 4), the warpage of the asymmetric metal foil-clad laminate in condition A and after reflow soldering was significantly improved, exceeding 5 mm, with the warpage after reflow soldering far exceeding that in condition A.

[0059] As a result of comparing Examples 1 and 5 with Comparative Examples 1 and 4, the modulus and T g When the XY-CTE is approximately the same, the smaller the XY-CTE, the greater the ability to withstand deformation, which contributes to a reduction in the amount of warpage, especially after reflow soldering. However, it was found that a decrease in the elastic modulus of the prepreg has a more obvious effect on the reduction in the amount of warpage.

[0060] The applicant declares that the above is only a specific embodiment of the present invention, and is not intended to limit the protection scope of the present invention. It is clear to those skilled in the art that any changes or substitutions that can be easily thought of within the technical scope disclosed in the present invention should be included in the protection scope and disclosure scope of the present invention.

Claims

1. An asymmetric metal foil clad laminate comprising one or at least two laminated low modulus prepregs and metal foils of different thicknesses coated on both sides of the one or at least two laminated low modulus prepregs, The low modulus prepreg has an elastic modulus after curing of 22 GPa or less, Both sides of the one or at least two laminated low modulus prepregs are coated with metal foil, and the difference in thickness of the metal foils on both sides of the one or at least two laminated low modulus prepregs is 35 μm or more; The amount of warpage of the asymmetric metal foil-clad laminate in state A and after reflow soldering is both 5 mm or less, The low modulus prepreg has a T g of 230°C or higher after curing. Asymmetric metal foil clad laminate.

2. The low modulus prepreg has an elastic modulus after curing of 20 GPa or less. The asymmetric metal foil-clad laminate according to claim 1 .

3. The low modulus prepreg has an elastic modulus of 5 GPa or more after curing. The asymmetric metal foil-clad laminate according to claim 1 or 2.

4. The low modulus prepreg has an XY-CTE of 18 ppm / °C or less after curing. The asymmetric metal foil-clad laminate according to any one of claims 1 to 3.

5. Both sides of the one or at least two laminated low modulus prepregs are coated with metal foil, The thickness of the metal foil on one side of the one or at least two laminated low modulus prepregs is 35 μm or less, and the thickness of the metal foil on the other side is 70 μm or more. The asymmetric metal foil-clad laminate according to any one of claims 1 to 4.

6. The thickness of the metal foil covering one side of the low modulus prepreg is 35 μm or less, and the thickness of the metal foil on the other side is 70 to 420 μm. The asymmetric metal foil-clad laminate according to any one of claims 1 to 5.

7. The low modulus prepreg has a Tg of 250°C or higher after curing. The asymmetric metal foil-clad laminate according to any one of claims 1 to 6.

8. The asymmetric metal foil clad laminate according to any one of claims 1 to 7 is included. Printed circuit board.

Images