Adhesive sheet for use in filling and application thereof

Abstract

This invention provides an adhesive sheet for filling adhesive and its application. The adhesive sheet is formed by rolling and laminating a PET film, a first adhesive layer, a prepreg, a second adhesive layer, and a PET film in sequence. The prepreg has a minimum melt viscosity of 3000-10000 Pa·s between 60 and 160°C. The first and second adhesive layers each have a minimum melt viscosity of 300-2000 Pa·s independently between 60 and 160°C. This invention, by setting highly fluid adhesive layers on both sides of the prepreg with low fluidity, enables the adhesive sheet to have excellent filling capacity in the Z-axis direction, while maintaining low fluidity in the X / Y directions. This results in good uniformity of board thickness after filling and pressing. Furthermore, when applied to thick copper fillers, the adhesive sheet can solve the cracking problem in the inter-line area after multiple reflow soldering processes. The filled and pressed board is also less prone to warping, resulting in high reliability of the printed circuit board when carrying high currents.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board technology and relates to an adhesive sheet for filling adhesive and its application. Background Technology

[0002] In the printed circuit board (PCB) industry, copper foil with a thickness of ≥105μm is generally referred to as thick copper foil. With the development of PCB technology, circuits require greater current, leading to the increasing use of thick copper foil. A typical application is to make the inner layer board a thick copper core board, and then laminate prepregs on both sides to form a multilayer board. However, due to the thickness of the copper foil, the filling of the prepreg becomes more difficult, easily resulting in resin voids caused by incomplete filling. One solution is to increase the resin content in the prepreg, but there is an upper limit to the amount of resin adhering to the prepreg. To address this issue, attempts were made to replace the prepreg with a resin film. However, the resin film experienced excessive flow during lamination, often resulting in resin flowing out of the thick copper core board, leading to poor thickness uniformity of the entire board.

[0003] CN101665016A discloses a method for manufacturing a prepreg for thick copper multilayer printed circuit boards and the prepreg itself. It employs a composite laminate structure of adhesive film / prepreg / adhesive film, which can effectively solve the aforementioned resin void defects during filling. However, it still suffers from excessive resin flow during lamination. Furthermore, it was found that even when the filled areas are very full, crack defects frequently appear after multiple reflow soldering heat treatments. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an adhesive sheet for filling adhesive and its application.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides an adhesive sheet for filling adhesive, wherein the adhesive sheet for filling adhesive is formed by rolling and laminating a PET film, a first adhesive layer, a prepreg, a second adhesive layer, and a PET film in sequence. The prepreg has a minimum melt viscosity of 3000-10000 Pa·s (e.g., 3000 Pa·s, 4000 Pa·s, 5000 Pa·s, 6000 Pa·s, or 7000 Pa·s) between 60 and 160°C (e.g., 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or 160°C). The first adhesive layer and the second adhesive layer each have a minimum melt viscosity value of 300 to 2000 Pa·s (e.g., 300 Pa·s, 500 Pa·s, 800 Pa·s, 100 Pa·s, 110 Pa·s, 120 Pa·s, 130 Pa·s, 140 Pa·s, 150 Pa·s, or 160 Pa·s) between 60 and 160°C (e.g., 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or 160°C).

[0007] In the process of thick copper filling, on the one hand, in order to improve filling performance, it is necessary to reduce the minimum melt viscosity of the adhesive sheet to increase the fluidity of the resin; on the other hand, in order to avoid resin flow at the board edge, it is necessary to increase the minimum melt viscosity of the adhesive sheet to reduce the fluidity of the resin. The two are contradictory.

[0008] This invention provides adhesive layers on both sides of the prepreg and independently controls the minimum melt viscosity of the prepreg, the first adhesive layer, and the second adhesive layer. The high melt viscosity of the prepreg ensures that the resin has low flowability in the X / Y direction during the filling process, resulting in good thickness uniformity of the board after filling and pressing. The use of the low melt viscosity of the first and second adhesive layers gives the adhesive sheet excellent filling ability in the Z-axis direction.

[0009] Preferably, the reinforcing material of the prepreg is selected from E-Glass 1017 fiberglass cloth, E-Glass 1027 fiberglass cloth, E-Glass 1037 fiberglass cloth, E-Glass 106 fiberglass cloth, E-Glass 1078 fiberglass cloth or E-Glass 1080 fiberglass cloth.

[0010] Preferably, the flexural modulus of the cured prepreg is 10-15 GPa, for example, 10 GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, or 15 GPa. During the filling process, the adhesive sheet of the present invention experiences a large amount of resin melt flow in the Z-axis direction, leading to differences in the microscopic distribution of resin components near the thick copper wire regions. This makes it prone to cracking defects after multiple reflow soldering heat treatments. The reinforcing material in the prepreg can provide support for the first and second adhesive layers. By controlling the flexural modulus of the cured prepreg, the overall stress distribution of the adhesive sheet during heat treatment can be mitigated, improving the warping of the sheet and cracking in the inter-wire regions.

[0011] Preferably, the curing temperature of the prepreg is 170-200℃ (e.g., 170℃, 175℃, 180℃, 185℃, 190℃, 195℃ or 200℃), and the curing time is 60-90 minutes (e.g., 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes or 90 minutes).

[0012] Preferably, the thickness of the prepreg is 30-100 μm, for example, it can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm. If the prepreg thickness is too thin, it cannot provide effective support; if the prepreg thickness is too thick, it is not conducive to the thinning of the printed circuit board.

[0013] Preferably, the thickness of the first adhesive layer and the second adhesive layer is independently 30-200 μm, for example, it can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 150 μm, 180 μm or 200 μm. If the thickness of the first adhesive layer and the second adhesive layer is too thin, the preparation of the resin layer is difficult, and there is a risk of exposure of the reinforcing material; if the thickness of the first adhesive layer and the second adhesive layer is too thick, it is not conducive to the thinning of the printed circuit board.

[0014] Preferably, the Z-axis CTE of the first and second adhesive layers after curing is independently 15-30 ppm / ℃, for example, 15 ppm / ℃, 18 ppm / ℃, 20 ppm / ℃, 23 ppm / ℃, 25 ppm / ℃, 28 ppm / ℃, or 30 ppm / ℃. In this invention, the CTE of thick copper is approximately 17 ppm / ℃, the CTE of the reinforcing fiberglass cloth in the X / Y directions is approximately 12-15 ppm / ℃, and the CTE in the Z-axis direction is approximately 80-90 ppm / ℃. Different materials exhibit different CTE characteristics. By controlling the Z-axis CTE of the first and second adhesive layers after curing, this invention can harmonize the differences in CTE between different materials, thus improving the cracking problem in the inter-line area when the adhesive sheet is applied to thick copper filler.

[0015] Preferably, the curing temperature of the first adhesive layer and the second adhesive layer is independently 170-200℃ (e.g., 170℃, 175℃, 180℃, 185℃, 190℃, 195℃ or 200℃), and the curing time is 60-90 minutes (e.g. 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes or 90 minutes).

[0016] Preferably, the temperature of the roller pressing is 60-120℃, for example 60℃, 65℃, 70℃, 75℃, 80℃, 90℃, 100℃, 110℃ or 120℃, and the pressure is 1.0-5.0kN, for example 1.0kN, 1.5kN, 2.0kN, 2.5kN, 3.0kN, 3.5kN, 4.0kN, 4.5kN or 5.0kN.

[0017] Preferably, the roller speed is 0.5-3.0 m / min, for example 0.5 m / min, 0.8 m / min, 1.0 m / min, 1.2 m / min, 1.5 m / min, 1.8 m / min, 2.0 m / min, 2.5 m / min or 3.0 m / min.

[0018] On the other hand, the present invention provides a metal foil laminate, the metal foil laminate comprising at least one adhesive sheet as described above and metal foil covering one or both sides of the laminated adhesive sheet.

[0019] Preferably, the metal foil is a copper foil.

[0020] On the other hand, the present invention provides a printed circuit board, the printed circuit board comprising one or at least two laminated adhesive sheets as described above or a metal foil laminate as described above.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention provides an adhesive layer with high fluidity on both sides of a prepreg with low fluidity, giving the adhesive sheet excellent filling ability in the Z-axis direction while having low fluidity in the X / Y directions. This results in good uniformity of board thickness after filling and pressing. Furthermore, when the adhesive sheet is used for filling thick copper, it can solve the cracking problem in the inter-line area after multiple reflow solderings. The board is also less prone to warping after filling and pressing, and the printed circuit board produced has good reliability when carrying high current. Detailed Implementation

[0023] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0024] Example 1

[0025] This embodiment provides an adhesive sheet, which is formed by rolling and laminating a PET film, a first adhesive layer, a prepreg, a second adhesive layer, and a PET film in sequence.

[0026] Preparation of resin composition 1A for adhesive layer:

[0027] 100 parts by weight of epoxy resin (YX4000, Mitsubishi Chemical), 30 parts by weight of curing agent (DDS, 4,4'-diaminodiphenyl sulfone, Atu, India), 20 parts by weight of phenoxy resin (YX7553BH30, Mitsubishi Chemical), 350 parts by weight of silica (SC2050, Admateches, Japan) and 0.5 parts by weight of 2-methylimidazole were added to butanone solvent and stirred for 2 hours to form a resin solution with a solid content of 65%.

[0028] The above resin solution is coated onto a PET release film, dried, and then baked in a 120°C oven for 5 minutes to obtain a resin film with a semi-cured resin layer (thickness of 50μm). A PET protective film is then applied to the adhesive surface to obtain an adhesive layer with a PET protective film, denoted as resin film 1.

[0029] The lowest melt viscosity of resin film 1 between 60 and 160°C was measured to be 1000 Pa·s, and the Z-axis CTE after curing at 180°C for 80 minutes was 20 ppm / °C.

[0030] Preparation of resin composition 1B for prepreg:

[0031] 100 parts by weight of epoxy resin (NC3000, Nippon Kayaku), 80 parts by weight of phenolic resin (7851-H, Meiwa, Japan), 50 parts by weight of silica (SC2050, Admateches, Japan) and 0.5 parts by weight of 2-methylimidazole were added to butanone solvent and stirred for 2 hours to form a resin solution with a solid content of 65%.

[0032] The above resin solution was impregnated onto E-Glass 106 fiberglass cloth, dried, and then baked in an oven at 150°C for 5 minutes to obtain a semi-cured prepreg. The thickness of the prepreg was controlled to be 60 μm, and it was denoted as prepreg 1.

[0033] The lowest melt viscosity of prepreg 1 between 60 and 160°C was measured to be 5000 Pa·s, and the flexural modulus after curing at 180°C for 80 minutes was 12 GPa.

[0034] After removing the PET protective film from two resin films 1 with PET protective film, a prepreg 1 is sandwiched between the two adhesive layers. The adhesive sheet is obtained by pressing with a roller press (temperature 100℃, pressure 3.5kN, speed 1.5m / min), and is denoted as adhesive sheet 1 for filling.

[0035] A copper core board with a thickness of 105μm and an L / S of 200μm / 200μm was selected. The core board / filler adhesive sheet 1 / core board was laminated with a pressure of 30Kg, a temperature of 190℃ and a pressing time of 90 minutes to obtain a thick copper multilayer board, which is referred to as multilayer board 1.

[0036] Adhesive layer resin composition 2A-5A:

[0037] The components and contents of the adhesive layer resin compositions 2A-5A are shown in Table 1. All "parts by weight" are calculated based on solid content and do not include solvents, dispersants, etc. The preparation method is the same as that of the adhesive layer resin composition 1A.

[0038] Table 1

[0039]

[0040] Preparation of resin compositions 2B-5B for prepregs:

[0041] The components and contents of the resin compositions 2B-5B for prepregs are shown in Table 2. All “parts by weight” are calculated based on solid content and do not include solvents, dispersants, etc. The preparation method is the same as that of the resin composition 1B for prepregs.

[0042] Table 2

[0043]

[0044]

[0045] Examples 2-3, Comparative Examples 1-4

[0046] The preparation methods of the multilayer boards in Examples 2-3 and Comparative Examples 1-4 are the same as those in Example 1. The first adhesive layer, the second adhesive layer and the prepreg used are shown in Table 3.

[0047] The performance of the multilayer boards of Examples 1-3 and Comparative Examples 1-4, as well as the resin films (first adhesive layer and second adhesive layer) and prepregs used, was tested using the following methods:

[0048] (1) Minimum melt viscosity value: The rheological curves of the first adhesive layer, prepreg and second adhesive layer samples were tested using an Anton Paar MCR302 rheometer. The test temperature range was set to 30-190℃ and the heating rate was 3℃ / min. After the test, the minimum melt viscosity value that appeared between 60 and 160℃ was read from the corresponding rheological curve.

[0049] (2) Z-axis CTE (coefficient of thermal expansion): After curing the first adhesive layer and the second adhesive layer at 180°C for 80 minutes, the CTE was measured according to the TMA test method specified in IPC-TM-650 2.4.24.5.

[0050] (3) Flexural modulus: The DMA test was performed using the DMA test method specified in IPC-TM-650 2.4.24.

[0051] (4) Thickness range of multilayer board: The thickness of the filler layer at the four corners and the middle position of the multilayer board is tested by grinding and slicing. The thickness range of these 5 points is calculated. The smaller the absolute value of the thickness range, the better.

[0052] (5) Warpage of multilayer boards: The warpage of multilayer boards is tested according to the bowing and twisting specified in IPC-TM-650 2.4.22.1.

[0053] (6) Quality evaluation of the inter-line area of ​​multilayer board: After the multilayer board is reflowed 6 times (reflow peak temperature 260℃), 100 samples are taken from the inter-line area, ground and sliced, and the inter-line area is observed for cracks: crack ratio ≤1% is recorded as "excellent", crack ratio ≥6% is recorded as "poor", and the rest is recorded as "good".

[0054] Table 3

[0055]

[0056] As can be seen from Table 3, in Embodiments 1-3 of the present invention, by setting a highly fluid adhesive layer on both sides of the prepreg with low fluidity, the thickness uniformity of the plate after filling and pressing is good, and the thickness difference is 4-7μm. At the same time, when the adhesive sheet is applied to thick copper filler, it can solve the cracking problem in the inter-line area after multiple reflow solderings, and the plate is not easy to warp after filling and pressing, with a warping degree of 0.2-0.5mm.

[0057] Compared with Example 1, the minimum melt viscosity values ​​of the first and second adhesive layers in Comparative Example 1 are lower, and the Z-axis CTE is higher, resulting in a thickness difference of up to 13 μm and a warpage of up to 0.8 mm in the multilayer board.

[0058] Compared with Example 1, the minimum melt viscosity values ​​of the first and second adhesive layers in Comparative Example 2 are higher, and the Z-axis CTE is lower, resulting in a poor quality evaluation of the inter-line area of ​​the multilayer board.

[0059] Compared with Example 1, the minimum melt viscosity and flexural modulus of the prepreg in Comparative Example 3 were lower, resulting in a thickness difference of up to 7 μm in the multilayer board and a quality evaluation of only "good" for the inter-line area.

[0060] Compared with Example 1, the minimum melt viscosity of the prepreg in Comparative Example 4 is higher and the flexural modulus is lower, resulting in a poor quality evaluation of the inter-line area of ​​the multilayer board.

[0061] The applicant declares that the present invention is illustrated by the above embodiments to demonstrate the adhesive sheet for filling adhesive and its application, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An adhesive sheet for filling adhesive, characterized in that, The adhesive sheet for filling is formed by rolling and laminating a PET film, a first adhesive layer, a prepreg, a second adhesive layer, and a PET film in sequence. The prepreg has a minimum melt viscosity of 5000-10000 Pa·s between 60 and 160°C, and the flexural modulus of the cured prepreg is 10-15 GPa. The first adhesive layer and the second adhesive layer each have a minimum melt viscosity value of 300-1000 Pa·s, which are independently between 60 and 160°C; the Z-axis CTE of the first adhesive layer and the second adhesive layer after curing is independently 15-30 ppm / °C.

2. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The reinforcing material of the prepreg is selected from E-Glass 1017 fiberglass cloth, E-Glass 1027 fiberglass cloth, E-Glass 1037 fiberglass cloth, E-Glass 106 fiberglass cloth, E-Glass 1078 fiberglass cloth or E-Glass 1080 fiberglass cloth.

3. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The curing temperature of the prepreg is 170-200℃, and the curing time is 60-90 minutes.

4. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The thickness of the prepreg is 30-100 μm.

5. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The thickness of the first adhesive layer and the second adhesive layer are each independently 30-200 μm.

6. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The curing temperature of the first adhesive layer and the second adhesive layer are each 170-200℃, and the curing time is 60-90 minutes.

7. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The temperature of the roller press is 60-120℃, and the pressure is 1.0-5.0 kN.

8. The adhesive sheet for filling adhesive according to claim 1, characterized in that, The roller speed is 0.5-3.0 m / min.

9. A metal foil-coated laminate, characterized in that, The metal foil laminate contains at least one adhesive sheet for filling as described in any one of claims 1-8 and a metal foil covering one or both sides of the laminated adhesive sheet.

10. A printed circuit board, characterized in that, The printed circuit board includes one or at least two laminated adhesive sheets for filling as described in any one of claims 1-8, or includes a metal foil laminate as described in claim 9.

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