A method for manufacturing a PET copper-plated film with a gradient interface structure

Abstract

The application relates to a manufacturing method of a PET copper-plated film with a gradient interface structure. The composite film comprises a PET substrate, a microstructure layer arranged on the surface of the PET substrate, a metal adhesion transition layer arranged on the microstructure layer, and a copper functional layer arranged on the metal adhesion transition layer. The grain size of the copper functional layer near the interface region is smaller than that near the surface region. The mechanical embedding effect formed by the microstructure layer and the interface transition effect formed by the metal adhesion transition layer are matched, so that the interface bonding state and the structural stability under the conditions of thermal cycling and bending are improved.

Description

Technical Field

[0001] This invention relates to the field of flexible conductive materials technology, and in particular to a method for manufacturing a PET copper-plated film with a gradient interface structure through interface microstructure regulation and metal adhesion transition layer construction to improve interface bonding state, bending resistance and stability. It is mainly used in the fields of flexible circuits, high-speed cables and flexible shielding. Background Technology

[0002] Existing copper-plated PET films often employ physical roughening or simple plasma activation treatment followed by direct electroplating of the copper layer. This type of structure typically suffers from problems such as insufficient adhesion between the copper layer and PET, easy delamination after thermal cycling, easy cracking during bending, high residual stress in the copper layer, and difficulty in controlling the grain structure. Through repeated experiments during product manufacturing, the applicant discovered that the above problems are related to the fact that the interfaces are mostly near-planar or sharply roughened, lacking a controllable mechanical interlocking structure, and lacking a gradient transition design along the thickness direction. Summary of the Invention

[0003] Design objective: To provide a PET copper-plated composite film structure and its preparation method that have a more stable interface bonding state, better bending resistance and higher thermal cycling stability, so as to improve the problems of insufficient interface bonding between PET and copper layer, easy delamination, easy cracking and stress concentration in the existing technology.

[0004] Design Scheme: To improve the interfacial bonding, thermal cycling stability, bending resistance, and conductivity consistency of PET copper-plated film, this invention adopts the following synergistic structural design: (1) Improved interface bonding state: A microstructure layer is formed on the surface of the PET substrate, and a metal adhesion transition layer is set on it, so that the interface has both mechanical interlocking and interlayer transition functions, which is beneficial to improving peel performance and interface bonding state.

[0005] (2) Improved structural stability under thermal mismatch conditions: In view of the difference in thermal expansion coefficients between PET and copper, a metal transition sublayer and a copper functional layer with different grain size are set near the interface, so that the mechanical and microstructure near the interface undergoes a transitional change, which is beneficial to improving the interface stability under thermal cycling conditions.

[0006] (3) Improved bending resistance: The copper functional layer forms a grain size difference structure along the thickness direction, with the interface region having a smaller grain structure and the surface region having a relatively larger grain structure, which is beneficial to improving the structural stability under bending conditions.

[0007] (4) Improved conductivity consistency: The metal adhesion transition layer provides a continuous conductive surface and improves the plating uniformity. Combined with the dense copper functional layer structure, it helps to reduce local resistance abnormalities caused by interface defects and uneven deposition.

[0008] The design of the microstructure layer is one of the technical features of this invention. This structure is used to construct an interface morphology with spatial undulations on the PET surface, distinguishing it from near-planar contacts or sharp, roughened contacts. Preferably, the microstructure has a height of 0.5–3 μm and a spacing of 1–10 μm; the microstructure outline is arc-shaped or approximately arc-shaped and without sharp corners. The "no sharp corners" can be determined by the outline obtained through surface morphology measurement.

[0009] The design of the metal adhesion transition layer is the second technical feature of this invention. The metal adhesion transition layer includes an adhesion sublayer compatible with the PET interface and a transition sublayer compatible with the copper layer. The adhesion sublayer is Ti and / or Cr, with a thickness of 3–30 nm; the transition sublayer is Ni and / or a Ni alloy, with a thickness of 20–150 nm. This layer improves the polymer-metal interface bonding state and provides a continuous conductive surface for subsequent copper layer formation.

[0010] The design of the copper functional layer is the third technical feature of this invention. The grain size of the copper functional layer increases from the interface region to the surface region along its thickness direction. Preferably, the grain size in the interface region is 50–100 nm, and the grain size in the surface region is 200–500 nm; the grain size can be obtained by cross-sectional TEM or EBSD measurement and according to prescribed statistical methods. This type of microstructure is beneficial for improving the microstructure coordination of the copper functional layer near the interface and in the surface region.

[0011] Description of effects and explanation of test caliber: The effects of the present invention, such as peel strength, bending life, thermal cycling stability, sheet resistance and residual stress, are based on the comparative data of the examples and comparative examples under the same test methods and conditions; wherein the peel strength is tested by the 180° peel method, and the test methods and criteria for bending life, thermal cycling and residual stress are given in the "Test Methods" section.

[0012] In summary, the present invention, through the synergistic structural design of "microstructure layer - metal adhesion transition layer - copper functional layer", achieves a synergistic effect in interface morphology, interlayer transition and copper layer microstructure, thereby improving the interface bonding state and structural stability under thermal cycling and bending conditions; the above effects are based on the comparison results of the embodiments and comparative examples under the same test conditions.

[0013] The distinguishing feature of this invention is that a microstructure layer is constructed on the surface of PET, and a metal adhesion transition layer and a copper functional layer with a grain size in the interface region smaller than that in the surface region are formed thereon, forming the following hierarchical structure: PET substrate → microstructure layer → metal adhesion transition layer → copper functional layer.

[0014] (1) Microstructure layer: Surface morphology parameters include microstructure height and spacing. The microstructure outline is arc-shaped or approximately arc-shaped and without sharp corners.

[0015] (2) Metal adhesion transition layer: including adhesion sublayer Ti and / or Cr and transition sublayer Ni and / or Ni alloy, and a Cu seed layer may be provided if necessary.

[0016] (3) Copper functional layer: The grain size in the interface region is 50–100 nm, and the grain size in the surface region is 200–500 nm. The grain size tends to increase along the thickness direction.

[0017] Compared with conventional planar PET direct copper plating structures and / or structures with only a single adhesion layer, the present invention has the following advantages: 1) The combination design of microstructure layer, metal adhesion transition layer and copper functional layer can improve the interface bonding state; 2) By setting metal adhesion transition layer and copper functional layer with interface region grain size smaller than surface region grain size, the structural stability under thermal cycling conditions can be improved; 3) By controlling the microstructure of copper functional layer, the structural stability under bending conditions can be improved; 4) The above effects are based on the comparison results of the embodiments and comparative examples under the same test conditions.

[0018] In summary, this invention, by constructing a synergistic structural system of a microstructure layer, a metal adhesion transition layer, and a copper functional layer, improves the interfacial bonding state, structural stability under bending conditions, interfacial stability under thermal cycling conditions, and conductivity consistency without significantly increasing the material thickness. The above effects are based on the comparison results of the embodiments and comparative examples under the same test conditions. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0020] Figure 2 This is a schematic diagram of the microstructure of the PET surface, with the following parameters: height 0.5–3 μm, spacing 1–10 μm, and the microstructure outline is arc-shaped or approximately arc-shaped.

[0021] Figure 3 This is a schematic diagram of the interface hierarchy, used to illustrate the structural changes of the metal adhesion transition layer and the copper functional layer along the thickness direction.

[0022] Figure 4 This is a schematic diagram of the difference in grain size in the copper functional layer, where the surface layer is the relatively large grain region, the middle layer is the transition region, and the bottom layer is the smaller grain region. Detailed Implementation

[0023] Terminology Definitions and Test Methods 1) Microstructure layer: refers to the PET surface being composed of multiple microstructure units, the cross-sectional profile of which is arc-shaped or approximately arc-shaped and does not contain sharp corners; the height and spacing of the microstructure are measured by white light interferometer, AFM or SEM morphology statistics respectively.

[0024] 2) Interface region and surface region: The interface region refers to the range of 0–0.5 μm in the copper functional layer from the metal adhesion transition layer / copper interface; the surface region refers to the range of 0–0.5 μm in the free surface of the copper functional layer.

[0025] 3) Grain size: refers to the equivalent diameter of the grain, which is obtained by cross-sectional TEM or EBSD; the number of grains in each region shall not be less than 50 (or the equivalent area shall be used to meet the statistical stability).

[0026] 4) Peel strength: The 180° peel method was used for testing. The strip width was 10 mm (converted to N / cm), the peel speed was 50 mm / min, and the stable peel plateau value was recorded.

[0027] 5) Surface resistance: Measured at 25℃ using the four-probe method, unit mΩ / □.

[0028] 6) Bending life: Under the condition of bending radius of 3 mm, repeated bending is defined as one cycle, and the failure criterion is the appearance of through crack or conductive failure.

[0029] 7) Thermal cycling stability: The system is subjected to 100 thermal cycles at temperatures ranging from -40℃ to 120℃. After the cycles, the interface is observed using an optical microscope or cross-section to determine if there is any visible delamination.

[0030] 8) Residual stress: The residual stress in the copper layer is measured by XRD (sin²ψ method) or curvature method, in MPa.

[0031] Example 1: 1) PET surface treatment: PET thickness 25 μm, laser microstructure processing, surface Ra=0.8 μm, microstructure height 1.2 μm, spacing 5 μm.

[0032] 2) Surface polarity modification: oxygen plasma treatment, surface energy ≥60 mN / m.

[0033] 3) Metal adhesion transition layer: Cr 12 nm, Ni 60 nm.

[0034] 4) Copper functional layer deposition: pulse electroplating; grain size in the interface region is about 70 nm, and grain size in the surface region is about 320 nm; total copper layer thickness is 12 μm; residual stress is 38 MPa.

[0035] 5) Performance: According to the test methods in this instruction manual, the peel strength is 3.1 N / cm; no through cracks were observed after 8000 bending cycles; the surface resistivity is 2.8 mΩ / □.

[0036] Example 2: Based on Example 1, the thickness of the copper functional layer was adjusted to 20 μm and the height of the microstructure was adjusted to 2 μm, while the other conditions remained the same; according to the test method in this specification, the peel strength was 3.4 N / cm.

[0037] Example 3 (vacuum deposition method): PET thickness 25 μm; microstructure height 1.2 μm; plasma power 150 W; Cr 10 nm; Ni 60 nm; Cu seed layer 100 nm; electroplated copper thickness 12 μm; residual stress 38 MPa; peel strength 3.1 N / cm according to the test method in this specification; no through cracks were observed after 8000 bending cycles.

[0038] Example 4 (chemical plating): PET thickness 25 μm; microstructure height 1.5 μm; sensitized and activated SnCl2+PdCl2; chemically plated NiP thickness 0.3 μm, phosphorus content 8 wt%; electroplated copper thickness 15 μm; residual stress 45 MPa; peel strength 2.9 N / cm according to the test method in this specification; no through cracks observed after 7000 bending cycles.

[0039] Comparative Example 1 (No Metal Adhesion Transition Layer): No metal adhesion transition layer was formed on the microstructured PET, and copper was directly electroplated (12 μm thick). According to the test methods in this specification, the results were: residual stress 82 MPa; peel strength 1.2 N / cm; through-crack appeared after 2000 bending cycles; visible delamination was observed after thermal cycling.

[0040] Comparative Example 2 (no microstructure and no grain size difference): The PET surface was roughened by sandblasting to form a sharp, rough morphology, without forming the microstructure described; a copper layer with insignificant grain size difference was formed using conventional DC electroplating. According to the test method in this specification, the results were: peel strength approximately 1.6 N / cm; cracks appeared after 5000 bending cycles.

[0041] Comparative conclusions: As can be seen from the comparative examples, under the same or similar copper layer thickness, the introduction of a microstructure layer and a metal adhesion transition layer is beneficial to improving peel performance and reducing residual stress; further, the use of a copper functional layer with a smaller grain size in the interface region than in the surface region is beneficial to improving structural stability under bending and thermal cycling conditions.

[0042] It should be understood that the above embodiments are for illustrating the present invention, and not for limiting the scope of protection of the present invention; the scope of protection of the present invention is defined by the claims.

Claims

1. A method for manufacturing a copper-plated PET film with a gradient interface structure, characterized in that... The process includes the following steps: S1) forming a microstructure layer on the surface of a PET substrate; S2) performing surface polarity modification treatment on the PET surface where the microstructure is formed; S3) forming a metal adhesion transition layer on the microstructure layer; S4) forming a copper functional layer on the metal adhesion transition layer, and adjusting the deposition parameters and / or electroplating parameters to make the grain size in the copper functional layer near the interface region smaller than the grain size near the surface region.

2. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: Step S1 involves forming the microstructure layer using one or more of the following methods: laser microstructure processing, imprint microstructure molding, solvent-induced surface reconstruction, or plasma-controlled etching.

3. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: The microstructures formed in step S1 have a height of 0.5–3 μm and a spacing of 1–10 μm.

4. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: Step S2 employs oxygen plasma or argon / oxygen mixed plasma treatment, and the surface energy of the treated PET is not less than 55 mN / m.

5. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: In step S3, an adhesion sublayer and a transition sublayer are deposited sequentially by magnetron sputtering or vacuum evaporation. The adhesion sublayer is Ti and / or Cr with a thickness of 3–30 nm, and the transition sublayer is Ni and / or Ni alloy with a thickness of 20–150 nm.

6. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: Step S3 involves forming a Ni or Ni alloy layer with a thickness of 0.05–1.0 μm by chemical plating.

7. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: A copper seed layer with a thickness of 50–200 nm is further formed between steps S3 and S4.

8. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: Step S4 uses pulse electroplating to form the copper functional layer.

9. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: Step S4 controls the current density, pulse duty cycle, and additive system to make the grain size of the interface region in the obtained copper functional layer 50–100 nm and the grain size of the surface region 200–500 nm.

10. The method for manufacturing a PET copper-plated film with a gradient interface structure according to claim 1, characterized in that: The thickness of the copper functional layer is 1–35 μm.

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