Manufacturing method of low-line-resistance OLED circuit board

Abstract

The invention relates to a manufacturing method of a low-line-resistance OLED circuit board, and the method comprises the steps: substrate pretreatment, circuit patterning, pulse electroplating, film removal and flash etching, the substrate pretreatment step comprises the steps of sputtering a titanium / copper composite seed layer on the surface of a substrate, and then electroplating a seed copper layer on the titanium / copper composite seed layer; in the flash etching step, the surface of the intermediate plate is subjected to flash etching through etching liquid, the titanium / copper composite seed layer and the seed copper layer outside the copper layer range are completely removed, then drying is conducted, and the low-line-resistance OLED circuit board is obtained. And under the condition that the etching amount of the seed layer is very small, the loss of the exposed part of the circuit is very small, so that the size of the circuit is very accurate under the condition that the thickness precision and the line width precision are ensured. The line width / spacing reaches 30 [mu] m / 30 [mu] m, and the lateral erosion rate is lt; and the completeness of high-frequency signals is ensured, the line resistance is low, and the current density is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed circuit board manufacturing, in particular to a manufacturing method of low-line-resistance OLED circuit board. BACKGROUND

[0002] OLED (Organic Light Emitting Display) circuit board is an important component in organic light emitting display. In order to manufacture foldable screen, some OLED circuit boards are made of flexible printed circuit board (FPC). In FPC manufacturing, the traditional subtractive process forms circuit by etching copper foil, which is limited by the initial thickness of copper foil (usually 9-12 μm), resulting in high line resistance in high-density or large-current applications, causing the following problems: 1. Signal loss and heat generation: high line resistance increases transmission loss (such as high-speed signal attenuation) and local heating, affecting FPC reliability.

[0003] 2. Insufficient current carrying capacity: thin copper circuit cannot meet the demand of large current (such as vehicle electronics, high-power LED module), which needs to be widened to occupy wiring space.

[0004] 3. Process limitations: the traditional etching process has obvious side etching effect, making it difficult to realize fine circuit with high thickness-to-diameter ratio (copper thickness / line width), restricting FPC miniaturization and high-density design.

[0005] Chinese patent CN115643696B discloses a preparation process of circuit board, including steps of depositing seed layer, pressing film, exposing, developing, electroplating, removing film and removing seed layer. These are common operations in MSAP process, but there are deficiencies when manufacturing circuit with high line width-to-pitch ratio. Because the precision of ordinary exposure electroplating method is limited, even if the same design drawing is referred to, the line spacing is limited very narrow at the beginning, but serious line side etching will occur when removing the seed layer, causing the line width / pitch ratio to decrease.

[0006] Therefore, it is necessary to design a new manufacturing method to avoid the above problems. SUMMARY

[0007] The main purpose of the present application is to provide a manufacturing method of low-line-resistance OLED circuit board, which can obtain circuit with high line width-to-pitch ratio and complete high-frequency signal.

[0008] The present application achieves the above-mentioned purpose by the following technical scheme: a manufacturing method of low-line-resistance OLED circuit board, including the following steps: S1, substrate pretreatment: sputtering a titanium / copper composite seed layer on the surface of the substrate, the thickness of the titanium / copper composite seed layer being 50-200 nm, and then electroplating a seed copper layer on the titanium / copper composite seed layer, the thickness of the seed copper layer being 2-3 microns; S2, circuit pattern: coating a photoresist on the surface of the titanium / copper composite seed layer, and then defining a circuit pattern on the photoresist by LDI method, removing the uncured photoresist, and matching the exposed area of the titanium / copper composite seed layer to the range of the circuit pattern; S3, pulse electroplating: plating a copper layer on the exposed part of the titanium / copper composite seed layer by pulse electroplating method to form a circuit, the total thickness of the copper layer being 20-40 microns; S4, film removal: removing the cured photoresist to completely expose the un-plated copper area of the titanium / copper composite seed layer, obtaining an intermediate plate, and then rinsing the surface of the intermediate plate with water and drying; S5, flash etching: flash etching the surface of the intermediate plate with an etching liquid to completely remove the titanium / copper composite seed layer and the seed copper layer outside the range of the copper layer, and then drying to obtain a low-line-resistance OLED circuit board.

[0009] Specifically, the photoresist is coated on the surface of the titanium / copper composite seed layer by a pressing film method.

[0010] Specifically, the pulse electroplating is delivered by a vertical continuous electroplating method.

[0011] Specifically, the line width precision in step S2 is controlled within ±5 microns.

[0012] Specifically, the substrate is a flexible substrate, including a bending area and a transition area located around the bending area; the copper layer in step S3 is obtained by twice pulse electroplating, each time increasing the copper thickness by 10-20 microns, wherein the windowing range of the photoresist in the first pulse electroplating includes the bending area and the transition area, and the windowing range of the photoresist in the second pulse electroplating includes the bending area but not the transition area.

[0013] Further, the material of the substrate is polyimide.

[0014] The beneficial effects of the technical scheme of the present application are: 1. Because the thickness of the seed layer itself is very small, only a very small amount of etching is needed to break the connection between the lines. The etchant actually contacts the upper part and the sidewall of the line, but in the case of a small amount of seed layer etching, the loss of the exposed part of the line will also be small. Therefore, in the case of ensuring the thickness precision and line width precision, the size of the line will also be very accurate. The line width / pitch is 30 microns / 30 microns, and the side etching rate is less than 5%, ensuring the integrity of high-frequency signals.

[0015] 2. The line resistance is reduced by 15-30% compared to ordinary processes, and the current density is increased from 3A / mm² to 10A / mm².

[0016] 3. The gradient copper layer allows for a bending radius as low as 1mm, and the resistance change rate is less than 3% after 100,000 cycles, making it suitable for dynamic scenarios such as wearable devices. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the low line resistance OLED circuit board in Example 1; Figure 2 This is a process flow diagram of the low line resistance OLED circuit board in Example 2.

[0018] The diagram is marked as follows: 1-Substrate, 11-Bending area, 12-Transition area, 2a-Titanium / copper composite seed layer, 2b-Seed copper layer, 3-Photoresist, 31-Cured photoresist, 32-Uncured photoresist, 4-Copper layer, 5-Circuit. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments.

[0020] Example 1: like Figure 1 As shown, a method for manufacturing a low-line-resistance OLED circuit board is characterized by the following steps: S1. Substrate pretreatment: A titanium / copper composite seed layer 2a is sputtered on the surface of substrate 1. The thickness of the titanium / copper composite seed layer 2a is 50~200nm. Then, a seed copper layer 2b is electroplated on the titanium / copper composite seed layer 2a. The thickness of the seed copper layer 2b is 2~3μm.

[0021] To obtain a high-precision OLED circuit board with a small number of lines, this method must ensure the precision of line 5 (including both width and thickness directions). The seed layer is a conductive metal layer uniformly distributed across the surface of substrate 1, used to conduct electricity during electroplating and provide an adhesion surface for copper, and it needs sufficient adhesion to substrate 1. In subsequent steps, line 5 consists of a thinner seed layer and a thicker copper layer 3. The seed layer not covered by copper layer 3 needs to be etched away. However, the more etching is done, the greater the width loss of line 5 and the greater the roughness. Therefore, to reduce the amount of etching, a very thin seed layer must be obtained at the beginning of the process. Because the method of placing metal foil itself is too thick for line 5 and has poor adhesion to substrate 1, sputtering is used.

[0022] The sputtered material is selected from titanium-copper composite material, which has the advantages of ensuring electrical conductivity and adhesion to the substrate 1 and the copper layer 4. For titanium, firstly, high-energy titanium particles can break the chemical bonds such as C=O and C-N on the surface of the polyimide, and part of the titanium atoms will recombine with these broken bonds to form chemical bonds such as Ti-O and Ti-N; secondly, titanium atoms can form π-d orbital interaction with the benzene ring in the polyimide molecular chain, enhancing the interface electronic coupling; thirdly, the titanium layer will partially penetrate into the micro concave and defects on the surface of the polyimide during the deposition process, forming a mechanical interlocking structure. For copper, as an excellent conductive layer, it provides a current path for subsequent electroplating; forms a low-resistance ohmic contact with titanium; and its face-centered cubic structure provides a good epitaxial growth template for subsequent electroplated copper. Studies have shown that the adhesion of the titanium / copper composite seed layer 2a can usually reach more than 18.34 N / cm, far exceeding the requirements of the electronic industry standard. Therefore, selecting titanium-copper composite material can achieve the required thin and uniform thickness of the seed layer, while also achieving easy conductivity, good adhesion, and easy etching.

[0023] S2, circuit pattern: applying photoresist 3 on the surface of the seed copper layer 2b, then defining a circuit pattern on the photoresist 3 by LDI (laser direct imaging) method, removing the uncured photoresist 32, and making the exposed area of the seed copper layer 2b match the range of the circuit pattern.

[0024] This step is to expose the surface of the seed layer where the circuit 5 needs to be manufactured by exposure and development. However, laser is used as the exposure source here because of its high precision, with line width precision controlled within ±5 μm. In this way, the initial width of the circuit can be closer to the designed size when electroplating.

[0025] S3, pulse electroplating: forming a copper layer 4 on the exposed part of the seed copper layer 2b by pulse electroplating, forming a circuit 5, and the total thickness of the copper layer 4 is 20-40 μm.

[0026] Pulse plating is a plating method in which the plating circuit is periodically turned on and off, or a certain waveform pulse is superimposed on the fixed direct current. Because a thicker diffusion layer is formed at the interface between the cathode and the solution when plating with direct current, the concentration of metal ions on the cathode surface is reduced, causing concentration polarization, which limits the speed of electrodeposition. Using a larger current density not only cannot increase the plating speed, but also increases the amount of hydrogen gas precipitated on the cathode, reduces the current efficiency, and deteriorates the quality of the plating layer, resulting in hydrogen embrittlement, pinholes, pitting, burning, and bubbling. Pulse plating has a relevant off time, during which the consumed metal ions diffuse to the vicinity of the cathode. When the next on time comes, the concentration of metal ions near the cathode is restored, so a higher current density can be used. The peak current of pulse plating can be much higher than the average current, which promotes the formation of crystal seeds at a higher speed than the growth of crystals, resulting in a finer, more closely arranged, and less porous plating layer with increased hardness. Compared with ordinary plating, this method has the advantages of a smooth and dense plating layer, good adhesion, high current efficiency, and good environmental performance. Therefore, the copper layer 4 obtained by this plating method has small voids, and even if the thickness of the copper layer 4 is low, it can still maintain a relatively low resistance (40-60% lower than ordinary plating resistance under the same size).

[0027] S4, film removal: remove the cured photoresist 31 to completely expose the un-plated copper area of the seed copper layer 2b, obtain an intermediate plate, then rinse the surface of the intermediate plate with water and dry it.

[0028] The part of the seed layer covered by the copper layer 4 will remain to form the circuit 5, but the part of the seed layer not covered by the copper layer 4 (covered by the cured photoresist 31) needs to be etched away, otherwise the circuits 5 will be in a short-circuit state. Therefore, the cured photoresist 31 needs to be cleaned first using a stripping liquid, and then the liquid is removed.

[0029] S5, flash etching: use an etching liquid to flash etch the surface of the intermediate plate to remove the titanium / copper composite seed layer 2a at the un-plated copper area, then dry it to obtain a low-line-resistance OLED circuit board.

[0030] Because the thickness of the seed layer itself is very small, only a small amount of etching is needed to break the connection between the circuits 5. The etchant will actually come into contact with the upper part and the sidewall of the circuit 5, but in the case of a small amount of seed layer etching, the loss of the exposed part of the circuit 5 will also be small. Therefore, under the condition that the thickness accuracy and line width accuracy have been guaranteed, the size of the circuit 5 will also be very accurate. The line width / pitch is 30 μm / 30 μm, and the side etching rate is <5%, ensuring high-frequency signal integrity. After the above steps, the line resistance is reduced by 15-30% compared with the ordinary process, and the current density is increased from 3 A / mm² to 10 A / mm².

[0031] Example 2: AsFigure 2 The application discloses a manufacturing method of a low-line-resistance OLED circuit board, and has the characteristics that the manufacturing method comprises the following steps: S1, substrate pretreatment: a titanium / copper composite seed layer 2a is sputtered on the surface of a substrate 1, the thickness of the titanium / copper composite seed layer 2a is 50-200 nm, then a seed copper layer 2b is electroplated on the titanium / copper composite seed layer 2a, and the thickness of the seed copper layer 2b is 2-3 microns. The substrate 1 is a flexible substrate and is made of polyimide (PI). The substrate 1 comprises a bending area 11 and a transition area 12 located around the bending area 11; S2, circuit pattern: photoresist 3 is coated on the surface of the seed copper layer 2b, then a circuit pattern is defined on the photoresist 3 by means of an LDI (laser direct imaging) method, the uncured photoresist 32 is removed, and the exposed area of the seed copper layer 2b matches the range of the circuit pattern. The windowing range of the photoresist 3 comprises the bending area 11 and the transition area 12.

[0032] S3, pulse electroplating: a copper layer with a thickness of 10-20 microns is first electroplated on the exposed part of the seed copper layer 2b by means of pulse electroplating, the windowing range of the photoresist 3 in the second pulse electroplating comprises the bending area 11 but does not comprise the transition area 12, then a copper layer with a thickness of 10-20 microns is electroplated on the exposed part of the first copper layer by means of pulse electroplating, thereby forming a circuit 5, and the total thickness of the copper layer 4 is 20-40 microns.

[0033] S4, film removal: the cured photoresist 31 is removed, the non-copper-plated area of the seed copper layer 2b is completely exposed, thereby obtaining an intermediate plate, then the surface of the intermediate plate is washed with water and dried.

[0034] S5, flash etching: the surface of the intermediate plate is subjected to flash etching with an etching liquid, the titanium / copper composite seed layer 2a and the seed copper layer 2b at the non-copper-plated area are removed, then drying is performed, thereby obtaining a flexible low-line-resistance OLED circuit board.

[0035] The windowing range of the two pulse electroplating operations herein is reduced, thereby forming a trapezoidal copper layer 6 near the bending area 11, so that the copper layer 6 is deformed but still has a proper thickness when the substrate 1 at the bending area 11 is bent (the copper layer 6 at the outer side is stretched and thinned). The gradient copper layer makes the bending radius as low as 1 mm (the resistance change rate is less than 3% after 100,000 cycles), and is suitable for dynamic scenes such as wearable devices.

[0036] The above merely describes some embodiments of the application. For those skilled in the art, without departing from the concept of the application, several modifications and improvements can be made, and these all belong to the protection scope of the application.

Claims

1. A method of manufacturing a low line resistance OLED wiring board, characterized by the steps of The application relates to a method for manufacturing a low-line-resistance OLED circuit board. S1, substrate pretreatment: a titanium / copper composite seed layer with a thickness of 50-200 nm is sputtered on the surface of a substrate, and then a seed copper layer with a thickness of 2-3 microns is electroplated on the titanium / copper composite seed layer; S2, circuit pattern: photoresist is coated on the surface of the seed copper layer, and then a circuit pattern is defined on the photoresist by an LDI method, and the uncured photoresist is removed, so that the exposed area of the seed copper layer matches the range of the circuit pattern; S3, pulse electroplating: a copper layer with a total thickness of 20-40 microns is plated on the exposed part of the titanium / copper composite seed layer by a pulse electroplating method, so as to form a circuit; S4, film removal: the cured photoresist is removed, so that the un-plated copper area of the titanium / copper composite seed layer is completely exposed, and an intermediate plate is obtained, then the surface of the intermediate plate is washed with water and dried; S5, flash etching: the surface of the intermediate plate is subjected to flash etching with an etching liquid, so that the titanium / copper composite seed layer and the seed copper layer outside the range of the copper layer are completely removed, and then drying is conducted, so as to obtain the low-line-resistance OLED circuit board.

2. The method of manufacturing a low-line resistance OLED wiring board according to claim 1, wherein: The photoresist is covered on the surface of the titanium / copper composite seed layer by a pressing film mode.

3. The method of manufacturing a low-line resistance OLED wiring board according to claim 1, wherein: The pulse electroplating is transported by a vertical continuous electroplating mode.

4. The method of manufacturing a low-line resistance OLED wiring board according to claim 1, wherein: The line width precision in the step S2 is controlled within + / - 5 microns.

5. The method of manufacturing a low-line resistance OLED wiring board according to claim 1, wherein: The substrate is a flexible substrate, which comprises a bending area and a transition area located at the periphery of the bending area; the copper layer is obtained by twice pulse electroplating in the step S3, and the copper thickness is increased by 10-20 microns each time, wherein the windowing range of the photoresist in the first pulse electroplating includes the bending area and the transition area, and the windowing range of the photoresist in the second pulse electroplating includes the bending area but does not include the transition area.

6. The method of manufacturing a low-line resistance OLED wiring board according to claim 5, wherein: The material of the substrate is polyimide.

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