A processing method for improving the performance of IC carrier board gold fingers

Abstract

The application discloses a processing method for improving the performance of IC carrier board gold fingers, and adds a copper chloride copper reduction treatment step after hole filling electroplating and before film stripping. The acid copper chloride etching liquid is used for selectively etching the surface of the electroplated copper layer, so that the arc-shaped gold finger prototype originally higher in the center than in the periphery is changed into a concave shape lower in the middle and higher in the periphery. This active control method fundamentally eliminates the cross-section defects left by the electroplating process, and provides a structural basis for subsequent flash etching to form a regular rectangular cross-section. The concave shape formed by the copper chloride copper reduction treatment is matched with the side etching amount generated in the subsequent flash etching process. The gold finger processed by the method has a regular rectangular cross-section, avoids the problems of impedance discontinuity and increased signal reflection caused by the traditional'steamed bun-shaped' or'mushroom-shaped' cross-section, and effectively improves the signal integrity performance of the gold finger. The regular rectangular cross-section ensures the accurate cooperation between the gold finger and the connector slot.

Description

Technical Field

[0001] This invention relates to the technical field of circuit board manufacturing, and in particular to a processing method for improving the performance of gold fingers on IC substrates. Background Technology

[0002] Gold fingers (or edge connectors) are a set of conductive contacts located on the edge of a printed circuit board (PCB) for electrical connection between the board and external components via connector insertion. Due to gold's excellent conductivity and oxidation resistance, gold fingers are typically manufactured using a gold plating process. As electronic products trend towards miniaturization and high density, increasingly stringent requirements are being placed on the linewidth / spacing accuracy, cross-sectional shape, and surface quality of gold fingers.

[0003] The modified semi-additive process (mSAP) is a process between the traditional subtractive and fully additive processes. Its core logic is as follows: first, an extremely thin seed copper layer is formed; then, the target circuitry is selectively thickened through electroplating; and finally, the base copper is removed by rapid etching. The mSAP process can achieve high-density interconnects with line widths / spacings of 30–40 μm or even smaller, and is widely used in high-precision circuit board fields such as substrate-like PCBs and IC substrates.

[0004] However, the following technical challenges exist when applying the mSAP process to gold finger manufacturing:

[0005] The cross-section of the gold finger after the through-hole electroplating is shown in the attached diagram in the instruction manual. Figure 1 The image shows a "bun-shaped" arch. In the mSAP process, after exposure and development to form the gold finger pattern window, through-hole plating is required within the window to form the gold finger prototype. During through-hole plating, due to differences in current density and other factors, the surface of the electroplated copper layer often exhibits an arc shape (i.e., "bun-shaped") with the center higher than the periphery. (See [reference needed]). Figure 2 The copper deposition rate is faster at the edge of the dry film window because the current density is higher there, and the reduction rate of copper ions is significantly higher than in the center. Therefore, the coating preferentially grows from the sides of the window towards the center. As the coating on both sides thickens rapidly, the diffusion channels for copper ions gradually narrow and are forced to concentrate in the center. Simultaneously, the current density in the center increases, causing the copper deposition rate in the center to exceed that of the edge, ultimately forming an upward-bulging arc / convex structure. During etching, CZ, and pretreatment micro-etching, the boundary layer and turbulence effects generated by the etching solution spray and flow further increase the etching on both sides due to hydrodynamic forces, resulting in a similar "bun-like" shape. This arched cross-sectional shape prevents the gold finger from forming a regular rectangular cross-section after the base copper on both sides is removed during subsequent flash etching, severely affecting the signal transmission performance and insertion / removal accuracy of the gold finger. Summary of the Invention

[0006] The purpose of this invention is to solve the problems in the prior art and to propose a processing method that improves the performance of gold fingers on IC substrates.

[0007] To achieve the above objectives, this invention proposes a processing method for improving the performance of gold fingers on IC substrates, comprising the following steps: Step S1, providing a copper-clad laminate for gold fingers, and covering the upper surface of the copper-clad laminate with a photosensitive dry film; Step S2, outer layer mSAP exposure, exposing the photosensitive dry film on the surface of the copper-clad laminate to ultraviolet light according to a preset pattern; Step S3, outer layer mSAP development, dissolving the exposed photosensitive dry film with a specific chemical developer to form a window of the gold finger pattern on the photoresist layer; Step S4, outer layer via-filling electroplating, performing via-filling electroplating on the window formed in step S3 to form a gold finger prototype; Step S5, copper chloride reduction treatment, applying copper chloride to the copper-reducing process in step S1... 4. The electroplated gold finger prototype undergoes copper reduction treatment to create a concave shape with a lower center and higher periphery; Step S6: Outer layer mSAP stripping removes the photosensitive dry film covering the copper-clad laminate surface; Step S7: Pre-bake before flash etching removes the moisture absorbed by the copper-clad laminate during the previous wet process; Step S8: Outer layer flash etching quickly removes the base copper on the copper-clad laminate surface to form circuitry and reshapes the gold finger prototype into a regular rectangular shape; Step S9: Solder resist coating coats an insulating protective layer onto the copper-clad laminate surface; Step S10: Soft gold electroplating deposits a layer of gold on the gold finger surface to form a final high-quality contact surface.

[0008] Preferably, in step S4, the electroplating current is 85-90A, the temperature is 23.5-24.4℃, and the spray pressure is 0.18-0.22 kg / cm². 2 The downward spray pressure is 0.18-0.22 kg / cm². 2 The linear velocity is 0.28-0.32 m / s.

[0009] Preferably, in step S4, the electroplating current is 88A, the temperature is 23.9℃, and the spray pressure is 0.2kg / cm². 2 The downward spray pressure is 0.2 kg / cm². 2 The linear velocity is 0.3 m / s.

[0010] Preferably, in step S5, the temperature during the copper chloride reduction treatment is 48-52℃ and the spray pressure is 2.8-3.2 kg / cm². 2 The downward spray pressure is 2.8-3.2 kg / cm2, and the linear velocity is 4.8-5.2 m / s.

[0011] Preferably, in step S5, the copper chloride copper reduction treatment is performed at a temperature of 50°C and an upward spray pressure of 3 kg / cm². 2 The downward spray pressure is 3 kg / cm. 2 The linear speed is 5 m / s.

[0012] Preferably, in step S8, the temperature during the outer layer flash etching treatment is 28-32℃ and the spray pressure is 1.5-1.7 kg / cm². 2 The downward spray pressure is 1.5-1.7 kg / cm². 2 The linear velocity is 3.3-3.7 m / s.

[0013] Preferably, in step S8, the temperature during the outer layer flash etching treatment is 28-32℃ and the spray pressure is 1.5-1.7 kg / cm². 2 The downward spray pressure is 1.5-1.7 kg / cm². 2 The linear velocity is 3.3-3.7 m / s.

[0014] Preferably, before the solder resist coating in step S9, a solder resist roughening step is included to roughen the surface of the copper-clad laminate, thereby increasing the micro-roughness of the copper surface and improving the adhesion between the ink and the copper-clad laminate.

[0015] Preferably, an outer AOI step is included before the solder resist coating in step S9, in which the AOI equipment is used to perform a high-precision optical scan on the flash-etched circuit to detect and mark various defects.

[0016] The beneficial effects of this invention's processing method for improving the performance of IC substrate gold fingers are as follows: This invention adds a copper chloride reduction treatment step after through-hole plating and before film stripping. Using an acidic copper chloride etching solution, the surface of the electroplated copper layer is selectively etched, transforming the original arc-shaped gold finger, with a higher center and periphery, into a concave shape with a lower center and higher periphery. This active control method fundamentally eliminates cross-sectional defects left over from the electroplating process, providing a structural basis for subsequent flash etching to form a regular rectangular cross-section. The concave shape formed by the copper chloride reduction treatment has a depth that matches the amount of lateral etching generated during the subsequent flash etching process. During flash etching, while the base copper on both sides of the gold finger is removed, the sides of the gold finger body are subjected to a certain amount of lateral etching. Because the gold finger surface is pre-formed with a concave shape with a lower center and higher periphery, the cross-section of the gold finger after flash etching is precisely shaped into a regular rectangle. This design cleverly transforms the originally harmful "lateral etching" into a shaping method, achieving precise control of the gold finger's cross-sectional shape. The gold fingers processed by the method of this invention have a regular rectangular cross-section, avoiding problems such as impedance discontinuity and increased signal reflection caused by traditional "bun-shaped" or "mushroom-shaped" cross-sections, effectively improving the signal integrity (SI) performance of the gold fingers. At the same time, the regular rectangular cross-section ensures a precise fit between the gold fingers and the connector slot, improving the reliability of insertion and removal and extending service life.

[0017] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cross-section of a bun-shaped gold finger.

[0019] Figure 2 This is a diagram illustrating the formation of the bun-shaped gold finger.

[0020] Figure 3 This is a schematic diagram of the outer layer hole-filling electroplating in step S4.

[0021] Figure 4 This is a schematic diagram of step S5, copper chloride copper reduction treatment.

[0022] Figure 5 This is a schematic diagram of the outer mSAP peeling process in step S6.

[0023] Figure 6 This is a schematic diagram of the outer layer flash erosion in step S8.

[0024] Figure 7 This is a schematic diagram of step S10, which involves over-coarsening the anti-weld layer.

[0025] Figure 8 This is a schematic diagram of step S12, electroplating soft gold. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0027] In the description of this invention, it should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to or indirectly connected to the other element.

[0028] In the description of this invention, it should be noted that the terms "center," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0029] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Example 1:

[0031] This invention discloses a processing method for improving the performance of gold fingers on IC substrates, comprising the following steps: Step S1, providing a copper-clad laminate for gold fingers, covered with a photosensitive dry film. The copper-clad laminate includes a substrate and a bottom copper layer covering the surface of the substrate, the thickness of which is 1-3 μm. A photosensitive dry film is coated on the surface of the copper layer of the copper-clad laminate, preferably a negative photoresist dry film. The photosensitive dry film can be coated by hot-pressing using a vacuum laminator to ensure that there are no air bubbles or wrinkles between the dry film and the copper surface. Step S2: Outer layer mSAP exposure. According to a preset gold finger pattern, the photosensitive dry film on the surface of the copper-clad laminate is exposed to ultraviolet light. During the exposure process, ultraviolet light passes through a photomask (mask plate) and irradiates the photosensitive dry film. The photosensitive dry film in the irradiated area undergoes a polymerization reaction, and its chemical structure changes. The exposure energy needs to be precisely controlled to ensure the clarity and resolution of the pattern edges. Step S3: Outer layer mSAP development. The exposed photosensitive dry film is developed using a specific chemical developer. For negative photoresist, the developer dissolves the unexposed (i.e., unpolymerized) dry film areas, leaving dry film windows on the copper surface corresponding to the gold finger pattern. These windows precisely expose the underlying copper layer that needs to be electroplated for thickening. Step S4, outer layer via filling electroplating, see [link to documentation]. Figure 3 In step S3, through-hole electroplating is performed within the dry film window to thicken the exposed base copper layer, forming the gold finger prototype. The thickness of the electroplated copper layer is 5–20 μm. Due to the current density distribution and the effect of additives during electroplating, the surface of the gold finger prototype is not flat after electroplating, but rather has an arc shape with the center higher than the periphery (i.e., "bun-shaped"). The electroplating current is 88 A, the temperature is 23.9 °C, and the spray pressure is 0.2 kg / cm². 2 The downward spray pressure is 0.2 kg / cm². 2 The linear velocity is 0.3 m / s. Step S5, copper reduction treatment with copper chloride, see [link / reference]. Figure 4 This is the most crucial step in the invention. The gold finger prototype formed by electroplating in step S4 is subjected to copper reduction treatment using an acidic copper chloride etching solution. The acidic copper chloride etching solution has the following composition: copper chloride content 330–360 g / L, hydrochloric acid content 35–45 g / L. The etching temperature is 45–55°C, the etching time is 30–120 seconds, and the etching depth is 1–5 μm; the processing temperature is 50°C, and the spray pressure is 3 kg / cm². 2 The downward spray pressure is 3 kg / cm. 2The line speed is 5 m / s. Acidic copper chloride etching is a mature etching system in PCB manufacturing, with advantages such as low cost and easy regeneration. During the etching process, the etching solution uniformly chemically etches the surface of the electroplated copper layer. Because the surface of the gold finger prototype is an arc shape with the center higher than the periphery, the raised part in the center is etched with a relatively larger amount, while the lower part at the periphery is etched with a relatively smaller amount. After precise etching control, the surface of the gold finger prototype transforms into a concave shape with a lower center and a higher periphery, such as... Figure 5 As shown. The depth of this concave shape is 1-5 μm, and the cross-section is an inverted arc-shaped groove. This step uses copper chloride to reduce copper content, actively correcting the "bun-shaped" arched defect left over from the through-hole electroplating process into a concave shape, laying the foundation for subsequent flash etching to form a regular rectangular cross-section. Step S6, outer layer mSAP peeling, see [reference]. Figure 5 Remove the photosensitive dry film covering the surface of the copper-clad laminate. An alkaline stripping solution can be used to peel the cured photosensitive dry film from the copper layer surface, exposing the complete electroplated copper layer and the underlying copper layer. Step S7, pre-bake: Bake the copper-clad laminate after stripping at 110–150℃ for 5–20 minutes. The purpose of baking is to remove the moisture absorbed by the copper-clad laminate during the previous wet processes (such as developing, electroplating, and stripping), preventing residual moisture from vaporizing and causing the board to delaminate (split) during subsequent flash etching or high-temperature processes. Step S8, outer layer flash etching, see [link to relevant documentation]. Figure 6 The copper-clad laminate (CCL) was subjected to flash etching using a hydrogen peroxide / sulfuric acid etching solution. This rapidly removed the underlying copper (1–3 μm thick) not covered by the electroplated copper layer, while simultaneously shaping the gold fingers into regular rectangles. The processing temperature was 30℃, and the spray pressure was 1.6 kg / cm². 2 The downward spray pressure is 1.6 kg / cm². 2 The etching speed is 3.5 m / s. The flash etching solution uniformly etches all exposed copper surfaces in a very short time, completely removing the underlying copper layer while only a small portion of the electroplated copper layer is etched away. During this process, because the surface of the gold finger prototype has a pre-formed concave shape with a low center and high periphery, the lateral etching (side etching) of the flash etching solution precisely etches away the raised periphery of the concave shape, thus shaping the cross-section of the gold finger into a regular rectangle, such as... Figure 7 As shown. In other words, the depth of the recessed shape is matched with the amount of lateral etching during flash etching, so that the cross-section of the gold finger after flash etching is a regular rectangle. The aspect ratio of the cross-section of the regular rectangle is 1:1 to 1:3. Step S9, outer layer AOI (automatic optical inspection), using AOI equipment to perform high-precision optical scanning on the flash-etched circuit, detecting and marking various defects, such as open circuits, short circuits, recesses, and notches. AOI inspection can detect defective products early after flash etching, preventing defects from flowing into subsequent processes, effectively controlling costs and ensuring yield. Step S10, solder mask coarsening, see [reference]. Figure 7The copper-clad laminate (CCL) surface undergoes an ultra-roughening treatment for solder resist. A sulfuric acid / hydrogen peroxide system is used to chemically etch the copper surface, increasing its micro-roughness and creating a uniform micro-rough structure. The ultra-roughening treatment temperature is 30℃±4℃, and the treatment time is 30–60 seconds. This treatment significantly improves the adhesion between the solder resist ink and the copper surface, preventing the solder resist layer from peeling, blistering, or detaching in subsequent processes. Step S11: Solder resist coating. An insulating protective layer (solder resist ink, commonly known as "green oil") is coated onto the CCL surface, and the solder resist layer is created through exposure, development, and heat curing processes. The solder resist layer must precisely cover all circuits while leaving a precise "window" for the gold finger area, meaning the gold finger area is not covered by the solder resist layer to allow for subsequent soft gold plating. Step S12: Soft gold plating. (See [reference needed]) Figure 8 On the surface of the gold fingers, a layer of gold is deposited through electroplating to form the final high-quality contact surface. Electroplating soft gold involves sequential nickel plating and gold plating steps: first, a layer of nickel is electroplated as a barrier layer to prevent diffusion between gold and copper; then, a layer of gold is electroplated. In the gold plating step, the thickness of the gold layer is 3–6 μm (i.e., 120–240 microinches), and the current density is 5–40 A / dm². The thickness of the gold layer must be strictly controlled within the process requirements; too thin a layer results in insufficient wear resistance, while too thick a layer leads to excessive cost.

[0032] Example 2:

[0033] Based on Example 1, the difference between this example and Example 1 lies in the different process parameters for the copper chloride reduction treatment. In this example, the composition of the acidic copper chloride etching solution is: copper chloride content 340-350 g / L, hydrochloric acid content 38-42 g / L. The depth of the recessed shape is 2-3 μm. The remaining steps are the same as in Example 1.

[0034] Comparative example:

[0035] To verify the technical effect of the present invention, a comparative example was set up. The comparative example adopted the same mSAP process flow as Example 1, but did not include the copper chloride copper reduction treatment in step S5. That is, after the through-hole electroplating, subsequent steps such as stripping, pre-bake for flash etching, and outer layer flash etching were performed directly.

[0036] Comparative tests showed that in the comparative example, the cross-section of the gold fingers after flash etching was "bun-shaped" or "mushroom-shaped," failing to form a regular rectangle; while in Example 1, the cross-section of the gold fingers after flash etching was a regular rectangle, with an aspect ratio consistently within the range of 1:1 to 1:3. In signal integrity testing, Example 1 showed an approximately 15% improvement in impedance consistency and an approximately 20% reduction in insertion loss compared to the comparative example.

[0037] All standard parts used in this application can be purchased from the market. The specific connection methods of each part adopt conventional methods such as bolts, rivets, and welding that are mature in the existing technology. The internal components of the electric slide rail, cylinder, welding machine, electric telescopic rod and controller all adopt conventional models in the existing technology, and their internal structure belongs to the existing technology structure. Workers can complete the normal operation of them according to the existing technical manual. In addition, the circuit connection adopts the conventional connection method in the existing technology, and will not be described in detail here.

[0038] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection for this invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of this invention, or equivalent structural or procedural transformations made using the description and drawings of this invention, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of protection of this invention.

Claims

1. A processing method for improving the performance of gold fingers on an IC substrate, characterized in that, Includes the following steps: Step S1: Provide a gold finger copper-clad laminate, and cover the upper surface of the copper-clad laminate with a photosensitive dry film; Step S2, outer layer mSAP exposure, the photosensitive dry film on the surface of the copper-clad laminate is exposed to ultraviolet light according to the preset pattern; Step S3, outer layer mSAP development, using a specific chemical developer to dissolve the exposed photosensitive dry film, forming a window of gold finger pattern on the photoresist layer; Step S4: Outer layer via-filling electroplating. The via-filling electroplating is performed on the window formed in step S3 to form the gold finger prototype. Step S5, copper chloride copper reduction treatment, copper chloride is used to reduce the copper of the gold finger prototype formed by electroplating in step S4, so that the surface of the gold finger prototype presents a concave shape with a low center and a high periphery. Step S6: Peel off the outer mSAP layer to remove the photosensitive dry film covering the surface of the copper-clad laminate. Step S7, pre-bake to remove the moisture absorbed by the copper-clad laminate during the previous wet process; Step S8, outer layer flash etching, quickly removes the bottom copper on the surface of the copper-clad board to form a circuit, and shapes the gold finger prototype into a regular rectangular shape; Step S9, Solder resist coating: Applying an insulating protective layer to the surface of the copper-clad laminate; Step S10, electroplating soft gold: A layer of gold is deposited on the surface of the gold fingers by electroplating to form the final high-quality contact surface.

2. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 1, characterized in that: In step S4, the electroplating current is 85-90A, the temperature is 23.5-24.4℃, and the spray pressure is 0.18-0.22 kg / cm². 2 The downward spray pressure is 0.18-0.22 kg / cm². 2 The linear velocity is 0.28-0.32 m / s.

3. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 2, characterized in that: In step S4, the electroplating current is 88A, the temperature is 23.9℃, and the spray pressure is 0.2kg / cm². 2 The downward spray pressure is 0.2 kg / cm². 2 The linear velocity is 0.3 m / s.

4. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 1, characterized in that: In step S5, the copper chloride reduction treatment is carried out at a temperature of 48-52℃ and an upward spray pressure of 2.8-3.2 kg / cm². 2 The downward spray pressure is 2.8-3.2 kg / cm². 2 The linear velocity is 4.8-5.2 m / s.

5. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 4, characterized in that: In step S5, the copper chloride copper reduction treatment is performed at a temperature of 50°C and an upward spray pressure of 3 kg / cm². 2 The downward spray pressure is 3 kg / cm. 2 The linear speed is 5 m / s.

6. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 1, characterized in that: In step S8, the temperature during the outer layer flash etch treatment is 28-32℃, and the spray pressure is 1.5-1.7 kg / cm². 2 The downward spray pressure is 1.5-1.7 kg / cm². 2 The linear velocity is 3.3-3.7 m / s.

7. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 6, characterized in that: In step S8, the outer layer flash etch treatment is performed at a temperature of 30°C and an upper spray pressure of 1.6 kg / cm². 2 The downward spray pressure is 1.6 kg / cm². 2 The linear speed is 3.5 m / s.

8. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 1, characterized in that: Before the solder resist coating in step S9, a solder resist roughening step is also included to roughen the surface of the copper-clad laminate, increase the micro-roughness of the copper surface, and improve the adhesion between the ink and the copper-clad laminate.

9. The processing method for improving the performance of gold fingers on an IC substrate as described in claim 1, characterized in that: Before the solder resist coating in step S9, an outer AOI step is also included, in which the AOI equipment is used to perform a high-precision optical scan on the flash-etched circuit to detect and mark various defects.

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