Dry film processing method for packaging substrate and packaging substrate

Abstract

The application discloses a dry film processing method of a packaging substrate and the packaging substrate, and the dry film processing method of the packaging substrate comprises the following steps: performing a dry film curing treatment on a packaging substrate subjected to a developing treatment; wherein a non-plating area of the packaging substrate is covered with a dry film; transferring the packaging substrate to a pre-dissolution tank to perform a pre-dissolution treatment on the dry film; performing a selective nickel-palladium-gold treatment on the packaging substrate, and removing the dry film. Through the method, the application can significantly reduce the dissolution risk of organic matters in the dry film, and effectively guarantee the stability of a chemical nickel-palladium-gold plating tank solution.

Description

Technical Field

[0001] This application relates to the field of printed circuit board manufacturing, and in particular to a dry film treatment method for a packaging substrate and the packaging substrate. Background Technology

[0002] With the development of communication technology, signal transmission rates are increasing exponentially. While packaging substrates are becoming increasingly powerful, their space is continuously shrinking, making module integration a trend. Currently, in the packaging field, the scale of SIP (System-in-Package) packaging substrates is gradually increasing, leading to a growing demand for various composite surface treatments. Especially with product performance upgrades, the trend of packaging forms shifting from WB (Wire Bonding) to FC (Flip Chip) is evident. Correspondingly, ENEPIG+OSP (Electroless Nickel Electroless Palladium Immersion Gold + Organic Solderability Preservative) surface treatment technology for packaging substrates has become a clear 5G substrate technology trend.

[0003] However, organic matter in the dry film will precipitate out when immersed in high-temperature electroless nickel, palladium, and gold baths, affecting the properties of the solution and leading to insufficient coating thickness, poor uniformity, and nickel corrosion risk at the end of the nickel / palladium / gold bath's life. Summary of the Invention

[0004] This application provides a dry film treatment method for packaging substrates, which can reduce the leaching of dry film in electroless nickel-palladium-gold plating bath, reduce the risk of bath contamination, improve the uniformity of nickel-palladium-gold plating thickness, and reduce the risk of nickel corrosion.

[0005] To address the aforementioned technical problems, this application provides a dry film processing method for a packaging substrate, comprising: performing a dry film curing process on a packaging substrate that has undergone development treatment; wherein the non-plated areas of the packaging substrate are covered with a dry film; transferring the packaging substrate to a pre-dissolution tank to perform a pre-dissolution process on the dry film; performing a selective nickel-palladium-gold treatment on the packaging substrate and removing the dry film.

[0006] The process includes a dry film curing treatment of the encapsulation substrate after development; wherein the step of covering the non-plated areas of the encapsulation substrate with dry film includes: feeding the encapsulation substrate through a board feeding machine and conveying it through a curing section at a set conveying speed, and then collecting it by a board collecting machine after ultraviolet curing.

[0007] The transmission speed is set to a range of 1.9-2.1 meters per minute; the curing time for the dry film curing process is 20-22 seconds.

[0008] In the dry film curing process, the exposure energy is 100-900 millijoules per square centimeter, the dominant wavelength is 320-400 nanometers, and the energy uniformity is greater than or equal to 85%; where energy uniformity is the ratio of the minimum energy value to the maximum energy value within the effective irradiated surface.

[0009] The step of transferring the packaging substrate to a pre-dissolution tank and pre-dissolving the dry film includes: placing the packaging substrate in a pre-dissolution tank containing a pre-dissolution agent and immersing it for a set time to perform pre-dissolution treatment in order to remove uncrosslinked substances remaining after curing.

[0010] The pre-dissolving agent is an aminocarboxylate complex system, mainly composed of aminocarboxylate and chloride, with a concentration of 100 ml per liter.

[0011] The pH value of the pre-dissolved reagent is 6.8-7.6, the temperature is 55-65 degrees Celsius, and the set time range is 11.5-12.5 minutes.

[0012] Before the steps of selective nickel-palladium-gold treatment and removing the dry film from the packaging substrate, the process includes: sequentially performing degreasing treatment, micro-etching treatment, acid washing treatment, pre-immersion treatment, activation treatment, and post-immersion treatment on the packaging substrate; wherein the packaging substrate must be washed with water after each treatment.

[0013] The step of performing selective nickel-palladium-gold treatment on the packaging substrate and removing the dry film includes: sequentially placing the packaging substrate into a nickel bath, a palladium bath, and a gold bath for chemical deposition treatment, and then removing the dry film.

[0014] To solve the above-mentioned technical problems, this application provides a packaging substrate that can be prepared by performing a dry film processing method for packaging substrates as described above.

[0015] The beneficial effects of this application are as follows: This application provides a dry film processing method for a packaging substrate, which involves performing a dry film curing process on the packaging substrate after development treatment; wherein the non-plating areas of the packaging substrate are covered with a dry film; the packaging substrate is transferred to a pre-dissolution tank for pre-dissolution treatment of the dry film; the packaging substrate is then subjected to selective nickel-palladium-gold treatment, and the dry film is removed. The amount of organic matter leaching from the final film is effectively suppressed, significantly reducing the risk of contamination in the electroless plating bath. The deposition rates of the nickel and palladium baths remain stable throughout their lifespan, and the decay of the gold bath's deposition rate at the end of its lifespan is significantly improved. Simultaneously, the surface morphology of the ink layer remains intact, the first-piece pass rate stability of the selective nickel-palladium-gold treatment is greatly improved, nickel corrosion defects are significantly reduced, and the long-term reliability of the product is further enhanced. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of one embodiment of the dry film processing method for the packaging substrate provided in this application; Figure 2 This is a structural diagram of the dry film processing method for the packaging substrate provided in this application; Detailed Implementation The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0018] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0019] Please see Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the dry film processing method for the packaging substrate provided in this application.

[0020] S11: Dry film curing treatment is performed on the packaging substrate that has undergone development treatment; wherein, the non-plated areas of the packaging substrate are covered with dry film.

[0021] After development, the packaging substrate, with dry film covering the non-plated areas, undergoes dry film curing. This dry film curing can be performed using UV (Ultraviolet) curing. Specifically, the developed packaging substrate is first automatically fed into the curing section by a loading machine. The curing section employs a horizontal UV curing device. Through a symmetrical UV light source layout, a stable horizontal transport system, and balanced thermal field management, the packaging substrate is ensured to complete curing as it passes through the UV light source area under set transport speed, UV exposure energy, and energy uniformity conditions. Under the set UV exposure energy conditions, UV light excites the photoinitiator in the dry film, generating active free radicals, which in turn initiate the polymerization reaction of the acrylate resin, forming a dense three-dimensional cross-linked network. This significantly increases the cross-linking density of the dry film, effectively strengthening its resistance to subsequent chemical plating. Finally, the cured packaging substrate is received by a receiving machine located at the curing section exit. Specifically, the transmission speed is set to 1.9 to 2.1 meters per minute, which, in conjunction with the length of the curing section, ensures that the substrate remains in the curing section for 20 to 22 seconds. This ensures that the dry film receives sufficient UV light irradiation, preventing excessive dry film dissolution or decreased adhesion due to insufficient curing. The exposure energy of the UV light source during the curing stage needs to be controlled between 100 and 900 millijoules per square centimeter, with a preferred range of 300 to 360 millijoules per square centimeter. The dominant wavelength of the UV light source is set in the range of 320 to 400 nanometers, preferably 365 nanometers, to match the absorption peak direction of commonly used dry film photoinitiators, ensuring efficient photochemical reactions. The UV energy uniformity needs to be greater than or equal to 85%, achieved by uniformly distributing the irradiated surface energy to avoid uneven curing caused by local energy deviations. For example, this can be measured using a UV radiometer or UV energy meter, collecting data by uniformly distributing points (such as the nine-point method) along the width and length of the irradiated surface, and calculating the ratio of the minimum to the maximum energy value to verify whether the uniformity meets the standard.

[0022] In a specific application scenario, after the packaging substrate undergoes development, the dry film completely covers the unplated areas, while the exposed pad areas exhibit a clean copper surface, preparing for subsequent selective deposition. The packaging substrate is first automatically fed by a board feeding machine, smoothly passing through the UV curing section at a transmission speed of 1.9 meters per minute. The curing section is equipped with a high-pressure mercury lamp as the UV light source, with the main wavelength set at 365 nanometers. The packaging substrate receives uniform ultraviolet light irradiation as it passes through, with the exposure energy controlled at 300 millijoules / square centimeter and the energy uniformity maintained above 85%. After a 22-second curing process, the packaging substrate is automatically collected by a board receiving machine and transferred to the next process.

[0023] S12: Transfer the packaging substrate to the pre-dissolution tank to pre-dissolve the dry film.

[0024] The cured encapsulation substrate is moved into a pre-dissolution tank containing a specific reagent for pre-dissolution treatment of the dry film. Specifically, the encapsulation substrate is immersed in the pre-dissolution tank containing a specific reagent at a preset temperature. After a set time, the reagent selectively dissolves and complexes trace amounts of uncrosslinked resin, unreacted monomers, and small molecule additives remaining in the cured dry film. After pre-dissolution, the encapsulation substrate is removed from the tank and washed with water. To ensure sufficient contact between the encapsulation substrate and the reagent, the pre-dissolution tank can also incorporate a bubble system or a oscillating transmission mechanism. The convection of the reagent is enhanced by bubble agitation or the reciprocating motion of the encapsulation substrate, ensuring continuous renewal of the reagent on the dry film surface and improving dissolution efficiency and uniformity. The reagent system is an aminocarboxylate complex system, mainly composed of aminocarboxylate and chloride, with a concentration of 100 ml / L. The pH of the solution is set within a neutral range of 6.8 to 7.6 to avoid corrosion of the copper and ink surfaces by strong acids and alkalis; the temperature is controlled between 55 and 65 degrees Celsius to ensure optimal solubility of the aminocarboxylate complex system. The encapsulation substrate is placed in a pre-dissolution bath and immersed for 11.5 to 12.5 minutes within the preset temperature and pH range to ensure a complete dissolution reaction and maintain production efficiency. For example, a combination of pH 7.0 and temperature 65 degrees Celsius, or a combination of pH 6.8 and temperature 55 degrees Celsius, or a combination of pH 7.6 and temperature 62 degrees Celsius can be used, with treatment times of 11.5 minutes, 12.0 minutes, or 12.5 minutes. This chemical system has a gentle yet efficient complexing and dissolving ability for uncrosslinked dry film resins, and can precisely remove trace amounts of uncrosslinked substances that may still exist after UV curing. This significantly reduces the risk of the dry film contaminating expensive chemicals in the subsequent main plating bath. At the same time, it has excellent compatibility with the copper and ink surfaces of the product. The processing time is controlled within 11.5 to 12.5 minutes to ensure that no corrosion or damage is caused to the substrate.

[0025] In a specific application scenario, the UV-cured encapsulation substrate is transferred to a pre-dissolution tank for processing. This tank contains 1 liter of aminocarboxylate complex reagent, with a preset temperature of 55 degrees Celsius and a preset pH of 6.8. After the encapsulation substrate is immersed, a bubbling system at the bottom of the tank continuously generates uniform bubbles, agitating the reagent and creating turbulence. Simultaneously, oscillating mechanisms on both sides of the tank cause the encapsulation substrate to oscillate slightly at a frequency of 5 times per minute. This dual convection method ensures that the dry film surface remains in constant contact with fresh reagent. Within a set time of 12.5 minutes, the reagent fully dissolves and complexes any remaining trace amounts of uncrosslinked resin and small-molecule additives in the dry film. After processing, the encapsulation substrate is removed and enters a three-stage washing section, where deionized water spray removes surface dissolutions and reagent residues, allowing it to proceed to subsequent processes in a clean state.

[0026] S13: Perform selective nickel-palladium-gold treatment on the packaging substrate and remove the dry film.

[0027] After the pre-dissolution treatment is completed, the packaging substrate enters the selective nickel-palladium-gold deposition and subsequent film removal stage. First, the packaging substrate needs to undergo a strict nickel-palladium-gold pretreatment to ensure that the copper surface of the exposed pad area is clean, slightly rough, and catalytically active. The packaging substrate successively undergoes degreasing treatment, micro-etching treatment, acid pickling treatment, pre-dip treatment, activation treatment, and post-dip treatment, and the packaging substrate needs to be washed with water after each treatment. Specifically, the packaging substrate is rinsed in a water bath to remove residual chemicals, then enters a degreasing bath where alkaline cleaning agents or ultrasonic cleaning are used to remove grease and organic contaminants from the surface of the packaging substrate, ensuring no residue remains. After a second water rinse, it enters a micro-etching bath using copper sulfate or copper chloride solution, where a weak acid solution slightly etches the copper surface to increase roughness, thereby improving the adhesion of subsequent plating layers. After rinsing to terminate the reaction, it enters a dilute sulfuric acid or dilute hydrochloric acid pickling bath to remove trace oxides and activate the copper surface, for example, using a 5% to 10% dilute hydrochloric acid or sulfuric acid solution. Subsequently, it is rinsed again and passed through a pre-dip bath, for example, using a mild surfactant solution such as palladium chloride solution to uniformly wet the surface of the packaging substrate to protect the subsequent chemical solutions. After rinsing, it enters an activation bath where palladium salt solutions such as palladium chloride solution are used to deposit a catalytic layer on the copper surface. It is then rinsed again and subjected to a post-dip bath, where a stabilizing solution such as citric acid solution is used to prevent surface oxidation and maintain the activity of the palladium layer. Finally, it undergoes a multi-stage water rinse with pure water to complete the pretreatment.

[0028] After completing the nickel-palladium-gold pretreatment, the packaging substrate undergoes nickel-palladium-gold deposition. It is sequentially immersed in a nickel bath, a palladium bath, and a gold bath for chemical deposition, and finally the dry film is removed. Specifically, the packaging substrate first enters a nickel bath containing a chemical nickel deposition solution. This solution typically uses sodium hypophosphite as a reducing agent. Under an acidic environment with nickel sulfate as the main salt and a high temperature of 85-90 degrees Celsius, the automatic deposition of a nickel-phosphorus alloy is initiated on the exposed pad surface. A temperature control system and circulating filtration maintain solution homogeneity. The packaging substrate remains in the bath for 20-30 minutes, gradually depositing a chemical nickel layer. After nickel deposition, the packaging substrate is washed with water and then placed in a palladium bath. This bath contains a weakly acidic chemical palladium solution containing palladium compounds, complexing agents, and reducing agents, and remains at a temperature of 50-60 degrees Celsius. For 5-10 minutes, a palladium layer is deposited through a combination of displacement and autocatalytic reactions, effectively preventing the diffusion of nickel from the gold layer and thus preventing nickel corrosion. The packaged substrate then enters a gold bath containing a cyanide-containing or environmentally friendly cyanide-free sulfite chemical immersion solution. It remains at 80-85 degrees Celsius for 8-12 minutes, utilizing the oxidizing properties of gold ions to displace the metal atoms on the palladium surface, depositing a thin gold layer. After gold deposition, the packaged substrate enters a drying section where surface moisture is removed using hot air or infrared drying to prevent oxidation or moisture absorption of the gold layer, ensuring a dry and clean plating surface. Finally, the packaged substrate undergoes a stripping process, where a high-concentration sodium hydroxide solution peels off the dry film, exposing the original copper surface in the unplated areas.

[0029] In a specific application scenario, the packaged substrate enters a degreasing tank and is treated with RW-901 acidic degreasing agent at a concentration of 60-90 ml / L at 40-50 degrees Celsius for 5 minutes to remove grease and organic contaminants from the copper surface. This is followed by hot water rinsing and double water rinsing to remove residual chemicals. Next, it enters a micro-etching tank and is treated with a micro-etching solution composed of 100 g / L SPS (Sodium polyanetholesulfonate) and 20 ml / L sulfuric acid at 25-30 degrees Celsius for 1-2 minutes to micro-etch the copper surface. The substrate is roughened to enhance adhesion. After rinsing with water, it enters an acid pickling tank and is immersed in 40 ml / L dilute sulfuric acid at room temperature for 1 minute to remove trace oxides generated by micro-etching. Next, the encapsulation substrate enters a pre-dip tank and is treated with 10-15 ml / L sulfuric acid at room temperature for 30-60 seconds to protect the subsequent activation solution. Then, it enters an activation tank and is treated with 15 ml / L sulfuric acid and 150 ml / L RW-903 activator at 25-30 degrees Celsius for 1-2 minutes to deposit a catalyst layer on the copper surface. Finally, it enters a post-dip tank and is treated with 15 ml / L sulfuric acid at room temperature for 30-60 seconds. After completing the preliminary treatments, the next step, nickel-palladium-gold deposition, is performed on the encapsulation substrate. The packaging substrate first enters a nickel bath and is deposited at 85-90 degrees Celsius for 20-30 minutes to form a nickel layer on the exposed pad area. It then enters a palladium bath and is deposited at 50-60 degrees Celsius for 5-10 minutes to coat the nickel layer with a palladium layer. Finally, it enters a gold bath and is deposited at 80-85 degrees Celsius for 8-12 minutes to deposit a gold layer on top of the palladium layer. After deposition, the packaging substrate is washed and dried, resulting in a complete nickel, palladium, and gold three-layer structure on the pad area.

[0030] Please see Figure 2 , Figure 2 This is a structural diagram of the dry film processing method for the packaging substrate provided in this application.

[0031] The packaging substrate uses a substrate 201 as the bottom support, with a copper layer 202 covering the substrate 201. A solder resist layer 203 covers a portion of the surface of the copper layer 202 to protect the copper surface of non-soldering areas. The solder pad areas, which require selective surface treatment, have their copper surfaces exposed for subsequent deposition. In the initial stage of the process, through film lamination and development, a first dry film 2071 and a second dry film 2072 are attached to specific areas on both sides of the packaging substrate, precisely covering the non-copper-plated areas. Subsequently, the packaging substrate enters the pre-dissolution bath and chemical plating process, where reactions occur sequentially in the exposed solder pad areas: first, a nickel layer 204 is deposited; then, a palladium layer 205 is deposited on the surface of the nickel layer 204; finally, a gold layer 206 is deposited on the palladium layer 205. During this process, the first dry film 2071 and the second dry film 2072 protect the underlying solder resist layer 203 and copper layer 202, ensuring that the plating solution does not contact the non-plated areas. After the gold layer 206 is deposited and dried, the packaging substrate enters the stripping process. The first dry film 2071 and the second dry film 2072 are completely stripped using a high-temperature, high-concentration sodium hydroxide solution, exposing the solder resist layer 203 and the copper layer 202 that were originally protecting them. The final packaged substrate presents a complete stack of nickel layer 204, palladium layer 205, and gold layer 206 in the pad area, while the non-plated areas are covered by the solder resist layer 203, achieving precise selective surface treatment.

[0032] Through the above steps, this embodiment uses UV curing treatment to increase the crosslinking density of the dry film, thereby reducing the leaching of the dry film in the electroless nickel-palladium-gold plating bath. Furthermore, the pre-dissolution treatment removes uncrosslinked resin and impurities, thereby reducing the risk of dry film contamination of the plating bath. The combination of these two methods improves the uniformity of the nickel-palladium-gold plating thickness while reducing the risk of nickel corrosion.

[0033] The above are merely embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural changes made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A method for dry film processing of a packaging substrate, characterized in that, include: The encapsulation substrate that has undergone development treatment is subjected to dry film curing treatment; wherein, the non-plated areas of the encapsulation substrate are covered with dry film; The packaging substrate is transferred to a pre-dissolution tank to pre-dissolve the dry film; The packaging substrate is subjected to a nickel-palladium-gold treatment, and the dry film is removed.

2. The dry film treatment method according to claim 1, characterized in that, The step of performing dry film curing on the developed packaging substrate, wherein the non-plated areas of the packaging substrate are covered with dry film, includes: The packaging substrate is fed by a board feeding machine and conveyed through the curing section at a set transmission speed. After being cured by ultraviolet light, it is collected by a board receiving machine.

3. The dry film treatment method according to claim 2, characterized in that, The set transmission speed range is 1.9-2.1 meters per minute; the curing time for dry film curing is 20-22 seconds.

4. The dry film treatment method according to claim 1, characterized in that, The exposure energy in the dry film curing process is 100-900 millijoules per square centimeter, the dominant wavelength is 320-400 nanometers, and the energy uniformity is greater than or equal to 85%; wherein, the energy uniformity is the ratio of the minimum energy value to the maximum energy value within the effective irradiated surface.

5. The dry film treatment method according to claim 1, characterized in that, The step of transferring the packaging substrate to the pre-dissolution tank and performing pre-dissolution treatment on the dry film includes: The encapsulation substrate is placed in a pre-dissolution tank containing a pre-dissolution agent and immersed for a set time to perform pre-dissolution treatment in order to remove uncrosslinked substances remaining after curing.

6. The dry film treatment method according to claim 5, characterized in that, The pre-dissolving agent is an aminocarboxylate complex system, mainly composed of aminocarboxylate and chloride, with a concentration of 100 ml per liter.

7. The dry film treatment method according to claim 5, characterized in that, The pre-dissolving agent has a pH value of 6.8-7.6 and a temperature of 55-65 degrees Celsius; the set time range is 11.5-12.5 minutes.

8. The dry film treatment method according to claim 1, characterized in that, Before the step of performing selective nickel-palladium-gold treatment on the packaging substrate and removing the dry film, the procedure includes: The packaging substrate is subjected to degreasing, micro-etching, pickling, pre-immersion, activation, and post-immersion treatment in sequence; and the packaging substrate is washed with water after each treatment.

9. The dry film treatment method according to claim 1, characterized in that, The steps of performing selective nickel-palladium-gold treatment on the packaging substrate and removing the dry film include: The encapsulation substrate is sequentially placed in a nickel bath, a palladium bath, and a gold bath for chemical deposition treatment, and the dry film is then removed.

10. A packaging substrate, characterized in that, The encapsulation substrate is prepared using the dry film processing method as described in any one of claims 1-9.

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