Organic weldability protective film and preparation method thereof

Abstract

The invention discloses a preparation method of an organic solderable protective film, which comprises the following steps: carrying out controllable micro-etching treatment on the surface of a metal substrate, so that the arithmetic mean roughness of the surface of the metal substrate is less than or equal to 0.20 mu m, and microscopic bulges on the surface of the metal substrate are of smooth hill-shaped structures; and performing preimpregnation treatment and OSP film forming treatment on the surface of the metal substrate in sequence to form the organic weldability protective film. According to the method disclosed by the invention, the uniformity of the organic weldability protective agent film layer and the reliability of high temperature resistance and chemical corrosion resistance are improved by accurately regulating and controlling the microstructure of the copper surface.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging substrate surface treatment, in particular to an organic solderability preservative film and a preparation method thereof. BACKGROUND

[0002] With the rapid development of high-end electronic products such as artificial intelligence, 5G communication and new energy vehicles, the reliability and integration of packaging substrates are increasingly required. The organic solderability preservative (OSP) process is widely used in consumer electronics and packaging due to its low cost, simple process, and reliable soldering points.

[0003] The standard OSP process flow includes oil removal, micro-etching, pre-impregnation, OSP film formation, water washing, and drying. The micro-etching process is crucial as it forms micro-roughness on the copper surface to increase the specific surface area and enhance the adhesion of the OSP film. However, traditional micro-etching processes often only focus on the total amount of micro-etching and roughness, ignoring the micro-morphology formed after etching, which often leads to the formation of a "peak-valley" structure on the copper surface (as shown in FIG. a), where the OSP film deposited on the protruding peaks is too thin, while it may accumulate at the bottom of the recessed valleys. This uneven film distribution is easily damaged during the subsequent reflow soldering high-temperature process and the strong flux cleaning process, resulting in copper surface exposure, oxidation, and ultimately causing poor soldering or corrosion risk, which severely restricts the reliability of products in high-end ball planting products. Figure 1 a SUMMARY

[0004] The present application aims to solve the technical problems in the prior art by providing an organic solderability preservative film and a preparation method thereof. By precisely controlling the roughness and micro-morphology of the metal substrate, the uniformity, high-temperature resistance, and chemical corrosion resistance of the organic solderability preservative film are improved.

[0005] To achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of an organic solderability preservative film is provided, comprising the following steps: controlling the micro-etching treatment on the surface of the metal substrate, so that the arithmetic average roughness of the surface of the metal substrate is less than or equal to 0.20 μm, and the micro-protrusions on the surface of the metal substrate are smooth hill-like structures; forming an organic solderability preservative film by sequentially performing pre-impregnation treatment and OSP film formation treatment on the surface of the metal substrate.

[0006] In the above-mentioned solution, the arithmetic average roughness is 0.15 μm to 0.19 μm.

[0007] In the above scheme, the controllable micro-etching treatment on the surface of the metal substrate comprises: The surface of the cleaned metal substrate is subjected to a controllable micro-etching treatment, and the micro-etching amount is controlled to be in the range of 0.8 μm to 1.2 μm; preferably, the micro-etching amount is 1.0 μm.

[0008] In the above scheme, the cleaning comprises alkaline degreasing and overflow water washing.

[0009] In the above scheme, the controllable micro-etching treatment is carried out in a micro-etching tank, and the controllable micro-etching treatment comprises controlling the solution concentration, the oxidizing agent concentration and the treatment time during the micro-etching treatment.

[0010] In the above scheme, the controllable micro-etching treatment is carried out at 30°C, and the micro-etching time is 60-78 seconds.

[0011] In the above scheme, the OSP film-forming treatment is carried out at 40°C, and the soaking time is 120-156 seconds.

[0012] In the above scheme, the metal substrate is copper, and the whole plate thickness is 0.1-1.2 mm.

[0013] According to another aspect of the present application, there is provided an organic solderability preservative film obtained by the above method for preparing an organic solderability preservative film.

[0014] Overall, the above technical scheme conceived by the present application can achieve the following beneficial effects compared with the prior art: (1) The present application provides an organic solderability preservative film, which is an ideal metal substrate surface morphology with the dual characteristics of "low roughness-smooth peak shape"; this morphology itself constitutes an ideal substrate for uniform and dense deposition of OSP chemical solution, thereby ensuring the quality of the subsequent film layer from the root; since the OSP film layer has uniform thickness and is combined more firmly with the smooth copper surface, it can still maintain extremely high coverage integrity after experiencing high-temperature reflow soldering (peak temperature up to 235-245°C) and strong chemical solvent cleaning, effectively preventing oxidation problems caused by copper exposure.

[0015] (2) The method for preparing an organic solderability preservative film provided by the present application can be applied to various micro-etching systems and does not depend on specific chemical solution formulations, thereby having good process compatibility and broad industrial application prospects; by monitoring the Ra value and observing the SEM morphology, the quality of the micro-etching process can be quickly and quantitatively evaluated, thereby realizing fine control of the production process. BRIEF DESCRIPTION OF DRAWINGS

[0016] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a better understanding of the preferred embodiments, and are not intended to be limiting of the application. Moreover, in the drawings, like reference numerals denote similar parts throughout the several views. In the drawings: Figure 1 SEM images of the copper surface morphology after optimization in the embodiments of the application Figure 1 b) and before optimization (conventional process, Figure 1 a).

[0017] Figure 2 SEM images of the OSP film surface morphology before (a) and after (b) optimization in the embodiments of the application.

[0018] Figure 3 Temperature curve diagram simulating the reflow soldering process in the embodiments of the application.

[0019] Figure 4 FIB-SEM cross-sectional view in the embodiments of the application. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the present application and should not be used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0021] It should be understood that the size of the serial number of each step in the embodiments does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0022] Embodiment 1 The present application provides a preparation method of an organic solderability preservative film, which comprises: In the embodiments of the present application, a 0.4mm thick FR-4 copper-clad plate is selected as the substrate.

[0023] S1, pretreatment: the 0.4mm thick FR-4 copper-clad plate substrate is sequentially subjected to alkaline oil removal and secondary overflow rinsing.

[0024] S2, copper surface morphology optimization: the substrate is treated in a micro-etching tank at 30°C. The micro-etching amount is precisely controlled at 1.0 μm by controlling the solution concentration, oxidizing agent concentration and treatment time. Specifically, in this embodiment, the sulfuric acid concentration is controlled at 55 g / L, the hydrogen peroxide concentration is controlled at 4.5 g / L, and the micro-etching time is controlled at 60 seconds. After treatment, the copper surface roughness Ra value is measured to be 0.18 μm, and SEM observation confirms that the micro-protrusions are in the form of smooth hills.

[0025] S3, OSP film formation: after micro-etching, the substrate is treated by water washing and pre-soaking, and then is immersed in an OSP film forming tank at 40°C for 120 seconds to form an OSP film.

[0026] S4, post-treatment: after water washing, hot air drying is performed at 80°C to obtain an organic solderability preservative film.

[0027] Example 2 An organic solderability preservative film sample prepared in Example 1 is subjected to reliability testing. S1, reflow soldering test: 3 times of simulated reflow are performed using the reflow temperature curve shown in Figure 3 , with a peak temperature of 245°C.

[0028] S2, flux cleaning: after soldering using a flux, the industry standard solvent cleaning agent is used for cleaning.

[0029] S3, performance detection: cross-section analysis (FIB-SEM) is performed on the tested sample using a focused ion beam-scanning electron microscope. The results are shown in Figure 4 b, the OSP film layer is continuous and complete, the average film thickness is maintained within the design requirement range, and there is no copper surface exposure.

[0030] Comparative Example The same substrate as in Example 1 is treated using a traditional micro-etching process, and the micro-etching amount is also 1.0 μm. After treatment, the copper surface roughness Ra value is 0.24 μm, and SEM shows that there are a large number of sharp copper peaks on the surface, as shown in Figure 1 ( Figure 1 a is the traditional process, Figure 1 b is the process of the present application). It can be seen that the peak shape is smooth and uniformly distributed after optimization of the present application. Subsequently, the same OSP film formation and reliability testing are performed, as shown in Figure 2 ( Figure 1 a is the traditional process, Figure 1 b is the process of the present application). It can be seen that the film layer is more uniform and flat after optimization of the present application. Figure 4 is a FIB-SEM cross-section view, which directly shows the comparison of the uniformity and integrity of the OSP film before and after reflow soldering and cleaning (a) before optimization, the copper peak leaks copper and is not continuous, (b) after optimization, the film thickness is uniform and continuous), and FIB-SEM cross-section analysisFigure 4 a) The OSP film on the top of the sharp protrusion is broken after reflow soldering and cleaning, and the copper surface is exposed.

[0031] In summary, the preparation method of the organic solderability preservative film of the present application creates a copper surface topography with low roughness (Ra ≤ 0.20 μm) and smooth peak characteristics by precisely controlling the micro-etching process; this topography is the key to ensuring uniform deposition of the OSP film and successfully resisting subsequent reflow soldering thermal stress and flux cleaning chemical stress; this method significantly improves the final product reliability of the OSP treated substrate, and is particularly suitable for high-density packaging fields with strict quality requirements.

[0032] It should be noted that, according to the needs of implementation, each step described in the present application can be split into more steps, or two or more steps or part of the operations of the steps can be combined into new steps to achieve the purpose of the present application.

[0033] Those skilled in the art will readily understand that the above description is only of the preferred embodiments of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an organic solderable protective film, characterized in that: Includes the following steps: Controllable micro-etching is performed on the surface of the metal substrate to make the arithmetic mean roughness of the metal substrate surface less than or equal to 0.20 μm, and the micro-protrusions on the surface of the metal substrate are smooth hill-like structures. A pre-dip treatment and an OSP film-forming treatment are performed sequentially on the surface of a metal substrate to form an organic solderable protective film.

2. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The arithmetic mean roughness is 0.15 μm to 0.19 μm.

3. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The controlled micro-etching process on the surface of the metal substrate includes: The cleaned metal substrate surface is subjected to controlled micro-etching treatment, with the micro-etching amount controlled within the range of 0.8μm to 1.2μm.

4. The method for preparing an organic solderable protective film according to claim 3, characterized in that, The micro-etching depth is 1.0 μm.

5. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The cleaning process includes alkaline degreasing and overflow rinsing.

6. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The controlled micro-etching process is carried out in a micro-etching tank, and includes controlling the solution concentration, oxidant concentration and processing time during the micro-etching process.

7. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The controllable micro-etching process is carried out in a temperature range below 30°C, and the micro-etching time is 60-78 seconds.

8. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The OSP film formation treatment was carried out at 40°C for 120-156 seconds.

9. The method for preparing an organic solderable protective film according to claim 1, characterized in that, The metal substrate is made of copper, and the overall thickness of the plate is 0.1-1.2 mm.

10. An organic solderable protective film, obtained by the preparation method of an organic solderable protective film according to any one of claims 1-9.

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