TW202421853A - Micro-corrosive liquid and application thereof in presenting boundary line of interface of cu-ni elemental metal plating layer - Google Patents

Abstract

The present invention discloses a micro-corrosive liquid and its application in presenting boundary line of interface of Cu-Ni elemental metal plating layer. The micro-corrosive liquid comprises hydrogen peroxide solution with mass volume percentage of 2.5%-15%. The use of hydrogen peroxide solution with low concentration enables the boundary line at the interface of Cu-Ni elemental metal plating layer to be presented clearly, which facilitates accurate measurement of the thickness of the elemental metal plating layer and reduces the SEM image measurement error. The micro-corrosive liquid of the present invention is composed of simple composition, can be substituted by medical hydrogen peroxide, is cheap, safe for corrosion operation, less harmful, owns long shelf life and can be applied broadly.

Description

A micro-corrosive liquid and its application in revealing the boundary line of Cu-Ni interface in single metal coating

The embodiments of the present invention relate to the field of metal surface treatment technology, for example, a micro-corrosive liquid and its application in revealing the boundary line of the Cu-Ni interface of a single metal coating.

The Cu substrate surface on the printed circuit board (PCB) is often treated with immersion gold to prevent oxidation of the Cu substrate. However, gold wires are usually generated during the immersion gold process, causing circuit short circuits. Therefore, the Cu substrate surface is treated with nickel before immersion gold to isolate the diffusion between Au and Cu. At the same time, the soldering layer also requires a nickel layer with sufficient thickness.

For the Cu substrate on the PCB, after being treated with nickel, a cross-section (X-section) is made, and the nickel thickness is measured by SEM to confirm the coating quality. Since the backscattered electron (BSE) imaging of SEM is based on the signal receiver receiving the physical signal intensity of the sample carried by the BSE electrons to change the grayscale level of the image, the part with a larger atomic number has a higher BSE yield, and it appears as a bright area in the image. Since Ni (atomic number 28) and Cu (atomic number 29) have similar atomic numbers, the grayscale levels of the images are similar during SEM imaging. Therefore, when the copper layer surface is nickel-plated, the boundary between the Ni layer and the Cu layer cannot be effectively distinguished during SEM imaging, resulting in the inability to measure the thickness of the Ni layer.

Common metal etching solutions currently include _H2O2 -ammonia-water etching solutions _or sulfuric acid-containing layering agents. However _, the mixed solution _H2O2 -ammonia-water etching solutions used for metal corrosion have low hydrogen peroxide content and are complex to prepare. The volatility of ammonia means that the effective time of the etching solution can only be maintained for 2 hours, otherwise it will affect the corrosion effect. In addition, etching solutions are mostly used for electroplated copper-chemical copper boundary corrosion. For sulfuric acid-containing layering agents used for surface corrosion of intermetallic compounds formed by welding, the rate of oxidation of Ni and Cu by dilute sulfuric acid is relatively slow, and the corrosion effect is poor in a short period of time, so the layering agent has poor timeliness when used for Cu-Ni boundary corrosion. After the Cu-Ni cross section was corroded by the layering agent for 5 minutes, the boundary between the Ni layer and the Cu layer was still unclear, and the copper layer only showed slight corrosion marks, and the corrosion was uneven.

As mentioned above, the previous technologies cannot achieve clear stratification of the Cu-Ni interface of the single metal coating, so when the thickness of the metal coating on the printed circuit board needs to be confirmed, it is impossible to perform accurate measurement. Therefore, in the technical field to which the present invention belongs, it is hoped to develop a micro-corrosive liquid that can achieve clear stratification of the Cu-Ni interface of the single metal coating.

The following is a summary of the topics that are described in detail in this specification. This summary is not intended to limit the scope of the claims.

The embodiment of the present invention provides a micro-corrosive liquid and its application in showing the boundary line of the Cu-Ni interface of the single metal coating, and in particular provides a micro-corrosive liquid for clearly showing the boundary line of the Cu-Ni interface of the single metal coating and its application.

On the one hand, an embodiment of the present invention provides a micro-corrosive solution for revealing the boundary line of the Cu-Ni interface of a single metal coating, wherein the micro-corrosive solution comprises a hydrogen peroxide aqueous solution having a mass volume percentage concentration of 2.5% to 15%.

In the present invention, a dilute hydrogen peroxide solution is used to make the boundary line of the Cu-Ni interface of the single metal coating clearly appear, so that the thickness of the metal coating can be accurately measured. Only by accurately confirming the thickness of each coating layer, especially the thickness of the Ni layer, can it be guaranteed that the Ni thickness in the printed circuit board is sufficient to prevent the diffusion between Au and Cu, and at the same time meet the welding requirements of the printed circuit board welding layer.

The micro-corrosive liquid of the present invention has simple ingredients and can be replaced by medical hydrogen peroxide. It is cheap, the corrosion operation is safe, and the harm is small. Although hydrogen peroxide will slowly decompose under room temperature, the corrosion liquid can be valid for half a year with reference to the validity period of medical hydrogen peroxide. The boundary between the Cu-Ni metal layers after corrosion is clearer, which reduces the measurement error of SEM images.

In the present invention, the hydrogen peroxide solution is an aqueous solution of hydrogen peroxide. In the present invention, the concentration of the hydrogen peroxide solution used can be 2.5% to 15%, such as 3%, 5%, 10%, 12% or 15%, and ideally 3 to 15%. In the present invention, if the concentration of the hydrogen peroxide solution is lower than 2.5%, the corrosion effect is not obvious due to the low concentration of hydrogen peroxide, and the Ni-Cu layer does not show a boundary line. If the concentration of the hydrogen peroxide solution is higher than 15%, the concentration of the hydrogen peroxide solution is too high, resulting in honeycomb pits on the copper surface, deterioration of the surface morphology, and loose copper oxide residues on the slice surface. At the same time, special attention should be paid to the safety of the high-concentration hydrogen peroxide solution during use.

In the present invention, the micro-etching time of the hydrogen peroxide solution is 5 seconds to 15 minutes, such as 30 seconds, 1 minute, 3 minutes, 5 minutes, 10 minutes or 15 minutes. After 5 seconds of etching, the Cu-Ni layer can be clearly distinguished. In order to obtain the best surface morphology, the etching time can be extended to 5 minutes, but it is recommended not to exceed 30 minutes, because if the etching time is too long, obvious honeycomb pits will appear on the copper surface. Therefore, the ideal etching time is 30 seconds to 15 minutes, and more preferably 30 seconds to 5 minutes.

In summary, in the present invention, the Ni-Cu surface morphology is best after etching with a hydrogen peroxide etching solution with a content of 2.5% to 15% for 30 seconds to 15 minutes. When the concentration of hydrogen peroxide corrosive solution is less than 1% and the corrosion time is less than 5 seconds, there is no obvious corrosion and the Cu-Ni layer cannot show the boundary line; when the concentration of hydrogen peroxide corrosive solution is less than 2% and the corrosion time is 5 to 30 seconds, the Cu-Ni layer will be slightly corroded and the boundary line will not be obvious; when the concentration of hydrogen peroxide corrosive solution is higher than 15% and the corrosion time is higher than 15 minutes, honeycomb pits will appear on the copper surface, loose copper oxide will remain, and the surface morphology will deteriorate. In addition, high-concentration hydrogen peroxide has strong oxidizing properties, so safety should be paid attention to when using it. At the same time, the extension of corrosion time will also reduce work efficiency.

On the other hand, an embodiment of the present invention provides a method for revealing the boundary line of the Cu-Ni interface of a single metal coating, wherein the method uses the micro-corrosive solution as described above.

Ideally, the method comprises the following steps: (1) slicing the Cu-Ni coated sample, grinding and polishing the sliced sample cross section; (2) adding a hydrogen peroxide aqueous solution with a mass percentage concentration of 2.5% to 15% to the sliced cross section after the treatment in step (1) to perform micro-corrosion, and observing the boundary line of the Cu-Ni interface of the single metal coating under a scanning electron microscope.

In the present invention, the polishing in step (1) can be polishing with sandpaper.

Ideally, the polishing in step (1) is performed using 180 grit, 800 grit, 2000 grit and 2400 grit sandpaper in sequence.

In the present invention, the polishing in step (1) is a polishing method commonly used in the technical field to which the present invention belongs, for example, polishing can be performed using an aluminum oxide polishing liquid, the purpose of which is to ensure that there are no obvious scratches on the surface of the slice cross section.

In the present invention, a hydrogen peroxide solution is evenly applied on the cross section of the slice.

Ideally, for the slice section treated in step (1), the amount of the hydrogen peroxide solution used in step (2) is 1.0 to 1.5 mL/cm ² , for example 1.0 mL/cm ² , 1.1 mL/cm ² , 1.2 mL/cm ² , 1.3 mL/cm ² , 1.4 mL/cm ² or 1.5 mL/cm ² , calculated based on the area of the section.

Ideally, the microcorrosion time of step (2) is from 1 second to 120 minutes, for example, from 1 second, 3 seconds, 5 seconds, 20 seconds, 30 seconds, 50 seconds, 1 minute, 3 minutes, 5 minutes, 10 minutes, 30 minutes, 50 minutes, 60 minutes, 80 minutes, 100 minutes or 120 minutes, ideally from 30 seconds to 5 minutes, and more preferably from 30 seconds to 5 minutes.

In the present invention, after the hydrogen peroxide solution is used to micro-etch the slice section after the treatment in step (1), the residual etching solution on the slice surface is wiped off with a clean dust-free cloth.

In the present invention, by using the low-concentration hydrogen peroxide solution to perform micro-etching on the slice cross section for a short time (5 to 30 seconds), Ni and Cu can form different appearances and show a clear boundary line, and the Ni layer and the Cu layer can be clearly distinguished under a SEM electron microscope.

In the present invention, since the activity of metal Ni is greater than that of Cu, after the metal coating cross section is sliced, Ni will be rapidly oxidized by _O2 in the air and form a thin and dense oxide layer on its surface, while the oxidation of Cu by _O2 in the air is relatively slow. When the present invention uses low-concentration hydrogen peroxide to oxidize Ni and Cu, a thin and dense oxide film has been formed on the Ni surface of the sliced cross section, which will prevent hydrogen peroxide from further oxidizing Ni. As for the Cu layer, hydrogen peroxide will oxidize the Cu layer to form a relatively thick, relatively loose and porous oxide layer (CuO), and it is impossible to form a passivation layer to further prevent the oxidation of Cu on the surface. Therefore, due to the different surface morphologies, a clear boundary appears at the junction of the two metal elements between Ni and Cu.

The method of the present invention utilizes low-concentration hydrogen peroxide to perform micro-corrosion, has low environmental requirements, is safe and reliable, can be performed at normal temperature and pressure, and has a short corrosion time.

On the other hand, the embodiments of the present invention provide the application of the micro-corrosive solution or the method for revealing the boundary line of the Cu-Ni interface of the single metal coating as described above in the quality control of printed circuit boards.

Compared with the related technologies, the embodiments of the present invention have the following effects: In the embodiments of the present invention, the use of a dilute hydrogen peroxide solution can make the boundary line of the Cu-Ni interface of the single metal coating clearly present, so that the thickness of the metal coating can be accurately measured, reducing the measurement error of the SEM image. The micro-corrosion liquid of the present invention has a simple composition and can be replaced by medical hydrogen peroxide. It is cheap, the corrosion operation is safe, the harm is small, the storage time is long, and it has broad application prospects.

Other aspects will become apparent after reading and understanding the diagram and detailed description.

The technical means of the present invention are further explained below through specific implementation methods. Those with ordinary knowledge in the technical field to which the present invention belongs should understand that the above-mentioned embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. [Implementation Example 1]

This embodiment provides a micro-corrosive liquid for clearly showing the boundary line of the Cu-Ni interface of the single metal coating. The micro-corrosive liquid is a 3% hydrogen peroxide aqueous solution.

The method for revealing the boundary line of the Cu-Ni interface of a single metal coating using the micro-corrosive liquid specifically comprises the following steps: (1) slicing a Cu-Ni coating sample, polishing the sample cross section with 180 mesh, 800 mesh, 2000 mesh and 2400 mesh sandpaper in sequence, and then polishing with an alumina polishing liquid (TROJAN AO-W alumina polishing liquid, alumina particle size 0.05 um); (2) adding a 3% hydrogen peroxide solution to the cross section of the slice treated in step (1), evenly spreading it, and calculating the amount of the hydrogen peroxide solution added is 1.0 mL/ ^cm2 based on the area of the cross section. , micro-corrosion was performed for 30 seconds, and the boundary line of the Cu-Ni interface of the single metal coating was observed under a scanning electron microscope, as shown in Figure 1. Figure 2 is a scanning electron microscope image of the cross section of the sample that has not been micro-corroded (i.e., the cross section of the slice after step (1) treatment). It can be seen from Figure 1 that the boundary line of the Cu-Ni interface is clearly presented, while it can be seen from Figure 2 that the boundary line of the Cu-Ni interface of the cross section of the sample that has not been micro-corroded is not obvious. [Comparison Example 1]

The only difference from Example 1 is that the micro-corrosive liquid used is a 0.5% hydrogen peroxide solution. [Comparative Example 2]

The only difference from Example 1 is that the micro-corrosive liquid used is a 1.0% hydrogen peroxide solution. [Comparative Example 3]

The only difference from Example 1 is that the micro-corrosive liquid used is a 2.0% hydrogen peroxide solution. [Example 2]

The only difference from Example 1 is that the micro-corrosive liquid used is a 5.0% hydrogen peroxide solution. [Example 3]

The only difference from Example 1 is that the micro-corrosive liquid used is a 10% hydrogen peroxide solution. [Example 4]

The only difference from Example 1 is that the micro-corrosive liquid used is a 15% hydrogen peroxide solution. [Comparative Example 4]

The only difference from Example 1 is that the micro-corrosive liquid used is a 20% hydrogen peroxide solution. [Comparative Example 5]

The only difference from Example 1 is that the micro-corrosive liquid used is a 25% hydrogen peroxide solution. [Comparative Example 6]

The only difference from Example 1 is that the micro-corrosive liquid used is a 30% hydrogen peroxide solution.

In order to explore the effect of different hydrogen peroxide concentrations on Cu-Ni corrosion, the morphology of Au-Ni-Cu after being exposed to hydrogen peroxide of different concentrations for the same corrosion time (30 seconds) was compared. When the concentration of hydrogen peroxide is lower than 1%, no obvious boundary appears at the Cu-Ni interface (Comparative Example 1, the SEM image of the cross section of the sample after micro-corrosion is shown in Figure 3), and 1% to 2% only slightly corrodes the copper region at the Cu-Ni interface (Comparative Examples 2 and 3, the SEM images of the cross section of the sample after micro-corrosion are shown in Figures 4 and 5). When the concentration of hydrogen peroxide is 3% to 15% (Examples 1 to 4, the SEM images of the cross section of the sample after micro-corrosion are shown in Figures 1, 6 to 8), the Cu-Ni interface has a clear boundary. The Cu-Ni interface gradually becomes obvious. As the corrosion concentration increases, the Cu-Ni boundary line becomes more obvious. The copper surface is evenly corroded, and the copper layer surface tends to be flat. When the hydrogen peroxide concentration is greater than 15% (Comparison Examples 4 to 6, the electron microscope images of the cross-section of the sample after micro-corrosion are shown in Figures 9 to 11), although the Cu-Ni interface has an obvious boundary line, due to the excessive concentration of hydrogen peroxide, honeycomb-shaped pits appear on the surface of the copper layer. The higher the concentration, the more obvious the honeycomb phenomenon. At the same time, a large amount of debris remains on the surface of the copper layer, and the morphology quality of the copper layer becomes worse and worse. [Comparison Example 7]

The only difference from Example 1 is that the corrosion time is 1 second. [Comparative Example 8]

The only difference from Example 1 is that the corrosion time is 5 seconds. [Example 5]

The only difference from Example 1 is that the corrosion time is 1 minute. [Example 6]

The only difference from Example 1 is that the corrosion time is 5 minutes. [Example 7]

The only difference from Example 1 is that the corrosion time is 15 minutes. [Comparative Example 9]

The only difference from Example 1 is that the corrosion time is 30 minutes. [Comparative Example 10]

The only difference from Example 1 is that the corrosion time is 60 minutes. [Comparative Example 11]

The only difference from Example 1 is that the corrosion time is 120 minutes.

In order to find the optimal corrosion time of hydrogen peroxide, the morphology of Cu-Ni after etching for different times with hydrogen peroxide corrosion solution at the same concentration (3%) was compared. After hydrogen peroxide etching for 1 second, no obvious boundary appeared at the Cu-Ni interface, and only slight corrosion occurred in the copper region at the Cu-Ni interface (Comparative Example 7, the electron microscope image of the cross section of the sample after micro-corrosion is shown in Figure 12); after hydrogen peroxide etching for 5 to 30 seconds, the boundary of the Cu-Ni interface gradually became obvious, but the copper surface was not uniformly corroded, and a small amount of uncorroded area remained on the copper surface (Comparative Example 8 and Example 1, the electron microscope images of the cross section of the sample after micro-corrosion are shown in Figure 13 and Figure 1). As the etching time increases, the uncorroded area gradually decreases; after hydrogen peroxide etching for 1 to 15 minutes (Examples 5 to 7 , the electron microscope images of the sample cross section after micro-corrosion are shown in Figures 14 to 16), the Cu-Ni interface has a clear boundary line, and the copper surface is evenly corroded, and the copper layer surface tends to be flat; hydrogen peroxide etching for 30 to 120 minutes (Comparison Examples 9 to 11, the electron microscope images of the sample cross section after micro-corrosion are shown in Figures 17 to 19), although the Cu-Ni interface has a clear boundary line, due to the long-term corrosion of hydrogen peroxide, honeycomb-like pits appear on the surface of the copper layer, and the longer the corrosion time, the more obvious the honeycomb phenomenon is. At the same time, a large amount of velvety debris appears on the copper surface, and the quality of the copper surface morphology is getting worse and worse. [Comparison Example 12]

The difference from Example 1 is that a layering agent is used instead of the hydrogen peroxide solution used in Example 1. The layering agent is a mixed solution of alcohol and sulfuric acid (25 mL of alcohol stock solution + 1 mL of 10% (weight%) sulfuric acid). The slice section treated in step (1) is corroded for 2 minutes with the layering agent. The scanning electron microscope of the Cu-Ni interface is shown in Figure 20. As can be seen from Figure 20, no obvious boundary appears at the Cu-Ni interface. [Comparative Example 13]

The difference from Example 1 is that _H2O2 -ammonia-water etching liquid is used instead of the hydrogen peroxide solution used in Example 1. _{The H2O2} - _ammonia -water etching liquid is composed of 32% ammonia water and pure water mixed in a ratio of 1:1 (V:V) to form 50 mL ammonia solution, followed by the addition of 1.0 mL 36% hydrogen peroxide solution. The slice section treated in step (1) is etched with the etching liquid for 2 minutes. The scanning electron microscope image of the Cu-Ni interface is shown in FIG21. As can be seen from FIG21, due to the _low content of _H2O2 , no obvious boundary appears at the Cu-Ni interface. In addition, the etching liquid has a complex configuration and a short effective period.

The inventor declares that the present invention uses the above-mentioned embodiments to illustrate the micro-corrosive liquid of the present invention and its application in revealing the boundary line of the Cu-Ni interface of the single metal coating, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those with ordinary knowledge in the relevant technical field should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

without

The drawings are used to provide a further understanding of the technical means of this article and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical means of this article and do not constitute a limitation of the technical means of this article.

[Figure 1] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 1. [Figure 2] is a scanning electron microscope image of the cross section of the slice after step (1) in Example 1 without microcorrosion. [Figure 3] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 1. [Figure 4] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 2. [Figure 5] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 3. [Figure 6] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 2. [Figure 7] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 3. [Figure 8] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 4. [Figure 9] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 4. [Figure 10] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 5. [Figure 11] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 6. [Figure 12] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 7. [Figure 13] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 8. [Figure 14] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 5. [Figure 15] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 6. [Figure 16] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Example 7. [Figure 17] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 9. [Figure 18] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 10. [Figure 19] is a scanning electron microscope image of the cross section of the sample after microcorrosion in Comparative Example 11. [Figure 20] is a scanning electron microscope image of the cross section of the sample after corrosion using a layering agent in Comparative Example 12. [Fig. 21] is a scanning electron microscope image of the cross section of the sample after being etched using _H2O2 - _ammonia -water etching solution in Comparative Example 13.

Claims (12)

A micro-corrosive liquid for revealing the boundary line of the Cu-Ni interface of a single metal coating is characterized in that the micro-corrosive liquid comprises a hydrogen peroxide aqueous solution with a mass volume percentage concentration of 2.5% to 15%. A micro-corrosive liquid for revealing the boundary line of the Cu-Ni interface of a single metal coating as described in claim 1, wherein the mass volume percentage concentration of the hydrogen peroxide aqueous solution is 3% to 15%. A method for revealing the boundary line of the Cu-Ni interface of a single metal coating, characterized in that the method uses a micro-corrosive liquid for revealing the boundary line of the Cu-Ni interface of a single metal coating as described in claim 1 or 2. The method as described in claim 3, wherein it comprises the following steps: (1) slicing the Cu-Ni coated sample, and grinding and polishing the cross section of the sliced sample; (2) adding the micro-corrosion liquid to the cross section of the slice treated in step (1) to perform micro-corrosion, wherein the micro-corrosion comprises a hydrogen peroxide aqueous solution with a mass volume percentage concentration of 2.5% to 15%, and then observing the boundary line of the Cu-Ni interface of the single metal coating under a scanning electron microscope. The method as described in claim 4, wherein the polishing in step (1) is performed using sandpaper. The method as described in claim 5, wherein the polishing in step (1) is performed using 180 grit, 800 grit, 2000 grit and 2400 grit sandpaper in sequence. The method as described in claim 4, wherein the polishing in step (1) is performed using an aluminum oxide polishing solution. The method as claimed in claim 4, wherein, for the slice section treated in step (1), the amount of the hydrogen peroxide solution used in step (2) is 1.0 to 1.5 mL/cm ² , calculated based on the area of the section. The method as described in claim 4, wherein the micro-corrosion time in step (2) is 1 second to 120 minutes. The method as described in claim 9, wherein the micro-corrosion time in step (2) is 30 seconds to 15 minutes. The method as described in claim 10, wherein the micro-corrosion time in step (2) is 30 seconds to 5 minutes. A micro-corrosive liquid for revealing the boundary line of the Cu-Ni interface of a single metal coating as described in claim 1 or 2, or a method for revealing the boundary line of the Cu-Ni interface of a single metal coating as described in any one of claims 3 to 11, used in the quality control of printed circuit boards.