Patent Application
20250146135
The present disclosure relates to a flexible copper clad laminate, and in particular to a flexible copper clad laminate that is resistant to electrochemical corrosion.
The flexible copper clad laminate (FCCL) is generally produced by the wet metallization, which forms a nickel layer on the surface of the polyimide substrate and then electroplates a copper layer on the nickel layer.
By forming the nickel layer between the copper layer and the polyimide substrate, the peel strength between the metal conductive layer, which is formed by the nickel layer and the copper layer, and the polyimide substrate can be increased, thereby improving the structural strength of the flexible copper clad laminate.
However, in the conventional process of manufacturing the flexible printed circuit (FPC) board by using the flexible copper clad laminate and performing subsequent electroless nickel immersion gold (ENIG) treatment, the reduction potential of nickel (−0.25V) is lower than that of copper (+0.34V). As a result, during the ENIG process, when gold ions are reduced, metallic nickel is prone to losing electrons, leading to the oxidation and corrosion of the nickel layer, a phenomenon also known as electrochemical corrosion.
Furthermore, if the nickel layer is oxidized and corroded, it may cause the metal circuits to separate from the polyimide substrate, destroying the structure of the flexible printed circuit board.
Therefore, in the technical field of the present disclosure, there is room for further improvement in the flexible copper clad laminate with electrochemical corrosion resistance.
The inventors of the present disclosure have discovered that the nickel-cooper alloy layer of the present disclosure is not corroded due to electron loss in acidic gold plating solutions and does not affect the etching of the circuit production. In other words, by utilizing an electroless plating method and a specific composition of the nickel-copper alloy layer, it is possible to enhance the corrosion potential of the nickel-copper alloy layer in the sulfuric acid solution and obtain a flexible copper clad laminate with both electrochemical corrosion resistance and sufficient peel strength.
To solve the above problems, a flexible copper clad laminate according to one aspect of the present disclosure includes a polyimide substrate; a nickel-copper alloy layer, formed on at least one side of the polyimide substrate by electroless plating and comprising nickel, copper and phosphorus, wherein a content of the copper is more than 30 wt % of the nickel-copper alloy layer, a content of the phosphorus is less than 5 wt % of the nickel-copper alloy layer, and a corrosion potential of the nickel-copper alloy layer in a 0.02 vol % sulfuric acid solution is greater than −20 mV; and a copper layer formed on a side of the nickel-copper alloy layer away from the polyimide substrate and combined with the nickel-copper alloy layer to form a metal conductive layer.
In an embodiment, the content of the copper is less than 80 wt % of the nickel-copper alloy layer.
In an embodiment, the nickel-copper alloy layer is a single-layer coating.
In an embodiment, the nickel-copper alloy layer further includes at least one selected from the group consisting of iron, cobalt, molybdenum, tungsten, tin, chromium and zinc.
In an embodiment, the copper layer is formed on the nickel-copper alloy layer by electroplating, and a thickness of the copper layer is 0.2˜20 μm.
In an embodiment, a peel strength between the metal conductive layer and the polyimide substrate is greater than or equal to 0.7 kgf/cm.
One aspect of the present disclosure is completed in view of the above-mentioned conventional problems, and its purpose is to provide a flexible copper clad laminate that is resistant to electrochemical corrosion and has sufficient peel strength.
The following is a description of the implementation of the present disclosure through specific examples. Those skilled in the art can understand other advantages and effects of the present disclosure from the content disclosed in this specification. The present disclosure can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified and changed in various ways based on different viewpoints and applications without departing from the spirit of the present disclosure.
Unless otherwise stated in the text, the terms “A˜B” used in the specification and the appended claims include the meaning of “between A and B”. For example, the term “10 to 40 wt %” includes the meaning of “between 10 wt % and 40 wt %.”
First, please refer to
Next, as shown in
The polyimide substrate is a sheet/film-like substrate made of polyimide (PI). Its thickness can be about 5˜150 μm and is not particularly limited. In addition, the polyimide substrate can also be made of transparent polyimide, for example, a polyimide with a transmittance greater than 87%. In addition, the polyimide substrate can be a commercial product, for example, a polyimide film made by Taimide Tech. Inc., model number TX6-025, can be used.
The nickel-copper alloy layer includes nickel, copper and phosphorus. Specifically, by including sodium hypophosphite as a reducing agent in the electroless plating solution, phosphorus will also co-deposits as one of the alloy components during the reduction deposition of nickel ions. In the present disclosure, a content of the phosphorus is less than 5 wt % of the nickel-copper alloy layer and can be controlled by the composition of the electroless plating solution and operation conditions. This is because if the content of the phosphorus is equal to or more than 5 wt % of the nickel-copper alloy layer, there will be obvious metal residues under the H2O2/H2SO4 etching solution, which will cause the line width to become larger during subsequent ENIG of the circuit.
Next, in the nickel-copper alloy layer of the present disclosure, the content of the copper is more than 30 wt % of the nickel-copper alloy layer. This is because the reduction potential of copper is greater than the reduction potential of nickel. Therefore, by including a specific proportion of copper in the nickel-copper alloy layer, the situation that metallic nickel loses electrons and is oxidized and corroded during ENIG can be reduced. Furthermore, if the content of the copper is less than 30 wt % of the nickel-copper alloy layer, the corrosion potential of the nickel-copper alloy layer in a 0.02 vol % sulfuric acid solution may be less than −20 mV, and the electrochemical corrosion resistance cannot be achieved.
Then, the inventors found that if the content of the copper is greater than 80 wt % of the nickel-copper alloy layer, the peel strength between the metal conductive layer and the polyimide substrate will significantly decrease, and the structural strength of the FCCL may be reduced. Therefore, the content of the copper is preferably more than 30 wt % and less than 80 wt % of the nickel-copper alloy layer, and the content of the copper is more preferably 40 wt %˜60 wt % of the nickel-copper alloy layer.
On the other hand, in addition to nickel, copper and phosphorus, any metal that can be co-deposited with nickel may be appropriately added into the nickel-copper alloy layer according to the characteristics to be obtained, and is not particularly limited. Specifically, the nickel-copper alloy layer of the present disclosure may further include at least one selected from the group consisting of iron, cobalt, molybdenum, tungsten, tin, chromium and zinc. In addition, the total thickness of the double-sided metallized nickel-copper alloy layer may be 100˜250 nm, preferably 160˜200 nm. On the other hand, the thickness of the single-sided metallized nickel-copper alloy layer is preferably 80˜100 nm.
Here, the thickness of the nickel-copper alloy layer can be measured using an X-ray film thickness measuring instrument (purchased from General Scientific Technology Corp., model FISCHERSCOPE® XDL210). Specifically, by placing a 10 cm*10 cm coating sample on the measuring table, the total thickness of the nickel-copper alloy layer can be measured.
In addition, the nickel-copper alloy layer of the present disclosure can be a single plating layer, that is, it can achieve the effect of resisting electrochemical corrosion without being combined with other layers, thereby saving production costs.
Next, in the present disclosure, the nickel-copper alloy layer is electroless plated to form a plating layer on at least one side of the polyimide substrate. As for the electroless plating, it can be the conventional electroless plating method (based on the principle of redox reaction, using a strong reducing agent in a solution containing metal ions to reduce the metal ions into metal that deposits on the surface of various materials to form a dense coating) and is not particularly limited. In addition, as for a specific example of electroless plating, first, a roll-shaped polyimide substrate (purchased from Taimide Tech. Inc., model TX6-025) is placed in a corona treatment machine (purchased from Wedge Co., Ltd., Japan) for continuous hydrophilic modification treatment. The operation conditions are power 3 kw and speed 3 m/min.
Next, the hydrophilic treated polyimide substrate is cut into a size of 20 cm*20 cm, and immersed in a 2 wt % KOH solution at 40° C. for 150 seconds. Then, refer to the SLP metallization process (SLP process) of Japan Okuno Chemical Industries Co., Ltd. for catalyst addition, and use SLP series electroless nickel plating reagents (including SLP-200, SLP-300, SLP-400, SLP-500) to carry out charge adjustment, pre-dipping, catalyzation, acceleration steps sequentially. The operation conditions are described below.
1. The hydrophilic treated polyimide substrate is soaked in the SLP-200 solution at 65° C. for 75 seconds to adjust the charge, taken out and washed with water. 2. The polyimide substrate is continuously soaked in SLP-300 solution at 25° C. for 25 seconds and SLP-400 solution for 75 seconds to make the catalyst adhere to the surface of the polyimide substrate, taken out and washed. 3. Next, the polyimide substrate is soaked in SLP-500 solution at 35° C. for 75 seconds to activate the catalyst, taken out and washed to form a polyimide substrate with palladium catalyst on one or both sides. Afterwards, the polyimide substrate with the palladium catalyst is subject to the above-mentioned electroless plating treatment to form the nickel-copper alloy layer; wherein the palladium catalyst is from the above-mentioned SLP series of electroless nickel plating reagents.
The copper layer of the present disclosure is not particularly limited as long as it is a copper layer that can form subsequent etched circuits. Furthermore, in one embodiment of the present disclosure, the copper layer is preferably plated on the nickel-copper alloy layer by electroplating. As for the electroplating solution that can be used for the copper layer, it may be a commercial product, for example, the copper sulfate electroplating solution (available from All-In-Line Chemicals Enterprise Co., Ltd.) and the like may be used. In addition, the thickness of the copper layer is preferably 0.2˜20 μm.
Specifically, the electroplated copper layer may be carried out in the following manner: the polyimide substrate plated with the nickel-copper alloy layer is fixed with a stainless steel frame, and is first immersed in a 3 vol % H2SO4 solution for 1 minute to clean the surface, and then put into an electroplating tank (for example, a 20 L electroplating copper tank, available from Surchem International Corp.) for copper plating. The electroplating area is 15 cm*15 cm. The electroplating solution contains 150 g/L H2SO4, 120 g/L CuSO4 and 50 ppm chloride ions. It may also contain an appropriate amount of brightener and leveler if necessary. In addition, the power supply conditions for electroplating are 6 A/3V for 2 minutes. The electroplated copper layer of about 1 μm thick can be obtained on one side or both sides after washing and drying.
Herein, the thickness of the copper layer may be measured using a copper thickness measuring instrument (available from Shin Shen Instruments Co., Ltd.). Specifically, a 10 cm*10 cm FCCL sample is placed on the measurement table, and the copper layer thickness can be measured by evenly contacting the four-point probe with the FCCL copper surface.
First, please refer to
Here, in an embodiment, the nickel-copper alloy layer 2 may also be formed on the first surface 11 and the second surface 12 simultaneously. Under such circumstance, the copper layers 3 are respectively formed on the sides of the two nickel-copper alloy layers 2 away from the polyimide substrate 1.
Next, regarding the electroless plating method and the electroplating method, conventional electroless plating methods and electroplating methods may be used, and are not particularly limited. Specifically, the aforementioned electroless plating method and electroplating method may be used, which will not be described again herein.
Hereinafter, although various Examples and Comparative Examples are used to demonstrate the present disclosure concretely, the present disclosure is not limited to these Examples and Comparative Examples.
The corrosion potential of the nickel-copper alloy layer may be measured using potentiostat (model: BioLogic/SP-50e) and flat plate corrosion test tank (model: ABT-TA-F029) purchased from Aurora Borealis Technology Co., Ltd.
First, the sample of the polyimide substrate plated with the nickel-copper alloy layer was immersed in a 3 vol % sulfuric acid solution for 30 seconds, washed, and then placed in a flat plate corrosion test tank as a working electrode for electrochemistry test. In the test, the auxiliary electrode was a platinum electrode, the reference electrode was a calomel electrode, and the 0.02 vol % sulfuric acid solution was used as the electrolyte. After connecting the potentiostat and opening the operation software, the Tafel Plot in the corrosion test mode was selected, the scan rate was set to 300 mV/min, and the scan range was from −0.5V to 0.2V, and then the corrosion potential of the nickel-copper alloy layer in the 0.02 vol % sulfuric acid solution could be measured.
The peel strength of the polyimide substrate and the metal conductive layer in the flexible copper clad laminate was measured using the universal tensile testing machine (Model: QC-538M1) purchased from Cometech Testing Machines Co. First, the copper layer thickness of the flexible copper clad laminate was adjusted to 18 μm, the circuit was made according to the specification of IPC-TM-650 2.4.9, and a 90° peel strength test was conducted on the universal tensile testing machine.
In the present disclosure, those with peel strength greater than or equal to 0.9 kgf/cm are marked as o, those with peel strength greater than or equal to 0.7 kgf/cm but less than 0.9 kgf/cm are marked as Δ, and those with peel strength less than 0.7 kgf/cm are marked as x.
A scanning electron microscope (SEM, model: JEOL/JSM-6510) with an X-ray Energy Dispersive Spectroscope (EDS, model: INCAx-act/51-ADD0076) purchased from Jiedong Co., Ltd. was used to analyze the nickel-copper alloy layer plated on the polyimide substrate. The sample was placed directly into the SEM without gold plating. After vacuuming, EDS was used to analyze the elemental composition of the nickel-copper alloy layer within the area of 200 μm*150 μm.
The microscope (model: VK-X3000) from Keyence in Taiwan was used, the etched flexible printed circuit board sample was directly placed on the analysis platform, and a 50× optical lens was used to observe the finest wiring area (line width/line space=25/25 μm), to confirm the shape and whether there is any metal residue at outer edge.
In addition, in the present disclosure, those with no metal residue are marked as o, those with trace metal residues are marked as Δ, and those with obvious metal residues (unclean etching) are marked as x. Among them, the definition of no metal residue means that there are no traces at the edge of the wiring, the definition of trace metal residue is that the width of the trace at the edge of the wiring is less than or equal to 2 μm, and the definition of obvious metal residue is that the width of the trace at the edge of the wiring is greater than 2 μm.
In the present disclosure, the circuit adhesion after ENIG was judged visually, and the observation range was the fine circuit area with line width/line space=25/25 μm. As long as any fine circuit area in the entire flexible printed circuit board had peeling or lifting visible to the naked eye, it was defined as poor circuit adhesion and marked as x. Conversely, if all fine circuit areas had complete circuits and were well bonded with the polyimide substrate, the circuit adhesion was good and marked as o.
First, a polyimide (PI) substrate plated with a nickel-copper alloy layer on both sides having a total thickness of about 200 nm was taken as a sample, and then soaked in a H2O2/H2SO4 etching solution at room temperature for 20 seconds, taken out, washed and dried. Next, a UV-Vis spectrometer (model: JASCO/V-750) from Sunway Scientific Corp. was used to analyze the degree of coating residue on the PI substrate. Using the unplated PI substrate as a baseline, the absorbance value of the etched sample at a wavelength of 500 nm was measured. In addition, the higher the absorbance value, the more the remaining amount of the plating layer, which meant that the nickel-copper alloy layer was less likely to be etched.
If at least one of the characteristics in Table 1 below is x, the overall evaluation is x; if at least one of the characteristics is Δ, the overall evaluation is Δ; and if all characteristics are o or meet the requirements, the overall evaluation is o.
The roll-shaped polyimide substrate (purchased from Taimide Tech. Inc., model TX6-025) was subjected to continuous hydrophilic modification treatment in a corona treatment machine (purchased from Wedge Co., Ltd., Japan). The operation conditions were power 3 kw and speed 3 m/min. Then, the hydrophilic treated polyimide substrate was cut into a size of 20 cm*20 cm and soaked in a 2 wt % KOH solution at 40° C. for 150 seconds.
First, referring to the above, the SLP metallization process (SLP process) of Japan Okuno Chemical Industries Co., Ltd. was used to successively carry out charge adjustment, pre-dipping, catalyzation, acceleration steps on the polyimide substrate after hydrophilic treatment to obtain a polyimide substrate with palladium catalyst on both sides.
Secondly, an electroless plating solution was prepared in a 5-liter beaker (the bath capacity was 5 L). The electroless plating solution contained 98.5 g nickel sulfate, 7.9 g copper sulfate, 106 g sodium hypophosphite, 205 g sodium citrate and 124 g boric acid was adjusted to a pH of 8.5 with 50 wt % NaOH solution. Next, the above-mentioned polyimide substrate with palladium catalyst was immersed in the electroless plating solution and reacted at a temperature of 40° C. The reaction time was controlled to be 2 to 3 minutes to maintain the total thickness of the plating layer between 200±20 μm. The polyimide substrate was taken out, washed and dried to form a polyimide substrate plated with a nickel-copper alloy layer (a ternary alloy including nickel/copper/phosphorus) on both sides.
According to the aforementioned method, an electroplated copper layer with a copper thickness of about 1 μm was formed on the nickel-copper alloy layer plated on both sides of the polyimide substrate to obtain a flexible copper clad laminate.
Next, please refer to
Then, as shown in
The specific steps were as what follows: 1. The FPC was soaked in the ProSelect UC K solution at 40° C. for 5 minutes to clean the surface, taken out and washed with water. 2. Then, the FPC was soaked in the MicroEtch C solution at 30° C. for 60 seconds to remove the oxide layer on the surface of the copper circuit by micro-etching, taken out and washed with water. 3. The FPC was soaked in the 25 vol % sulfuric acid solution at 25° C. for 3 minutes, taken out and washed with water. 4. The FPC was soaked in the Aurotech Activator conc. solution at 25° C. for 1 minute to activate the catalyst, taken out and washed with water. 5. The FPC was soaked in the Aurotech FL Plus Post Dip K solution at 25° C. for 3 minutes to remove the catalyst on the polyimide substrate, taken out and washed with water. 6. Then, the FPC was soaked in the Aurotech SIT Plus solution with a pH of 4.8 at 78° C. for 6 minutes to deposit a nickel-phosphorus alloy layer with a thickness of 2˜4 μm, taken out and washed with water. 7. Finally, the FPC was soaked in the Aurotech SF Plus solution containing potassium gold cyanide (purchased from Super Dragon Technology Engineering Co., Ltd.) as a gold salt with a pH of 5.5 at 82° C. for 4 minutes to deposit a gold layer (indicated by the reference numeral 4 as shown in
Finally, the metal concentration of the electroless plating solution, the composition of the nickel-copper alloy layer and the characteristics of the nickel-copper alloy layer of Example 1 are summarized in Tables 1 and 2. In addition, the measurement method of each characteristic may be referred to the above description and will not be repeated here.
The above-mentioned polyimide substrate with palladium catalyst on both sides was soaked in the SLP-660 plating solution (purchased from Okuno Chemical Industries Co., Ltd.), reacted at 36° C. for 2 minutes and 30 seconds, taken out, washed with water and dried. After drying, a polyimide substrate plated with nickel/phosphorus alloy having a total thickness of about 200 μm on both sides can be formed.
Thereafter, the electroplating of the copper layer, the circuit production and the electroless nickel immersion gold, etc. were performed in the same manner as in Example 1 to obtain the flexible copper clad laminate and flexible printed circuit board of Comparative Example 1.
Next, in the same manner as in Example 1, the metal concentrations of Ni and Cu in the electroless plating solution and the composition of the nickel-copper alloy layer were changed based on Table 1 below (i.e., changing the amount of nickel sulfate and the amount of copper sulfate) to obtain the flexible copper clad laminates and the flexible printed circuit boards of Comparative Examples 2˜6 and Examples 2˜6. In addition, the metal concentration of the electroless plating solution, the composition of the nickel-copper alloy layer and the characteristics of the nickel-copper alloy layer of Comparative Examples 2˜6 and Examples 2˜6 are summarized in Tables 1 and 2.
solution
alloy layer
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etching
etching
etching
etching
indicates data missing or illegible when filed
First of all, it can be known from Table 1 that because Examples 1 to 6 all use electroless plating to form the nickel-copper alloy layer, and the content of copper in the nickel-copper alloy layer is more than 30 wt % and the content of phosphorus in the nickel-copper alloy layer is less than 5 wt %, so it can make the corrosion potential of the nickel-copper alloy layer in the 0.02 vol % sulfuric acid solution greater than −20 mV, resulting in the effect of electrochemical corrosion resistance.
Next, because the content of the copper in the nickel-copper alloy layers of Comparative Examples 1 to 5 is less than 30 wt %, the corrosion potential of the nickel-copper alloy layers produced by these Comparative Examples is less than −20 mV, which does not meet the requirements. In addition, because the phosphorus content in the nickel-copper alloy layers of Comparative Examples 2 to 5 is more than 5 wt %, metal remains during etching, resulting in unclean etching.
Specifically, please refer to
Furthermore, because all the contents of the copper in the nickel-copper alloy layers of Comparative Examples 1 to 3 are very low, and the nickel-copper alloy layers of Comparative Examples 1 to 2 do not even contain copper, the corrosion potential of these Comparative Examples is very low (less than −70 mV), such that there is circuit peeling after ENIG, the circuit adhesion is poor, and it does not meet the requirements.
Specifically, please refer to
Next, in Example 1, since a trace amount of metal remains, the etching properties and the overall evaluation are marked as A. Furthermore, in Example 6, although the corrosion potential of −11.6 mV is achieved, the peel strength and overall evaluation are marked as because the peel strength is 0.868 kgf/cm, which is slightly smaller than the specification value of 0.9 kgf/cm.
In addition, in Comparative Example 6, although the etching property, corrosion potential and circuit adhesion are all marked as o or meet the requirements, because the content of the copper in the nickel-copper alloy layer is more than 80 wt %, the peeling strength is significantly reduced to only 0.654 kgf/cm, so the peel strength and overall evaluation are marked as x.
Next, from Table 2 and
First, as shown in Table 2 and
By utilizing the electroless plating method and the specific composition of the nickel-copper alloy layer, the present disclosure can increase the corrosion potential of the nickel-copper alloy layer in the sulfuric acid solution and can obtain the flexible copper clad laminate that is resistant to electrochemical corrosion and has sufficient peel strength.
The present invention is not limited to the implementation aspects described above, various changes can be made within the scope indicated in the claims, and embodiments obtained by appropriately combining the technical means disclosed in different implementation aspects are also included in the technical scope of the present invention.
While the present disclosure has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the present disclosure set forth in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 112142862 | Nov 2023 | TW | national |
This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No(s). 112142862 filed in Taiwan, R.O.C. on Nov. 7, 2023, the entire contents of which are hereby incorporated by reference.
