CN103484840B - For the preparation of the activator of embed type sheet resistance, the preparation method of embed type sheet resistance and embed type sheet resistance - Google Patents

Abstract

The invention relates to an activator for preparing embedded film resistors, a preparation method of embedded film resistors and embedded film resistors. The activator for preparing embedded thin film resistors includes water, zinc sulfate, DL-sodium malate and zinc powder, wherein the concentration of zinc sulfate is 20-200g/L, the concentration of DL-sodium malate The concentration is 10-50g/L, and the concentration of the zinc powder is 5-30g/L. The activator is chlorine and palladium free. It has been proved by experiments that after activating the substrate with this activator, the nickel-phosphorus thin film can be electroless plated on the substrate at a lower temperature, the energy consumption is low, and chlorine is not introduced into the electroless plating solution, which ensures that the plating solution stability. Activation with the above-mentioned activator is beneficial to reduce the preparation cost of the embedded thin film resistor, and because the stability of the plating solution is ensured, it is beneficial to ensure the quality of the nickel phosphorus film, thereby ensuring that the embedded thin film resistor has better performance. .

Description

Activator for preparing embedded thin film resistors, method for preparing embedded thin film resistors, and embedded thin film resistors

technical field

The invention relates to the technical field of electronic materials and components, in particular to an activator for preparing embedded thin-film resistors, a preparation method for embedded thin-film resistors, and embedded thin-film resistors.

Background technique

With the development of high integration and high density of integrated circuits, as well as the high frequency and high speed of digital signal transmission, the printed circuit board (PCB) is required to develop in the direction of miniaturization and portability. Embedded resistor technology can save a large amount of PCB mounting surface area, which can increase the freedom of wiring and integration density of PCB. Therefore, embedded resistor technology will become the mainstream packaging technology in the future, and embedded thin-film resistors have become a current research hotspot.

At present, alloys such as nickel-chromium (Ni-Cr) or nickel-phosphorus (Ni-P) are mainly used as embedded resistance materials, and embedded thin film resistors are prepared by magnetron sputtering or electroless plating. Compared with the magnetron sputtering method, the cost of electroless plating is lower and is conducive to large-scale production, but the current method of electroless plating to prepare embedded thin film resistors requires the use of noble metal activators such as palladium (Pd) and high temperature. chemical plating. For example, using Pd containing chloride ions as an activator, the electroless coating is performed at a temperature of 90±2°C. This not only increases the production cost, but also may bring chloride ions into the plating solution, resulting in instability of the plating solution. In addition, at higher temperatures, the generated steam will pollute the surrounding environment.

Contents of the invention

Based on this, it is necessary to provide an activator for preparing embedded thin film resistors that does not contain chlorine and palladium.

Further, a method for preparing an embedded thin film resistor and an embedded thin film resistor prepared by the method are provided.

An activator for preparing embedded thin film resistors, comprising water, zinc sulfate, DL-sodium malate and zinc powder, wherein the concentration of the zinc sulfate is 20-200g/L, the DL-malic acid The concentration of sodium is 10-50g/L, and the concentration of the zinc powder is 5-30g/L.

A method for preparing an embedded thin film resistor, comprising the steps of:

provide the substrate;

activating the substrate with the above-mentioned activator for preparing embedded thin film resistors to obtain an activated substrate;

Preparing a nickel-phosphorus film on the surface of the activated substrate by electroless plating to obtain a substrate laminated with a nickel-phosphorus film;

Pressing the PCB substrate and the substrate laminated with the nickel-phosphorus film, and laminating the nickel-phosphorus film on the PCB substrate; and

The substrate and the nickel-phosphorus thin film are etched to obtain an embedded thin-film resistor.

In one embodiment, the step of activating the substrate with the above-mentioned activator for preparing the embedded thin film resistor includes the step of pasting a photosensitive film on the substrate and then exposing.

In one of the embodiments, after attaching a photosensitive film on the substrate, and then exposing, the step of activating the substrate with the above-mentioned activator for preparing embedded thin film resistors also includes activating the substrate. Steps for washing the substrate.

In one of the embodiments, the washing step is to wash with a detergent first, and then pickle with a sulfuric acid solution with a mass concentration of 5%.

In one embodiment, the substrate is copper foil, and the copper foil has a relatively smooth surface and a rough surface, and the nickel-phosphorus thin film is laminated on the rough surface of the copper foil.

In one embodiment, the step of activating the substrate with the above-mentioned activator for preparing embedded thin-film resistors is as follows: keeping the above-mentioned activator for preparing embedded-type thin-film resistors at a temperature of 20° C. 60° C., and then soak the substrate in the activator at a temperature of 20° C. to 60° C. for 1 minute to 10 minutes.

In one of the embodiments, the step of preparing a nickel-phosphorus film on the surface of the activated substrate by electroless plating to obtain a substrate laminated with a nickel-phosphorus film is as follows: the activated substrate is Put the bottom into the electroless plating solution at a temperature of 20°C to 90°C for 0.5 minutes to 5 minutes.

In one of the embodiments, the electroless plating solution per liter contains 5-80 grams of nickel sulfate, 5-80 grams of sodium hypophosphite, 10-80 grams of buffer, 1-5 mg of stabilizer and 10 mg of complexing agent. ~80 grams.

In one of the embodiments, the step of laminating the PCB substrate and the substrate laminated with the nickel-phosphorus film, and laminating the nickel-phosphorus film on the PCB substrate is as follows: A substrate with a nickel-phosphorus film is placed on the PCB substrate, and the nickel-phosphorus film is laminated on the PCB substrate, and then the prepreg is clamped between the nickel-phosphorus film and the PCB substrate, vacuumized, After the heat treatment, the substrate laminated with the nickel-phosphorus thin film is pasted on the PCB substrate.

In one embodiment, the heat treatment step is to keep warm at 100°C-140°C for 1 hour, and then keep warm at 140°C-180°C for 1 hour.

In one of the embodiments, the step of etching the substrate and the nickel phosphorus film comprises:

Etching the substrate and the nickel-phosphorus film by using a first etchant; and

Etching the substrate with a second etchant.

In one embodiment, the first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate, and the second etching solution is a mixed aqueous solution of copper chloride, ammonium chloride and ammonia water.

An embedded thin film resistor prepared by the above preparation method.

The above-mentioned activator used to prepare embedded thin film resistors does not contain chlorine and expensive noble metal palladium. It has been proved by experiments that after the substrate is activated by using this activator, it can be electroless plated on the substrate at a relatively low temperature. Nickel-phosphorus thin film, low energy consumption, and does not introduce chlorine into the chemical plating solution, which ensures the stability of the plating solution. Activation with the above-mentioned activator is beneficial to reduce the preparation cost of the embedded thin film resistor, and because the stability of the plating solution is ensured, it is beneficial to ensure the quality of the nickel phosphorus film, thereby ensuring that the embedded thin film resistor has better performance. .

Description of drawings

Fig. 1 is the flowchart of the preparation method of the embedded thin film resistance of one embodiment;

Fig. 2 is a schematic diagram of the preparation method of the embedded thin film resistor shown in Fig. 1;

Fig. 3 is the EDS figure of the nickel-phosphorus thin film of embodiment 1;

Fig. 4 is the SEM figure of the nickel-phosphorus thin film of embodiment 1;

Fig. 5 is the SEM picture of another magnification of the nickel-phosphorus thin film of embodiment 1;

Fig. 6 is the temperature coefficient of resistance (TCR) curve of the buried thin film resistor of embodiment 1 and embodiment 2;

FIG. 7 is an SEM image of the nickel-phosphorus thin film of Example 3. FIG.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, specific implementations of the present invention will be described in detail below in conjunction with the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described here, and those skilled in the art can make similar improvements without departing from the connotation of the present invention, so the present invention is not limited by the specific implementations disclosed below.

An activator for preparing embedded thin film resistors according to one embodiment includes water, zinc sulfate (ZnSO ₄ ), DL-sodium malate and zinc powder.

Wherein, zinc sulfate and DL-sodium malate are dissolved in water, and zinc powder is dispersed in water. The concentration of zinc sulfate is 20-200g/L, the concentration of DL-sodium malate is 10-50g/L, and the concentration of zinc powder is 5-30g/L.

Compared with the expensive precious metal palladium, the prices of zinc sulfate, DL-sodium malate and zinc powder are lower, which makes the price of the activator used to prepare embedded thin film resistors lower, which is conducive to reducing the cost of embedded thin film resistors. The fabrication cost of the resistor.

Moreover, the above-mentioned activator used to prepare the embedded thin film resistor does not contain chlorine, and after using the activator to activate the substrate, no chlorine ions will be introduced into the chemical plating solution during chemical plating, which can ensure the stability of the chemical plating solution. stability.

Experiments show that after the substrate is activated by using the activator, the nickel-phosphorus thin film can be electrolessly plated on the substrate at a relatively low temperature, and the energy consumption is low. Moreover, due to the lower temperature of the chemical coating, less steam is generated and less environmental pollution.

Please refer to FIG. 1 , a method for preparing an embedded thin film resistor in an embodiment includes the following steps:

Step S110: providing a substrate.

Please also refer to FIG. 2 , the substrate 10 can be copper foil, aluminum foil or aluminum-magnesium alloy, etc., preferably copper foil. Copper foil has relatively smooth and rough sides. If the surface of other substrates is relatively smooth, one of the surfaces of the substrate needs to be roughened to improve the adhesion of the subsequent electroless plating.

Firstly, the substrate 10 is cut to a required size, and then a photosensitive film (not shown) is pasted on the smooth surface of the substrate 10 and exposed to light to protect the substrate in the subsequent chemical coating step.

The substrate 10 is further washed. Washing includes washing with a detergent, and then pickling with a sulfuric acid solution with a mass concentration of 5%.

Dissolving alkaline detergent in water to prepare detergent, heating the detergent to 30°C-60°C, and then placing the substrate 10 in the detergent at a temperature of 30°C-60°C for ultrasonic treatment for 1 minute to 10 minutes Minutes to remove the oil on the surface of the substrate 10.

After ultrasonic treatment in detergent for 1-10 minutes, the substrate 10 is taken out and cleaned with deionized water. Then place the substrate 10 in a sulfuric acid solution with a mass concentration of 5% at room temperature and soak for 1 minute to 10 minutes, take it out and wash it with deionized water, and set it aside.

The purpose of pickling after washing with detergent is to remove the oxide film, scale and rust products on the surface of the substrate 10, so as to prevent the oxide film, scale and rust products from adversely affecting the subsequently prepared nickel-phosphorus film.

Step S120: activating the substrate with the above-mentioned activator for preparing the embedded thin film resistor to obtain an activated substrate.

Keep the above activator for the embedded thin film resistor at 20° C. to 60° C., soak the washed substrate 10 in the activator at a temperature of 20° C. to 60° C. for 1 minute to 10 minutes, and then Remove and rinse with deionized water.

After activation, a zinc layer is deposited on the surface of the substrate 10 opposite to the photosensitive film.

Step S130 : using an electroless plating method to prepare a nickel-phosphorus film on the surface of the activated substrate to obtain a substrate laminated with nickel-phosphorus films.

Electroless plating solution uses water as solvent. Each liter of electroless plating solution contains 5-80 grams of nickel sulfate (NiSO ₄ ), 5-80 grams of sodium hypophosphite (NaH ₂ PO ₂ ), 10-80 grams of buffer, 1-5 mg of stabilizer and complexing agent 10-80 grams.

Wherein, the buffering agent is preferably sodium acetate or potassium acetate, which is used to maintain the pH value of the electroless plating solution within a set range.

The stabilizer is preferably thiourea.

The complexing agent is preferably at least one of sodium citrate, DL-sodium malate and lactic acid. The role of the complexing agent is to complex nickel ions and release a fixed amount of nickel ions during the electroless plating process.

When in use, first adjust the pH value of the electroless plating solution to 1-12 with a pH regulator. The pH regulator is preferably at least one of ammonia water, dilute sulfuric acid, sodium hydroxide and potassium hydroxide.

Preferably, every liter of electroless plating solution also includes 10 g of ammonium chloride. The electroless plating by using the chemical plating solution containing ammonium chloride can be carried out at normal temperature, has low energy consumption, and is environmentally friendly.

The activated substrate is placed in an electroless plating solution at a temperature of 20° C. to 90° C. for 0.5 minutes to 5 minutes. Zinc on the surface of the substrate first undergoes a substitution reaction with nickel ions in the electroless plating solution. The electrons provided by sodium phosphate are reduced and adhered to the surface of the nascent nickel layer.

The nascent nickel has a catalytic effect, and the reaction of water and hypophosphite produces atomic hydrogen adsorbed on the self-catalytic surface. The reaction formula is shown in the following formula (2); the surface-adsorbed hydrogen reduces nickel and phosphorus on the self-catalytic surface , the reaction formulas are shown in the following formulas (3) and (4); while reducing nickel-phosphorus, atomic hydrogen combines to form hydrogen and precipitates.

(1) Zn+Ni ²⁺ →Ni+Zn ²⁺ ;

(2) H ₂ PO ₂ ^- +H ₂ O→HPO ₃ ^2- +H ⁺ +2H _adsorption ;

(3) Ni ²⁺ +2H _adsorption → Ni+2H ⁺ ;

(4) H ₂ PO ₂ ^- +H ⁺ +H _adsorption ^- → 2H ₂ O+P;

(5) 2H _adsorption + 2e ^- → H ₂ .

Through the above reactions (1) to (5), the nickel phosphorus thin film 20 laminated on the substrate is formed.

Step S140: Pressing the PCB substrate and the substrate on which the nickel-phosphorus film is laminated, and laminating the nickel-phosphorus film on the PCB substrate.

Remove the photosensitive film on the substrate 10, then wash the substrate 10 with deionized water and dry it, place the substrate 10 laminated with the nickel-phosphorus film 20 on the PCB substrate 30, and make the nickel-phosphorus film 20 laminated on the PCB On the substrate 30, a prepreg (not shown in the figure) is clamped between the nickel-phosphorus film 20 and the PCB substrate 30, vacuumized, heat-treated, and the pressure is kept at 10 MPa, and the PCB substrate 30 and the substrate on which the nickel-phosphorus film 20 is laminated 10 to perform pressure bonding, so that the substrate 10 laminated with the nickel-phosphorus thin film 20 is attached to the PCB substrate 30 .

Preferably, the step of heat treatment is to keep warm at 100°C-140°C for 1 hour, and then keep warm at 140°C-180°C for 1 hour, so as to tightly press the substrate 10 laminated with the nickel-phosphorous film 20 and the PCB substrate 30, The substrate 10 laminated with the nickel-phosphorus thin film 20 is closely attached to the surface of the PCB substrate 30 .

Step S150: Etching the substrate and the nickel-phosphorus thin film to obtain a buried thin-film resistor.

The etching includes the steps of etching the substrate 10 and the nickel-phosphorous film 20 with a first etching solution and etching the substrate 10 with a second etching solution. The substrate 10 is etched a second time with the second etchant.

The first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate. Preferably, the concentration of sodium thiosulfate is 20g/L, and the concentration of anhydrous copper sulfate is 30g/L.

The second etching solution is a mixed aqueous solution of copper chloride, ammonium chloride and ammonia water. Preferably, the concentration of copper chloride is 30 g/L, the concentration of ammonium chloride is 45 g/L, and the amount of ammonia water added makes the pH of the second etching solution 1-12. A more preferred pH value is 9.

Firstly, paste a photosensitive film on the surface of the substrate 10 away from the nickel-phosphorus thin film 20, and then use the first film paper for exposure and development. The first film has a pattern consistent with the resistance model required for this step. After development, soak the sample in the first etching solution for 5 minutes to 10 minutes to etch away part of the substrate 10 and part of the nickel-phosphorous film 20, leaving a square unformed buried resistance sample.

After the above samples were cleaned with deionized water and dried, a photosensitive film was pasted on the surface of the substrate 10 away from the nickel-phosphorus film 20, and then exposed and developed with a second film paper. The second film has a pattern consistent with the final desired resistance model. Put the sample etched by the first etching solution into the second etching solution and soak for 5 minutes to 10 minutes, so as to etch away the excess substrate 10 without affecting the integrity of the plating layer and obtain the embedded type resistor, as shown in Figure 2.

Preferably, during the etching process, the temperature of the second etchant is kept at 30°C-60°C.

The preparation method of the above-mentioned embedded thin-film resistor uses the above-mentioned activator for preparing the embedded thin-film resistor that does not contain chlorine and palladium to activate the substrate, so that the subsequent chemical coating can be performed at a lower temperature, and the energy consumption is low. , the preparation process is simple and the preparation cost is low. The prepared embedded thin film resistor has the advantages of adjustable sheet resistance and temperature coefficient of resistance value.

Moreover, since the activator used does not contain chlorine, it will not introduce chloride ions into the chemical plating solution, which ensures the stability of the plating solution, helps to ensure the quality of the nickel-phosphorus film, and prepares an embedded film with better performance. resistance.

Moreover, since the electroless plating is carried out at a lower temperature, less steam is generated and less environmental pollution is caused.

An embedded thin film resistor prepared by the above preparation method according to an embodiment. Since the above-mentioned activator not containing chlorine is used to activate the substrate in the preparation process, the temperature of the plating solution is guaranteed, so that the quality of the nickel-phosphorus thin film is high, which is beneficial to improving the performance of the embedded thin film resistor.

Moreover, since the above-mentioned activator does not contain expensive palladium, the price is relatively low, which can increase the preparation cost of the embedded thin film resistor and is beneficial to reduce the cost of the embedded thin film resistor.

Further elaborate below by specific embodiment.

Example 1

Fabrication of Embedded Thin Film Resistors

1. Provide 8cm×4cm copper foil. The copper foil has a relatively smooth surface and a rough surface. Paste a photosensitive film on the smooth surface of the copper foil and expose it;

2. Weigh 10g of washing powder, add 400ml of deionized water, and prepare detergent for degreasing. Put the copper foil in step 1 into the detergent, ultrasonically treat it for 10 minutes, then take it out and wash it with deionized water;

3. Take 20ml of concentrated sulfuric acid and prepare it as dilute sulfuric acid with a mass fraction of 5%. Put the copper foil treated in step 2 into the dilute sulfuric acid, pickle it for 10 minutes, and then take it out and wash it with deionized water;

4. Weigh 35g of zinc sulfate, 3.5g of DL-sodium malate and 5g of zinc powder into deionized water to prepare 200mL of activator for the preparation of embedded thin film resistors, heat the activator to 40°C, and then 3 The treated copper foil is soaked in the activator for 10 minutes, and then cleaned with deionized water;

5. Weigh 15.00g of sodium hypophosphite, 12.50g of nickel sulfate, 10.00g of sodium citrate, 10.00g of sodium acetate and 0.5mg of thiourea and dissolve them in deionized water to make a 500ml solution. Adjust the pH to 5 with dilute sulfuric acid. Stir the plating solution for 1 hour, then put it in a constant temperature water bath, heat it to 88°C, put the copper foil treated in step 4 into the solution, and plate it for 30 seconds, and plate a nickel-phosphorus film on the rough surface of the copper foil. Obtain a copper foil laminated with a nickel-phosphorus film, then take it out, wash it with deionized water, and dry it;

6. Put the sample processed in step 5 on the PCB substrate, make the nickel-phosphorus film laminated on the PCB substrate, then clamp the prepreg between the PCB substrate and the nickel-phosphorus film, put it into the tablet press, and vacuumize. Insulate at 120°C for one hour and at 150°C for one hour, keep the pressure at _10MPa , press the copper foil laminated with nickel-phosphorus film and PCB substrate together, and then cool naturally;

7. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then expose and develop with the first film paper, soak the sample in step 6 in the first etching solution for 5 minutes, and then take it out with deionized water Cleaning; wherein, the first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate, the concentration of sodium thiosulfate is 20g/L, and the concentration of anhydrous copper sulfate is 30g/L;

8. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then use the second film paper to expose and develop, soak the sample in step 7 in the second etching solution for 5 minutes, and then take it out with deionized water Washing and drying to obtain an embedded film; wherein, the second etching solution is a mixed aqueous solution of copper chloride, ammonium chloride and ammonia water, the concentration of anhydrous copper sulfate is 30g/L, and the concentration of ammonium chloride is 45g /L, the amount of ammonia water added makes the pH value of the second etching solution 9.

The components of the activator and electroless plating solution for preparing the embedded thin film resistor in Example 1 are shown in Table 1 below.

Table 1

FIG. 3 is an EDS diagram of the nickel-phosphorus thin film of Example 1. FIG. The atomic percentage and mass percentage of nickel and phosphorus can be obtained from Fig. 3, see Table 2 below.

Table 2

Fig. 4 is an SEM image of the nickel-phosphorus thin film of Example 1, wherein the magnification is 60,000 times, the working distance is 6.1mm, the high voltage is 10.00KV, and the detector is ETD. It can be seen from Figure 4 that the thickness of the nickel-phosphorus film is about 1 micron.

5 is an SEM image of another magnification of the nickel-phosphorus thin film of Example 1, wherein the magnification is 8000 times, the working distance is 5.6mm, the high voltage is 5.00KV, and the detector is ETD. It can be seen from Figure 5 that the surface of the coating is almost the same as the rough surface of the copper foil, uneven.

Example 2

Fabrication of Embedded Thin Film Resistors

1. Provide 8cm×4cm copper foil. The copper foil has a relatively smooth surface and a rough surface. Paste a photosensitive film on the smooth surface of the copper foil and expose it;

2. Weigh 10g of washing powder, add 400ml of deionized water, and prepare detergent for degreasing. Put the copper foil in step 1 into the detergent, ultrasonically treat it for 10 minutes, then take it out and wash it with deionized water;

3. Take 20ml of concentrated sulfuric acid and prepare it as dilute sulfuric acid with a mass fraction of 5%. Put the copper foil treated in step 2 into the dilute sulfuric acid, pickle it for 10 minutes, and then take it out and wash it with deionized water;

4. Weigh 35g of zinc sulfate, 3.5g of DL-sodium malate and 5g of zinc powder into deionized water to prepare 200mL of activator for the preparation of embedded thin film resistors, heat the activator to 40°C, and then 3 The treated copper foil is soaked in the activator for 10 minutes, and then cleaned with deionized water;

5. Weigh 10.04g of sodium hypophosphite, 10.07g of nickel sulfate, 10.00g of ammonium chloride, 8.00g of sodium citrate, 8.00g of sodium acetate and 0.5mg of thiourea and dissolve them in deionized water to make a 400ml solution. Adjust pH=8 with sulfuric acid, stir the plating solution for 1 hour, put the copper foil treated in step 4 into the solution at room temperature, and plate for 1 minute, and plate a nickel-phosphorus film on the rough surface of the copper foil to obtain a laminated Copper foil with nickel-phosphorus film, then take it out, wash it with deionized water, and dry it;

6. Put the sample processed in step 5 on the PCB substrate, make the nickel-phosphorus film laminated on the PCB substrate, then clamp the prepreg between the PCB substrate and the nickel-phosphorus film, put it into the tablet press, and vacuumize. Insulate at 120°C for one hour, at 150°C for one hour, keep the pressure at 10MPa, press the copper foil laminated with the nickel-phosphorus film and the PCB substrate together, and then cool naturally;

7. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then expose and develop with the first film paper, soak the sample in step 6 in the first etching solution for 10 minutes, and then take it out with deionized water Cleaning; wherein, the first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate, the concentration of sodium thiosulfate is 20g/L, and the concentration of anhydrous copper sulfate is 30g/L;

8. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then use the second film paper to expose and develop, soak the sample in step 7 in the second etching solution for 10 minutes, and then take it out with deionized water Washing and drying to obtain an embedded film; wherein, the second etching solution is a mixed aqueous solution of anhydrous copper sulfate, ammonium chloride and ammonia water, the concentration of copper chloride is 30g/L, and the concentration of ammonium chloride is 45g /L, the amount of ammonia water added makes the pH value of the second etching solution 9.

The components of the activator and electroless plating solution used for preparing the embedded thin film resistor in Example 2 are shown in Table 3 below.

table 3

FIG. 6 is the temperature coefficient of resistance (TCR) curves of the embedded thin-film resistors of Embodiment 1 and Embodiment 2. FIG. It can be seen from FIG. 6 that the embedded thin film resistances of Embodiment 1 and Embodiment 2 change very little with temperature, and the resistance value is very stable.

Example 3

Fabrication of Embedded Thin Film Resistors

1. Provide 8cm×4cm copper foil. The copper foil has a relatively smooth surface and a rough surface. Paste a photosensitive film on the rough surface of the copper foil and expose it;

2. Weigh 10g of washing powder, add 400ml of deionized water, and prepare detergent for degreasing. Put the copper foil in step 1 into the detergent, ultrasonically treat it for 10 minutes, then take it out and wash it with deionized water;

3. Take 20ml of concentrated sulfuric acid and prepare it as dilute sulfuric acid with a mass fraction of 5%. Put the copper foil treated in step 2 into the dilute sulfuric acid, pickle it for 10 minutes, and then take it out and wash it with deionized water;

4. Weigh 35g of zinc sulfate, 3.5g of DL-sodium malate and 5g of zinc powder into deionized water to prepare 200mL of activator for the preparation of embedded thin film resistors, heat the activator to 40°C, and then 3 The treated copper foil is soaked in the activator for 10 minutes, and then cleaned with deionized water;

5. Weigh 15.00g of sodium hypophosphite, 12.50g of nickel sulfate, 10.00g of ammonium chloride, 8.00g of sodium citrate, 8.00g of sodium acetate and 0.0005g of thiourea and dissolve them in deionized water to make a 400ml solution. Sodium oxide adjusts the pH=8, stirs the plating solution for 1 hour, then puts it in a constant temperature water bath, heats it to 88°C, puts the copper foil treated in step 4 into the solution, and applies plating for 1 minute, on the smooth surface of the copper foil Nickel-phosphorus film is plated on the top to obtain a copper foil laminated with nickel-phosphorus film, then taken out, cleaned with deionized water, and dried;

6. Put the sample processed in step 5 on the PCB substrate, make the nickel-phosphorus film laminated on the PCB substrate, then clamp the prepreg between the PCB substrate and the nickel-phosphorus film, put it into the tablet press, and vacuumize. Insulate at 120°C for one hour, at 150°C for one hour, keep the pressure at 10MPa, press the copper foil laminated with the nickel-phosphorus film and the PCB substrate together, and then cool naturally;

7. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then expose and develop with the first film paper, soak the sample in step 6 in the first etching solution for 5 minutes, and then take it out with deionized water Cleaning; wherein, the first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate, the concentration of sodium thiosulfate is 20g/L, and the concentration of anhydrous copper sulfate is 30g/L;

8. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then use the second film paper to expose and develop, soak the sample in step 7 in the second etching solution for 5 minutes, and then take it out with deionized water Washing and drying to obtain an embedded film; wherein, the second etching solution is a mixed aqueous solution of anhydrous copper sulfate, ammonium chloride and ammonia water, the concentration of copper chloride is 30g/L, and the concentration of ammonium chloride is 45g /L, the amount of ammonia water added makes the pH value of the second etching solution 9.

The components of the activator and electroless plating solution used for preparing the embedded thin film resistor in Example 3 are shown in Table 4 below.

Table 4

Fig. 7 is an SEM image of the nickel-phosphorus thin film of Example 3, wherein the magnification is 8000 times, the working distance is 5.5mm, the high voltage is 5.00KV, and the detector is ETD. It can be seen from Figure 7 that the nickel-phosphorus thin film is plated on the smooth surface of the copper foil, and the surface of the obtained nickel-phosphorus thin film is also relatively smooth, which is consistent with the smooth surface of the copper foil.

From the comparison of Figure 5 and Figure 7, it can be seen that the nickel-phosphorus film is formed on the rough surface of the copper foil, and the surface of the nickel-phosphorus film is relatively rough. High adhesion.

Comparative example 1

Fabrication of Embedded Thin Film Resistors

1. Provide 8cm×4cm copper foil. The copper foil has a relatively smooth surface and a rough surface. Paste a photosensitive film on the smooth surface of the copper foil and expose it;

2. Weigh 10g of washing powder, add 400ml of deionized water, and prepare detergent for degreasing. Put the copper foil in step 1 into the detergent, ultrasonically treat it for 10 minutes, then take it out and wash it with deionized water;

3. Take 20ml of concentrated sulfuric acid and prepare it as dilute sulfuric acid with a mass fraction of 5%. Put the copper foil treated in step 2 into the dilute sulfuric acid, pickle it for 10 minutes, and then take it out and wash it with deionized water;

4. Soak the copper foil processed in step 3 in the stannous chloride solution for sensitization, the sensitization solution is a mixed aqueous solution of stannous chloride and concentrated hydrochloric acid, wherein the concentration of stannous chloride is 40g/L, concentrated The concentration of hydrochloric acid is 100ml/L; place it at room temperature for 3 minutes, take it out and wash it with deionized water, and put it in the palladium activator. The palladium activation solution is a mixed aqueous solution of palladium chloride and concentrated hydrochloric acid, wherein the palladium chloride The concentration is 0.1g/L, the concentration of concentrated hydrochloric acid is 10ml/L, put it at room temperature for 4min, then take it out again and wash it with deionized water;

5. Weigh 15.00g of sodium hypophosphite, 12.50g of nickel sulfate, 10.00g of ammonium chloride, 8.00g of sodium citrate, 8.00g of sodium acetate and 0.0005g of thiourea and dissolve them in deionized water to make a 400ml solution. Adjust the pH to 8 with sodium oxide, stir the plating solution for 1 hour, put it in a constant temperature water bath, heat it up to 88°C, put the copper foil treated in step 4 into the solution, and apply plating for 1 minute. Nickel-phosphorus film is plated on the top to obtain a copper foil laminated with nickel-phosphorus film, then taken out, cleaned with deionized water, and dried;

6. Put the sample processed in step 5 on the PCB substrate, make the nickel-phosphorus film laminated on the PCB substrate, then clamp the prepreg between the PCB substrate and the nickel-phosphorus film, put it into the tablet press, and vacuumize. Insulate at 120°C for one hour, at 150°C for one hour, keep the pressure at 10MPa, press the copper foil laminated with the nickel-phosphorus film and the PCB substrate together, and then cool naturally;

7. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then expose and develop with the first film paper, soak the sample in step 6 in the first etching solution for 5 minutes, and then take it out with deionized water Cleaning; wherein, the first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate, the concentration of sodium thiosulfate is 20g/L, and the concentration of anhydrous copper sulfate is 30g/L;

8. Paste a photosensitive film on the surface of the copper foil away from the nickel-phosphorus film, then use the second film paper to expose and develop, soak the sample in step 7 in the second etching solution for 5 minutes, and then take it out with deionized water Wash and dry to obtain an embedded film; wherein, the second etching solution is a mixed aqueous solution of anhydrous copper sulfate, ammonium chloride and ammonia, the concentration of anhydrous copper sulfate is 30g/L, and the concentration of ammonium chloride is 45g/L, the amount of ammonia added makes the pH value of the second etching solution 9.

The sheet resistance values of the embedded thin-film resistors of Examples 1-3 and Comparative Example 1 were tested with a digital source ammeter, and the test results are shown in Table 5.

table 5

From Table 5, the sheet resistance of the embedded thin film resistors of Examples 1-3 is larger than that of Comparative Example 1.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. A method for preparing an embedded thin film resistor, comprising the steps of: provide the substrate; Activating the substrate with an activator for preparing embedded thin film resistors to obtain an activated substrate, the activator for preparing embedded thin film resistors includes water, zinc sulfate, DL-malic acid Sodium and zinc powder, wherein the concentration of the zinc sulfate is 20-200g/L, the concentration of the DL-sodium malate is 10-50g/L, and the concentration of the zinc powder is 5-30g/L; Preparing a nickel-phosphorus film on the surface of the activated substrate by electroless plating to obtain a substrate laminated with a nickel-phosphorus film; Pressing the PCB substrate and the substrate laminated with the nickel-phosphorus film, and laminating the nickel-phosphorus film on the PCB substrate; and Etching the substrate and the nickel-phosphorus thin film to obtain an embedded thin-film resistor; The step of pressing the PCB substrate and the substrate laminated with the nickel-phosphorus thin film, and laminating the nickel-phosphorus thin film on the PCB substrate is specifically: placing the substrate laminated with the nickel-phosphorus thin film placed on the PCB substrate, and laminated the nickel-phosphorus film on the PCB substrate, then clamped the prepreg between the nickel-phosphorus film and the PCB substrate, vacuumized and heat-treated the laminated The substrate of the nickel-phosphorus film is bonded on the PCB substrate; The heat treatment step is to keep warm at 100°C-140°C for 1 hour, and then keep warm at 140°C-180°C for 1 hour; The step of etching the substrate and the nickel phosphorus film comprises: Etching the substrate and the nickel-phosphorus film by using a first etchant; and Etching the substrate with a second etchant. 2. the preparation method of embedded type thin film resistance according to claim 1 is characterized in that, the step of activating described substrate with the activator for preparing embedded type thin film resistance as claimed in claim 1 The method includes the step of affixing a photosensitive film on the substrate and then exposing. 3. The method for preparing an embedded thin film resistor according to claim 2, wherein a photosensitive film is pasted on the substrate, and after exposure, the method for preparing an embedded resistor as claimed in claim 1 is used. Before the step of activating the substrate with the activator of the embedded thin film resistor, the step of washing the substrate is also included. 4 . The method for preparing embedded thin film resistors according to claim 3 , wherein the washing step is to wash with a detergent first, and then pickle with a sulfuric acid solution with a mass concentration of 5%. 5 . 5. The method for preparing an embedded thin film resistor according to claim 1, wherein the substrate is copper foil, and the copper foil has a relatively smooth surface and a rough surface, and the nickel-phosphorus thin film is laminated on the rough surface of the copper foil. 6. The preparation method of embedded thin film resistor according to claim 1, characterized in that, the step of activating the substrate with the activator for preparing embedded thin film resistor as claimed in claim 1 Specifically: keep the activator for preparing embedded thin film resistors as claimed in claim 1 at 20°C to 60°C, and then place the substrate in the activator at a temperature of 20°C to 60°C. Soak for 1 to 10 minutes. 7. the preparation method of embedded type thin-film resistance according to claim 1 is characterized in that, described employing electroless plating method prepares nickel-phosphorus film on the surface of the substrate after described activation, obtains and is stacked with nickel-phosphorus film The step of the substrate is specifically: placing the activated substrate in an electroless plating solution at a temperature of 20° C. to 90° C. for 0.5 minutes to 5 minutes. 8. The method for preparing an embedded thin film resistor according to claim 7, wherein the electroless plating solution per liter contains 5 to 80 grams of nickel sulfate, 5 to 80 grams of sodium hypophosphite, and 10 grams of buffering agent. ～80 grams, stabilizer 1～5 mg and complexing agent 10～80 grams. 9. The preparation method of embedded thin film resistor according to claim 1, characterized in that, the first etching solution is a mixed aqueous solution of sodium thiosulfate and anhydrous copper sulfate, and the second etching solution It is a mixed aqueous solution of copper chloride, ammonium chloride and ammonia water. 10. An embedded thin film resistor prepared by the preparation method according to any one of claims 1-9.