CN111405771A - A kind of manufacturing method of printed circuit conductive line - Google Patents

Abstract

A manufacturing method of a printed circuit conductive circuit relates to the technical field of printed circuit board manufacturing. Including: 1) growing a tin seed layer on the surface of the printed circuit insulating substrate, 2) covering a patterned dry film on the tin seed layer, 3) electroplating copper to form a copper conductive circuit, 4) removing the dry film, 5 ) heat treatment of the substrate obtained after the previous step, so that the copper conductive circuit and the tin seed layer are eutectic and integrated; 6) the tin seed layer is etched to obtain a printed circuit conductive circuit. In the method of the invention, the etching speed of the tin layer is fast, the precision is high, and the circuit is complete without side etching, which is conducive to the manufacture of high-precision circuit boards; It prevents the local defects caused by the inconsistent etching speed of the tin seed layer and the copper conductive line, ensures the bonding force between the conductive line and the underlying insulating medium, and makes the circuit pattern with good heat resistance, high stability and high reliability.

Description

A kind of manufacturing method of printed circuit conductive line

technical field

The invention relates to the technical field of printed circuit board manufacturing, in particular to a manufacturing method of a printed circuit conductive circuit.

Background technique

As a "bridge" that carries electronic components and connects circuits, printed circuit boards are widely used in communication electronics, consumer electronics, computers, automotive electronics, industrial control, medical equipment, national defense and aerospace and other fields. indispensable presence. In recent years, with the accelerated evolution of cloud technology, 5G network construction, big data, artificial intelligence, sharing economy, Industry 4.0, and the Internet of Things, the market has put forward higher requirements for PCB manufacturing technology. The need for density, high precision, and miniaturization, its manufacturing technology and process urgently need reform and innovation, and the first is the production technology of fine circuit patterns.

At present, more than 99% of enterprises in the printed circuit board industry are using traditional printed circuit board circuit pattern making technology. The core of this technology is to use a resist layer to cover the protected circuit pattern, and then use etching solution to etch away the copper surface. Unnecessary parts on the board, so as to obtain the required circuit pattern. Copper etching solution is divided into alkaline etching solution and acid etching solution. When using alkaline etching solution, the tin plating layer is used as the resist layer. A typical process is: pretreatment of copper clad laminate → coating photoresist → exposure → development → formation of anti-plating layer → pattern plating tin → fading Film → etching copper → tin stripping → optical inspection, the schematic diagram of the process is shown in Figure 2; when using acid etching solution, the dry resist film is used as the resist layer, a typical process is CCL pretreatment → coating light Photoresist→exposure→development→formation of resist layer→etching copper→film stripping→optical inspection. The schematic diagram of the process is shown in FIG. 3 . The advantages of this traditional printed circuit board circuit pattern manufacturing technology are that the technology is mature, the equipment is perfect, and the product manufacturing qualification rate is high. However, due to side etching during etching, this technology will bring an inevitable problem, that is, when the circuit When the line width and line spacing are further reduced, the gap between the upper width and the lower width of the line will further increase, and even a serious over-etching phenomenon will occur, which will have a great adverse effect on signal transmission.

During the etching process, the etching time varies with the thickness of the copper layer. When the copper layer thickness is smaller, the required etching time is shorter. Short etching time is beneficial to reduce side etching, thereby improving the quality of fine lines. Therefore, someone proposed a new technology. The main body of the technology is different from the core of the traditional circuit pattern production method. The seed layer is used to grow the desired circuit pattern on the seed layer, thereby avoiding the process of etching a large amount of copper and the side etching problem caused by etching the copper layer.

In this production technology using the thin copper layer as the seed layer, it can be further divided into: electroless copper plating, lamination of thick copper and then thinning, magnetron sputtering deposition of copper, etc. according to the deposition method of the thin copper layer. Among them, electroless copper plating is to use the reducing agent in the plating solution in the absence of an applied current, and on the substrate with catalytic activity, the metal ions in the plating solution are reduced to metal atoms and then deposited on the surface of the substrate. The reducing agent is generally formaldehyde. Although the deposited copper layer has the same thickness and can evenly cover the surface of the substrate, the bonding force between the electroless copper plating layer and the substrate is obviously insufficient, and it is easy to cause serious problems of line peeling. This is especially true of epoxy resin substrates that are commonly used today. When mounting components, the circuit board generally has to go through a high temperature of 230°C to 260°C. Poor bonding force can easily lead to the delamination of the copper layer and the dielectric layer and the generation of air bubbles after a certain thermal stress test of the circuit board. and other defects. [Electronic Components and Materials, 2014, 33(02): 6-9+15] also mentioned that: electroless copper may have crystal defects including dislocations, twins, grain boundaries, etc.; electroless copper plating layer The copper mass fraction, density, and elongation rate of copper are usually lower than those of electroplated copper. Therefore, after rapid etching, a side-etching state of bottom etch is easily formed between the chemical copper surface and the dielectric layer, which further reduces the contact area of the circuit.

Lamination thick copper thinning is a new process improved on the traditional method of laminating ultra-thin copper as a seed layer. [Printed Circuit Information, 2013(08):9-13] proposed that the thickness of the copper foil should be appropriate for the thinning process of laminating thick copper. If the copper foil is too thick, a large amount of copper needs to be reduced. The corrosion rate of all parts of the copper surface cannot be completely consistent, which will result in uneven bite corrosion; if the thickness of the copper foil is too thin, it will be more difficult to make a copper-clad laminate, and the thin copper foil will be laminated during lamination. It is prone to scratches and wrinkles when it is used, and the production cost of thin copper foil is high. Due to the increase in signal transmission rate and frequency, the fine lines of printed circuit boards are required to be smooth and flat, so the process of laminating thick copper and then thinning it cannot meet the requirements.

The method of depositing a thin copper seed layer by magnetron sputtering has the characteristics of simple equipment operation, controllable deposition area, and good bonding force between the copper layer and the substrate. It can greatly reduce the pollution to the environment. However, magnetron sputtering equipment has high cost, strict requirements and very low production efficiency, so it cannot be widely used in mass production of printed circuit boards at present. [Printed Circuit Information, 2014(01):38-39+58] pointed out that different sputtering conditions have a great influence on the stripping strength of the lines, and good bonding force can only be achieved under appropriate sputtering conditions.

In addition to using a thin copper layer as the seed layer, similarly, [Printed Circuit Information, 2017, 25(z1): 213-217] mentioned a new conductive circuit fabrication method using an electroless nickel layer as the seed layer. This method avoids etching a large amount of copper, while reducing the problem of impaired signal transmission caused by side etching. However, there are still some problems with this method. First, the bonding force between the nickel and the epoxy resin board is related to the thickness of the electroless nickel plating layer: when the thickness of the electroless nickel layer reaches 8 μm, the bonding force exceeds the copper thickness of 35 μm. However, with the increase of the thickness of the chemical nickel layer, the time required for nickel etching increases, and because the metal nickel is prone to passivation in the air, it further increases The difficulty of etching has a great impact on the reliability of the circuit; the second is that it is difficult for nickel and copper to achieve metal integration at lower temperatures. Metal integration is conducive to solving the problem of stress concentration between metal layers, reducing the formation of side corrosion and increasing the reliability of the circuit. The higher temperature heat treatment conditions will increase the cost of the processing process and the risk of circuit failure due to oxidation of the copper surface.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for manufacturing a conductive circuit of a printed circuit in view of the defects existing in the background technology. In the invention, a thin layer of tin is grown on an insulating substrate as a seed layer, and then a desired circuit pattern is prepared thereon, and the tin layer in the non-circuit pattern area is quickly etched away during the etching process. Compared with the traditional circuit pattern manufacturing process of the printed circuit board, the present invention avoids a large number of processes of etching the copper layer and the side etching problem caused by etching the copper layer; The poor bonding force between the electroless copper plating layer and the substrate leads to the problems of easy stripping of the circuit and poor thermal stability, which avoids the formation of side etching and the reduction of the contact area of the circuit, and also avoids the failure of the circuit pattern due to uneven bite and roughness. The problem of meeting the requirements of high-frequency and high-speed signal transmission also avoids the problem that mass production cannot be achieved due to high production costs and low efficiency; The passivation of the nickel plating layer and the reduction of the reliability of the circuit caused by the excessive thickness of the nickel layer avoid the oxidation of the copper surface by the high temperature heat treatment and the difficulty in realizing the integration of copper and nickel metals.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

A method for manufacturing a conductive circuit of a printed circuit, comprising the following steps:

Step 1: grow a tin seed layer on the surface of the printed circuit insulating substrate;

Step 2: Cover the tin seed layer grown in Step 1 with a patterned dry film as a plating resist;

Step 3: electroplating copper on the tin seed layer area of the substrate obtained in step 2 that is not covered by the dry film to form a copper conductive circuit;

Step 4: removing the dry film on the substrate obtained after the copper electroplating in Step 3;

Step 5: heat-treating the substrate obtained after the treatment in Step 4, so that the copper conductive circuit and the tin seed layer are eutectic and integrated;

Step 6: Etch the area of the tin seed layer on the surface of the substrate obtained after the treatment in Step 5, which is not covered by the electroplated copper layer, to obtain a printed circuit conductive circuit.

Further, the printed circuit insulating substrate described in step 1 is selected from paper-based printed boards made of epoxy resin, phenolic resin, polyester resin, polyimide and other materials, epoxy glass fiber cloth printed boards, It is one of various insulating substrate materials such as composite substrate printed boards, special substrate printed boards, etc.

Further, the thickness of the tin seed layer grown in step 1 is 1-2 μm, and the adopted method is electroless plating technology or direct electroplating technology. One of the electroless plating techniques includes reduction electroless tin plating, disproportionation reaction electroless tin plating and immersion plating electroless tin plating, wherein the reduction electroless tin plating is performed on a substrate with catalytic activity under the condition of no applied current. The metal ions in the plating solution are reduced to metal atoms and deposited on the surface of the substrate. The direct electroplating technology of the second method is to first coat a conductive layer on the surface of the printed circuit insulating substrate, and then enter the process of electroplating tin, wherein the conductive layer can be palladium series (using palladium or its compound as the conductive substance), with high conductivity. Molecular series (such as polypyrrole, polyaniline), carbon black series (carbon black conductive film), etc.

Further, the patterned dry film in step 2 can be completed by using a photographic plate or by a laser direct imaging technology. Among them, the method of photographing the negative plate uses the film as a mask, and the circuit pattern is transferred to the circuit board through the exposure process to form an anti-plating mask pattern; the anti-plating mask pattern is used for the pattern plating process, that is, a protective After the electroplating resist material forms a negative phase pattern on the circuit board, pattern copper plating is performed to grow the desired circuit pattern part. The laser direct imaging technology is a technology that uses the principle of laser direct imaging to directly project the circuit pattern in the form of a laser beam on a circuit board coated with photoresist to realize the pattern transfer. Its main advantages are: no need to use a photographic plate , simplifies the production process, greatly improves the production efficiency, and because the scale setting mode is flexible, the alignment accuracy of the machine is greatly improved, and the error of graphic transfer is reduced.

Further, the thickness of the copper conductive circuit in step 3 is 5-100 μm.

Further, the copper electroplating described in step 3 includes the processes of cleaning, roughening and electroplating, wherein the electroplating solution used during electroplating is sulfate type, pyrophosphate type, fluoroborate type or cyanide type, and sulfate type. The most common type of additives include brighteners, levelers, inhibitors and auxiliary additives such as chloride ions.

Further, when removing the dry film from the substrate in step 4, a sodium hydroxide solution of 3wt%-5wt% is used, the temperature is 50-60°C, and the removal method is soaking or mechanical spraying.

Further, the temperature of the heat treatment in step 5 is 180°C to 200°C, and the heat treatment time is 30s. After heat treatment, the copper-tin interface will undergo a series of actions such as mutual bonding, infiltration, migration, and diffusion between tin and copper atoms. After cooling and solidification, a thin layer of compound similar to "tin alloy" will quickly form and gradually thicken This copper-tin interface alloy compound is also called IMC (Intermetallic Compound).

Further, the etching treatment in step 6 adopts a chemical method tank-type soaking or spraying.

Further, the line width of the conductive circuit of the printed circuit obtained in step 6 is 8 μm˜3 mm.

The present invention provides a method for manufacturing a conductive circuit of a printed circuit. The technical core is to deposit a thin tin seed layer and grow a desired circuit pattern on the seed layer, and the tin in the non-circuit pattern area is rapidly etched during the etching process. Compared with the traditional circuit pattern manufacturing process of the printed circuit board (the schematic diagrams of the main process flow are shown in Figures 2 and 3), the seed layer technology is an improved semi-additive method which is different from the traditional subtractive method manufacturing process. method, directly growing the required circuit patterns, avoiding a large number of processes of etching the copper layer, etching the extremely thin seed layer metal to avoid side etching problems such as insufficient etching or excessive etching; compared with the thin copper layer as the seed layer of the circuit The pattern manufacturing process realizes metal integration through heat treatment, which avoids the problems of poor thermal stability of the circuit pattern, easy foaming and peeling, avoids the formation of side etching and the reduction of the contact area of the circuit, and also avoids the roughness of the copper surface. Under the action of the skin effect, the resistance increases, the loss increases, and the signal transmission is distorted, which leads to the inability to meet the requirements of high-frequency and high-speed signal transmission. It also avoids the inability to achieve mass production due to high production costs and low efficiency Compared with the circuit pattern manufacturing process in which the thin nickel layer is used as the seed layer, the thickness of the tin seed layer is extremely thin, and the tin is not easily passivated in the air, and the time required for rapid etching is extremely short, which is beneficial to reduce the copper circuit. In addition, the two metals of copper and tin are eutectic to form a uniform IMC layer, which eliminates the original obvious dividing line between copper and tin, releases the stress between metals, and prevents the tin seed layer from interacting with The local defects caused by the inconsistent etching speed of copper conductive lines ensure the bonding force between the conductive lines and the underlying insulating medium, reduce the formation of side etching, enhance the reliability of the circuit pattern, and avoid the high temperature heat treatment on the copper surface. Oxidation and difficulty in achieving copper-nickel metal integration.

To sum up, compared with the prior art, the beneficial effects of the present invention are:

Compared with the existing similar manufacturing technology, the method for manufacturing a conductive circuit of a printed circuit provided by the present invention overcomes various deficiencies in the implementation process. Its advantages are mainly manifested in: (1) the tin layer etching speed is fast, the accuracy is high, the circuit is complete without side etching and the surface is uniform and smooth, which is conducive to the production of high-precision circuit boards and stable high-frequency and high-speed signal transmission; (2) two kinds of copper and tin Metal eutectic forms a uniform alloy layer, releases the stress between metals, prevents local defects caused by inconsistent etching speeds between the tin seed layer and the copper conductive wire, ensures the bonding force between the conductive wire and the underlying insulating medium, reduces the The formation of side etch is eliminated, so that the circuit pattern has good heat resistance, high stability and high reliability; (3) the manufacturing conditions of the process are simple, the manufacturing cost is reduced, and the large-scale mass production is facilitated.

It can be found that the new method for manufacturing conductive lines of printed circuit substrates has obvious advantages in all aspects, whether compared with traditional processes or similar seed layer growth technologies. According to the above theoretical analysis, in the processes of chemical tin plating, tin electroplating, copper electroplating, film stripping, tin etching and other processes involved in the method for making conductive lines of printed circuit substrates of the present invention, the plating solution, film stripping solution, etching solution, etc. There are no special requirements for the manufacturer, model, etc., and it can be a qualified potion additive produced by any manufacturer.

Description of drawings

1 is a process flow diagram of a method for manufacturing a printed circuit conductive circuit provided by the present invention;

Fig. 2 is the process flow diagram of the manufacturing method of the traditional printed circuit conductive line using alkaline etching solution;

3 is a process flow diagram of a method for making a conventional printed circuit conductive circuit using an acidic etching solution;

FIG. 4 is a schematic diagram of the effect and a metallographic section diagram of Example 1; wherein, FIG. 4-(a) is a schematic diagram of the effect of growing a tin seed layer on an epoxy resin substrate, and FIG. 4-(b) is a growth diagram on the epoxy resin substrate. The metallographic section view of the tin seed layer, Figure 4-(c) is a schematic diagram of the effect of the electroplated copper layer on the surface of the tin seed layer, and Figure 4-(d) is the metallographic section view of the electroplated copper layer on the surface of the tin seed layer, Figure 4- (e) is a schematic diagram of the effect of generating a copper-tin alloy after heat treatment, and FIG. 4-(f) is a metallographic section view of the copper-tin alloy generated after heat treatment;

5 is a cross-sectional SEM image and an EDS spectrogram of the conductive circuit after heat treatment in Example 1;

FIG. 6 is a cross-sectional metallographic section view of the conductive circuit of the printed circuit obtained on the epoxy resin substrate in Example 1. FIG.

Detailed ways

The present application will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can understand the solutions and features of the present invention.

Example 1

A 20mm*100mm epoxy resin substrate was cut, and after plasma surface treatment, a tin seed layer with a thickness of 2 μm was grown on the surface of the substrate by electroless tin plating by immersion plating according to the formula of the plating solution shown in Table 1; Cover the patterned dry film; then electroplate copper according to the bath formula shown in Table 2, and form copper conductive lines on the tin seed layer area not covered by the dry film on the surface of the substrate. The dry film was removed in sodium oxide solution; then heat-treated at 180°C for 30s, taken out after heat-treatment and cooled to room temperature naturally; finally, the area of the tin seed layer not covered by the electroplated copper layer was etched to obtain a printed circuit conductive line.

Table 1 The plating solution formula for growing tin seed layer

Bath composition concentration stannous sulfate 20g/L Thiourea 70g/L citric acid 40g/L sodium hypophosphite 70g/L Quinol 4g/L Emulsifier (OP-10) 1mL/L sulfuric acid 2.5mL/L

Table 2 The plating solution formula of electroplating copper

Bath composition concentration Copper sulfate pentahydrate 75g/L sulfuric acid 240g/L Chloride 60mg/L Sodium Polydithiopropane Sulfonate (SPS) 1mg/L Ethylene oxide-propylene oxide block copolymer (EO/PO) 500mg/L

Observe the growth of tin seed layer on the epoxy resin substrate, the electroplated copper layer on the surface of the tin seed layer, the formation of copper-tin alloy layer after heat treatment, and the slices of the printed circuit conductive circuit obtained on the epoxy resin substrate under a metallographic microscope , the results are shown in Fig. 4-(b), Fig. 4-(d), Fig. 4-(f) and Fig. 6, respectively. The cross-section of the conductive line after heat treatment was observed under a scanning electron microscope, and the elements of the cross-section were analyzed by EDS. The results are shown in Figure 5. It can be seen from the figure: (1) The thickness of the tin seed layer grown on the epoxy resin substrate is about 2 μm; (2) After the copper layer is electroplated on the surface of the tin seed layer, the thickness of the tin and copper metal layers is about 6 μm; ( 3) After the heat treatment, the copper-tin boundary disappears, and the copper layer and the tin layer are eutectic to form a copper-tin alloy; (4) The conductive circuit pattern of the printed circuit finally obtained on the epoxy resin substrate is complete, and the degree of side corrosion of the circuit is complete. lighter.

Use 3M Type 600 1/2" wide pressure sensitive tape to firmly adhere to the surface of the conductive traces to exclude air from under the pressure sensitive tape. Complete the action of tearing off the tape within 1 minute after pressing the tape. When tearing off the tape, keep it at a roughly right angle to the surface of the conductive circuit, and quickly apply a pulling force. Complete three tests using the same procedure and method, using uncontaminated tape for each test. The test results show that the bonding force between the conductive line and the underlying epoxy resin substrate is good. The peel strength test result is 0.86N/mm as measured by the peel strength tester, which meets the minimum peel strength specified by the IPC-TM650 standard.

Example 2

Compared with Example 1, the difference between this example is that 15mm*100mm PI (Polyimide, polyimide) is used as the substrate, and the surface treatment method is immersed in 1mol/L KOH solution for 10 minutes. The remaining steps are the same as Example 1 is the same.

Example 3

Compared with Example 1, the difference between this example is that 15mm*100mm PET (PolyethyleneTerephthalate, polyethylene terephthalate) is used as the substrate, and the surface treatment is immersed in 1mol/L KOH solution for 10 minutes. The rest of the steps are the same as in Example 1.

The above-mentioned example only expresses an embodiment of the present invention, and its description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims (5)

1. a preparation method of a printed circuit conductive circuit, is characterized in that, comprises the following steps: Step 1: grow a tin seed layer on the surface of the printed circuit insulating substrate; Step 2: Cover the tin seed layer grown in Step 1 with a patterned dry film as a plating resist; Step 3: electroplating copper on the tin seed layer area of the substrate obtained in step 2 that is not covered by the dry film to form a copper conductive circuit; Step 4: removing the dry film on the substrate obtained after the copper electroplating in Step 3; Step 5: heat-treating the substrate obtained after the treatment in Step 4, so that the copper conductive circuit and the tin seed layer are eutectic and integrated; Step 6: Etch the area of the tin seed layer on the surface of the substrate obtained after the treatment in Step 5, which is not covered by the electroplated copper layer, to obtain a printed circuit conductive circuit. 2 . The method for manufacturing a conductive circuit of a printed circuit according to claim 1 , wherein the tin seed layer grown in step 1 has a thickness of 1-2 μm. 3 . 3 . The method for manufacturing a conductive circuit of a printed circuit according to claim 1 , wherein the patterned dry film in step 2 is obtained by using a photographic plate or by using a laser direct imaging technique. 4 . 4 . The method for manufacturing a conductive circuit of a printed circuit according to claim 1 , wherein the thickness of the copper conductive circuit in step 3 is 5-100 μm. 5 . 5 . The method for manufacturing a printed circuit conductive line according to claim 1 , wherein the temperature of the heat treatment in step 5 is 180° C.˜200° C., and the heat treatment time is 30 s. 6 .

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