A PCB browning treatment liquid and preparation method thereof

Abstract

The invention discloses a PCB browning treatment liquid and a preparation method thereof, and relates to the technical field of circuit board treatment agents. The browning treatment liquid is prepared from the following components: 80-120 g / L of concentrated sulfuric acid, 10-20 g / L of hydrogen peroxide, 8-16 g / L of corrosion inhibitor, 20-50 mg / L of halogen ions, 10-20 g / L of anhydrous ethanol, and the balance is deionized water. The prepared browning treatment liquid has high copper loading and good thermal stability, and can play a role in efficient corrosion inhibition and protection for copper surfaces. The solution after browning treatment is clear and has no precipitation, thereby reducing the problem of PCB short circuit. After the treatment liquid is browned, the interlayer peeling strength of a multilayer board formed after lamination is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of circuit board treatment agents, and in particular to a PCB browning treatment liquid and a preparation method thereof. Background Art

[0002] Printed circuit board (PCB) is one of the indispensable electronic components in the electronics industry. It is a platform to ensure the electrical interconnection of various electronic components. It is used in almost all electronic devices, from calculators, smart phones, laptops to aerospace equipment, military weapon systems, etc. PCB is very diverse in material selection, layer requirements and production process to meet the needs of different types of electronic products, so there are different classification methods according to different standards. The polymer substrate used in PCB manufacturing is glass fiber cloth reinforced epoxy resin, acrylic resin, polytetrafluoroethylene and polyimide and other polymers. A layer of copper foil is covered on one or both sides of the polymer substrate, and then a dry film is covered on the copper surface. After exposure, development, etching and other processes, a circuit pattern is formed on the copper surface. Single-sided or double-sided printed circuit boards are usually made in this way.

[0003] Since the electrical interconnection provided by single-sided and double-sided boards is very limited, the currently widely used multi-layer circuit boards were developed. Double-sided boards are also called inner-layer boards. Double-sided boards are stacked up, and the layers are separated by semi-cured resin. After lamination, a multi-layer board is formed.

[0004] In the production and manufacturing of printed circuit boards, improving and improving the interlayer bonding strength has always been an important research content to improve the thermal stability of multilayer boards. Since the 1980s, in order to improve the bonding strength between copper and resin, micro-etching methods (such as sodium persulfate and sulfuric acid, etc.), black oxide method (Black oxide) and brown oxide method (Brown oxide) have been used successively.

[0005] Most of the black oxidation solutions on the market use sodium chlorite and sodium hydroxide as the main raw materials, and sodium carbonate is added as a buffer. However, the use of the sodium carbonate system as a buffer has the following disadvantages: the alkalinity of the entire tank solution is relatively high and the buffering performance is poor, which is not conducive to the operator's control of the alkalinity of the solution. Poor control of alkalinity will directly lead to a loose structure of the generated black oxide layer, and the copper surface treated by the black oxidation method is prone to uneven color, and is easy to break when combined with the resin later, so that the peel strength between the copper surface and the resin is not high, usually only maintained between 7.0 and 8.0 N / cm. The current mainstream treatment technology for improving the bonding strength of the inner layer is the browning method (sulfuric acid and hydrogen peroxide system), also known as the organic copper oxidation method.

[0006] The copper surface treated by the browning process is an organic copper film layer, which is controlled by organic additives to control the corrosion of the copper surface. The oxidant oxidizes Cu to form Cu2O, and then the organic additive and Cu2O form an organic copper oxide layer through chemical bonding. This organic copper oxide film layer can provide better interface bonding between copper and prepreg (PP) resin. Since Cu2O has better thermal stability than CuO and better chemical corrosion resistance, the pink circle problem around the drill hole can be avoided as much as possible during the subsequent hole metallization process. After the copper treated by browning is pressed with the substrate resin, it has higher peel strength and better heat resistance. Compared with the complex black oxidation process, the browning process is simple and easy, with a short operation process, which is convenient for production monitoring.

[0007] Chinese patent document CN202010365227.1 discloses a browning liquid for printed circuit boards, which belongs to the field of circuit board technology and is made of the following components: an aqueous solution of an inorganic acid, an oxidant, a corrosion inhibitor, a stabilizer, an inorganic salt, an additive, a plasticizer, and N-methylpyrrolidone; the inorganic acid is one of sulfuric acid, nitric acid, and phosphoric acid, the oxidant is hydrogen peroxide, and the corrosion inhibitor is one of benzotriazole and 4-hydroxybenzotriazole.

[0008] During the reaction between copper and browning liquid, copper is continuously dissolved in the browning liquid to become divalent copper ions because it is in an acidic medium and hydrogen peroxide is present. Therefore, in the actual production process, as the number of copper plates contacted by the browning liquid increases, the copper ion content in the solution increases. In the prior art, the copper loading of the browning treatment liquid is low. When the copper ion concentration exceeds 25g / L, the decomposition rate of hydrogen peroxide accelerates, resulting in the formation of a large amount of dark brown sludge-like precipitation in the solution, causing the solution to fail. The solution must be replaced or a portion of the solution must be drained, and a new solution must be added to reduce the copper ion content in the solution to maintain the efficacy of the solution. Summary of the invention

[0009] In order to solve the shortcomings of the prior art, the purpose of the present invention is to provide a PCB browning treatment liquid and a preparation method thereof. The prepared browning treatment liquid has a high copper load and good thermal stability, can play an efficient corrosion inhibition and protection role on the copper surface, and the solution after the browning treatment is clear and has no precipitation, which reduces the PCB short circuit problem. After the treatment liquid is browned, the interlayer peeling strength of the multilayer board formed after lamination is effectively improved.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] A PCB browning treatment liquid is prepared from the following components: 80-120 g / L of concentrated sulfuric acid, 10-20 g / L of hydrogen peroxide, 8-16 g / L of corrosion inhibitor, 20-50 mg / L of halogen ions, 10-20 g / L of anhydrous ethanol, and the balance is deionized water.

[0012] Preferably, the method for preparing the corrosion inhibitor comprises the following steps:

[0013] (1) 2-Mercaptobenzimidazole and cinnamaldehyde are added to anhydrous ethanol, ultrasonically vibrated, nitrogen is continuously introduced, azobisisobutyronitrile is added dropwise under stirring, heated in a water bath for reaction, and the reactants are washed to obtain compound a; the main reaction process is as follows:

[0014]

[0015] (2) Compound a and tris(hydroxymethyl)aminomethane are added to a solvent, stirred and mixed evenly, then glacial acetic acid is added dropwise, stirred and reacted, the reaction liquid is filtered, the filtrate is allowed to stand and cool, crystals are precipitated, and the corrosion inhibitor is obtained.

[0016] The main reaction process is as follows:

[0017]

[0018] Preferably, in step (1), the weight ratio of 2-mercaptobenzimidazole, cinnamaldehyde and azobisisobutyronitrile is 15:13.2-15.8:0.28-0.56.

[0019] Preferably, in step (1), ultrasonic oscillation is performed for 5 to 15 minutes, the reaction conditions are stirring at 50 to 80° C. for 4 to 8 hours, and the reactants are rinsed with methanol or acetonitrile after the reaction is completed.

[0020] Preferably, in step (2), the solvent is a mixture of methanol and acetonitrile in a volume ratio of 1:1 to 3.

[0021] Preferably, in step (2), the weight ratio of compound a, tris(hydroxymethyl)aminomethane and glacial acetic acid is 24.6-31.5:9.8-15.6:0.3-1.1.

[0022] Preferably, in step (2), the stirring reaction conditions are 20-60° C. for 8-14 h.

[0023] Preferably, the concentration of the concentrated sulfuric acid is 95-98 wt %.

[0024] Preferably, the halogen ions are provided by NaCl or KCl.

[0025] The present invention also claims protection for a method for preparing the PCB browning treatment liquid, comprising the following steps: adding concentrated sulfuric acid, hydrogen peroxide, corrosion inhibitor, halogen ions, and anhydrous ethanol to deionized water according to a formula, and mixing them evenly to obtain the PCB browning treatment liquid.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) The present invention provides a PCB browning treatment liquid, which is prepared by compounding concentrated sulfuric acid, hydrogen peroxide, a corrosion inhibitor, halogen ions, anhydrous ethanol, and deionized water. The prepared browning treatment liquid has a high copper loading capacity and good thermal stability, and can play a highly efficient corrosion inhibition and protection role on the copper surface. The solution after the browning treatment is clear and has no precipitation, which reduces the problem of PCB short circuit. After the treatment liquid is browned, the interlayer peeling strength of the multilayer board formed after lamination is effectively improved.

[0028] 2) The present invention provides a corrosion inhibitor for PCB browning treatment liquid, firstly, the thiol group in 2-mercaptobenzimidazole and the unsaturated double bond in cinnamaldehyde undergo a thiol-ene reaction, and a benzene ring and an aldehyde group are introduced to obtain a compound a, and then the aldehyde group in the compound a and the amino group in trishydroxymethylaminomethane undergo a Schiff base reaction under the action of a glacial acetic acid catalyst, and an imine and a large number of hydroxyl groups are introduced to prepare an aromatic Schiff base compound corrosion inhibitor; the corrosion inhibitor contains a large number of lone pairs of electrons of heteroatoms such as N, O, and S and a large π bond of the benzene ring, which can be combined with the empty orbital of the copper atom to form a stable organic metal complex on the copper surface, thereby firmly adsorbing on the metal surface to form a passivation film, thereby producing a corrosion inhibition effect. The corrosion inhibitor also contains a large number of hydroxyl groups, which can react with the divalent copper ions in the browning solution to form a complex reaction, effectively slowing down the accumulation rate of copper ions in the browning solution, increasing the maximum allowable copper loading, and extending the service life of the browning solution. The hydroxyl group can also form an intramolecular hydrogen bond with the imino group in imidazole, thereby improving the thermal stability of the corrosion inhibitor to a certain extent. In addition, the Schiff base structure in the corrosion inhibitor carries a positive charge, and the metal has a negative charge on the surface in an acidic solution with a large number of negative ions. Therefore, the corrosion inhibitor can produce physical and chemical adsorption with the copper surface through electrostatic interaction and chemical bonding, forming a dense and firmly adhered protective film on the copper surface, thereby producing a more efficient and lasting corrosion inhibition effect. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0030] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased from commercial sources or synthesized from raw materials purchased from commercial sources.

[0031] A method for preparing a PCB browning treatment solution comprises the following steps:

[0032] (1) 15 g of 2-mercaptobenzimidazole and 13.2-15.8 g of cinnamaldehyde were added to 50 mL of anhydrous ethanol, and ultrasonically vibrated for 5-15 min. Nitrogen was continuously introduced to remove dissolved oxygen in the mixture. 0.28-0.56 g of azobisisobutyronitrile was added dropwise under stirring. The mixture was stirred at 50-80° C. for 4-8 h. After the reaction was completed, the reactant was washed with methanol and acetonitrile to obtain compound a.

[0033] (2) adding 24.6-31.5 g of compound a and 9.8-15.6 g of tris(hydroxymethyl)aminomethane to a solvent (methanol and acetonitrile mixed in a volume ratio of 1:1-3), stirring and mixing evenly, then dropwise adding 0.3-1.1 g of glacial acetic acid, stirring and reacting at 20-60° C. for 8-14 h, filtering the reaction liquid, and standing the filtrate to cool and precipitate crystals to obtain the corrosion inhibitor;

[0034] (3) 80-120 g of 95-98 wt% concentrated sulfuric acid, 10-20 g of hydrogen peroxide, 8-16 g of corrosion inhibitor, 20-50 mg of halogen ions, and 10-20 g of anhydrous ethanol are mixed evenly, and deionized water is added to adjust to 1 L. After stirring evenly, the PCB browning treatment solution is obtained.

[0035] The present invention will be further described below through specific embodiments.

[0036] Example 1

[0037] A method for preparing a PCB browning treatment solution comprises the following steps:

[0038] (1) 15 g of 2-mercaptobenzimidazole and 15.8 g of cinnamaldehyde were added to 50 mL of anhydrous ethanol, and ultrasonically vibrated for 15 min. Nitrogen was continuously introduced to remove dissolved oxygen in the mixture. 0.56 g of azobisisobutyronitrile was added dropwise under stirring. The mixture was stirred at 80° C. for 4 h. After the reaction was completed, the reactant was rinsed with methanol and acetonitrile to obtain compound a.

[0039] (2) 31.5 g of compound a and 15.6 g of tris(hydroxymethyl)aminomethane were added to a solvent (methanol and acetonitrile were mixed in a volume ratio of 1:3), stirred and mixed evenly, and then 1.1 g of glacial acetic acid was added dropwise, stirred and reacted at 60° C. for 8 h, the reaction liquid was filtered, and the filtrate was allowed to stand and cool to precipitate crystals to obtain the corrosion inhibitor;

[0040] (3) 120 g of 98 wt % concentrated sulfuric acid, 20 g of hydrogen peroxide, 16 g of corrosion inhibitor, 50 mg of NaCl, and 20 g of anhydrous ethanol were mixed evenly, and deionized water was added to adjust to 1 L. After stirring evenly, the PCB browning treatment solution was obtained.

[0041] Example 2

[0042] A method for preparing a PCB browning treatment solution comprises the following steps:

[0043] (1) 15 g of 2-mercaptobenzimidazole and 14.5 g of cinnamaldehyde were added to 50 mL of anhydrous ethanol, and ultrasonically vibrated for 10 min. Nitrogen was continuously introduced to remove dissolved oxygen in the mixture. 0.42 g of azobisisobutyronitrile was added dropwise under stirring, and the mixture was stirred at 75° C. for 6 h. After the reaction was completed, the reactant was rinsed with methanol and acetonitrile to obtain compound a;

[0044] (2) 28.1 g of compound a and 12.7 g of tris(hydroxymethyl)aminomethane were added to a solvent (methanol and acetonitrile were mixed in a volume ratio of 1:3), stirred and mixed evenly, and then 0.7 g of glacial acetic acid was added dropwise, stirred and reacted at 40° C. for 11 h, the reaction liquid was filtered, and the filtrate was allowed to stand and cool to precipitate crystals to obtain the corrosion inhibitor;

[0045] (3) 100 g of 98 wt % concentrated sulfuric acid, 15 g of hydrogen peroxide, 12 g of corrosion inhibitor, 35 mg of NaCl, and 15 g of anhydrous ethanol were mixed evenly, and deionized water was added to adjust to 1 L. After stirring evenly, the PCB browning treatment solution was obtained.

[0046] Example 3

[0047] A method for preparing a PCB browning treatment solution comprises the following steps:

[0048] (1) 15 g of 2-mercaptobenzimidazole and 13.2 g of cinnamaldehyde were added to 50 mL of anhydrous ethanol, and ultrasonically vibrated for 5 min. Nitrogen was continuously introduced to remove dissolved oxygen in the mixture. 0.28 g of azobisisobutyronitrile was added dropwise under stirring, and the mixture was stirred at 50° C. for 8 h. After the reaction was completed, the reactant was rinsed with methanol and acetonitrile to obtain compound a;

[0049] (2) 24.6 g of compound a and 9.8 g of tris(hydroxymethyl)aminomethane were added to a solvent (methanol and acetonitrile were mixed in a volume ratio of 1:3), stirred and mixed evenly, and then 0.3 g of glacial acetic acid was added dropwise, stirred and reacted at 20° C. for 14 h, the reaction liquid was filtered, and the filtrate was allowed to stand and cool to precipitate crystals to obtain the corrosion inhibitor;

[0050] (3) 80 g of 98 wt% concentrated sulfuric acid, 10 g of hydrogen peroxide, 8 g of corrosion inhibitor, 20 mg of halogen ions, and 10 g of anhydrous ethanol were mixed evenly, and deionized water was added to adjust to 1 L. After stirring evenly, the PCB browning treatment solution was obtained.

[0051] Comparative Example 1

[0052] A method for preparing a PCB browning treatment solution comprises the following steps:

[0053] (1) 15 g of 2-mercaptobenzimidazole and 15.8 g of cinnamaldehyde were added to 50 mL of anhydrous ethanol, and ultrasonically vibrated for 15 min. Nitrogen was continuously introduced to remove dissolved oxygen in the mixture. 0.56 g of azobisisobutyronitrile was added dropwise under stirring. The mixture was stirred at 80° C. for 4 h. After the reaction was completed, the reactant was rinsed with methanol and acetonitrile to obtain compound a.

[0054] (2) 120 g of 98 wt % concentrated sulfuric acid, 20 g of hydrogen peroxide, 16 g of compound a, 50 mg of NaCl, and 20 g of anhydrous ethanol were mixed evenly, and deionized water was added to adjust the mixture to 1 L. After stirring evenly, the PCB browning treatment solution was obtained.

[0055] Comparative Example 2

[0056] A method for preparing a PCB browning treatment solution comprises the following steps:

[0057] 120 g of 98 wt % concentrated sulfuric acid, 20 g of hydrogen peroxide, 16 g of 2-mercaptobenzimidazole, 50 mg of NaCl, and 20 g of anhydrous ethanol were mixed evenly, and deionized water was added to adjust the mixture to 1 L. After stirring evenly, the PCB browning treatment solution was obtained.

[0058] The performance of the browning treatment liquid prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was tested. The copper loading of the browning treatment liquid was detected by ion chromatography. After the copper surface was browned and pressed, the delamination and bursting of the board after 6 heat shocks were tested with reference to IPC-TM-650 No. 2.6.8. The peel strength was tested with reference to IPC-TM-650 No. 2.4.8. The lifespan was judged by observing the appearance of the browning liquid and the presence of precipitation.

[0059] Table 1 Browning treatment liquid performance test results

[0060]

[0061]

[0062] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A PCB browning treatment solution, characterized in that: It is made of the following components: concentrated sulfuric acid 80-120 g / L, hydrogen peroxide 10-20 g / L, corrosion inhibitor 8-16 g / L, halogen ion 20-50 mg / L, anhydrous ethanol 10-20 g / L, and the balance is deionized water; The preparation method of the corrosion inhibitor comprises the following steps: (1) 2-Mercaptobenzimidazole and cinnamaldehyde are added to anhydrous ethanol, ultrasonically vibrated, nitrogen is continuously introduced, azobisisobutyronitrile is added dropwise under stirring, heated in a water bath for reaction, and the reactants are washed to obtain compound a; the main reaction process is as follows: (2) Compound a and tris(hydroxymethyl)aminomethane are added to a solvent, stirred and mixed evenly, then glacial acetic acid is added dropwise, stirred and reacted, the reaction liquid is filtered, the filtrate is allowed to stand and cool, crystals are precipitated, and the corrosion inhibitor is obtained; the main reaction process is as follows:

2. The browning treatment liquid according to claim 1, characterized in that In step (1), the weight ratio of 2-mercaptobenzimidazole, cinnamaldehyde and azobisisobutyronitrile is 15: 13.2～15.8：0.28～0.56。 3. The browning treatment liquid according to claim 1, characterized in that: In step (1), ultrasonic oscillation is performed for 5 to 15 minutes, and the reaction conditions are stirring at 50 to 80° C. for 4 to 8 hours. After the reaction is completed, the reactant is rinsed with methanol or acetonitrile.

4. The browning treatment liquid according to claim 1, characterized in that In step (2), the solvent is a mixture of methanol and acetonitrile in a volume ratio of 1:1 to 3.

5. The browning treatment liquid according to claim 1, characterized in that: In step (2), the weight ratio of compound a, tris(hydroxymethyl)aminomethane and glacial acetic acid is 24.6-31.5:9.8-15.6:0.3-1.

1.

6. The browning treatment liquid according to claim 1, characterized in that: In step (2), the stirring reaction conditions are 20-60° C. for 8-14 h.

7. The browning treatment liquid according to claim 1, characterized in that: The concentration of the concentrated sulfuric acid is 95-98 wt %.

8. The browning treatment liquid according to claim 1, characterized in that: The halogen ions are provided by NaCl and KCl.

9. A method for preparing the PCB browning treatment solution according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: adding concentrated sulfuric acid, hydrogen peroxide, corrosion inhibitor, halogen ions and anhydrous ethanol into deionized water according to a formula, and mixing them evenly to obtain the PCB browning treatment liquid.

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