Solder resist ink and method for manufacturing solder resist on a circuit board

Abstract

The application discloses a kind of solder resist ink and circuit board solder resist manufacturing method. Among them, the solder resist ink includes the following component raw materials: thermosetting epoxy-phenolic resin prepolymer 100 mass parts;Microcapsule curing agent 6~8 phr;Silicon-aluminum hydroxide powder flame retardant filler 25~35 phr;Phthalocyanine green pigment 3~5 phr;DBE-BCS mixed solvent 15~20 phr;Polyether modified siloxane leveling agent 0.3~0.5 phr;Phosphate adhesion promoter 0.2~0.4 phr;Circuit board solder resist manufacturing first uses the solder resist ink inkjet printing to obtain solder resist pattern, then microwave preheating and hot air curing are carried out.The solder resist ink of the application adopts thermosetting epoxy-phenolic system to cooperate latent curing agent, completely cancels the light initiator and active diluent of traditional UV ink, and cost is lower and curing time is shorter;By silicon powder and aluminum hydroxide synergistic flame retardant, it can pass through soldering tin test under halogen-free condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of circuit board; more particularly, it relates to a solder resist ink and a solder resist manufacturing method of circuit board. BACKGROUND

[0002] Traditional solder resist ink for circuit board usually uses UV (ultraviolet) curable ink, which contains acrylate oligomer, photoinitiator (3-5 wt.%), reactive diluent (15-20 wt.%), halogen flame retardant (8-12 wt.%), and color filler, etc. The typical process for making solder resist pattern of circuit board using such solder resist ink includes the following steps: screen printing or curtain coating UV ink → ultraviolet exposure → dilute alkali development → secondary UV curing.

[0003] Since UV curable ink relies on ultraviolet sensitive components to achieve free radical polymerization, it has the following inherent defects: 1) the photoinitiator and reactive diluent are expensive, and the residual photoinitiator after curing is easy to migrate to the solder resist surface, resulting in a decrease in insulation reliability; 2) the exposure-development process is long, the equipment occupies a large area, and the energy consumption is high; 3) uneven distribution of ultraviolet energy during exposure can cause side etching and line width loss, making it difficult to achieve high resolution in fine lines below 50 μm; 4) the photosensitive resin system needs to use halogen-containing flame retardant to pass the solder resistance test, which has great environmental pressure. SUMMARY

[0004] In order to at least partially solve the problems of the prior art, the first aspect of the present application provides a solder resist ink for inkjet printing to make solder resist pattern of circuit board; the solder resist ink comprises:

[0005] thermosetting epoxy-phenolic resin prepolymer 100 parts by mass;

[0006] microcapsule curing agent 6-8 phr;

[0007] silicon-aluminum hydroxide powder flame retardant filler 25-35 phr;

[0008] phthalocyanine green pigment 3-5 phr;

[0009] DBE-BCS mixed solvent 15-20 phr;

[0010] polyether modified siloxane leveling agent 0.3-0.5 phr;

[0011] phosphate adhesion promoter 0.2-0.4 phr.

[0012] Further, the thermosetting epoxy-phenolic resin prepolymer is polymerized from bisphenol A / F type epoxy resin and phenolic epoxy resin, wherein the mass ratio of the bisphenol A / F type epoxy resin to the phenolic epoxy resin is 6-4:1.

[0013] Preferably, the epoxy equivalent weight of the thermosetting epoxy-phenolic resin prepolymer is 180-200 g / eq, so that the solder resist pattern has good heat resistance and chemical resistance.

[0014] Further, the microcapsule curing agent is prepared by dissolving dicyandiamide and imidazole-epoxy adduct in a proper amount of ethylene glycol butyl ether at a mass ratio of 1:0.05-0.15, then dropping into the melamine-formaldehyde prepolymer under shearing conditions, adjusting the pH to 5-6, and then performing in-situ polymerization.

[0015] Preferably, the number average particle size D50 of the microcapsule curing agent is 1-3 μm.

[0016] Further, the silicon-aluminum hydroxide powder flame-retardant filler is modified by adding silicon powder and aluminum hydroxide powder at a mass ratio of 2:1 into anhydrous ethanol solution containing 1-2 wt.% of 3-aminopropyl triethoxysilane, refluxing, filtering, and drying to obtain a hydrophobically modified silicon-aluminum hydroxide powder flame-retardant filler.

[0017] Further, the viscosity of the solder resist ink is 8-12 cP, which can be adapted to high-precision nozzles such as Ricoh Gen5 and Fujifilm Samba, to realize inkjet direct writing with a line width / pitch of 50 μm.

[0018] The second aspect of the present application discloses a circuit board solder resist manufacturing method, comprising the following steps:

[0019] S10, after heating the circuit board to 45-55℃, using the solder resist ink described above to inkjet print a solder resist pattern on the surface of the circuit board;

[0020] S20, microwave preheating to reduce the viscosity of the solder resist ink to ≤5 cP, to promote leveling;

[0021] S30, hot air curing to make the curing degree of the solder resist ink ≥95%.

[0022] According to one specific embodiment of the present application, the parameters of the microwave preheating are: frequency 2.45 GHz, power density 2-4 W / cm², temperature 60-80℃, and time 30-60 s.

[0023] According to one specific embodiment of the present application, step S30 uses a hot air circulating tunnel furnace for curing, and the parameters of the hot air curing are: temperature 120-150℃, and time 15-30 min.

[0024] The technical solution of the present application has the following beneficial effects:

[0025] 1. The solder resist ink of the present application completely cancels the photoinitiator and active diluent, directly reduces the raw material cost by more than 30% compared with traditional UV curing ink, and reduces VOC emissions.

[0026] 2. The solder resist ink of the present application adopts a thermosetting epoxy-phenolic system combined with a latent curing agent, and is crosslinked and cured after microwave preheating at 60-80 ℃ and hot baking at 120-150 ℃, the curing time is shortened from 30-60 min of traditional UV system to 15-30 min, and the cured film has higher Tg (glass transition temperature) and insulation reliability and lower CTE (thermal expansion coefficient).

[0027] 3. The solder resist ink of the present application can meet the IPC-SM-840 solder resistance requirement of 288 ℃ / 10 s without blistering by synergistic flame retardation of silicon powder and aluminum hydroxide powder.

[0028] 4. The production of the circuit board solder resist of the present application does not need to be subjected to ultraviolet exposure, the process steps are reduced from "coating-exposure-development-secondary curing" to "inkjet-microwave preheating-hot air curing", which significantly reduces equipment investment and energy consumption. DETAILED DESCRIPTION

[0029] In the following description, many specific details are set forth in connection with the implementation in order to provide a thorough understanding of the present application, but it should be understood that the following implementation and detailed description are only for the purpose of illustration and do not limit the scope of protection of the present application.

[0030] Solder resist ink

[0031] The present application provides a green solder resist ink without photoinitiator, which comprises the following raw material components:

[0032] Thermosetting epoxy-phenolic resin prepolymer 100 parts by mass;

[0033] Microcapsule curing agent 6-8 phr;

[0034] Silicon-aluminum hydroxide powder flame retardant filler 25-35 phr;

[0035] Phthalocyanine green pigment 3-5 phr;

[0036] DBE-BCS mixed solvent 15-20 phr;

[0037] Polyether modified siloxane leveling agent 0.3-0.5 phr;

[0038] Phosphate adhesion promoter 0.2-0.4 phr.

[0039] Specifically, the preparation method of the solder resist ink comprises the following steps:

[0040] Step S1: resin prepolymerization

[0041] Bisphenol A / F type epoxy resin E51 and phenolic epoxy resin F51 were put into the reaction kettle at a mass ratio of 6:1~4:1, dehydrated at 90~110℃, vacuum degree-0.09 MPa, stirring for 30 min, to get prepolymer P0 with epoxy equivalent EEW=180~200 g / eq.

[0042] Epoxy equivalent EEW (Epoxy Equivalent Weight, molecular weight / number of epoxy groups in each molecule) determines the amount of curing agent, epoxy resin needs to react with curing agent to form the final product, the required curing agent can be calculated by EEW. Generally, the lower the EEW value, the more epoxy groups contained in unit mass of resin, the shorter the molecular chain, the greater the crosslinking potential, the network density after curing may be higher, tend to have higher heat resistance and chemical resistance.

[0043] In the present application, the epoxy equivalent of the thermosetting epoxy-phenolic resin prepolymer is 180~200 g / eq, and the solder resist pattern obtained has good heat resistance and chemical resistance.

[0044] Step S2: latent curing agent microencapsulation

[0045] First, dicyandiamide (DICY) and imidazole-epoxy adduct (such as Aradur 3986 of American Huntsman Company) were dissolved in ethylene glycol butyl ether (BCS) at a mass ratio of 1:0.05~1:0.15 to obtain a solution with a total concentration of dicyandiamide (DICY) and imidazole-epoxy adduct of 10%~17 wt.%, which can ensure good fluidity of the solution, facilitating dropwise addition and subsequent reaction. Then, it was added dropwise into the melamine-formaldehyde prepolymer (its amount was 20~100% of the total amount of dicyandiamide and imidazole-epoxy adduct) used to form the capsule wall material under the condition of 40℃ and 500 rpm shearing, the pH was adjusted to 5~6, and the in-situ polymerization was carried out for 60 min to form microcapsule curing agent C1 with number average particle size D50=1~3μm, which can ensure rapid release of active amine above 120℃.

[0046] Step S3: surface modification of functional filler

[0047] Silicon powder (5~10μm) and aluminum hydroxide powder (1~3μm) were added to anhydrous ethanol solution containing 3-aminopropyl triethoxysilane KH-550 at a mass ratio of 2:1, refluxed at 60℃ for 2h, and then filtered and dried to obtain hydrophobic modified filler F1 with surface contact angle θ≥110°.

[0048] Silicon powder and aluminum hydroxide powder are commonly used flame-retardant fillers, but their surfaces are usually hydrophilic, which is not conducive to uniform dispersion in the solder resist ink system, and may also cause problems such as nozzle blockage during inkjet printing. By using anhydrous ethanol solution of 3-aminopropyl triethoxysilane (KH-550) to modify the surface of the silicon powder and aluminum hydroxide powder, the surface of the silicon powder and aluminum hydroxide powder can be hydrophobized, the dispersibility of the silicon powder and aluminum hydroxide powder in the ink can be improved, the nozzle blockage phenomenon during inkjet printing can be prevented, and the compatibility between the filler and the ink matrix can also be improved.

[0049] Step S4: Homogeneous dispersion of ink

[0050] In a planetary centrifugal deaerator, the following are sequentially added: 100 parts by mass of the prepolymer P0 of step S1, 6-8 phr of the microcapsule curing agent C1 of step S2, 25-35 phr of the modified filler F1 of step S3, 3-5 phr of a high-temperature-resistant phthalocyanine green pigment (such as Heliogen Green L 8730 from BASF), 15-20 phr of a binary ester (DBE)-BCS mixed solvent (volume ratio 1:1), 0.3-0.5 phr of a polyether-modified siloxane leveling agent (such as SL-506 from SLOK), and 0.2-0.4 phr of a phosphate adhesion promoter (such as a methacrylic acid phosphate adhesion promoter).

[0051] At a rotation speed of 2000 rpm, a vacuum of -0.08 MPa, and a dispersion time of 30 min, an inkjet ink INK-A with a viscosity η=8-12 cP (centipoise, 25°C) and a surface tension γ=30-35 mN / m is obtained.

[0052] Solder resist manufacturing of circuit board

[0053] The circuit board solder resist manufacturing method of the present application comprises the following steps:

[0054] S10, after heating the circuit board to 45-55°C, using the aforementioned solder resist ink to inkjet print a solder resist pattern on the surface of the circuit board; wherein the inkjet printing can use a Ricoh Gen5 nozzle to achieve a line width of 50 μm.

[0055] S20, microwave preheating to reduce the viscosity of the solder resist ink to ≤5 cP and promote leveling; wherein the parameters of the microwave preheating are: frequency 2.45 GHz, power density 2-4 W / cm², temperature 60-80°C, and time 30-60 s.

[0056] S30, hot air curing to make the curing degree of the solder resist ink ≥95%; specifically, using a hot air circulating tunnel furnace for curing, and the parameters of the hot air curing are: temperature 120-150°C, and time 15-30 min.

[0057] During hot air curing, the microcapsules rupture and release the curing agent, and the solder resist ink undergoes the following cross-linking reactions: epoxy group + amine group → β-hydroxy tertiary amine network, epoxy group + hydroxyl group → ether bond cross-linking.

[0058] The present invention will now be described in further detail with reference to the embodiments.

[0059] Example 1

[0060] Solder resist ink

[0061] The solder resist ink of Example 1 comprises the following raw material components:

[0062] 100 parts by weight of thermosetting epoxy-phenolic resin prepolymer;

[0063] Microcapsule curing agent 7 phr;

[0064] Silicon-aluminum hydroxide powder flame retardant filler 30 phr;

[0065] Phthalocyanine green pigment 4 phr;

[0066] DBE-BCS mixed solvent 18 phr;

[0067] Polyether-modified siloxane leveling agent 0.4 phr;

[0068] Phosphate adhesion promoter 0.3 phr.

[0069] The preparation method of the solder resist ink in Example 1 includes the following steps:

[0070] Step S1: Resin prepolymerization

[0071] Bisphenol A type epoxy resin E51 and phenolic epoxy resin F51 were added to a reactor at a mass ratio of 5:1 and stirred for 30 min at 100℃ and a vacuum degree of -0.09 MPa to dehydrate, thereby obtaining a prepolymer with an epoxy equivalent EEW of 180~200 g / eq.

[0072] Step S2: Microencapsulation of latent curing agent

[0073] Dicyandiamide (DICY) and imidazole-epoxy adduct (Aradur 3986 from Huntsman, USA) were dissolved in an appropriate amount of ethylene glycol butyl ether (BCS) at a ratio of 1:0.1 to obtain a solution with a total concentration of approximately 15 wt.% for dicyandiamide and imidazole-epoxy adduct. This solution was then added dropwise to melamine-formaldehyde prepolymer (50% of the total amount of dicyandiamide and imidazole-epoxy adduct) under shear conditions of 40°C and 500 rpm. The pH was adjusted to 5-6, and in-situ polymerization was carried out for 60 min to form microcapsule curing agents with a number average particle size D50 of 1-3 μm.

[0074] Step S3: Functional filler surface modification

[0075] Silica powder (5-10 μm) and aluminum hydroxide (1-3 μm) were added to a 3- aminopropyltriethoxysilane KH-550 solution with a content of 1.5 wt.% in anhydrous ethanol at a mass ratio of 2:1, and refluxed at 60°C for 2h. After filtration and drying, a hydrophobic modified filler with a surface contact angle θ≥110° was obtained.

[0076] Step S4: Ink homogenization and dispersion

[0077] In a planetary centrifugal deaerator, the following were sequentially added: 100 parts by mass of the prepolymer P0 of step S1, 7 phr of the microcapsule curing agent C1 of step S2, 30 phr of the modified filler F1 of step S3, 4 phr of a high-temperature-resistant phthalocyanine green pigment (Heliogen Green L 8730 from BASF), 18 phr of a dibasic ester (DBE)-BCS mixed solvent, 0.4 phr of a polyether-modified siloxane leveling agent (SL-506 from SLOK), and 0.3 phr of a phosphate adhesion promoter. The dispersion was carried out at a rotation speed of 2000 rpm, a vacuum of -0.08 MPa, and for 30 min.

[0078] It was tested that the solder resist ink of Example 1 had a viscosity η=10±1 cP (centipoise, 25°C) and a surface tension γ=32±1 mN / m.

[0079] <Manufacture of circuit board solder resist>

[0080] S10, after heating the circuit board to 50°C, the solder resist ink described above was used to inkjet print a solder resist pattern on the surface of the circuit board; wherein the inkjet printing can use a Ricoh Gen5 nozzle to achieve a line width of 50 μm.

[0081] S20, microwave preheating to reduce the viscosity of the solder resist ink to ≤5 cP to facilitate leveling; wherein the parameters of the microwave preheating are: frequency 2.45 GHz, power density 3 W / cm², temperature 70°C, and time 45 s.

[0082] S30, hot air curing to make the curing degree of the solder resist ink ≥95%; specifically, a hot air circulation tunnel furnace with a power of 3 kW / m² was used for curing, and the parameters of the hot air curing are: temperature 130°C, and time 25 min.

[0083] Example 2

[0084] The difference between Example 2 and Example 1 is that the solder resist ink in Example 2 includes the following raw material components:

[0085] Thermosetting epoxy-phenolic resin prepolymer 100 parts by mass;

[0086] Microcapsule curing agent 8 phr;

[0087] Silicon-aluminum hydroxide powder flame retardant filler 35 phr;

[0088] Phthalocyanine green pigment 3 phr;

[0089] DBE-BCS mixed solvent 15 phr;

[0090] Polyether modified siloxane leveling agent 0.3 phr;

[0091] Phosphate adhesion promoter 0.4 phr.

[0092] The solder resist ink in Example 2 was tested to have a viscosity η = 10 ± 1 cP (centipoise, 25 °C), a surface tension γ = 32 ± 1 mN / m.

[0093] Example 3

[0094] Example 3 differs from Example 1 in that the solder resist ink in Example 3 includes the following raw material components:

[0095] Thermosetting epoxy-phenolic resin prepolymer 100 parts by mass;

[0096] Microcapsule curing agent 6 phr;

[0097] Silicon-aluminum hydroxide powder flame retardant filler 25 phr;

[0098] Phthalocyanine green pigment 5 phr;

[0099] DBE-BCS mixed solvent 20 phr;

[0100] Polyether modified siloxane leveling agent 0.5 phr;

[0101] Phosphate adhesion promoter 0.2 phr.

[0102] The solder resist ink in Example 3 was tested to have a viscosity η = 10 ± 1 cP (centipoise, 25 °C), a surface tension γ = 32 ± 1 mN / m.

[0103] Performance testing of solder resist pattern (cured film)

[0104] The test standards / conditions used by the present application are as follows:

[0105] Pencil hardness: ASTM D3363.

[0106] Glass transition temperature (Tg): DSC heating rate 10 °C / min.

[0107] Coefficient of thermal expansion (CTE): TMA (Thermal Mechanical Analysis) 50~260℃.

[0108] Solder resistance: IPC-SM-840.

[0109] Insulation reliability: IEC 61189-3.

[0110] The test results are shown in Table 1 below:

[0111] Table 1: Comparison of test results

[0112] Test item Conventional UV ink Example 1 Example 2 Example 3 Pencil hardness 6H ≥6H ≥6H ≥6H Tg 120~130℃ ≥150℃ ≥155°C 145~150°C CTE (50-260°C) 60-80 pm / °C ≤30 ppm / °C ≤28 ppm / °C 30-35 ppm / °C Solder resistance Need to contain halogen flame retardant Halogen-free pass 288°C / 10s test Halogen-free pass 288°C / 10s test Halogen-free pass 288°C / 10s test Insulation reliability 1 x 10 7 Ω (85°C / 85% RH, 500 h) ≥ 1 x 10 8 Ω (85°C / 85% RH, 1000 h) ≥ 1 x 10 8 Ω (85°C / 85% RH, 1000 h) ≥ 1 x 10 8 Ω (85°C / 85% RH, 1000 h)

[0113] Generally, the power of the exposure machine for traditional UV ink solder mask manufacturing is ≥10 kW / m², and the heating power consumption of the developing machine is ≥5 kW, while the microwave preheating power of the solder mask manufacturing of the present application is 2~4 W / cm², and the hot air curing power is 3 kW / m², which is significantly lower in energy consumption compared with the traditional process.

[0114] In addition, compared with the traditional UV curing ink, the solder mask ink of the present application completely cancels the harmful substances of photoinitiator, active diluent and halogen flame retardant, solves the problem of poor surface curing caused by oxygen inhibition in the traditional UV system which needs to rely on ultraviolet light to initiate free radical polymerization, improves the process yield from 90~92% to ≥98%, and significantly reduces VOC emissions (from ≥300 g / L to ≤120 g / L, in line with GB 30981-2020).

[0115] Although the present application is disclosed above with specific embodiments, these specific embodiments are not intended to limit the scope of the present application. Any person of ordinary skill in the art can make some changes / replacements without departing from the scope of the present application, and any equivalent changes made in accordance with the present application should be covered by the protection scope of the present application.

Claims

1. A method for fabricating solder mask on a circuit board, characterized in that... Includes the following steps: S10, After heating the circuit board to 45~55℃, use solder resist ink to inkjet print solder resist patterns on the surface of the circuit board. S20, microwave preheating, to reduce the viscosity of solder resist ink to ≤5cP; microwave preheating temperature 60~80℃, time 30~60s; S30, hot air curing, to achieve a curing degree of ≥95% for the solder resist ink; hot air curing temperature 120~150℃, time 15~30min; The solder resist ink is used for printing solder resist patterns on circuit boards and includes the following raw materials: 100 parts by weight of thermosetting epoxy-phenolic resin prepolymer; Microcapsule curing agent 6~8 phr; Silicon-aluminum hydroxide powder flame retardant filler 25~35 phr; Phthalocyanine green pigment 3~5 phr; DBE-BCS mixed solvent 15~20 phr; Polyether-modified siloxane leveling agent 0.3~0.5 phr; Phosphate ester adhesion promoter 0.2~0.4 phr; The thermosetting epoxy-phenolic resin prepolymer is obtained as follows: bisphenol A type epoxy resin E51 and phenolic epoxy resin F51 are added to a reaction vessel at a mass ratio of 6:1 to 4:1, and the mixture is stirred for 30 minutes at 90 to 110°C and a vacuum of -0.09 MPa to remove water; the epoxy equivalent of the thermosetting epoxy-phenolic resin prepolymer is 180 to 200 g / eq. The microcapsule curing agent is prepared as follows: first, dicyandiamide and imidazole-epoxy adduct are dissolved in an appropriate amount of ethylene glycol butyl ether at a mass ratio of 1:0.05~0.15, and then dropped into melamine-formaldehyde prepolymer under shear conditions. After adjusting the pH to 5~6, in-situ polymerization is carried out. The silicon-aluminum hydroxide powder flame retardant filler is modified as follows: silicon powder and aluminum hydroxide powder are added to an anhydrous ethanol solution containing 1~2 wt.% of 3-aminopropyltriethoxysilane at a mass ratio of 2:

1. After reflux reaction, the mixture is filtered and dried to obtain hydrophobically modified silicon-aluminum hydroxide powder flame retardant filler.

2. The method for fabricating solder mask on a circuit board according to claim 1, characterized in that: The number-average particle size D50 of the microcapsule curing agent is 1~3μm.

3. The method for fabricating solder mask on a circuit board according to any one of claims 1 to 2, characterized in that: The viscosity of the solder resist ink at 25°C is 8~12 cP.

4. The method for fabricating solder mask on a circuit board according to claim 1, characterized in that... The microwave preheating frequency is 2.45 GHz, and the power density is 2~4 W / cm².

5. The method for fabricating solder mask on a circuit board according to claim 1, characterized in that... Step S30 involves curing using a hot air circulating tunnel oven.