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CN-121194389-B - Novel flexible printed circuit board and camera module prepared based on solderable low-temperature silver paste

CN121194389BCN 121194389 BCN121194389 BCN 121194389BCN-121194389-B

Abstract

The invention discloses a novel flexible printed circuit board and a camera module prepared based on solderable low-temperature silver paste, which belong to the technical field of electronic materials and devices, wherein conductor patterns in the flexible printed circuit board comprise main circuit patterns and auxiliary functional structures formed by the solderable low-temperature solidified silver paste; the welding low-temperature silver paste has a curing temperature of 87-103 ℃, comprises conductive filler, a high-molecular resin system, an ester solvent, a curing agent, a silane coupling agent, a polyamide wax thixotropic agent, a polysiloxane defoamer, a modified carbon nano tube, modified antimony tin oxide powder, a modified ceramic filler and a low-stress modifier, wherein the high-molecular resin system comprises hydrogenated bisphenol A epoxy resin, biphenyl epoxy resin and polyacrylate-CTBN copolymer, and the conductive filler comprises silver-coated copper sheet powder, nano silver wires and low-temperature alloy powder.

Inventors

  • YIN WENGANG
  • LU TAN
  • LUO BING
  • LI QIANG

Assignees

  • 北京中科纳通电子技术有限公司

Dates

Publication Date
20260508
Application Date
20250911

Claims (10)

  1. 1. A flexible printed circuit board prepared based on solderable low-temperature silver paste comprises a flexible insulating substrate and a conductor pattern arranged on the substrate, and is characterized in that the conductor pattern comprises a main circuit pattern formed by calendared copper and an auxiliary functional structure formed by the solderable low-temperature silver paste in a local area of the main circuit pattern, wherein the auxiliary functional structure comprises at least one of a VCM (voice coil motor) driving circuit area, a sensor micro-pad area and a lens holder connecting area; the welding low-temperature silver paste has a curing temperature of 87-103 ℃, and comprises, by mass, 60-72 parts of conductive filler, 12-18 parts of high-molecular resin system, 18-30 parts of ester solvent, 3-6 parts of curing agent, 1-5 parts of silane coupling agent, 0.8-1.5 parts of polyamide wax thixotropic agent, 0.1-0.3 part of polysiloxane defoamer, 0.3-1 part of modified carbon nano tube, 0.5-1.5 parts of modified antimony tin oxide powder, 1-2 parts of modified ceramic filler and 0.8-1.5 parts of low-stress modifier; The high polymer resin system comprises (0.9-1.1): (0.3-0.5) hydrogenated bisphenol A epoxy resin, biphenyl epoxy resin and polyacrylate-carboxyl terminated liquid nitrile rubber copolymer, wherein the conductive filler comprises silver coated copper sheet powder, nano silver wires and low-temperature alloy powder, the D50 range of the silver coated copper sheet powder is 1.0-3.0 mu m, the diameter-thickness ratio is >15, the length of the nano silver wires is 25-45 mu m, the diameter is 30-60 nm, and the low-temperature alloy powder is low-temperature alloy powder with the D50 range of 3-8 mu m.
  2. 2. The flexible printed circuit board according to claim 1, wherein the conductive filler comprises silver-clad copper sheet-like powder, nano silver wires and low-temperature alloy powder in a mass ratio of (1.2-1.8): 1 (0.1-0.3); the low-temperature alloy powder is Sn57.6Bi40Ag2.4 or Sn58Bi42, the curing agent is novolac resin with the mass ratio of (4-5) 1 and imidazole accelerator, the imidazole accelerator is 2-phenylimidazoline or 2-heptadecylimidazole, the silane coupling agent is a mixture of KH-560 with the mass ratio of (1-2) and a silane coupling agent with an anti-migration function, the silane coupling agent with the anti-migration function is KH-590 or phenylmethyltriethoxysilane, the polysiloxane defoamer is a non-silicon defoamer containing foam breaking polysiloxane, and the ester solvent is any one of diethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate or butyl butyrate.
  3. 3. The flexible printed circuit board according to claim 1, wherein the biphenyl type epoxy resin has an epoxy value of 0.50eq/100 g-0.65 eq/100g and a viscosity of 5000 mPa.s-12000 mPa.s at 25 ℃, and the polyacrylate-carboxyl terminated liquid nitrile rubber copolymer is prepared by mixing methyl methacrylate, butyl acrylate and carboxyl terminated liquid nitrile rubber in a mass ratio of (4-5): 1, in the presence of a t-butyl peroxy-2-ethylhexanoate initiator, performing an active radical polymerization reaction at 75 ℃ for 3-5 hours, wherein the mass fraction of carboxyl groups in the carboxyl terminated liquid nitrile rubber is 0.5% -0.7%, the number average molecular weight is 3000 Da-5000 Da, and the mass of the t-butyl peroxy-2-ethylhexanoate initiator is 1.0% -2.0% of the total mass of the methyl methacrylate, the butyl acrylate and the carboxyl terminated liquid nitrile rubber.
  4. 4. The flexible printed circuit board according to claim 1, wherein the preparation method of the modified ceramic filler is that aluminum nitride powder with the particle size of 0.05-0.15 μm is dispersed in absolute ethyl alcohol, a mixed modifier of silane coupling agent KH-560 with the mass ratio of 1 (2-3) and polyethyleneimine is added, the mixed modifier is subjected to ultrasonic stirring reaction for 2-3 hours at 60-70 ℃ at 300-500W, and is calcined for 1-2 hours at 90-105 ℃ after being filtered, wherein the total mass of the mixed modifier is 4-6% of the total mass of the aluminum nitride powder.
  5. 5. The flexible printed circuit board according to claim 1, wherein the polyamide wax thixotropic agent is a polyamide wax formed by condensing ricinoleic acid, dimer fatty acid and ethylenediamine, and the specific operation of activating the polyamide wax thixotropic agent before use is that the polyamide wax is added into a mixed solvent of isopropyl alcohol and propylene glycol methyl ether acetate with a volume ratio of 1:1.5-2.0, aminopropanol is added, the activation temperature is controlled to be 45-55 ℃, the stirring speed is 800-1200 r/min, and the mixture is dispersed and activated at a high speed for 15-30 min, wherein the mass ratio of the polyamide wax, the mixed solvent and the aminopropanol is 1 (4-6) (0.1-0.2).
  6. 6. The flexible printed circuit board according to claim 1, wherein the preparation process of the modified carbon nanotubes is as follows in parts by mass: A1, preparing an electrolyte, namely dispersing 15 parts of carbon nano tubes in 350-450 parts of 1-ethyl-3-methylimidazole bistrifluoromethane sulfonyl imide ionic liquid, adding 3-5 parts of 3-aminopropyl triethoxysilane as a functionalization reagent, and performing ultrasonic treatment for 40-60 min at 500-700W to form a suspension electrolyte; A2, performing electrochemical treatment, namely placing the suspension electrolyte into an electrolytic cell, taking a graphite rod as an anode and a platinum sheet as a cathode, and performing electrolytic reaction for 1.5 h-2.5 h under the stirring of the voltage of 2.5V-3.5V and the voltage of 500 r/min-700 r/min; A3, carrying out post-reaction treatment, namely filtering to obtain a solid after the reaction is finished, alternately centrifugally washing the solid with ethanol and deionized water, carrying out vacuum drying at 70-80 ℃ for 8-12 h to obtain the modified carbon nanotube, wherein the conductivity of the supernatant is less than 5 mu S/cm.
  7. 7. The flexible printed circuit board according to claim 1, wherein the preparation process of the modified antimony tin oxide powder is as follows in parts by mass: B1, preparing a suspension, namely dispersing 10 parts of antimony tin oxide powder with an average particle size of 20-40 nm into 200-250 parts of isopropanol, adding 0.5-1 part of polyvinylpyrrolidone, and performing ultrasonic treatment for 50-70 min at 600-800W to prepare the suspension; B2, in-situ polymerization, namely adding 0.8-1.2 parts of 3, 4-ethylenedioxythiophene monomer into the suspension, stirring for 40-60 min at 15-20 ℃, dropwise adding 3 parts of ethanol solution with the mass concentration of 8-12% potassium persulfate, controlling the dropwise adding temperature to be 20-24 ℃, and reacting for 8-10 h; And B3, carrying out post-reaction treatment, namely after the reaction is finished, carrying out suction filtration, repeatedly washing a filter cake with ethanol and acetone until the filtrate is colorless, carrying out vacuum drying on the filter cake at 60-70 ℃ for 24-36 hours, and sieving the filter cake with a 1000-1250 mesh sieve after grinding to obtain the modified antimony tin oxide powder.
  8. 8. The flexible printed circuit board according to claim 1, wherein the low-stress modifier is carboxyl-terminated polybutadiene acrylonitrile core-shell rubber particles with an average particle diameter ranging from 100nm to 200nm, and the preparation method comprises the following steps of: C1, preparing core emulsion: Placing 80-100 parts of carboxyl-terminated liquid nitrile rubber, 5-10 parts of acrylonitrile, 15-25 parts of deionized water, 1.0-2.5 parts of allyloxy hydroxypropyl sodium sulfonate and 0.5-1.5 parts of pH buffering agent in a reaction kettle, emulsifying for 30-60 min under the stirring of 65-75 ℃ and 200 r/min-400 r/min, then heating to 125-135 ℃ and maintaining the pressure at 0.35-0.45 MPa, reacting for 3-5 h, and cooling and discharging after the reaction is finished to obtain core emulsion; C2, pre-emulsification of shell monomer: mixing 40-60 parts of methyl methacrylate, 2-5 parts of beta-hydroxyethyl methacrylate, 1-3 parts of vinyl triethoxysilane, 1.0-2.0 parts of sodium allyloxy hydroxypropyl sulfonate and 50-70 parts of deionized water, and carrying out high-speed shearing and emulsification for 20-40 min at a speed of 1000-3000 r/min to obtain a shell pre-emulsion; C3, seed emulsion preparation: Adding 20-30 parts of the core emulsion prepared in the step C1 into a reaction kettle, diluting to a solid content of 5-10%, heating to 75-80 ℃, introducing nitrogen for protection, adding 0.1-0.3 part of potassium persulfate aqueous solution with a mass concentration of 2-5% and 1-3 parts of the shell pre-emulsion prepared in the step C2 under stirring, and reacting for 20-40min to obtain seed emulsion; C4, core-shell emulsion polymerization: dripping the residual shell pre-emulsion prepared in the step C2 and 0.5-1.2 parts of potassium persulfate aqueous solution with the mass concentration of 2% -5% into the seed emulsion, controlling the dripping temperature to be 78-82 ℃, and preserving heat and curing for 1.5-2.5 hours after the dripping is finished; And C5, post-treatment: Cooling to room temperature, filtering and discharging by using a 100-200 mesh screen, demulsifying, washing, vacuum drying, grinding, and sieving by using a 500-800 mesh screen to obtain the carboxyl-terminated polybutadiene acrylonitrile core-shell rubber particles.
  9. 9. The flexible printed circuit board of claim 1, wherein the solderable low temperature silver paste is prepared by: s1, adding an ester solvent into a reaction kettle, adding a high polymer resin system, stirring at 60-80 ℃ until the resin is dissolved, adding a silane coupling agent and a polysiloxane defoamer, cooling to room temperature, adding a curing agent, keeping the temperature of the solution below 30 ℃, and stirring until all phases are completely dissolved and mixed to obtain a carrier solution; s2, adding a polyamide wax thixotropic agent into the carrier solution, and stirring and mixing at room temperature to obtain a mixed solution A; s3, adding low-temperature alloy powder and modified ceramic filler into the mixed solution A, and stirring and mixing at room temperature to obtain a mixed solution B; s4, adding the silver-coated copper sheet-like powder and the nano silver wires into the mixed solution B, adding the low-stress modifier, and stirring and mixing at room temperature to obtain a mixed solution C; S5, adding the modified carbon nano tube and the modified antimony tin oxide powder into the mixed solution C, stirring and mixing, and controlling the stirring temperature not to exceed 30 ℃ to obtain a mixed solution D; S6, transferring the mixed solution D onto a three-roller machine, firstly adjusting the gap between a fast roller and a middle roller to 65-75 mu m, adjusting the gap between the middle roller and a slow roller to 25-35 mu m, and grinding for 1-2 times, then adjusting the gap between the fast roller and the middle roller to 35-45 mu m, adjusting the gap between the middle roller and the slow roller to 5-15 mu m, and grinding for 1-2 times, wherein the total grinding time is 2-4 times, so as to obtain ground silver paste; S7, transferring the ground silver paste into a vacuum stirring kettle, stirring and mixing at the vacuum degree of less than or equal to-0.095 MPa, and packaging the silver paste after stirring to obtain the weldable low-temperature silver paste.
  10. 10. A camera module based on solderable low-temperature silver paste comprises the flexible printed circuit board as claimed in any one of claims 1-9 and an image sensor chip and/or a VCM driving chip soldered on a conductor pattern of the circuit board through a chip scale packaging process, and is characterized in that the image sensor chip is soldered on a sensor micro-pad area of the conductor pattern, solder used for soldering is Sn42Bi58 low-temperature solder, the soldering parameters are that the peak temperature is 110 ℃ plus or minus 3 ℃ and the time is 60s plus or minus 10s, the VCM driving chip is adhered to a VCM driving circuit area of the conductor pattern through anisotropic conductive adhesive, and the curing condition is maintained for 20min at 90 ℃.

Description

Novel flexible printed circuit board and camera module prepared based on solderable low-temperature silver paste Technical Field The invention relates to the technical field of electronic materials and devices, in particular to a novel flexible printed circuit board and a camera module prepared based on solderable low-temperature silver paste. Background The flexible printed circuit board has become a key carrier for realizing high image quality, miniaturization, multi-camera collaboration and optical anti-shake functions of the intelligent camera module by virtue of excellent light and thin characteristics and three-dimensional deformation adaptability. The camera module, especially the main shooting and periscope type long focus module, puts forward more severe performance requirements on the flexible printed circuit board. The method comprises the steps of firstly, high-precision miniaturization challenge, compact stacking of the multi-shot array and the module, extremely high wiring density of the flexible printed circuit board, line width/line distance of less than or equal to 20 mu m, pad size of less than or equal to 40 mu m and x 40 mu m for connecting an image sensor and a VCM driving chip, secondly, strong mechanical reliability, continuous micro-motion of an optical anti-shake component and mobile phone drop impact, excellent fatigue resistance and high bonding strength of a welding point, capability of avoiding signal interruption caused by micro-crack generation, thirdly, thermal-mechanical stress challenge, extremely sensitivity of a CMOS sensor to temperature, requirement of a reflow soldering process, capability of overcoming internal stress caused by mismatch of thermal expansion coefficients and prevention of warping and image module decoking. Therefore, for manufacturing the precise flexible printed circuit board facing the camera module, the silver paste must have ultra-low temperature curing characteristics, high resolution printing capability, high welding reliability and excellent mechanical-thermal stress resistance. Disclosure of Invention The invention aims to provide a novel flexible printed circuit board and a camera module prepared based on a weldable low-temperature silver paste, so as to solve the outstanding problems that the existing flexible printed circuit board technology cannot simultaneously meet the ultra-high precision wiring, high-reliability connection and ultra-low temperature manufacturing requirements of the camera module, overcome the heat loss and cold risk of a sensor caused by high curing temperature of the traditional silver paste, eliminate the performance failure of an image module caused by insufficient welding strength or concentrated thermal stress of the silver paste, and avoid the quality defects of broken fine lines, signal attenuation and the like caused by poor leveling property or insufficient conductive stability of the silver paste. In order to achieve the above object, the present invention provides the following solutions: The invention provides a novel flexible printed circuit board prepared based on solderable low-temperature silver paste, which comprises a flexible insulating substrate and a conductor pattern arranged on the substrate, wherein the conductor pattern comprises a main circuit pattern formed by calendaring copper and an auxiliary functional structure formed by the solderable low-temperature silver paste in a local area of the main circuit pattern, wherein the auxiliary functional structure comprises at least one of a VCM (voice coil module) driving circuit area, a sensor micro-pad area and a lens seat connecting area; The curing temperature of the weldable low-temperature silver paste is 87-103 ℃, and the weldable low-temperature silver paste comprises, by mass, 60-72 parts of conductive filler, 12-18 parts of high-molecular resin system, 18-30 parts of ester solvent, 3-6 parts of curing agent, 1-5 parts of silane coupling agent, 0.8-1.5 parts of polyamide wax thixotropic agent, 0.1-0.3 part of polysiloxane defoamer, 0.3-1 part of modified carbon nano tube, 0.5-1.5 parts of modified antimony tin oxide powder, 1-2 parts of modified ceramic filler and 0.8-1.5 parts of low-stress modifier; The high polymer resin system comprises (0.9-1.1): (0.3-0.5) hydrogenated bisphenol A epoxy resin, biphenyl epoxy resin and polyacrylate-carboxyl terminated liquid nitrile rubber copolymer, wherein the conductive filler comprises silver coated copper sheet powder, nano silver wires and low-temperature alloy powder, the D50 range of the silver coated copper sheet powder is 1.0-3.0 mu m, the diameter-thickness ratio is >15, the length of the nano silver wires is 25-45 mu m, the diameter is 30-60 nm, and the low-temperature alloy powder is low-temperature alloy powder with the D50 range of 3-8 mu m. Specifically, the conductive filler comprises (1.2-1.8) silver-coated copper sheet powder, nano silver wires and low-temperature alloy powder in a mass