Manufacturing method of automobile laser radar rigid-flex PCB (printed circuit board)

Abstract

The invention relates to the technical field of electronic device manufacturing, and discloses an automobile laser radar rigid-flexible PCB manufacturing method, which comprises the following steps: preparing a rigid layer-flexible layer-covering layer composite base material, performing plasma activation on a flexible layer copper surface, spraying a coupling agent, and pre-curing to form a bonding layer; the method comprises the following steps of: preparing a golden finger region, precisely pasting a PI (Polyimide) protective adhesive tape coated with nano TiO2 on the golden finger region, constructing an eight-layer structure by adopting a staged laminating process, forming an interconnection structure through laser drilling and hole metallization, and finally processing the outline of the golden finger by combining a precise mold and carrying out UV (Ultraviolet) photolysis surface treatment. The performance of the rigid-flex board is improved through collaborative innovation of materials and processes; heat conduction and bending resistance are optimized through gradient filler; the multi-scale bonding enhances the damp-heat resistance of the interface; photolysis-adhesive tape synergistically cleans residual adhesive; the signal loss is reduced through plasma-laser; stress relief and warping prevention are achieved through staged pressing, and the stability and signal integrity of the high-density rigid-flex board in high-frequency, mechanical and thermal environments are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic device manufacturing, and specifically to a method for manufacturing a rigid-flex PCB for an automotive laser radar. Background Art

[0002] With the rapid development of autonomous driving and intelligent sensing technologies, LiDAR, as a core environmental sensing device, faces urgent demands for miniaturization and high reliability in its transmitter modules. In the automotive electronics field, the transmitter must integrate laser arrays, drive circuits, and optical components within a limited space. This poses dual challenges to the high-density interconnection and mechanical shock resistance of the circuit board. The current mainstream rigid-flexible board split design relies on multi-stage connector adapters, which not only takes up space and makes the module bulky, but is also prone to contact failure under conditions such as long-term vehicle vibration and temperature cycling, seriously restricting the large-scale application of automotive LiDAR.

[0003] Existing architectures that stack discrete rigid and flexible boards via connectors suffer from systemic flaws: multi-level transfer interfaces extend signal paths, and impedance mismatch exacerbates waveform distortion in high-frequency pulse signals. Stress concentration at mechanical connections increases the risk of solder joint cracking during module drop tests. Differences in thermal expansion coefficients between rigid and flexible boards induce cyclical thermal stress, accelerating interface fatigue failure. This is especially true in scenarios like LiDAR transmitters, which require both millimeter-level mounting accuracy and signal rates exceeding 10Gbps. Traditional split-type designs struggle to balance high integration with long-term reliability.

[0004] In response to the above problems, the present invention proposes a method for manufacturing a rigid-flex PCB for automotive laser radar. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for manufacturing a rigid-flex PCB for automotive lidar, which solves the problem that high-density rigid-flex printed circuit boards are difficult to simultaneously achieve high-reliability interconnection, resistance to mechanical shock and high-frequency signal integrity under complex working conditions.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for manufacturing a rigid-flex PCB for an automotive laser radar, comprising the following steps:

[0007] a. Preparing a composite substrate comprising a rigid layer, a flexible layer and a cover layer;

[0008] In step a, a three-layer structure of a rigid layer, a flexible layer, and a modified polyimide cover layer is used to achieve a gradient transition in mechanical properties through the rigidity and flexibility matching of different materials.

[0009] The rigid layer FR-4 high Tg substrate provides structural support through its high glass transition temperature (≥180°C). Its thermal expansion coefficient matches that of the LiDAR metal housing, reducing temperature cycling stress.

[0010] In the flexible layer polyimide / HA copper foil composite, the microscopic columnar crystal structure (grain size ≤ 5μm) of the HA copper foil (high ductility annealed copper) works synergistically with the bending resistance of the polyimide to achieve dynamic bending times > 100,000 times;

[0011] The modified polyimide covering layer forms a thermal conductivity gradient distribution through the interfacial intercalation effect of nanofillers (hydroxylated boron nitride + zirconium phosphate), with the surface 0.8-1.2W / m·K → the bottom layer 0.3-0.5W / m·K, which not only improves the heat dissipation capacity but also maintains flexibility.

[0012] b. Plasma activation treatment is performed on the copper surface of the flexible layer;

[0013] c. Spray an interface coupling agent on the activated copper surface and pre-cure it to form a bonding layer;

[0014] The plasma activation and coupling agent spraying process in steps bc creates a high-bonding interface through a dual physical-chemical effect:

[0015] Ar / O2 plasma treatment bombards the copper surface with high-energy particles, selectively removing organic pollutants and generating nanoscale roughness (Ra = 20-50nm), while activating the hydroxyl (-OH) active sites on the copper surface;

[0016] The silanol groups of γ-aminopropyltriethoxysilane in the interface coupling agent condense with the hydroxyl groups on the copper surface, the alkoxy groups of the titanate coupling agent coordinate with the carboxylic acid groups of the polyimide, and the hyperbranched polyester enhances the interface toughness through topological entanglement, forming a composite bonding network of covalent bond-coordination bond-physical entanglement.

[0017] d. Apply PI-based protective tape to the gold finger area of the flexible layer. Coat the surface of the tape with a 200±20nm thick TiO2 layer with a bonding tolerance of ±0.05mm.

[0018] e. Laminating the rigid layer and the flexible layer in stages to form an eight-layer stack;

[0019] The staged pressing process in step d achieves a dynamic balance between molecular chain relaxation and cross-linking reaction through temperature-pressure timing control:

[0020] The first stage of heating causes the polyimide molecular chains to initially stretch, avoiding local stress concentration caused by sudden heating;

[0021] The second stage is to maintain the temperature within a window below the thermal decomposition temperature of polyimide (>300°C) but above its glass transition temperature (Tg=220-250°C) to promote the synergy between the epoxy resin cross-linking reaction and the rearrangement of the polyimide molecular chain.

[0022] The third stage of controlled cooling suppresses the generation of interlayer shear stress by matching the cooling rate to the CTE difference of the materials.

[0023] f. Laser drilling and hole metallization of the laminated substrate;

[0024] g. Process the gold finger area through precision mold;

[0025] h. Implement UV photolysis treatment on the processed gold finger area;

[0026] i. Complete surface metallization treatment.

[0027] Step d) solves the micro-nanoscale processing defects in the gold finger area through full process control of protection-processing-cleaning:

[0028] The TiO2 coating of the PI-based protective tape inhibits the adsorption of organic volatiles during the lamination process through a photocatalytic effect, and its nanometer-scale thickness (200±20nm) provides protection while avoiding demolding stress;

[0029] UV photolysis treatment uses ultraviolet light of a specific wavelength to stimulate the breakage of CH bonds in residual organic matter, and combines it with ozone to generate volatile small molecules (CO2, H2O) in situ oxidation, achieving contactless cleaning;

[0030] The coordinated parameter design of laser drilling and hole metallization eliminates the carbide layer and optimizes the hole wall morphology through plasma cleaning, so that the copper layer presents a preferred crystal plane orientation along the hole wall, improving the integrity of high-frequency signal transmission.

[0031] Preferably, the covering layer in step a is a modified polyimide film, which is prepared by the following steps:

[0032] The polyimide precursor is mixed with hydroxylated boron nitride nanosheets and zirconium phosphate nanowires, which comprises, by weight:

[0033] Polyimide precursor 92.5-94.5;

[0034] Hydroxylated boron nitride nanosheets 0.7-1.1:

[0035] Zirconium phosphate nanowires 0.4-0.8;

[0036] Disperse at an ultrasonic frequency of 40±2kHz and a power density of 0.5-0.8W / mL for 25-35min to form a gradient dispersion system;

[0037] The film is formed by a slit coating process with a coating speed of 1.2-1.8m / min.

[0038] Preferably, in step a:

[0039] The rigid layer is FR-4 high Tg substrate with a thickness of 105±10μm;

[0040] The flexible layer is made of HA copper foil with a thickness of 12±1μm.

[0041] Preferably, the gas composition of the plasma activation treatment in step b is Ar and O2, with a volume ratio of 3.8:1 to 4.2:1, and the plasma activation treatment parameters in step b include:

[0042] RF power 280-320W, processing time 25-35s, vacuum degree 8-12P.

[0043] Preferably, the interfacial coupling agent in step c comprises, by weight:

[0044] γ-aminopropyltriethoxysilane 3.2-4.8 parts;

[0045] 1.0-1.8 parts of titanate coupling agent;

[0046] 0.4-0.8 parts of hyperbranched polyester;

[0047] 95-105 parts of a mixed solvent of ethanol and water;

[0048] The volume ratio of the ethanol and water mixed solvent is 8.5:1-9.5:1. The spray film thickness in step c is controlled to be 25-45 nm, the pre-curing temperature is 75-85° C., and the time is 4-6 min.

[0049] Preferably, the staged pressing in step d comprises:

[0050] The first stage of heating: from 80-100℃ to 150-160℃ at a rate of 2-3℃ / min;

[0051] The second stage of constant temperature: maintain at 175-185℃ for 45-60min;

[0052] The third stage of cooling: natural cooling to below 60℃;

[0053] The pressing pressure is controlled at 8-10kg / cm 2 .

[0054] Preferably, the laser drilling in step f is implemented by the following steps:

[0055] CO2 laser is used for blind hole processing, and the parameters include:

[0056] Wavelength 9.4±0.1μm, pulse energy 18-22mJ;

[0057] Aperture 75±8μm, hole position accuracy ≤±15μm;

[0058] Laser repetition frequency 5-8kHz;

[0059] Plasma cleaning is performed to remove the carbonized layer on the hole wall. The gas composition of the plasma cleaning process is CF4 and O2, with a volume ratio of 3:1 to 5:1. The cleaning parameters include:

[0060] RF power is 150-180W, and treatment time is 45-60s.

[0061] Preferably, in step g, the nickel layer thickness of the gold finger is 3.5-4.5 μm, and the gold layer thickness is 0.08-0.12 μm.

[0062] Preferably, the UV photolysis treatment parameters in step h include:

[0063] Wavelength 365±5nm;

[0064] Irradiance 10±0.5mW / cm 2 ;

[0065] Processing time: 30±2s.

[0066] Preferably, the metallization treatment of the holes in step f is carried out by the following steps:

[0067] Perform chemical copper deposition, the parameters include:

[0068] The plating solution contains 25-35g / L copper sulfate and 8-12g / L EDTA;

[0069] Temperature 45-50°C, deposition rate 0.8-1.2 μm / min;

[0070] Implement full-board electroplating to thicken the copper layer, the parameters include:

[0071] Current density 2.0-2.5A / dm2;

[0072] Coating thickness 15±3μm;

[0073] The plating solution contains copper ions at a concentration of 50-60 g / L.

[0074] The present invention provides a method for manufacturing a rigid-flex PCB for automotive laser radar. It has the following beneficial effects:

[0075] 1. This invention achieves both high thermal conductivity and low thermal expansion coefficient within a polyimide matrix through a gradient dispersion design of the composite filler system, overcoming the conflict between heat dissipation and deformation caused by the single function of traditional homogeneous materials. The multi-scale synergistic effect of boron nitride nanosheets and zirconium phosphate nanowires not only establishes a continuous heat conduction channel, but also enhances the inter-molecular force through the nano-confinement effect, resulting in the material's excellent heat dissipation efficiency and bending resistance under high-temperature conditions.

[0076] 2. This invention utilizes a ternary coupling agent system, creating a multi-level reinforced network of rigid-flexible interfaces through a cross-scale bonding mechanism combining covalent bonds, coordination bonds, and physical entanglement. This design not only significantly enhances initial bond strength but also effectively inhibits interface degradation in hot and humid environments through dynamic bond reconstruction and energy dissipation mechanisms, resolving the technical challenge of hydrolysis failure associated with traditional single-agent coupling agent systems.

[0077] 3. This invention incorporates a synergistic cleaning technology combining functionalized protective tape and UV photolysis. Through the dual effects of physical isolation and photocatalytic decomposition, it completely eliminates micron-level adhesive residue contamination in delicate areas such as gold fingers. Compared to traditional mechanical cleaning or chemical treatments, this solution achieves molecular-level cleaning without damaging the coating, ensuring the electrical reliability of high-density interconnects.

[0078] 4. This invention utilizes a synergistic process of plasma cleaning and laser drilling to form a low-dielectric fluorinated layer on the hole wall while precisely controlling its roughness, significantly reducing high-frequency signal transmission losses. Compared to conventional cleaning processes, this technology simultaneously optimizes the hole wall's electrical properties and topographical accuracy through the coupled effects of selective etching and surface passivation, thus breaking through the dielectric loss bottleneck of high-frequency signal transmission.

[0079] 5. This invention achieves dynamic matching of resin fluidity and curing rate through temperature-pressure sequential control. This design allows rigid / flex material layers with different thermal expansion coefficients to release internal stresses in a gradient manner during the lamination process, fundamentally resolving the substrate warping and delamination issues caused by sudden heating and pressing in traditional single-stage processes, thereby improving the structural stability of highly complex rigid-flex boards. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0081] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0082] Please see the attached Figure 1 The present invention provides a method for manufacturing a rigid-flex PCB for automotive laser radar through the following three embodiments. The specific contents are as follows:

[0083] Example 1-3:

[0084] Example 1:

[0085] Step a: Composite substrate preparation

[0086] Covering preparation:

[0087] 93.5 parts by mass of polyimide precursor, 0.9 parts by mass of hydroxylated boron nitride nanosheets, and 0.6 parts by mass of zirconium phosphate nanowires were mixed;

[0088] Dispersion was performed at an ultrasonic frequency of 40 kHz and a power density of 0.65 W / mL for 30 min;

[0089] The slit coating speed is 1.5 m / min.

[0090] Rigid layer: FR-4 high Tg substrate, thickness 105μm;

[0091] Flexible layer: HA copper foil thickness 12μm.

[0092] Step b: Plasma activation treatment

[0093] Gas composition: Ar and O2 volume ratio 4:1;

[0094] The RF power was 300 W, the treatment time was 30 s, and the vacuum degree was 10 Pa.

[0095] Step c: Interface coupling agent spraying

[0096] Formula: 4.0 parts of γ-aminopropyltriethoxysilane, 1.4 parts of titanate coupling agent, 0.6 parts of hyperbranched polyester, 100 parts of ethanol / water (9:1);

[0097] The spray film thickness is 35nm, the pre-curing temperature is 80℃, and the time is 5min.

[0098] Step d: Apply protective tape

[0099] The tape fitting position tolerance is ±0.05mm.

[0100] Step e: Lamination in stages

[0101] The first stage: from 90℃ to 155℃ at 2.5℃ / min;

[0102] The second stage: constant temperature at 180℃ for 50min;

[0103] The third stage: natural cooling to 60℃;

[0104] Pressing pressure 9kg / cm 2 .

[0105] Step f: Laser drilling and hole metallization

[0106] Laser parameters: wavelength 9.4 μm, pulse energy 20 mJ, aperture 75 μm, repetition rate 6 kHz;

[0107] Plasma cleaning: CF4 / O2 volume ratio 4:1, RF power 165W, processing time 50s;

[0108] Chemical copper deposition: copper sulfate 30g / L, EDTA 10g / L, temperature 48°C, deposition rate 1.0μm / min;

[0109] Full plate electroplating: current density 2.3A / dm 2 , coating thickness 15μm, copper ion concentration 55g / L.

[0110] Step h: UV photolysis treatment

[0111] Wavelength 365nm, irradiance 10mW / cm 2 , time 30s.

[0112] Step i: Complete surface metallization treatment.

[0113] Example 2:

[0114] Step a: Composite substrate preparation

[0115] Covering preparation:

[0116] 92.5 parts by mass of polyimide precursor, 0.7 parts by mass of hydroxylated boron nitride nanosheets, and 0.4 parts by mass of zirconium phosphate nanowires;

[0117] Ultrasonic frequency 38 kHz, power density 0.5 W / mL, dispersion 25 min;

[0118] Coating speed: 1.2 m / min.

[0119] Rigid layer: FR-4 high Tg substrate thickness 95μm;

[0120] Flexible layer: HA copper foil thickness 11μm.

[0121] Step b: Plasma activation treatment

[0122] Ar / O2 volume ratio 3.8:1, RF power 280W, processing time 25s, vacuum degree 8Pa.

[0123] Step c: Interface coupling agent spraying

[0124] Formula: 3.2 parts of γ-aminopropylsilane, 1.0 part of titanate, 0.4 part of hyperbranched polyester, 95 parts of ethanol / water (8.5:1);

[0125] The spray film thickness is 25 nm, the pre-curing temperature is 75 ° C, and the time is 4 minutes.

[0126] Step e: Lamination in stages

[0127] Stage 1: 80°C → 150°C (rate 2°C / min);

[0128] The second stage: constant temperature at 175℃ for 45min;

[0129] Pressing pressure 8kg / cm 2 .

[0130] Step f: Laser drilling and hole metallization

[0131] Laser parameters: wavelength 9.3 μm, pulse energy 18 mJ, aperture 67 μm, repetition rate 5 kHz;

[0132] Plasma cleaning: CF4 / O2 volume ratio 3:1, RF power 150W, processing time 45s;

[0133] Chemical copper deposition: copper sulfate 25g / L, EDTA 8g / L, temperature 45°C, deposition rate 0.8μm / min;

[0134] Full plate electroplating: current density 2.0A / dm 2 , coating thickness 12μm, copper ion concentration 50g / L.

[0135] Step h: UV photolysis treatment

[0136] Wavelength 360nm, irradiance 9.5mW / cm 2 , time 28s.

[0137] Step i: Complete surface metallization treatment.

[0138] Example 3:

[0139] Step a: Composite substrate preparation

[0140] Covering preparation:

[0141] 94.5 parts by mass of polyimide precursor, 1.1 parts by mass of hydroxylated boron nitride nanosheets, and 0.8 parts by mass of zirconium phosphate nanowires;

[0142] Ultrasonic frequency 42 kHz, power density 0.8 W / mL, dispersion 35 min;

[0143] Coating speed: 1.8 m / min.

[0144] Rigid layer: FR-4 high Tg substrate thickness 115μm;

[0145] Flexible layer: HA copper foil thickness 13μm.

[0146] Step b: Plasma activation treatment

[0147] Ar / O2 volume ratio 4.2:1, RF power 320W, processing time 35s, vacuum degree 12Pa.

[0148] Step c: Interface coupling agent spraying

[0149] Formula: 4.8 parts of γ-aminopropylsilane, 1.8 parts of titanate, 0.8 parts of hyperbranched polyester, 105 parts of ethanol / water (9.5:1);

[0150] The spray film thickness is 45nm, the pre-curing temperature is 85℃, and the time is 6min.

[0151] Step e: Lamination in stages

[0152] Stage 1: 100°C → 160°C (rate 3°C / min);

[0153] The second stage: constant temperature at 185℃ for 60min;

[0154] Pressing pressure 10kg / cm 2 .

[0155] Step f: Laser drilling and hole metallization

[0156] Laser parameters: wavelength 9.5 μm, pulse energy 22 mJ, aperture 83 μm, repetition rate 8 kHz;

[0157] Plasma cleaning: CF4 / O2 volume ratio 5:1, RF power 180W, processing time 60s;

[0158] Chemical copper deposition: copper sulfate 35g / L, EDTA 12g / L, temperature 50°C, deposition rate 1.2μm / min;

[0159] Full plate electroplating: current density 2.5A / dm 2 , coating thickness 18μm, copper ion concentration 60g / L.

[0160] Step h: UV photolysis treatment

[0161] Wavelength 370nm, irradiance 10.5mW / cm 2 , time 32s.

[0162] Step i: Complete surface metallization treatment.

[0163] Comparative Examples 1-7:

[0164] Comparative Example 1:

[0165] Compared with Example 1, the difference is that: in step a, no hydroxylated boron nitride nanosheets and zirconium phosphate nanowires are added during the preparation of the covering layer, only 94.0 parts by mass of the polyimide precursor is used, and the other process parameters are the same as those in Example 1.

[0166] Comparative Example 2:

[0167] Compared with Example 1, the difference is that in step c, only 4.0 parts of γ-aminopropyltriethoxysilane is used as the interfacial coupling agent, and no titanate coupling agent and hyperbranched polyester are added. The other process parameters are the same as those in Example 1.

[0168] Comparative Example 3:

[0169] Compared with Example 1, the difference is that step d (applying the protective tape) is omitted, and laser drilling and subsequent processing are directly performed on the laminated substrate. The other process parameters are the same as those in Example 1.

[0170] Comparative Example 4:

[0171] Compared with Example 1, the difference is that the pressing process in step e adopts a single-stage temperature increase (directly from 80°C to 185°C at 5°C / min, constant temperature for 50 minutes and then natural cooling), the temperature and pressure are not controlled in stages, and the other process parameters are the same as those in Example 1.

[0172] Comparative Example 5:

[0173] Compared with Example 1, the difference is that the plasma cleaning gas composition in step f is pure O2 (volume ratio 0:1) and CF4 is not used. The other process parameters are the same as those in Example 1.

[0174] Comparative Example 6:

[0175] Compared with Example 1, the difference is that step h (UV photolysis treatment) is omitted, and the surface metallization treatment is directly performed on the processed gold finger area. The other process parameters are the same as those in Example 1.

[0176] Comparative Example 7:

[0177] Compared with Example 1, the difference is that: in step f, plasma cleaning is not performed during laser drilling, and the carbonized layer on the hole wall is removed only by mechanical grinding. The other process parameters are the same as those in Example 1.

[0178] Test Example 1-5:

[0179] Test Example 1: Covering Thermal-Mechanical Performance Test Experiment Description

[0180] Purpose of the experiment:

[0181] Verify the improvement effect of the modified polyimide covering layer (containing hydroxylated boron nitride nanosheets and zirconium phosphate nanowires) on thermal conductivity, coefficient of thermal expansion (CTE) and bending strength.

[0182] Experimental Materials:

[0183] Test sample:

[0184] The modified polyimide covering layer (containing nanofiller) prepared in Example 1;

[0185] Pure polyimide covering layer (without nanofiller) prepared in Comparative Example 1.

[0186] Sample specifications:

[0187] Dimensions: 50mm×50mm×0.1mm(thickness);

[0188] There were 3 samples in each group and the average value was taken.

[0189] Experimental equipment:

[0190] Thermal conductivity test: steady-state heat flow instrument (LFA467NanoFlash, NETZSCH);

[0191] CTE test: thermomechanical analyzer (TMA402F3, NETZSCH);

[0192] Bending strength test: universal material testing machine (Instron 5967).

[0193] Experimental steps:

[0194] 1. Thermal conductivity test

[0195] Place the sample on the heat flow instrument test bench and apply thermal grease on the upper and lower surfaces;

[0196] Set the heat source temperature to 50°C and the cold end temperature to 25°C, and record the steady-state heat flow value;

[0197] According to the formula Calculate thermal conductivity (Q: heat flow, d: thickness, A: area, ΔT: temperature difference).

[0198] 2. CTE test

[0199] The specimen is fixed in the TMA fixture along the length direction;

[0200] The temperature was raised from 30°C to 200°C at a rate of 5°C / min;

[0201] The linear expansion rate in the range of 30-150°C was recorded and the average CTE was calculated.

[0202] 3. Bending strength test

[0203] The specimen was placed horizontally in a three-point bending fixture with a span of 40 mm;

[0204] Load at a rate of 1 mm / min until fracture, and record the maximum load F max ;

[0205] Bending strength (L: span, b: width, h: thickness).

[0206] Experimental data:

[0207] Table 1: Summary of test results of thermal-mechanical properties of cover

[0208]

[0209]

[0210] Summary: The experimental results show that by introducing a composite filler system of hydroxylated boron nitride nanosheets and zirconium phosphate nanowires into a polyimide matrix, the thermodynamic properties of the coating are significantly optimized. The gradient dispersion structure of the nanofiller works synergistically through two mechanisms: the boron nitride nanosheets, with their two-dimensional layered structure, form a continuous thermal conductive network in the lateral direction, effectively improving thermal conductivity and suppressing anisotropic expansion; the zirconium phosphate nanowires are interspersed between the polyimide molecular chains along the thickness direction, enhancing the inter-molecular chain forces through the nano-confinement effect, thereby simultaneously improving the material's bending resistance. This multi-level structural design at the nanoscale enables the material to achieve a balance between thermal management capabilities and mechanical strength, overcoming the performance limitations of traditional homogeneous polyimide films due to single functionalization.

[0211] The interface enhancement effect in this system is reflected in the regulation of the compatibility between the filler and the matrix. The active hydroxyl groups on the surface of hydroxylated boron nitride hydrogen bond with the amine groups of the polyimide precursor, while the phosphate groups on the surface of the zirconium phosphate nanowires produce ion-dipole interactions with the imide rings of the polyimide. This multi-type interface bonding mechanism not only improves the dispersion of the filler, but also optimizes the stress transfer path, allowing the material to maintain stable interlayer bonding during thermal cycling. The significant improvement in bending strength in the experimental data (305-328MPavs.241-263MPa) verifies the effectiveness of this mechanism, indicating that the nanofiller is not a simple physical doping, but achieves molecular-level regulation of the rigid-flexible interface through chemical interactions.

[0212] The regulatory effect of process parameters on performance is further confirmed in this experiment. The frequency selection of 40±2kHz and the power density control of 0.5-0.8W / mL during the ultrasonic dispersion process ensure the directional arrangement and gradient distribution of the nanofillers in the matrix, which is the key to achieving improved thermal conductivity and reduced CTE. The speed range of 1.2-1.8m / min in the slit coating process regulates the orientation of the molecular chain through shear force, so that the filler distribution in the film formation process matches the rheological properties of the matrix. The thermal conductivity and mechanical strength of Comparative Example 1 dropped significantly due to the lack of a filler system, which reversely proves the inseparability of material design and process parameters in this solution. The two together constitute the technical core of the performance breakthrough.

[0213] Test Example 2: Interface Bonding Strength Test Experiment Description

[0214] Purpose of the experiment:

[0215] Verify the effect of the ternary coupling agent system (γ-aminopropyltriethoxysilane + titanate coupling agent + hyperbranched polyester) on improving the copper-polyimide interface bonding strength and its durability in high temperature and high humidity environments.

[0216] Experimental Materials:

[0217] Test sample:

[0218] The rigid-flex PCB sample prepared in Example 1 (containing a ternary coupling agent);

[0219] The sample prepared in Comparative Example 2 (containing only γ-aminopropyltriethoxysilane).

[0220] Sample specifications:

[0221] Size: 100mm×10mm (the area between copper foil and polyimide is 10mm×10mm);

[0222] There were 3 samples in each group and the average value was taken.

[0223] Experimental equipment:

[0224] Peel strength test: universal material testing machine (Instron 5967, equipped with 90° peeling fixture);

[0225] High temperature and high humidity aging chamber (temperature accuracy ±0.5°C, humidity accuracy ±3%RH).

[0226] Experimental steps:

[0227] 1. Initial peel strength test

[0228] Fix the sample on the testing machine and set the peeling angle to 90°;

[0229] Peel off the copper foil at a rate of 50 mm / min and record the peeling force curve;

[0230] The average peel strength (unit: N / mm) was calculated.

[0231] 2. High temperature and high humidity aging treatment

[0232] Place the sample in an aging chamber and set the conditions to 85°C / 85%RH;

[0233] Continuous treatment for 500 hours;

[0234] Remove the sample and return to room temperature for 24 hours before repeating the peel strength test.

[0235] Experimental data:

[0236] Table 2: Summary of interface bonding strength test results

[0237]

[0238] Summary: The experimental results show that the interface bonding strength and aging resistance of the ternary coupling agent system are significantly better than those of the single coupling agent system. The core mechanism is that the silanol group of γ-aminopropyltriethoxysilane forms a covalent bond with the hydroxyl group on the copper surface, providing basic bonding strength; the alkoxy group of the titanate coupling agent forms a coordination bond with the polyimide carboxylic acid group, enhancing the chemical stability of the interface; the hyperbranched polyester disperses local stress through the topological entanglement of the molecular chain, inhibiting crack propagation. The three work together to construct a multi-level interface reinforcement network of "covalent anchoring-coordination stabilization-physical toughening", which increases the initial peel strength to 1.58-1.72N / mm, and can still maintain a strength retention rate of more than 90% under high temperature and high humidity environments, breaking through the technical bottleneck of the traditional single coupling agent system with a single bonding mechanism and insufficient anti-aging ability.

[0239] The key to improving interface durability lies in the synergistic effect of titanate and hyperbranched polyester. The coordination bonds of titanate can be dynamically reconstructed in a hot and humid environment, avoiding bond breakage caused by the intrusion of water molecules; the three-dimensional entangled structure of hyperbranched polyester delays the initiation of interfacial microcracks through a physical energy dissipation mechanism. In the experimental data, the peel strength of Comparative Example 2 dropped sharply after aging (55.3-65.8% retention rate). It is precisely because of the lack of synergistic protection of the above two components that the single silane coupling agent is prone to hydrolysis and bond scission under hot and humid conditions, resulting in interface failure.

[0240] The regulatory effect of process parameters on interfacial properties cannot be ignored. Precise control of the pre-curing temperature (75-85°C) ensures the full spreading and directional arrangement of the coupling agent molecules on the substrate surface, and the ratio of ethanol / water mixed solvent (8.5:1-9.5:1) optimizes the adsorption kinetics of the coupling agent by adjusting the polarity of the solution. In Comparative Example 2, due to the lack of synergistic effects of titanate and hyperbranched polyester, even with the same process parameters, it is still impossible to achieve a comprehensive improvement in interfacial performance. This further confirms the inseparability of the material system and process conditions, which together constitute the technical basis for a long-term and reliable rigid-flex interface.

[0241] Test Example 3: Gold Finger Area Cleanliness Test Experiment Description

[0242] Purpose of the experiment:

[0243] Verify the effects of protective tape (TiO2 coated PI tape) and UV photolysis treatment on the removal of residual glue in the gold finger area and the bonding strength of the coating.

[0244] Experimental Materials:

[0245] Test sample:

[0246] The rigid-flex PCB (including protective tape + UV treatment) prepared in Example 1;

[0247] Sample prepared in Comparative Example 3 (without protective tape);

[0248] The sample prepared in Comparative Example 6 (without UV treatment).

[0249] Sample specifications:

[0250] Gold finger area size: 15mm×2mm;

[0251] There were 3 samples in each group and the average value was taken.

[0252] Experimental equipment:

[0253] X-ray fluorescence spectrometer (XRF) (to detect sulfur and chlorine content);

[0254] Tape peel tester (3M tape No. 600, IPC-TM-6502.4.1 standard);

[0255] Optical microscope (100 times magnification to observe the coating morphology).

[0256] Experimental steps:

[0257] 1. Surface residual glue rate test

[0258] Use XRF to perform element scanning on the gold finger area (area 10mm×2mm);

[0259] Detect the peak area intensity of sulfur (S) and chlorine (Cl) elements (representing the amount of epoxy adhesive residue); calculate the relative adhesive residue rate (%) based on the standard sample (no adhesive residue).

[0260] 2. Coating adhesion test

[0261] Apply the 3M tape tightly to the gold finger area and press it three times to ensure there are no bubbles.

[0262] Quickly peel off the tape in a 180° direction;

[0263] Observe the coating shedding situation under a microscope and record the shedding area ratio.

[0264] Experimental data:

[0265] Table 3: Summary of gold finger area cleanliness test results

[0266]

[0267]

[0268] Summary: The results of this experiment show that the residual glue contamination in the gold finger area is effectively controlled through the synergistic effect of applying TiO2-coated PI protective tape before lamination and UV photolysis treatment. The core mechanism is that the TiO2 nanolayer is activated by heat during the lamination process, and the volatilized epoxy resin residual glue is decomposed into CO2 and H2O through photocatalysis to prevent its deposition on the surface of the gold finger; at the same time, the precise fitting of the protective tape and the substrate (tolerance ±0.05mm) forms a physical barrier to block the penetration of liquid resin. In the experimental data, the residual glue rate of Example 1 (0.05-0.11%) is significantly lower than that of Example 3 (2.17-2.65%) without using tape, which proves that this protective design solves the pain point of the difficulty in removing residual glue in the traditional process from the source.

[0269] The enhanced cleaning effect of UV photolysis is reflected in the deep removal of trace residues. Ultraviolet light with a wavelength of 365±5nm selectively stimulates the cleavage of C-H bonds in organic matter. The resulting free radicals undergo a chain oxidation reaction with ozone, completely decomposing organic contaminants adsorbed within the microscopic grooves of the gold finger. Although Comparative Example 6 employed protective tape but did not undergo UV treatment, its adhesive residue rate (0.48-0.61%) and coating shedding (5-12%) were still higher than those in Example 1 (0.05-0.11%, no shedding). This demonstrates that relying solely on physical isolation cannot completely eliminate nanoscale contamination, requiring a photochemical synergy to achieve molecular-level cleaning.

[0270] The precise matching of process parameters is the key to achieving the technical effect. The TiO2 coating thickness of 200±20nm optimizes the balance between photocatalytic activity and flexibility. Too thin will lead to insufficient catalytic efficiency, while too thick will easily cause the tape to crack. UV irradiance is 10±0.5mW / cm 2 The setting ensures sufficient decomposition of organic matter while preventing oxidation of the gold surface due to excessive energy. The failure cases of Comparative Examples 3 and 6 confirm the necessity of the above parameter system, demonstrating that this solution, through the cross-scale synergy of material modification (TiO2 functionalized tape) and process innovation (UV photolysis), has broken through the technical bottleneck of high-precision PCB gold finger reliability.

[0271] Test Example 4: Hole Wall Quality and Signal Integrity Test Experiment Description

[0272] Purpose of the experiment:

[0273] Verify the synergistic effect of CF4 / O2 plasma cleaning and CO2 laser drilling on the improvement of hole wall roughness and high-frequency signal loss.

[0274] Experimental Materials:

[0275] Test sample:

[0276] The rigid-flex PCB prepared in Example 1 (CF4 / O2 plasma cleaning);

[0277] Sample prepared in Comparative Example 5 (pure O2 plasma cleaning);

[0278] Sample prepared in Comparative Example 7 (mechanical cleaning).

[0279] Sample specifications:

[0280] Drilling diameter: 0.2±0.02mm;

[0281] There were 3 samples in each group and the average value was taken.

[0282] Experimental equipment:

[0283] Laser confocal microscope (Olympus LEXTOLS5000, measuring the hole wall roughness Ra); high-frequency network analyzer (Keysight N5227B, 10 GHz signal test);

[0284] Microsection preparation tool (for cutting hole cross-sections for observation).

[0285] Experimental steps:

[0286] 1. Hole wall roughness test

[0287] Cut the specimen along the axial direction of the drill hole to prepare microsections;

[0288] The pore wall surface was scanned using a laser confocal microscope (scanning area 100 μm × 100 μm); the software automatically calculated the Ra value (ISO4287 standard).

[0289] 2. High frequency signal loss test

[0290] Connect the sample to the network analyzer and calibrate it to 10 GHz;

[0291] Use a coaxial probe to touch the copper layers at both ends of the drilled hole;

[0292] Record the insertion loss value (dB / cm) and repeat 3 times to take the average.

[0293] Experimental data:

[0294] Table 4: Summary of hole wall quality and signal loss test results

[0295]

[0296]

[0297] Summary: The experimental results show that the synergistic effect of CF4 / O2 mixed gas plasma cleaning and laser drilling process significantly improves the hole wall quality and signal integrity. The core mechanism is that CF4 is dissociated into active fluorine radicals in the plasma, preferentially etching the amorphous carbon structure in the carbonized layer of the hole wall; O2 converts the residual organic pollutants into CO2 and H2O through oxidation reaction. The optimization of the mixed gas ratio (CF4:O2=3:7) enables the etching selectivity to achieve the best balance, which can remove the carbonized layer while avoiding excessive etching of the substrate. In the experimental data, the hole wall roughness of Example 1 (1.0-1.3μm) is much lower than that of Comparative Example 5 (pure O2 causes the oxide layer to be loose, Ra=2.4-3.1μm) and Comparative Example 7 (mechanical cleaning residual microcracks, Ra=4.6-5.3μm), verifying the directional cleaning advantage of the mixed gas system.

[0298] The reduction in high-frequency signal loss is due to the change in the chemical state of the pore wall surface after plasma cleaning. CF4 / O2 treatment forms a micron-scale fluoride layer on the pore wall, whose dielectric constant (ε≈2.1) is lower than that of the polyimide substrate (ε≈3.5), reducing the dielectric loss of electromagnetic wave propagation; at the same time, the passivation effect of the fluoride layer on the copper layer inhibits the formation of surface copper oxide, reducing the additional loss caused by the skin effect. Comparative Example 5 forms a porous oxide layer (ε≈4.0) due to pure O2 treatment, resulting in an insertion loss (0.53-0.62dB / cm) significantly higher than that of Example 1 (0.25-0.31dB / cm), indicating that a single oxidation cleaning cannot achieve the simultaneous optimization of dielectric properties and conductivity.

[0299] Precise control of process parameters is the key to achieving technical effects. Selective excitation of plasma cleaning power (300-350W) ensures that the activity threshold of fluorine / oxygen radicals matches, which can fully react while avoiding damage to the substrate; the coordinated control of gas flow rate (20-25sccm) and reaction chamber pressure (50-80Pa) optimizes the free radical diffusion path, so that the etching effect is evenly distributed in the depth direction of the hole wall. When mechanical cleaning is used in Comparative Example 7, although the macroscopic carbon slag is removed, the residual stress and surface defects at the microscopic level (such as the Ra value of 4.6-5.3μm in the data) still cause signal loss as high as 1.08-1.25dB / cm, which in turn confirms the technical necessity of this solution to break through the bottleneck of high-density interconnect signal integrity through physical-chemical coordinated cleaning.

[0300] Test Example 5: Experimental description of substrate warpage test after lamination

[0301] Purpose of the experiment:

[0302] Verify the improvement effect of the staged pressing process (low-temperature pre-curing + high-temperature final pressing) on suppressing substrate warping and interlayer delamination.

[0303] Experimental Materials:

[0304] Test sample:

[0305] The rigid-flex PCB prepared in Example 1 (staged lamination);

[0306] The sample prepared in Comparative Example 4 (single-stage pressing).

[0307] Sample specifications:

[0308] Size: 200mm×200mm (four-layer board structure);

[0309] There were 3 samples in each group and the average value was taken.

[0310] Experimental equipment:

[0311] Three-point warpage measuring instrument (micrometer accuracy ±1μm, IPC-TM-6502.4.22 standard);

[0312] Scanning ultrasonic microscope (SAT) (50 MHz probe, to detect delamination defects);

[0313] Constant temperature and humidity chamber (pretreatment conditions: 25°C / 50% RH, equilibration for 24 hours).

[0314] Experimental steps:

[0315] 1. Warpage test

[0316] Place the specimen horizontally on a three-point support platform (support point spacing 180 mm);

[0317] Use a micrometer to measure the vertical distance Δh between the center point and the support plane;

[0318] Warpage (L: support span).

[0319] 2. Interlayer delamination detection

[0320] Apply ultrasonic coupling agent to the surface of the sample;

[0321] The SAT probe scans along the XY direction and records the delamination area ratio;

[0322] Delamination area ≥ 0.1mm 2 Determined to be a valid defect.

[0323] Experimental data:

[0324] Table 5: Summary of substrate warpage test results after lamination

[0325] Specimen type Warpage (%) Layered area ratio (%) Example 1-1 0.32 0 Example 1-2 0.41 0.03 Examples 1-3 0.28 0 Comparative Example 4-1 1.57 2.15 Comparative Example 4-2 1.82 3.07 Comparative Example 4-3 1.43 1.89

[0326] Summary: Experimental results demonstrate that the staged lamination process significantly improves substrate flatness and interlayer bonding quality by precisely controlling resin fluidity and thermal stress release pathways. The core mechanism is that the low-temperature pre-curing stage (80-100°C) allows the epoxy resin to slowly fill the pores of the reinforcement material and initially crosslink, avoiding localized flow imbalances caused by a sudden drop in viscosity. The high-temperature final lamination stage (180-190°C) increases the crosslinking density after sufficient resin infiltration, gradually adapting the thermal expansion coefficient differences between the layers (CTE rigid layer: 12-15ppm / °C vs. flexible layer: 19-22ppm / °C) through a gradient curing process. In the experimental data, the warpage of Example 1 (0.28-0.41%) was approximately 75% lower than that of Comparative Example 4 (1.43-1.82%). This is because the staged process disperses the interlayer stress peaks across different temperature ranges, rather than the concentrated internal stress accumulation caused by rapid curing in a single-stage lamination process.

[0327] The suppression of interlayer delamination is due to the optimization of the interface microstructure by the staged process. The three-dimensional network skeleton formed in the pre-curing stage provides physical support for the subsequent high-temperature pressing, allowing the resin to repair micron-scale interface defects during the secondary flow, while the rapid gelation of the resin in the single-stage process leads to insufficient filling (the delamination area of ​​Comparative Example 4 reaches 1.89-3.07%). Synchronous thermal analysis (DSC) shows that the staged process changes the resin curing exothermic peak from a single-stage concentrated peak to a double-stage broad peak, proving that the reaction kinetics control effectively delays the cross-linking rate, which is highly consistent with the result of almost no delamination in Example 1 observed by ultrasonic scanning microscopy (SAT).

[0328] The timing matching of process parameters is the key to achieving technical effects. The setting of pre-curing time (30±2min) enables the resin to reach a conversion rate of 60-70%, maintaining a certain fluidity and structural stability; the stepped loading of the final pressing pressure (2.5-3.0MPa) compensates for the shrinkage differences of different material layers through mechanical energy input. Even if the same temperature parameters are used in comparative example 4 but the staged control is missing, its warpage and delamination data are still significantly deteriorated, which in turn confirms the necessity of the coordination of time-pressure-temperature multi-dimensional parameters in this solution. This cross-scale process design breaks through the limitations of traditional pressing technology on the manufacture of high-density rigid-flex boards.

[0329] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a rigid-flex PCB for automotive laser radar, characterized in that: The following steps are involved: a. Preparing a composite substrate comprising a rigid layer, a flexible layer and a cover layer; b. Plasma activation treatment is performed on the copper surface of the flexible layer; c. Spray an interface coupling agent on the activated copper surface and pre-cure it to form a bonding layer; d. Apply PI-based protective tape to the gold finger area of the flexible layer. Coat the surface of the tape with a 200±20nm thick TiO2 layer with a bonding tolerance of ±0.05mm. e. Laminating the rigid layer and the flexible layer in stages to form an eight-layer stack; f. Laser drilling and hole metallization of the laminated substrate; g. Process the gold finger area through precision mold; h. Implement UV photolysis treatment on the processed gold finger area; i. Complete surface metallization treatment.

2. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: The covering layer in step a is a modified polyimide film, which is prepared by the following steps: The polyimide precursor is mixed with hydroxylated boron nitride nanosheets and zirconium phosphate nanowires, which comprises, by weight: Polyimide precursor 92.5-94.5; Hydroxylated boron nitride nanosheets 0.7-1.1: Zirconium phosphate nanowires 0.4-0.8; Disperse at an ultrasonic frequency of 40±2kHz and a power density of 0.5-0.8W / mL for 25-35min to form a gradient dispersion system; The film is formed by a slit coating process with a coating speed of 1.2-1.8m / min.

3. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: In the step a: The rigid layer is FR-4 high Tg substrate with a thickness of 105±10μm; The flexible layer is made of HA copper foil with a thickness of 12±1μm.

4. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: The gas composition of the plasma activation treatment in step b is Ar and O2, with a volume ratio of 3.8:1 to 4.2:

1. The plasma activation treatment parameters in step b include: RF power 280-320W, processing time 25-35s, vacuum degree 8-12P.

5. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: The interface coupling agent in step c comprises, by weight: γ-aminopropyltriethoxysilane 3.2-4.8 parts; 1.0-1.8 parts of titanate coupling agent; 0.4-0.8 parts of hyperbranched polyester; 95-105 parts of a mixed solvent of ethanol and water; The volume ratio of the ethanol and water mixed solvent is 8.5:1-9.5:

1. The spray film thickness in step c is controlled to be 25-45 nm, the pre-curing temperature is 75-85° C., and the time is 4-6 min.

6. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: The staged pressing in step e includes: The first stage of heating: from 80-100℃ to 150-160℃ at a rate of 2-3℃ / min; The second stage of constant temperature: maintain at 175-185℃ for 45-60min; The third stage of cooling: natural cooling to below 60℃; The pressing pressure is controlled at 8-10kg / cm 2 .

7. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: The laser drilling in step f is performed by the following steps: CO2 laser is used for blind hole processing, and the parameters include: Wavelength 9.4±0.1μm, pulse energy 18-22mJ; Aperture 75±8μm, hole position accuracy ≤±15μm; Laser repetition frequency 5-8kHz; Plasma cleaning is performed to remove the carbonized layer on the hole wall. The gas composition of the plasma cleaning process is CF4 and O2, with a volume ratio of 3:1 to 5:

1. The cleaning parameters include: RF power is 150-180W, and treatment time is 45-60s.

8. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: In step g, the nickel layer thickness of the gold finger is 3.5-4.5 μm, and the gold layer thickness is 0.08-0.12 μm.

9. The method for manufacturing a rigid-flex PCB for automotive laser radar according to claim 1, characterized in that: The UV photolysis treatment parameters in the step h include: Wavelength 365±5nm; Irradiance 10±0.5mW / cm 2 ; Processing time: 30±2s.

10. The method for manufacturing a rigid-flex PCB for an automotive laser radar according to claim 1, wherein: The metallization treatment of the holes in step f is carried out by the following steps: Perform chemical copper deposition, the parameters include: The plating solution contains 25-35g / L copper sulfate and 8-12g / L EDTA; Temperature 45-50°C, deposition rate 0.8-1.2 μm / min; Implement full-board electroplating to thicken the copper layer, the parameters include: Current density 2.0-2.5A / dm2; Coating thickness 15±3μm; The plating solution contains copper ions at a concentration of 50-60 g / L.

Images