Liquid cooling heat dissipation device based on high-viscosity anti-seismic material, preparation method and electronic equipment

Abstract

The invention discloses a liquid cooling heat dissipation device based on a high-viscosity anti-seismic material, a preparation method and electronic equipment. The liquid cooling heat dissipation device comprises a metal substrate and a high-viscosity anti-seismic heat conduction layer wrapping the metal substrate. The high-viscosity anti-seismic heat-conducting layer takes an epoxy resin continuous phase dispersed with a composite heat-conducting filler as a marine phase and takes a core-shell rubber particle dispersed phase distributed in the marine phase as an island phase; through component compounding, a sea-island two-phase structure is obtained, different functions are distributed to different phase regions, and the contradiction among high adhesion, high heat conductivity and high shock resistance is solved, so that the liquid cooling heat dissipation device simultaneously meets the requirements that the heat conductivity coefficient is larger than or equal to 3.2 W / m.K, the tensile shear strength is larger than or equal to 18.9 MPa, and the loss factor is larger than or equal to 0.13.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging materials, and in particular to a liquid cooling heat dissipation device based on high-adhesion shock-resistant material, a preparation method and electronic equipment. BACKGROUND

[0002] With the rapid development of semiconductor devices towards high power, high density and miniaturization, the chip heat flux rises sharply, and the heat dissipation problem has become a key bottleneck restricting its performance and reliability. In power devices (such as IGBT, SiC MOSFET), high-performance computing chips and 5G radio frequency modules, the heat generated by the chip during operation must be efficiently dissipated through the packaging structure, otherwise it will lead to performance degradation, shortened life and even thermal failure of the device. Therefore, the thermal management capability of the packaging material directly determines the overall performance and long-term reliability of the electronic device.

[0003] The commonly used packaging materials at present cannot simultaneously meet the three key indicators of high adhesion strength, high thermal conductivity and high damping shock resistance. There is a profound physical and chemical contradiction between the three: first, high adhesion depends on the formation of strong interfacial bonding between the polymer matrix (such as epoxy resin) and the substrate, but the polymer itself is a poor conductor of heat, and the strong scattering of phonons by its molecular chains severely limits the improvement of thermal conductivity; second, high damping (shock resistance) requires materials with movable soft phases to dissipate vibration energy, while high thermal conductivity requires a rigid, continuous filler network as a high-speed channel for phonons, which are in conflict with each other in micro-mechanism - increasing the rigid filler can improve the thermal conductivity, but it will significantly stiffen the matrix, inhibit the movement of chain segments, and result in a decrease in damping performance; third, in order to pursue high thermal conductivity, high filling strategy is adopted, which will cause problems such as high viscosity of the system, poor wettability, and increased interfacial defects, thereby degrading the actual adhesion strength and effective thermal conductivity. Therefore, the traditional "simple blending" material design idea has reached the performance bottleneck and cannot achieve the synergistic optimization of the three.

[0004] Therefore, a new scheme of a liquid cooling heat dissipation device is needed to simultaneously consider the adhesion performance, thermal conductivity performance and shock resistance performance of the liquid cooling heat dissipation device, so as to meet the requirements of the liquid cooling heat dissipation device as a packaging material. SUMMARY

[0005] Therefore, the present application provides a liquid cooling heat dissipation device based on high-adhesion shock-resistant material, a preparation method and electronic equipment, which solves the problem of how to simultaneously consider the adhesion performance, thermal conductivity performance and shock resistance performance of the liquid cooling heat dissipation device.

[0006] To achieve the above technical purpose, the present application adopts the following technical scheme: In a first aspect, the application provides a liquid cooling heat dissipation device based on high-viscosity anti-vibration material, comprising a metal substrate, a high-viscosity anti-vibration heat-conducting layer coated on the metal substrate; the high-viscosity anti-vibration heat-conducting layer takes a continuous phase of epoxy resin dispersed with composite heat-conducting fillers as a sea phase, and takes a dispersed phase of core-shell rubber particles distributed in the sea phase as an island phase.

[0007] Preferably, the high-viscosity anti-vibration heat-conducting layer comprises the following components in mass fraction: 55-70 parts of epoxy resin, 15-25 parts of core-shell structure rubber particles, and 20-35 parts of composite heat-conducting fillers.

[0008] Preferably, in the core-shell structure rubber particles, the core layer is crosslinked polybutadiene rubber, and the shell layer is polymethyl methacrylate.

[0009] Preferably, the composite heat-conducting fillers are a composite of spherical copper powder plated with nickel and flaky boron nitride.

[0010] Preferably, the mass ratio of the spherical copper powder plated with nickel and the flaky boron nitride is 3-6:1.

[0011] Preferably, the particle size of the core-shell rubber particles is 10-20 μm, and the particle size of the composite heat-conducting fillers is 1-8 μm.

[0012] Preferably, the thickness of the shell layer of the core-shell structure rubber particles accounts for 10%-20% of the total diameter of the particles. In a second aspect, the application provides a preparation method of a liquid cooling heat dissipation device, comprising the following steps: S1. Pre-disperse the composite heat-conducting fillers and part of the epoxy resin by shearing to prepare a high-heat-conducting master batch; S2. Mix the high-heat-conducting master batch, core-shell rubber particles, the remaining epoxy resin, and a curing agent, disperse by a three-roll mill, and then vacuum degassing to obtain a high-viscosity anti-vibration heat-conducting slurry; S3. Coat the slurry on the surface of the metal substrate, and then perform step-by-step temperature rising curing to form a high-viscosity anti-vibration heat-conducting layer.

[0013] Preferably, in step S2, the roll gap of the three-roll mill is set to 10-50 μm, and the grinding frequency is 2-4 times; in step S3, the step-by-step temperature rising curing is first pre-curing at 80-90 ℃ for 1-2 hours, and then final curing at 130-150 ℃ for 2-3 hours.

[0014] In a third aspect, the application provides an electronic device comprising the liquid cooling heat dissipation device.

[0015] The application has the following beneficial effects: the application assigns different functions to different phase regions through component compounding to obtain a "sea-island" two-phase structure, solves the contradiction among high adhesion, high thermal conductivity and high shock resistance, and enables the liquid cooling heat dissipation device to simultaneously meet the conditions of a thermal conductivity of ≥3.2 W / m·K, a tensile shear strength of ≥18.9 MPa, and a loss factor of ≥0.13. DETAILED DESCRIPTION

[0016] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0017] The application provides a liquid cooling heat dissipation device based on a high-adhesion shock-resistant material, which comprises a metal substrate and a high-adhesion shock-resistant thermal conductive layer wrapped around the metal substrate; the high-adhesion shock-resistant thermal conductive layer takes a continuous phase of epoxy resin with dispersed composite thermal conductive fillers as a sea phase and takes a dispersed phase of core-shell rubber particles as an island phase.

[0018] In the application, the contradiction among high adhesion, high thermal conductivity and high shock resistance is solved through component compounding. The reason is that the "sea-island" two-phase structure of the application assigns different functions to different phase regions to achieve performance synergy. The role of the epoxy resin is to form a continuous sea phase matrix, which on the one hand provides structural adhesion to firmly combine with the heating element and on the other hand serves as a carrier to wrap and fix the composite thermal conductive fillers. The filler particles in the resin are in contact and overlap with each other to form a penetrating "filler network", which together with the resin wrapping it forms a new composite continuous phase. The high thermal conductivity of the composite thermal conductive fillers forms a three-dimensional heat transfer path. The "sea phase" is a composite rigid phase with the epoxy resin as the matrix and the thermal conductive fillers as the skeleton, which bears the functions of thermal conduction and adhesion. The core-shell rubber particles dispersed in the epoxy phase as the island phase can reversibly deform to absorb and dissipate mechanical energy when subjected to vibration, while the hard shell layer ensures good interfacial compatibility and bonding force with the epoxy resin sea phase, thereby imparting high damping properties to the material without damaging the integrity of the overall structure.

[0019] In some embodiments, the metal substrate is a copper heat dissipation bottom plate.

[0020] In some embodiments, the high-adhesion shock-resistant thermal conductive layer comprises the following components by mass fraction: 55-70 parts of epoxy resin, 15-25 parts of core-shell structure rubber particles, and 20-35 parts of composite thermal conductive fillers.

[0021] In this embodiment, if the epoxy resin is too little, the continuous phase matrix is incomplete, the bonding strength is reduced, and the filler and rubber particles cannot be fully wrapped, resulting in structural defects; if the epoxy resin is too much, the relative content of the thermally conductive filler and the rubber particles is insufficient, and both the thermal conductivity and the damping performance will be significantly reduced. If the core-shell rubber particles are too little, the damping effect is insufficient, and the shock resistance is limited; if too much, it will excessively destroy the continuity of the marine phase, degrade the bonding strength and the connectivity of the thermal conduction network. If the composite thermally conductive filler is too little, it cannot form an effective thermal conduction path, and the thermal conductivity is low; if too much, it will cause the viscosity of the slurry to increase sharply, making it difficult to process, and making the material too rigid, weakening the shock resistance.

[0022] In some embodiments, the core layer of the core-shell structure rubber particle is cross-linked polybutadiene rubber, and the shell layer is polymethyl methacrylate.

[0023] In this embodiment, the core-shell structure rubber particle can achieve high-efficiency damping and toughening functions. The soft core of cross-linked polybutadiene rubber (PBR) has high elasticity and can effectively absorb and dissipate vibration impact energy as a micro-spring; the hard shell of polymethyl methacrylate (PMMA) can ensure the stable and uniform dispersion of the rubber particles and form a firm interface bond with the matrix due to its excellent thermodynamic compatibility with the epoxy resin marine phase. This structure not only fully utilizes the damping effect of the soft core, but also avoids the poor compatibility problem that may be caused by simple physical blending. When stressed, the rubber particles can effectively induce plastic deformation of the matrix, thereby absorbing energy and improving overall shock resistance and reliability.

[0024] In some embodiments, the composite thermally conductive filler is a composite of spherical copper powder coated with nickel and flaky boron nitride.

[0025] In this embodiment, the composite thermally conductive filler constructs an efficient and stable three-dimensional thermal conduction network in the marine phase, which is preferentially distributed in the continuous phase of the epoxy resin. The spherical copper powder coated with nickel serves as the main framework of the thermal conduction network, utilizing the extremely high intrinsic thermal conductivity of copper for primary heat transport, and its spherical shape helps maintain the flowability and processability of the system at high filler loadings. The nickel coating layer mainly prevents copper oxidation and significantly improves the interface wettability with the epoxy resin, reducing the interface thermal resistance. Flaky boron nitride, as a connecting bridge of the thermal conduction network, utilizes its two-dimensional flaky structure and high in-plane thermal conductivity to bridge between spherical copper powder particles, effectively connecting isolated thermal conduction points and significantly improving the connectivity and efficiency of the thermal conduction network.

[0026] In some embodiments, the mass ratio of the spherical copper powder coated with nickel to the flaky boron nitride is 3-6:1.

[0027] In this embodiment, if the proportion is too large, the content of flaky BN is relatively insufficient, it is difficult to fully bridge the spherical copper powder, the thermal conduction network connectivity is poor, and the thermal conduction efficiency is limited; if the proportion is too small, too much flaky filler will greatly increase the viscosity of the system, leading to processing difficulties, and will excessively rigidify the epoxy resin matrix, weakening the damping performance of the material.

[0028] In some embodiments, the average particle size of the core-shell rubber microparticles is 1-8 μm; the average particle size of the composite thermal conductive filler is 10-20 μm.

[0029] In this embodiment, the particle size of the core-shell rubber microparticles (island phase) is smaller than the particle size of the spherical copper powder (sea phase skeleton), and in the process of forming the sea-island structure, the large particle filler first forms the skeleton, and the small particle rubber microparticles are filled in the voids thereof, forming a "particle grading" structure; in some embodiments, the density of the composite thermal conductive filler is greater than that of the core-shell rubber microparticles. If the particle size of the rubber microparticles is too large, it will become a huge defect, seriously damaging the continuity of the matrix; if the particle size of the rubber microparticles is too small, its damping efficiency may change, and the too large specific surface area easily affects the processing fluidity.

[0030] In some embodiments, the thickness of the shell layer of the core-shell structure rubber microparticles accounts for 10%-20% of the total diameter of the microparticles.

[0031] In this embodiment, if the shell layer thickness is too large, the over-thick hard shell will excessively constrain the deformation ability of the soft core, weakening its energy dissipation efficiency; if the shell layer thickness is too small, the shell layer may not be able to provide stable and firm interfacial bonding, leading to poor compatibility of the rubber phase with the epoxy resin matrix, and easy occurrence of phase separation or defects at the interface.

[0032] The present application provides a preparation method of a liquid cooling heat dissipation device, comprising the following steps: S1. Pre-dispersing the composite thermal conductive filler and part of the epoxy resin by shearing to prepare a high thermal conductive master batch; S2. Mixing the high thermal conductive master batch, core-shell rubber microparticles, the remaining epoxy resin and a curing agent, and then grinding and dispersing by a three-roll grinder to obtain a high-viscosity shock-resistant thermal conductive slurry after vacuum degassing; S3. Coating the slurry on the surface of a metal substrate, and curing by stepwise heating to form a high-viscosity shock-resistant thermal conductive layer.

[0033] In the present application, a step-by-step mixing method is adopted, which is beneficial to forming the sea-island structure of the present application, and the reason is that this method controls the time sequence of adding components, preferentially disperses the high thermal conductive filler in the epoxy resin to form a preliminary network structure (sea phase skeleton), and then adds the core-shell rubber microparticles. The thermal conductive filler is preferentially distributed in the continuous phase of the epoxy resin, and the rubber microparticles are "expelled" to the gaps of the filler network to form "islands".

[0034] In some embodiments, in step S2, the roll gap of the three-roll mill is set to 10-50 pm, and the grinding frequency is 2-4 times; in step S3, the stepwise temperature curing is as follows: first, pre-curing at 80-90 °C for 1-2 hours, then increasing the temperature to 130-150 °C to complete the final curing for 2-3 hours.

[0035] In this embodiment, within the parameter limit range, it is beneficial to achieve uniform dispersion while protecting the integrity of the core-shell structure and forming a stable microstructure. If the roll gap is too small or the grinding frequency is too high, the spherical structure of the core-shell rubber particles may be damaged, affecting their damping function; if the roll gap is too large or the grinding frequency is too low, the filler may not be uniformly dispersed, resulting in agglomerates, affecting the thermal conduction network and overall performance. If the pre-curing temperature is too high or the time is too short, solvent evaporation or rapid reaction may easily produce bubbles and internal stress; if the final curing temperature is insufficient or the time is not enough, the crosslinking reaction may not be complete, affecting the strength of the matrix.

[0036] The present application provides an electronic device, such as an IGBT module, comprising a liquid cooling heat dissipation device used as a packaging material.

[0037] Raw material preparation Core-shell structure rubber particles: In a 1 L reaction kettle equipped with a stirrer, a thermometer, and a nitrogen inlet, 400 g of deionized water and 2 g of sodium dodecyl sulfate (SDS) as an emulsifier were added. After purging oxygen with nitrogen, 100 g of butadiene monomer was added. The temperature was raised to 70 °C, and 0.5 g of potassium persulfate (KPS) was added as an initiator to start the reaction. The reaction was carried out at 70 °C and a stirring speed of 200 rpm for 12 hours, resulting in PBR latex with an average particle size of about 4.3 pm. The PBR latex system was stabilized at 75 °C. 20 g of methyl methacrylate (MMA) monomer and 0.1 g of KPS initiator were dissolved in 50 g of water, and slowly added to the reaction system at a rate of 1 mL / min using a constant pressure dropping funnel. After the addition was completed, the reaction was continued at 75 °C for 4 hours. After the reaction was completed, the emulsion was cooled to room temperature, and 5 wt% of calcium chloride aqueous solution was added to break the emulsion. The precipitate was filtered and washed repeatedly with deionized water until it was neutral, and finally dried in a vacuum oven at 60 °C for 24 hours to obtain white powder core-shell rubber particles. The final product was characterized using a laser particle size analyzer and transmission electron microscopy (TEM), confirming an average particle size of 5±0.5 pm, and the shell thickness of the core-shell rubber particles accounted for 15% of the total particle diameter.

[0038] Surface nickel-plated spherical copper powder: 100 g of commercial spherical copper powder (purity > 99.9%, particle size distribution D50 = 15 μm) was placed in a 10% dilute sulfuric acid solution and ultrasonically cleaned for 5 minutes to remove surface oxides. Then washed with deionized water to neutral, and then washed with acetone and quickly placed in a 60°C oven for short drying. The cleaned copper powder was immersed in a sensitization solution containing 10 g / L stannous chloride and 40 mL / L hydrochloric acid, slowly stirred at room temperature for 10 minutes. After filtration, it was immersed in an activation solution containing 0.5 g / L palladium chloride, slowly stirred at room temperature for 5 minutes. After filtration, it was washed thoroughly with deionized water. A chemical nickel plating solution was prepared: nickel sulfate 25 g / L, sodium hypophosphite 30 g / L, sodium citrate 15 g / L, sodium acetate 15 g / L, and the pH value was adjusted to 8.5-9.0 with ammonia water. The activated copper powder was added to the plating solution, the temperature was controlled at 85±2°C, the mechanical stirring speed was 150 rpm, and the reaction time was 30 minutes. After the reaction was completed, the copper powder was filtered, washed with deionized water and ethanol in turn, and finally dried in a 80°C vacuum oven for 2 hours. The average particle size of the surface nickel-plated spherical copper powder was maintained at 15 μm.

[0039] The present application is further illustrated by the following specific examples. Example 1

[0040] A liquid cooling heat dissipation device based on high-viscosity shock-resistant material, comprising a metal substrate, a high-viscosity shock-resistant heat-conducting layer coated on the metal substrate; the high-viscosity shock-resistant heat-conducting layer takes a continuous phase of epoxy resin dispersed with composite heat-conducting fillers as a sea phase, and takes a dispersed phase of core-shell rubber particles distributed in the sea phase as an island phase.

[0041] A preparation method of the liquid cooling heat dissipation device, comprising the following steps: S1. 24 parts of nickel-plated copper powder, 6 parts of flaky BN, and 30 parts of epoxy resin are added to a planetary mixer and high-speed shearing dispersed at 2000 rpm for 40 minutes to prepare a high-heat-conducting masterbatch; S2. The high-heat-conducting masterbatch, the remaining 30 parts of epoxy resin, 20 parts of core-shell rubber particles, a curing agent, and an accelerator are poured into a stirred tank and mixed at a medium speed (1000 rpm) for 20 minutes, then circulated and ground by a three-roll grinder (the roll gap is set to 25 μm) for 3 times, and finally vacuum debubbling at -0.098 MPa for 30 minutes to obtain a high-viscosity shock-resistant heat-conducting slurry; S3. The slurry is coated on the surface of an oxygen-free copper substrate by a screen printing process, a simulated chip (size 5 mm x 5 mm) is attached, and then placed in a program-controlled temperature oven, and the curing program is: heating to 85°C at 2°C / min, holding for 1.5 hours; then heating to 140°C at 1°C / min, holding for 2.5 hours; then the temperature is lowered to below 60°C and taken out, and the preparation is completed.

[0042] Examples 2-3 A liquid cooling heat dissipation device based on high-viscosity shock-resistant material, other contents are the same as example 1, the difference is that the amount of core-shell structure rubber particles is 15 parts, 25 parts, respectively.

[0043] Example 4-5 A liquid cooling heat dissipation device based on high-viscosity shock-resistant material, other contents are the same as example 1, the difference is that the ratio of nickel-plated copper powder and flaky BN is 4:1, and the amount of composite thermal conductive filler is 20 parts, 35 parts.

[0044] Comparative example 1 A liquid cooling heat dissipation device, other contents are the same as example 1, the difference is that the core-shell structure rubber particles are replaced by epoxy resin.

[0045] Comparative example 2 A liquid cooling heat dissipation device, other contents are the same as example 1, the difference is that the composite thermal conductive filler is replaced by epoxy resin.

[0046] Comparative example 3 A liquid cooling heat dissipation device, other contents are the same as example 1, the difference is that the core-shell structure rubber particles are replaced by PBR rubber powder.

[0047] Comparative example 4 A liquid cooling heat dissipation device, other contents are the same as example 1, the difference is that the composite thermal conductive filler is replaced by flaky BN.

[0048] Comparative example 5 A liquid cooling heat dissipation device, other contents are the same as example 1, the difference is that the process adopts one-step mixing method: according to the proportion, the nickel-plated copper powder, flaky BN, core-shell rubber particles, curing agent and epoxy resin are poured into the stirred tank, mixed at medium speed (1000 rpm) for 20 minutes, then circulated by three-roll grinder (the roll gap is set to 25 μm) for 3 times, and finally vacuum degassing at -0.098 MPa for 30 minutes.

[0049] Test and evaluation Test the performance of the liquid cooling heat dissipation device of different examples and comparative examples, the results are shown in table 1: Thermal conductivity: measured by laser flash method (LFA), according to ASTM E1461 standard; Tensile shear strength: the prepared thermal conductive layer is used as adhesive to bond two copper sheets, measured by universal material testing machine, according to ASTM D1002 standard; Loss factor (tan δ): tested by dynamic mechanical analyzer (DMA) at 50℃, 1Hz frequency, tan δ value directly reflects the damping performance (shock resistance) of the material, the larger the value, the better the shock resistance.

[0050] Table 1 test results ;

[0051] The application solves the contradiction among high adhesion, high thermal conductivity and high shock resistance by assigning different functions to different phase regions through component compounding, so that the liquid cooling heat dissipation device simultaneously meets the conditions of thermal conductivity ≥ 3.2 W / m·K, tensile shear strength ≥ 18.9 MPa, and loss factor ≥ 0.13.

[0052] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A liquid cooling heat sink based on high viscous seismic resistant material, characterized in that, The high-adhesion anti-vibration and heat-conducting layer is coated on the metal substrate, and comprises a continuous phase of epoxy resin dispersed with composite heat-conducting fillers as a sea phase, and a dispersed phase of core-shell rubber particles as island phases.

2. The liquid cooling heat sink based on high-sticky seismic material according to claim 1, characterized in that, The high-adhesion anti-vibration and heat-conducting layer comprises the following components by mass fraction: 55-70 parts of epoxy resin, 15-25 parts of core-shell rubber particles, and 20-35 parts of composite heat-conducting fillers.

3. The liquid cooling heat sink based on high-sticky seismic material according to claim 1, characterized in that, The core layer of the core-shell rubber particles is cross-linked polybutadiene rubber, and the shell layer is polymethyl methacrylate.

4. The liquid cooling heat sink based on high-sticky seismic material according to claim 1, wherein, The composite heat-conducting fillers are a composite of spherical copper powder plated with nickel and flaky boron nitride.

5. The liquid cooling heat sink based on high-sticky seismic material according to claim 1, wherein, The mass ratio of the spherical copper powder plated with nickel and the flaky boron nitride is 3-6:

1.

6. The liquid cooling heat sink based on high-sticky seismic material according to claim 1, wherein, The particle size of the core-shell rubber particles is 10-20 μm, and the particle size of the composite heat-conducting fillers is 1-8 μm.

7. The liquid cooling heat sink based on high viscous seismic resistant material according to claim 3, characterized in that, The thickness of the shell layer of the core-shell rubber particles accounts for 10-20% of the total diameter of the particles.

8. A method of manufacturing a liquid cooling heat sink according to any one of claims 1-7, characterized in that, The method comprises the following steps: S1. Pre-dispersing the composite heat-conducting fillers and part of the epoxy resin by shearing to prepare a high-heat-conducting master batch; S2. Mixing the high-heat-conducting master batch, core-shell rubber particles, the remaining epoxy resin, and a curing agent, and then grinding and dispersing the mixture by a three-roll grinder to obtain a high-adhesion anti-vibration and heat-conducting slurry after vacuum degassing; S3. Coating the slurry on the surface of the metal substrate, and then curing the slurry by stepwise heating to form the high-adhesion anti-vibration and heat-conducting layer.

9. The production method according to claim 8, characterized by, In step S2, the roll gap of the three-roll grinder is set to 10-50 μm, and the grinding frequency is 2-4 times; in step S3, the stepwise heating curing is first pre-curing at 80-90 °C for 1-2 hours, and then final curing at 130-150 °C for 2-3 hours.

10. An electronic device comprising the liquid cooling heat dissipation device according to any one of claims 1-7.

Images