Expanded microsphere foaming method and system based on laser selective heating

Abstract

The invention relates to the technical field of material foaming, in particular to an expanded microsphere foaming method and system based on selective laser heating, and the method comprises the following steps: processing a material layer with expanded microspheres on a substrate, generating a preset foaming area according to a target foaming structure, and projecting a laser beam into the material layer of the preset foaming area to form a foamed structure; the projected material layer absorbs laser energy, the temperature rises to be higher than the initial foaming temperature of the expanded microspheres, a foaming structure is formed through expansion, the laser beam is moved away, a foaming area is rapidly cooled, and the expanded microsphere structure is solidified and shaped. Laser energy only acts on a laser irradiation point, real local foaming is achieved, thermal damage is avoided, laser switching response is extremely fast, foaming starting and ending time can be accurately controlled, accordingly, the foaming ratio is accurately controlled, and pollution and mechanical damage possibly caused by traditional contact type heating are avoided through non-contact machining.

Description

TECHNICAL FIELD

[0001] The application is a kind of expansion microsphere foaming method and system based on laser selective heating, belonging to the field of material foaming technology. BACKGROUND

[0002] Expansion microspheres are micro-particles with a thermoplastic polymer shell wrapped around a low-boiling liquid hydrocarbon foaming agent. After being heated to its starting temperature, the polymer shell softens, and the internal foaming agent vaporizes to generate pressure, causing the microsphere to expand by tens or even hundreds of times in volume. Finally, it cools and sets, forming a closed foam structure. This foaming method is widely used in coatings, inks, textiles, lightweight composites, aerospace, and medical fields due to its light weight, thermal insulation, sound absorption, and other characteristics.

[0003] Traditional heating methods mainly use hot air ovens, infrared radiation, and hot plate contact heating. Although these methods are mature, they have obvious limitations. First, the overall heating method is difficult to achieve local foaming of specific areas of the workpiece, and the shape of the foam is difficult to control. Heat will spread to non-target areas, causing unnecessary deformation or performance changes, and also causing waste of heat. Second, these heating methods have large thermal inertia, inaccurate temperature control, slow heating and cooling speed, and difficulty in accurately controlling the start and stop of the foaming process, which can easily lead to excessive foaming or insufficient foaming, limiting the applicable foaming occasions. Therefore, there is an urgent need for a new foaming technology that can achieve high time accuracy, non-contact, and local temperature control. SUMMARY

[0004] To solve the problems in the prior art, the application provides an expansion microsphere foaming method and system based on laser selective heating.

[0005] The technical solution adopted by the application to solve its technical problems is: An expansion microsphere foaming method based on laser selective heating, the method comprising the following steps: Step S1: Process a material layer with expansion microspheres on a substrate; The material layer can be a mixture containing expansion microspheres, and can also contain resins, paints, inks, etc. When processing electronic component insulation bumps, the expansion microsphere addition ratio can be set to 5%-15%. After mixing a plurality of mixed materials according to the proportion, they are added to an injection molding machine with a barrel temperature lower than the starting foaming temperature of the micro-expansion ball for stirring and heating and melting to ensure uniform mixing. The desired shape can be manufactured through a mold.

[0006] Step S2: Generate a preset foaming area according to the target foaming structure; After generating the preset foaming area, a path program or mask pattern for controlling the motion of the laser can be generated according to the preset area; The specific process for generating the path program is as follows: Use CAD or other drawing software to create two-dimensional / three-dimensional models of the target foaming pattern.

[0007] Export the CAD model to a format compatible with the laser control system, such as G-code or DXF format, and set the laser scanning parameters in the control software, such as a scan line spacing of 20μm.

[0008] The control system has built-in path planning algorithms, such as serpentine scanning and spiral scanning, to select the optimal path according to the shape of the pattern. For example, circular bumps use spiral scanning (scanning layer by layer from the center to the outer circle to ensure uniform heating), while long strip textures use serpentine scanning (scanning back and forth along the length of the texture to improve efficiency).

[0009] Using a mask is another way to achieve selective laser irradiation. Its core principle is to utilize the mask's "transmittance / blocking" properties, allowing the laser beam to be projected onto the material layer only through the mask's "transmittance area," thereby achieving foaming in a predetermined area. The specific principle is as follows: A mask is an optical element with a "preset pattern," and it is divided into physical masks and digital masks: Physical masks, such as chrome-plated glass masks, have chrome-plated areas on the glass substrate that are light-blocking areas, through which lasers cannot pass, and unplated areas that are light-transmitting areas, through which lasers can pass. The shape of the light-transmitting areas is consistent with the target foaming pattern. Digital masks, such as DMDs (Digital Micromirror Devices), consist of hundreds of thousands of independently flippable micromirrors. When the micromirrors rotate clockwise, the laser is reflected to the material layer (equivalent to the "transparent area"), and when they rotate counterclockwise, the laser is reflected to the absorber (equivalent to the "shielding area"). Digital patterns are formed by controlling the flipping state of the micromirrors.

[0010] Taking a physical mask as an example, the mask is placed between the laser and the material layer. The laser beam first irradiates the mask, and only the laser in the transparent area can pass through the mask and be accurately projected onto the corresponding area of ​​the material layer. The microspheres in this area absorb the laser energy and foam. The material layer corresponding to the shaded area is not irradiated by the laser and remains in an unfoamed state.

[0011] Step S3: Project a laser beam into the material layer of the preset foaming area; The laser beam is emitted by a laser and, combined with the aforementioned path procedure or through a mask pattern, is accurately projected onto a predetermined area of ​​the material layer.

[0012] Step S4: The projected material layer absorbs laser energy, and its temperature rises above the initial foaming temperature of the expanding microspheres, causing it to expand and form a foamed structure, while the areas not irradiated by the laser remain unfoamed.

[0013] When the efficiency of the expanded microspheres in the material layer to absorb laser wavelengths is high, only the expanded microspheres need to absorb laser light to generate heat and expand.

[0014] When the efficiency of the expanded microspheres in the material layer in absorbing laser wavelengths is low, other photothermal conversion fillers can be mixed and added to the material layer containing the expanded microspheres to assist in absorbing laser energy and transferring heat to the expanded microspheres, ensuring that the expanded microspheres expand the bubbles.

[0015] Step S5: Remove the laser beam, the foamed area cools rapidly, and the expanded microsphere structure solidifies and sets.

[0016] Furthermore, for applications with different foaming requirements, at least two motion paths can be generated based on the preset foaming area. Applications with the same foaming requirements are scanned in the same path, while applications with different foaming requirements are scanned in the next scan after changing the parameters. This multi-scan design improves the accuracy of foaming.

[0017] Furthermore, for applications with different foaming requirements, at least two mask patterns can be generated based on the preset foaming area. Applications with the same foaming requirements are scanned in the same mask pattern, while different mask patterns are scanned sequentially. The pattern can be set to scan the one with the longer scanning path first, and then scan in order from the longest to the shortest path. This multi-scan design improves the accuracy of foaming.

[0018] Furthermore, the method also includes a database of preset substrate and laser parameters, using a substrate detection sensor to identify different types of substrates in the material layer, and automatically calling up matching laser parameters based on the identified type.

[0019] A system for implementing the above method includes: Laser emitting unit: Used to generate laser light that can be projected onto the material layer.

[0020] The laser emitting unit can generate lasers of different wavelengths and powers to adapt to the bubbling of various material layers. The laser generating unit can be a fiber laser, a CO2 laser, or a semiconductor laser.

[0021] Beam control unit: used to guide and manipulate the laser beam projected onto the material layer; The beam control unit also includes a galvanometer system, an optical lens group, a digital micromirror device, or a spatial light modulator.

[0022] Motion platform: Used to support and precisely move the substrate, working in conjunction with the beam control unit to accurately project the laser beam onto a preset area of ​​the material layer.

[0023] The motion platform can be a high-precision electric translation stage, whose motion axis system is selected to realize three-dimensional movement of X / Y / Z three-axis system. The high-precision electric translation stage is driven by a servo motor, and is equipped with an encoder and ball screw transmission to realize precise control of motion speed and position. The carrier platform in the high-precision electric translation stage is used to place the substrate and the material layer on the substrate. The substrate is fixed on the carrier platform by a vacuum suction cup or clamp, which facilitates its stable placement during the laser projection process.

[0024] Control system: Electrically connected to the laser emitting unit, beam control unit and motion platform, used to control relevant parameters involved in the laser projection process; The parameters involved in controlling the laser projection process include laser power, frequency, scanning path and scanning speed, as well as platform movement, and it has a built-in preset foaming pattern program.

[0025] Furthermore, the system also includes a real-time monitoring unit for real-time monitoring of the temperature or morphology of the foaming area and feeding the signal back to the control system to achieve closed-loop control.

[0026] The real-time monitoring unit can be an infrared thermal imager or a CCD camera.

[0027] The beneficial effects of this invention are: 1. The energy in this invention is applied only to the laser irradiation point, achieving true localized foaming and avoiding thermal damage. It is particularly suitable for foaming processing on heat-sensitive substrates.

[0028] 2. In this invention, laser is used for scanning heating. The laser has an extremely fast switching response, which can precisely control the start and end times of foaming, thereby precisely controlling the foaming ratio.

[0029] 3. This invention is a non-contact processing method, which avoids the pollution and mechanical damage that may be caused by traditional contact heating.

[0030] 4. This invention allows for easy and quick changes to the foaming pattern by altering the laser scanning path and parameters, without the need to change the mold, making it ideal for customized production of small batches and multiple varieties.

[0031] 5. In this invention, energy is highly concentrated for use in the target area, reducing energy waste. Detailed Implementation

[0032] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0033] In the first embodiment, the present invention provides a method and system for expanding microspheres based on laser selective heating. The system includes a fiber laser, a galvanometer scanning system, a focusing lens, a three-dimensional moving platform, a control system, and an infrared thermometer.

[0034] Step S1: Mix the expanded microspheres with epoxy resin evenly and print them on the circuit board to form a material layer; Step S2: Import the circuit insulation bump pattern that needs to be foamed into the control system, generate the preset foaming area, and generate the path program to control the movement of the laser based on the preset area. Step S3: The control system drives the laser to emit continuous laser light, which is then projected onto the material layer of the preset foaming area according to the path of the laser's movement. Step S4: The expanded microspheres and epoxy resin in the material layer absorb light energy and generate heat, and the temperature rises instantly to a level higher than the foaming temperature of the expanded microspheres (120°C). The microspheres in this area expand rapidly, increase in volume, and form an insulating bump structure.

[0035] Step S5: After laser scanning, the laser beam is removed, and the foamed area cools and solidifies rapidly.

[0036] The substrate is a polyimide substrate. Throughout the process, the substrate was not subjected to thermal damage due to its low thermal conductivity and minimal temperature rise in the non-irradiated area.

[0037] The second embodiment differs from the first embodiment in that it employs a high-power CO2 laser and a DMD digital mask system; In step S2, a binary mask file corresponding to the preset foaming area is generated using a computer.

[0038] In step S3, a CO2 laser beam is expanded and uniformly irradiated onto the DMD chip. The DMD reflects the laser beam and projects it onto the preset foaming area according to the mask pattern.

[0039] In step S4, the temperature of the area projected by the laser rises sharply, causing the microspheres to bubble, while the shadowed area remains unchanged.

[0040] This method can achieve the formation of large-area patterns in a single exposure, with extremely fast processing speed.

[0041] In the third embodiment, while the first and second embodiments involve a single scan, this invention can generate multiple motion paths based on a preset foaming area when different foaming requirements exist. Paths with the same foaming requirement are scanned within the same path or the same mask pattern. After changing parameters for different foaming requirements, the control system sets the sequence of the multiple scans for the next scan.

[0042] The multi-scan design improves scanning accuracy.

[0043] Fourth embodiment: In the above embodiments, the identification of the substrate and the setting of the laser parameters are all manually set, which lacks convenience and intelligence. Therefore, the present invention can also preset a database of substrate and laser parameters in the control system before use, and add a substrate detection sensor. The substrate detection sensor is used to identify the types of different substrates in the material layer. The control system automatically calls the matching laser parameters according to the identified types. The called laser parameters and the identified substrate types can be displayed on the control panel for manual review before proceeding to the next step.

[0044] Preferably, the laser light source is replaceable, making it easy to match the corresponding light source parameters.

[0045] This method increases the flexibility and convenience of use.

[0046] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for expanding microspheres based on laser selective heating, characterized in that: include: S1: Processing a material layer with expanded microspheres on a substrate; S2: Generate a preset foaming area based on the target foaming structure; S3: A laser beam is projected onto the material layer of the preset foaming area; S4: The material layer being projected absorbs laser energy, and its temperature rises above the initial foaming temperature of the expanding microspheres, causing it to expand and form a foamed structure. S5: Remove the laser beam, the foaming area cools rapidly, and the expanded microsphere structure solidifies and sets.

2. The method for expanding microspheres based on laser selective heating according to claim 1, characterized in that: In step S2, after generating the preset foaming area, a motion path program for controlling the laser that emits laser light can be generated based on the preset area.

3. The method for expanding microspheres based on laser selective heating according to claim 1, characterized in that: In step S2, after generating the preset foaming area, a mask pattern can be generated based on the preset area.

4. The method for expanding microspheres based on laser selective heating according to claim 2, characterized in that: At least two motion paths are generated based on the preset foaming area. The same foaming requirement is scanned in the same path, and the parameters for different foaming requirements are changed before the next scan.

5. The method for expanding microspheres based on laser selective heating according to claim 3, characterized in that: At least two mask patterns are generated based on the preset foaming area. The same foaming requirements are scanned in the same mask pattern, while different mask patterns are scanned in separate scans.

6. The method for expanding microspheres based on laser selective heating according to any one of claims 1-5, characterized in that: The method further includes: A database of preset substrate and laser parameters; Substrate detection sensors are used to identify the types of different substrates in a material layer; The system automatically retrieves the matching laser parameters based on the identified type.

7. A system for implementing the laser-selective heating-based microsphere foaming method according to any one of claims 1-6, characterized in that: The system includes: Laser emitting unit: used to generate laser light that can be projected onto the material layer; Beam control unit: used to guide and manipulate the laser beam projected onto the material layer; Motion platform: Used to support and precisely move the substrate, working in conjunction with the beam control unit to accurately project the laser beam onto a preset area of ​​the material layer; Control system: Electrically connected to the laser emitting unit, beam control unit and motion platform, used to control the relevant parameters involved in the laser projection process.

8. The laser-selective heating-based microsphere foaming system according to claim 7, characterized in that: The laser generating unit is one of a fiber laser, a CO2 laser, and a semiconductor laser; The beam control unit includes a galvanometer system, an optical lens group, and a digital micromirror device; The motion platform adopts a high-precision electric translation stage, and its motion axis system is selected as an X / Y / Z three-axis system that can realize three-dimensional movement.

9. The laser-selective heating-based expansion microsphere foaming system according to claim 7, characterized in that: The relevant parameters involved in controlling the laser projection process include the laser power, frequency, scanning path, scanning speed, as well as the platform's moving speed, direction, and distance.

10. The laser-selective heating-based expansion microsphere foaming system according to claim 7, characterized in that: The system also includes a real-time monitoring unit for real-time monitoring of the temperature or morphology of the foaming area and feeding the signal back to the control system.