Method for improving mechanical strength of silver / silica gel composite material and application of silver / silica gel composite material in flexible electronic packaging

Abstract

The invention provides a method for improving the mechanical strength of a silver / silica gel composite material and application of the silver / silica gel composite material in flexible electronic packaging. Allyl X (X is chlorine, bromine or iodine) is added into platinum catalytic addition curing silica gel and then is mixed with silver powder, so that the toughness and fracture energy of the silver-silica gel conductive composite material are remarkably improved. The breaking strength of the composite material obtained by the preparation method disclosed by the invention reaches 4 MPa and is far higher than 1.5 MPa of the composite material without allyl X (X is chlorine, bromine or iodine), the resistivity of the cured composite material wire is 1.1-8.5 * 10 <-4 > omega cm, and the composite material wire has excellent conductivity. The elongation at break is 100-120%, and the tensile property is excellent.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronics and packaging materials, specifically relating to a method for improving the mechanical strength of silver / silicone composite materials and its application in flexible electronics. Background Technology

[0002] Flexible hybrid circuits are the most promising method for the industrialization of flexible electronics. They involve mounting traditional rigid electronic components onto an elastic polymer substrate and achieving electrical interconnection through stretchable interconnects. Many materials are used for stretchable interconnects in flexible electronics. Among them, silver powder-silicone composites are receiving increasing attention due to their good conductivity and stretchability, which well meet the requirements of stretchable interconnects. However, when used as pads to bond rigid electronic component leads, their low tensile strength makes them prone to large deformation under strain, transferring stress to the bonding area between the pad and the lead. This can easily cause the lead to separate from the pad, leading to device failure. If the conductive material in the pad area has a higher stress-strain strength than the silver powder-silicone composite material in the interconnect area, allowing the pad area to maintain relatively small deformation during device strain, it will help reduce lead detachment and improve device reliability. However, the mechanical strength of the conductive material in the pad area cannot be much higher than that of the silver powder-silicone composite material. Otherwise, the connection point between the silver powder-silicone composite material interconnect and the pad will become a new stress concentration point, which is prone to breakage of the connection between the interconnect and the pad during repeated stretching of the device. In addition, the pad should also have good compatibility with the silver powder-silicone composite material used as the interconnect, so that the two have good electrical contact performance and good tensile strength. For example, due to the large difference in modulus between the traditional copper pad and the silver powder-silicone composite material, the connection point between the interconnect made of the silver powder-silicone composite material and the copper pad will become a new easy breakage point when the device is stretched. In addition, the bonding strength between the silver powder-silicone composite material and copper is low, which further increases the risk of breakage. In fact, the pin material of traditional hard electronic components is mostly copper or aluminum. There have been many reports on enhancing the bonding strength between the silver powder-silicone composite material and copper [1, 2, 3]. For example, the PBS and PDMS dual network enhancement mechanism proposed by Tang et al. increased the bonding shear strength between the composite material and the copper substrate to 2.87 MPa [1]. At this point, the fracture failure is no longer an interfacial failure, but rather a cohesive failure of the material. Improving the mechanical strength of the silver powder-silicone composite material itself could potentially further increase the upper limit of the bond strength between the composite material and the copper substrate.

[0003] Traditional composite reinforcement methods may introduce new problems. For example, using silane coupling agents requires forming MO-Si bonds on the silver powder surface, which reduces the electrical contact between silver powder particles and decreases the conductivity of the composite. Adding carbon fibers leads to a decrease in stretchability. Adding carbon nanotubes does not reduce conductivity, but dispersing carbon nanotubes in silica gel is difficult. Poor dispersion significantly reduces the stretchability of the composite. Achieving good dispersion requires surface treatment or additional processing of carbon nanotubes, which increases costs. Furthermore, silver-filled epoxy matrix composites are unsuitable due to the large difference in modulus between them and the silica gel matrix, as well as their lack of adhesion to silica gel.

[0004] References: 1. Tang M , et al. High-adhesion PDMS / Ag conductive composites for flexible hybrid integration. Chemical Engineering Journal 451, 138730 (2023). 2. Zhao D , et al. Flexible Hybrid Integration Enabled xsOn-SkinElectronics for Wireless Monitoring of Electrophysiology and Motion. IEEE Transactions on Biomedical Engineering 69, 1340-1348 (2022). 3. Zhao J , et al. Three-Dimensional Interconnect Technologies for Advanced Flexible Electronics. Advanced Materials 2025, e10294 (2025). Summary of the Invention

[0005] The purpose of this invention is to provide a simple and convenient method for improving the mechanical strength of silver / silicone composite materials and its application in flexible electronic packaging.

[0006] The present invention proposes a method for improving the mechanical strength of silver / silicone composite materials, the specific steps of which are as follows: (1) Use of allyl X: Mix allyl X with silica gel that has been cured by platinum-catalyzed hydrosilylation to obtain a mixture; wherein: the mass ratio of allyl X to silica gel is 1:500-1:10000; (2) Preparation of silver / silicone composite material: Silver powder and the mixture obtained in step (1) are ground and mixed together to obtain reinforced silver / silicone composite material, wherein the mass ratio of silver powder to silicone is 2.5:1~4.5:1.

[0007] In this invention, in the allyl X mentioned in step (1), X is any one of chlorine, bromine or iodine, and the allyl X is any one of allyl chloride, allyl bromine or allyl bromine.

[0008] In this invention, the silver powder in step (2) has a particle size of 0.05 to 10 micrometers and its morphology is any one of spherical, plate-like or dendritic.

[0009] In this invention, the silver powder in step (2) is mixed with the mixture obtained in step (1), and the mixing includes, but is not limited to, any one of grinding, stirring or planetary mixing.

[0010] The application of the enhanced silver / silicone composite material obtained by the preparation method of the present invention in flexible electronics is as follows: the silver / silicone composite material prepared in step (2) is patterned into stretchable interconnect lines, pads or conductive adhesives used to bond the pins of electronic components to the pads by any one of the following methods: stencil coating, screen printing, dispensing or printing. Then the silver / silicone composite material is cured and shaped by heating.

[0011] In this invention, the heating and curing temperature is controlled at 100-200℃, and the curing time is 0.3-2 hours.

[0012] The beneficial effects of this invention are that the composite material obtained by the above method exhibits significantly enhanced mechanical strength while maintaining its electrical conductivity and tensile strength. The resistivity of the cured composite material wire is 1.1-8.5 × 10⁻⁶. -4 It has excellent electrical conductivity (Ω cm) and a stretchability of 100%–120%, exhibiting excellent stretchability. Its mechanism of action lies in the fact that the double bond of allyl X (where X is chlorine, bromine, or iodine) participates in the hydrosilylation curing reaction of silica gel, thereby embedding into the silica gel chain segments, while halogen atoms can form complexes with silver. The interfacial bonding force provided by the complexation is much stronger than van der Waals forces, effectively transferring the load from the weaker polymer matrix to the high-strength / high-stiffness filler (such as nanoparticles or fibers), fully utilizing the reinforcing potential of the filler. When the interface is under stress, these dynamic bonds can undergo reversible fracture and recombination through "decomplexation-recomplexation," converting mechanical energy into chemical energy for dissipation, rather than instantly causing brittle interfacial failure or filler debonding, thus significantly improving the material's toughness and fracture energy. Attached Figure Description

[0013] Figure 1This is a stress-strain curve of silver-silicone composite material before and after the addition of allyl X (X is chlorine, bromine or iodine).

[0014] Figure 2 These are photographs of silver-silicone composite materials with added allyl iodine patterned into stretchable circuits and used to bond electronic components. Detailed Implementation

[0015] The present invention will be further illustrated by the following examples. Example 1

[0016] A method for improving the mechanical strength of silver / silicone composite materials and its application in flexible electronic packaging. The preparation method of this invention mainly involves adding an appropriate amount of allyl X (X is chlorine, bromine, or iodine) to the silver-silicone composite material. Specifically: (1) Add an appropriate amount of allyl iodine to the silicone system cured by platinum-catalyzed hydrosilylation reaction (such as Dow Corning 184 silicone); (2) The silver powder and the mixture obtained in step (1) are thoroughly ground and mixed to obtain a silver powder-silicone composite material; the silver powder is specifically 2-micron flake silver powder; (3) The composite material obtained in step (3) is patterned into stretchable lines, pads or conductive adhesives used to bond the pins and pads of electronic components by means of template coating, screen printing, dispensing or printing. (4) The composite material with patterned or bonded electronic components is cured by heating.

[0017] The specific steps are as follows: A. Add 0.02 g of allyl iodine to 10 g of Dow Corning 184 silicone (colloid to curing agent mass ratio of 10:1) and stir thoroughly to obtain a mixture; B. Grind and mix 30 grams of silver powder with the mixture obtained in step A to obtain a composite material slurry; C. Patterning composite materials into interconnect lines or pads on stretchable substrates such as silicone by stencil scraping; D. The patterned composite material obtained in step C is cured by heating. The heating temperature is 160 °C and the heating time is 1 hour.

[0018] The resistivity of the cured sample was 2.8 ± 0.05 × 10⁻⁶. -4 It has an Ω cm content and excellent electrical conductivity. It also has a stretchability of 120%, indicating excellent stretchability. Example 2

[0019] The specific steps for improving the preparation of silver / silicone composite materials and their application in flexible electronic packaging are as follows: A. Add 0.005 g of allyl bromide to 10 g of Dow Corning 184 silicone (colloid to curing agent mass ratio of 10:1) and stir thoroughly to obtain a mixture; B. Grind and mix 30 grams of silver powder with the mixture obtained in step A to obtain a composite material slurry; the silver powder used is 10-micron dendritic silver powder. C. Patterning composite materials into interconnect lines or pads on stretchable substrates such as silicone by stencil scraping; D. The patterned composite material obtained in step C is cured by heating. The heating temperature is 200 °C and the heating time is 0.3 hours.

[0020] The resistivity of the cured sample was 1.1 ± 0.05 × 10⁻⁶. -4 It has an Ω cm content and excellent electrical conductivity. It is 100% stretchable and has excellent stretchability. Example 3

[0021] The specific steps for improving the preparation of silver / silicone composite materials and their application in flexible electronic packaging are as follows: A. Add 0.001 g of allyl chloride to 10 g of Dow Corning 184 silicone (colloid to curing agent mass ratio of 10:1) and stir thoroughly until homogeneous; B. Grind and mix 35 grams of silver powder with the mixture obtained in step A to obtain a composite material slurry; the silver powder used is 0.05 micron spherical silver powder. C. Patterning composite materials into interconnect lines or pads on stretchable substrates such as silicone by stencil scraping; D. Heat curing the patterned composite material obtained in step C. Heating temperature: 100 °C, heating time: 2 hours.

[0022] The resistivity of the cured sample was 2.6 ± 0.05 × 10⁻⁶. -4 It has an Ω cm content and excellent electrical conductivity. Its stretchability is 115%, indicating excellent stretchability. Example 4

[0023] The specific steps for improving the preparation of silver / silicone composite materials and their application in flexible electronic packaging are as follows: A. Add 0.008 g of allyl iodine to 10 g of Dow Corning 184 silicone (colloid to curing agent mass ratio of 10:1) and stir thoroughly until homogeneous; B. Grind and mix 32 grams of silver powder with the mixture obtained in step A to obtain a composite material slurry; the silver powder used is 10-micron dendritic silver powder. C. Apply the composite material obtained in step B to the pads obtained in implementation case 1-3 by dispensing, and then mount the electronic components, paying attention to the alignment of the pins with the pads; D. Heat curing the composite material from step C. Heating temperature: 150 °C, heating time: 1 hour.

[0024] After curing, the pins are bonded to the pads. Figure 2 A temperature sensing circuit fabricated using a post-silver-silica composite material with added allyl iodine and other electronic components was demonstrated. The circuit still functioned normally after 1000 cycles at a 30% stretch rate, exhibiting good reliability. Example 5

[0025] The specific steps for improving the preparation of silver / silicone composite materials and their application in flexible electronic packaging are as follows: A. Add 0.001 g of allyl bromide to 10 g of Dow Corning 184 silicone (colloid to curing agent mass ratio of 10:1) and stir thoroughly until homogeneous; B. Grind and mix 25 grams of silver powder with the mixture obtained in step A to obtain a composite material slurry; the silver powder used is 2-micron flake silver powder. C. Patterning composite materials into interconnect lines or pads on stretchable substrates such as silicone by stencil scraping; D. The patterned composite material obtained in step C is cured by heating. The heating temperature is 140 °C and the heating time is 1.2 hours.

[0026] The resistivity of the cured sample was 8.5 ± 0.05 × 10⁻⁶. -4 It has an Ω cm content and excellent electrical conductivity. Its stretchability is 130%, indicating excellent stretchability.

[0027] The above-described embodiments are a detailed description of a method for improving the mechanical strength of silver / silicone composite materials and its application in flexible electronic packaging. They are illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for improving the mechanical strength of silver / silicon rubber composites, characterized in that The specific steps are as follows: (1) Use of allyl X: mix allyl X with silica gel solidified by platinum-catalyzed silicon hydrogen addition, to obtain a mixture; wherein: the mass ratio of allyl X to silica gel is 1:500-1:10000; (2) Preparation of silver / silica gel composite material: grind and mix silver powder with the mixture obtained in step (1), to obtain an enhanced silver / silica gel composite material, wherein: the mass ratio of silver powder to silica gel is 2.5:1~4.5:

1.

2. The method of claim 1, wherein In step (1), the allyl X is any one of allyl chloride, allyl bromide or allyl bromide.

3. The method of claim 1, wherein In step (2), the particle size of the silver powder is 0.05~10 microns, and the morphology is any one of spherical, flaky or dendritic.

4. The method of claim 1, wherein In step (2), the silver powder is mixed with the mixture obtained in step (1) by any one of grinding mixing, stirring mixing or planetary mixing.

5. Use of the reinforced silver / silica gel composite material obtained by the preparation method of claim 1 in flexible electronics. The specific steps are as follows: pattern the silver / silica gel composite material prepared in step (2) into stretchable interconnecting lines, pads or conductive adhesive for bonding electronic component pins and pads by any one of film plate scraping, screen printing, dispensing or printing, and then heat to solidify and shape the silver / silica gel composite material.

6. Use according to claim 5, characterized in that The heating and solidification temperature is controlled to be 100-240℃, and the solidification time is 0.3-1 hour.

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