Novel electronic price tag FPC prepared based on weldable silver paste and preparation method

Abstract

The invention discloses a novel electronic price tag FPC prepared based on weldable silver paste, which comprises a base material printed with a silver paste circuit, a display unit used for displaying a price tag identifier, a driving unit, a communication unit and a power supply unit welded with the silver paste circuit, and the silver paste circuit is prepared by mixing and printing composite silver powder, an organic carrier and a modifier. The preparation method comprises the steps of (1) substrate pretreatment, (2) preparation of weldable silver paste, (3) silver paste printing, (4) low-temperature curing and (5) component welding. The conductive circuit is formed through direct printing and low-temperature curing of the weldable silver paste with low surface energy and high oxidation resistance, low-temperature welding of components can be realized without a gold plating layer, the process is simple, the production period is greatly shortened, and the equipment cost and the material cost are effectively reduced; the electrical resistivity after curing can be greatly reduced, the matching property of a silver paste circuit and a base material is better, and the bending resistance is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible electronic technology, and in particular to a novel electronic price tag FPC prepared based on a solderable silver paste and a preparation method. BACKGROUND

[0002] Currently, the preparation of traditional flexible circuit boards mainly relies on the "copper foil-substrate-etching" process: first, a copper foil is laminated on a polyimide (PI) or polyester (PET) substrate, a circuit is formed by photolithography / etching, and a solderable protective layer is formed by surface treatment (such as chemical nickel-gold plating, electroplating gold); however, the traditional process is complex, the equipment investment cost is high, and the production cost is also greatly increased by plating gold and other processes, and the chemical nickel-gold plating layer is prone to "black plate" defects, which increases the soldering void rate and affects the electrical connection reliability. Therefore, the present application proposes a novel electronic price tag FPC prepared based on a solderable silver paste and a preparation method to solve the problems existing in the prior art. SUMMARY

[0003] In view of the above problems, the present application aims to provide a novel electronic price tag FPC prepared based on a solderable silver paste and a preparation method. The novel electronic price tag FPC prepared based on a solderable silver paste and a preparation method directly prints and low-temperature cures a conductive circuit using a solderable silver paste with low surface energy and high oxidation resistance, which can realize low-temperature soldering of components without a gold plating layer, has a simple process, greatly shortens the production cycle, effectively reduces the equipment cost and material cost, and is suitable for light, thin, flexible, and low-cost electronic price tag requirements.

[0004] To achieve the purpose of the present application, the present application realizes the following technical scheme: a novel electronic price tag FPC prepared based on a solderable silver paste, comprising a substrate, a silver paste circuit, a display unit, a driving unit, a communication unit, and a power supply unit, the substrate is printed with a silver paste circuit, the display unit is used to display the price tag identification, the driving unit, the communication unit, and the power supply unit are soldered with the silver paste circuit, and the silver paste circuit is printed and made by mixing a composite silver powder, an organic carrier, and a modifier.

[0005] A preparation method of a novel electronic price tag FPC prepared based on a solderable silver paste, comprising the following steps:

[0006] Step one, substrate pretreatment, select a flexible substrate and pretreat it by plasma cleaning;

[0007] Step two, preparing the solderable silver paste, mixing the composite silver powder, organic carrier and modifier according to the mass percentage of 70-90%:10-30%:0.5-2% to obtain the solderable silver paste;

[0008] Step three, silver paste printing, printing the circuit pattern on the substrate using the solderable silver paste;

[0009] Step four, low-temperature curing, placing the printed substrate in a vacuum drying oven, heating to 80-120℃ at a rate of 1-5℃ / min and keeping for 10-30min, then heating to 130-160℃ at a rate of 1-5℃ / min and keeping for 30-90min to complete the silver paste curing;

[0010] Step five, component soldering, using reflow soldering process to solder the electronic components of the electronic price tag on the silver paste circuit to prepare the electronic price tag FPC.

[0011] Further improvement lies in that the plasma cleaning in step one uses Ar / O2 mixed gas, the power is 50-200W, and the cleaning time is 10-60s.

[0012] Further improvement lies in that the composite silver powder in step two includes 10-30% of nano silver powder and 70-90% of micron silver powder, the particle size of the nano silver powder is ≤100nm, and the particle size of the micron silver powder is 1-5μm; the organic carrier includes 5-10% of low molecular weight epoxy resin, 3-8% of acrylate leveling agent and 2-5% of silicone thixotropic agent, and the balance is a mixed solvent of pine oil / diethylene glycol butyl ether; the modifier is a mixture obtained by mixing amino silane coupling agent and fluorine-containing surfactant according to a mass ratio of 3:1.

[0013] Further improvement lies in that the composite silver powder includes 12-20% of nano silver powder and 75-80% of micron silver powder, the particle size of the nano silver powder is 10-100nm, and the particle size of the micron silver powder is 1-3μm; the softening point of the low molecular weight epoxy resin is 50-70℃, the acrylate leveling agent is one of BYK-333 and BYK-306, and the silicone thixotropic agent is one of BYK-410 and BYK-430; the fluorine-containing surfactant is one of potassium perfluorooctylsulfonate and potassium perfluorohexylsulfonate.

[0014] Further improvement lies in that the viscosity of the solderable silver paste prepared in step two at 25℃ is 8000-15000 , and the volume resistivity after curing is ≤8 .

[0015] Further improvement lies in that: the printing in step three adopts silk screen printing or inkjet printing, the silk screen printing has a printing screen mesh number of 100-400 meshes and a thickness of 3-25 microns, the printed line width / line distance is 30-50 microns / 30-50 microns, the inkjet printing has a nozzle diameter of 10-50 microns, the number of layers is 2-3 layers, the thickness of a single layer is 2-10 microns, and the line width / line distance is 10-30 microns / 10-30 microns.

[0016] Further improvement lies in that: the vacuum degree of the vacuum drying box in step four is-0.05--0.1 MPa.

[0017] The application has the advantages that: the application directly prints and low-temperature cures the conductive circuit by using the low-surface-energy and high-oxidation-resistance solderable silver paste, realizes low-temperature soldering of components and devices without gold plating layer, has simple process, greatly shortens the production cycle, effectively reduces the equipment cost and material cost, the silver paste is composed of composite silver powder, organic carrier and surface modifier, the synergy of the composite silver powder obtained by mixing nano silver powder and micron silver powder can greatly reduce the resistivity after curing, the silver paste circuit has better matching with the substrate, effectively improves the bending resistance, and is suitable for the demand of light, thin, flexible and low-cost electronic price tag. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The application has the advantages that: the application directly prints and low-temperature cures the conductive circuit by using the low-surface-energy and high-oxidation-resistance solderable silver paste, realizes low-temperature soldering of components and devices without gold plating layer, has simple process, greatly shortens the production cycle, effectively reduces the equipment cost and material cost, the silver paste is composed of composite silver powder, organic carrier and surface modifier, the synergy of the composite silver powder obtained by mixing nano silver powder and micron silver powder can greatly reduce the resistivity after curing, the silver paste circuit has better matching with the substrate, effectively improves the bending resistance, and is suitable for the demand of light, thin, flexible and low-cost electronic price tag. DETAILED DESCRIPTION

[0019] In order to deepen the understanding of the application, the application will be further described in the following embodiments, and the embodiments are only used to explain the application and do not constitute a limitation on the protection scope of the application.

[0020] Electronic price tag (ESL) as a kind of intelligent display equipment to replace traditional paper label, has been widely used in retail, logistics and other fields. Its core component is flexible printed circuit board (FPC), which needs to meet the requirements of light and thin (thickness ≤50 microns), flexible (resistant to 10 5 times or more bending), low cost (single cost <0.5 dollars) and high reliability (long-term stable display).

[0021] At present, the preparation of traditional flexible circuit board mainly depends on the "copper foil-substrate-etching" process: first, the copper foil is pressed on the polyimide (PI) or polyester (PET) substrate, the circuit is formed by photoetching / etching, and then the surface treatment such as chemical nickel plating and gold plating is carried out to form a weldable protective layer with a thickness of ≥0.05 microns; however, this process has the following significant defects:

[0022] Complex process: the traditional process needs to go through drilling, electroplating seed layer, pattern transfer, etching, film removal, surface treatment and other processes, the production cycle is long≥24 hours, and it needs photoetching machine, electroplating line and other equipment, so the equipment investment is high;

[0023] High cost: the consumption of copper foil and precious metals such as gold and nickel is large, and the surface treatment process accounts for more than 30% of the production cost;

[0024] Limited flexibility: the thermal expansion coefficient (CTE) of copper foil and substrate is large (copper CTE≈17ppm / ℃, and PI≈13ppm / ℃), and long-term bending easily leads to circuit rupture;

[0025] Welding hazard: the chemical nickel-gold layer is prone to "black plate" defects, i.e. nickel layer oxidation, which leads to an increase in welding cavity rate, and the welding cavity rate is >5%, affecting the reliability of electrical connection.

[0026] Although silver paste printing technology has been concerned in recent years due to its low cost and low temperature process, the weldability of the circuit is generally insufficient: the surface of the traditional silver paste (such as thermosetting silver paste) is prone to oxidation after curing, and the wetting angle with solder (such as Sn-Ag-Cu) is >60° (the wetting angle of the traditional gold plating layer is <20°), so an additional gold plating layer is needed to realize welding, which cannot truly simplify the process.

[0027] Based on the above problems, according to Figure 1 The embodiment of the present application provides a new type of electronic price tag FPC prepared based on weldable silver paste, which comprises a substrate, a silver paste circuit, a display unit, a driving unit, a communication unit and a power supply unit, the silver paste circuit is printed on the substrate, the display unit is used for displaying price tag identification, the driving unit, the communication unit and the power supply unit are welded with the silver paste circuit, and the silver paste circuit is printed by mixing composite silver powder, an organic carrier and a modifier.

[0028] The display unit is realized by electrophoretic display film (thickness 20-50μm), OLED or LED, the driving unit is a driving IC, the size is 0201-0402 (length x width≤1.0mm x 0.5mm), the communication unit is a flexible antenna, the frequency range is 860-960MHz (RFID frequency band) or 2.4-2.5GHz (Wi-Fi / Bluetooth frequency band), and the power supply unit is a button cell or a thin film battery.

[0029] A preparation method of a new type of electronic price tag FPC prepared based on weldable silver paste, comprising the following steps:

[0030] Step one, substrate pretreatment, selecting a flexible substrate, and adopting plasma cleaning for pretreatment;

[0031] The plasma cleaning adopts Ar / O2 mixed gas, the power is 50-200W, and the cleaning time is 10-60s.

[0032] Step two, preparing the solderable silver paste, mixing the composite silver powder, organic carrier and modifier according to the mass percentage of 70-90%:10-30%:0.5-2% to obtain the solderable silver paste;

[0033] The composite silver powder includes 12-20% of nano silver powder and 75-80% of micron silver powder, the particle size of the nano silver powder is 10-100 nm, and the particle size of the micron silver powder is 1-3 μm; the organic carrier includes 5-10% of low molecular weight epoxy resin, 3-8% of acrylate leveling agent and 2-5% of silicone thixotropic agent, and the balance is a mixed solvent of terpineol / diethylene glycol butyl ether; the modifier is a mixture of amino silane coupling agent and fluorine-containing surfactant according to a mass ratio of 3:1, the general formula of the amino silane coupling agent is R-NH2·Si(OR’)3, R is C1-C6 alkyl, and R’ is C1-C3 alkyl;

[0034] The softening point of the low molecular weight epoxy resin is 50-70℃, the acrylate leveling agent is BYK-333, the silicone thixotropic agent is BYK-410, and the fluorine-containing surfactant is potassium perfluorooctyl sulfonate;

[0035] The viscosity of the prepared solderable silver paste at 25℃ is 8000-15000 , and the volume resistivity after curing is ≤8 .

[0036] Step three, silver paste printing, printing the circuit pattern on the substrate using the solderable silver paste;

[0037] Specifically, silk screen printing or inkjet printing is adopted, the printing screen mesh number of the silk screen printing is 100-400 meshes, the thickness is 3-25 μm, and the line width / line spacing is 30-50 μm / 30-50 μm; the nozzle diameter of the inkjet printing is 10-50 μm, the layer number is 2-3 layers, the single layer thickness is 2-10 μm, and the line width / line spacing is 10-30 μm / 10-30 μm.

[0038] Step four, low-temperature curing, placing the printed substrate in a vacuum drying box with a vacuum degree of -0.05--0.1 MPa, heating to 80-120℃ at a rate of 1-5℃ / min and keeping for 10-30 min, and then heating to 130-160℃ at a rate of 1-5℃ / min and keeping for 30-90 min to complete the silver paste curing.

[0039] Step five, component soldering, soldering the electronic components of the electronic price tag on the silver paste circuit by using the reflow soldering process to prepare the electronic price tag FPC. Example 1

[0040] In this embodiment, the solderable silver paste circuit board of the PI substrate is prepared by using the above method:

[0041] Substrate pretreatment: 25 μm thick PI film was selected, and Ar / O2=3:1 mixed gas and 100 W power were used for 30 s plasma cleaning to remove surface organic contaminants.

[0042] Silver paste preparation: 80% composite silver powder, 12% organic carrier, 0.8% surface modifier, and the rest was a mixture of 3:1 volume ratio of terpineol / diethylene glycol butyl ether solvent were weighed according to the mass ratio, and ball-milled and dispersed at 300 rpm for 4 h to prepare the silver paste.

[0043] The composite silver powder was prepared by mixing 75% micron silver with a particle size of 3 μm and 25% nanosilver with a particle size of 50 nm; the organic carrier contained 6% epoxy resin E-51, 5% acrylate leveling agent BYK-333, 1% thixotropic agent BYK-410, and the rest was a mixture of terpineol / diethylene glycol butyl ether solvent; the surface modifier was prepared by mixing KH-550:F-53B at a volume ratio of 3:1.

[0044] Printing and curing: 200 mesh silk screen printing, line width / line spacing 30 μm / 30 μm, printing thickness 15 μm; pre-curing at 120°C for 30 min in a vacuum drying oven, and final curing at 150°C for 60 min.

[0045] Component soldering test: Sn-Ag-Cu solder (Sn-3Ag-0.5Cu) was used, the reflow soldering peak temperature was 230°C, the time was 20 s, and 0.1 0402 type resistor was soldered, the test soldering tension was ≥55 cN, and the wetting angle was 22°; the assembled silver paste circuit with display unit, driving unit, communication unit, and power unit was obtained to obtain a new type of electronic price tag FPC. Example 2

[0046] In this embodiment, the solderable silver paste circuit board antenna of the TPU substrate was prepared by the above method:

[0047] Substrate pretreatment: 50 μm thick TPU film, Ar / O2=1:1 mixed gas and 80 W power were used for 20 s plasma cleaning to remove surface organic contaminants.

[0048] Silver paste preparation: 90% composite silver powder, 9% organic carrier, 1% surface modifier, and the rest was a solvent, which were weighed according to the mass ratio, and ball-milled and dispersed at 300 rpm for 4 h to prepare the silver paste.

[0049] The composite silver powder is made of 80% micron silver with a particle size of 5 microns and 20% nano silver with a particle size of 80 nm; the organic carrier comprises 5% epoxy resin E-44, 3% acrylate leveling agent BYK-333, 1% thixotropic agent BYK-410, and the balance is a mixed solvent of pine oil and diethylene glycol butyl ether; the surface modifier is made by mixing KH-550 and F-53B at a volume ratio of 3:1.

[0050] Printing and curing: inkjet printing, nozzle diameter 30 microns, 3 layers, line width / line spacing 50 microns / 50 microns, curing conditions 120°C x 30 min→150°C x 60 min.

[0051] Antenna welding integration: overlap the flexible RFID antenna (silver paste material, thickness 20 microns) with the silver paste circuit on the circuit board by 2 mm, reflow soldering at 230°C for 25 s, and the test antenna return loss is -20 dB@915 MHz.

[0052] Finally, the welded silver paste circuit is assembled with the display unit, the driving unit, the communication unit and the power unit to obtain a new electronic price tag FPC.

[0053] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A new type of electronic price tag FPC prepared based on a solderable silver paste, characterized by: The electronic price tag FPC comprises a substrate, a silver paste circuit, a display unit, a driving unit, a communication unit and a power supply unit, the silver paste circuit is printed on the substrate, the display unit is used for displaying price tag identification, the driving unit, the communication unit and the power supply unit are welded with the silver paste circuit, and the silver paste circuit is made by mixing and printing composite silver powder, an organic carrier and a modifier.

2. A method for preparing a new type of electronic price tag FPC based on a solderable silver paste, characterized by, The method comprises the following steps: Step one, substrate pretreatment, selecting a flexible substrate and adopting plasma cleaning for pretreatment; Step two, preparing a solderable silver paste, mixing the composite silver powder, the organic carrier and the modifier according to the mass percentage of 70-90%:10-30%:0.5-2% to obtain the solderable silver paste; Step three, silver paste printing, printing the circuit pattern on the substrate by using the solderable silver paste; Step four, low-temperature curing, placing the printed substrate in a vacuum drying oven, heating to 80-120 DEG C at a rate of 1-5 DEG C / min and keeping for 10-30 min, then heating to 130-160 DEG C at a rate of 1-5 DEG C / min and keeping for 30-90 min to complete the silver paste curing; Step five, component soldering, welding the electronic components of the electronic price tag on the silver paste circuit by using a reflow soldering process to obtain the electronic price tag FPC.

3. The method for preparing a new type of electronic price tag FPC based on a solderable silver paste according to claim 2, characterized in that: In the step one, the plasma cleaning adopts Ar / O2 mixed gas, the power is 50-200 W, and the cleaning time is 10-60 s.

4. The method for preparing a new type of electronic price tag FPC based on a solderable silver paste according to claim 2, characterized in that: In the step two, the composite silver powder comprises 10-30% of nano silver powder and 70-90% of micron silver powder, the particle size of the nano silver powder is less than or equal to 100 nm, and the particle size of the micron silver powder is 1-5 mu m; the organic carrier comprises 5-10% of low molecular weight epoxy resin, 3-8% of acrylate leveling agent and 2-5% of organosilicon thixotropic agent, and the balance is a mixed solvent of pine oil and diethylene glycol butyl ether; the modifier is a mixture of amino silane coupling agent and fluorine-containing surfactant according to a mass ratio of 3:

1.

5. The method for preparing a new type of electronic price tag FPC based on a solderable silver paste according to claim 4, characterized in that: In the step two, the composite silver powder comprises 10-30% of nano silver powder and 70-90% of micron silver powder, the particle size of the nano silver powder is less than or equal to 100 nm, and the particle size of the micron silver powder is 1-5 mu m; the organic carrier comprises 5-10% of low molecular weight epoxy resin, 3-8% of acrylate leveling agent and 2-5% of organosilicon thixotropic agent, and the balance is a mixed solvent of pine oil and diethylene glycol butyl ether; the modifier is a mixture of amino silane coupling agent and fluorine-containing surfactant according to a mass ratio of 3:

1.

6. The method for preparing a new type of electronic price tag FPC based on a solderable silver paste according to claim 2, characterized in that: The solderable silver paste prepared in the second step has a viscosity of at 25°C, and a volume resistivity of ≤ after curing.

7. The method for preparing a new type of electronic price tag FPC based on a solderable silver paste according to claim 2, characterized in that: In the step three, printing is performed by silk screen printing or inkjet printing, the silk screen printing has a mesh number of 100-400 meshes and a thickness of 3-25 mu m, and the printed line width / line spacing is 30-50 mu m / 30-50 mu m; the inkjet printing has a nozzle diameter of 10-50 mu m, 2-3 layers, a single layer thickness of 2-10 mu m, and a line width / line spacing of 10-30 mu m / 10-30 mu m.

8. The method for preparing a new type of electronic price tag FPC based on a solderable silver paste according to claim 2, characterized in that: In the step four, the vacuum degree of the vacuum drying oven is-0.05--0.1 MPa.

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