Server novel FPC prepared based on weldable silver paste and preparation method thereof

Abstract

The invention discloses a novel server FPC (Flexible Printed Circuit) prepared based on weldable silver paste, which comprises a weldable silver paste circuit layer printed on the surface of a flexible substrate, a covering protection layer covering the surface of the flexible substrate printed with the weldable silver paste circuit layer, and a reinforcing layer adhered to a non-weldable silver paste circuit layer area, the weldable silver paste circuit layer is obtained by printing weldable silver paste prepared by mixing modified silver powder, an organic tin-silver complex, an organic carrier, a functional additive and an antioxidant, and the method comprises the steps of 1, material pretreatment and preparation, 2, silver paste printing, 3, low-temperature curing treatment, 4, protection treatment and 5, component welding. Through the collaborative design of the spherical modified silver powder, the organic tin-silver complex and the low-shrinkage flexible polymer, the interfacial tension of the molten solder can be reduced, gold plating or OSP pretreatment is not needed, the welding reliability is improved, meanwhile, the process is simplified, the equipment investment is greatly reduced, the labor cost is greatly reduced, and the production period is greatly shortened.

Description

Technical Field

[0001] This invention relates to the field of flexible printed circuit board technology, and in particular to a novel server FPC based on solderable silver paste and its preparation method. Background Technology

[0002] With the explosive growth in server computing power demand, the high-frequency, high-speed interconnection requirements of internal electronic components have placed higher demands on the performance of flexible printed circuit boards (FPCs).

[0003] Traditional server FPC metallization processes mainly rely on "copper-based + surface gold plating," which suffers from complex manufacturing processes, high equipment investment, poor welding reliability, and susceptibility to defects such as incomplete soldering or poor solder wetting. In recent years, silver paste printing technology has been attempted for FPCs due to its simple process and excellent conductivity. However, existing silver pastes generally suffer from the bottleneck of "poor solderability." Therefore, this invention proposes a novel server FPC based on solderable silver paste and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0004] To address the aforementioned issues, the present invention aims to propose a novel server FPC based on solderable silver paste and its preparation method. This novel server FPC based on solderable silver paste utilizes the synergistic design of spherical modified silver powder, organotin-silver complex, and low-shrinkage flexible polymer to reduce the interfacial tension of molten solder. Furthermore, it eliminates the need for gold plating or OSP pretreatment, thus improving soldering reliability. The high adhesion between the silver paste and the flexible substrate, along with the low-shrinkage design, effectively enhances the flexibility and adaptability of the circuit board, meeting the low-loss transmission requirements of high-frequency signals in servers. Simultaneously, the simplified process significantly reduces equipment investment, labor costs, and production cycle.

[0005] To achieve the objectives of this invention, the following technical solution is provided: A novel server FPC based on solderable silver paste, comprising a flexible substrate, a solderable silver paste circuit layer, a protective cover layer, and a reinforcing layer. The solderable silver paste circuit layer is printed on the surface of the flexible substrate. The protective cover layer covers the surface of the flexible substrate on which the solderable silver paste circuit layer is printed. The reinforcing layer is bonded to the non-solderable silver paste circuit layer area. The solderable silver paste circuit layer is obtained by printing solderable silver paste. The solderable silver paste is prepared by mixing 82-86% by mass of modified silver powder, 0.5-1.2% of organotin-silver complex, 3-8% of organic carrier, 2-5% of functional additives, and 0.1-0.5% of antioxidant. The modified silver powder is obtained by surface modification with a silane coupling agent.

[0006] Further improvements include: the thickness of the flexible substrate is 12.5-50μm; the thickness of the solderable silver paste circuit layer is 10-30μm, and the printed line width is 5-20μm; the peel strength between the flexible substrate and the solderable silver paste circuit layer is ≥3N / mm; and the thickness of the protective covering layer is 10-25μm, with a peel strength between the protective covering layer and the solderable silver paste circuit layer ≥2N / mm.

[0007] A further improvement is that the flexible substrate is one of polyimide, polyetheretherketone, or polyethersulfone, and the protective covering layer is thermosetting polyimide or acrylate adhesive.

[0008] Further improvements are made in that: the modified silver powder has a particle size D50 of 0.5-2 μm; the organotin-silver complex is a dibutyltin-silver isocyanate complex; the organic carrier contains acrylic resin, dispersant, and solvent; the functional additives are glass powder with a particle size ≤1 μm and polyamide-imide; and the antioxidant is 2,6-di-tert-butyl-p-cresol.

[0009] A further improvement is that the solvent is prepared by mixing terpineol and diethylene glycol butyl ether in a volume ratio of 3:1, the dispersant is a polycarboxylate, and the glass powder is a Bi2O3-B2O3-SiO2 system glass powder.

[0010] A further improvement is that an anti-oxidation transition layer with a thickness of 0.5-2μm is provided between the contact surface of the protective layer and the solderable silver paste circuit layer. This layer is formed by the reaction of the silane coupling agent on the surface of the modified silver powder in the solderable silver paste with the material of the protective layer.

[0011] A method for fabricating a novel server FPC based on solderable silver paste includes the following steps:

[0012] Step 1: Material pretreatment and preparation. The flexible substrate is pretreated by plasma cleaning. Then, modified silver powder, organotin-silver complex, organic carrier, functional additives and antioxidants are mixed to prepare solderable silver paste.

[0013] Step 2: Silver paste printing. Solderable silver paste is printed onto the surface of the pretreated flexible substrate according to the circuit pattern to form a solderable silver paste circuit.

[0014] Step 3: Low-temperature curing treatment. The printed flexible substrate is placed in a hot air oven for heating and drying curing, and then naturally cooled to room temperature to obtain a solderable silver paste circuit layer.

[0015] Step 4: Protective treatment. A protective liquid precursor is coated onto the surface of the flexible substrate to cover the solderable silver paste circuit layer. After pre-curing at 80-120℃ for 30 minutes, the reinforcing layer is attached to the surface of the non-circuit area and hot-pressed to form the protective cover and the reinforcing layer.

[0016] Step 5: Component soldering. The electronic components of the electronic label are soldered onto the silver paste circuit using a reflow soldering process to prepare the new server FPC.

[0017] Further improvements are made in the following ways: In step one, the plasma cleaning is performed using an Ar / O2 mixed gas at a power of 100-200W for 3-5 minutes; in step two, the printing method is either screen printing or inkjet printing, with a line width / spacing of 5-20μm. When using screen printing, the mesh count is 150-300 mesh; when using inkjet printing, the nozzle diameter is 20-50μm, and the printing speed is 50-100mm / s.

[0018] A further improvement is made in step three: the hot air oven is first heated to 100°C at a rate of 2°C / min and held for 30 minutes, and then heated to 150°C at a rate of 5°C / min and held for 60 minutes before being allowed to cool naturally.

[0019] The further improvement is that the hot pressing temperature in step four is 160-180℃, the pressure is 0.5-1MPa, and the hot pressing time is 30min.

[0020] The beneficial effects of this invention are as follows: By synergistically designing spherical modified silver powder, organotin-silver complex, and low-shrinkage flexible polymer, this invention can reduce the interfacial tension of molten solder and eliminate the need for gold plating or OSP pretreatment, thereby improving welding reliability. The high bonding strength and low shrinkage design of the silver paste with the flexible substrate effectively enhance the flexibility and adaptability of the circuit board, meeting the requirements of low-loss transmission of high-frequency signals in servers. The method of this invention simplifies the process, significantly reduces equipment investment, labor costs, and production cycle, and is suitable for high-frequency and high-speed interconnection scenarios in servers. Attached Figure Description

[0021] Figure 1 This is a cross-sectional schematic diagram of the present invention.

[0022] Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0023] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0024] With the explosive growth in server computing power demand, the high-frequency and high-speed interconnection requirements of internal electronic components have placed higher demands on the performance of flexible printed circuit boards (FPCs): on the one hand, FPCs need to have excellent electrical conductivity to reduce signal transmission loss; on the other hand, they need to be able to reliably connect under harsh environments such as high-frequency vibration and alternating temperature and humidity of servers, while the bending resistance of flexible substrates (such as polyimide PI and polyether ether ketone PEEK) requires the metal circuits to have high ductility.

[0025] Traditional server FPC metallization processes primarily employ a "copper-based + surface gold plating" method. The specific process includes: flexible substrate cleaning → drilling → PVD deposition of a copper seed layer → electroless copper plating for thickening → electroplating of copper (forming conductor lines) → surface treatment (such as micro-etching, OSP) → nickel-gold plating (typically 5-15 μm thick). This process has the following significant drawbacks:

[0026] The process is complex and costly. Traditional processes require 7-10 steps, especially the copper / gold electroplating step, which consumes a large amount of precious metals and requires significant equipment investment.

[0027] The reliability of welding is limited. Although the gold plating layer is resistant to oxidation, uneven thickness can easily lead to the "black plate" problem. During welding, it is easy to have poor solder joints or poor solder wetting.

[0028] Insufficient flexibility and a large difference in the coefficient of thermal expansion (CTE) between copper circuits and flexible substrates can easily lead to cracking of copper circuits due to long-term bending. This requires additional thickening of the substrate or thinning of the copper layer, further sacrificing conductivity.

[0029] In recent years, silver paste printing technology has become popular due to its simple process and excellent conductivity (silver's intrinsic conductivity is approximately 6.3 × 10⁻⁶). 7 S / m, higher than copper's 5.96×10 7 Silver paste (S / m) has been attempted for use in FPC, but existing silver paste generally suffers from the bottleneck of "poor solderability" - after the silver paste is cured, organic residues or oxide layers are easily formed on the surface, and the wetting angle with solder (such as SnAgCu) is >60°, while the wetting angle of traditional gold plating is <20°. Additional pretreatment such as plasma cleaning and chemical nickel-gold plating is required before soldering, which cannot meet the high-efficiency manufacturing requirements of server FPC.

[0030] Based on the above issues, according to Figure 1 and Figure 2As shown, this embodiment provides a novel server FPC based on solderable silver paste, comprising a flexible substrate, a solderable silver paste circuit layer, a protective cover layer, and a reinforcing layer. The solderable silver paste circuit layer is printed on the surface of the flexible substrate, the protective cover layer covers the surface of the flexible substrate on which the solderable silver paste circuit layer is printed, and the reinforcing layer is bonded to the non-solderable silver paste circuit layer area. The solderable silver paste circuit layer is obtained by printing solderable silver paste, which is made by mixing 82-86% modified silver powder, 0.5-1.2% organotin-silver complex, 3-8% organic carrier, 2-5% functional additives, and 0.1-0.5% antioxidant by mass percentage. The modified silver powder is obtained by surface modification with a silane coupling agent.

[0031] The addition of organotin-silver complexes can reduce the interfacial tension of molten solder, inhibit anion migration, and enhance solder joint strength.

[0032] The flexible substrate has a thickness of 12.5-50μm; the solderable silver paste circuit layer has a thickness of 10-30μm and a printed line width of 5-20μm; the peel strength between the flexible substrate and the solderable silver paste circuit layer is ≥3N / mm; the protective cover has a thickness of 10-25μm and a peel strength between it and the solderable silver paste circuit layer is ≥2N / mm.

[0033] The flexible substrate is one of polyimide, polyetheretherketone, or polyethersulfone, and the protective covering layer is thermosetting polyimide or acrylate adhesive.

[0034] The modified silver powder has a particle size D50 of 0.5-2 μm, the organotin-silver complex is a dibutyltin-silver isocyanate complex, the organic carrier includes acrylic resin, dispersant and solvent, the functional additives are glass powder with a particle size ≤1 μm and polyamide imide, and the antioxidant is 2,6-di-tert-butyl-p-cresol.

[0035] The solvent was prepared by mixing terpineol and diethylene glycol butyl ether in a volume ratio of 3:1, the dispersant was polycarboxylate, and the glass powder was a Bi2O3-B2O3-SiO2 system glass powder.

[0036] An anti-oxidation transition layer with a thickness of 0.5-2μm is provided between the contact surface of the protective layer and the solderable silver paste circuit layer. It is formed by the reaction of the silane coupling agent on the surface of the modified silver powder in the solderable silver paste with the material of the protective layer.

[0037] A method for fabricating a novel server FPC based on solderable silver paste includes the following steps:

[0038] Step 1: Material pretreatment and preparation. A plasma cleaning method is used to pretreat the flexible substrate with Ar / O2 mixed gas at a power of 100-200W for 3-5 minutes to remove surface organic contaminants. Then, modified silver powder, organotin-silver complex, organic carrier, functional additives and antioxidants are mixed in the following weight percentages: 86%, 0.8%, 8%, 5% and 0.2% to prepare solderable silver paste.

[0039] Step 2: Silver paste printing. Solderable silver paste is printed onto the surface of the pretreated flexible substrate according to the circuit pattern to form a solderable silver paste circuit.

[0040] The line width / spacing of screen printing or inkjet printing is 5-20μm. When using screen printing, the mesh count of the screen is 150-300 mesh; when using inkjet printing, the nozzle diameter is 20-50μm and the printing speed is 50-100mm / s.

[0041] Step 3: Low-temperature curing treatment. The printed flexible substrate is placed in a hot air oven for heating and drying curing. Specifically, the temperature is first raised to 100°C at a rate of 2°C / min and held for 30 minutes, then raised to 150°C at a rate of 5°C / min and held for 60 minutes. Then it is allowed to cool naturally to room temperature to obtain a solderable silver paste circuit layer.

[0042] Step 4: Protective treatment. A protective liquid precursor is coated onto the surface of the flexible substrate to cover the solderable silver paste circuit layer. After pre-curing at 90°C for 30 minutes, the reinforcing layer is attached to the surface of the non-circuit area and hot-pressed at 180°C and 0.8MPa for 30 minutes to form the protective cover and the reinforcing layer.

[0043] Step 5: Component soldering. The electronic components of the electronic label are soldered onto the silver paste circuit using a reflow soldering process to prepare the new server FPC.

[0044] Example 1

[0045] This embodiment provides an example of fabricating a novel server FPC using screen printing technology:

[0046] The flexible substrate is made of polyimide with a thickness of 25μm and an initial surface energy of ≥40mN / m. After being cleaned with Ar / O2 mixed gas at a power of 150W for 3 minutes to remove organic contaminants from the surface, the surface energy is increased to 55-60mN / m.

[0047] The solderable silver paste formulation consists of 86% modified silver powder, 0.8% organotin-silver complex, 8% organic carrier, 5% functional additives, and 0.2% antioxidant (2,6-di-tert-butyl-p-cresol).

[0048] The modified silver powder is a spherical silver powder with a D50 of 1 μm after modification with γ-aminopropyltriethoxysilane, and the amount of silane used in the modification is 0.5 wt%; the organic carrier contains 40% acrylic epoxy resin, 50% terpineol and diethylene glycol butyl ether mixed solvent in a volume ratio of 3:1, and 10% polycarboxylate dispersant; the functional additives contain 78.5% glass powder and 21.5% polyamide imide.

[0049] Using a screen printing machine with a 200-mesh polyester screen (20μm thick, aperture ratio ≥70%), silver paste is printed onto the surface of a polyimide substrate. The printing pressure is 0.5MPa, the squeegee speed is 50mm / s, forming a line pattern with a line width of 20μm and a spacing of 20μm. The printed line is 10cm long and 20μm wide, and the theoretical resistance of a single line is ≈0.01Ω.

[0050] The printed substrate is placed in a hot air circulating oven and heated to 100°C at 2°C / min, and held for 30 min (solvent evaporation stage); then heated to 150°C at 5°C / min and held for 60 min (resin crosslinking and glass powder melting stage), and then naturally cooled to room temperature to form a solderable silver paste circuit layer (thickness 22μm).

[0051] Liquid thermosetting polyimide was coated onto the surface of the solderable silver paste circuit layer to a thickness of 15 μm (scalpel coating, 15 μm gap); it was then placed in a vacuum hot press at 120°C and 0.3 MPa for 30 min to pre-cur. Subsequently, the reinforcing layer was bonded to the surface of the non-circuit area and hot-pressed at 180°C and 0.8 MPa for 30 min to form a protective layer and a reinforcing layer (total thickness 30 μm).

[0052] After hot pressing, due to the reaction between the silane coupling agent on the surface of the modified silver powder in the solderable silver paste and the material of the protective layer, an antioxidant transition layer with a thickness of 0.9 μm is formed between the protective layer and the contact surface of the solderable silver paste circuit layer.

[0053] Using a CO2 laser windowing machine, windows (0.8 mm in diameter) are opened in the pad area of ​​the solderable silver paste circuit layer (windowing accuracy ±15 μm) to expose the pads for soldering. Finally, the electronic components of the electronic label are soldered onto the silver paste circuit using a reflow soldering process to prepare a new type of server FPC.

[0054] The peel strength between the flexible substrate and the solderable silver paste circuit layer of the prepared FPC is 8.3 N / mm; the thickness of the protective layer is 18 μm and the peel strength between it and the solderable silver paste circuit layer is 4.6 N / mm.

[0055] Example 2

[0056] This embodiment provides an example of fabricating a novel server FPC using inkjet printing technology:

[0057] The flexible substrate is made of polyetheretherketone (PEEK) with a thickness of 12.5 μm and an initial surface energy of ≥35 mN / m. After cleaning with Ar / O2 mixed gas at a power of 100 W for 3 min, organic contaminants on the surface are removed, and the surface energy is increased to 52 mN / m.

[0058] The solderable silver paste formulation consists of 86% modified silver powder, 0.8% organotin-silver complex, 8% organic carrier, 5% functional additives, and 0.2% antioxidant (2,6-di-tert-butyl-p-cresol).

[0059] The modified silver powder is a spherical silver powder with a D50 of 1 μm after modification with γ-aminopropyltriethoxysilane, and the amount of silane used in the modification is 0.5 wt%; the organic carrier contains 40% acrylic epoxy resin, 50% terpineol and diethylene glycol butyl ether mixed solvent in a volume ratio of 3:1, and 10% polycarboxylate dispersant; the functional additives contain 78.5% glass powder and 21.5% polyamide imide.

[0060] Using an inkjet printer with a nozzle diameter of 30μm, a droplet volume of 15pl, and a printing speed of 80mm / s, solderable silver paste is printed onto the surface of a polyetheretherketone substrate to form a line pattern with a line width of 15μm and a spacing of 15μm. The resulting line is 5cm long and 15μm wide, with a theoretical resistance of approximately 0.006Ω for a single line.

[0061] The printed substrate was placed in a constant temperature oven and heated to 100℃ at a rate of 2℃ / min and held for 30 minutes. Then it was heated to 150℃ at a rate of 5℃ / min and held for 60 minutes. It was then allowed to cool naturally to room temperature. The thickness of the silver paste circuit layer was 12μm.

[0062] An acrylic adhesive was coated onto the surface of the solderable silver paste circuit layer to a thickness of 10 μm (spin coating, 2000 rpm); UV curing was then performed at a wavelength of 365 nm and a power of 500 mW / cm². 2 The process takes 60 seconds; then the reinforcing layer is bonded to the surface of the non-circuit area and hot-pressed at 180°C and 0.8MPa for 30 minutes to form a protective layer and a reinforcing layer (total thickness 22μm).

[0063] After hot pressing, due to the reaction between the silane coupling agent on the surface of the modified silver powder in the solderable silver paste and the material of the protective layer, an anti-oxidation transition layer with a thickness of 1.2μm is formed between the protective layer and the contact surface of the solderable silver paste circuit layer.

[0064] Using a CO2 laser windowing machine, windows (0.8 mm in diameter) are opened in the pad area of ​​the solderable silver paste circuit layer (windowing accuracy ±15 μm) to expose the pads for soldering. Finally, the electronic components of the electronic label are soldered onto the silver paste circuit using a reflow soldering process to prepare a new type of server FPC.

[0065] The peel strength between the flexible substrate and the solderable silver paste circuit layer in the prepared FPC is 8.1 N / mm; the thickness of the protective covering layer is 19 μm and the peel strength between it and the solderable silver paste circuit layer is 4.8 N / mm.

[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A novel server FPC based on solderable silver paste, characterized in that: The device comprises a flexible substrate, a solderable silver paste circuit layer, a protective overlay, and a reinforcing layer. The solderable silver paste circuit layer is printed on the surface of the flexible substrate. The protective overlay covers the surface of the flexible substrate on which the solderable silver paste circuit layer is printed. The reinforcing layer is bonded to the non-solderable silver paste circuit layer area. The solderable silver paste circuit layer is obtained by printing solderable silver paste. The solderable silver paste is prepared by mixing 82-86% modified silver powder, 0.5-1.2% organotin-silver complex, 3-8% organic carrier, 2-5% functional additives, and 0.1-0.5% antioxidant by mass percentage. The modified silver powder is obtained by surface modification with a silane coupling agent.

2. The novel server FPC based on solderable silver paste according to claim 1, characterized in that: The flexible substrate has a thickness of 12.5-50 μm; the solderable silver paste circuit layer has a thickness of 10-30 μm and a printed line width of 5-20 μm; the peel strength between the flexible substrate and the solderable silver paste circuit layer is ≥3 N / mm; the protective covering layer has a thickness of 10-25 μm and a peel strength between it and the solderable silver paste circuit layer is ≥2 N / mm.

3. A novel server FPC based on solderable silver paste according to claim 1, characterized in that: The flexible substrate is one of polyimide, polyetheretherketone, or polyethersulfone, and the protective covering layer is thermosetting polyimide or acrylate adhesive.

4. A novel server FPC based on solderable silver paste according to claim 1, characterized in that: The modified silver powder has a particle size D50 of 0.5-2 μm, the organotin-silver complex is a dibutyltin-silver isocyanate complex, the organic carrier includes acrylic resin, dispersant and solvent, the functional additives are glass powder with a particle size ≤1 μm and polyamide imide, and the antioxidant is 2,6-di-tert-butyl-p-cresol.

5. A novel server FPC based on solderable silver paste according to claim 1, characterized in that: The solvent is prepared by mixing terpineol and diethylene glycol butyl ether in a volume ratio of 3:1, the dispersant is a polycarboxylate, and the glass powder is a Bi2O3-B2O3-SiO2 system glass powder.

6. A novel server FPC based on solderable silver paste according to claim 1, characterized in that: An antioxidant transition layer with a thickness of 0.5-2 μm is provided between the contact surface of the protective layer and the solderable silver paste circuit layer. It is formed by the reaction of the silane coupling agent on the surface of the modified silver powder in the solderable silver paste with the material of the protective layer.

7. A method for fabricating a novel server FPC based on solderable silver paste, characterized in that, Includes the following steps: Step 1: Material pretreatment and preparation. The flexible substrate is pretreated by plasma cleaning. Then, modified silver powder, organotin-silver complex, organic carrier, functional additives and antioxidants are mixed to prepare solderable silver paste. Step 2: Silver paste printing. Solderable silver paste is printed onto the surface of the pretreated flexible substrate according to the circuit pattern to form a solderable silver paste circuit. Step 3: Low-temperature curing treatment. The printed flexible substrate is placed in a hot air oven for heating and drying curing, and then naturally cooled to room temperature to obtain a solderable silver paste circuit layer. Step 4: Protective treatment. A protective liquid precursor is coated onto the surface of the flexible substrate to cover the solderable silver paste circuit layer. After pre-curing at 80-120℃ for 30 minutes, the reinforcing layer is attached to the surface of the non-circuit area and hot-pressed to form the protective cover and the reinforcing layer. Step 5: Component soldering. The electronic components of the electronic label are soldered onto the silver paste circuit using a reflow soldering process to prepare the new server FPC.

8. The method for preparing a novel server FPC based on solderable silver paste according to claim 7, characterized in that: In step one, the plasma cleaning is performed using an Ar / O2 mixed gas at a power of 100-200W for 3-5 minutes. In step two, the printing method is either screen printing or inkjet printing, with a line width / spacing of 5-20μm. When using screen printing, the mesh count is 150-300 mesh; when using inkjet printing, the nozzle diameter is 20-50μm, and the printing speed is 50-100mm / s.

9. The method for preparing a novel server FPC based on solderable silver paste according to claim 7, characterized in that: In step three, the hot air oven is first heated to 100°C at a rate of 2°C / min and held at that temperature for 30 minutes, and then heated to 150°C at a rate of 5°C / min and held at that temperature for 60 minutes before being allowed to cool naturally.

10. A method for preparing a novel server FPC based on solderable silver paste according to claim 7, characterized in that: In step four, the hot pressing temperature is 160-180℃, the pressure is 0.5-1MPa, and the hot pressing time is 30min.

Images