A new type of soft and hard connection circuit board prepared based on a weldable silver paste

Abstract

The application discloses a new type of soft and hard connection circuit board prepared based on weldable silver paste, which comprises a rigid circuit board provided with a splicing groove, a splicing block arranged in the splicing groove, and positioning teeth distributed between the front end of the splicing block and the splicing groove, a flexible circuit board arranged on the upper side of the splicing block, sintered silver paste circuit layers arranged on the rigid circuit board and the flexible circuit board, a flexible welding disc arranged on the sintered silver paste circuit layer at the front end of the positioning teeth, and a rigid welding disc arranged on the end of the sintered silver paste circuit layer on the rigid circuit board at the front side of the positioning teeth; the application is combined with the bonding force of silver paste sintering through a mechanical splicing structure, effectively improves the bonding strength, simultaneously simplifies the production process, effectively reduces the production cost, and utilizes the heat conductivity of silver to help the electrical components produced integrally to quickly dissipate heat, improves the product life, and reduces the influence of high temperature on temperature-sensitive electrical components.

Description

Technical Field

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

[0002] Rigid-flex PCBs combine the support of rigid boards with the flexibility of flexible boards, making them widely used in aerospace, medical equipment, wearable electronics, and other fields. Traditional rigid-flex PCBs are manufactured using a lamination method, which involves bonding the flexible circuit layer (FPC) and the rigid circuit layer (PCB) together with prepreg using acrylic or epoxy resin adhesives under high temperature and pressure.

[0003] Traditional processing methods require multiple laminations and drilling, which are demanding in terms of precision, complex in process, and costly. In addition, the mismatch in the thermal expansion coefficients of the rigid and flexible parts leads to poor thermomechanical reliability at the connection interface, making electrical connection failures more likely. Furthermore, the high-temperature and high-pressure lamination process limits the embedded integration production of some temperature-sensitive components, causing component damage and failure. Therefore, this invention proposes a novel flexible-rigid interconnect circuit board based on solderable silver paste to solve the problems existing in the prior art. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to propose a novel flexible and rigid interconnect circuit board based on solderable silver paste. This novel flexible and rigid interconnect circuit board, based on solderable silver paste, effectively improves the bonding strength through a mechanical splicing structure combined with the bonding force of silver paste sintering. At the same time, it simplifies the production process and effectively reduces production costs. Through the wiring and sintering of the low-temperature sinterable silver paste, the thermal conductivity of silver can be used to help the heat of the integrally produced electrical components dissipate quickly, thereby improving product lifespan.

[0005] To achieve the objectives of this invention, the following technical solution is provided: A novel flexible-rigid interconnect circuit board based on solderable silver paste, comprising a rigid circuit board, a splicing mechanism, and a flexible circuit board. The splicing mechanism includes a splicing groove, a splicing block, positioning teeth, a sintered silver paste circuit layer, a flexible soldering pad, and a rigid soldering pad. The rigid circuit board is provided with a splicing groove, and a splicing block is provided in the splicing groove. Positioning teeth are also adapted to be distributed between the front end of the splicing block and the splicing groove. Tooth grooves adapted to the positioning teeth are also distributed on the front side of the splicing groove. A flexible circuit board is provided on the upper side of the splicing block. A sintered silver paste circuit layer is provided on both the rigid circuit board and the flexible circuit board, and is formed by printing. A flexible soldering pad is provided on the sintered silver paste circuit layer at the front end of the positioning teeth. A rigid soldering pad is provided at the end of the sintered silver paste circuit layer on the rigid circuit board located in front of the positioning teeth. The sintered silver paste circuit layer is formed by printing with low-temperature sinterable silver paste, which is made by mixing silver powder, composite flux, organic carrier, and additives.

[0006] Further improvements include: both the flexible and rigid welding pads are formed by low-temperature sintering silver paste printing and connected by heating and welding; the splicing groove and splicing block have a wedge-shaped fitting structure when viewed from above; and the flexible circuit board is provided with a high-temperature resistant coating layer.

[0007] A further improvement is that the mass percentage of the mixture of silver powder, composite flux, organic carrier and additives in the low-temperature sinterable silver paste is 70%-90%: 5%-15%: 3%-8%: 2%-5%.

[0008] A further improvement is that the silver powder has a particle size of 15-50 nm, and the composite flux is made by mixing Bi2O3, ZnO and glass powder in a mass percentage of 50%-70%:20%-30%:10%-20%.

[0009] A further improvement is that the organic carrier is a mixture of ethyl cellulose and pine oil in a volume ratio of 2-3:1, and the additive is lecithin.

[0010] A method for fabricating a novel flexible-rigid interconnect circuit board based on solderable silver paste includes the following steps:

[0011] Step 1: Fabricate splicing groove structure on rigid circuit board, and fabricate splicing block and positioning tooth structure to match it. Use lamination connection method to tightly press splicing block and positioning tooth structure to flexible circuit board.

[0012] Step 2: First, Bi2O3, ZnO and glass powder are mixed to prepare a composite flux. Then, ethyl cellulose and pine oil are mixed to prepare an organic carrier. Finally, silver powder, composite flux, organic carrier and additives are mixed to prepare a silver paste that can be sintered at low temperature.

[0013] Step 3: Print sintered silver paste circuit layers on rigid and flexible circuit boards, and print rigid solder pads on the sintered silver paste circuit layers near the splicing groove.

[0014] Step 4: Apply a high-temperature resistant coating layer to the printed flexible circuit board, and at the same time set a flexible solder pad at the front end of the positioning tooth structure that is connected to the sintered silver paste circuit layer on the flexible circuit board.

[0015] Step 5: Install the splicing block and positioning tooth structure into the splicing groove. At this time, the flexible welding pad and the rigid welding pad are overlapped. Finally, heat treatment is performed to fuse the flexible welding pad and the low-temperature sinterable silver paste of the rigid welding pad to complete the welding and obtain the flexible and rigid connection circuit board.

[0016] Further improvements are made in the following ways: in step one, the splicing groove structure, splicing block and positioning tooth structure on the rigid circuit board are machined by a milling machine; in step two, when preparing the composite flux, Bi2O3, ZnO and glass powder are first mixed, and then added to a ball mill for ball milling dispersion. The ball milling speed is 200-400 rpm and the ball milling time is 1-2 hours. The resulting composite flux has a particle size distribution of 1-10 μm.

[0017] A further improvement is that, in step three, the sintered silver paste circuit layer is printed using one of the following methods: screen printing, inkjet printing, or precision dispensing, resulting in a sintered silver paste circuit layer thickness of 20-30 μm.

[0018] A further improvement is that the heating treatment in step five is carried out under an inert gas protective atmosphere, and the heating temperature is 300-400℃, wherein the inert gas is either nitrogen or argon.

[0019] The beneficial effects of this invention are as follows: This invention effectively solves the problem of poor thermomechanical reliability in traditional adhesive bonding by using a mechanical splicing structure combined with the bonding force of silver paste sintering. The bonding strength is effectively improved, while the production process is simplified and the production cost is effectively reduced. By using low-temperature sintering silver paste for wiring and sintering, the thermal conductivity of silver can be used to help the heat of the integrated electrical components dissipate quickly, thereby improving product life and reducing the impact of high temperature on temperature-sensitive electrical components. Attached Figure Description

[0020] Figure 1 This is a top view of the structure of the present invention.

[0021] Figure 2 This is a side sectional view of the present invention.

[0022] The components include: 1. Rigid circuit board; 2. Flexible circuit board; 3. Splicing groove; 4. Splicing block; 5. Positioning teeth; 6. Sintered silver paste circuit layer; 7. Flexible welding pad; 8. Rigid welding pad; 9. High temperature resistant coating layer. 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] Rigid-Flex PCBs combine the support of rigid boards with the flexibility of flexible boards, and are widely used in aerospace, medical devices, wearable electronics and other fields.

[0025] Traditional rigid-flex PCBs are manufactured using a lamination method, which involves bonding the flexible circuit layer (FPC) and the rigid circuit layer (PCB) together with prepreg (PP) using an acrylic or epoxy resin adhesive under high temperature and pressure. This traditional method has many drawbacks.

[0026] 1. Complex process and high cost: It requires multiple laminations and drilling, and the alignment accuracy is extremely high, resulting in a relatively low yield.

[0027] 2. Thermomechanical reliability issues: Due to the mismatch in the coefficients of thermal expansion (CTE) of the rigid and flexible parts, the connection interface is prone to delamination and cracking under temperature cycling or mechanical bending stress, leading to electrical connection failure.

[0028] 3. Z-axis interconnect performance bottleneck: Traditional processes use mechanical drilling followed by chemical plating (PTH) to achieve vertical interconnects between layers. In small apertures and flexible areas, the copper layer on the hole wall is prone to cracking, resulting in poor reliability.

[0029] 4. Compatibility issues: The high-temperature and high-pressure lamination process limits the direct embedded integration of certain temperature-sensitive components (such as some sensors).

[0030] Based on the above issues, according to Figure 1 and Figure 2 As shown, this embodiment provides a novel rigid-flex circuit board based on solderable silver paste, including a rigid circuit board 1, a splicing mechanism, and a flexible circuit board 2. The splicing mechanism includes a splicing groove 3, splicing blocks 4, positioning teeth 5, a sintered silver paste circuit layer 6, a flexible soldering pad 7, and a rigid soldering pad 8. The rigid circuit board 1 is provided with a splicing groove 3, and splicing blocks 4 are disposed in the splicing groove 3. Positioning teeth 5 are also adapted and distributed between the front end of the splicing block 4 and the splicing groove 3. Positioning teeth 5 are also distributed on the front side of the splicing groove to adapt to the positioning teeth. The toothed groove and splicing block 4 are provided with a flexible circuit board 2. Both the rigid circuit board 1 and the flexible circuit board 2 are provided with sintered silver paste circuit layers 6. The sintered silver paste circuit layer 6 at the front end of the positioning tooth 5 is provided with a flexible soldering pad 7. The end of the sintered silver paste circuit layer 6 on the rigid circuit board 1 located in front of the positioning tooth 5 is provided with a rigid soldering pad 8. The sintered silver paste circuit layer 6 is formed by printing low-temperature sinterable silver paste. The low-temperature sinterable silver paste is made by mixing silver powder, composite flux, organic carrier and additives.

[0031] Both the flexible welding pad 7 and the rigid welding pad 8 are formed by low-temperature sintering silver paste printing and connected by heating welding. The splicing groove 3 and the splicing block 4 have a wedge-shaped fitting structure when viewed from above. The flexible circuit board 2 is provided with a high-temperature resistant coating layer 9.

[0032] The mass percentage of silver powder, composite flux, organic carrier and additives in the low-temperature sinterable silver paste is 70%-90%: 5%-15%: 3%-8%: 2%-5%.

[0033] The silver powder has a particle size of 15-50nm, and the composite flux is made by mixing Bi2O3, ZnO and glass powder in a mass percentage of 50%-70%:20%-30%:10%-20%.

[0034] The organic carrier is a mixture of ethyl cellulose and pine oil in a volume ratio of 2-3:1, and the additive is lecithin.

[0035] A method for fabricating a novel flexible-rigid interconnect circuit board based on solderable silver paste includes the following steps:

[0036] Step 1: Using a milling machine, a splicing groove 3 structure is machined on the rigid circuit board 1, and a matching splicing block 4 and positioning tooth 5 structure are machined. The splicing block 4 and positioning tooth 5 structure are then tightly pressed onto the flexible circuit board 2 using a lamination connection method.

[0037] Step 2: First, Bi2O3, ZnO and glass powder are mixed to prepare a composite flux. Then, ethyl cellulose and pine oil are mixed to prepare an organic carrier. Finally, silver powder, composite flux, organic carrier and additives are mixed to prepare a silver paste that can be sintered at low temperature.

[0038] In the preparation of the composite flux, Bi2O3, ZnO and glass powder are first mixed, and then added to a ball mill for ball milling dispersion. The ball milling speed is 200-400 rpm and the ball milling time is 1-2 hours. The particle size distribution of the obtained composite flux is 1-10 μm.

[0039] Step 3: Print sintered silver paste circuit layer 6 on rigid circuit board 1 and flexible circuit board 2, and print rigid solder pad 8 on the sintered silver paste circuit layer 6 near the splicing groove 3.

[0040] When printing the sintered silver paste circuit layer 6, one of the following methods is used: screen printing, inkjet printing, or precision dispensing. The resulting sintered silver paste circuit layer 6 has a thickness of 20-30μm.

[0041] Step 4: Apply a high-temperature resistant film layer 9 to the printed flexible circuit board 2, and at the same time, set a flexible soldering pad 7 at the front end of the positioning tooth 5 structure, which is connected to the sintered silver paste circuit layer 6 on the flexible circuit board 2.

[0042] Step 5: Install the splicing block 4 and positioning tooth 5 into the splicing groove 3. At this time, the flexible welding disk 7 and the rigid welding disk 8 are stacked. Finally, heat treatment is performed to fuse the flexible welding disk 7 with the low-temperature sinterable silver paste of the rigid welding to complete the welding and obtain the flexible and rigid connection circuit board.

[0043] The heat treatment is carried out under an inert gas protective atmosphere at a temperature of 300-400℃, wherein the inert gas is either nitrogen or argon.

[0044] Example

[0045] This embodiment provides a method for fabricating a novel flexible-rigid interconnect circuit board based on solderable silver paste, including:

[0046] Step 1: Using a milling machine, a splicing groove 3 structure is machined on the rigid circuit board 1, and a matching splicing block 4 and positioning tooth 5 structure are machined. The splicing block 4 and positioning tooth 5 structure are then tightly pressed onto the flexible circuit board 2 using a lamination connection method.

[0047] Step 2: First, Bi2O3, ZnO and glass powder are mixed to prepare a composite flux. Then, ethyl cellulose and pine oil are mixed in a volume ratio of 3:1 to prepare an organic carrier. Finally, silver powder, composite flux, organic carrier and additives are mixed in a mass percentage of 75%:15%:8%:2% to prepare a low-temperature sinterable silver paste.

[0048] In the preparation of the composite flux, Bi2O3, ZnO and glass powder are first mixed in a mass percentage of 65%:20%:15%, and then added to a ball mill for ball milling dispersion. The ball milling speed is 350 rpm and the ball milling time is 2 hours. The resulting composite flux has a particle size distribution of 1-10 μm.

[0049] Step 3: Print sintered silver paste circuit layer 6 on rigid circuit board 1 and flexible circuit board 2, and print rigid solder pad 8 on the sintered silver paste circuit layer 6 near the splicing groove 3.

[0050] The thickness of the sintered silver paste circuit layer 6 was 24μm when it was printed by screen printing.

[0051] Step 4: Apply a high-temperature resistant film layer 9 to the printed flexible circuit board 2, and at the same time, set a flexible soldering pad 7 at the front end of the positioning tooth 5 structure, which is connected to the sintered silver paste circuit layer 6 on the flexible circuit board 2.

[0052] Step 5: Install the splicing block 4 and positioning tooth 5 into the splicing groove 3. At this time, the flexible welding disk 7 and the rigid welding disk 8 are stacked. Finally, heat treatment is performed to fuse the flexible welding disk 7 with the low-temperature sinterable silver paste of the rigid welding to complete the welding and obtain the flexible and rigid connection circuit board.

[0053] The heat treatment is carried out under an argon protective atmosphere at a temperature of 340℃.

[0054] 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 flexible and rigid interconnect circuit board based on solderable silver paste, characterized in that: The system includes a rigid circuit board (1), a splicing mechanism, and a flexible circuit board (2). The splicing mechanism includes a splicing groove (3), a splicing block (4), positioning teeth (5), a sintered silver paste circuit layer (6), a flexible soldering pad (7), and a rigid soldering pad (8). The rigid circuit board (1) is provided with a splicing groove (3), and a splicing block (4) is provided in the splicing groove (3). Positioning teeth (5) are also adapted to be distributed between the front end of the splicing block (4) and the splicing groove (3). A flexible circuit board (2) is provided on the upper side of the splicing block (4). Both the rigid circuit board (1) and the flexible circuit board (2) are provided with sintered silver paste circuit layers (6). The sintered silver paste circuit layer (6) at the front end of the positioning tooth (5) is provided with a flexible soldering pad (7). The end of the sintered silver paste circuit layer (6) on the rigid circuit board (1) located in front of the positioning tooth (5) is provided with a rigid soldering pad (8). The sintered silver paste circuit layer (6) is formed by printing low-temperature sinterable silver paste. The low-temperature sinterable silver paste is made by mixing silver powder, composite flux, organic carrier and additives.

2. The novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 1, characterized in that: Both the flexible welding pad (7) and the rigid welding pad (8) are formed by low-temperature sintering silver paste printing and connected by heating welding. The splicing groove (3) and the splicing block (4) are wedge-shaped fitting structures when viewed from above. The flexible circuit board (2) is provided with a high-temperature resistant coating layer (9).

3. A novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 1, characterized in that: The mass percentage of the mixture of silver powder, composite flux, organic carrier and additives in the low-temperature sinterable silver paste is 70%-90%: 5%-15%: 3%-8%: 2%-5%.

4. A novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 1, characterized in that: The silver powder has a particle size of 15-50 nm, and the composite flux is made by mixing Bi2O3, ZnO and glass powder in a mass percentage of 50%-70%:20%-30%:10%-20%.

5. A novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 1, characterized in that: The organic carrier is a mixture of ethyl cellulose and pine oil in a volume ratio of 2-3:1, and the additive is lecithin.

6. A method for fabricating a novel flexible and rigid interconnect circuit board based on solderable silver paste according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Process the splicing groove (3) structure on the rigid circuit board (1), and process the splicing block (4) and positioning tooth (5) structure that are compatible with it. Then, use the lamination connection method to tightly press the splicing block (4) and positioning tooth (5) structure with the flexible circuit board (2). Step 2: First, Bi2O3, ZnO and glass powder are mixed to prepare a composite flux. Then, ethyl cellulose and pine oil are mixed to prepare an organic carrier. Finally, silver powder, composite flux, organic carrier and additives are mixed to prepare a silver paste that can be sintered at low temperature. Step 3: Print sintered silver paste circuit layers (6) on rigid circuit board (1) and flexible circuit board (2), and print rigid solder pads (8) on the sintered silver paste circuit layer (6) near the splicing groove (3). Step 4: Apply a high-temperature resistant film layer (9) to the printed flexible circuit board (2), and at the same time, set a flexible soldering pad (7) at the front end of the positioning tooth (5) structure that is connected to the sintered silver paste circuit layer (6) on the flexible circuit board (2). Step 5: Install the splicing block (4) and positioning tooth (5) structure into the splicing groove (3). At this time, the flexible welding disk (7) and the rigid welding disk (8) are stacked. Finally, heat treatment is performed to make the flexible welding disk (7) and the rigid welding low-temperature sinterable silver paste fuse together to complete the welding and obtain the flexible and rigid connection circuit board.

7. The method for preparing a novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 6, characterized in that: In step one, the splicing groove (3) structure, splicing block (4) and positioning tooth (5) structure on the rigid circuit board (1) are processed by milling machine; in step two, Bi2O3, ZnO and glass powder are mixed first, and then added to a ball mill for ball milling dispersion. The ball milling speed is 200-400 rpm and the ball milling time is 1-2 hours. The particle size distribution of the obtained composite flux is 1-10 μm.

8. The method for preparing a novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 6, characterized in that: In step three, the sintered silver paste circuit layer (6) is printed using one of screen printing, inkjet printing or precision dispensing. The resulting sintered silver paste circuit layer (6) has a thickness of 20-30 μm.

9. A method for preparing a novel flexible and rigid interconnect circuit board based on solderable silver paste according to claim 6, characterized in that: The heating treatment in step five is carried out under an inert gas protective atmosphere, and the heating temperature is 300-400℃, wherein the inert gas is either nitrogen or argon.

Images