High-precision any-layer interconnection soft and hard combination board and processing technology thereof

Abstract

This invention provides a high-precision arbitrary-layer interconnect rigid-flex PCB and its processing technology, belonging to the field of rigid-flex PCB manufacturing technology, including the following steps: Step S1. Fabricating circuitry on the flexible PCB and simultaneously fabricating alignment target points at preset positions on the flexible PCB, virtually dividing the flexible PCB into multiple independent alignment units through the alignment target points; Step S2. Pre-lamination process of the flexible PCB; S3. First lamination; S4. First blind via fabrication; S5. First circuitry fabrication and target point avoidance; S6. Second lamination; S7. Second blind via fabrication; S8. Fabricating circuitry on the stacked units to form a high-precision arbitrary-layer interconnect rigid-flex PCB. The high-precision arbitrary-layer interconnect rigid-flex PCB of this invention uses alignment target points on the flexible PCB as a permanent reference to eliminate accumulated errors, and the matrix target points are virtually divided into blocks to compensate for irregular deformation of the large board; the copper openings in each layer are ≥2mm to ensure target point recognition accuracy, and the entire process uses a single reference, not limited by the number of laminations.

Description

Technical Field

[0001] This invention relates to the field of rigid-flex PCB manufacturing technology, and in particular to a high-precision rigid-flex PCB with arbitrary layer interconnection and its processing technology. Background Technology

[0002] In the production of high-order arbitrary-layer interconnect rigid-flex PCBs, a blind via ring size of <65μm is a high-precision manufacturing requirement. Traditional processing techniques have the following core defects: 1) Multiple reference transfers result in large cumulative errors: In the traditional process of 6-layer boards, target points are first made on L3 / L4 layers, L2 / L5 are laminated, and holes are drilled on L3 / L4 target points. Then, new target points are made on L2 / L5, L1 / L6 are laminated, and holes are drilled on L2 / L5 target points. The alignment deviations from X-Ray, laser, and exposure are superimposed, resulting in blind via misalignment and insufficient rings. 2) Irregular deformation of large boards cannot be compensated: Traditionally, only 4 target points are set at the four corners of the large board, but the irregular deformation of rigid-flex boards is more difficult to control than that of rigid circuit boards, and cannot compensate for local twisting and expansion in the middle area. 3) Multi-layer copper shielding of target points: The outer layer has no copper avoidance design, and the superposition of copper layers leads to a decrease in X-Ray recognition accuracy; 4) Extremely low yield: The yield of traditional processes is only 80%-85%, which cannot meet the mass production requirements of high-end products. Summary of the Invention

[0003] The purpose of this invention is to overcome and supplement the deficiencies in the existing technology, and to provide a high-precision arbitrary layer interconnect rigid-flex board and its processing technology, so as to achieve a stable blind via Ring of <65μm, eliminate cumulative errors, and improve product yield.

[0004] The technical solution adopted in this invention is: A manufacturing process for a high-precision, arbitrary-layer interconnect rigid-flex PCB, comprising the following steps: Step S1. Fabricate flexible circuit board circuits and alignment target points: Provide a flexible circuit board, fabricate circuits on the flexible circuit board, and fabricate alignment target points at preset positions on the flexible circuit board. Virtually divide the flexible circuit board into multiple independent alignment units through the alignment target points. Step S2. Process before flexible board lamination: The pre-set bending area of ​​the flexible board is attached to the cover film and pressed quickly, then browned and baked, and a peelable adhesive is attached to the pre-set bending area. S3. First lamination: The copper foil, the first semi-cured adhesive sheet, the flexible board, the first semi-cured adhesive sheet, and the copper foil are stacked and laminated in the order from bottom to top to form a laminated structure; S4. First blind hole fabrication: The alignment target point in each independent alignment unit is located and the first blind hole is made by laser. Finally, the first blind hole is electroplated. S5. First circuit fabrication and target avoidance: Based on the alignment target, fabricate the circuit on the laminated structure. At the position of the alignment target of the corresponding flexible board, open the copper foil to form an avoidance part to obtain a semi-finished circuit board. S6. Second lamination: The semi-finished circuit board is browned, and the copper foil, the second semi-cured adhesive sheet, the semi-finished circuit board, the second semi-cured adhesive sheet, and the copper foil are stacked in the order from bottom to top to form a stacked unit. The stacked unit is then laminated for the second time. S7. Second blind hole fabrication: The alignment target point in each independent alignment unit is located and the second blind hole is made by laser, followed by electroplating of the second blind hole; S8. Second circuit fabrication: Using the alignment target as a reference, fabricate circuits on the stacked units to form a high-precision arbitrary layer interconnected rigid-flex board.

[0005] Preferably, the processing technology of the high-precision arbitrary layer interconnect rigid-flex board includes: in step S1, the flexible board includes a substrate, an upper copper foil layer and a lower copper foil layer disposed on both sides of the substrate, and circuits are fabricated on the upper copper foil layer and the lower copper foil layer. The alignment target is a circular solid copper target with a diameter of 0.8-1.2mm.

[0006] Preferably, the processing technology of the high-precision arbitrary-layer interconnect rigid-flex board includes the following: in step S2, the fast pressing temperature is 165-185℃, the fast pressing time is 1-3 min, and the fast pressing pressure is 60-100 kg; the browning treatment speed is 3.0-4.5 m / min, the browning treatment temperature is 30-40℃, the micro-etching rate of browning is 30-60 μ″, the baking temperature is 120-150℃, and the baking time is 60-90 min; the peelable length is 0.125-0.25 mm smaller on each side than the preset bending area. Preferably, the processing technology of the high-precision arbitrary layer interconnect rigid-flex board includes: in step S3, the first semi-cured adhesive sheet is windowed in the preset bending area of ​​the flexible board to form a windowed portion, the length of the windowed portion being 0.125-0.5mm longer on each side than the preset bending area length; the pressing temperature is 180-230℃, the pressing time is 90-150min, and the pressing pressure is 380-500psi.

[0007] Preferably, the processing technology of the high-precision arbitrary layer interconnect rigid-flex board includes the following: in step S4, the surface of the first blind hole is circular, the cross-section is inverted trapezoidal, and the copper plating depth of the first blind hole after electroplating is ≥85%.

[0008] Preferably, the processing technology of the high-precision arbitrary layer interconnect rigid-flex board includes: in step S5, the fabrication of circuits on the stacked structure specifically involves: cleaning the stacked structure and pressing a dry film, sequentially grabbing the alignment target points of the independent alignment units for alignment and exposure, and then developing and etching.

[0009] Preferably, the processing technology of the high-precision arbitrary layer interconnect rigid-flex board includes the following: during exposure, the position of the alignment target point of the flexible board is not exposed, and the copper foil at the position of the alignment target point is etched to make it open windowed, and the length of the avoidance part is 2-4mm longer than the length of the alignment target point.

[0010] Preferably, the processing technology of the high-precision arbitrary layer interconnect rigid-flex board includes the following: in step S6, the browning rate is 3.0-4.5 m / min, the browning temperature is 30-40℃, the micro-etching rate of the browning solution is 50-80 μ″; the pressing temperature is 180-230℃, the pressing time is 90-150 min, and the pressing pressure is 380-500 psi.

[0011] Preferably, the processing technology of the high-precision arbitrary-layer interconnect rigid-flex board includes: between step S5 and step S6, step a is repeated at least once, and step a specifically includes: a1. Lamination: The semi-finished circuit board is browned and then the copper foil, the second semi-cured adhesive sheet, the semi-finished circuit board, the second semi-cured adhesive sheet, and the copper foil are stacked in the order from bottom to top to form a laminated unit. The laminated unit is then laminated. a2. Blind hole fabrication: The alignment target point in each independent alignment unit is located and the second blind hole is drilled by laser, followed by electroplating of the second blind hole; a3. Circuit fabrication: Using the alignment target as a reference, fabricate the circuit on the laminated structure. At the position of the alignment target corresponding to the flexible circuit board, open the copper foil to form a clearance part to obtain a semi-finished circuit board.

[0012] A high-precision, arbitrary-layer interconnect rigid-flex PCB includes: a flexible board; alignment target points are set at preset positions on the flexible board, which virtually divide the flexible board into multiple independent alignment units; a cover film is attached to a preset bending area of ​​the flexible board; first semi-cured adhesive sheets are respectively provided on both sides of the flexible board; copper foil is respectively provided on the side of the first semi-cured adhesive sheets away from the flexible board to form an overlay structure; a first blind via is provided between the alignment target points and the bending area in the overlay structure; windows are opened on the copper foil corresponding to the alignment target points of the flexible board to form a clearance portion; at least one layer of second semi-cured adhesive sheets is provided on the side of the copper foil away from the first semi-cured adhesive sheets; copper foil is provided on the outer side of each layer of second semi-cured adhesive sheets; second blind vias are provided on the second semi-cured adhesive sheets and copper foil corresponding to the positions of the first blind vias; and copper foil is provided on the outermost layer of the rigid-flex PCB.

[0013] Advantages of this invention: (1) The high-precision arbitrary layer interconnection hard and soft board of the present invention has a positioning target point set on the soft board as a permanent reference to eliminate cumulative error, and the matrix target point is virtually divided into blocks to compensate for the irregular deformation of the large board; the copper window of each layer is ≥2mm to ensure the accuracy of target point recognition, and the whole process has a single reference and is not limited by the number of pressing.

[0014] (2) The high-precision arbitrary layer interconnection hard and soft board and its processing technology of the present invention have a stable blind hole ring of <65μm, meet the accuracy standard, interlayer alignment accuracy ≤±25μm, deviation in the middle area reduced by ≥60%, and product yield increased to over 99%.

[0015] (3) The high-precision arbitrary layer interconnect rigid-flex board processing technology of the present invention divides the large board into multiple independent alignment units by matrix-type multi-target points made on the flexible board layer within the same lamination large board; in the subsequent laser drilling and circuit exposure processes, the machine tool grabs the matrix-type alignment target points made on the flexible board layer in each unit, independently compensates for local expansion and contraction and irregular deformation, and offsets the expansion and contraction and deformation deviations generated during the lamination of the large board; after the first blind hole processing is completed, the matrix-type alignment target points of the flexible board layer are used as the reference during the first circuit fabrication; at the same time, during the circuit fabrication, the copper layer is opened at the position of the matrix-type alignment target points of the corresponding flexible board layer to avoid the copper foil superposition and obstruction during subsequent lamination, which affects the identification of the matrix-type alignment target points of the flexible board layer.

[0016] (4) The high-precision arbitrary layer interconnection rigid-flex board of the present invention uses matrix-type multi-target points as the only reference for the whole process. Regardless of whether the number of pressing times is 2, 3 or more, the blind hole making and circuit exposure processes only capture the original alignment target points of the flexible board layer. The subsequent processes do not add or transfer the reference target points, thus eliminating the cumulative error of multiple alignments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the flexible circuit board of the present invention.

[0018] Figure 2 This is a schematic diagram of the flexible circuit board of the present invention, which is divided into independent alignment units.

[0019] Figure 3 This is a schematic diagram of the flexible board bonding peelable adhesive structure of the present invention.

[0020] Figure 4 This is a schematic diagram of the composite structure of the present invention.

[0021] Figure 5 This is a schematic diagram of the laser-drilled first blind hole structure of the composite structure of the present invention.

[0022] Figure 6 This is a schematic diagram of the structure of the first blind hole filling electroplating of the present invention.

[0023] Figure 7 This is a schematic diagram of the structure of the semi-finished circuit board of the present invention.

[0024] Figure 8 This is a schematic diagram of the structure of the stacking unit of the present invention.

[0025] Figure 9 This is a schematic diagram of the laser-drilled second blind hole structure of the composite structure of the present invention.

[0026] Figure 10 This is a schematic diagram of the structure of the second blind hole filling electroplating of the present invention.

[0027] Figure 11 This is a schematic diagram of the structure of the high-precision arbitrary layer interconnect rigid-flex board of Embodiment 1 of the present invention.

[0028] Figure 12 This is a schematic diagram of the structure of the high-precision arbitrary layer interconnect rigid-flex board of Embodiment 2 of the present invention.

[0029] Figure 13 This is a schematic diagram of the structure of the high-precision arbitrary layer interconnect rigid-flex board of Embodiment 3 of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to specific accompanying drawings and embodiments.

[0031] Example 1 A manufacturing process for a high-precision, arbitrary-layer interconnect rigid-flex PCB, comprising the following steps: Step S1. As Figures 1-2 Fabrication of flexible circuit board circuits and alignment target points: Provide flexible circuit board 1 with dimensions of 500×615mm, divided into 4 independent alignment units; blind via diameter of 75μm, required ring width of 52~64μm, alignment deviation ≤±25μm; flexible circuit board thickness of 25μm PI+18μm rolled copper foil.

[0032] Circuits are fabricated on the flexible circuit board 1, and alignment target points 1-6 are fabricated at preset positions on the flexible circuit board 1. The flexible circuit board 1 is virtually divided into multiple independent alignment units S through the alignment target points 1-6. The flexible circuit board 1 includes a substrate 1-1, an upper copper foil layer 1-2 and a lower copper foil layer 1-3 disposed on both sides of the substrate 1-1. Circuits are fabricated on the upper copper foil layer 1-2 and the lower copper foil layer 1-3. The alignment target points 1-6 are circular solid copper target points with a diameter D1 of 1.0 mm. Step S2. Figure 3The process before laminating the flexible board layer 1 is as follows: 25μm PI cover film 1-4 is laminated to the preset bending areas 1-8 of the flexible board 1 and fast-pressed at a temperature of 170℃ for 3 minutes and a pressure of 80kg; then browning and baking are performed at a speed of 3.5m / min, a temperature of 35℃, a micro-etching rate of 40u″, a baking temperature of 130℃, and a baking time of 6 minutes; and peelable adhesive 1-5 is laminated to the preset bending areas. The length of peelable adhesive 1-5 is L1, which is 0.15mm longer than the single side of the preset bending areas. S3. First pressing: as follows Figure 4 The copper foil 3, the first semi-cured adhesive sheet 2, the flexible board 1, the first semi-cured adhesive sheet 2, and the copper foil 3 are stacked and pressed together for the first time in the order from bottom to top to form a stacked structure. The first semi-cured adhesive sheet 2 is made to open a window in the preset bending area of ​​the flexible board 1 to form a window 2-1. The length of the window 2-1 is 0.15mm longer on each side than the preset bending area length. The pressing temperature is 190℃, the pressing time is 110min, and the pressing pressure is 420psi. S4. First blind hole fabrication: as follows Figure 5 The alignment target points 1-6 within each independent alignment unit S are located and the first blind hole 5 is drilled using a laser. The surface of the first blind hole 5 is circular, and the cross-section is an inverted trapezoid. After electroplating, the copper plating depth of the first blind hole 5 is ≥85%. Figure 6 Finally, the first blind hole 5 is filled with electroplating, with a minimum filling depth of 90%. S5. First Circuit Construction and Target Avoidance: (e.g.) Figure 7 Using alignment target points 1-6 as a reference, circuits are fabricated on the laminated structure. At the corresponding alignment target points 1-6 of the flexible board 1, windows are opened in the copper foil 3 to form clearance parts 1-7, thus obtaining a semi-finished circuit board. The specific process for fabricating circuits on the laminated structure is as follows: the laminated structure is cleaned and the film is pressed dry. Alignment target points 1-6 of the independent alignment unit S are sequentially picked up and exposed. During exposure, the positions of alignment target points 1-6 of the flexible board 1 are not exposed. The copper foil 3 at the positions of alignment target points 1-6 is etched to make it open. The length of the avoidance part 1-7 is 2mm longer than the length of alignment target points 1-6, the target diameter is 1.0mm, and the single-sided allowance is 0.5mm. Then, development and etching are performed. S6. Second pressing: as shown Figure 8The semi-finished circuit board is subjected to browning treatment at a rate of 3.5 m / min, a temperature of 35°C, and a micro-etching rate of 40 μ″. The copper foil 3, the second semi-cured adhesive sheet 4, the semi-finished circuit board, the second semi-cured adhesive sheet 4, and the copper foil 3 are stacked in a bottom-up order to form a stacked unit. The stacked unit is then subjected to a second pressing at a temperature of 180-230°C, a pressing time of 90-150 min, and a pressing pressure of 380-500 psi. S7. Second blind hole fabrication: as follows Figure 9 The alignment target points 1-6 within each independent alignment unit S are located, and a second blind hole 6 is drilled using a laser, as shown. Figure 10 Then, the second blind hole 6 is electroplated; S8. Second circuit design: (e.g.) Figure 11 Using the alignment target points 1-6 as a reference, circuits are fabricated on the stacked units to form a high-precision arbitrary layer interconnected rigid-flex board.

[0033] like Figure 11 A high-precision, arbitrary-layer interconnect rigid-flex PCB includes a flexible PCB 1. Alignment target points 1-6 are set at preset positions on the flexible PCB 1, virtually dividing the flexible PCB 1 into multiple independent alignment units S. A cover film 1-4 is attached to a preset bending area of ​​the flexible PCB 1. First semi-cured adhesive sheets 2 are respectively provided on both sides of the flexible PCB 1. Copper foil 3 is provided on the side of the first semi-cured adhesive sheet 2 away from the flexible PCB 1 to form an overlay structure. A first blind hole 5 is provided between the alignment target points 1-6 and the bending area in the overlay structure. Windows are opened on the copper foil 3 corresponding to the alignment target points 1-6 of the flexible PCB 1 to form clearance portions 1-7. A second semi-cured adhesive sheet 4 is provided on the side of the copper foil 3 away from the first semi-cured adhesive sheet 2. Copper foil 3 is provided on the outer side of the second semi-cured adhesive sheet 4. Second blind holes 6 are provided on the second semi-cured adhesive sheet 4 and the copper foil 3 corresponding to the positions of the first blind holes 5.

[0034] Example 2 A manufacturing process for a high-precision, arbitrary-layer interconnect rigid-flex PCB, comprising the following steps: Step S1. Fabrication of flexible circuit board circuits and alignment targets: Provide a flexible circuit board 1 with dimensions of 500×615mm and 4×4 matrix alignment targets on the board surface. Fabricate circuits on the flexible circuit board 1 and simultaneously fabricate alignment targets 1-6 at preset positions on the flexible circuit board 1. Virtually divide the flexible circuit board 1 into 9 independent alignment units S through the alignment targets 1-6. The flexible circuit board 1 includes a substrate 1-1, an upper copper foil layer 1-2 and a lower copper foil layer 1-3 disposed on both sides of the substrate 1-1. Fabricate circuits on the upper copper foil layer 1-2 and the lower copper foil layer 1-3. The alignment targets 1-6 are circular solid copper targets with a diameter of 1mm. The blind via diameter is 75μm, the ring width is required to be 48~60μm, and the overall board alignment deviation is ≤±25μm. Step S2. Pre-lamination process of flexible board layer 1: Lay 25μm cover film 1-4 onto the preset bending area of ​​flexible board 1 and perform fast pressing. The fast pressing temperature is 170℃, the fast pressing time is 3min, and the fast pressing pressure is 80kg. Then, perform browning treatment and baking. The browning treatment speed is 3.5m / min, the browning treatment temperature is 35℃, the browning micro-etching rate is 40u″, the baking temperature is 130℃, and the baking time is 60min. Then, lay peelable adhesive 1-5 onto the preset bending area. The length of peelable adhesive 1-5 is 0.15mm smaller than the preset bending area on one side. S3. First pressing: The copper foil 3, the first semi-cured adhesive sheet 2, the flexible board 1, the first semi-cured adhesive sheet 2, and the copper foil 3 are stacked and pressed together in the order from bottom to top to form a stacked structure. The first semi-cured adhesive sheet 2 is made to open a window in the preset bending area of ​​the flexible board 1 to form a window 2-1. The length of the window 2-1 is 0.15mm longer on each side than the preset bending area length. The pressing temperature is 190℃, the pressing time is 110min, and the pressing pressure is 420psi. S4. First blind via fabrication: Position the alignment target points 1-6 within each independent alignment unit S and drill the first blind via 5 using a laser. The surface of the first blind via 5 is circular, and the cross-section is an inverted trapezoid. After electroplating, the copper plating depth of the first blind via 5 is ≥85%. Finally, perform hole-filling electroplating on the first blind via 5, with a minimum hole-filling depth of 90%. S5. First circuit fabrication and target avoidance: Based on the alignment target 1-6, the circuit is fabricated on the stacked structure. The copper foil at the target position is completely removed by etching at the position of the alignment target 1-6 on the corresponding flexible board 1. The copper foil 3 is opened to form the avoidance part 1-7 with an opening size of 2.0mm, a target diameter of 1.0mm, and a single-sided allowance of 0.5mm to obtain a semi-finished circuit board. The specific process for fabricating circuits on the laminated structure is as follows: the laminated structure is cleaned and the film is pressed dry. Alignment target points 1-6 of the independent alignment unit S are picked up in sequence and exposed. During exposure, the positions of alignment target points 1-6 of the flexible board 1 are not exposed. The copper foil 3 at the positions of alignment target points 1-6 is etched to make it open window. The length of the clearance part 1-7 is 2mm longer than the length of alignment target points 1-6. Then, development and etching are performed. S6. Second lamination: The semi-finished circuit board is subjected to browning treatment at a rate of 3.5 m / min, a temperature of 35°C, and a micro-etching rate of 40 μ″ for the browning solution. The copper foil 3, the second semi-cured adhesive sheet 4, the semi-finished circuit board, the second semi-cured adhesive sheet 4, and the copper foil 3 are stacked in a bottom-up order to form a laminated unit. The laminated unit is then subjected to a second lamination at a temperature of 190°C, a time of 110 min, and a pressure of 420 psi. S7. Second blind hole fabrication: Position the alignment target points 1-6 within each independent alignment unit S and drill the second blind hole 6 using a laser, then electroplat the second blind hole 6. S8. Second circuit fabrication: Based on the alignment target points 1-6, fabricate circuits on the stacked units to form a high-precision arbitrary layer interconnected rigid-flex board.

[0035] Between steps S5 and S6, step a is repeated once. Step a is as follows: a1. Pressing: The semi-finished circuit board is browned and then the copper foil 3, the second semi-cured adhesive sheet 4, the semi-finished circuit board, the second semi-cured adhesive sheet 4, and the copper foil 3 are stacked in the order from bottom to top to form a stacked unit, and the stacked unit is pressed together. a2. Blind hole fabrication: Position the alignment target points 1-6 within each independent alignment unit S and drill the second blind hole 6 using a laser, followed by electroplating the second blind hole 6; a3. Circuit fabrication: Using alignment target points 1-6 as a reference, fabricate circuits on the laminated structure. At the corresponding alignment target points 1-6 of the flexible board 1, open the copper foil 3 to form the avoidance part 1-7, and obtain the semi-finished circuit board.

[0036] like Figure 12 A high-precision, arbitrary-layer interconnect rigid-flex PCB includes a flexible board 1. Alignment target points 1-6 are set at preset positions on the flexible board 1, virtually dividing the flexible board 1 into multiple independent alignment units S. A cover film 1-4 is attached to a preset bending area of ​​the flexible board 1. First semi-cured adhesive sheets 2 are respectively provided on both sides of the flexible board 1. Copper foil 3 is provided on the side of the first semi-cured adhesive sheet 2 away from the flexible board 1 to form an overlay structure. A first blind hole 5 is provided between the alignment target points 1-6 and the bending area in the overlay structure. Windows are opened on the copper foil 3 corresponding to the alignment target points 1-6 of the flexible board 1 to form clearance portions 1-7. Two layers of second semi-cured adhesive sheets 4 are provided on the side of the copper foil 3 away from the first semi-cured adhesive sheets 2. Copper foil 3 is provided on the outer side of each layer of second semi-cured adhesive sheets 4. Second blind holes 6 are provided on the second semi-cured adhesive sheets 4 and copper foil 3 corresponding to the positions of the first blind holes 5. Copper foil 3 is provided as the outermost layer of the rigid-flex PCB.

[0037] Example 3 A manufacturing process for a high-precision, arbitrary-layer interconnect rigid-flex PCB, comprising the following steps: Step S1. Fabrication of flexible circuit board circuits and alignment targets: Provide a flexible circuit board 1 with dimensions of 500×615mm. Fabricate circuits on the flexible circuit board 1, and simultaneously fabricate alignment targets 1-6 at preset positions on the flexible circuit board 1. The alignment targets on the flexible circuit board 1 are arranged in a 4×4 matrix, virtually dividing the flexible circuit board 1 into 12 independent alignment units S through the alignment targets 1-6. The flexible circuit board 1 includes a substrate 1-1, an upper copper foil layer 1-2 and a lower copper foil layer 1-3 disposed on both sides of the substrate 1-1. The substrate 1-1 is 25μm PI, and the upper copper foil layer 1-2 and the lower copper foil layer 1-3 are 18μm thick. Fabricate circuits on the upper copper foil layer 1-2 and the lower copper foil layer 1-3. The alignment targets 1-6 are circular solid copper targets with a diameter of 1mm. The blind via diameter is 75μm, requiring a Ring. The ring width is 45~58μm, and the alignment deviation of the entire board is ≤±25μm. The entire flexible board is divided into 12 independent alignment units based on the matrix target points. When making blind holes and exposing the circuit, the stage reads the original target points of the bottom layer of the flexible board in the unit and independently compensates for the expansion, contraction and torsion deformation within the unit. Step S2. Pre-lamination process of flexible board layer 1: Lay 25μm cover film 1-4 onto the preset bending area of ​​flexible board 1 and perform fast pressing. The fast pressing temperature is 170℃, the fast pressing time is 3min, and the fast pressing pressure is 80kg. Then, perform browning treatment and baking. The browning treatment speed is 3.5m / min, the browning treatment temperature is 35℃, the browning micro-etching rate is 40u″, the baking temperature is 130℃, and the baking time is 60min. Then, lay peelable adhesive 1-5 onto the preset bending area. The length of peelable adhesive 1-5 is 0.15mm smaller than the preset bending area on one side. S3. First pressing: The copper foil 3, the first semi-cured adhesive sheet 2, the flexible board 1, the first semi-cured adhesive sheet 2, and the copper foil 3 are stacked and pressed together in the order from bottom to top to form a stacked structure. The first semi-cured adhesive sheet 2 is made to open a window in the preset bending area of ​​the flexible board 1 to form a window 2-1. The length of the window 2-1 is 0.15mm longer on each side than the preset bending area length. The pressing temperature is 190℃, the pressing time is 110min, and the pressing pressure is 420psi. S4. First blind via fabrication: Position the alignment target points 1-6 within each independent alignment unit S and drill the first blind via 5 using a laser. The surface of the first blind via 5 is circular, and the cross-section is an inverted trapezoid. After electroplating, the copper plating depth of the first blind via 5 is ≥85%. Finally, perform hole-filling electroplating on the first blind via 5, with a minimum hole-filling depth of 90%. S5. First circuit fabrication and target avoidance: Based on the alignment target 1-6, fabricate the circuit on the laminated structure. At the position of the alignment target 1-6 on the corresponding flexible board 1, open the copper foil 3 to form the avoidance part 1-7, and obtain the semi-finished circuit board. The specific process for fabricating circuits on the laminated structure is as follows: the laminated structure is cleaned and the film is pressed dry. Alignment target points 1-6 of the independent alignment unit S are picked up and exposed in sequence. During exposure, the positions of alignment target points 1-6 of the flexible board 1 are not exposed. The copper foil 3 at the positions of alignment target points 1-6 is etched to make it open window. The length of the clearance part 1-7 is 3mm longer than the length of alignment target points 1-6. Then, development and etching are performed. S6. Second lamination: The semi-finished circuit board is subjected to browning treatment at a rate of 3.5 m / min, a temperature of 35°C, and a micro-etching rate of 60 μ″ for the browning solution. The copper foil 3, the second semi-cured adhesive sheet 4, the semi-finished circuit board, the second semi-cured adhesive sheet 4, and the copper foil 3 are stacked in a bottom-up order to form a laminated unit. The laminated unit is then subjected to a second lamination at a temperature of 190°C, a time of 110 min, and a pressure of 420 psi. S7. Second blind hole fabrication: Position the alignment target points 1-6 within each independent alignment unit S and drill the second blind hole 6 using a laser, then electroplat the second blind hole 6. S8. Second circuit fabrication: Based on the alignment target points 1-6, fabricate circuits on the stacked units to form a high-precision arbitrary layer interconnected rigid-flex board.

[0038] Between steps S5 and S6, there is a repetition of step a, which is repeated twice. Step a is as follows: a1. Pressing: The semi-finished circuit board is browned and then the copper foil 3, the second semi-cured adhesive sheet 4, the semi-finished circuit board, the second semi-cured adhesive sheet 4, and the copper foil 3 are stacked in the order from bottom to top to form a stacked unit, and the stacked unit is pressed together. a2. Blind hole fabrication: Position the alignment target points 1-6 within each independent alignment unit S and drill the second blind hole 6 using a laser, followed by electroplating the second blind hole 6; a3. Circuit fabrication: Using alignment target points 1-6 as a reference, fabricate circuits on the laminated structure. At the corresponding alignment target points 1-6 of the flexible board 1, open the copper foil 3 to form the avoidance part 1-7, and obtain the semi-finished circuit board.

[0039] like Figure 13A high-precision, arbitrary-layer interconnect rigid-flex PCB includes a flexible board 1. Alignment target points 1-6 are set at preset positions on the flexible board 1, virtually dividing the flexible board 1 into multiple independent alignment units S. A cover film 1-4 is attached to a preset bending area of ​​the flexible board 1. First semi-cured adhesive sheets 2 are respectively provided on both sides of the flexible board 1. Copper foil 3 is provided on the side of the first semi-cured adhesive sheet 2 away from the flexible board 1 to form an overlay structure. A first blind hole 5 is provided between the alignment target points 1-6 and the bending area in the overlay structure. Windows are opened on the copper foil 3 corresponding to the alignment target points 1-6 of the flexible board 1 to form clearance portions 1-7. At least one layer of second semi-cured adhesive sheet 4 is provided on the side of the copper foil 3 away from the first semi-cured adhesive sheet 2. Copper foil 3 is provided on the outer side of each layer of second semi-cured adhesive sheet 4. Second blind holes 6 are provided on the second semi-cured adhesive sheet 4 and copper foil 3 corresponding to the positions of the first blind holes 5. Copper foil 3 is provided on the outermost layer of the rigid-flex PCB.

[0040] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A processing technology for a high-precision, arbitrary-layer interconnect rigid-flex PCB, characterized in that: Includes the following steps: Step S1. Fabricate flexible circuit board circuit and alignment target points: Provide a flexible circuit board (1), fabricate circuit on the flexible circuit board (1), and fabricate alignment target points (1-6) at preset positions on the flexible circuit board (1). The flexible circuit board (1) is virtually divided into multiple independent alignment units (S) through the alignment target points (1-6). Step S2. Process before lamination of flexible board layer (1): Lay the cover film (1-4) onto the preset bending area of ​​the flexible board (1) and press it quickly, then perform browning treatment and baking, and then lay the peelable adhesive (1-5) onto the preset bending area. S3. First pressing: The copper foil (3), the first semi-cured adhesive sheet (2), the flexible board (1), the first semi-cured adhesive sheet (2), and the copper foil (3) are stacked and pressed together in the order from bottom to top to form a stacked structure; S4. First blind hole fabrication: The alignment target point (1-6) in each independent alignment unit (S) is located and the first blind hole (5) is made by laser. Finally, the first blind hole (5) is electroplated. S5. First circuit fabrication and target avoidance: Based on the alignment target (1-6), the circuit is fabricated on the stacked structure. At the position of the alignment target (1-6) of the corresponding flexible board (1), the copper foil (3) is opened to form an avoidance part (1-7) to obtain a semi-finished circuit board. S6. Second pressing: The semi-finished circuit board is browned and then the copper foil (3), the second semi-cured adhesive sheet (4), the semi-finished circuit board, the second semi-cured adhesive sheet (4), and the copper foil (3) are stacked in the order from bottom to top to form a stacked unit. The stacked unit is then pressed for the second time. S7. Second blind hole fabrication: The alignment target point (1-6) in each independent alignment unit (S) is located and the second blind hole (6) is made by laser. Then the second blind hole (6) is electroplated. S8. Second circuit fabrication: Using the alignment target points (1-6) as a reference, fabricate circuits on the stacked units to form a high-precision arbitrary layer interconnected rigid-flex board.

2. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: In step S1, the flexible circuit board (1) includes a substrate (1-1), an upper copper foil layer (1-2) and a lower copper foil layer (1-3) disposed on both sides of the substrate (1-1), and circuits are fabricated on the upper copper foil layer (1-2) and the lower copper foil layer (1-3). The alignment target (1-6) is a circular solid copper target with a diameter of 0.8-1.2 mm.

3. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: In step S2, the fast pressing temperature is 165-185℃, the fast pressing time is 1-3 min, and the fast pressing pressure is 60-100 kg; the browning treatment speed is 3.0-4.5 m / min, the browning treatment temperature is 30-40℃, the micro-etching rate of browning is 30-60 μ″, the baking temperature is 120-150℃, and the baking time is 60-90 min; the length of the peelable adhesive (1-5) is 0.125-0.25 mm smaller on one side than the preset bending area.

4. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: In step S3, the first semi-cured adhesive sheet (2) is opened in the pre-set bending area of ​​the flexible board (1) to form an opening part (2-1). The length of the opening part (2-1) is 0.125-0.5mm longer on one side than the pre-set bending area length. The pressing temperature is 180-230℃, the pressing time is 90-150min, and the pressing pressure is 380-500psi.

5. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: In step S4, the surface of the first blind hole (5) is circular and the cross-section is an inverted trapezoid. After electroplating, the copper plating depth of the first blind hole (5) is ≥85%.

6. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: In step S5, the fabrication of circuits on the stacked structure is specifically carried out as follows: the stacked structure is cleaned and the film is pressed dry. The alignment target points (1-6) of the independent alignment unit (S) are picked up in sequence for alignment and exposure. Then, development and etching are performed.

7. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 6, characterized in that: During exposure, the position of the alignment target (1-6) of the flexible board (1) is not exposed, and the copper foil (3) at the position of the alignment target (1-6) is etched to make it open window. The length of the avoidance part (1-7) is 2-4mm longer than the length of the alignment target (1-6).

8. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: The browning rate in step S6 is 3.0-4.5 m / min, the browning temperature is 30-40℃, the micro-etching rate of the browning agent is 50-80 u″, the pressing temperature is 180-230℃, the pressing time is 90-150 min, and the pressing pressure is 380-500 psi.

9. The processing technology of the high-precision arbitrary-layer interconnect rigid-flex board as described in claim 1, characterized in that: Between steps S5 and S6, step a is repeated at least once. Step a is as follows: a1. Pressing: The semi-finished circuit board is browned and then the copper foil (3), the second semi-cured adhesive sheet (4), the semi-finished circuit board, the second semi-cured adhesive sheet (4), and the copper foil (3) are stacked in the order from bottom to top to form a stacked unit. The stacked unit is then pressed together. a2. Blind hole fabrication: The alignment target point (1-6) in each independent alignment unit (S) is located and the second blind hole (6) is made by laser. Then the second blind hole (6) is electroplated. a3. Circuit fabrication: Using the alignment target point (1-6) as a reference, fabricate the circuit on the stacked structure. At the position of the alignment target point (1-6) of the corresponding flexible board (1), open the copper foil (3) to form the avoidance part (1-7) to obtain the semi-finished circuit board.

10. A high-precision, arbitrary-layer interconnect rigid-flex PCB, characterized in that: The flexible board (1) includes a pre-set alignment target point (1-6) on a pre-set position. The alignment target point (1-6) virtually divides the flexible board (1) into multiple independent alignment units (S). A cover film (1-4) is attached to a pre-set bending area of ​​the flexible board (1). A first semi-cured adhesive sheet (2) is provided on both sides of the flexible board (1). A copper foil (3) is provided on the side of the first semi-cured adhesive sheet (2) away from the flexible board (1) to form a stacked structure. A second copper foil (3) is provided between the alignment target point (1-6) and the bending area in the stacked structure. A blind hole (5) is provided. The copper foil (3) is opened at the position of the alignment target point (1-6) of the flexible board (1) to form a clearance part (1-7). At least one layer of second semi-cured adhesive sheet (4) is provided on the side of the copper foil (3) away from the first semi-cured adhesive sheet (2). Copper foil (3) is provided on the outer side of each layer of second semi-cured adhesive sheet (4). Second blind holes (6) are provided at the positions of the second semi-cured adhesive sheet (4) and copper foil (3) corresponding to the first blind hole (5). Copper foil (3) is provided on the outermost layer of the rigid-flex board.

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