Multi-layer airgap circuit board manufacturing process

Abstract

The invention provides a manufacturing process of a multilayer airgap circuit board, which comprises the steps of preparing positioning pins, preparing a substrate, preparing an inner-layer board covering film, preparing an outer-layer covering film, preparing an adhesive board, laminating the inner-layer board covering film, laminating the adhesive board, laminating the outer-layer board and laminating the outer-layer covering film. The inner-layer board covering film, the upper-layer adhesive plate and the lower-layer adhesive plate are uniform in size and are produced in a whole-board attaching mode, so that the unit covering film, the upper-layer adhesive plate and the lower-layer adhesive plate are not overlapped, the phenomenon that the surface of a traditional multi-layer soft board is uneven after being laminated is avoided, and when an outer-layer circuit is produced, the production efficiency is greatly improved. The corrosion-resistant material can be tightly attached to the surface of the multi-layer soft board, and a hyperfine circuit can be produced. And meanwhile, the airgap cavity laminated structure of the single-sided soft board, the double-sided soft board and the single-sided soft board is used, so that the bending performance of the multi-layer soft board and the alignment degree between the patterns of each layer are ensured, and the method can be widely applied to production of various intelligent wearable printed circuit boards and is worthy of popularization and application.

Description

Technical Field

[0001] This invention relates to the field of circuit board technology, and more particularly to a manufacturing process for a multilayer Airgap circuit board. Background Technology

[0002] With the advent of the intelligent era, intelligent wearable devices such as AI / AR glasses have become increasingly popular among consumers, experiencing rapid growth in recent years. CINNO Research data shows that domestic sales of AI / AR glasses increased by 45% year-on-year in the first quarter of 2025. Intelligent wearable devices are widely used in education, healthcare, industry, entertainment, and other fields. These products are small in size but complex in function. To meet these precision requirements, the circuit board, as the cornerstone of intelligent wearable devices, needs to have multi-layered, intricate circuitry and maximize assembly space utilization (flexibility).

[0003] Traditional AI / AR glasses and other intelligent wearable devices use circuit boards with line widths / spacings of 4mil / 4mil or more. These circuit boards mostly employ rigid-flex PCBs or traditional multi-layer flexible PCBs. Rigid-flex PCBs are thicker and have lower space utilization compared to pure flexible PCBs. Traditional multi-layer pure flexible PCBs, on the other hand, have completely bonded flexible boards together, resulting in excessive thickness in bending areas, poor bending performance, and a tendency for electrical performance defects after bending. They typically use multiple double-sided flexible PCBs stacked together, which can easily lead to conductor misalignment between different flexible boards, resulting in low yield rates after drilling.

[0004] To avoid the shortcomings of poor bending performance and conductor misalignment between different flexible boards in traditional multilayer flexible boards, the industry has introduced the Airgap cavity design. This design removes the adhesive material from the flexible board areas that need to be bent, creating a cavity structure that improves bending performance. Currently, the industry practice is to laminate two or more flexible board cores together. However, regardless of the lamination method, the cover film of the flexible board area is laminated one by one. Each laminated cover film will have a positional offset with inconsistent orientation. The adhesive material (pure glue) is laminated as a whole, and the cover film and adhesive material cannot be completely aligned. To avoid conductor exposure, the adhesive material must be laminated on the cover film.

[0005] As attached Figure 8 As shown, for the Airgap cavity structure where two flexible core boards are laminated: because the adhesive material is located between the two cover films, during the lamination process, the adhesive material will overflow into the middle of the cover films, causing the two cover films to stick together and affecting the bending performance.

[0006] As attached Figure 9As shown, for the Airgap cavity structure of multiple flexible PCB core boards laminated together: a height difference (bulge) will be formed in the overlapping area of ​​the cover film and the adhesive material, and the height of the bulge caused by the adhesive material is more than 20 micrometers (in order to ensure the bonding effect, the thickness of the adhesive material needs to be greater than or equal to the thickness of the cover film, and the minimum thickness of the cover film in the industry is currently more than 22 micrometers). This height difference will affect the bonding effect between the resist film and the board surface and the exposure effect in the circuit forming process. If the resist film is not tightly bonded to the board surface, the chemical solution will penetrate under the resist film during the circuit etching process, resulting in open circuits or small defects in the etched circuit under the resist film at the bulge position. Therefore, this type of design can only produce products with conductor line width / spacing of 4mil / 4mil or more, and cannot complete the fine circuit production, which cannot meet the increasing functional requirements of wearable devices (it is necessary to increase the wiring density and reduce the line width / spacing to 2.0mil / 2.0mil or less). Summary of the Invention

[0007] The problem to be solved by this invention is to provide a multilayer airgap circuit board manufacturing process that improves bending performance, ensures the alignment accuracy of conductors on both sides, and reduces pattern offset between different layers of the flexible circuit board.

[0008] To solve the above technical problems, a multilayer Airgap circuit board manufacturing process provided by this invention is adopted, which includes the following steps:

[0009] S1. Preparation of positioning pins: Prepare four positioning pins;

[0010] S2. Substrate Preparation: According to the product shape requirements, cut out the first flexible substrate and the third flexible substrate from the single-sided flexible substrate. Both the first flexible substrate and the third flexible substrate include a conductor layer and a first dielectric layer. According to the product shape requirements, cut out the second flexible substrate from the double-sided flexible substrate. The second flexible substrate includes an upper conductor layer, a second dielectric layer, and a lower conductor layer. According to the product requirements, expose and etch out the double-sided circuits of several delivery units on the second flexible substrate, and cut out the first positioning holes that match the positioning pins at the four corners of the second flexible substrate.

[0011] S3. Inner layer cover film preparation: Cut two inner layer cover films according to the shape of the second flexible substrate; cut second positioning holes at the four corners of the inner layer cover film to match the first positioning holes; cut unit cover films corresponding to the delivery units on the inner layer cover film. When cutting the unit cover films, several connecting ribs need to be reserved so that the unit cover films can be peeled off from the inner layer cover films.

[0012] S4. Preparation of outer cover film: Cut the upper cover film and lower cover film according to the shape of the first flexible substrate and the third flexible substrate respectively.

[0013] S5. Preparation of adhesive boards: Cut out the upper adhesive board and the lower adhesive board according to the shape of the second flexible substrate; cut out the positions on the upper adhesive board and the lower adhesive board corresponding to the unit cover film to form a hollow groove, and match the hollow groove with the unit cover film; cut out the third positioning hole at the four corners of the upper adhesive board and the lower adhesive board, which is aligned with the first positioning hole.

[0014] S6. Inner layer cover film bonding: Insert four positioning pins into the four first positioning holes of the second flexible substrate respectively, with the two ends of the positioning pins passing through the two end faces of the first positioning holes respectively; by aligning the positioning pins with the second positioning holes, bond the two inner layer cover films to the two sides of the second flexible substrate respectively, and achieve pre-bonding of the unit cover film to the surface of the delivered unit by locally heating the unit cover film, and then remove the excess inner layer cover film material outside the unit cover film;

[0015] S7. Adhesive board bonding: By aligning the positioning pins with the third positioning hole, the upper adhesive board and the lower adhesive board are bonded to the upper and lower surfaces of the second flexible substrate, respectively. The upper adhesive board and the lower adhesive board are heated to achieve pre-bonding between the upper adhesive board and the surface of the second flexible substrate. Then, the positioning pins are removed from the first positioning hole and the third positioning hole.

[0016] S8. Outer layer lamination: The first flexible substrate and the third flexible substrate are respectively aligned and bonded to the surface of the upper adhesive board and the lower adhesive board, so that the first dielectric layer of the first flexible substrate and the third flexible substrate are respectively bonded to the surface of the upper adhesive board and the lower adhesive board, and lamination operation is performed.

[0017] S9. Lamination of outer cover film: Align and laminate the upper cover film and the lower cover film to the surfaces of the first flexible substrate and the third flexible substrate respectively; heat the upper cover film and the lower cover film to achieve adhesion between the upper cover film and the lower cover film and the surfaces of the first flexible substrate and the third flexible substrate.

[0018] Preferably, the thickness of the upper adhesive board and the lower adhesive board is a, and the thickness of the inner layer cover film is b, where 0 < ab ≤ 5 μm.

[0019] Preferably, in step S3, a 0.1mm wide connecting rib is reserved at the four corners of the unit covering film.

[0020] Preferably, in step S2, after cutting out the first flexible substrate and the third flexible substrate, it is also necessary to perform single-sided lamination, single-sided etching, and AOI processes.

[0021] Preferably, in step S2, a DI exposure machine is used to expose the second flexible substrate.

[0022] Preferably, in step S7, when the upper adhesive plate and the lower adhesive plate are respectively attached to the upper surface and the lower surface of the second flexible substrate, it is necessary to ensure that the edge of the unit cover film is aligned with the cutout groove and does not overlap.

[0023] Preferably, in step S8, a high-speed press is used to perform a pressing operation between the first flexible substrate, the second flexible substrate, and the third flexible substrate.

[0024] The beneficial effects of this invention are as follows: This invention provides a multilayer Airgap circuit board manufacturing process, including the preparation of positioning pins, substrate preparation, preparation of inner layer cover film, preparation of outer layer cover film, preparation of adhesive board, lamination of inner layer cover film, lamination of adhesive board, pressing of outer layer board, and lamination of outer layer cover film. By designing the inner layer cover film, upper adhesive board, and lower adhesive board to have the same dimensions and using a whole-board lamination method, there is no overlap between the unit cover film and the upper and lower adhesive boards, avoiding the uneven surface phenomenon after lamination of traditional multilayer flexible boards. This allows the etching inhibitor material to adhere tightly to the surface of the multilayer flexible board during the production of outer layer circuits, thereby enabling the production of ultra-fine circuits with line width / spacing of 2mil / 2mil and below. Simultaneously, the use of a single-sided flexible board + double-sided flexible board + single-sided flexible board Airgap cavity stack-up structure ensures the bending performance of the multilayer flexible board and the alignment between the patterns of each layer. This method can be widely used in the production of various smart wearable printed circuit boards and is worthy of widespread application. Attached Figure Description

[0025] Figure 1 A top view of the second flexible substrate of the present invention is shown.

[0026] Figure 2 A top view of the inner layer cover film of the present invention is shown.

[0027] Figure 3 A top view of the upper adhesive plate of the present invention is shown.

[0028] Figure 4 An example is shown: a top view of the product after step S6 of the present invention.

[0029] Figure 5 An example is shown: a top view of the product after step S7 of the present invention.

[0030] Figure 6 An example of the product cross-section view after step S7 of the present invention is shown.

[0031] Figure 7 A cross-sectional view of the finished product of the present invention is shown.

[0032] Figure 8 This invention illustrates the current state of existing cavity structure products consisting of two flexible core boards laminated together.

[0033] Figure 9 This invention illustrates the current state of existing cavity structure products based on the lamination of multiple flexible core boards.

[0034] Explanation of reference numerals: 2. First flexible substrate; 20. Conductor layer; 21. First dielectric layer; 3. Third flexible substrate; 4. Second flexible substrate; 40. Upper conductor layer; 41. Second dielectric layer; 42. Lower conductor layer; 43. Delivery unit; 44. First positioning hole; 5. Inner layer cover film; 5. Second positioning hole; 50. Unit cover film; 51. Connecting rib; 52. Upper cover film; 6. Lower cover film; 7. Upper adhesive board; 8. Hollow groove; 80. Third positioning hole; 81. Lower adhesive board; 9. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure.

[0036] Based on the embodiments described in this disclosure, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this disclosure.

[0037] refer to Figure 1-9 .

[0038] This invention provides a manufacturing process for a multilayer Airgap circuit board, comprising the following steps:

[0039] S1. Preparation of positioning pins: Prepare four positioning pins;

[0040] S2. Substrate Preparation: Based on product shape requirements, a first flexible substrate 2 and a third flexible substrate 3 are cut from a single-sided flexible substrate. Both the first flexible substrate 2 and the third flexible substrate 3 include a conductor layer 20 and a first dielectric layer 21. Based on product shape requirements, a second flexible substrate 4 is cut from a double-sided flexible substrate. The second flexible substrate 4 includes an upper conductor layer 40, a second dielectric layer 41, and a lower conductor layer 42. Based on product requirements, double-sided lines for several delivery units 43 are exposed and etched on the second flexible substrate 4. First positioning holes 44 matching the positioning pins are cut at the four corners of the second flexible substrate 4. Figure 1 This is a top view of the second flexible substrate 4;

[0041] S3. Inner Layer Cover Film Preparation: Cut two inner layer cover films 5 according to the shape of the second flexible substrate 4; cut second positioning holes 50 at the four corners of the inner layer cover film 5 to align with the first positioning holes 44; cut unit cover films 51 corresponding to the delivery unit 43 from the inner layer cover film 5. When cutting the unit cover film 51, several connecting ribs 52 need to be reserved so that the unit cover film 51 can be peeled off from the inner layer cover film 5. Figure 2 Top view of the inner layer covering film 5;

[0042] S4. Preparation of outer cover film: Cut the upper cover film 6 and the lower cover film 7 according to the shape of the first flexible substrate 2 and the third flexible substrate 3 respectively.

[0043] S5. Preparation of adhesive boards: Cut the upper adhesive board 8 and the lower adhesive board 9 according to the shape of the second flexible substrate 4; cut out the upper adhesive board 8 and the lower adhesive board 9 at the positions corresponding to the unit cover film 51 to form a hollow groove 80, which matches the unit cover film 51; cut out the third positioning hole 81 at the four corners of the upper adhesive board 8 and the lower adhesive board 9, which aligns with the first positioning hole 44. Figure 3 This is a top view of the upper adhesive board 8;

[0044] S6. Inner Layer Cover Film Lamination: Insert four positioning pins into the four first positioning holes 44 of the second flexible substrate 4, with both ends of the positioning pins passing through the end faces of the first positioning holes 44. Align the positioning pins with the second positioning holes 50 to laminate the two inner layer cover films 5 onto the two sides of the second flexible substrate 4. Local heating of the unit cover film 51 is used to pre-bond the unit cover film 51 to the surface of the delivery unit 43. Then, remove any excess inner layer cover film 5 material outside the unit cover film 51. The processing effect is shown in the attached figure. Figure 4 ;

[0045] S7. Adhesive Plate Bonding: By aligning the positioning pins with the third positioning hole 81, the upper adhesive plate 8 and the lower adhesive plate 9 are bonded to the upper and lower surfaces of the second flexible substrate 4, respectively. Pre-bonding of the upper adhesive plate 8 and the lower adhesive plate 9 to the surface of the second flexible substrate 4 is achieved by heating them. Then, the positioning pins are removed from the first positioning hole 44 and the third positioning hole 81. The processing effect is shown in the attached figure. Figure 5 , 6 ;

[0046] S8. Outer layer lamination: The first flexible substrate 2 and the third flexible substrate 3 are respectively aligned and bonded to the surfaces of the upper adhesive board 8 and the lower adhesive board 9, so that the first dielectric layer 21 of the first flexible substrate 2 and the third flexible substrate 3 are respectively bonded to the surfaces of the upper adhesive board 8 and the lower adhesive board 9, and lamination operation is performed.

[0047] S9. Lamination of the outer cover film: The upper cover film 6 and the lower cover film 7 are aligned and laminated onto the surfaces of the first flexible substrate 2 and the third flexible substrate 3, respectively; the upper cover film 6 and the lower cover film 7 are heated to achieve adhesion between the upper cover film 6 and the lower cover film 7 and the surfaces of the first flexible substrate 2 and the third flexible substrate 3. The processing effect is shown in the attached figure. Figure 7 .

[0048] The processing steps include positioning pin preparation, substrate preparation, inner layer cover film preparation, outer layer cover film preparation, adhesive board preparation, inner layer cover film lamination, adhesive board lamination, outer layer lamination, and outer layer cover film lamination. By designing the inner layer cover film 5, upper adhesive board 8, and lower adhesive board 9 to be the same size and using a whole-board lamination method, there is no overlap between the unit cover film 51 and the upper and lower adhesive boards 8 and 9. This avoids the uneven surface phenomenon after lamination of traditional multilayer flexible circuit boards, allowing the etching inhibitor material to adhere tightly to the surface of the multilayer flexible circuit board during the production of outer layer circuits. This enables the production of ultra-fine circuits with line width / spacing of 2mil / 2mil and below. Simultaneously, the use of a single-sided flexible circuit board + double-sided flexible circuit board + single-sided flexible circuit board airgap cavity stack-up structure ensures the bending performance of the multilayer flexible circuit board and the alignment between the patterns of each layer. It can be widely used in the production of various smart wearable printed circuit boards and is worthy of widespread application.

[0049] Based on the above embodiments, the thickness of the upper adhesive plate 8 and the lower adhesive plate 9 is a, and the thickness of the inner plate covering film 5 is b, 0 < ab ≤ 5 μm, which can ensure the bonding effect. After pressing, the height difference at the junction of the two can be reduced to within 5 micrometers, and the integrity of the airgap structure can be guaranteed without affecting the bending performance.

[0050] Based on the above embodiments, in step S3, 0.1mm wide connecting ribs 52 are reserved at the four corners of the unit cover film 51 to facilitate the bonding of the inner layer cover film 5 and the subsequent removal of excess material on the inner layer cover film 5.

[0051] Based on the above embodiments, in step S2, after cutting out the first flexible substrate 2 and the third flexible substrate 3, it is also necessary to perform single-sided lamination, single-sided etching, and AOI processes to complete the preparation of the first flexible substrate 2 and the third flexible substrate 3.

[0052] Based on the above embodiments, in step S2, the second flexible substrate 4 is exposed using a DI exposure machine to ensure that the double-sided pattern position of the second flexible substrate 4 is accurate.

[0053] Based on the above embodiments, in step S7, when the upper adhesive plate 8 and the lower adhesive plate 9 are respectively attached to the upper and lower surfaces of the second flexible substrate 4, it is necessary to ensure that the edge of the unit cover film 51 is aligned with the cutout groove 80 and does not overlap, so as to improve product quality.

[0054] Based on the above embodiments, in step S8, a fast press is used to perform a pressing operation between the first flexible substrate 2, the second flexible substrate 4, and the third flexible substrate 3 to achieve rapid pressing and avoid misalignment between the boards.

[0055] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A manufacturing process for a multilayer AirGap circuit board, characterized in that, It includes the following steps: S1. Preparation of positioning pins: Prepare four positioning pins; S2. Substrate preparation: According to the product shape requirements, cut out the first flexible substrate and the third flexible substrate from the single-sided flexible substrate. The first flexible substrate and the third flexible substrate both contain a conductor layer and a first dielectric layer. According to the product shape requirements, a second flexible substrate is cut out from the double-sided flexible substrate. The second flexible substrate includes an upper conductor layer, a second dielectric layer, and a lower conductor layer. According to product requirements, several double-sided lines of delivery units are exposed and etched on the second flexible substrate, and first positioning holes matching the positioning pins are cut at the four corners of the second flexible substrate. S3. Inner layer cover film preparation: Cut two inner layer cover films according to the shape of the second flexible substrate; cut second positioning holes at the four corners of the inner layer cover film to align with the first positioning holes; cut unit cover films corresponding to the delivery unit on the inner layer cover film. When cutting the unit cover film, several connecting ribs need to be reserved so that the unit cover film can be peeled off from the inner layer cover film. S4. Preparation of outer cover film: Cut the upper cover film and lower cover film according to the shape of the first flexible substrate and the third flexible substrate respectively. S5. Preparation of adhesive boards: Cut out upper and lower adhesive boards according to the shape of the second flexible substrate; cut out the upper and lower adhesive boards at the positions corresponding to the unit cover film to form hollow grooves, which match the unit cover film; cut out third positioning holes at the four corners of the upper and lower adhesive boards to align with the first positioning holes. S6. Inner layer cover film bonding: Insert the four positioning pins into the four first positioning holes of the second flexible substrate respectively, with the two ends of the positioning pins passing through the two end faces of the first positioning holes respectively. By aligning the positioning pins with the second positioning holes, the two inner layer cover films are respectively bonded to the two sides of the second flexible substrate. The unit cover film is then pre-bonded to the surface of the delivery unit by local heating. The remaining material of the inner layer cover film outside the unit cover film is then removed. S7. Adhesive Plate Bonding: By aligning the positioning pins with the third positioning holes, the upper adhesive plate and the lower adhesive plate are bonded to the upper and lower surfaces of the second flexible substrate, respectively. The upper adhesive plate and the lower adhesive plate are heated to achieve pre-bonding between the upper adhesive plate and the surface of the second flexible substrate. Then, the positioning pins are removed from the first positioning holes and the third positioning holes. S8. Outer layer lamination: The first flexible substrate and the third flexible substrate are respectively aligned and attached to the surfaces of the upper adhesive board and the lower adhesive board, so that the first dielectric layer of the first flexible substrate and the third flexible substrate are respectively attached to the surfaces of the upper adhesive board and the lower adhesive board, and lamination operation is performed. S9. Lamination of the outer cover film: The upper cover film and the lower cover film are respectively aligned and laminated onto the surfaces of the first flexible substrate and the third flexible substrate; the upper cover film and the lower cover film are heated to achieve bonding between the upper cover film and the lower cover film and the surfaces of the first flexible substrate and the third flexible substrate.

2. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, The thickness of the upper adhesive board and the lower adhesive board is a, and the thickness of the inner layer cover film is b, where 0 < ab ≤ 5 μm.

3. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, The thickness of the first dielectric layer and the second dielectric layer is ≤25μm.

4. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, In step S3, a 0.1mm wide connecting rib is reserved at the four corners of the unit covering film.

5. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, In step S2, after cutting out the first flexible substrate and the third flexible substrate, single-sided lamination, single-sided etching, and AOI processes are required.

6. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, In step S2, the second flexible substrate is exposed using a DI exposure machine.

7. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, In step S7, when the upper adhesive plate and the lower adhesive plate are respectively attached to the upper surface and the lower surface of the second flexible substrate, it is necessary to ensure that the edge of the unit cover film is aligned with the cutout groove and does not overlap.

8. The manufacturing process of a multilayer Airgap circuit board according to claim 1, characterized in that, In step S8, a high-speed press is used to press the first flexible substrate, the second flexible substrate, and the third flexible substrate together.

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