Detection Method for Copper Ion Migration at the Cavity Formed by the Flexible Board Opening Area and the Adhesive

Abstract

The present invention discloses a method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue, which includes respectively providing an inner flexible substrate and an outer flexible substrate provided with an opening area; setting a detection component manufacturing area on the inner flexible substrate; using bonding glue to make the inner flexible substrate and the outer flexible substrate into a multilayer board, and opening the multilayer board based on the opening area to form a cavity between the opening area and the bonding glue; at the same time, manufacturing a detection component on the detection component manufacturing area, and the detection component is used to detect the copper ion migration situation of the cavity; performing electrical measurement on the detection component, and according to the electrical measurement result, obtaining the copper ion migration situation of the cavity. By introducing a detection component in the inner layer at the same time during the conventional processes of pasting glue and opening the cover of the multilayer board in the present invention, and using it as a new electrical measurement point for electrical measurement, the true situation of copper ion migration at the cavity can be discriminated, the production error rate can be reduced, and the product yield can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible circuit board manufacturing, and in particular to a method for detecting copper ion migration in a cavity formed between a cover opening area of a flexible circuit board and glue. Background Art

[0002] Flexible printed circuits (FPCs) are highly reliable and flexible printed circuit boards made from polyimide or polyester film. They are categorized by thickness and number of layers into single-sided, double-sided, and multi-layer (three or more) boards. The higher the number of layers and the thicker the FPC, the worse its bending performance and reliability requirements. Therefore, conventional FPC designs utilize single-sided and double-sided manufacturing processes for circuit boards that require bending. However, with the advancement of electronic products, FPCs, as a key component of many electronic products, are increasingly integrating more and more functions. This increased functionality requires dense wiring and multi-layer designs to accommodate more circuits and prevent cross-signal interference. This creates a need for multi-layer FPCs that offer both bending functionality and high reliability. To address this complex process, FPCs are designed with bending zones or decapping areas (also known as decapping areas) at locations where bending is required. Layer reduction in the bending zones of multi-layer FPCs is used to improve bending performance and reliability. Among them, layer reduction is to remove the upper layer or local areas of the upper and lower layers of the outer layer of the multi-layer board through the manufacturing process, so that the multi-layer board can be turned into a three-layer board or a two-layer board in the local area.

[0003] In addition, as electronic products are becoming increasingly thinner and lighter, multi-layer boards will make it difficult to reduce the thickness of electronic products. In this case, the thickness of local areas of the multi-layer board that affect the product thickness also needs to be reduced by reducing the layer.

[0004] The industry currently uses a post-decapping process to reduce layers in the decapping area of the outer layer of a multilayer board. In this process, no glue is required in the decapping area. Furthermore, to prevent the glue used to bond the outer and inner layers of the multilayer board from overflowing and flowing into the decapping area, which would make it difficult to remove the decapping area (i.e., copper scrap and insulation scrap in the decapping area difficult to remove), the glue between the outer and inner layers of the multilayer board needs to be recessed. This means the opening in the glue needs to be larger than the opening in the decapping area. Consequently, a void forms between the cut in the decapping area and the glue.

[0005] However, the circuit in the void is prone to copper ion migration, which may lead to a short circuit in the circuit and thus form defective products. Currently, the ET measurement process in the flexible board manufacturing field cannot detect the situation of the void and cannot determine whether copper ion migration has occurred. Summary of the Invention

[0006] In view of this, the present invention provides a method for detecting copper ion migration at the void formed by the opening area and the glue of a flexible board, so as to solve the problem in the prior art that the copper ion migration situation at the void formed by the opening area and the glue cannot be detected, resulting in a high defective rate of products.

[0007] The present invention provides a method for detecting copper ion migration at the void formed by the opening area and the glue of a flexible board, including:

[0008] Providing an inner flexible substrate and an outer flexible substrate with an opening area respectively;

[0009] Setting a detection component manufacturing area on the inner flexible substrate;

[0010] Using bonding glue to make the inner flexible substrate and the outer flexible substrate into a multi-layer board, and based on the opening area, opening the multi-layer board to form a void between the opening area and the bonding glue; at the same time, manufacturing a detection component on the detection component manufacturing area, wherein the detection component is used to detect the copper ion migration situation of the void;

[0011] Performing electrical measurement on the detection component, and obtaining the copper ion migration situation of the void according to the electrical measurement result.

[0012] Optionally, a waste area and an effective area for forming an inner circuit layer are provided on the inner flexible substrate, and the detection component manufacturing area is located in the waste area.

[0013] Optionally, the step of using bonding glue to make the inner flexible substrate and the outer flexible substrate into a multi-layer board includes:

[0014] Forming an inner circuit layer on the effective area of the inner flexible substrate according to a preset flexible board circuit design; at the same time, forming a detection circuit layer on the detection component manufacturing area of the inner flexible substrate according to a preset flexible board circuit design;

[0015] Providing bonding glue;

[0016] Based on the opening area, setting a corresponding detection opening area on the detection component manufacturing area;

[0017] According to the opening area and the detection opening area, the bonding glue is die-cut to form a first glue opening corresponding to the effective area and a second glue opening corresponding to the detection component manufacturing area on the bonding glue; wherein, the size of the cross-section of the first glue opening is larger than the size of the cross-section of the opening area, and the size of the cross-section of the second glue opening is larger than the size of the cross-section of the detection opening area;

[0018] Based on the opening area, the first glue opening, the detection opening area and the second glue opening, the outer flexible substrate is bonded to the inner flexible substrate formed with the inner circuit layer and the detection circuit layer by using the die-cut bonding glue to form the multilayer board.

[0019] Optionally, the difference between the size of the cross-section of the first glue opening and the size of the cross-section of the opening area is the same as the difference between the size of the cross-section of the second glue opening and the size of the cross-section of the detection opening area.

[0020] Optionally, the size of the cross-section of the detection opening area is greater than 5 mm.

[0021] Optionally, opening the multilayer board based on the opening area to form a cavity between the opening area and the bonding glue includes:

[0022] Laser the opening area on the multilayer board, and at the same time laser the detection opening area on the multilayer board;

[0023] Simultaneously peel off the waste from the lasered opening area and the detection opening area to form the cavity between the opening area and the first glue opening, and form a detection cavity between the detection opening area and the second glue opening.

[0024] Optionally, manufacturing the detection component on the detection component manufacturing area includes:

[0025] On the detection component manufacturing area corresponding to the multilayer board, at positions close to the second glue opening, two detection interfaces electrically connected to the detection circuit layer inside the multilayer board are respectively manufactured;

[0026] Among them, the two detection interfaces are also respectively located on both sides of the second glue opening; used to detect the copper ion migration situation of the detection cavity formed at the second glue opening, and the copper ion migration situation of the detection cavity is the same as that of the cavity.

[0027] Optionally, electrically measuring the detection component, and obtaining the copper ion migration situation of the cavity according to the electrical measurement result, includes:

[0028] Connect two test probes to the two detection interfaces respectively and perform electrical tests on the two detection interfaces;

[0029] When the electrical test result is a short circuit, it is determined that copper ion migration has occurred at both the detection cavity and the cavity;

[0030] When the electrical test result is an open circuit, it is determined that no copper ion offset has occurred at both the detection cavity and the cavity.

[0031] Optionally, on the detection component production area corresponding to the multilayer board, at positions close to the second glue opening, two detection interfaces electrically connected to the detection circuit layer of the inner layer of the multilayer board are respectively fabricated, including:

[0032] On the detection component production area corresponding to the multilayer board, at positions close to the second glue opening, two blind holes are respectively formed; wherein, each blind hole penetrates from the outermost layer of the multilayer board to the copper layer on the surface of the inner layer flexible substrate of the inner layer;

[0033] On the two blind holes, corresponding outer pads and inner pads are respectively fabricated; wherein, each outer pad is electrically connected to the detection circuit layer of the inner layer of the multilayer board through the corresponding blind hole and the corresponding inner pad;

[0034] Based on the two blind holes and the corresponding outer pads and inner pads, two detection interfaces electrically connected to the detection circuit layer are obtained.

[0035] Optionally, the distance between the two inner pads and the nearby second glue opening is greater than or equal to 1 mm.

[0036] Optionally, the cross-sectional dimensions of the two outer pads are greater than or equal to 1.5 mm.

[0037] Optionally, the detection circuit layer includes two outer dummy lines and multiple groups of inner interconnections;

[0038] The two outer dummy lines are respectively located on both sides of all the inner interconnections to protect all the inner interconnections;

[0039] Each group of the inner interconnections includes multiple lines cross-connected to the two inner pads, and each line conforms to the preset flexible board line design.

[0040] Advantages of the present invention: A detection component area is provided on the inner flexible substrate located in the inner layer of the multi-layer board to fabricate a detection component. Then, the inner flexible substrate and the outer flexible substrate are made into a multi-layer board using bonding glue and the cover is opened. During this process, the detection component is fabricated in the detection component fabrication area at the same time. This detection component can be used to detect the copper ion migration in the voids formed during the gluing and cover opening processes. According to the electrical measurement of this detection component, the copper ion migration detection at the voids formed by the cover opening area and the glue of the flexible board is realized.

[0041] The method for detecting copper ion migration at the voids formed by the cover opening area and the glue of the flexible board in the present invention leads out a detection component as a new electrical measurement point for electrical measurement in the detection component fabrication area provided on the inner flexible substrate during the conventional processes of gluing and cover opening of the multi-layer board. It overcomes the defect that the traditional ET measurement process in the field of flexible board fabrication cannot determine whether copper ion migration occurs at the voids, and can truly identify the actual situation of copper ion migration at the voids formed by the cover opening area and the glue. According to the discrimination result, defective products with short circuits caused by copper ion migration are screened out in advance, reducing the production error rate and improving the product yield at the time of factory shipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings. The drawings are schematic and should not be construed as imposing any limitation on the present invention. In the drawings:

[0043] Figure 1 Shows a flowchart of a method for detecting copper ion migration at the voids formed by the cover opening area and the glue of a flexible board in an embodiment of the present invention;

[0044] Figure 2 Shows a cross-sectional structure diagram of the structure of a multi-layer board near the cover opening area after the cover is opened in an embodiment of the present invention;

[0045] Figure 3 Shows a top view structure diagram of the structure of a multi-layer board near the cover opening area after the cover is opened in an embodiment of the present invention;

[0046] Figure 4 Shows a cross-sectional structure diagram of the detection component in an embodiment of the present invention;

[0047] Figure 5 Shows a top view structure diagram of the detection component in an embodiment of the present invention;

[0048] Figure 6 Shows a top view structure diagram of the detection circuit layer in an embodiment of the present invention;

[0049] Figure 7 Shows a micrograph of a section of a void in an embodiment of the present invention;

[0050] Figure 8 It shows a schematic layout diagram of 5 detection components on the entire board in an embodiment of the present invention.

[0051] Explanation of reference numerals:

[0052] 1. Structure of the multi-layer board near the opening area after opening the cover, 2. Detection component, 3. Entire board, 11. First inner layer board, 12. First outer layer board, 13. First adhesive layer, 14. Void, 21. Second inner layer board, 22. Second outer layer board, 23. Second adhesive layer, 24. Detection void, 25. Detection interface, 111. Inner layer circuit layer, 121. Opening area, 131. First adhesive opening, 211. Detection circuit layer, 221. Detection opening area, 231. Second adhesive opening, 251. Blind hole, 252. Outer pad, 253. Inner pad, 2111. Outer dummy line, 2112. Inner interconnecting line. Detailed implementation manners

[0053] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0054] Embodiment

[0055] A method for detecting copper ion migration at the void formed by the opening area and the adhesive of a flexible board, as Figure 1 shown, includes the following steps:

[0056] S1, respectively provide an inner flexible substrate and an outer flexible substrate provided with an opening area;

[0057] S2, set a detection component manufacturing area on the inner flexible substrate.

[0058] Specifically, the inner flexible substrate is a layer board located in the inner layer of the multi-layer board, and the outer flexible substrate is a layer board located in the outer layer of the multi-layer board, and the outer flexible substrate is usually a circuit board that needs to be opened in a local area.

[0059] The inner flexible substrate is a double-sided board or a multi-layer board, and the outer flexible substrate is a single-sided board or a double-sided board. In this embodiment, the inner flexible substrate is taken as an example of a double-sided board, and the outer flexible substrate is taken as an example of a single-sided board for illustration. Among them, the double-sided board is specifically a double-sided copper-clad substrate composed of double-layer copper foil and PI (i.e., polyimide) substrate, and the double-layer copper foils are respectively located on both sides of the PI substrate; the single-sided board is specifically a single-sided copper-clad substrate composed of one layer of copper foil and PI substrate.

[0060] Preferably, a waste area and an effective area for forming an inner layer circuit layer are provided on the inner layer flexible substrate, and the detection component manufacturing area is located in the waste area.

[0061] A flexible printed circuit board usually has an area for laying out core circuits, which is called a circuit area or an effective area, and the remaining area is called a waste area. The detection component manufacturing area for manufacturing the detection components for inner layer lead-out is arranged on the waste area of the inner layer flexible substrate, which will not affect the core circuits of the inner layer flexible substrate, makes full use of the materials in the waste area, and is convenient for manufacturing the detection components simultaneously with the conventional manufacturing process of the multi-layer board subsequently. There is no need to separately add materials and process flows, with high material utilization rate and high production efficiency.

[0062] It should be noted that since the outer layer flexible substrate needs to be attached to the inner layer flexible substrate, therefore, when the multi-layer board after the outer layer flexible substrate is attached to the inner layer flexible substrate, the opening area on the multi-layer board corresponds to the position of the opening area on the original outer layer flexible substrate, and the detection component manufacturing area on the multi-layer board also corresponds to the position of the detection component manufacturing area on the original inner layer flexible substrate.

[0063] As Figure 1 shown in S3, use bonding glue to make the inner layer flexible substrate and the outer layer flexible substrate into a multi-layer board, and based on the opening area, open the multi-layer board to form a cavity between the opening area and the bonding glue; at the same time, manufacture a detection component on the detection component manufacturing area, wherein the detection component is used to detect the copper ion migration situation of the cavity.

[0064] Preferably, in S3, using bonding glue to make the inner layer flexible substrate and the outer layer flexible substrate into a multi-layer board includes:

[0065] S31: Form an inner layer circuit layer on the effective area of the inner layer flexible substrate according to a preset flexible board circuit design; at the same time, form a detection circuit layer on the detection component manufacturing area of the inner layer flexible substrate according to a preset flexible board circuit design;

[0066] S32: Provide bonding glue;

[0067] S33: Based on the opening area, set a corresponding detection opening area on the detection component manufacturing area;

[0068] S34: Punch the bonding glue according to the opening area and the detected opening area to form a first glue opening corresponding to the effective area and a second glue opening corresponding to the detection component manufacturing area on the bonding glue; wherein, the size of the cross-section of the first glue opening is larger than the size of the cross-section of the opening area, and the size of the cross-section of the second glue opening is larger than the size of the cross-section of the detected opening area;

[0069] S35: Based on the opening area, the first glue opening, the detected opening area and the second glue opening, use the punched bonding glue to bond the outer flexible substrate to the inner flexible substrate formed with the inner circuit layer and the detection circuit layer to form the multilayer board.

[0070] According to the preset flexible board circuit design, an inner circuit layer that meets the preset line width requirements and circuit requirements can be fabricated; since the waste area of the inner flexible substrate is an area where no circuit needs to be designed, in this embodiment, a detection component manufacturing area is set in this waste area, and a detection circuit layer is formed according to the same line width requirements and line pitch requirements in the preset flexible board circuit design, which is convenient for subsequently simulating the real situation of the voids formed on the flexible board based on the detection circuit layer that meets the same requirements as the inner circuit layer, laying a circuit foundation for detecting the copper ion migration situation of the voids, and the detection result is highly reliable; after the circuit manufacturing of the effective area and the detection component is completed, the detected opening area on the detection component manufacturing area is set according to the opening area, which is convenient for subsequently forming an opening in the detected opening area of the detection component that is the same as the opening area, and then punching the bonding glue (i.e., the bonding glue) according to the opening area and the detected opening area, and then using the bonding glue formed with the first glue opening and the second glue opening to bond the inner flexible substrate and the outer flexible substrate, which can further make the glue pasting situation in the finally manufactured detection component in the detection component manufacturing area exactly the same as the glue pasting situation on the effective area of the flexible board, that is, further enabling the detection component to accurately and reliably detect the real copper ion migration situation of the voids formed on the flexible board.

[0071] Preferably, the difference between the size of the cross-section of the first glue opening and the size of the cross-section of the opening area is the same as the difference between the size of the cross-section of the second glue opening and the size of the cross-section of the detected opening area.

[0072] Since the cavity is formed by the first glue opening that is retracted relative to the opening area and the opening area, the size of the cross-section of the first glue opening is larger than the size of the cross-section of the opening area, that is, there is a certain difference between the size of the cross-section of the first glue opening and the size of the cross-section of the opening area; and the difference between the size of the cross-section of the second glue opening and the size of the cross-section of the detection opening area is the same as this difference, which can ensure that the detection cavity formed between the subsequent second glue opening and the detection opening area is exactly the same as the above cavity, improving the reliability and accuracy of the detection component for detecting the copper ion migration situation in the cavity. The above difference can be determined according to the actual situation.

[0073] Preferably, the size of the cross-section of the detection opening area is greater than 5 mm.

[0074] With the detection opening area of the above size, it is convenient for the opening of the multilayer board in the detection component production area, and then it is convenient to form a detection component that can accurately detect the copper ion migration situation.

[0075] It should be noted that the shapes of the opening area and the detection opening area are rectangular or circular. In this embodiment, it is rectangular, so the sizes of the cross-sections of both the opening area and the detection opening area refer to the length of the rectangle. And the shapes of the first glue opening and the second glue opening are the same as or similar to the shapes of the opening area and the detection opening area. No matter what shape, it only needs to ensure that the sizes of the cross-sections of the first glue opening and the second glue opening are larger than the sizes of the cross-sections of the opening area and the detection opening area.

[0076] Preferably, in S3, based on the opening area, the multilayer board is opened, and a cavity is formed between the opening area and the bonding glue, including:

[0077] S36: Laser the opening area on the multilayer board, and at the same time laser the detection opening area on the multilayer board;

[0078] S37: Simultaneously peel off the waste from the lasered opening area and the detection opening area, forming the cavity between the opening area and the first glue opening, and forming a detection cavity between the detection opening area and the second glue opening.

[0079] The above processes of laser and waste peeling are conventional processes for opening the multilayer board. By laser and waste peeling the detection opening area while performing the conventional process of opening, on the one hand, it can ensure that the detection cavity has the same copper ion migration situation as the cavity, perfectly simulate the cavity, and ensure the reliability of the detection component; on the other hand, it does not require a separate additional process flow, realizing the improvement of production efficiency.

[0080] Specifically, in this embodiment, the cross-sectional view structure diagram of the structure of the multilayer board near the opening area after opening in S36 - S37 is as Figure 2As shown, its corresponding top view structure diagram is as Figure 3 shown. In Figure 2 , 1 is the structure of the multi-layer board near the opening area after opening the cover. 11 is the inner flexible substrate (also known as the first inner layer board) of the multi-layer board located in the effective area. 12 is the outer flexible substrate (also known as the second outer layer board) of the multi-layer board near the opening area. 13 is the bonding glue (also known as the first glue layer) between the first inner layer board 11 and the first outer layer board 12. 121 is the opening area. 131 is the first glue opening. 14 is the cavity formed between the opening area 121 and the first glue opening 131. In Figure 3 , 111 is the circuit on the first inner layer board exposed outside after opening the cover of the multi-layer board, that is, the inner circuit layer (it should be understood that this inner circuit layer is designed according to the preset flexible board circuit. Figure 3 The parallel distributed inner circuit layers in Figure 4 are just one of them. This inner circuit layer can also be other distribution shapes. Here, only the position of the inner circuit layer is shown). In this embodiment, the cross-sectional view structure diagram of the detection component formed in the detection component manufacturing area after opening the cover in S36 - S37 is as Figure 5 shown, and its corresponding top view structure diagram is as Figure 4 shown. In Figure 5 , 2 is the detection component. 21 is the inner flexible substrate (also known as the second inner layer board) in the detection component located in the detection component manufacturing area. 22 is the outer flexible substrate (also known as the second outer layer board) in the detection component located in the detection component manufacturing area. 23 is the bonding glue (also known as the second glue layer) between the second inner layer board 21 and the second outer layer board 22. 221 is the detection opening area. 231 is the second glue opening. 24 is the detection cavity formed between the detection opening area 221 and the second glue opening 231. In Figures 2 to 5 , it can be seen that the structure of the detection component is basically the same as the structure of the multi-layer board near the opening area after opening the cover, except that there are 2 additional detection interfaces (i.e., Figure 3 25 in

[0081] Preferably, in S3, manufacturing the detection component on the detection component manufacturing area includes:

[0082] S38: On the detection component manufacturing area corresponding to the multi-layer board, at positions close to the second glue opening, respectively manufacture two detection interfaces that are electrically connected to the detection circuit layer of the inner layer of the multi-layer board;

[0083] Wherein, the two detection interfaces are respectively located on both sides of the second glue opening; used for detecting the copper ion migration condition of the detection cavity formed at the second glue opening, and the copper ion migration condition of the detection cavity is the same as that of the cavity.

[0084] Since the detection cavity is formed by the second glue opening and the detection opening area, setting the two detection interfaces near the second glue opening in the detection component manufacturing area can facilitate accurately detecting the copper ion migration condition of the detection cavity, and then judging the copper ion migration condition of the cavity. The two detection interfaces are located on both sides of the second glue opening, which can avoid misjudgment caused by regarding the copper ion migration condition of a single-side glue opening as that of the entire detection cavity, and reduce the misjudgment rate; since the detection cavity is in contact with the inner detection circuit layer, if copper ion migration occurs in the detection cavity, its copper ions come from the detection circuit layer. Similarly, since the cavity is in contact with the inner layer circuit of the inner layer, if copper ion migration occurs in the cavity, its copper ions come from the inner layer circuit layer. Therefore, conduction between the detection interface and the detection circuit layer can ensure directly judging the copper ion migration condition based on the electrical measurement of the detection component subsequently.

[0085] Preferably, S38 includes:

[0086] S381: Form two blind holes respectively at positions near the second glue opening on the detection component manufacturing area corresponding to the multilayer board; wherein, each blind hole penetrates from the outermost layer of the multilayer board to the copper layer on the surface of the inner-layer flexible substrate of the inner layer;

[0087] S382: Manufacture corresponding outer pads and inner pads respectively on the two blind holes; wherein, each outer pad is conducted with the detection circuit layer of the inner layer of the multilayer board through the corresponding blind hole and the corresponding inner pad;

[0088] Obtain two detection interfaces conducted with the detection circuit layer according to the two blind holes and the corresponding outer pads and inner pads.

[0089] By manufacturing two blind holes penetrating to the copper layer on the surface of the inner-layer flexible substrate and then connecting the corresponding pads, it can ensure that the manufactured detection component is led out from the inner layer of the multilayer board, and then ensure the smooth realization of detecting the copper ion migration condition at the cavity.

[0090] Specifically, as Figure 4 and Figure 5 shown, Figure 4 shows the cross-sectional structure of 2 detection interfaces 25 in the detection component, Figure 5 shows the top view structure of 2 detection interfaces 25 in the detection component. In Figure 4 and Figure 5Among them, 251 is a blind via, 252 is an external pad, and 253 is an internal pad. The two external pads 252 are sequentially connected to the detection circuit layer 211 through the corresponding blind vias 251 and internal pads 253.

[0091] Specifically, in this embodiment Figure 5 the specific structure of the detection circuit layer and its connection relationship with the two internal pads are as Figure 6 shown. In Figure 6 it, the detection circuit layer 211 includes two external dummy lines 2111 and multiple groups of internal interconnecting lines 2112 ( Figure 6 specifically 3 groups, the first group is the lines within the black dotted line box, and the other two groups are the two groups of lines located below the first group of internal interconnecting lines); the two external dummy lines 2111 are respectively located on both sides of all the internal interconnecting lines 2112, and are used to protect all the internal interconnecting lines 2112 to avoid the influence of the chemical solution in wet processes such as etching on the internal interconnecting lines 2112 on the inner side; each group of internal interconnecting lines 2112 includes multiple lines that are alternately interconnected with the two internal pads 253, and each line meets the preset flexible circuit board line design.

[0092] It should be noted that in each group of internal interconnecting lines 2112, each line meeting the preset flexible circuit board line design means that the line width of each line meets the line width requirement in the preset flexible circuit board line design, and the line pitch between every two adjacent lines meets the line pitch requirement in the preset flexible circuit board line design. The number of groups of internal interconnecting lines depends on the types of line width requirements and line pitch requirements in the preset flexible circuit board line design, that is, if there are multiple types of line width requirements and line pitch requirements in the preset flexible circuit board line design, one or more of the smallest line width requirements and line pitch requirements can be selected according to the actual situation to design the corresponding number of groups of internal interconnecting lines, so that the line width of each group of internal interconnecting lines meets one or more of the smallest line width requirements and line pitch requirements; if there is only one type of line width requirement and only one type of line pitch requirement in the preset flexible circuit board line design, only one group of internal interconnecting lines can be designed so that the line width of this group of internal interconnecting lines meets this one type of line width requirement and line pitch requirement; if there is only one type of line width requirement and multiple types of line pitch requirements in the preset flexible circuit board line design, one or more of the smallest line pitch requirements can also be selected from these multiple line pitch requirements, and then combined with this one type of line width requirement to design the corresponding number of groups of internal interconnecting lines, so that the line width of each group of internal interconnecting lines meets this one type of line width requirement, and the line pitch respectively meets one or more of the smaller line pitch requirements; if there is only one type of line pitch requirement and multiple types of line width requirements in the preset flexible circuit board line design, it is the same as the situation where there is only one type of line width requirement and multiple types of line pitch requirements in the preset flexible circuit board line design, and will not be elaborated here. As Figure 6 shown, the number of groups of internal interconnecting lines 2112 is 3, the line pitch requirements between the lines in the 3 groups are the same, there is only 1 type, and there are 2 types of line width requirements.

[0093] In addition, among the internal interconnections 2112 in each group, the multiple lines that are alternately interconnected with the two internal pads 253 mean that the internal pads connected by adjacent two lines are staggered, that is, the first line is connected to the first internal pad, the second line is connected to the second internal pad, the third line is connected to the first internal pad, the fourth line is connected to the second internal pad, and so on; or, the first line is connected to the second internal pad, the second line is connected to the first internal pad, the third line is connected to the second internal pad, the fourth line is connected to the first internal pad, and so on. The number of lines is determined according to the actual situation, such as Figure 6 , the number of lines in the internal interconnections 2112 in each group is 5.

[0094] For multiple groups of internal interconnections interconnected by the above internal line staggering, it is convenient to perform electrical testing through the staggered multiple groups of internal interconnections when copper ion migration occurs at the void, ensuring that the electrical test results in abnormal situations, that is, short circuits, can be detected.

[0095] Preferably, the distance between the two internal pads and the nearby second glue opening is greater than or equal to 1 mm.

[0096] With the internal pads set with the above distance, it can ensure that based on the internal pads, the electrical test results of the detection voids at the second glue opening can be accurately and reliably detected, and then the copper ion migration situation at the void can be obtained.

[0097] Preferably, the cross-sectional dimensions of the two external pads are both greater than or equal to 1.5 mm.

[0098] With the external pads set with the above dimensions, it can ensure that during subsequent electrical testing, the test probe can be accurately connected to the detection interface and will not contact other materials around the detection interface, resulting in invalid electrical testing and reducing the detection error rate.

[0099] It should be noted that the shape of the blind hole is usually a regular figure, such as a circle and a rectangle. When it is a circle, the cross-sectional dimension of the blind hole is the diameter. When it is a rectangle, the cross-sectional dimension of the blind hole is the length and / or width of the rectangle; the shape of the pad is similar to that of the blind hole, and the meaning of its cross-sectional dimension is the same as that of the blind hole, which will not be elaborated here. In this embodiment, the shape of the blind hole is a circle, so its cross-sectional dimension is specifically the diameter of the circle, and the shape of the pad is a rectangle, and its cross-sectional dimension is specifically the length of the rectangle.

[0100] Such as Figure 1 As shown in, S4, perform electrical testing on the detection component, and according to the electrical test results, obtain the copper ion migration situation of the void.

[0101] Preferably, S4 includes:

[0102] S41: Connect two test probes to the two detection interfaces respectively, and perform electrical measurement on the two detection interfaces;

[0103] S42: When the electrical measurement result is a short circuit, it is determined that copper ion migration has occurred at both the detection cavity and the cavity;

[0104] When the electrical measurement result is an open circuit, it is determined that no copper ion offset has occurred at both the detection cavity and the cavity.

[0105] Since the two detection interfaces are electrically connected to the detection circuit layer, if the electrical measurement result between the two test probes connected to the two detection interfaces, then copper ion migration must have occurred in the detection cavity near the detection interface, resulting in a short circuit of the circuit. Furthermore, it can be determined that copper ion migration has also occurred in the cavity; conversely, it can be determined that no copper ion offset has occurred at both the detection cavity and the cavity; the above electrical measurement and determination method based on two detection interfaces led out from the inner layer has a simple and easy-to-implement judgment mechanism and high reliability.

[0106] In a specific embodiment, when the electrical measurement result is detected as a short circuit through electrical measurement, the structure of the multilayer board at the cavity is sliced and observed through a microscope, and the result is as Figure 7 shown. In Figure 7 , the area where the two black regions meet is the cavity, and the white line in the cavity is the copper ion that has migrated. Further, an X-ray fluorescence spectrometer is used to perform elemental analysis on the cavity in Figure 7 , and the result is shown in the following table. From the following table, it can be seen that the weight proportion of copper element in the cavity is the largest, indicating that there are a large number of migrated copper ions in the cavity.

[0107] Table Results of elemental analysis of the cavity in this embodiment

[0108] Element Weight ratio Wt(%) C 14.28 O 8.01 Al 0.34 P 0.19 S 0.33 Cu 76.85 Total amount 100

[0109] It should be noted that the inner flexible substrate, outer flexible substrate, detection component and the multilayer board fabricated thereby in this embodiment are all for a single-piece flexible board product. However, in actual production processes, multiple flexible board products are usually fabricated on a whole board to achieve mass production. Therefore, in actual production, if the circuit designs of the flexible board products fabricated on the whole board are all the same, at least 3 identical detection components can be fabricated in the waste area of the whole board according to the layout space of the whole board to detect the copper ion migration situation at the cavities of all the flexible board products on the board, as Figure 8 shown. This Figure 8 shows the situation of fabricating 5 detection components 2. Figure 8The 3 in it represents the entire board; if the circuit designs of the flexible board products manufactured on the entire board are inconsistent, the detection components corresponding to each design can be separately manufactured according to the preset flexible board circuit designs (i.e., line width requirements and circuit requirements) of each flexible board product, so as to achieve the purpose of detecting the copper ion migration at the voids in the flexible board products under each design.

[0110] For the above detection method, a detection component area is set on the inner flexible substrate located in the inner layer of the multilayer board to manufacture the detection component, and then the inner flexible substrate and the outer flexible substrate are made into a multilayer board by using bonding glue, and the cover is opened. During this process, the detection component is manufactured in the detection component manufacturing area at the same time, and the detection component can be used to detect the copper ion migration at the voids formed during the glue application and cover opening processes; according to the electrical measurement of the detection component, the copper ion migration detection at the voids formed by the flexible board cover opening area and the glue is realized.

[0111] For the method for detecting copper ion migration at the voids formed by the flexible board cover opening area and the glue in this embodiment, by introducing the detection component as a new electrical measurement point for electrical measurement in the detection component manufacturing area provided on the inner flexible substrate during the conventional processes of glue application and cover opening of the multilayer board, it overcomes the defect that the traditional ET measurement process in the field of flexible board manufacturing cannot determine whether copper ion migration occurs at the voids, and can truly determine the actual situation of copper ion migration at the voids formed by the cover opening area and the glue. According to the determination result, the defective products with short circuits caused by copper ion migration are screened out in advance, reducing the production error rate and improving the product yield at the time of factory shipment.

[0112] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue, characterized in that, Comprising: Providing an inner flexible substrate and an outer flexible substrate provided with an opening area respectively; providing a detection component manufacturing area on the inner flexible substrate; the inner flexible substrate is provided with a waste area and an effective area for forming an inner circuit layer, and the detection component manufacturing area is located in the waste area; Using bonding glue to fabricate the inner flexible substrate and the outer flexible substrate into a multilayer board; forming an inner circuit layer on the effective area of the inner flexible substrate according to a preset flexible board circuit design; at the same time, forming a detection circuit layer on the detection component manufacturing area of the inner flexible substrate according to a preset flexible board circuit design; providing bonding glue; based on the opening area, providing a corresponding detection opening area on the detection component manufacturing area; According to the opening area and the detection opening area, punching the bonding glue to form a first glue opening corresponding to the effective area and a second glue opening corresponding to the detection component manufacturing area on the bonding glue; wherein, the cross-sectional dimension of the first glue opening is larger than the cross-sectional dimension of the opening area, and the cross-sectional dimension of the second glue opening is larger than the cross-sectional dimension of the detection opening area; based on the opening area, the first glue opening, the detection opening area and the second glue opening, using the punched bonding glue, attaching the outer flexible substrate to the inner flexible substrate formed with the inner circuit layer and the detection circuit layer to form the multilayer board; And based on the opening area, opening the multilayer board to form a cavity between the opening area and the bonding glue; laser-ablating the opening area on the multilayer board, and at the same time laser-ablating the detection opening area on the multilayer board; simultaneously tearing off the waste of the laser-ablated opening area and the detection opening area, forming the cavity between the opening area and the first glue opening, and forming a detection cavity between the detection opening area and the second glue opening; Meanwhile, a detection component is fabricated on the detection component fabrication area, where the detection component is used to detect the copper ion migration situation of the cavity; on the detection component fabrication area corresponding to the multilayer board, at positions close to the second glue opening, two detection interfaces electrically connected to the detection circuit layer of the inner layer of the multilayer board are respectively fabricated; wherein, the two detection interfaces are respectively located on both sides of the second glue opening; for detecting the copper ion migration situation of the detection cavity formed at the second glue opening, and the copper ion migration situation of the detection cavity is the same as that of the cavity; on the detection component fabrication area corresponding to the multilayer board, at positions close to the second glue opening, two blind holes are respectively formed; wherein, each blind hole penetrates from the outermost layer of the multilayer board to the copper layer on the surface of the inner layer flexible substrate of the inner layer; on the two blind holes, corresponding outer pads and inner pads are respectively fabricated; wherein, each outer pad is electrically connected to the detection circuit layer of the inner layer of the multilayer board through the corresponding blind hole and the corresponding inner pad; two detection interfaces electrically connected to the detection circuit layer are obtained according to the two blind holes and the corresponding outer pads and inner pads; The detection component is electrically measured, and according to the electrical measurement result, the copper ion migration situation of the cavity is obtained.

2. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, wherein The difference between the cross-sectional size of the first glue opening and the cross-sectional size of the opening area is the same as the difference between the cross-sectional size of the second glue opening and the cross-sectional size of the detection opening area.

3. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, characterized in that, The cross-sectional size of the detection opening area is greater than 5 mm.

4. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, wherein The electrically measuring the detection component and obtaining the copper ion migration situation of the cavity according to the electrical measurement result includes: Connect two test probes to the two detection interfaces respectively, and electrically measure the two detection interfaces; When the electrical measurement result is a short circuit, it is determined that copper ion migration occurs at both the detection cavity and the cavity; When the electrical measurement result is an open circuit, it is determined that no copper ion offset occurs at both the detection cavity and the cavity.

5. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, wherein The distance between each of the two inner pads and the nearby second glue opening is greater than or equal to 1 mm.

6. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, wherein The cross-sectional size of each of the two outer pads is greater than or equal to 1.5 mm.

7. According to the method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue as claimed in claim 1, the detection circuit layer includes two outer dummy lines and multiple groups of inner interconnections; The two outer dummy lines are respectively located on both sides of all the inner interconnections for protecting all the inner interconnections; Each group of the inner interconnections includes multiple lines cross-connected with the two inner pads, and each line conforms to the preset flexible board line design.

8. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 7, characterized in that In each group of the inner interconnections, the inner pads connected by two adjacent inner interconnections are arranged alternately.

9. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, wherein The inner layer flexible substrate is a layer board located in the inner layer of the multilayer board, and the outer layer flexible substrate is a layer board located in the outer layer of the multilayer board; The inner layer flexible substrate is a double-sided board or a multilayer board, and the outer layer flexible substrate is a single-sided board or a double-sided board.

10. The method for detecting copper ion migration at the cavity formed by the flexible board opening area and the glue according to claim 1, wherein The shapes of the opening area and the area for detecting the opening are rectangular or circular.

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