Micro blind hole of circuit board

Abstract

The utility model is suitable for PCB board technical field provides a kind of micro blind hole of circuit board, including the bottom disc being arranged on first circuit layer and the first blind hole and the first top disc being arranged on second circuit layer, the bottom of first blind hole is connected with bottom disc;The upper surface of bottom disc is equipped with micro groove structure, for increasing the interface contact area between first blind hole and bottom disc.The utility model is by being arranged micro groove structure on blind hole bottom disc surface, significantly increase interface contact area, promote binding force and electrical connection reliability, effectively inhibit delamination risk, to improve the overall structural stability and long-term use performance of HDI circuit board.

Description

Technical Field

[0001] This utility model belongs to the field of PCB board technology, and in particular relates to a miniature blind via for a circuit board. Background Technology

[0002] In the manufacturing process of high-density interconnect (HDI) multilayer printed circuit boards (PCBs), there are strict requirements for the size control of laser blind vias. It is usually stipulated that the upper and lower diameters of the blind vias must not be less than 45μm to ensure that there is sufficient contact area between the blind via and the bottom copper pad, thus ensuring the reliability of the electrical connection.

[0003] In a typical process flow, the bottom copper pad (chassis) is first electroplated with copper. Then, blind vias are formed in the dielectric layer above the chassis using laser drilling, followed by electroplating to fill the blind vias. Because the electroplating processes for the chassis and blind vias are performed in separate steps, electroplating stress inevitably exists between the copper layers of both. If the contact area between the blind via and the chassis is insufficient, cracks or even delamination can easily occur at this interface during subsequent assembly or use of the circuit board, leading to poor contact or functional failure.

[0004] Traditional machining processes using CO2 laser drilling result in blind holes that are truncated cones (larger at the top and smaller at the bottom) with essentially flat surfaces. To ensure the lower hole diameter meets the minimum requirement of 45μm, it is usually necessary to increase the laser energy or the number of pulses. However, this simultaneously leads to a further enlargement of the upper hole diameter. An excessively large hole diameter disrupts the current distribution during electroplating, causing uneven current density between the hole opening and the hole interior. This results in an excessively thin plating layer on the hole wall or even copper-free defects, severely impacting the product's electrical performance and long-term reliability.

[0005] Therefore, optimizing the morphology of blind vias and controlling the uniformity of via diameter are crucial for improving the interconnect reliability and manufacturing yield of HDI boards. In light of the above, there is an urgent need to develop a micro-blind via for circuit boards to overcome the shortcomings in current practical applications. Summary of the Invention

[0006] The purpose of this invention is to provide a miniature blind via for a circuit board, which aims to solve the problems mentioned in the background art.

[0007] This invention is implemented as follows: a micro blind via of a circuit board includes a chassis disposed on a first circuit layer and a first blind via and a first top plate disposed on a second circuit layer. The bottom of the first blind via is connected to the chassis. The upper surface of the chassis is provided with a micro-groove structure to increase the interface contact area between the first blind via and the chassis.

[0008] In a further technical solution, the micro-groove structure is a concentric circular groove or a vortex-shaped groove.

[0009] In a further technical solution, the cross-section of the micro-groove is U-shaped.

[0010] In a further technical solution, the depth H of the U-shaped groove, the opening width D1 of the U-shaped groove, and the spacing D2 between adjacent U-shaped grooves respectively satisfy the following ranges: 1μm≤H≤5μm; 10μm≤D1≤30μm; 10μm≤D2≤30μm.

[0011] In a further technical solution, the bottom diameter W of the first blind hole satisfies: 40μm≤W≤60μm.

[0012] In a further technical solution, the chassis, the first blind hole, and the first top plate are all made of copper.

[0013] A further technical solution also includes a third circuit layer disposed above the second circuit layer, wherein the third circuit layer is provided with a second blind via and a second top plate, and the bottom of the second blind via is connected to the first top plate to form a stacked blind via structure.

[0014] A further technical solution is that the upper surface of the first top plate is provided with a micro-groove structure to increase the interface contact area with the second blind hole.

[0015] The present invention provides a miniature blind via for a circuit board, which has the following advantages: By setting concentric or spiral micro-U-shaped groove structures on the surface of the bottom copper pad of the blind via, the interface contact area between the blind via and the chassis is significantly increased (more than 30% higher than the traditional planar structure), which effectively enhances the interface bonding force, improves the stress concentration problem caused by step electroplating, suppresses the risk of crack initiation and delamination, prevents the blind via from being pulled off, and improves the reliability of interlayer electrical connections. This significantly improves the structural stability and electrical performance of HDI circuit boards under complex assembly and long-term use conditions. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of the first circuit layer, the second circuit layer, and the first blind via of the circuit board of this utility model; Figure 2 This is a cross-sectional schematic diagram of the concentric circular groove of the blind hole chassis of this utility model; Figure 3 This is a top view of the concentric circular groove of the blind hole chassis of this utility model; Figure 4 This is a cross-sectional schematic diagram of the vortex groove of the blind hole chassis of this utility model; Figure 5 This is a top view of the vortex groove of the blind hole chassis of this utility model; Figure 6 This is a schematic diagram showing the connection between the first blind hole and the second blind hole of this utility model; In the diagram: 1-First layer circuit, 2-Second layer circuit, 3-Third layer circuit, 4-First blind hole, 5-Second blind hole, 6-Interface, 1A-Base, 2A-First top plate, 3A-Second top plate, W-Bottom diameter of blind hole, Depth of HU-shaped groove, D1-Opening width of U-shaped groove, D2-Spacing of U-shaped groove. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this utility model and are not intended to limit this utility model.

[0018] The specific implementation of this utility model will be described in detail below with reference to specific embodiments.

[0019] like Figure 1 As shown, a micro-blind via of a circuit board according to an embodiment of this utility model is fabricated using an arbitrary layer high-density interconnect (HDI) process. It includes a first circuit layer 1, a second circuit layer 2, and a first blind via 4. A base plate 1A is provided on the first circuit layer 1. The second circuit layer 2 is disposed above the first circuit layer 1. The second circuit layer 2 has the first blind via 4 and a first top plate 2A. The first blind via 4 is a circular hole, and the first top plate 2A is also circular. The top of the first blind via 4 is connected to the first top plate 2A, and the bottom of the first blind via 4 is connected to the base plate 1A.

[0020] The chassis 1A is circular, and its upper surface is a copper layer formed in the same layer as the first circuit layer 1. The first blind via 4 is formed by a frustum-shaped cavity created by laser ablation in the dielectric layer above the chassis 1A, and copper is electroplated into the cavity. The copper filling in the first blind via 4 and the copper layer of the first top chassis 2A are formed simultaneously through a single electroplating process during the construction of the second circuit layer 2, therefore there is no interface between them, resulting in a complete and continuous conductive bond.

[0021] However, since the chassis 1A was electroplated before the blind via was formed, while the copper filling layer of the blind via was electroplated afterward, there is a difference in the process timing between the two, resulting in the formation of interface 6 between the upper surface of chassis 1A and the bottom copper filling layer of the first blind via 4. This interface 6 is a potentially weak area in terms of reliability.

[0022] To improve the bonding strength and electrical connection reliability of this interface, such as Figure 2 and Figure 3As shown, a concentric circular groove structure is provided on the upper surface of the chassis 1A (i.e., there is a concentric circular groove interface between the copper layer of the chassis 1A and the copper layer at the bottom of the first blind hole 4). The groove is formed by UV laser ablation or pattern transfer etching process, which aims to increase the actual contact area between the bottom of the blind hole and the chassis 1A, thereby enhancing the interface bonding force and alleviating electroplating stress concentration.

[0023] The concentric circular groove has a U-shaped cross-section, with its outer diameter ≤ the bottom diameter W of the first blind hole 4, and W satisfies: 40μm ≤ W ≤ 60μm. The geometric parameters of the groove can be adjusted according to process requirements. The depth H of the U-shaped groove, the opening width D1 of the U-shaped groove, and the spacing D2 between adjacent U-shaped grooves respectively satisfy the following ranges: 1μm≤H≤5μm; 10μm≤D1≤30μm; 10μm≤D2≤30μm.

[0024] In addition, such as Figure 4 and Figure 5 As shown, a vortex-shaped groove structure can also be used on the chassis 1A instead of the concentric circular groove, and it can also be prepared by UV laser or pattern transfer etching process to further expand the interface contact area and improve stress distribution. The vortex-shaped groove also has a U-shaped cross section, and its outer diameter is ≤ the bottom diameter W of the blind hole. The depth H of the U-shaped groove, the opening width D1 of the U-shaped groove, and the spacing D2 between adjacent U-shaped grooves are in the same range as those of the concentric circular groove.

[0025] Preferably, the chassis 1A, the first blind via 4, and the first top plate 2A are all made of copper; and the copper layer of the chassis 1A is formed when the first circuit layer 1 is manufactured, while the copper layers of the first blind via 4 and the first top plate 2A are formed when the second circuit layer 2 is manufactured.

[0026] like Figure 6 As shown, this structure can also be extended to a multi-layer stacked blind via design. A third circuit layer 3 is provided above the second circuit layer 2, which includes a second top plate 3A and a second blind via 5. The top of the second blind via 5 is connected to the second top plate 3A, the bottom of the second blind via 5 is connected to the first top plate 2A, and the second blind via 5 covers the first blind via 4, forming a double-layer micro blind via structure with superimposed layers, achieving higher density interlayer interconnection.

[0027] In addition, the second blind hole 5 is a circular hole, and both the second blind hole 5 and the second top plate 3A are made of copper.

[0028] There is a groove-shaped interface between the copper layer of the first top plate 2A and the copper layer at the bottom of the second blind hole 5, and the groove cross-section is a U-shaped groove.

[0029] The present invention provides a micro blind via for a circuit board in the above embodiments. By setting a micro-groove structure (such as a concentric circle or a vortex-shaped U-shaped groove) on the surface of the bottom copper disk (chassis) of the blind via, the interface contact area between the blind via and the chassis 1A is significantly increased, which can improve the contact area by more than 30% compared with the traditional planar structure.

[0030] This design effectively enhances interfacial adhesion, improves the distribution of electroplating stress caused by step-by-step electroplating, suppresses the risk of crack initiation and delamination at the interface, and prevents blind vias from being pulled off during subsequent processing or use. Simultaneously, sufficient contact area ensures the reliability of interlayer electrical connections, improves the structural stability and electrical performance of HDI circuit boards under complex assembly and long-term service conditions, and solves the technical problem of decreased reliability caused by poor bonding between blind vias and the chassis 1A in existing technologies.

[0031] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0032] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A micro blind via of a circuit board, comprising a base (1A) disposed on a first circuit layer (1) and a first blind via (4) and a first top plate (2A) disposed on a second circuit layer (2), wherein the bottom of the first blind via (4) is connected to the base (1A), characterized in that, The upper surface of the chassis (1A) is provided with a micro-groove structure to increase the interface contact area between the first blind hole (4) and the chassis (1A).

2. The micro blind via of the circuit board according to claim 1, characterized in that, The micro-groove structure is a concentric circular groove or a vortex-shaped groove.

3. The micro blind via of the circuit board according to claim 2, characterized in that, The cross-section of the micro-groove is U-shaped.

4. The micro blind via of the circuit board according to claim 3, characterized in that, The depth H of the micro-groove, the opening width D1 of the micro-groove, and the spacing D2 between adjacent micro-grooves respectively satisfy the following ranges: 1μm≤H≤5μm; 10μm≤D1≤30μm; 10μm≤D2≤30μm.

5. The micro blind via of the circuit board according to claim 4, characterized in that, The bottom diameter W of the first blind hole (4) satisfies: 40μm≤W≤60μm.

6. The micro blind via of the circuit board according to claim 5, characterized in that, The chassis (1A), the first blind hole (4) and the first top plate (2A) are all made of copper.

7. The micro blind via of the circuit board according to any one of claims 1-6, characterized in that, It also includes a third circuit layer (3) disposed above the second circuit layer (2), wherein the third circuit layer (3) is provided with a second blind hole (5) and a second top plate (3A), and the bottom of the second blind hole (5) is connected to the first top plate (2A) to form a stacked blind hole structure.

8. The micro blind via of the circuit board according to claim 7, characterized in that, The upper surface of the first top plate (2A) is provided with a micro-groove structure to increase the interface contact area with the second blind hole (5).

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