A method for forming a high-density integrated circuit board

Abstract

The application provides a forming manufacturing method of a high-density integrated circuit board, which comprises the following steps: dividing a board surface into a high-density wiring area, a dense hole area, a local integrated area and an outer forming area according to the structure of the circuit board, and setting line, hole, slot edge and outer shape compensation respectively; roughening and pre-baking the core board after the inner layer wiring is manufactured; slotting, windowing, pre-cavity or insert site processing the local integrated area; vacuumizing and pre-pressing the core board, the semi-cured sheet and the functional layer after being stacked according to the layer sequence and being locked; measuring and heat setting the press board; drilling, depth control drilling, milling, cavity finishing and outer forming; and finally detecting the size and structure of the formed board. The application solves the problems of stress and water vapor difficult to control before and after pressing, local structure easy to warp and deform, poor quality of holes and slots in the forming process and insufficient size stability after forming in the prior art.

Description

Technical Field

[0001] This invention relates to the field of circuit boards, and more particularly to a method for molding and manufacturing a high-density integrated circuit board. Background Technology

[0002] As electronic products trend towards miniaturization, thinning, and high integration, printed circuit boards (PCBs) not only require denser wiring, smaller vias, and more layers, but also often need to incorporate cavities, thinning areas, insert areas, or heat dissipation mounting areas in specific regions to meet the needs of device mounting, packaging, and heat dissipation. Existing PCB manufacturing processes typically include core board fabrication, surface roughening, lamination, drilling, forming, and post-processing. While these processes can meet the production requirements of ordinary PCBs, they still have significant shortcomings in the fabrication of high-density integrated circuit boards.

[0003] On the one hand, insufficient release of moisture and residual stress in the core board and prepreg before lamination can easily lead to layer misalignment, delamination, shrinkage, and dimensional drift during lamination or subsequent heating. On the other hand, local cavities, areas of varying thickness, and insert areas often form asymmetrical stacks, which can easily cause warping, local collapse, and dimensional instability during lamination. Furthermore, drilling, milling, and shaping in densely packed hole areas, groove edges, and board edges can easily result in problems such as hole collapse, hole wall burrs, edge flash, and local machining deviations, affecting subsequent assembly accuracy and product reliability.

[0004] Therefore, it is necessary to provide a new method for molding and manufacturing high-density integrated circuit boards to solve the above-mentioned technical problems. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for molding and manufacturing a high-density integrated circuit board, which solves the problems in the prior art such as difficulty in controlling stress and moisture before and after lamination, easy warping and deformation of local structures, poor quality of holes and grooves during molding, and insufficient dimensional stability after molding.

[0006] The high-density integrated circuit board forming and manufacturing method provided by the present invention includes the following steps: S1. Based on the structural characteristics of the high-density integrated circuit board, the board surface is divided into a high-density wiring area, a dense via area, a local integration area, and a shape forming area, and line compensation, via compensation, slot edge compensation, and shape compensation are set respectively; wherein, the local integration area is one or more of the following: cavity area, local thinning area, insert area, and heat dissipation mounting area. S2. The core board with the inner layer circuit fabrication completed is roughened and pre-baked to remove moisture from the core board and release internal stress. S3. The local integration area is pre-grooved, windowed, pre-cavitated, or processed with inserts to form a local functional transition structure. S4. Stack the core board, prepreg and functional layer in sequence according to the design, and lock them in place by a combination of hot melt fixing and mechanical positioning to form the blank to be pressed. S5. After vacuuming the blank to be pressed, pre-pressing and shaping and main pressing and curing are performed to allow the semi-cured sheet to complete the flow filling and curing bonding to form a pressed plate. S6. Perform expansion and contraction retest on the pressed plate, and correct the subsequent drilling or shaping parameters based on the retest results. Then, perform heat setting treatment on the pressed plate to release residual stress. S7. The press plate is subjected to one or more of the following processing methods: drilling, controlled-depth drilling, milling, cavity finishing and shape forming. A hard support layer is provided on at least one side of the drilling surface and the drilling surface in the processing area to reduce hole collapse, burrs and flash. S8. Perform dimensional and structural inspections on the formed circuit board. Once the board is confirmed to be qualified, proceed to the subsequent surface treatment or depaneling process.

[0007] Preferably, in step S1, independent line compensation is used for the high-density wiring area, independent hole position compensation is used for the dense hole area, groove edge compensation and glue flow allowance reserve compensation are used for the local integration area, and contour shrinkage compensation is used for the external forming area; and a first positioning reference hole and a second re-measurement reference hole are set on the process edge, the first positioning reference hole is used for pre-stack positioning, and the second re-measurement reference hole is used for expansion and contraction measurement after pressing.

[0008] Preferably, in step S2, the pre-baking temperature is 5-10°C higher than the glass transition temperature of the prepreg used, the pre-baking time is 25-35 minutes, and the stacking height is no more than 60 mm; the surface roughening is a browning treatment or an equivalent roughening treatment to improve the bonding strength of the pressing interface.

[0009] Preferably, in step S3, when the local integration area is a concave cavity area or a locally thinned area, a separate groove or pre-concave cavity processing is performed first, and the flatness of the groove bottom is controlled; when the local integration area is an insert area or a heat dissipation installation area, the metal insert or heat-conducting block is first placed into the pre-made groove, and then resin is used to fill and fix it, and local fixation is performed to prevent displacement during subsequent transportation or pressing.

[0010] Preferably, in steps S4 and S5, the mechanical positioning is riveting positioning or pin positioning; the staged vacuum pressing includes: first, vacuuming for 5 to 10 minutes, then pre-pressing and shaping at 90 to 110°C to soften the prepreg and fill local gaps, then continuing to heat up and apply a molding pressure of 25 to 40 kg / cm² for main pressing and curing; for asymmetric laminated structures, buffer balance plates are set on opposite sides of the laminates to reduce pressing warping.

[0011] Preferably, in step S7, the hard support layer is disposed on both sides of the drilling inlet and drilling outlet surfaces in the processing area, and the hard support layer is one of FR-4 hard smooth plate, metal thin plate or heat-resistant composite support plate; the drilling process adopts a zoned toolpath control method, cross-zone skip drilling is used for dense hole areas, segmented tool entry is used for local thick copper areas or insert areas, and the number of holes processed by a single tool is limited for micro-hole areas.

[0012] Preferably, in step S7, when performing shape forming or cavity finishing, a small cutting depth and multiple trimming method is adopted; for the board edge area, a temporary covering layer is retained on the edge to be formed so that the edge of the substrate is covered during milling, thereby reducing edge burrs and flash; the temporary covering layer is one of a copper foil covering layer, a solder resist covering layer, or a hard protective layer.

[0013] Preferably, in step S8, the size detection and structural detection include at least two of AOI detection, X-ray detection, cross-section detection, two-dimensional size detection, and appearance detection; wherein, two-dimensional size detection is used to detect the groove width, cavity depth, and external dimensions, X-ray detection is used to detect the positional deviation of the dense hole area and the local integration area, and cross-section detection is used to detect the hole wall quality, resin filling state, and interlayer bonding state.

[0014] The beneficial effects of this invention are: 1. This invention reduces uneven shrinkage, layer misalignment, and hole position offset during the lamination process by pre-processing the core board before lamination and combining it with zoning compensation and post-lamination retesting correction. It also improves the dimensional consistency of high-density wiring areas and dense hole areas, and reduces the risks of board bursting, layer misalignment, and subsequent mounting misalignment.

[0015] 2. By preforming, locking, and stacking the local integrated area in stages, and by setting a buffer balance structure, this invention can improve the stress state of the cavity area, thinning area, insert area, or local heat dissipation area during the pressing process, reduce warping, local collapse, and interface instability, and improve the molding integrity and dimensional stability of the local structure.

[0016] 3. The present invention adopts a support-type forming method in the drilling, controlled depth machining, milling and shaping stages, which can reduce the impact on the hole wall and edge material during the processing, reduce hole collapse, hole wall burrs, groove wall burrs and edge burrs, and improve the forming quality of high-density hole area and dissimilar material area.

[0017] 4. This invention adds a heat setting and inspection step after the main molding process, which can release residual stress in advance and correct dimensional changes caused by heat, reduce heat shrinkage defects in subsequent assembly processes, and improve product consistency and manufacturing yield.

[0018] 5. This invention organically combines partition compensation, pretreatment, local preforming, locking pressing, support molding, and heat setting to form a complete process chain, which is applicable to various high-density integrated circuit board structures and has good practicality and promotion value. Attached Figure Description

[0019] Figure 1 This is a flowchart of the molding and manufacturing method of the present invention; Figure 2 This is a partial structural diagram of the high-density integrated circuit board of the present invention; Figure 3 This is a schematic diagram of the support-type drilling forming of the present invention.

[0020] The diagram is labeled as follows: 1. High-density wiring area; 2. Dense via area; 3. Partial integration area; 4. Cavity; 5. Component mounting position; 6. Shape forming area; 7. Upper support plate; 8. Circuit board; 9. Lower support plate; 10. Drill bit; 11. Area for holes to be processed. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Please refer to the following: Figure 1 , Figure 2 as well as Figure 3 ,in Figure 1 This is a flowchart of the molding and manufacturing method of the present invention; Figure 2 This is a partial structural diagram of the high-density integrated circuit board of the present invention; Figure 3 This is a schematic diagram of the support-type drilling forming of the present invention.

[0023] In the specific implementation process, such as Figures 1-3 The illustration further explains the method for fabricating a high-density integrated circuit board according to the present invention. It should be noted that the following embodiments are only for illustrating the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions made based on the concept of the present invention regarding the process sequence, material selection, structural dimensions, or process parameters should fall within the scope of protection of the present invention.

[0024] The high-density integrated circuit board fabricated in this embodiment is used for miniaturized control modules. The circuit board has a six-layer structure, with finished board dimensions of 120 mm × 80 mm and a thickness of 1.20 mm ± 0.08 mm. The board simultaneously includes a high-density wiring area, a dense via area, a partial integration area, and a shaping area, wherein: The high-density wiring area is located in the middle of the board and is used to install fine-pitch main control chips. The local line width / spacing is 0.075 mm. The dense via area is located around the high-density wiring area and has rows of through holes with a finished hole diameter of 0.20 mm. The local integration area is located on one side of the board and is a recessed mounting area for installing small sensor devices. The finished size of the recess is 14.00 mm × 14.00 mm and the depth is 0.25 mm. The shaping area is located at the edge of the plate and the connection end, and is used to form the edge outline of the plate and the installation notch.

[0025] The following manufacturing method is used in this embodiment: First, the board surface is divided into zones according to the product structure. Compensation values ​​are set separately for high-density wiring areas, dense via areas, partial integration areas, and shape-forming areas; uniform compensation for the entire board is not used.

[0026] In the high-density wiring area, the line pattern is increased by 0.012 mm on one side to compensate for the reduction in line width caused by subsequent etching; the dense hole area is based on the finished hole diameter of 0.20 mm, and the drilling diameter is preset to 0.28 mm, and then corrected according to the expansion and contraction data of the first piece; a 0.10 mm fine-tuning allowance is reserved for the cavity boundary of the local integration area; and a 0.15 mm machining allowance is reserved for the outline of the shape forming area.

[0027] Two types of reference holes are set on the edge of the board: one type is the positioning reference hole, used for pre-stacking and lamination alignment; the other type is the re-measurement reference hole, used for expansion and contraction measurement after lamination and for subsequent drilling and milling correction. The positioning reference hole and the re-measurement reference hole are set separately to avoid mutual interference between lamination locking and dimensional inspection.

[0028] In this embodiment, a high-Tg fiberglass resin substrate is used to fabricate the core board. After the inner layer circuitry is completed, the copper surface of the core board is first subjected to a browning treatment to form a uniform roughened layer, thereby enhancing the bonding strength between the copper surface and the prepreg. After browning, the core board is placed in an oven for pre-baking. The pre-baking temperature is set at 155℃, the pre-baking time is 30 minutes, and the stacking height is controlled within 60 mm. The purpose of pre-baking is twofold: first, to remove adsorbed moisture from the core board and between the boards, avoiding voids caused by localized evaporation during lamination; and second, to release some internal stress in the core board before lamination, reducing uneven shrinkage after subsequent lamination. After pre-baking, the core board is cooled to room temperature in a clean environment before proceeding to the next process.

[0029] Since a recessed mounting area is provided on one side of the plate in this embodiment, a local pre-forming process is performed before formal pressing. Specifically, a shallow groove is pre-milled on the upper core plate corresponding to the recessed area. The groove dimensions are set to 13.80 mm × 13.80 mm, with a pre-milling depth of 0.15 mm, and allowance is reserved around all four sides for subsequent finishing. This step does not form the final recessed cavity in one step, but rather reduces the cutting amount required for subsequent forming and simultaneously creates a local thickness difference in advance, making stress changes before and after pressing more controllable.

[0030] After pre-milling, the groove area should be inspected, requiring a flat bottom without obvious tool marks, chipping, or burrs. The flatness of the groove bottom should be controlled within 0.03 mm. For areas with minor burrs on the groove edges, use a fine grinding brush to treat them; burrs must not be carried into the lamination process.

[0031] The core boards and prepregs are stacked sequentially according to the six-layer board structure. Due to the presence of pre-milled shallow grooves in the local integration area, the thickness distribution in this area is asymmetrical after stacking, which can easily lead to unilateral stress deviation during the pressing process. Therefore, a buffer balance plate is added locally on the side opposite to the cavity to make the stress distribution of the board blank more uniform when under pressure.

[0032] After stacking, heat fusion is first performed at the process edge to initially bond the layers together; then, rivets are used for mechanical locking. In this embodiment, six rivet points are evenly distributed along the process edge. Heat fusion fixation prevents interlayer slippage during handling and loading, while rivet locking restricts planar movement before the main lamination. Together, these two methods ensure good interlayer correspondence between the high-density wiring area and the dense via area before the main lamination.

[0033] The slab with the locking mechanism completed is fed into the laminating equipment for vacuum pressing. First, a vacuum is drawn for 8 minutes to remove air and some volatiles between the layers, and then two-stage pressing is performed.

[0034] The first stage is the pre-compression and shaping stage: The temperature is controlled at 100℃, the pressure at 10 kg / cm², and the holding time is 15 min. This stage mainly softens the semi-cured sheet, allowing it to fill the tiny gaps between layers, while preventing significant slippage of the slab.

[0035] The second stage is the main pressure curing stage: After pre-pressing and shaping, the temperature is raised to 185℃, while the pressure is gradually increased to 32 kg / cm², and the temperature is maintained for 90 minutes to allow the prepreg to flow, impregnate and cure, ultimately forming an integral pressed board.

[0036] After pressing, continue to maintain pressure and cool until the temperature drops below 130℃ before releasing the pressure and unpacking the board. This prevents localized springback caused by sudden pressure release before the resin has stabilized.

[0037] In this embodiment, due to the asymmetrical thickness structure in the local integration area, warpage is controlled by a combination of local buffer balancing plates, vacuum pre-compression, and main pressure curing. The warpage rate of the pressed board is significantly lower than that of the control board without buffer balancing plates. After the pressed board is removed, the dimensional expansion and contraction in the X and Y directions are measured using the re-measurement reference hole on the process edge as a reference. In this embodiment, the first board shows a shrinkage of approximately 0.07% in the X direction and approximately 0.05% in the Y direction. Based on these results, the drilling and shaping programs are modified so that the drilling center and board edge contour are based on the actual dimensions after pressing, rather than the dimensions of the theoretical drawings.

[0038] After the retest is completed, the laminated sheet undergoes heat setting. The heat setting temperature is 150℃, and the holding time is 40 minutes. This process is performed before the actual drilling and milling. Its purpose is not to re-cure, but to further release the residual stress after lamination, so that the sheet will not experience significant secondary shrinkage during subsequent drilling, shaping, and customer reflow soldering processes. After heat setting, drilling, cavity finishing, and shape shaping are performed.

[0039] For densely packed hole areas with a finished hole diameter of 0.20 mm, 0.6 mm thick FR-4 hard smooth plates are applied to both the drilling entry and exit surfaces of the plate to form a double-support structure. The purpose is to provide rigid support to the hole opening area when the drill bit enters and exits the plate, reducing hole opening collapse, hole wall roughening, and bottom surface burrs.

[0040] Drilling is performed using zoned toolpath control: For densely packed holes, instead of cutting in a discontinuous, sequential manner, a cross-zone skipping drilling method is adopted to reduce local heat concentration. For holes near the edge of the local integration area, a segmented feed method is adopted to reduce sudden changes in local stress; the number of holes processed by a single drill bit is limited, and the drill bit is replaced when the set number of holes is reached to avoid increased roughness and burrs on the hole wall due to tool wear.

[0041] In the preliminary process, the cavity in the local integration area only underwent shallow pre-milling. After pressing, a controlled-depth finishing process was used to form the final cavity. The finishing process employed a multi-step edge trimming technique with small depths of cut, each cut not exceeding 0.05 mm, gradually reducing the cavity depth to 0.25 mm. Finally, the surrounding edges were cleaned. The finished cavity required intact boundaries, a flat bottom without obvious step marks, smooth corner transitions, and no chipping or burrs. To avoid localized fiber exposure, the groove edges were lightly trimmed with fine-grained abrasive material after finishing; secondary groove expansion using strong cutting methods was not permitted.

[0042] The board edge contour is formed using a milling method. During the outer shape formation, a temporary process edge and a covering layer are retained on the board edge to ensure that the edge to be milled is covered during processing, which reduces edge fiber lifting and burr formation. After the main contour is formed, the temporary process edge is removed. After forming, the board edge is deburred, with a focus on checking the connection ports, inner right-angle corners, and mounting notch positions.

[0043] After drilling and cavity finishing, the hole walls and locally machined surfaces undergo adhesive removal and activation treatment. This embodiment uses a combination of chemical adhesive removal and plasma-assisted treatment. First, conventional adhesive removal processes are used to remove residual adhesive from the hole walls. Then, plasma activation treatment is applied to the locally integrated areas and cavity edges to further purify and roughen the local resin surface. This treatment results in better adhesion of subsequent plating on the hole walls and locally machined surfaces, while also reducing discontinuities in the hole wall plating caused by residual adhesive. For areas where resin buildup is slightly higher than the surrounding surface, local light grinding is performed to smooth the transition between the locally integrated area and adjacent areas.

[0044] After molding, multiple testing methods are used. This embodiment employs the following combination of testing methods: First, a 2D measuring instrument was used to inspect the cavity dimensions, depth, and overall board dimensions, confirming that the cavity dimensions reached 14.00 mm × 14.00 mm and the depth was 0.25 mm ± 0.02 mm. Second, AOI was used to inspect the integrity of the high-density wiring area, focusing on checking for broken lines, gaps, or residual copper in the fine line areas. Next, X-rays were used to inspect the relative positions of the dense via areas and local integration areas, confirming that there was no significant misalignment caused by lamination or drilling. Finally, samples were taken and sections were cut to inspect the via wall quality, via copper continuity, resin condition at the groove edges, and interlayer bonding. The inspection revealed no significant collapse at the via openings, smooth via walls, no continuous burrs at the cavity boundaries, and no delamination or voids between layers. After passing inspection, the board proceeded to the solder mask, surface treatment, character printing, and final board separation processes.

[0045] The high-density integrated circuit board fabricated using the above method exhibits stable interlayer alignment and suppressed local warping even when local cavity structures, high-density wiring areas, and dense via areas coexist. The cavity boundaries are clear after molding, and burrs at the via openings and board edges are significantly reduced. After heat setting, the dimensional changes are reduced when heated again, making it suitable for assembling fine-pitch devices.

[0046] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for forming and manufacturing a high-density integrated circuit board, comprising the following steps: S1. Based on the structural characteristics of the high-density integrated circuit board, the board surface is divided into a high-density wiring area, a dense via area, a partial integration area, and a shape forming area, and compensation amounts for wiring, vias, slot edges, and shapes are set for each area; among these, The local integration area is one or more of the following: cavity area, local thinning area, insert area, and heat dissipation mounting area; S2. The core board with the inner layer circuit fabrication completed is roughened and pre-baked to remove moisture from the core board and release internal stress. S3. The local integration area is pre-grooved, windowed, pre-cavitated, or processed with inserts to form a local functional transition structure. S4. Stack the core board, prepreg and functional layer in sequence according to the design, and lock them in place by a combination of hot melt fixing and mechanical positioning to form the blank to be pressed. S5. After vacuuming the blank to be pressed, pre-pressing and shaping and main pressing and curing are performed to allow the semi-cured sheet to complete the flow filling and curing bonding to form a pressed plate. S6. Perform expansion and contraction retest on the pressed plate, and correct the subsequent drilling or shaping parameters based on the retest results. Then, perform heat setting treatment on the pressed plate to release residual stress. S7. The press plate is subjected to one or more of the following processing methods: drilling, controlled-depth drilling, milling, cavity finishing and shape forming. A hard support layer is provided on at least one side of the drilling surface and the drilling surface in the processing area to reduce hole collapse, burrs and flash. S8. Perform dimensional and structural inspections on the formed circuit board. Once the board is confirmed to be qualified, proceed to the subsequent surface treatment or depaneling process.

2. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In step S1, independent line compensation is used for the high-density wiring area, independent hole position compensation is used for the dense hole area, groove edge compensation and glue flow margin reserve compensation are used for the local integration area, and contour shrinkage compensation is used for the external forming area; and a first positioning reference hole and a second re-measurement reference hole are set on the process edge. The first positioning reference hole is used for pre-stack positioning, and the second re-measurement reference hole is used for expansion and contraction measurement after pressing.

3. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In step S2, the pre-baking temperature is 5-10°C higher than the glass transition temperature of the prepreg used, the pre-baking time is 25-35 minutes, and the stacking height is no more than 60 mm; the surface roughening is a browning treatment or an equivalent roughening treatment to improve the bonding strength of the pressing interface.

4. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In step S3, when the local integration area is a concave cavity area or a locally thinned area, a separate groove or pre-concave cavity processing is performed first, and the flatness of the groove bottom is controlled; when the local integration area is an insert area or a heat dissipation installation area, the metal insert or heat-conducting block is first placed into the prefabricated groove, and then resin is used to fill and fix it, and local fixation is performed to prevent displacement during subsequent transportation or pressing.

5. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In steps S4 and S5, the mechanical positioning is riveting positioning or pin positioning; the staged vacuum pressing includes: first, vacuuming for 5 to 10 minutes, then pre-pressing and shaping at 90 to 110°C to soften the prepreg and fill local gaps, then continuing to heat up and apply a molding pressure of 25 to 40 kg / cm² for main pressing and curing; for asymmetric laminated structures, buffer balance plates are set on opposite sides of the laminates to reduce pressing warping.

6. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In step S7, the hard support layer is set on both sides of the drilling inlet and drilling outlet of the processing area, and the hard support layer is one of FR-4 hard smooth plate, metal thin plate or heat-resistant composite support plate; the drilling process adopts a zoned toolpath control method, cross-zone skip drilling is used for dense hole areas, segmented tool entry is used for local thick copper areas or insert areas, and the number of holes processed by a single tool is limited for micro-hole areas.

7. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In step S7, when shaping the shape or refining the cavity, a small cutting depth and multiple trimming method is adopted; for the edge area of ​​the board, a temporary covering layer is retained on the edge to be shaped so that the edge of the substrate is covered during milling to reduce edge burrs and flash; the temporary covering layer is one of copper foil covering layer, solder resist covering layer or hard protective layer.

8. The method for forming and manufacturing a high-density integrated circuit board according to claim 1, characterized in that, In step S8, the size detection and structural detection include at least two of the following: AOI detection, X-ray detection, cross-section detection, two-dimensional size detection, and appearance detection. Among them, two-dimensional size detection is used to detect the groove width, cavity depth, and external dimensions; X-ray detection is used to detect the positional deviation of the dense hole area and the local integration area; and cross-section detection is used to detect the hole wall quality, resin filling state, and interlayer bonding state.

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