Bga area thickening manufacturing method and pcb board

Abstract

The application relates to the technical field of PCB processing, and discloses a BGA area thickening manufacturing method, which comprises the following steps: providing a substrate with completed conductive via manufacturing, wherein the substrate has a first surface and a second surface; forming a first circuit pattern on the first surface through a pattern transfer process, wherein the first circuit pattern comprises a plurality of BGA pads located in a preset BGA area; selectively forming a mask layer on the first surface, so that the non-BGA area is covered by the mask layer and the BGA area remains exposed; and electroplating the exposed BGA area. The application aims to solve the problem of flatness defects caused by the limited design compensation of the uneven electroplating of the large-area BGA area.

Description

Technical Field

[0001] This invention relates to the field of PCB board processing technology, specifically to a method for thickening the BGA area and a PCB board. Background Technology

[0002] As electronic products evolve towards higher performance and greater integration, the demand for printed circuit boards (PCBs) housing large-size BGA (Ball Grid Array) packaged chips is increasing. The PCB manufacturing process typically involves a series of steps, including lamination, drilling, electroplating, resin plugging, and pattern transfer, to form the circuit pattern, including the BGA pads, on the board surface. To improve the surface flatness of the BGA area, the industry often adds balancing copper during the design phase to compensate for the copper thickness difference between this area and the surrounding areas. Simultaneously, during the electroplating process, overall electroplating conditions are adjusted to achieve a more even copper thickness distribution across the board surface.

[0003] However, for large-area BGA areas exceeding 80mm×80mm, existing balanced copper addition methods cannot completely fill the copper thickness difference due to the need to maintain a safe distance from vias and existing patterns. Furthermore, due to the combined effects of edge effects during board plating and the high-density via plating requirements in the BGA area, the copper thickness in the BGA area is consistently too thin, creating a significant height difference with the surrounding non-BGA areas. As a result, the overall surface flatness of this area can generally only be controlled to be above 100 micrometers, making it difficult to achieve the flatness level of less than 50 micrometers required for high-reliability assembly. In severe cases, this directly leads to poor soldering and contact issues in chip bonding. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of flatness defects in large-area BGA regions caused by uneven electroplating and limited design compensation, and to propose a method for thickening BGA regions and a PCB board.

[0005] In a first aspect, embodiments of the present invention provide a method for thickening a BGA region, comprising: A substrate with conductive vias fabricated is provided, the substrate having a first surface and a second surface; A first circuit pattern is formed on the first surface by a pattern transfer process, the first circuit pattern including a plurality of BGA pads located within a preset BGA area. A masking layer is selectively formed on the first surface such that non-BGA areas are covered by the masking layer while the BGA areas remain exposed; Electroplating is performed on the exposed BGA area to deposit a thicker metal layer on the BGA pads and the exposed conductor surface, so that the surface of the BGA area forms a height step relative to the surface of the non-BGA area. Remove the masking layer; A curable filler material is applied to the first surface to form a filler layer that covers the height step. The filler layer, after curing, has the properties of being chemically removable and able to withstand mechanical abrasion. The filler layer and the protruding BGA area are thinned by a grinding process until the top of all BGA pads are exposed from the filler layer and together with the upper surface of the surrounding filler layer to form a flat surface. The remaining filler layer is completely peeled off from the first surface so that the BGA region protrudes from the non-BGA region in a boss-like shape. A second circuit pattern is formed on the second surface of the substrate by a pattern transfer process.

[0006] In one embodiment, providing a substrate with pre-fabricated conductive vias specifically includes: Multiple inner core boards and prepregs are stacked and pressed together to form a multilayer board; Through holes are drilled in the multilayer board and a conductive layer is formed on the hole wall by chemical copper plating and electroplating. The copper-plated through holes are then filled and blocked with resin, and finally a copper cap layer is electroplated on the top of the hole to flatten it.

[0007] In one embodiment, selectively forming a masking layer on the first surface specifically includes: The method involves laminating a dry film onto the first surface and selectively exposing and developing it using a photomask. The dry film in the non-BGA areas is retained to form a dry film masking layer with a thickness in the range of 50 to 200 μm; or, a thermosetting wet film is printed on the non-BGA areas using a screen with a stencil pattern and then baked to cure the wet film, forming a thermosetting wet film masking layer with a thickness in the range of 50 to 200 μm.

[0008] In one embodiment, the electroplating of the exposed BGA region includes selectively electroplating copper in the BGA region, wherein the thickness of the deposited metal thickening layer is controlled within the range of 25 to 175 μm, thereby creating a significant vertical drop between the surface of the BGA region and the surface of the non-BGA region.

[0009] In one embodiment, the curable filler material is liquid photosensitive peelable polyimide or thermosetting wet film resin, and the thickness of the cured filler layer is configured to be greater than the thickness of the metal thickening layer to completely cover all BGA pads that protrude due to the thickening.

[0010] In one embodiment, when the filler material is liquid photosensitive peelable polyimide, the application and curing process specifically involves: using a screen to print the liquid photosensitive peelable polyimide onto the entire first surface, with the printing speed controlled at 0.5–3 m / min and the squeegee pressure controlled at 1–6 kg / cm². Then, bake at a temperature of 60–100°C for 5–20 minutes to remove the solvent; Next, the entire image was exposed to ultraviolet light with an exposure energy range of 500–2000 mJ / cm². Finally, bake at 150–200°C for 60–120 minutes to fully cure and form the filler layer.

[0011] In one embodiment, when the filler material is a thermosetting wet film resin, the application and curing process specifically involves: using a screen to print the thermosetting wet film resin onto the entire first surface, with the printing speed controlled at 0.5–3 m / min and the squeegee pressure controlled at 1–6 kg / cm²; after printing, baking at a temperature of 150–200°C for 60–120 minutes to thermocure it and form a filler layer.

[0012] In one embodiment, the grinding process specifically includes the following steps: First, use a 300-500 mesh ceramic brush to perform 3-5 sets of coarse grinding to quickly remove most of the filler layer and protruding metal thickening layer; Next, wash with water to remove grinding debris; Then, use an 800-1200 mesh ceramic brush to perform 2-3 sets of fine grinding to eliminate the scratches left by coarse grinding and make the surface flatter. After fine grinding, the surface of the exposed copper pads is washed with water again, and then chemically etched with a micro-etching solution to remove the oxide layer; finally, it is washed with water and dried.

[0013] In one embodiment, before forming the filler layer, the method further includes: scanning the first surface using a non-contact profilometer to obtain an initial height difference between the BGA region and the non-BGA region; and dynamically adjusting the coating thickness of the filler material and / or the preset removal amount in the coarse grinding stage of the grinding process based on the initial height difference.

[0014] Secondly, embodiments of the present invention provide a PCB board having a first side and a second side, wherein the BGA area on the first side is in the shape of an integrally raised boss, and the top surfaces of all BGA pads in the BGA area are coplanar.

[0015] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: This invention does not attempt to compensate for copper thickness differences globally, but rather selectively thickens the BGA area independently on a board surface where the basic conductors have already been laid out. This localized, prioritized thickening compensates for the insufficient copper thickness caused by the plating of high-density via clusters in this area, proactively establishing a positive height difference between the BGA area and its surroundings, rather than passively accepting the negative depressions caused by uneven plating. Secondly, after thickening to form a raised structure, a sacrificial filler medium is introduced to level and cover the board surface, followed by staged mechanical grinding to uniformly thin the entire surface. This filling and co-grinding process transforms the originally uneven topography into a controllable flattening process, using the filler layer to provide a support reference for grinding, ensuring that all BGA pads are precisely cut off when reaching the same horizontal plane, thereby stabilizing the flatness of the area within an extremely low tolerance range. Finally, after planarization and removal of the filler medium, the BGA area naturally exhibits a raised bump configuration higher than adjacent areas. This actively constructed three-dimensional topology not only completely eliminates the contact gap during the assembly of large-size BGAs and chips, thus significantly improving interconnect reliability, but also avoids the problem of incomplete compensation caused by design spacing limitations by eliminating the need for complex balanced copper piling throughout the entire implementation process. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall thickening process of the present invention; Figure 2 This is a schematic diagram of selective masking and BGA region electroplating according to the present invention; Figure 3 This is a schematic diagram illustrating the application and thinning of the filler material according to the present invention; Figure 4 This is a schematic diagram of the filler layer peeling and boss forming of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] According to a first aspect of this application, a method for thickening a BGA region is provided, comprising: providing a substrate with conductive vias already fabricated, the substrate having a first surface and a second surface; forming a first circuit pattern on the first surface using a pattern transfer process, the first circuit pattern including a plurality of BGA pads located within a predetermined BGA region; selectively forming a masking layer on the first surface such that non-BGA regions are covered by the masking layer while the BGA regions remain exposed; and electroplating the exposed BGA regions to deposit a metal thickening layer on the BGA pads and the exposed conductor surfaces, such that the surface of the BGA regions is relatively thicker than that of the non-BGA regions. A height step is formed on the surface; the masking layer is removed; a curable filler material is applied to the first surface to form a filler layer covering the height step, the filler layer having the characteristics of being chemically removable and able to withstand mechanical grinding after curing; the filler layer and the protruding BGA area are thinned by a grinding process until the tops of all BGA pads are exposed from the filler layer and together with the upper surface of the surrounding filler layer to form a flat surface; the remaining filler layer is completely peeled off from the first surface so that the BGA area protrudes from the non-BGA area in the form of a boss; a second circuit pattern is formed on the second surface of the substrate by a pattern transfer process.

[0019] like Figure 1 As shown, first, a substrate with conductive vias already fabricated is prepared. This substrate serves as the base carrier for all subsequent processing. It is usually made by alternately stacking multiple inner core boards and prepregs, and then hot-pressing them into a whole. Through holes connecting the circuits of each layer are formed inside the substrate. The walls of the through holes have been metallized and resin-filled and capped with electroplating, so that the substrate has a first surface and a second surface that are relatively suitable for laying out circuit patterns.

[0020] Subsequently, a first circuit pattern, including the target BGA pads, is fabricated on the first surface of the substrate using a pattern transfer process. These BGA pads form the basis for the array of contacts that will ultimately interconnect with the chip solder balls. Next, the entire first surface is selectively masked using a masking material. The key to this step is to ensure that non-BGA areas are adequately protected from subsequent electroplating thickening, while fully exposing the BGA areas requiring thickening, thus achieving precise control over specific areas. After the masking layer is constructed, a metal layer of a predetermined thickness is deposited on the exposed BGA area surface, including the BGA pads and surrounding exposed conductors, using an electroplating process. This causes the surface height of this area to significantly exceed that of the protected non-BGA area due to the material accumulation, forming a regular height step between the two.

[0021] After electroplating, the masking layer is completely removed. At this point, it can be observed that the BGA area has bulged out as a whole. Figure 4 As shown. To achieve ultimate flatness of the raised area, this invention does not directly grind the surface with alternating soft and hard surfaces. Instead, it first coats the entire board surface with a curable filler material, completely covering and submerging the height steps formed by the BGA area protrusion, and waits for it to cure to form a hard sacrificial filler layer.

[0022] This filler layer provides uniform mechanical support for subsequent grinding, effectively preventing the pads from being pulled off or deformed due to uneven lateral shear forces during grinding. Next, the entire board is ground and thinned, removing the filler layer material while simultaneously grinding and thinning the protruding BGA area metal structure until the tops of all BGA pads are completely exposed from the filler layer, and the pad ends are coplanar with the upper surface of the surrounding remaining filler layer, achieving an overall flat surface. At this point, the remaining filler layer used for planarization is completely removed from the first surface using chemical or physical stripping methods, retaining the metal body of the BGA area, ultimately presenting it as a precision boss structure higher than the surrounding non-BGA areas. After completing the processing of the first side, the required second circuit pattern is fabricated on the second surface of the substrate using a similar pattern transfer method.

[0023] By combining selective thickening, dielectric filling homogenization, and synergistic polishing to cut off the process, the flatness of the BGA area has been significantly improved. The flatness level, which was originally limited to more than 100 micrometers due to uneven copper plating, has been directly optimized to within 50 micrometers. At the same time, the BGA area is made higher than the surrounding area, providing a reliable geometric shape guarantee for complete contact during subsequent chip assembly.

[0024] In an optional embodiment of this application, a substrate with conductive vias already fabricated is provided, specifically including: laminating and pressing multiple inner core boards and prepregs to form a multilayer board; drilling vias on the multilayer board and chemically plating and electroplating copper to form a conductive layer on the via wall; subsequently filling and blocking the copper-plated vias with resin; and finally electroplating a capping copper layer above the via opening to achieve via flattening.

[0025] According to the preset stacking structure, multiple inner core boards with completed inner layer patterns are stacked in sequence with prepreg sheets that serve as adhesive insulating layers. The prepreg sheets are then completely melted, flowed, and cured under high temperature and pressure conditions using a vacuum hot press, tightly bonding each inner core board into a single multilayer board.

[0026] Through-holes are machined through the multilayer board at predetermined locations using mechanical drilling or laser drilling. To enable electrical interconnection between the layers, a thin and dense conductive seed layer is first deposited on the hole wall using chemical copper plating. Then, the copper layer on the hole wall is thickened to the design thickness using full-board electroplating, forming a reliable interlayer conductive path.

[0027] Because the hollow structure at the center of a via can affect the quality of subsequent surface mounting or signal transmission, a special resin is filled into the via using vacuum plugging or scraper plugging processes. The resin is then baked to harden and shrink. Finally, electroplating is performed again above the resin-plugged via opening to deposit a cap copper layer that covers the resin surface and smoothly connects with the surrounding copper layer. This fills the originally recessed opening, laying a solid foundation for subsequent precision pattern fabrication and selective BGA area processing on a completely flat surface.

[0028] In an optional embodiment of this application, a masking layer is selectively formed on the first surface, specifically including: forming a dry film masking layer with a thickness in the range of 50 to 200 μm by laminating a dry film onto the first surface and selectively exposing and developing it using a photomask; retaining the dry film in the non-BGA areas; or forming a thermosetting wet film masking layer with a thickness in the range of 50 to 200 μm by printing a thermosetting wet film on the non-BGA areas using a screen with a perforated pattern and baking the wet film to cure it.

[0029] The first implementation uses dry film as the masking material. First, a layer of photosensitive dry film is attached to the entire first surface using a hot press roller, ensuring close adhesion to the copper surface. Then, a black-and-white or film photomask is used for alignment. On this photomask, the non-BGA areas correspond to the light-transmitting pattern, and the BGA areas correspond to the light-blocking pattern. Ultraviolet exposure causes the dry film in the non-BGA areas to undergo a cross-linking polymerization reaction. After a development process, the dry film in the unexposed BGA areas is washed away and dissolved using a developing solution. Finally, a complete and uniformly thick dry film masking layer is retained in the non-BGA areas. The thickness of the dry film masking layer can be selected within the range of 50 to 200 micrometers to provide sufficient anti-electroplating shielding capability.

[0030] The second method uses a thermosetting wet film as a masking material. Through screen printing, a viscous thermosetting wet film ink is printed onto the non-BGA areas using a screen with cutouts in the BGA areas, while no transfer occurs in the BGA areas. After printing, the board is placed in an oven for baking, causing the solvent inside the wet film to evaporate and undergo thermal cross-linking and curing. This ultimately forms a uniformly covering thermosetting wet film masking layer in the non-BGA areas, with a thickness also between 50 and 200 micrometers. Both methods can accurately expose the BGA areas while tightly masking the rest, providing a robust anti-plating protection boundary for subsequent localized selective electroplating thickening.

[0031] In an optional embodiment of this application, electroplating is performed on the exposed BGA region, including selective copper electroplating in the BGA region, wherein the thickness of the deposited metal thickening layer is controlled in the range of 25 to 175 μm, so that a significant vertical drop is formed between the surface of the BGA region and the surface of the non-BGA region.

[0032] like Figure 2 As shown, a substrate with the exposed BGA area and the remaining areas tightly protected by a masking layer is placed in a copper plating solution. The substrate is used as the cathode, and an electroplating current is applied to the BGA area. Due to the obstruction of the masking layer, copper ions can only be reduced and deposited on the uncovered BGA pads and the exposed conductor surface, achieving completely localized plating thickening.

[0033] By precisely controlling process parameters such as electroplating time and current density, a metal thickening layer is grown in a single step or in stages to a predetermined thickness of 25 to 175 micrometers. This thickness range fully compensates for the copper thickness lost in the BGA area during earlier stages such as via plating, and creates a clearly measurable vertical height step between the surface of this area and the adjacent protected non-BGA area surface.

[0034] In an optional embodiment of this application, the curable filler material is liquid photosensitive peelable polyimide or thermosetting wet film resin, and the thickness of the cured filler layer is configured to be greater than the thickness of the metal thickening layer to completely cover all BGA pads that protrude due to the thickening.

[0035] After electroplating the BGA area to increase its height and removing the masking layer, a noticeable raised structure appears on the first surface. At this point, a liquid photosensitive peelable polyimide with good flowability and filling capacity, or a viscous and thermosetting wet film resin, is selected as the filler material. It is applied to the entire first surface by printing or coating. The material flows naturally and covers the raised BGA area, completely burying all the high-protruding BGA pads below the liquid surface.

[0036] The absolute thickness of the solid filler layer formed after coating and curing is intentionally set to be greater than the thickness of the metal thickening layer, ensuring that even in the area with the most significant thickening, the highest point is seamlessly wrapped by the filler layer, with no hard protrusions exposed.

[0037] This fully encapsulated structure makes the filled surface appear as a uniform plane before mechanical grinding, providing a single contact interface for the next step of rough grinding. This allows the grinding contact to smoothly transition from the grinding filler material to the combination of the grinding filler material and the metal, avoiding the initial grinding impact force acting directly on the isolated metal pads, which could cause the pads to peel off or collapse.

[0038] In an optional embodiment of this application, when the filler material is liquid photosensitive peelable polyimide, the application and curing process specifically involves: printing the liquid photosensitive peelable polyimide onto the entire first surface using a screen printing plate, with the printing speed controlled at 0.5–3 m / min and the squeegee pressure controlled at 1–6 kg / cm²; subsequently, performing a short baking at a temperature of 60–100°C for 5–20 minutes to remove the solvent; then exposing the entire plate to ultraviolet light with an exposure energy range of 500–2000 mJ / cm²; and finally baking at a temperature of 150–200°C for 60–120 minutes to completely cure it and form the filler layer.

[0039] like Figure 3 As shown, the complete application process for using liquid photosensitive peelable polyimide as the filler material is illustrated. On the first surface where the BGA area has been thickened and the masking layer has been peeled off, a screen printing machine is used with a screen to evenly print and cover the entire surface with liquid photosensitive peelable polyimide ink. The printing speed is set between 0.5 and 3 meters per minute, and the squeegee pressure is set between 1 and 6 kilograms per square centimeter to ensure that the filler material can smoothly pass through the screen, fully adhere to the board surface, and flow into the gaps and corners around the thickened BGA area.

[0040] The printed wet film contains some solvent, which needs to be removed by a short baking process. The board is placed in an oven at 60 to 100 degrees Celsius for 5 to 20 minutes to allow the resin to initially dry and set but not completely cure.

[0041] The entire surface is then fully exposed to ultraviolet light, with the exposure energy controlled within the range of 500 to 2000 millijoules per square centimeter. This causes a cross-linking reaction within the photosensitive groups of the liquid photosensitive peelable polyimide, resulting in a peelable property that can be dissolved and removed later by a specialized stripping solution. After exposure, it is transferred to a high-temperature oven at 150 to 200 degrees Celsius and baked for 60 to 120 minutes to complete deep thermosetting, ultimately yielding a filler layer with moderate hardness, resistant to mechanical abrasion, and capable of being completely and cleanly removed later.

[0042] In an optional embodiment of this application, when the filler material is a thermosetting wet film resin, the application and curing process specifically involves: using a screen to print the thermosetting wet film resin onto the entire first surface, with the printing speed controlled at 0.5–3 m / min and the squeegee pressure controlled at 1–6 kg / cm²; after printing, baking at a temperature of 150–200°C for 60–120 minutes to thermocure it and form a filler layer.

[0043] In this process, screen printing equipment is used to uniformly print thermosetting wet film resin onto the entire surface of the first screen with a selected screen. The printing speed is between 0.5 and 3 meters per minute, and the squeegee pressure is between 1 and 6 kilograms per square centimeter. This ensures that the resin can overcome the influence of the raised steps in the BGA area and form a continuous film layer with a thickness sufficient to fill all the differences and wrap all the pads.

[0044] Unlike liquid photosensitive peelable polyimide, thermosetting wet film resin does not require exposure and short baking. After printing, it can be directly sent to a high-temperature oven and baked at 150 to 200 degrees Celsius for 60 to 120 minutes.

[0045] Under high temperature, the molecular chains of the wet film resin undergo chemical cross-linking, eventually solidifying into a filler layer with high hardness and abrasion resistance. This filler layer can also be peeled off with a suitable release solution after the abrasion process is complete. This method reduces process steps and improves production efficiency.

[0046] In an optional embodiment of this application, the grinding process specifically includes the following steps: first, using a 300-500 mesh ceramic brush to perform 3-5 sets of coarse grinding to quickly remove most of the filler layer and protruding metal thickening layer; then, washing with water to remove grinding debris; subsequently, using an 800-1200 mesh ceramic brush to perform 2-3 sets of fine grinding to eliminate scratches left by coarse grinding and make the surface more flat; after fine grinding, washing with water again, and then using a micro-etching solution to chemically micro-etch the exposed copper pad surface after fine grinding to remove the oxide layer; finally, washing with water and drying.

[0047] This process employs a progressive processing chain of "coarse grinding—cleaning—fine grinding—cleaning—micro-etching—water washing—drying". In the coarse grinding stage, 3 to 5 sets of ceramic brush rollers with a particle size of 300 to 500 mesh are configured. Through high-speed rotating cutting, the solidified filler layer and the metal thickened layer in the protruding BGA area below are thinned with a large amount of material removal and high efficiency, quickly approaching the preset target thickness.

[0048] After rough grinding, immediately rinse the board surface with plenty of deionized water to thoroughly remove the filler material debris and metal powder generated during grinding, preventing them from scratching the precision surfaces in subsequent processes. Then, proceed to the fine grinding stage, using 2 to 3 sets of high-mesh ceramic brush rollers with a particle size of 800 to 1200 to finely polish the surface after rough grinding, gradually eliminating friction marks and surface micro-protrusions produced by rough grinding, so that the BGA pad end faces and the filler layer surface achieve a near-mirror-like flatness.

[0049] After fine grinding, the surface is rinsed again with water. Then, a micro-etching solution is used to briefly chemically etch the exposed copper pads. This step effectively removes the extremely thin oxide layer and residual impurities newly formed on the copper surface during grinding, ensuring the pads have a clean, solderable, and fresh copper surface. Finally, the board is thoroughly rinsed and sent to the drying section to complete the entire grinding and planarization process.

[0050] In an optional embodiment of this application, before forming the filler layer, the method further includes: scanning the first surface using a non-contact profilometer to obtain an initial height difference between the BGA region and the non-BGA region; and dynamically adjusting the coating thickness of the filler material and / or the preset removal amount in the coarse grinding stage of the grinding process based on the initial height difference.

[0051] A closed-loop control mechanism involving online measurement and process parameter feedback adjustment was added before the filling and grinding processes. After removing the masking layer and before applying the filling material, a non-contact profile measuring instrument based on the principle of laser displacement sensor or white light interferometry was used to scan the entire first surface or along multiple sections of the BGA area. This accurately extracted the absolute height data of each point on the BGA area surface relative to the surrounding non-BGA area surface and calculated the initial height difference.

[0052] The control system dynamically adjusts subsequent process parameters based on the height difference. For example, if the height difference is too large, the preset coating thickness of the filler material can be increased accordingly to ensure complete embedding; or the preset pressing amount and residence time of the grinding brush in the coarse grinding stage can be adjusted according to the size of the height difference to achieve precise and efficient material removal.

[0053] This closed-loop control method can compensate for batch fluctuations in previous processes, ensuring that the final grinding cutoff position of each board is precisely located on the optimal plane where the BGA pad end face is just fully exposed, thereby stably maintaining the flatness of the finished BGA area at a high level within 50 micrometers.

[0054] According to a second aspect of this application, this application provides a PCB board including a board structure made by any of the aforementioned BGA region thickening manufacturing methods. The board structure has a first side and a second side, wherein the BGA region on the first side is in the shape of an integrally raised boss, and the top surfaces of all BGA pads in the BGA region are coplanar.

[0055] The PCB board has a first side and a second side, corresponding to the side where the first surface and the second surface are located, respectively. On its first side, the BGA area is not on the same plane as the surrounding non-BGA area, but presents a three-dimensional structure with an overall upward protrusion, and the height of this protrusion is consistent with the height step retained after selective electroplating thickening and grinding.

[0056] All BGA pads within this raised area have their outward-facing top surfaces strictly aligned within the same spatial plane, with no misalignment between them. This unique geometry allows the raised BGA area to make contact with the solder balls on the bottom of the chip before the surrounding areas during surface mount reflow soldering. This fundamentally eliminates the risk of poor soldering and contact caused by localized substrate depressions in large-area chips, resulting in more uniform soldering stress distribution and significantly improved interconnect reliability.

[0057] By changing the traditional processing sequence of passively accepting BGA area depressions, a board surface morphology reconstruction mechanism of "first locally raising, then globally leveling" is actively constructed, transforming the flatness of large-size BGA areas from a passive state constrained by uneven copper plating to an active manufacturing process that can be precisely controlled.

[0058] After completing the fabrication of the conductive vias and the first-side pattern transfer, instead of directly proceeding to full-board electroplating or balancing copper compensation, selective masking and localized electroplating processes are used to deposit a thicker metal layer only in the pre-defined BGA areas. This artificially transforms the originally thin, recessed low-lying areas, which were consumed by the high-density via plating, into a raised structure that is higher than the non-BGA areas. The establishment of this height step provides additional metal reserves from the source, serving as material reserves for subsequent planarization processes, completely eliminating the reliance on adding balancing copper from the design side.

[0059] Subsequently, a curable filler material is used to cover the entire raised area and the board surface, forming a sacrificial homogenizing dielectric layer. This filler layer, once cured, possesses both mechanical support and chemical peelability. Its function is to transform the originally heterogeneous surface composed of alternating hard and soft metal pads and insulating substrate into a uniform, moderately hard transitional surface. During polishing, the cutting force of the ceramic brush first acts on this homogeneous filler layer, then gradually transitions to the mixed layer of filler and metal. This avoids the pull-out or deformation caused by directly applying polishing impact to isolated pads. Simultaneously, the filler material provides an absolute horizontal support reference relative to the base surface for polishing.

[0060] Through progressive coarse and fine grinding, the filler layer and the raised metal thickening layer are thinned simultaneously until the tops of all BGA pads are just exposed on the filler layer surface, with both ending on the same plane. This planarization method of "coordinated grinding cutoff" precisely anchors the grinding endpoint at the moment the pad end face is just exposed, fundamentally ensuring the high consistency of all pads within the array. Finally, the remaining filler layer is peeled off, and the BGA area naturally exhibits a precise boss configuration where all pad top surfaces are coplanar and the overall surface is higher than the surrounding area.

[0061] Overall, all pads within the BGA area are on the same horizontal plane, and the flatness of the area can be stably controlled within 50 micrometers, completely eliminating gaps caused by microscopic undulations on the substrate surface during large-size chip assembly. At the same time, the BGA area is raised as a whole relative to the non-BGA area, and the raised area can preferentially contact the solder balls at the bottom of the chip during reflow soldering, fundamentally avoiding the risk of cold solder joints and poor contact, and significantly improving the assembly yield and long-term interconnect reliability of high-density ball grid array packages.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for thickening a BGA region, characterized in that, include: A substrate with conductive vias fabricated is provided, the substrate having a first surface and a second surface; A first circuit pattern is formed on the first surface by a pattern transfer process, the first circuit pattern including a plurality of BGA pads located within a preset BGA area. A masking layer is selectively formed on the first surface such that non-BGA areas are covered by the masking layer while the BGA areas remain exposed; Electroplating is performed on the exposed BGA area to deposit a thickened metal layer on the BGA pads and the exposed conductor surface, so that the surface of the BGA area forms a height step relative to the surface of the non-BGA area. Remove the masking layer; A curable filler material is applied to the first surface to form a filler layer that covers the height step. The filler layer, after curing, has the properties of being chemically removable and able to withstand mechanical abrasion. The filler layer and the protruding BGA area are thinned by a grinding process until the top of all BGA pads are exposed from the filler layer and together with the upper surface of the surrounding filler layer to form a flat surface. The remaining filler layer is completely peeled off from the first surface so that the BGA region protrudes from the non-BGA region in a boss-like shape. A second circuit pattern is formed on the second surface of the substrate by a pattern transfer process.

2. The method for thickening the BGA region according to claim 1, characterized in that, The provision of a substrate with pre-fabricated conductive vias specifically includes: Multiple inner core boards and prepregs are laminated together to form a multilayer board; Through holes are drilled in the multilayer board and a conductive layer is formed on the hole wall by chemical copper plating and electroplating. The copper-plated through holes are then filled and blocked with resin, and finally a copper cap layer is electroplated on the top of the hole to flatten it.

3. The method for thickening the BGA region according to claim 1, characterized in that, Selectively forming a masking layer on the first surface, specifically including: The method involves laminating a dry film onto the first surface and selectively exposing and developing it using a photomask. The dry film in the non-BGA areas is retained to form a dry film masking layer with a thickness in the range of 50 to 200 μm; or, a thermosetting wet film is printed on the non-BGA areas using a screen with a stencil pattern and then baked to cure the wet film, forming a thermosetting wet film masking layer with a thickness in the range of 50 to 200 μm.

4. The method for thickening the BGA region according to claim 1, characterized in that, The electroplating of the exposed BGA region includes selective copper electroplating in the BGA region, with the thickness of the deposited metal thickening layer controlled within the range of 25 to 175 μm, so that a significant vertical drop is formed between the surface of the BGA region and the surface of the non-BGA region.

5. The method for thickening the BGA region according to claim 1, characterized in that, The curable filler material is liquid photosensitive peelable polyimide or thermosetting wet film resin. The thickness of the cured filler layer is configured to be greater than the thickness of the metal thickening layer to completely cover all BGA pads that protrude due to the thickening.

6. The method for thickening the BGA region according to claim 5, characterized in that, When the filler material is liquid photosensitive peelable polyimide, the application and curing process is as follows: the liquid photosensitive peelable polyimide is printed on the first surface using a screen, the printing speed is controlled at 0.5 to 3 m / min, and the squeegee pressure is controlled at 1 to 6 kg / cm². Then, bake at a temperature of 60–100°C for 5–20 minutes to remove the solvent; Next, the entire image was exposed to ultraviolet light with an exposure energy range of 500–2000 mJ / cm². Finally, bake at 150–200°C for 60–120 minutes to fully cure and form the filler layer.

7. The method for thickening the BGA region according to claim 6, characterized in that, When the filler material is a thermosetting wet film resin, the application and curing process is as follows: the thermosetting wet film resin is printed on the entire first surface using a screen printing plate, the printing speed is controlled at 0.5 to 3 m / min, and the squeegee pressure is controlled at 1 to 6 kg / cm²; after printing, it is baked at a temperature of 150 to 200°C for 60 to 120 minutes to thermo-cur it and form a filler layer.

8. The method for thickening the BGA region according to claim 1, characterized in that, The grinding process specifically includes the following steps: First, use a 300-500 mesh ceramic brush to perform 3-5 sets of coarse grinding to quickly remove most of the filler layer and protruding metal thickening layer; Next, wash with water to remove grinding debris; Then, use an 800-1200 mesh ceramic brush to perform 2-3 sets of fine grinding to eliminate the scratches left by coarse grinding and make the surface flatter. After fine grinding, the surface of the exposed copper pads is washed with water again, and then chemically etched with a micro-etching solution to remove the oxide layer; finally, it is washed with water and dried.

9. The method for thickening the BGA region according to claim 8, characterized in that, Before forming the filler layer, the process further includes: scanning the first surface using a non-contact profile measuring instrument to obtain the initial height difference between the BGA region and the non-BGA region; and dynamically adjusting the coating thickness of the filler material and / or the preset removal amount in the coarse grinding stage of the grinding process based on the initial height difference.

10. A PCB board, characterized in that, The PCB board includes a board structure made by the BGA area thickening manufacturing method according to any one of claims 1 to 9. The board structure has a first side and a second side, the BGA area on the first side is in the shape of an integrally raised boss, and the top surfaces of all BGA pads in the BGA area are coplanar.

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