A method for filling and planarizing thick copper PCB
Patent Information
- Application Number
- CN202611484810.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-22
- Publication Date
- 2026-11-03
AI Technical Summary
In the solder mask process of thick copper PCBs, the height difference between the copper and non-copper surfaces makes it difficult to achieve uniformity in solder mask coating. Existing technologies require multiple solder mask printing processes, resulting in long production cycles, high costs, and low yields.
The adhesive film and release film are laminated in a vacuum environment and pressed together by a rigid pressure plate. After filling the gaps and removing air bubbles, the solder resist layer is coated and cured.
Shorten production cycle, reduce costs, improve yield, enhance flatness and reliability, and avoid the risk of high voltage leakage.
Smart Images
Figure CN123035620A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of PCB processing technology, and in particular to a method for filling and leveling thick copper PCBs with adhesive. Background Technology
[0002] With the rapid development of new energy vehicles, high-power power supplies, and industrial control, PCBs are gradually evolving towards higher current and higher reliability, leading to the increasingly widespread application of thick copper PCBs (copper thickness typically ≥3 oz, or 105 μm). Thick copper PCBs can carry greater current and offer better heat dissipation, thus finding widespread use in high-power motor drives, battery management systems, and PCB motor stators.
[0003] The solder mask process for thick copper PCBs is one of the key steps in the manufacturing process. The solder mask (also known as solder paste) covers the area of the PCB surface excluding the solder pads, serving functions such as insulation, oxidation prevention, and prevention of solder bridging. However, because the copper layer height of thick copper circuits is much greater than that of conventional PCBs (the copper thickness of conventional PCBs is typically 1 oz to 2 oz, or 35 μm to 70 μm), there is a significant height difference (step) between the copper surface and the non-copper surface (substrate area), which poses a serious challenge to the coating and uniformity of the solder mask.
[0004] The current industry practice for solder mask processing on thick copper PCBs is to use a multi-layer screen printing method. This involves printing the first layer of solder mask ink, pre-curing it, and then printing the second or even third layer until the height difference between the substrate area and the copper surface is gradually filled, resulting in a relatively smooth solder mask surface. This process lengthens the production cycle of a single board, significantly increases labor and equipment energy costs, and the multiple processes also increase the rate of defects such as dirt, foreign objects, and pinholes on the board surface, making mass production yield control difficult. Summary of the Invention
[0005] In view of this, the purpose of this application is to overcome the shortcomings of the prior art and provide a method for filling and leveling thick copper PCBs with adhesive.
[0006] This application provides the following technical solution: a method for filling and leveling thick copper PCBs with adhesive, comprising: Obtain release film, adhesive film, and PCB core board; The first pre-pressing process involves simultaneously laminating adhesive film and release film on both surfaces of the PCB core board in the thickness direction, and then performing a molding and pressing process in a vacuum environment. The second pre-pressing involves laminating a rigid pressure plate onto the surface of the release film, ensuring that the adhesive film completely fills the gaps in the PCB core board circuitry. The core board is flattened by removing the rigid pressure plate and release film to form a flat core board; The process involves screen printing solder resist, which involves coating a layer of solder resist onto the surface of a flat core board, followed by exposure, development, and curing according to a preset pattern to achieve surface insulation of the flat core board.
[0007] In some embodiments, obtaining the PCB core board includes: completing the cutting, inner layer pattern transfer, etching and AOI inspection of the substrate core board, and preparing a PCB core board with thick copper circuit patterns.
[0008] In some embodiments, obtaining the adhesive film includes: taking the frozen adhesive film out of a cold storage at less than -15 ℃ in advance, and thawing and dehumidifying it at room temperature.
[0009] In some embodiments, the first pre-pressing includes: covering the PCB core board with a release film, and during the vacuum pressing process, filling the gaps in the PCB core board with the release film for the first time, and removing air bubbles from the PCB core board.
[0010] In some embodiments, the thickness of the adhesive film is H, the copper thickness of the circuit in the PCB core board is h, the residual copper ratio is x, and the fine-tuning allowance for flattening the PCB core board is y. Where H, h, x, and y satisfy the relation: H = h (1-x)+y.
[0011] In some embodiments, before the step of screen printing solder resist, the method further includes: checking whether there are air bubbles inside the flat core board; If so, then perform the second pre-compression as described in step [step 2].
[0012] In some embodiments, during the second pre-pressing step, the rigid pressure plate completely covers the PCB core board.
[0013] In some embodiments, the outer diameter of the release film is D1, and the outer diameter of the PCB core board is D2, wherein D1 and D2 satisfy the relationship: D1 - D2 ≥ 10 mm.
[0014] In some embodiments, after the silkscreen solder resist is printed in step 1, the method further includes: surface treatment, in which a protective film is deposited on the gold finger area exposed by the open window of the silkscreen solder resist.
[0015] In some embodiments, the surface treatment described in the step further includes: electrical testing, measuring the voltage and resistance of the flat core board.
[0016] The embodiments of this application have the following advantages: This application uses a rigid pressure plate to constrain the flow direction of the adhesive film, control the flow rate and flow distance of the adhesive film, and reduce the thickness difference of the adhesive on the copper surface and the substrate area. This not only adapts to wiring with different residual copper ratios, but also improves the flatness quality of the PCB core board. In addition, compared with the prior art which requires multi-layer solder mask printing, this application uses an adhesive film to fill the outer layer of solder mask, which not only reduces the number of processes, reduces labor and material costs, but also reduces the fluctuation of production quality and improves the yield. Pressing with a rigid pressure plate makes the PCB core board more uniformly stressed and has better flatness. It can fill the gaps inside the PCB core board and remove air bubbles, thereby making the reliability of humid heat and cold heat cycles higher and further avoiding the risk of high voltage leakage.
[0017] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 A flowchart of a method for filling and leveling thick copper PCBs with adhesive, provided in some embodiments of this application, is shown. Detailed Implementation
[0020] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.
[0021] It should be noted that when an element is said to be "fixed" to another element, it can be directly on the other element or there may be an intervening element. When an element is said to be "connected" to another element, it can be directly connected to the other element or there may be an intervening element. Conversely, when an element is said to be "directly" on another element, there is no intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.
[0022] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.
[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the template description is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0025] like Figure 1 As shown, this application provides a method for leveling and filling thick copper PCBs with adhesive, which includes the following steps: Step S100: Obtain release film, adhesive film and PCB core board.
[0026] The release film is used to protect the adhesive film. It is removed before applying the film so that the photosensitive adhesive can adhere to the copper surface of the PCB.
[0027] It should be noted that obtaining the adhesive film includes: taking the frozen adhesive film out of a freezer at a temperature below -15°C in advance, and thawing and dehumidifying it at room temperature. At this time, there is no water vapor on the surface of the adhesive film, and the temperature of the thawed adhesive film is room temperature. The purpose of thawing and dehumidifying is to remove moisture and prevent delamination and cracking after pressing.
[0028] In this embodiment, the PCB core board is a PCB core board that already has a thick copper circuit pattern.
[0029] Step S200, the first pre-press, involves simultaneously laminating adhesive film and release film on both surfaces of the PCB core board in the thickness direction, and then performing a molding and pressing process in a vacuum environment.
[0030] For example, the PCB core board has an upper surface and a lower surface in the thickness direction, and an adhesive film and a release film are respectively stacked on the upper surface and the lower surface, wherein the adhesive film is stacked on the upper surface and the lower surface, and the release film is stacked on the surface of the adhesive film.
[0031] In some embodiments, an adhesive film is laminated on the upper or lower surface of the PCB core board, and a release film is laminated on the surface of the adhesive film.
[0032] In this embodiment, a vacuum press is used for the first pre-pressing, and the PCB core board is covered by the vacuum press airbag to ensure that the adhesive can fill the substrate area as much as possible during the first pre-attachment and squeeze out the air bubbles inside the PCB core board, thus ensuring reliability.
[0033] Step S300, second pre-pressing, a rigid pressure plate is laminated on the surface of the release film to completely fill the gaps in the PCB core board circuit.
[0034] It should be noted that due to the limited flow distance of the adhesive film and the fact that the protrusions of thick copper lines can push up the local adhesive film, adhesive residue will remain on the copper surface, resulting in uneven overall height of the copper surface and affecting the flatness of the solder resist.
[0035] Based on this, this step uses a rigid pressure plate for pressing, and the rigid constraint of the rigid pressure plate will apply reverse extrusion force to the uneven copper layer of the PCB core board: excess molten resin on the top surface of the copper circuit is squeezed laterally and forced to flow into the substrate recesses in the PCB core board between adjacent circuits; the substrate area in the PCB core board is directly compacted by the pressure of the rigid pressure plate, and the adhesive film completely fills the gaps, avoiding the occurrence of missing adhesive gaps or air bubbles.
[0036] Step S400: After removing the rigid pressure plate and release film, a flat core board is formed.
[0037] In this process, the rigid pressure plate is removed from the release film, and the release film is peeled off the PCB core board to obtain a flat core board.
[0038] Step S500: Screen printing solder resist. A layer of solder resist is coated on the surface of the flat core board. After exposure, development and curing according to the preset pattern, the surface insulation of the flat core board is completed.
[0039] In this process, a layer of photosensitive green oil is evenly coated onto the flat core board to form an insulating and protective solder resist layer.
[0040] It should be noted that the exposure process includes: precisely aligning the film with the preset solder resist window pattern with the Mark points in the flat core board, vacuum-tightening it to ensure the film is tightly adhered to the board surface, eliminating gaps and preventing blurry edges or misalignment of the pattern, followed by exposure under a UV lamp. The development process includes: sending the flat core board into a spray-type developing machine for development. After development, the flat core board is placed in a segmented heating tunnel oven for segmented heating to avoid rapid temperature changes that could cause bubbles or cracking.
[0041] This application uses a rigid pressure plate to constrain the flow direction of the adhesive film, controlling its flow rate and distance, and reducing the thickness difference between the copper surface and the substrate area. This not only adapts to wiring with different residual copper ratios but also improves the flatness of the PCB core board. In addition, compared with the existing technology that requires multi-layer solder mask printing, this application uses an adhesive film to fill the outer layer of solder mask, which not only reduces the number of processes, lowers labor and material costs, but also reduces production quality fluctuations and improves yield. The rigid pressure plate pressing makes the PCB core board more uniformly stressed and has better flatness. It can fill the gaps inside the PCB core board and remove air bubbles, thereby improving the reliability of damp heat and cold heat cycles and further avoiding the risk of high voltage leakage.
[0042] In some embodiments of this application, obtaining the PCB core board includes: completing the cutting, inner layer pattern transfer, etching and AOI inspection of the substrate core board, and preparing a PCB core board with thick copper circuit patterns.
[0043] The process of cutting the substrate core board includes material requisition and receiving inspection, layout and loading preparation, CNC cutting, edge grinding, cleaning and dust removal, pre-baking and dehumidification and stress release, and post-cutting inspection.
[0044] In addition, inner layer pattern transfer includes PCB core board material inspection, dry film lamination, pattern imaging, and development.
[0045] In this embodiment, etching includes feeding the dried PCB core board into the etching line, spraying it with etching solution, washing it with water after etching to remove the etching solution and prevent etching solution residue, and then removing the film.
[0046] It should be noted that the purpose of AOI inspection is to detect defects in inner layer circuit patterns, distinguish between true and false defects, screen repairable boards and scrapped boards, monitor process stability, ensure the consistency of inner layer patterns, and avoid the risk of layer deviation.
[0047] In some embodiments of this application, the first pre-pressing includes: covering the PCB core board with a release film, and during the vacuum pressing process, filling the gaps in the PCB core board with the adhesive film for the first time and expelling air bubbles from the PCB core board.
[0048] In some embodiments of this application, the thickness of the adhesive film is H, the copper thickness of the circuit in the PCB core board is h, the residual copper ratio is x, and the allowable fine-tuning amount for flattening the PCB core board is y.
[0049] Where H, h, x, and y satisfy the relation: H = h (1-x)+y.
[0050] It should be noted that the residual copper rate refers to the percentage of the total area of copper foil remaining in the inner core board after the inner layer pattern transfer and etching, divided by the total area of the core board substrate.
[0051] This application calculates the adhesive film thickness required to fill the gaps in the PCB core board by combining the copper thickness of the circuits, the residual copper ratio, and the fine-tuning allowance for flat PCB core board. This ensures that after the first and second pre-pressing, the total amount of adhesive film can just fill the gaps in the PCB core board, avoiding excessive redundancy of adhesive film. This not only avoids waste of adhesive film and reduces costs, but also improves production quality.
[0052] In some embodiments of this application, the step of screen printing solder resist is further included before checking whether there are air bubbles inside the flat core board.
[0053] Among these, visual inspection can be performed initially, scanning detection can be performed using a C-SAM scanning acoustic microscope, or thermal stress testing can be conducted.
[0054] If so, then perform the second pre-compression as described in step [step 2].
[0055] If air bubbles are detected remaining inside the flat core board, a second pre-compression is performed to expel the air bubbles and improve the production quality.
[0056] If not, proceed with the solder mask printing step.
[0057] In other words, if air bubbles or voids are not detected in the flat core board before the solder mask printing step, then the solder mask printing step is performed.
[0058] In some embodiments of this application, in the second pre-pressing step, the rigid pressure plate completely covers the PCB core board to ensure the uniformity of force on each area of the PCB core board during the second pre-pressing process through the rigid pressure plate, and to ensure that the adhesive film can completely fill the gaps inside the PCB core board, thereby improving the pressing quality.
[0059] In some embodiments of this application, the outer diameter of the release film is D1, and the outer diameter of the PCB core board is D2, wherein D1 and D2 satisfy the relationship: D1-D2≥10mm.
[0060] Understandably, the release film can completely cover the PCB core board.
[0061] In this embodiment, the outer diameter of the rigid platen is larger than the outer diameter of the release film to prevent adhesive on the rigid platen from contaminating the next batch of pre-pressed PCB core boards.
[0062] In some embodiments of this application, after the silkscreen solder mask step, the method further includes: surface treatment, which involves depositing a protective film on the gold finger area exposed by the silkscreen solder mask opening.
[0063] Understandably, this protective film can protect the exposed copper pads through the window opening, improving solderability and oxidation resistance.
[0064] In some embodiments of this application, the surface treatment described in the step further includes: electrical testing, measuring the voltage and resistance of the flat core board.
[0065] By detecting open circuits and short circuits in the circuitry of the flat core board, network connectivity is verified and boards with electrical defects are intercepted.
[0066] For example, the flat core board is placed on the test fixture, and the test points of the flat core board are contacted by probes to check whether there is continuity between all points of the same network to identify open circuits, and to check whether there is insulation between different networks to identify short circuits.
[0067] Understandably, this application adds rigid pressure plates on both the upper and lower sides as a pressure transmission medium, based on the flexible pressure application method of direct bonding of the adhesive film with vacuum airbag. By utilizing the non-deformable characteristics of the rigid pressure plates, the molten adhesive is forcibly diverted, thereby solving the material distribution problem of excess adhesive on the copper surface of the PCB core board and insufficient adhesive on the substrate.
[0068] This application achieves overall flatness of the PCB core board by using a rigid pressure plate to evenly press the entire board, eliminating the height difference of thick copper, and reducing the solder resist process that requires 3 to 4 times in the prior art to a single solder resist process, which greatly reduces production time and improves production efficiency.
[0069] By combining a vacuum environment with rigid limiting, interfacial bubbles are eliminated to the greatest extent, thereby improving interlayer bonding and long-term damp heat reliability.
[0070] In all examples shown and described herein, any specific values should be interpreted as merely exemplary and not as limitations; therefore, other examples of exemplary embodiments may have different values.
[0071] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0072] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.
Claims
1. A method for filling and leveling thick copper PCBs with adhesive, characterized in that, include: Obtain release film, adhesive film, and PCB core board; The first pre-pressing process involves simultaneously laminating adhesive film and release film on both surfaces of the PCB core board in the thickness direction, and then performing a molding and pressing process in a vacuum environment. The second pre-pressing involves laminating a rigid pressure plate onto the surface of the release film, ensuring that the adhesive film completely fills the gaps in the PCB core board circuitry. The core board is flattened by removing the rigid pressure plate and release film to form a flat core board; The process involves screen printing solder resist, which involves coating a layer of solder resist onto the surface of a flat core board, followed by exposure, development, and curing according to a preset pattern to achieve surface insulation of the flat core board.
2. The method for filling and leveling thick copper PCBs with adhesive according to claim 1, characterized in that, The process of obtaining the PCB core board includes: cutting the substrate core board, transferring the inner layer pattern, etching and AOI inspection, and preparing a PCB core board with thick copper circuit patterns.
3. The method for filling and leveling thick copper PCBs with adhesive according to claim 1, characterized in that, The process of obtaining the adhesive film includes: taking the frozen adhesive film out of a cold storage at a temperature of less than -15 ℃ in advance, and thawing and dehumidifying it at room temperature.
4. The method for filling and leveling thick copper PCBs according to claim 1, characterized in that, The first pre-pressing includes: covering the PCB core board with a release film, and during the vacuum pressing process, filling the gaps in the PCB core board with the adhesive film for the first time and expelling air bubbles from the PCB core board.
5. The method for filling and leveling thick copper PCBs with adhesive according to claim 1, characterized in that, The thickness of the adhesive film is H, the copper thickness of the circuit in the PCB core board is h, the residual copper ratio is x, and the fine-tuning allowance for flattening the PCB core board is y. Where H, h, x, and y satisfy the relation: H = h (1-x)+y.
6. The method for filling and leveling thick copper PCBs according to claim 1, characterized in that, Before the silkscreen solder resist is printed as described in the step, the following steps are also included: checking whether there are air bubbles inside the flat core board; If so, then perform the second pre-compression as described in step [step 2].
7. The method for filling and leveling thick copper PCBs according to claim 1, characterized in that, In the second pre-pressing step, the rigid pressure plate completely covers the PCB core board.
8. The method for filling and leveling thick copper PCBs according to claim 1, characterized in that, The outer diameter of the release film is D1, and the outer diameter of the PCB core board is D2. D1 and D2 satisfy the relationship: D1 - D2 ≥ 10 mm.
9. The method for filling and leveling thick copper PCBs with adhesive according to claim 1, characterized in that, The process after silkscreening solder resist as described in step 1 further includes: surface treatment, in which a protective film is deposited on the gold finger area exposed by the open window of the silkscreened solder resist.
10. The method for filling and leveling thick copper PCBs according to claim 9, characterized in that, The surface treatment described in step [1] further includes: electrical testing, which involves measuring the voltage and resistance of the flat core board.