A method for improving substrate warping

Abstract

The present invention discloses a method for improving the warping of a substrate. Through step S1, the key position where the warping problem is more serious can be accurately identified, so that the warping problem can be solved in a targeted manner later. Through steps S2 and S3, the influence of the residual copper rate difference on the warping of the substrate is further analyzed, and the residual copper rate difference judgment value P2 is set, so that those units that are seriously warped due to excessive residual copper rate differences can be accurately found; at the same time, after identifying the serious warping position, through step S4, it is proposed to redesign one of the two-sided graphic layers, and design the graphics at the serious warping position of the graphic layer with a higher residual copper rate to the other side of the graphic layer, so as to realize the flip design of the graphics, thereby changing the distribution of copper, to balance the stress distribution of the substrate during heating or cooling, significantly reduce the residual copper rate difference between the two-sided graphic layers, and can reduce rework and scrap caused by warping problems, and improve the overall quality of the product.

Description

Technical Field

[0001] The invention relates to a method for improving substrate warping. Background Art

[0002] As an indispensable component of modern electronic devices, printed circuit boards (PCBs) are responsible for connecting and supporting electronic components. However, during the production and use of PCBs, substrate warping has always been a major challenge for manufacturers. Substrate warping not only affects the yield and reliability of PCBs, but may also lead to failures in subsequent assembly processes such as chip mounting and welding, thereby increasing production costs and cycles.

[0003] China Publication No. CN111629533B discloses a method for improving the warpage of a PCB, which asymmetrically designs the copper density of the upper and lower equal-thickness parts of the PCB along the board thickness direction, so that the PCB can present the same warpage direction as the chip after welding and cooling, or increases the copper density of the middle layer of the PCB to reduce the overall shrinkage rate of the PCB, thereby reducing the warpage difference between the PCB and the chip, effectively improving the closeness of the two, and ensuring the product yield. However, the above method still has the following disadvantages:

[0004] 1. Increased complexity: Adjusting copper density by local copper reduction or thick copper plating increases the complexity and process difficulty of the manufacturing process. This not only requires precise process control, but may also introduce new manufacturing defects.

[0005] 2. Increased costs: Additional copper density adjustment steps, such as local copper reduction, thick copper plating, or adding intermediate boards / copper foils, will significantly increase production costs.

[0006] 3. Limited design flexibility: The adjustment of copper density is often limited by the overall design and functional requirements of the PCB, and it is difficult to optimize without affecting other performance parameters, which limits the flexibility in solving the warpage problem.

[0007] 4. Although the adjustment of copper density can improve warpage to a certain extent, the effect may not be significant enough, especially for complex structures and multi-layer PCBs. A single method may not be able to fully solve the problem.

[0008] Therefore, how to overcome the above-mentioned defects has become an important issue to be solved urgently by those skilled in the art. Summary of the invention

[0009] The present invention overcomes the shortcomings of the above-mentioned technology and provides a method for improving the warping of a substrate.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for improving substrate warping comprises the following steps:

[0012] Step S1, prepare a warped substrate to be tested, preset a warping degree judgment value P1, analyze the entire substrate to be tested, and preliminarily identify the key position where the warping exceeds the specified value P1 according to the judgment value P1; the key position is one or more units in a substrate;

[0013] Step S2, presetting a residual copper rate difference determination value P2, and further determining the initially identified key position according to the determination value P2, and analyzing the residual copper rate difference between layers for each unit in the key position;

[0014] Step S3: When the difference in residual copper rate between the upper and lower corresponding graphic layers of a certain unit is greater than a preset judgment value P2, the unit is judged to be a severely warped position;

[0015] Step S4, for the identified severe warping position, redesign one of the two-sided pattern layers, and design the pattern at the severe warping position of the pattern layer with a higher residual copper rate to the other side of the pattern layer to perform a flip design of the pattern, thereby reducing the difference in residual copper rates of the two-sided pattern layers;

[0016] Step S5: re-manufacture and process the substrate according to the re-designed Unit.

[0017] Preferably, the step S4 of "redesigning one of the two-sided pattern layers, designing the pattern at the severely warped position of the pattern layer with a higher residual copper rate to the other side of the pattern layer to perform a flip design of the pattern" includes:

[0018] S41, analyzing the line width of the original graphic layer, first determining which lines will be subject to width restrictions or affect performance after flipping, and determining these lines as key lines; excluding the key lines from flipping when flipping, and flipping non-key lines at severely warped positions;

[0019] S42, considering the spacing between graphic elements to perform flip design of the graphic, so as to avoid affecting the electrical performance of the substrate due to incorrect spacing after flipping; wherein the spacing between the graphic elements at least includes line spacing and pad spacing;

[0020] S43. Analyze the connection relationship between graphic elements and perform flipping design of the graphic to ensure that the original connection is not destroyed during the flipping process; among them, for graphic elements that need to be connected across layers, pay attention to the design and layout of the connection points.

[0021] Preferably, the warping degree determination value P1 in step S1 is 0.7% or 0.5% or 0.3%.

[0022] Preferably, the substrate to be tested comprises at least an A-side graphic layer at the top layer and a B-side graphic layer at the bottom layer;

[0023] The "residual copper rate difference value" described in step S3 is obtained according to the following steps:

[0024] The residual copper rate value of the A-side graphic layer is detected and recorded, and recorded as M; the residual copper rate value of the B-side graphic layer is detected and recorded, and recorded as N; the residual copper rate difference value = |MN|.

[0025] Preferably, the preset residual copper rate difference determination value P2 described in step S2 is selected by the following steps:

[0026] Collect the past warping conditions of the substrate, record the difference values ​​of residual copper rate corresponding to different warping degrees, and obtain the average value of the difference values ​​of initial residual copper rate corresponding to different levels of average warping degrees;

[0027] Take the average value of the initial residual copper rate difference value of a certain level that meets the substrate warpage requirement and the average value of the initial residual copper rate difference value of a smaller level, and take the average value of these two average values ​​as the copper rate difference judgment value P2 of this level;

[0028] Select P2 according to the actual production level requirements of different substrates.

[0029] Preferably, the step S1 of "preparing a warped substrate to be tested, presetting a warping degree determination value P1, analyzing the entire substrate to be tested, and preliminarily identifying a key position where the warping exceeds the specified value P1 according to the determination value P1" includes:

[0030] The three-dimensional topographic data of the substrate surface is obtained by using an optical measuring instrument and screened according to the warpage degree judgment value P1 to identify the Unit with more serious substrate warpage and record its position or coordinates;

[0031] Badmark the units with serious warping.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The method of the present application can accurately identify the key positions with more serious warping problems through step S1, that is, those units with warping degrees exceeding the specified value P1, avoiding the need for comprehensive redesign of the entire substrate, so that the warping problem can be solved in a targeted manner in the future. Through steps S2 and S3, not only the degree of warping is paid attention to, but also the influence of the residual copper rate difference on the substrate warping is further analyzed, and the residual copper rate difference judgment value P2 is set to accurately find out those units with serious warping caused by excessive residual copper rate differences; at the same time, after identifying the serious warping position, step S4 proposes to redesign one of the two-sided graphic layers, and design the graphics at the serious warping position of the graphic layer with a higher residual copper rate to the other side of the graphic layer, so as to realize the flip design of the graphics, thereby changing the distribution of copper, to balance the stress distribution of the substrate during heating or cooling, so as to significantly reduce the residual copper rate difference between the two-sided graphic layers, fundamentally solve the warping problem, thereby reducing rework and scrap caused by warping problems, improving the overall quality and stability of the product, and improving product competitiveness. Moreover, redesigning only the most serious Unit is conducive to reducing production costs. Moreover, redesigning only the most serious Unit is conducive to reducing production costs. In addition, the flip design of the graphic layer in the present application method provides a flexible way to adjust the distribution of the residual copper rate, so that the designer can better control the warping risk of the substrate while meeting the functional requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the method of this case.

[0035] Figure 2 This is a schematic diagram of the board structure in which the ordinary substrate to be tested is transformed into a substrate after the unit is redesigned at the key position.

[0036] Figure 3 This is a schematic diagram of the structure of a single unit of the substrate in this case.

[0037] Figure 2 The yellow part in the figure is the redesigned Unit; Figure 3 The red line corresponds to the A-side graphic layer at the top, and the yellow line corresponds to the B-side graphic layer at the bottom. DETAILED DESCRIPTION

[0038] The features of the present invention and other related features are further described in detail below through embodiments to facilitate understanding by those skilled in the art:

[0039] like Figures 1 to 3 As shown, a method for improving substrate warpage includes the following steps:

[0040] Step S1, prepare a warped substrate to be tested, preset a warping degree judgment value P1, analyze the entire substrate to be tested, and preliminarily identify the key position where the warping exceeds the specified value P1 according to the judgment value P1; the key position is one or more units in a substrate.

[0041] Step S2, presetting a residual copper rate difference determination value P2, and further determining the initially identified key position according to the determination value P2, and analyzing the residual copper rate difference between layers for each unit in the key position;

[0042] Step S3: When the difference in residual copper rate between the upper and lower corresponding graphic layers of a certain unit is greater than a preset judgment value P2, the unit is judged to be a severely warped position;

[0043] Step S4, for the identified severe warping position, redesign one of the two-sided pattern layers, and design the pattern at the severe warping position of the pattern layer with a higher residual copper rate to the other-sided pattern layer to perform a flip design of the pattern, thereby reducing the difference in residual copper rates of the two-sided pattern layers;

[0044] Step S5: re-manufacture and process the substrate according to the re-designed Unit.

[0045] In a specific implementation, the residual copper rate difference judgment value P is 25%. When the residual copper rate of the A-side graphic layer of a substrate to be tested is detected to be 95% and the residual copper rate of the B-side graphic layer is 5%, the residual copper rate difference between the two is 90%, which is greater than the residual copper rate difference judgment value P at this time, and it is determined that the substrate to be tested is prone to warping. When the substrate to be tested is a two-layer board structure, the substrate to be tested includes the A-side graphic layer at the top layer and the B-side graphic layer at the bottom layer. If the graphic layer with a higher residual copper rate is the A-side graphic layer, the graphic design at the severely warped position is moved to the B-side graphic layer to perform a flip design of the graphic, thereby reducing the difference in residual copper rates of the two-side graphic layers;

[0046] As described above, the method of the present application can accurately identify the key positions with more serious warping problems, that is, those units whose warping degree exceeds the specified value P1, through step S1, avoiding the need for comprehensive redesign of the entire substrate, so that the warping problem can be solved in a targeted manner in the future. Through steps S2 and S3, not only the degree of warping is paid attention to, but also the influence of the residual copper rate difference on the substrate warping is further analyzed, and the residual copper rate difference judgment value P2 is set, so that those units with serious warping caused by excessive residual copper rate difference can be accurately found; at the same time, after identifying the serious warping position, step S4 proposes to redesign one of the two-sided graphic layers, and design the graphic at the serious warping position of the graphic layer with a higher residual copper rate to the other side graphic layer, so as to realize the flip design of the graphic, thereby changing the distribution of copper, to balance the stress distribution of the substrate during heating or cooling, so as to significantly reduce the residual copper rate difference between the two-sided graphic layers, fundamentally solve the warping problem, thereby reducing rework and scrap caused by warping problems, improving the overall quality and stability of the product, and improving product competitiveness. Moreover, redesigning only the most serious Unit is conducive to reducing production costs. Moreover, redesigning only the most serious Unit is conducive to reducing production costs. In addition, the flip design of the graphic layer in the present application method provides a flexible way to adjust the distribution of the residual copper rate, so that the designer can better control the warping risk of the substrate while meeting the functional requirements.

[0047] Moreover, this solution does not require large-scale copper density adjustment or stacking structure changes for the entire substrate, but only requires flipping the design of the local graphic layer. This method not only reduces the complexity and cost of the manufacturing process, but also improves the flexibility and adjustability of the design, making it more suitable for warpage improvement of various complex structures and multi-layer PCBs.

[0048] Among them, the residual copper rate refers to the ratio of the copper area on the plane to the entire board area.

[0049] As a preferred implementation manner, the step S4 of "redesigning one of the two-sided pattern layers, designing the pattern at the severely warped position of the pattern layer with a higher residual copper rate to the other side of the pattern layer to perform a flip design of the pattern" includes:

[0050] S41. Analyze the line width of the original graphic layer to perform graphic flip design. First determine which lines may be subject to width restrictions or affect performance after flipping, determine these lines as key lines, exclude key lines from flipping, and flip non-key lines at severe warping positions. In this way, when performing graphic layer flip design, it can be ensured that the flipped graphics can not only effectively reduce the difference in residual copper rate, but also still meet the product's functional and performance requirements.

[0051] S42. Considering the spacing between graphic elements, the spacing between graphic elements includes line spacing and pad spacing. In this way, it is possible to ensure that the spacing meets the manufacturing process requirements during the flip design, and avoid problems such as short circuit or open circuit.

[0052] S43. Analyze the connection relationship between graphic elements to ensure that the original connection will not be destroyed during the flipping process. For elements that need to be connected across layers, it is necessary to pay attention to the design and layout of the connection points. In specific implementation, the automatic flip function in the CAD software can be used to quickly flip the graphic layer from one side to the other. During the flipping process, the software automatically considers the line width and spacing according to the method of this case, and tries to maintain the original connection relationship.

[0053] Specifically, the warpage determination value P1 in step S1 can be 0.7%, 0.5%, or 0.3%. In this way, considering the warpage requirements of different substrates, for example, PCBs with SMT generally require a warpage of 0.7%, and PCBs with CPS require a warpage of 0.5%. Circuit board factories with strong process capabilities can increase the PCB warpage standard to 0.3%.

[0054] As a preferred embodiment, when it is implemented, Figure 3 As shown, the substrate to be tested may be a two-layer board structure. When the substrate to be tested is a two-layer board structure, the substrate to be tested includes an A-side graphic layer at the top and a B-side graphic layer at the bottom.

[0055] The "residual copper rate difference value" is obtained according to the following steps:

[0056] The residual copper rate value of the A-side graphic layer is detected and recorded, and recorded as M; the residual copper rate value of the B-side graphic layer is detected and recorded, and recorded as N; the residual copper rate difference value = |MN|.

[0057] The residual copper rate difference determination value P2 in the preset residual copper rate difference determination value P2 described in step S2 is selected by the following steps:

[0058] Collect the warping conditions of the substrate in the past, record the residual copper rate difference values ​​corresponding to different warping degrees, and obtain the average value of the initial residual copper rate difference values ​​corresponding to the warping degrees of different grades; take the average value of the initial residual copper rate difference values ​​of a certain grade that meets the substrate warping requirements and the average value of the initial residual copper rate difference values ​​of a smaller grade, and take the average value of these two average values ​​as the copper rate difference judgment value P2 of this grade; select P2 according to the grade requirements of different substrates actually produced.

[0059] As shown in the following table, the warpage degree of the substrate is recorded. For example, the measured warpage is graded into 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, etc. The difference in residual copper rate between the A-side graphic layer and the B-side graphic layer corresponding to different warpage levels is recorded, and the average value is calculated.

[0060]

[0061] Based on the above table, for warpage requirements less than 0.7%, the average value of the residual copper rate difference between 0.7% and 0.6% can be selected, that is, (30% + 20%) / 2 = 25%; for warpage requirements less than 0.5%, the average value of the residual copper rate difference between 0.5% and 0.4% can be selected, that is, (15% + 12%) / 2 = 13.5%; for warpage requirements less than 0.3%, the average value of the residual copper rate difference between 0.4% and 0.4% can be selected, that is, (9% + 7%) / 2 = 8%; since the warpage requirement of most substrates is 0.7%, the preferred residual copper rate difference judgment value P is 25%. Specifically, the warpage degree warpage = single angle warpage height / (PCB diagonal length * 2) * 100%.

[0062] As described above, the present application selects a suitable P2 value by collecting past substrate warpage data, including the residual copper rate difference values ​​corresponding to different warpages; specifically, by calculating the average value of the corresponding residual copper rate difference values ​​for different warpages, so as to reflect the general situation of the residual copper rate difference under different warpage levels. Then, by taking the average value of the copper rate difference value of a certain level and the average value of the copper rate difference value of the next smaller level, and then taking the average value of these two average values, that is, the middle value, in order to better reflect the transition between the two levels, the P2 value can be set more accurately, and different warpage requirements can be more flexibly responded to, so as to ensure the warpage degree of the substrate in actual application, effectively identify and control the risk of substrate warpage, thereby improving the quality and stability of the substrate.

[0063] As a preferred embodiment, in specific implementation, the step S1 of "preparing a warped substrate to be tested, presetting a warping degree determination value P1, analyzing the entire substrate to be tested, and preliminarily identifying a key position where the warping exceeds the specified value P1 according to the determination value P1" includes:

[0064] The three-dimensional topographic data of the substrate surface is obtained by using an optical measuring instrument and screened according to the warpage degree judgment value P1 to identify the Unit with more serious substrate warpage and record its position or coordinates;

[0065] Badmark the units with serious warpage that are identified; in this way, through badmarking, those units with serious warpage can be quickly located, thus avoiding indiscriminate analysis and processing of the entire substrate, greatly improving the efficiency and pertinence of subsequent work. Moreover, after marking the units with serious warpage, only the residual copper rate difference of these units with badmarks can be analyzed, which not only reduces the amount of data analyzed, but also makes the analysis more accurate and effective.

[0066] As mentioned above, this case protects a method for improving substrate warping, and all technical solutions that are the same or similar to this case should be deemed to fall within the scope of protection of this case.

Claims

1. A method for improving substrate warpage, characterized in that: The following steps are involved: Step S1, prepare a warped substrate to be tested, preset a warping degree judgment value P1, analyze the entire substrate to be tested, and preliminarily identify the key position where the warping exceeds the specified value P1 according to the judgment value P1; the key position is one or more units in a substrate; Step S2, presetting a residual copper rate difference determination value P2, and further determining the initially identified key position according to the determination value P2, and analyzing the residual copper rate difference between layers for each unit in the key position; Step S3: When the difference in residual copper rate between the upper and lower corresponding graphic layers of a certain unit is greater than a preset judgment value P2, the unit is judged to be a severely warped position; Step S4, for the identified severe warping position, redesign one of the two-sided pattern layers, and design the pattern at the severe warping position of the pattern layer with a higher residual copper rate to the other side of the pattern layer to perform a flip design of the pattern, thereby reducing the difference in residual copper rates of the two-sided pattern layers; Step S5: re-manufacture and process the substrate according to the re-designed Unit.

2. A method for improving substrate warpage according to claim 1, characterized in that: The step S4 of "redesigning one of the two-sided pattern layers, designing the pattern at the severely warped position of the pattern layer with a higher residual copper rate to the other side of the pattern layer to perform a flip design of the pattern" includes: S41, analyzing the line width of the original graphic layer, first determining which lines will be subject to width restrictions or affect performance after flipping, and determining these lines as key lines; excluding the key lines from flipping when flipping, and flipping non-key lines at severely warped positions; S42, considering the spacing between graphic elements to perform flip design of the graphic, so as to avoid affecting the electrical performance of the substrate due to incorrect spacing after flipping; wherein the spacing between the graphic elements at least includes line spacing and pad spacing; S43. Analyze the connection relationship between graphic elements and perform flipping design of the graphic to ensure that the original connection is not destroyed during the flipping process; among them, for graphic elements that need to be connected across layers, pay attention to the design and layout of the connection points.

3. The method for improving substrate warpage according to claim 1, characterized in that: The warpage degree determination value P1 in step S1 is 0.7%, 0.5% or 0.3%.

4. The method for improving substrate warpage according to claim 1, characterized in that: The substrate to be tested at least includes an A-side graphic layer at the top layer and a B-side graphic layer at the bottom layer; The "residual copper rate difference value" described in step S3 is obtained according to the following steps: The residual copper rate value of the A-side graphic layer is detected and recorded, and recorded as M; the residual copper rate value of the B-side graphic layer is detected and recorded, and recorded as N; the residual copper rate difference value = |MN|.

5. A method for improving substrate warpage according to claim 1 or 4, characterized in that: The preset residual copper rate difference determination value P2 described in step S2 is selected by the following steps: Collect the past warping conditions of the substrate, record the difference values ​​of residual copper rate corresponding to different warping degrees, and obtain the average value of the difference values ​​of initial residual copper rate corresponding to different levels of average warping degrees; Take the average value of the initial residual copper rate difference value of a certain level that meets the substrate warpage requirement and the average value of the initial residual copper rate difference value of a smaller level, and take the average value of these two average values ​​as the copper rate difference judgment value P2 of this level; Select P2 according to the actual production level requirements of different substrates.

6. The method for improving substrate warpage according to claim 1, characterized in that: The step S1 of "preparing a warped substrate to be tested, presetting a warping degree determination value P1, analyzing the entire substrate to be tested, and preliminarily identifying a key position where the warping exceeds the specified value P1 according to the determination value P1" includes: The three-dimensional topographic data of the substrate surface is obtained by using an optical measuring instrument and screened according to the warpage degree judgment value P1 to identify the Unit with more serious substrate warpage and record its position or coordinates; Badmark the units with serious warping.

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