Expansion and contraction compensation method for high-alignment multi-layer PCB and PCB board

Abstract

The present application relates to the field of PCB board, specifically, a kind of for high alignment multilayer PCB expansion and contraction compensation method, the method is added step S34 between original step S3, S4, first measurement is carried out to each layer core plate, and repeat step S2, S3, continue S4;Increase step S45 between step S4, S5, second measurement is carried out to each layer core plate, and repeat step S2-S4, continue S5.The step S34 includes after etching the core plate is etched after baking, then first measurement expansion and contraction coefficient, and each layer core plate is compensated to be consistent.The step S45 includes after each layer core plate is browned after baking, then second measurement expansion and contraction coefficient, and each layer core plate is compensated to be consistent.Multiple baking improves the stability of PCB board, guarantees subsequent expansion and contraction is not too big.Multiple measurements can continuously correct the expansion and contraction of each layer core plate, so that the expansion and contraction of each layer core plate can be compensated according to the design copper thickness requirement, so that each layer core plate is compensated to be consistent, improves the accuracy of hole position.

Description

Technical Field

[0001] This invention relates to the field of PCB manufacturing, and more specifically, to a method for compensating for expansion and contraction of highly aligned multilayer PCBs and a PCB board. Background Technology

[0002] With the widespread adoption of HDI (High-Density Interconnect PCBs) and high-multilayer high-speed circuit boards (especially in 224GHz servers), the production of complex PCBs, particularly those using high-multilayer, high-density, and high-reliability interconnect technologies, demands extremely high hole-position accuracy compared to ordinary PCBs. This is especially true in high-layer and multilayer boards, where the increased number of layers, denser circuitry, and vias necessitates precise hole-position alignment. Ensuring accurate hole-position alignment is crucial for connecting precise upper and lower holes and circuitry. Insufficient hole-position accuracy can lead to poor connections between inner and outer layer circuitry, causing open or short circuits and impacting the electrical reliability of the PCB. High-precision hole-position alignment ensures accurate alignment of circuitry across layers, reducing electrical connection problems.

[0003] Therefore, minimizing or controlling the impact of hole position accuracy on the performance of high-layer and multilayer boards is crucial. Traditional solutions for handling inconsistent PCB expansion and contraction involve pre-calculating coefficients based on experience. These coefficients are not always accurate, requiring four test boards to be made before lamination. Then, a more accurate coefficient (the final coefficient) is assigned to each layer before final board fabrication to correct misalignment or deviation caused by inconsistent expansion and contraction. A conventional approach is to measure the PCB's expansion and contraction after lamination to provide compensation drill tape for stretched PCBs. This compensation is a linear compensation drill tape applied to all layers, i.e., square compensation. However, due to inconsistencies in the graphics and design of each layer (copper thickness, core board thickness, process parameters, etc.), the expansion and contraction of all layers are not uniform; they do not contract simultaneously. Some layers contract while others stretch. Therefore, the coefficient given after the final lamination cannot guarantee highly consistent expansion and contraction performance for each layer, only providing an approximate average. This means that the unified linear compensation drill tape system cannot accurately compensate for the hole position accuracy of each layer, only taking the average value of each layer, resulting in low alignment accuracy. Summary of the Invention

[0004] The present invention aims to overcome at least one of the defects (deficiencies) of the prior art and provide a method for high alignment multilayer PCB expansion and contraction compensation. This method solves the problem that the traditional uniform linear compensation drill tape system cannot accurately compensate for the hole position accuracy of each layer and can only take the average value of each layer, resulting in low alignment accuracy.

[0005] The technical solution adopted in this invention is a method for compensating for expansion and contraction of highly aligned multilayer PCBs, comprising the following steps:

[0006] S1, Pre-set expansion / contraction coefficient;

[0007] S2, Graphic Transfer;

[0008] S3, Inner layer etching;

[0009] S4, browning treatment;

[0010] S5, fusion and pressure plate;

[0011] S6, PL machine measures the core board expansion and contraction coefficient;

[0012] S7. Compensate the core board and provide the formal coefficients;

[0013] S8. Use formal coefficients to create the formal version;

[0014] Add step S34 between steps S3 and S4, perform the first measurement on each core layer, and repeat steps S2 and S3, then continue with S4;

[0015] Add step S45 between steps S4 and S5, perform a second measurement on each core layer, and repeat steps S2 to S4, continuing with S5.

[0016] The new process involves multiple measurements and compensations of the inner core board, improving its dimensional stability and enhancing control and measurement of its expansion and contraction. Multiple baking cycles improve the PCB's dimensional stability, ensuring that subsequent shrinkage or stretching is not excessive. Multiple measurements of the expansion and contraction coefficients continuously correct the expansion and contraction performance of each core board layer, ensuring that each layer's expansion and contraction is compensated specifically according to the designed copper thickness requirements. This consistent compensation across all core boards improves hole positioning accuracy.

[0017] Furthermore, step S34 includes etching and baking each core layer after etching, then measuring the expansion and contraction coefficient for the first time, and compensating each core layer to be consistent.

[0018] After etching, the inconsistent stress on the core board due to differences in copper design and distribution patterns leads to changes in expansion and contraction. Baking after etching improves the dimensional stability caused by uneven copper distribution after etching. Etching causes abrupt shrinkage of the copper area; baking stabilizes this shrinkage. A PL machine is used to initially measure the expansion and contraction changes caused by pattern differences after etching, and coefficients are revised based on the initial measurement results to compensate for the expansion and contraction of the core board caused by etching. Using the initial measurement and revised coefficients, the board is remade, and steps S2 and S3 are repeated. Each core board produced will have consistent expansion and contraction, avoiding situations where some core boards shrink while others stretch.

[0019] Furthermore, step S45 includes baking each core board after browning, then measuring the expansion and contraction coefficient a second time, and compensating each core board layer to be consistent.

[0020] After browning, a wet process is performed. Baking after browning removes moisture and further improves the dimensional stability of the core board, preventing severe deformation and abnormal expansion / contraction during the high-temperature, high-pressure lamination process. Baking after browning causes expansion / contraction in the core board. A PL machine is used to measure the expansion / contraction changes caused by browning and post-browning a second time. Based on the second measurement results, coefficients are revised to compensate for the expansion / contraction caused by browning and post-browning baking. The second measurement further corrects for the impact of the wet browning process on expansion / contraction, providing a final expansion / contraction coefficient before lamination, allowing for coefficient revision for the high-temperature, high-pressure lamination. Using the second measurement and revised coefficients, boards are remade, and steps S2 to S4 are repeated. Each core board produced will exhibit consistent expansion / contraction, avoiding situations where some core boards shrink while others stretch.

[0021] Furthermore, step S0, which involves baking the core board for the first time, is added before step S1.

[0022] Baking the incoming material for the first time can increase the dimensional stability of the core board, making it less susceptible to changes in its expansion and contraction due to high temperature and high humidity processes.

[0023] Furthermore, in step S0, the temperature of the first baking of the core board is 10 to 20 degrees higher than the material Tg, and the baking time is 1.5 to 2.5 hours.

[0024] Material Tg refers to the critical temperature at which the substrate transitions from a hard and brittle glassy state to a soft and elastic state. If the baking temperature is below the material Tg, the baking energy will be absorbed, failing to achieve the desired effect. Conversely, excessively high baking temperatures will directly damage the mechanical, electrical, and process reliability of the core board. Furthermore, excessively long baking times will impair the reliability and processability of the core board through thermal aging, oxidation, and stress accumulation.

[0025] Furthermore, the baking time after etching is longer than the first baking time and the baking time after browning.

[0026] After etching, the core board undergoes wet processes (such as acid etching and water washing), and moisture may penetrate deep into the resin. Therefore, prolonged baking is necessary to ensure dryness and prevent vaporization and board bursting during lamination. The uneven stress distribution between the etched copper foil pattern and the substrate requires prolonged constant-temperature relaxation to prevent subsequent alignment misalignment. Furthermore, the abrupt change in copper area distribution after etching, with significant differences in expansion and contraction, can be addressed by prolonged baking to fix these abnormal expansions and contractions in one go, effectively preventing further shrinkage or stretching and stabilizing material dimensions. The primary purpose of the first baking is to increase the dimensional stability of the inner core board. The post-browning baking primarily aims to remove moisture from the browning process and increase dimensional stability. Therefore, its baking time is shorter than the post-etching baking time.

[0027] Furthermore, the baking time after etching is 2.5 to 3.5 hours.

[0028] If the post-etching baking time is too short, residual moisture may cause delamination and delamination of the copper foil pattern. Insufficient stress relief after etching can lead to pattern deformation and misalignment. However, if the post-etching baking time is too long, it can cause material degradation and interface deterioration, sacrificing long-term reliability. Therefore, the post-etching baking time is set to 2.5 to 3.5 hours to ensure drying, fully relax the stress in the copper foil pattern, fix its expansion and contraction, and avoid affecting the material's performance.

[0029] Furthermore, during the graphic transfer in step S2, the alignment method of the LDI positioning hole drilling process is used to improve the accuracy of the upper and lower alignment of the graphic.

[0030] This invention uses drilling to achieve alignment, which avoids the UV light emitter's retainer from loosening due to repeated movements, thus preventing a decrease in positioning accuracy and misalignment of the upper and lower target points. The average FTB of traditional point alignment is 0.908 mil, while the average FTB of alignment using the LDI positioning hole drilling process is 0.527 mil, improving accuracy by 43.1%.

[0031] Furthermore, the LDI positioning hole process includes first drilling the positioning hole with a small drill bit, and then enlarging the hole with a large drill bit.

[0032] Before applying the dry film to the core board, positioning holes are drilled on the core board using a small drill bit. These positioning holes penetrate both the upper and lower surfaces of the core board. Then, the positioning holes are enlarged using a large drill bit, with different diameters to achieve directional positioning. The core board with the drilled holes is then fitted with the dry film, and the upper and lower patterns are aligned using an LDI (Low Displacement Diode) to ensure alignment accuracy. This drilling method avoids drill bit misalignment or tilting during drilling, further ensuring the alignment accuracy of the upper and lower patterns.

[0033] Furthermore, a multilayer PCB board manufactured using the aforementioned method for high-alignment multilayer PCB expansion and contraction compensation.

[0034] This invention also provides a multilayer PCB board manufactured using the aforementioned method for high-alignment multilayer PCB expansion and contraction compensation. Each core layer of this multilayer PCB board undergoes multiple baking and compensation processes, and after lamination, all core layers are compensated to be consistent, resulting in high hole position accuracy. This ensures precise alignment of the circuitry across each layer and improves the reliability of electrical performance.

[0035] Compared with existing technologies, the beneficial effects of this invention are as follows: Multiple baking steps in the original manufacturing process improve the dimensional stability of the PCB board, ensuring that subsequent shrinkage or stretching is not excessive. Multiple measurements of the expansion and contraction coefficients continuously correct the expansion and contraction performance of each core layer, ensuring that the expansion and contraction of each core layer is specifically compensated according to the designed copper thickness requirements, thereby ensuring consistent compensation for each core layer and improving the accuracy of hole positions. In step S34, each etched core layer is baked after etching, and the expansion and contraction coefficient is measured for the first time to ensure consistent compensation for each core layer. This improves the dimensional stability of the core board after etching and compensates for the expansion and contraction changes caused by differences in the etched pattern. In step S45, each browned core layer is baked after browning, and then the expansion and contraction coefficient is measured a second time to ensure consistent compensation for each core layer. On the one hand, it eliminates the moisture generated during the browning process; on the other hand, it further improves the dimensional stability of the core board, preventing severe deformation and abnormal expansion and contraction during the high-temperature and high-pressure lamination process. It also compensates for the expansion and contraction of the core board caused by browning and subsequent baking, providing a final expansion and contraction coefficient before lamination and revising the coefficient for the high-temperature and high-pressure lamination. Using a higher temperature for the first baking of the incoming material increases the dimensional stability of the core board, making it less susceptible to changes in its expansion and contraction behavior due to the high-temperature and high-humidity process. After etching, the copper area distribution undergoes abrupt changes, with significant differences in expansion and contraction. Long-term baking can fix these abnormal expansion and contraction in one go, effectively preventing further shrinkage or stretching. In the pattern transfer process, this invention uses an LDI positioning hole drilling process for alignment, avoiding the loosening of the UV light emitter caused by multiple movements in traditional point-to-point alignment methods, which leads to decreased positioning accuracy and misalignment of upper and lower target points. During drilling, a small drill bit is used to drill the positioning hole first, followed by a large drill bit for enlarging, preventing misalignment and further improving the accuracy of upper and lower pattern alignment. This high-alignment multilayer PCB expansion and contraction compensation method improves the accuracy of hole positions, ensures precise alignment of circuits on each layer, and enhances the reliability of the electrical performance of multilayer PCBs. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of the present invention.

[0037] Figure 2a This is a conventional method for aligning the upper and lower patterns on an LDI laser exposure machine.

[0038] Figure 2b This is a schematic diagram showing the UV light emitter after it has become loose.

[0039] Figure 3a A schematic diagram of drilling holes for LDI positioning.

[0040] Figure 3b This is a schematic diagram of applying dry film after drilling holes in the core board. Detailed Implementation

[0041] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0042] It should be understood that although the terms "first," "second," "third," etc., may be used in this invention to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this invention, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] Example 1

[0044] like Figure 1 As shown, a method for compensating for expansion and contraction in highly aligned multilayer PCBs includes the following steps:

[0045] S0. The incoming material is baked for the first time. The baking temperature here needs to be higher than the material Tg, preferably 10 to 20 degrees higher than the material Tg, and the baking time is 1.5 to 2.5 hours.

[0046] S1. Estimated expansion / contraction coefficient: Based on the graphics and materials provided by the customer, the expansion / contraction coefficient is estimated. This coefficient is estimated based on experience and is not very accurate.

[0047] S2, Graphic Transfer;

[0048] Pattern transfer requires ensuring the alignment accuracy of the upper and lower patterns on the core board. The traditional method involves applying a dry film to the core board and then using UV light to create four target points (one large and one small) on the top and bottom of the dry film. The different sizes of the target points help distinguish directions. However, with repeated movement of the fixture holding the UV light emitter, the fixture may loosen, leading to decreased positioning accuracy and misalignment of the upper and lower target points, affecting precision. This invention uses drilling to achieve alignment. Before applying the dry film to the core board, a small drill bit is used to drill positioning holes that penetrate both the upper and lower surfaces. Then, a large drill bit is used to enlarge the positioning holes, with different diameters, to achieve the positioning function of distinguishing directions. After drilling, the core board is coated with the dry film, and an LDI (Light Dip and Die) device is used to capture the drilled target points for upper and lower pattern alignment, ensuring the alignment accuracy of the upper and lower patterns. Using a small drill bit for positioning first, followed by enlarging with a large drill bit, effectively prevents drilling misalignment or tilting, thus ensuring verticality requirements and improving the alignment accuracy of the upper and lower patterns. The average FTB using traditional point alignment is 0.908 mil, while the average FTB using LDI positioning hole drilling process alignment is 0.527 mil, improving accuracy by 43.1%.

[0049] S3, Inner layer etching;

[0050] S34. Perform the first measurement on each core layer, and repeat steps S2 and S3, then continue to S4; step S34 includes etching and baking each core layer after etching, then measuring the expansion and contraction coefficient for the first time, and compensating each core layer to be consistent.

[0051] After etching, the copper area distribution undergoes abrupt changes, resulting in significant differences in expansion and contraction. Baking effectively prevents further shrinkage or stretching of the core board. The baking time here needs to be longer than the initial baking time and the subsequent baking time after browning. Preferably, the baking time here is 2.5 to 3.5 hours to fix the expansion and contraction. The baking temperature is 10 to 20 degrees Celsius higher than the material's Tg. After baking, a PL machine is used to measure the expansion and contraction changes caused by pattern differences after etching for the first time. The coefficient is then revised based on the results of the first measurement to compensate for the expansion and contraction of the core board caused by etching. Since each core layer has been compensated to be consistent in step S34, the board is remade using the expansion and contraction coefficients measured in the first step, and steps S2 and S3 are repeated. At this point, the expansion and contraction of each core layer is consistent, and there will be no situation where some layers shrink while others stretch.

[0052] S4, browning treatment;

[0053] S45. Perform a second measurement on each core layer, and repeat steps S2 to S4, then continue to S5; step S45 includes baking each core layer after browning, then measuring the expansion and contraction coefficient a second time, and compensating each core layer to be consistent.

[0054] Browning involves a wet process. Baking removes moisture and further improves the dimensional stability of the core board, preventing severe deformation and abnormal expansion / contraction during the high-temperature, high-pressure lamination process. The preferred baking time is 1.5 to 2.5 hours, with the baking temperature 10 to 20 degrees Celsius higher than the material's Tg. During browning and subsequent baking, the core board will experience expansion / contraction. A second measurement and compensation ensures that the expansion / contraction of each core layer is specifically compensated according to the designed copper thickness requirements. Since S45 has already compensated each core layer to be consistent, the board is remade using the expansion / contraction coefficient from the second measurement, and steps S2 to S4 are repeated. This time, the expansion / contraction of each core layer is consistent, preventing situations where some layers shrink while others stretch.

[0055] S5. Welding and pressing; check the alignment of the fusion plates and press them; during the pre-alignment of the fusion, it is necessary to observe the alignment and expansion / contraction of each layer to ensure that the core plates of each layer have been compensated to be consistent before pressing.

[0056] The S6 and PL machines measure the expansion and contraction coefficient of the core board. The pressing process involves high temperature and high pressure, and due to the differences in the patterns on each core board, its expansion, contraction, and dimensional stability will also change. Therefore, it is necessary to measure again.

[0057] S7. Compensate the core board and give the official coefficient; all core boards have been compensated to be consistent, so the coefficient given at this time is the official coefficient. Make the board again according to this compensation coefficient, and the expansion and contraction of each core board will be consistent.

[0058] S8. Use the formal coefficient to make the formal board. In step S7, all core layers have been compensated to be consistent. The formal board made according to this formal coefficient should provide a 1:1 ratio of drill tape to the drilling room, without the need for special compensation.

[0059] Using a high-alignment multilayer PCB expansion and contraction compensation method, the yield of PCB alignment after lamination can be improved to 83% with an alignment of less than 2.7mil, while the yield of ordinary process alignment with an alignment of less than 2.7mil is only 11%, resulting in an overall yield improvement of 72%.

[0060] Example 2

[0061] This embodiment provides a multilayer PCB board, which is manufactured using the method described in Embodiment 1 above.

[0062] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for compensating for expansion and contraction in highly aligned multilayer PCBs, comprising the following steps: S1, Pre-set expansion / contraction coefficient; S2, Graphic Transfer; S3, Inner layer etching; S4, browning treatment; S5, fusion and pressure plate; S6 and PL machines measure the expansion and contraction coefficient of the core board. S7. Compensate the core board and provide the formal coefficients; S8. Use formal coefficients to create formal versions; Its features are: Add step S34 between steps S3 and S4, perform the first measurement on each core layer, and repeat steps S2 and S3, then continue with S4; Add step S45 between steps S4 and S5, perform a second measurement on each core layer, and repeat steps S2 to S4, then continue with S5; Step S34 includes etching and baking each core layer after etching, then measuring the expansion and contraction coefficient for the first time, and compensating each core layer to be consistent. Step S45 includes baking each core board after browning, then measuring the expansion and contraction coefficient a second time, and compensating each core board layer to be consistent.

2. The method for compensating for expansion and contraction of highly aligned multilayer PCBs according to claim 1, characterized in that, Step S0 is added before step S1 to perform the first baking of the core board.

3. The method for compensating for expansion and contraction of highly aligned multilayer PCBs according to claim 2, characterized in that, In step S0, the temperature of the first baking of the core board is 10 to 15 degrees higher than the material Tg, and the baking time is 1.5 to 2.5 hours.

4. The method for compensating for expansion and contraction of highly aligned multilayer PCBs according to claim 2, characterized in that, The baking time after etching is longer than the first baking time and the baking time after browning.

5. The method for compensating for expansion and contraction of highly aligned multilayer PCBs according to claim 4, characterized in that, The baking time after etching is 2.5 to 3.5 hours.

6. The method for compensating for expansion and contraction of highly aligned multilayer PCBs according to claim 2, characterized in that, In step S2, during graphic transfer, the alignment method of the LDI positioning hole drilling process is used to improve the accuracy of the graphic's vertical alignment.

7. The method for compensating for expansion and contraction of highly aligned multilayer PCBs according to claim 6, characterized in that, The LDI positioning hole drilling process includes first drilling the positioning hole with a small drill bit, and then enlarging the hole with a large drill bit.

8. A multilayer PCB board, characterized in that, It is manufactured using the expansion and contraction compensation method for high-alignment multilayer PCBs as described in any one of claims 1 to 7.

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