A high aspect ratio PCB via pulse plating method based on the time evolution law of the plating capacity

Abstract

The application discloses a high-aspect-ratio PCB through-hole pulse electroplating method based on deep plating capacity time evolution law. The method comprises the following steps: (1) selecting at least two pulse electroplating waveforms with different positive and negative current density ratios and positive and negative time ratios, and performing single waveform electroplating experiments on target PCB through holes; (2) measuring the hole plating layer thickness and the plate surface plating layer thickness of the PCB through hole under different electroplating time conditions, and calculating the deep plating capacity TP value respectively; (3) according to the law of the deep plating capacity TP value changing with the electroplating time, the deep plating capacity advantage time interval corresponding to each pulse electroplating waveform is determined; (4) different pulse electroplating waveforms are matched and combined according to the deep plating capacity advantage time interval, and then the target PCB through hole is electroplated, so that the problem that a single waveform cannot simultaneously consider the deposition rate and uniformity in the electroplating of the high-aspect-ratio PCB through hole in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board (PCB) manufacturing technology, and specifically relates to a pulse electroplating method for high aspect ratio PCB through-holes based on the time evolution law of deep plating capability. Background Technology

[0002] As electronic devices evolve towards higher density and integration, the number of PCB layers continues to increase, leading to a sustained rise in the through-hole thickness-to-diameter ratio (thickness / diameter). High thickness-to-diameter ratios of 10:1, 15:1, and even 20:1 have become the industry norm. However, a higher thickness-to-diameter ratio makes mass transfer within the hole more difficult, resulting in uneven current distribution. This can cause excessively thick plating at the hole opening and insufficient plating inside, forming a "dog-bone" plating layer that severely impacts the reliability of electrical interconnects. Throwing Power (TP) is a key indicator for evaluating the quality of through-hole plating, referring to the ratio of the average plating thickness within the hole to the average plating thickness on the board surface. Currently, pulse plating technology is widely used to improve the uniformity of through-hole plating. However, existing pulse electroplating methods mostly use a single pulse waveform for the entire electroplating process, making it difficult to simultaneously address the mass transfer requirements of different electroplating stages: high current density is needed in the initial stage of electroplating to achieve rapid deposition, but low current density is required in the later stage for surface trimming to avoid edge effects; a single waveform cannot simultaneously meet the requirements of rapid deposition in the early stage and uniform trimming in the later stage, resulting in insufficient utilization of current efficiency and limited improvement in plating depth (TP). Therefore, there is an urgent need for a through-hole electroplating method that can dynamically adjust waveform parameters according to different electroplating stages and balance deposition rate and uniformity to solve the problem of poor plating quality in high aspect ratio through-holes. Summary of the Invention

[0003] The primary objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a high aspect ratio PCB through-hole pulse electroplating method based on the time evolution law of deep plating capability, so as to solve the problem that the single pulse waveform in the prior art cannot simultaneously meet the mass transfer conditions of different electroplating stages, thus resulting in insufficient deep plating capability.

[0004] Another objective of this invention is to provide an application of the pulse electroplating method for high aspect ratio PCB through-holes based on the time evolution law of deep plating capability.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A pulse electroplating method for high aspect ratio PCB through-holes based on the time evolution law of deep plating capability includes the following steps:

[0007] (1) Select at least two pulse electroplating waveforms with different forward and reverse current density ratios and forward and reverse time ratios, and conduct a single waveform electroplating experiment on the target PCB via, wherein the pulse parameters are set in a gradient decreasing manner;

[0008] (2) Measure the plating thickness in the PCB through holes and the plating thickness on the board surface under different plating time conditions, and calculate the deep plating capability TP value respectively;

[0009] (3) Based on the law of change of the deep plating capability TP value with electroplating time, determine the time interval of the deep plating capability advantage corresponding to each pulse electroplating waveform;

[0010] (4) Match and combine different pulse electroplating waveforms according to the time interval of the deep plating capability advantage, and then electroplat the target PCB through hole, so that the electroplating process adopts pulse electroplating waveforms with higher deep plating capability at different time stages. Through the matching and combination of the pulse electroplating waveforms, the deep plating capability of the high thickness-to-diameter ratio PCB through hole electroplating process is optimized and controlled.

[0011] Preferably, the pulse electroplating waveforms in step (1) are at least three types, and the pulse parameters are set in a gradient decreasing manner; more preferably, they include large waveforms, medium waveforms and small waveforms, wherein the large waveforms, medium waveforms and small waveforms have different forward and reverse current density ratios and forward and reverse time ratios.

[0012] Preferably, the thickness-to-diameter ratio of the PCB through-hole in step (1) is (10-20):1; more preferably 20:1.

[0013] Preferably, in step (2), the electroplating time range is 30 to 150 min; electroplating is performed on PCB through holes with different thickness-to-diameter ratios, and the electroplating time can be set to 30 min, 60 min, 90 min, 120 min, and 150 min respectively. The coating thickness changes of through holes with different thickness-to-diameter ratios at different positions (hole opening, hole middle, hole center) are observed, and the deep plating capability (TP) is calculated.

[0014] Preferably, the time interval of the deep plating capability advantage mentioned in step (3) is the electroplating time interval during which the deep plating capability TP reaches its peak or maintains a stable growth.

[0015] A composite pulse electroplating method suitable for through-holes in high aspect ratio PCBs specifically includes the following steps:

[0016] Electroplating of PCB vias is performed using a three-stage composite pulse waveform; wherein...

[0017] The first stage uses large waveform electroplating, and the electroplating time is 80-100 minutes.

[0018] The second stage uses a medium waveform for electroplating, and the electroplating time is 20 to 40 minutes.

[0019] The third stage uses small waveforms for electroplating, and the electroplating time is 20 to 40 minutes.

[0020] The pulse parameters of the large, medium, and small waveforms are set in a gradient decreasing manner.

[0021] Preferably, the forward current density of the electroplating is 15 ASF.

[0022] Preferably, the specific parameters of the large waveform are as follows: the ratio of forward to reverse current density is 1:3.2, and the ratio of forward to reverse time is 200:10.

[0023] Preferably, the specific parameters of the intermediate waveform are as follows: the ratio of forward to reverse current density is 1:2.5, and the ratio of forward to reverse time is 160:8.

[0024] Preferably, the specific parameters of the small waveform are as follows: the ratio of forward to reverse current density is 1:2.0, and the ratio of forward to reverse time is 120:6.

[0025] Preferably, the thickness-to-diameter ratio of the PCB through-hole is (10-20):1; more preferably, it is 20:1.

[0026] Preferably, the electroplating time for the first stage is 90 min, the electroplating time for the second stage is 30 min, and the electroplating time for the third stage is 30 min.

[0027] Preferably, when the above method is used for electroplating through-holes of PCBs with a thickness-to-diameter ratio of 20:1, the deep plating capability (TP) reaches 94.19%; when used for electroplating through-holes of PCBs with a thickness-to-diameter ratio of 15:1, the deep plating capability (TP) reaches 100.75%; and when used for electroplating through-holes of PCBs with a thickness-to-diameter ratio of 10:1, the deep plating capability (TP) reaches 110.79%.

[0028] The application of the pulse electroplating method for high aspect ratio PCB through holes based on the time evolution law of deep plating capability or the composite pulse electroplating method applicable to high aspect ratio PCB through holes in PCB through hole electroplating.

[0029] The thickness-to-diameter ratio of the PCB through-hole is (10-20):1; more preferably 20:1.

[0030] This invention provides a pulse electroplating control method suitable for high aspect ratio PCB through-holes. The method first conducts electroplating experiments with a single pulse waveform to systematically study the variation law of deep plating capability under different pulse waveform parameters (forward / reverse current density ratio, forward / reverse time ratio) and different plating time conditions, establishing a characteristic curve of deep plating capability changing with plating time. Then, based on the variation law, the dominant time interval of deep plating capability for different pulse waveforms is determined. In the actual electroplating process, different pulse waveforms are matched and combined according to the dominant time interval, so that the electroplating process uses pulse waveforms with higher deep plating capability at different time stages, thereby achieving optimized control of deep plating capability during the electroplating process of high aspect ratio PCB through-holes. This solves the problem in the prior art that a single waveform is difficult to simultaneously achieve deposition rate and uniformity in the electroplating of high aspect ratio PCB through-holes, enabling good deep plating capability and reliability in through-hole electroplating with different aspect ratios (10:1~20:1).

[0031] The present invention has the following advantages and effects compared with the prior art:

[0032] (1) The present invention is based on the electroplating control idea of ​​the time evolution law of deep plating capability, and guides the selection of pulse waveform by establishing the law of TP changing with time.

[0033] (2) This invention enables the electroplating process to adapt to the mass transfer conditions at different stages by matching and combining the advantageous ranges of different pulse waveforms, thereby improving the deep plating capability. This invention does not limit the number of pulse waveform switching stages, but rather performs waveform matching control based on the law of deep plating capability changing with electroplating time.

[0034] (3) The method of the present invention has excellent deep plating capability: In the electroplating of PCB through holes with a thickness ratio of 20:1, the deep plating capability reaches more than 94%, which significantly improves the electroplating quality of high thickness ratio through holes.

[0035] (4) The method of the present invention has a wide range of applications: it is applicable to PCB through-hole electroplating with a thickness-to-diameter ratio of 10:1 to 20:1, and can meet the manufacturing needs of PCBs of different specifications.

[0036] (5) The method of the present invention has high reliability: the PCB through holes after electroplating are verified by thermal stress test. There are no board bursting or hole cracking phenomena in the through holes of each thickness-to-diameter ratio after electroplating. The plating layer is firmly bonded and has good reliability, which can meet the reliability requirements of electronic products.

[0037] (6) The process of this invention is simple and controllable: no additional equipment is required, and it can be achieved simply by controlling the pulse power supply. The process is simple and has good universality and industrial application value.

[0038] (7) Based on in-depth research on the performance law of single waveform, the present invention scientifically constructs composite waveform, which exhibits gradient decrease. The technical solution has sufficient theoretical basis and experimental support. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the current-time pulses corresponding to the three waveforms in Example 1.

[0040] Figure 2 This is a graph showing the trend of TP (thickness ratio) versus electroplating time for a 20:1 through-hole under different single waveforms.

[0041] Figure 3 This is a graph showing the variation of TP (thickness ratio) with electroplating time for a 15:1 through-hole under different single waveforms.

[0042] Figure 4 This is a graph showing the variation of TP (thickness ratio) with electroplating time for a 10:1 through-hole under different single waveforms.

[0043] Figure 5 The images shown are cross-sectional views (magnified 200 times) of the through holes with different thickness-to-diameter ratios after electroplating of the composite waveform in Example 2; where (a): thickness-to-diameter ratio 20:1; (b): thickness-to-diameter ratio 15:1; (c): thickness-to-diameter ratio 10:1.

[0044] Figure 6 The images shown are cross-sectional views (magnified 200 times) of thermal stress test results for through holes with different thickness-to-diameter ratios after composite waveform electroplating in Example 2; where (a): thickness-to-diameter ratio 20:1; (b): thickness-to-diameter ratio 15:1; (c): thickness-to-diameter ratio 10:1.

[0045] Figure 7 The images shown are cross-sectional views (magnified 200 times) of the composite waveform after electroplating with different thickness-to-diameter ratios in Comparative Example 4; where (a): thickness-to-diameter ratio 20:1; (b): thickness-to-diameter ratio 15:1; (c): thickness-to-diameter ratio 10:1.

[0046] Figure 8 The images shown are cross-sectional views (magnified 200 times) of the composite waveform after electroplating with different thickness-to-diameter ratios in Comparative Example 5; where (a): thickness-to-diameter ratio 20:1; (b): thickness-to-diameter ratio 15:1; (c): thickness-to-diameter ratio 10:1.

[0047] Figure 9 The images shown are cross-sectional views (magnified 200 times) of the composite waveform after electroplating with different thickness-to-diameter ratios in Comparative Example 6; where (a): thickness-to-diameter ratio 20:1; (b): thickness-to-diameter ratio 15:1; (c): thickness-to-diameter ratio 10:1. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed according to conventional experimental conditions or experimental conditions recommended by the manufacturer. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0049] Example 1

[0050] I. Experimental study on the performance of a single waveform, including the following steps:

[0051] (1) Test board fabrication

[0052] A copper-clad laminate is taken, laminated, mechanically drilled, and shaped to produce a test board with a size of 5 cm × 15 cm. The board has multiple through holes to be plated. The through hole design parameters are: board thickness 3 mm, and through hole diameters of 0.15 mm, 0.2 mm, and 0.3 mm, respectively.

[0053] (2) Preprocessing

[0054] ①Plasma desmearing: The test board is placed in a plasma treatment device for plasma desmearing (the treatment adopts process conditions known in the art, which usually includes three stages: swelling, desmearing, and neutralization) to clean the hole walls and improve the adhesion of copper plating.

[0055] ② Horizontal copper plating:

[0056] The test board after plasma desmearing is subjected to horizontal copper plating treatment (the treatment adopts process conditions known in the art, which usually includes stages such as degreasing, water washing, micro etching, acid washing, water washing, pre-immersion, activation, water washing, acceleration and horizontal copper plating), and a thin copper layer is deposited on the hole wall as a conductive layer. Horizontal copper plating increases the copper layer thickness to 3~5 μm.

[0057] (3) Electroplating preparation

[0058] ① Cleaning the Haring tank: Rinse the Haring tank with deionized water, and then clean the Haring tank with a 5% H2SO4 solution for 5~10 min.

[0059] ② Plating solution preparation: Prepare the plating solution according to the following composition, and after bringing the volume to 1.5 L, transfer it to the Haring tank:

[0060] CuSO4·5H2O: 75 g / L, analytical grade, purchased from Xilong Scientific Co., Ltd.

[0061] H2SO4: 245 g / L, 98%, purchased from Xilong Scientific Co., Ltd.

[0062] Cl - 80 ppm, added in the form of HCl, 1 mol / L, purchased from Bolinda Technology Co., Ltd.

[0063] Additive A (PPRA): 14 mL / L, purchased from Guanghe Technology Co., Ltd.;

[0064] Additive B (PPRB): 0.8 mL / L, purchased from Guanghe Technology Co., Ltd.;

[0065] The rest is deionized water, prepared in the laboratory.

[0066] ③ Anode placement: Use phosphor bronze anodes (6×15 cm in size). 2 Purchased from Dongguan Tongda Metal Materials Co., Ltd., and placed on the left and right sides of the Harlin tank (1.5 L, custom-made).

[0067] ④ Test plate placement: Place the test plate vertically in the center of the Haring tank.

[0068] (4) Electroplating process

[0069] Electroplating was performed using a pulse power supply (model: HPNPF~2*Z10A12VF30A36V, manufacturer: Jiangxi Liyuan Haina Technology Co., Ltd.). This study set three single waveforms, fixed the forward current density at 15 ASF, and set the reverse current density according to the ratio of forward to reverse current density.

[0070] Large waveform: forward and reverse current density ratio is 1:3.2, forward and reverse time ratio is 200:10;

[0071] Medium waveform: forward and reverse current density ratio is 1:2.5, forward and reverse time ratio is 160:8;

[0072] Small waveform: the ratio of forward to reverse current density is 1:2.0, and the ratio of forward to reverse time is 120:6;

[0073] For each thickness-to-diameter ratio (20:1, 15:1, 10:1) and each waveform (large waveform, medium waveform, small waveform), the following electroplating time groups were set: 30 min group, 60 min group, 90 min group, 120 min group, and 150 min group.

[0074] (5) Post-processing

[0075] ① Water washing: After electroplating, remove the test plate and rinse it twice with deionized water, 1 minute each time;

[0076] ② Drying: Use cold air to dry the surface moisture of the test board.

[0077] (6) Slicing

[0078] ①Sampling: Use an automatic slicer (model: CJM~50, manufacturer: Dongguan Cijin Electronic Technology Co., Ltd.) to cut a 10 mm × 10 mm sample containing the test hole;

[0079] ②Pouring: The sample is potted with epoxy resin;

[0080] ③ Grinding and polishing: Grind with coarse sandpaper and then fine sandpaper until the cross-section of the hole is exposed, and then polish to a mirror finish;

[0081] ④ Micro-etching: Use micro-etching solution (H2O:NH3·H2O:H2O2=6:3:1, v / v / v; NH3·H2O and H2O2 were purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and the water was deionized water) to lightly etch and clearly show the coating interface;

[0082] ⑤ Cleaning: Rinse the polished sample in deionized water for 5 seconds to remove surface residue;

[0083] ⑥ Drying: Dry with cold air.

[0084] (7) Measurement of slice thickness data

[0085] Metallographic observation: The plating cross-section was observed under a metallographic microscope (specification: LEICA DM4M, manufacturer: Guangzhou Tenas Instrument Technology Co., Ltd.) (magnification 200x). The plating thickness at the copper surface, the hole opening, the middle third of the hole, and the hole was measured. The plating depth capability (TP) was calculated using the following formula: TP = (average plating thickness in the hole / average plating thickness on the board surface) × 100%. The experiment was repeated three times.

[0086] II. Results of Single Waveform Experiment:

[0087] 1. Experimental results of through holes with a thickness-to-diameter ratio of 20:1

[0088] Figure 1 The diagram shows the current-time pulses corresponding to the three waveforms, illustrating the characteristic differences in the ratio of forward and reverse current density and the time ratio of the different waveforms. Figure 2 The variation trend of TP with electroplating time for a 20:1 aspect ratio through-hole under different single waveforms is shown. The results indicate that:

[0089] Large waveform group: TP was 72.00% at 30 min of electroplating, decreased to 58.55% at 60 min, reached a peak of 78.72% at 90 min, decreased to 59.74% at 120 min, and slightly rebounded to 63.91% at 150 min. It can be seen that the large waveform exhibits fluctuations during the electroplating process, reaching the highest deep plating capability at 90 min, then decreasing significantly after 90 min, and although it rebounded at 150 min, it was still below the peak level.

[0090] Medium waveform group: TP was 29.41% at 30 min of electroplating, rising to 50.50% at 60 min, slightly decreasing to 46.66% at 90 min, reaching 46.77% at 120 min, and rising to 54.93% at 150 min. Throughout the electroplating process, the TP of the medium waveform group showed a trend of first rising and then fluctuating, with an overall slow increase, remaining within the range of 46% to 55% from 90 to 150 min, demonstrating relatively stable deep plating capability.

[0091] The small waveform group showed that TP was 26.65% at 30 min of electroplating, rising to 36.85% at 60 min, reaching 50.43% at 90 min, decreasing to 38.73% at 120 min, and rebounding to 46.53% at 150 min. The small waveform exhibited a fluctuating trend of first rising, then falling, and then rebounding during the electroplating process, reaching a relatively high level at 90 min, and then rebounding in the later stage (120~150 min), showing a certain potential to improve the coating inside the holes.

[0092] 2. Experimental results of through holes with a thickness-to-diameter ratio of 15:1

[0093] Figure 3 The variation trend of TP with electroplating time for a 15:1 aspect ratio through-hole under different single waveforms is shown. The results indicate that:

[0094] Large waveform group: TP was 77.25% at 30 min of electroplating, slightly decreased to 71.30% at 60 min, rebounded to a peak of 77.51% at 90 min, decreased to 65.82% at 120 min, and slightly rebounded to 69.85% at 150 min. The large waveform showed fluctuations during the electroplating process, with two higher points at 30 min and 90 min, and the overall TP value fluctuated between 65% and 78%.

[0095] Medium waveform group: TP was 40.89% at 30 min of electroplating, rising to 55.87% at 60 min, slightly decreasing to 54.94% at 90 min, rebounding to 58.45% at 120 min, and further increasing to 59.85% at 150 min. The medium waveform group showed an overall upward trend during electroplating, with TP gradually increasing from 55.87% to 59.85% between 60 and 150 min, indicating a steady improvement in deep plating capability.

[0096] The small waveform group showed that TP was 33.30% at 30 min of electroplating, rising to 41.93% at 60 min, reaching 62.85% at 90 min, decreasing to 50.10% at 120 min, and rebounding to 59.85% at 150 min. The small waveform exhibited a fluctuating trend of first rising, then falling, and then rising again during the electroplating process, reaching its peak at 90 min, and then rebounding significantly in the later stage (120~150 min), demonstrating a certain ability to improve in the later stage.

[0097] 3. Experimental results of through holes with a thickness-to-diameter ratio of 10:1

[0098] Figure 4 The variation trend of TP with electroplating time for a 10:1 aspect ratio through-hole under different single waveforms is shown. The results indicate that:

[0099] Large waveform group: TP was 71.07% at 30 min of electroplating, rising to 84.21% at 60 min, continuing to rise to 92.63% at 90 min, slightly decreasing to 90.34% at 120 min, and rebounding to 99.35% at 150 min. The large waveform showed an overall upward trend during the electroplating process, with faster growth in the 60-90 min range, a slight pullback at 120 min, and reaching its highest value at 150 min.

[0100] Medium waveform group: TP was 76.36% at 30 min of electroplating, rose to 89.38% at 60 min, fell to 79.29% at 90 min, rebounded to 82.63% at 120 min, and further rose to 85.11% at 150 min. The medium waveform showed a fluctuating trend of first rising, then falling, and then slowly rising again during the electroplating process. It reached a high point at 60 min and then fell back, before gradually recovering.

[0101] Small waveform group: TP was 70.52% at 30 min of electroplating, 70.99% at 60 min (basically flat), rose to 81.90% at 90 min, continued to rise to 84.66% at 120 min, and slightly decreased to 79.42% at 150 min. The small waveform showed a trend of being stable in the early stage, rising in the middle stage, and slightly declining in the later stage during the electroplating process, reaching the highest value at 120 min.

[0102] 4. Composite waveform construction and optimization

[0103] Based on the patterns derived from the single waveform experiments described above, a three-stage composite pulse waveform is constructed:

[0104] The first stage (large waveform electroplating): taking advantage of the high plating depth of large waveforms in the early and middle stages of electroplating, the electroplating time is 80~100 min;

[0105] The second stage (medium waveform electroplating): taking advantage of the stable deep plating ability of the medium waveform in the middle and later stages of electroplating, the electroplating time is 20~40 min;

[0106] The third stage (small waveform electroplating): taking advantage of the small waveform to enhance the deep plating ability in the later stage of electroplating, the electroplating time is 20~40 min.

[0107] Composite waveform optimization: Through experimental optimization, the optimal combination of electroplating time was determined to be: 90 min for large waveform electroplating, 30 min for medium waveform electroplating, 30 min for small waveform electroplating, and a total electroplating time of 150 min.

[0108] Example 2

[0109] Using the preferred composite waveform obtained in Example 1, electroplating verification was performed on PCB vias with different thickness-to-diameter ratios (20:1, 15:1, 10:1) to test the deep plating capability of vias with each thickness-to-diameter ratio. The specific steps are as follows:

[0110] (1) Following the method in steps (1)-(7) of Example 1, the difference is that this example performs a composite waveform electroplating experiment, that is, based on the conclusion of Example 1, a three-stage composite pulse waveform is constructed:

[0111] Phase 1: Using large waveform parameters, electroplating time is 90 min;

[0112] Second stage: Using medium waveform parameters, electroplating time is 30 min;

[0113] Third stage: Using small waveform parameters, the electroplating time is 30 min.

[0114] Figure 5The images show cross-sectional views (magnified 200x) of through holes with different thickness-to-diameter ratios after composite waveform electroplating. From these cross-sectional views, we can observe:

[0115] Through-hole with a thickness-to-diameter ratio of 20:1: The coating inside the hole is continuous and uniform, with no obvious thickening at the hole opening, and the TP reaches 94.19%.

[0116] Through-hole with a thickness-to-diameter ratio of 15:1: The coating distribution is more uniform, and the coating thickness at the center of the hole is slightly greater than that at the opening, with TP reaching 100.17%.

[0117] Through-hole with a thickness-to-diameter ratio of 10:1: The coating thickness inside the hole is uniform overall, and the coating thickness at the center of the hole is significantly greater than that at the opening, with TP reaching 110.19%.

[0118] (2) Reliability testing

[0119] The samples that had completed the thermal cycling (thermal stress) test (tin immersion test: immersion in rosin oil for 10 s → 288 ℃ lead-free tin furnace for 10 s → cooling, repeated 5 times) were potted, ground, polished and micro-etched. Under a metallographic microscope, no defects such as hole cracks, board bursts or copper layer fractures were observed.

[0120] Figure 6 The images show cross-sectional views of through-holes with different aspect ratios after composite waveform electroplating. The cross-sectional views reveal that after five thermal stress cycles, the plating layer on the hole wall bonded well to the substrate, with no delamination or blow-out phenomena, and no cracks at the hole corners. No defects such as blow-out or hole cracks were found in any of the tested samples, indicating that the through-holes electroplated using the method of this invention have good thermal reliability and meet the reliability requirements of the PCB industry.

[0121] Comparative Example 1

[0122] The method of Example 1 is the same, except that this comparative example uses a single waveform (large waveform) for continuous electroplating for 150 minutes.

[0123] Test results show: TP for thickness-to-diameter ratio 20:1: 63.91%; TP for thickness-to-diameter ratio 15:1: 69.85%; TP for thickness-to-diameter ratio 10:1: 99.35%.

[0124] Comparative Example 2

[0125] The method of Example 1 is the same, except that this comparative example uses a single waveform (medium waveform) for continuous electroplating for 150 minutes.

[0126] Test results show: TP for thickness-to-diameter ratio 20:1: 54.93%; TP for thickness-to-diameter ratio 15:1: 59.41%; TP for thickness-to-diameter ratio 10:1: 85.11%.

[0127] Comparative Example 3

[0128] The method of Example 1 is the same, except that this comparative example uses a single waveform (small waveform) for continuous electroplating for 150 minutes.

[0129] Test results show: TP for thickness-to-diameter ratio 20:1: 46.53%; TP for thickness-to-diameter ratio 15:1: 59.85%; TP for thickness-to-diameter ratio 10:1: 79.42%.

[0130] Compared with Comparative Examples 1-3, the composite waveform electroplating method of the present invention significantly improves the deep plating capability under three aspect ratios.

[0131] Comparative Example 4

[0132] The method of Example 1 is followed, except that the comparative example uses the following composite waveform parameters:

[0133] First stage: Electroplating for 90 minutes using small waveform parameters;

[0134] Second stage: Electroplating for 30 minutes using medium waveform parameters;

[0135] Third stage: Electroplating for 30 minutes using large waveform parameters.

[0136] Figure 7 The images show cross-sectional views (200x magnification) of through-holes with different thickness-to-diameter ratios after electroplating of the composite waveform. Test results show: TP: 56.57% for a thickness-to-diameter ratio of 20:1; TP: 62.37% for a thickness-to-diameter ratio of 15:1; and TP: 84.71% for a thickness-to-diameter ratio of 10:1.

[0137] Comparative Example 5

[0138] The method of Example 1 is followed, except that the comparative example uses the following composite waveform parameters:

[0139] First stage: Electroplating for 30 minutes using large waveform parameters;

[0140] Second stage: Electroplating for 30 minutes using medium waveform parameters;

[0141] Third stage: Electroplating for 90 minutes using small waveform parameters.

[0142] Figure 8 The images show cross-sectional views (200x magnification) of through holes with different thickness-to-diameter ratios after electroplating of the composite waveform. Test results show: TP: 64.53% for 20:1 thickness-to-diameter ratio; 70.29% for 15:1 thickness-to-diameter ratio; and 89.19% for 10:1 thickness-to-diameter ratio.

[0143] Comparative Example 6

[0144] The method of Example 1 is followed, except that the comparative example uses the following composite waveform parameters:

[0145] First stage: Electroplating for 90 minutes using medium waveform parameters;

[0146] Second stage: Electroplating for 30 minutes using large waveform parameters;

[0147] Third stage: Electroplating for 30 minutes using small waveform parameters.

[0148] Figure 9 The images show cross-sectional views (200x magnification) of through holes with different thickness-to-diameter ratios after electroplating of the composite waveform. Test results show: TP: 73.16% for 20:1 thickness-to-diameter ratio; 76.92% for 15:1 thickness-to-diameter ratio; and 93.90% for 10:1 thickness-to-diameter ratio.

[0149] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A pulse electroplating method for high aspect ratio PCB through-holes based on the time evolution law of deep plating capability, characterized in that: Includes the following steps: (1) Select at least two pulse electroplating waveforms with different forward and reverse current density ratios and forward and reverse time ratios, and conduct a single waveform electroplating experiment on the target PCB via, wherein the pulse parameters are set in a gradient decreasing manner; (2) Measure the plating thickness in the PCB through holes and the plating thickness on the board surface under different plating time conditions, and calculate the deep plating capability TP value respectively; (3) Based on the law of change of the deep plating capability TP value with electroplating time, determine the time interval of the deep plating capability advantage corresponding to each pulse electroplating waveform; (4) Match and combine different pulse electroplating waveforms according to the time interval of the deep plating capability advantage, and then electroplat the target PCB through hole.

2. The method according to claim 1, characterized in that: The pulse electroplating waveforms described in step (1) are at least three types, and the pulse parameters are set in a gradient decreasing manner; The thickness-to-diameter ratio of the PCB through-holes mentioned in step (1) is 10 to 20:1; In step (2), the electroplating time ranges from 30 to 150 min; The time interval for the advantage of deep plating capability mentioned in step (3) is the electroplating time interval during which the deep plating capability TP reaches its peak or maintains a stable growth.

3. A composite pulse electroplating method suitable for through-holes in high aspect ratio PCBs, characterized in that, Specifically, the process includes the following steps: electroplating the PCB vias using a three-stage composite pulse waveform; wherein... The first stage uses large waveform electroplating, and the electroplating time is 80 to 100 minutes. The second stage uses a medium waveform for electroplating, and the electroplating time is 20 to 40 minutes. The third stage uses small waveforms for electroplating, and the electroplating time is 20 to 40 minutes. The pulse parameters of the large, medium, and small waveforms are set in a gradient decreasing manner.

4. The method according to claim 3, characterized in that: The forward current density of the electroplating is 15 ASF; The specific parameters of the large waveform are as follows: the ratio of forward to reverse current density is 1:3.2, and the ratio of forward to reverse time is 200:10; The specific parameters of the waveform are as follows: the ratio of forward to reverse current density is 1:2.5, and the ratio of forward to reverse time is 160:8; The specific parameters of the small waveform are as follows: the ratio of forward to reverse current density is 1:2.0, and the ratio of forward to reverse time is 120:

6.

5. The method according to claim 3, characterized in that: The thickness-to-diameter ratio of the PCB through-hole is 10 to 20:

1.

6. The method according to claim 5, characterized in that: The thickness-to-diameter ratio of the PCB through-hole is 20:

1.

7. The method according to claim 3, characterized in that: The electroplating time for the first stage is 90 min, the electroplating time for the second stage is 30 min, and the electroplating time for the third stage is 30 min.

8. The application of the pulse electroplating method for high aspect ratio PCB through holes based on the time evolution law of deep plating capability as described in any one of claims 1 to 2, or the composite pulse electroplating method for high aspect ratio PCB through holes as described in claims 3 to 7, in PCB through hole electroplating.

9. The application according to claim 8, characterized in that: The thickness-to-diameter ratio of the PCB through-hole is 10 to 20:

1.

10. The application according to claim 9, characterized in that: The thickness-to-diameter ratio of the PCB through-hole is 20:1.

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