In the field of circuit board manufacturing, direct plating technology has always attracted much attention. However, when traditional processes are applied to thick boards, the Transmission Performance (TP value) is often lower than that of full-copper electroless copper processes due to non-conductive inner layers, with a gap of up to 15%. To overcome this challenge, MacDermid Alpha conducted in-depth research and found a solution. Through a series of experiments, it was found that the latest generation of graphite chemical—Shadow Plus—performs excellently in direct plating processes. Compared with traditional carbon-based chemicals, it has higher conductivity and finer particles, which can more effectively cover the inner layer surface and optimize current distribution.
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In the experiments, beaker tests were adopted to exclude equipment factors and focus on comparing chemical performance. The results showed that Shadow Plus chemicals are superior to earlier chemicals in terms of plating climbing rate, backlight coverage, initial plating time and time required to complete hole wall coverage. In particular, its initial copper deposition rate and hole wall full coverage time are significantly better than the first-generation graphite chemicals and carbon-based mixed chemicals. Observations by high-speed photography further confirmed this: Shadow Plus chemicals can complete hole wall coverage in just 40 seconds, while the first-generation takes 60 seconds and carbon-based chemicals take longer. Comprehensive various indicators, direct plating with Shadow Plus graphite chemicals can effectively improve the TP value of thick boards and make up for the shortcomings of traditional processes. This technology not only improves efficiency but also enhances reliability, providing a better metallization option for thick board circuit manufacturing.
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In the process of exploring high-reliability thick board plating solutions, MacDermid Alpha’s latest generation Shadow Plus chemicals are combined with pulse plating technology. To evaluate its performance, through-holes with a high aspect ratio of 15:1 were selected and tested on thick boards. Different from traditional DC plating, the rectifier of pulse plating generates reverse electric waves at a certain cycle of current output. This unique current waveform design changes the chemical properties of plating additives, especially the adsorption amount and migration rate of plating brighteners in the holes. This makes the current distribution in the holes of thick boards more uniform, thereby increasing the thickness of the entire hole wall.
Comparing the plating section diagrams of pulse plating chemicals and traditional DC plating chemicals on the same board, the advantage of pulse chemicals in the thickness of the inner hole wall plating is obvious. Due to the limitations of plating characteristics, the TP value of traditional DC plating may not exceed 80%, while pulse plating can effectively increase the copper thickness in the middle of the hole. The biggest advantage of MacDermid Alpha’s pulse plating chemicals is that they can increase the copper thickness in the middle of the hole. Compared with traditional DC plating, to plate the board to the same thickness, the current density may need to be reduced below 10 ASF, while pulse circuits can increase the current density above 10 ASF, achieving better TP values in the same plating time.
After calculating the economic benefits in cooperation with R&D units, it was found that although the rectifier for pulse plating is more expensive, the benefits it brings are also significant. The use of pulse plating can increase the TP value from 70% of DC plating to 100% or even higher. Under the same circuit area and copper ball cost, when pulse plating reaches 100 TP value, the copper consumption required for the hole copper thickness to reach 25μm is less, thus helping to save costs. The investment in pulse plating equipment can be recovered within a few months, and product quality is improved.
In addition, due to the improvement of TP value, the thickness of surface copper plating can also be reduced accordingly, and the overall output of pulse circuits can be increased by 40% in the same time. Combining direct plating with pulse plating can increase production capacity by at least 1.5 times in the same space. To verify the reliability of the combination of pulse plating and Shadow Plus chemicals, MacDermid Alpha conducted a number of reliability tests in cooperation with R&D units, including 22-layer ST test thick boards, and compared them with electroless copper. IST test results show that both 22-layer PTH thick boards and 6-layer microvia boards using the second-generation graphite Shadow Plus direct metallization process can pass 3,000 thermal cycle tests, fully demonstrating their excellent reliability.
As a professional solution provider deeply engaged in the PCB field, FUMAX closely follows the cutting-edge technological trends of the industry and has integrated leading process technologies such as MacDermid Alpha into its own product system to provide global customers with high-reliability and cost-effective PCB/PCBA solutions. Whether you need process optimization for high-end fine-line PCBs or support for high-aspect ratio thick board manufacturing, FUMAX can tailor solutions for you with rich industry experience and technical accumulation.
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