With the rapid development of surface mount technology, the future of printed circuit boards will inevitably move toward high-density packaging characterized by fine lines, small vias, and multiple layers. However, the copper plating process used to manufacture these advanced circuit boards will also face certain technical challenges. This article will explain the challenges of the process based on fundamental principles and explore potential solutions, with the hope of providing valuable insights to professionals in the PCB industry.<\/p>\n
With the rapid development of the semiconductor and computer industries, the manufacturing of printed circuit boards has become increasingly complex. We can use a \u201ccomplexity index\u201d to measure the difficulty of a circuit board. The formula for calculating this index is as follows:<\/p>\n
PCB Complexity Index = Number of PCB Layers \u00d7 Number of Traces Between Two Solder Pads \/ Distance Between Two Solder Pads (inches) \u00d7 Trace Width (mil)<\/strong><\/p>\n For example, a 16-layer board with a solder joint spacing of 0.1 inches, a trace width of 5 mils, and three traces between any two solder joints would have a complexity index of 96. Since the 1980s, the widespread adoption of surface-mount technology has driven the PCB industry toward the production of high-level multilayer boards, causing the complexity index to rise rapidly\u2014from around 20 for traditional PCBs to 100 or higher today.<\/p>\n First, let\u2019s look at the big picture. As for the surface of a circuit board, a large board typically measures approximately 24\u201d \u00d7 18\u201d. Achieving uniform plating thickness across both the center and the edges is no easy task. According to Faraday\u2019s law of electrolysis, the thickness of the plating is directly proportional to the applied current. Therefore, many factors influence current distribution, including the resistance of the solution, electrode polarization, the geometry of the workpiece, the distance between the anode and cathode, the magnitude of the applied current, and the mass transfer rate.<\/p>\n When the distribution of current on the electrode does not result in polarization or other interfering factors, it is referred to as the primary current distribution, which depends entirely on the geometry of the plating tank. When the distribution of current on the electrode does not result in polarization or other interfering factors, it is referred to as the primary current distribution, which depends entirely on the geometry of the plating tank. Whether the current distribution is uniform depends entirely on the design of the plating tank. If the plating tank is replaced by a conductor or insulator, the current distribution will be disrupted and will change.<\/p>\n To alter the current distribution, it is essential to focus on design concepts. For example, feasible methods include increasing the distance between the anode and cathode, enlarging the anode area, using insulating materials to alter the equipotential planes, employing auxiliary anodes to improve current distribution in low-current regions, and using auxiliary cathodes to disperse current in high-current regions.<\/p>\n The second aspect of current distribution is the secondary current distribution, which results from the primary current distribution being altered due to electrode polarization. Polarization occurs because electrochemical reactions near the electrode increase the resistance of the solution. To ensure the desired reaction proceeds smoothly, the applied voltage must be increased. Overpotential refers to the situation where ions near the electrode are consumed too rapidly as they participate in the electrode reaction, leading to overpotential. The total overpotential is the sum of the concentration overpotential and the activation overpotential, and it serves as an indicator of the degree of electrode polarization.<\/p>\n The distribution of the current is influenced by two factors: the resistance of the solution and the resistance resulting from polarization. The polarization parameter P is defined as follows:<\/p>\n P = R \/ Rp = \u03b1cFLj \/ RgTK<\/strong><\/p>\n Here, \u03b1c is the transfer coefficient, F is Faraday\u2019s constant, L is the anode-cathode distance, j is the average current density, Rg is the gas constant, T is the temperature, and K is the conductivity of the solution. If P <> 1, the current distribution tends toward a linear distribution, which depends entirely on the design of the plating tank.<\/p>\n Next, we will focus on micro-etching, particularly with regard to plated-through holes on circuit boards (PTH<\/a>). In recent years, the widespread adoption of surface-mount components has pushed printed circuit boards toward increasingly complex designs featuring fine lines, small vias, and multiple layers, presenting unprecedented challenges in drilling, resin removal, and copper plating. The issue of mass transfer within small vias poses a serious threat to the quality of through-hole plating (PTH).<\/p>\n Typically, the PTH manufacturing process begins with drilling, followed by the deposition of a layer of electroless copper inside the holes to enhance conductivity, and finally, an electroplating process to increase the thickness. However, drilling technology becomes increasingly complex for circuit boards with small hole diameters and high hole densities. Typically, these small holes have diameters of 0.1 mm or smaller, requiring a high-precision drilling process to ensure accurate hole placement and dimensions. Furthermore, the high density of small holes adds to the difficulty of the drilling process, as the distances between holes are very close, making misalignment likely.<\/p>\n Once drilling is complete, a layer of resin residue typically remains on the hole walls. This resin residue must be completely removed to ensure uniform copper plating on the hole walls during the subsequent chemical copper plating and electroplating processes. However, removing the resin residue is a complex process because it must be completely removed without compromising the quality of the hole walls.<\/p>\n Finally, the small holes on the circuit board must undergo an electroplating process to increase the thickness of the copper plating. This is also a complex process because the current distribution must be uniform to ensure an even copper layer both inside and outside the holes. At the same time, the holes are very close together, which can easily cause the current to concentrate in certain areas while becoming too diluted in others.<\/p>\n To address these challenges in circuit board manufacturing, manufacturers and engineers can take the following steps:<\/p>\n Overall, as high-density packaging for printed circuit boards continues to evolve, manufacturers must continually improve their processes and technologies to meet market demand. By investing in precision equipment, researching new materials, optimizing process control, and adopting advanced technologies, the printed circuit board manufacturing industry can overcome current challenges and embrace future trends.<\/p>\n [Note] This article is only a brief introduction; the actual manufacturing of printed circuit boards involves numerous complex factors and requires in-depth research and specialized knowledge. PCB manufacturers should take appropriate measures based on their specific needs and circumstances.<\/p>\n Further Reading<\/strong>\uff1a13 Rules for Laying Out Components on Printed Circuit Boards<\/a> \u00b7 34 Common IPC Standards for Printed Circuit Boards<\/a><\/p>","protected":false},"excerpt":{"rendered":" \u968f\u7740\u8868\u9762\u9ecf\u88c5\u6280\u672f\u7684\u84ec\u52c3\u53d1\u5c55\uff0c\u5370\u5237\u7535\u8def\u677f\u7684\u672a\u6765\u5fc5\u7136\u8d70\u5411\u7ec6\u7ebf\u3001\u5c0f\u5b54\u3001\u591a\u5c42\u4e4b\u9ad8\u5bc6\u5ea6\u5c01\u88c5\u578b\u6001\u3002\u7136\u800c\uff0c\u5236\u9020\u8fd9\u79cd\u9ad8\u5c42\u6b21\u7535\u8def […]<\/p>\n","protected":false},"author":1,"featured_media":10075,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"What Are the Challenges of Copper Plating on Multilayer PCBs? Methods for Controlling Primary and Secondary Current Distribution","description":"What are the challenges involved in the electroplating process for multilayer printed circuit boards? This article explains the key control factors\u2014such as primary and secondary current distribution and polarization parameters\u2014from both macro- and micro-etching perspectives. It provides directly applicable parameter values and operational guidelines."},"_slim_seo_primary_term_category":0,"_slim_seo_primary_term_post_tag":0,"footnotes":""},"categories":[406,26],"tags":[],"class_list":["post-2966","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-pcb-manufacturing","category-blog"],"_links":{"self":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts\/2966","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/comments?post=2966"}],"version-history":[{"count":4,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts\/2966\/revisions"}],"predecessor-version":[{"id":19508,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts\/2966\/revisions\/19508"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/media\/10075"}],"wp:attachment":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/media?parent=2966"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/categories?post=2966"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/tags?post=2966"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}From a macro perspective<\/h2>\n
Methods for Changing the Current Distribution Once<\/h3>\n
Secondary Current Distribution<\/h3>\n
Polarization Parameters<\/h3>\n
In terms of micro-etching<\/h2>\n
Drilling Technology<\/h3>\n
Removal of Resin Residue<\/h3>\n
Electroplating<\/h3>\n
How to Respond<\/h2>\n
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