Issue link: https://iconnect007.uberflip.com/i/1104607
78 PCB007 MAGAZINE I APRIL 2019 plating equipment. The numbers inside the cells reflect the aspect ratios. The table repre- sents the capability of various electrolytic cop- per formulations on the market. Each electro- lytic copper recipe has its own characteristic abilities with regards to aspect ratio. The leading-edge electrolytic formulation for microvia filling (Figure 5) has the following characteristics: • Plated with a current density of up to 2.5 A • Creates a ductility of 25% • Tensile strength of 35 kNm² • Dimple of less than 5 µm; plating time <40 minutes • 13 µm copper thickness on surface; at the same time, filling a 100*89 µm microvia completely Through-hole Filling With Copper The through-hole filling of holes with copper in mass production has its roots in 2005. The introduction of X-plating or bridge plating was the beginning. The bridging technology was developed to fill a through-hole completely with copper while avoiding inclusions. Such a completely filled through-hole does have many advantages for the design of electronic PCBs, such as thermal conductivity and signal integ- rity in high-frequency boards. A filled through-hole may be realized in dif- ferent ways. It may be plugged by a paste or filled by an electrolytic copper plating process. For larger hole sizes (i.e., diameter >500 µm), the plugging by a thermally conductive paste is the main process used. For smaller hole sizes (i.e., diameter <500 µm, feasible aspect ratio AR >0.5 and <5.0), the copper filling using the bridge plating technology shows many ad- vantages compared to paste plugging. First, the bridge plating technology needs fewer manufacturing steps compared to paste plug- ging (Figure 6). This has a significant benefit for the production cost. Figure 5: Copper-filled microvia cross-section plated with a leading-edge copper electrolyte. Figure 6: Plugging paste versus copper plating through-hole filling.