Reverse pulse plating is a technique used in printed circuit board (PCB) manufacturing to create high-quality, uniform metal deposits (finer grain size of the order less than 100nm) on the surface of a PCB. It is a variation of pulse plating, which is a type of electroplating process that involves applying a series of short electrical pulses to a substrate to deposit a layer of metal. However, in reverse pulse plating, the polarity of the electrical current is periodically reversed, creating a more efficient and controlled deposition process.
Numerous studies on pulsed current deposition date back to the 1960s and 70s but at that time the rectifiers were not yet able to generate very high and their prohibitive cost hampered the interest in this otherwise promising technique. Today the technology is mature and there are rectifiers on the market capable of supplying high currents with sufficiently short pulses with respect to the electrodeposition phenomena occurring at the electrode.
At the NetVia Group facility, the reverse pulse plating process begins with the application of a layer of resist material onto the surface of a copper-clad substrate. This resist material is then patterned using laser direct imaging to create the desired circuit pattern. The exposed copper is then etched away using an acid solution, leaving behind the circuit pattern. The PCB is then cleaned to remove any residual contaminants.
Next, the reverse pulse plating process begins. The PCB is submerged in an electrolytic solution containing metal ions of copper. An anode made of copper is also immersed in the solution. A cathode is then placed in contact with the PCB, and an electrical current is applied. The cathode is negatively charged, and the anode is positively charged, causing the metal ions to be attracted to the cathode and deposited onto the surface of the circuit board.
In reverse pulse plating, the polarity of the electrical current is periodically reversed. This reversal of polarity creates a more efficient and controlled deposition process, as it helps to prevent the formation of dendrites or tiny metal spikes that can grow from the surface of the PCB and cause short circuits. By periodically reversing the polarity of the current, the metal ions are deposited more evenly, creating a more uniform layer of metal.
Reverse pulse plating is particularly useful in the manufacturing of high-density interconnect (HDI) PCBs, which are used in advanced electronic devices such as smartphones and tablets. HDI printed circuit boards have a higher circuit density than traditional PCBs, which means that they require more precise and uniform metal deposition. Reverse pulse plating helps to ensure that the metal is deposited evenly and accurately, creating a high-quality PCB that can meet the demands of modern electronics. Pulse plating is becoming more advantageous because it leads to smoother and finer grain deposits along with reducing the variation of thickness from one part to the next. Plating speed and current efficiency are high while the raw material consumption is lower compared to traditional DC plating.
Reverse pulse plating is a powerful tool in the manufacturing of printed circuit boards here at the NetVia facility. It enables the precise and controlled deposition of metal onto the surface of a PCB, and the thickness of the deposits is extremely homogeneous over the entire surface, creating a high-quality product that meets the demands of modern electronics. By periodically reversing the polarity of the electrical current, reverse pulse plating helps to prevent the formation of dendrites and create a more uniform layer of metal. This makes it ideal for use in the production of HDI PCBs, circuit boards that require blind or buried vias, and high technology plated shut vias which are becoming increasingly important in the electronics industry. Not every PCB manufacturing facility has invested in this technology due to the cost and experience needed to implement it properly.