What Is PCB Electroplating Filling Process

The volume of electronic products is becoming more and more thin and short, and the direct stacking of vias on through-blind vias is a design method to obtain high-density interconnection. To do a good job of stacking holes, first of all, the flatness of the hole bottom should be done well. There are several production methods, and the electroplating hole filling process is one of the representative ones.

1. The advantages of electroplating and hole filling:

  (1) It is beneficial to design stack holes and on-disk holes;

  (2) Improve electrical performance and contribute to high frequency design;

  (3) Helps to dissipate heat;

  (4) The plug hole and electrical interconnection are completed in one step;

  (5) Blind holes are filled with electroplated copper, which has higher reliability and better conductivity than conductive glue.

  2. Physical influence parameters

  The physical parameters that need to be studied are: anode type, cathode and anode spacing, current density, agitation, temperature, rectifier and waveform, etc.

  (1) Anode type. When it comes to anode types, it is nothing more than soluble anodes and insoluble anodes. Soluble anodes are usually phosphorus-containing copper balls, which are easy to produce anode slime, pollute the plating solution, and affect the performance of the plating solution. Insoluble anode, good stability, no need for anode maintenance, no anode sludge, suitable for pulse or DC electroplating; but the consumption of additives is large.

  (2) Spacing between cathode and anode. The spacing design between the cathode and the anode in the electroplating via filling process is very important, and the design of different types of equipment is also different. No matter how it is designed, it should not violate Fara's first law.

  (3) Stir. There are many types of stirring, such as mechanical shaking, electric vibration, gas vibration, air stirring, jet flow, etc.

  For electroplating and hole filling, it is generally preferred to increase the jet design based on the configuration of the traditional copper cylinder. The number, spacing and angle of jets on the jet tube are all factors that have to be considered in the design of the copper cylinder, and a lot of tests are also required.

  (4) Current density and temperature. Low current density and low temperature can reduce the deposition rate of surface copper, while providing sufficient Cu2 and brightener into the hole. Under this condition, the hole filling ability is enhanced, but the plating efficiency is also reduced.

  (5) Rectifier. The rectifier is an important link in the electroplating process. At present, the research on electroplating and filling is mostly limited to full-board electroplating. If the pattern electroplating and filling are considered, the cathode area will become very small. At this time, high requirements are put forward for the output precision of the rectifier.

  The selection of the output precision of the rectifier should be determined according to the line of the product and the size of the via hole. The thinner the lines and the smaller the holes, the higher the accuracy requirements of the rectifier should be. Usually, it is advisable to choose a rectifier with an output accuracy within 5%.

  (6) Waveform. At present, from the waveform point of view, there are two types of electroplating and filling: pulse electroplating and DC electroplating. The traditional rectifier is used for DC electroplating and hole filling, which is easy to operate, but if the plate is thicker, it cannot be done. PPR rectifier is used for pulse electroplating and hole filling, which has many operation steps, but has strong processing ability for thicker in-process boards.