PCB Technical - Causes of uneven copper holes in high-frequency circuit boards

Question: What are the causes of uneven copper holes in high-frequency circuit boards(thick on one side and thin on the other)? What are the reasons for UNEVENPLATING (pulse plating is used)? How to improve? Does the amount of current have anything to do with the thickness of the plating and the width of the trace? What about the relationship?

Answer: I don't know whether your electroplating equipment uses a single rectifier or a bilateral control design. If it is a single rectifier control structure, the electroplating current distribution will be directly affected by the contact resistance. If the hole is deep and the uniformity of the liquid medicine flow is not ideal, the problem of uneven thickness of the unilateral hole will occur. In addition, I wonder whether you are discussing high-frequency circuit board full-board plating or line plating. If it is line plating, it can only be said that unevenness is inevitable. The difference lies in what level can be achieved in the full distance. Pulse electroplating belongs to AC electroplating, which is more sensitive to waveforms. If the contact condition is not ideal, unevenness of the left and right halves may also occur.

The electroplating uniformity of high-frequency circuit boards is divided into large areas and small areas. The unevenness of large areas has a higher possibility of improvement, but it is more difficult to improve local areas. Generally, when discussing the problem of uneven plating, the main consideration is the distribution of power lines. For electroplating, the so-called power line is an imaginary travel path formed by charged particles. The factors that affect the distribution of these imaginary routes include: anode configuration, cathode and anode distance high-frequency circuit board suspension mode, chemical solution stirring, circuit board swing, current density, gloss system type, shielding system design, etc.

For large areas, appropriate adjustments will help. But for small areas, especially for line electroplating, because the copper surface distribution is irregular, and the cathode configuration and design are fixed, the power line distribution will inevitably cause mutual repulsion. Uneven distribution. At present, most effective methods are improved by using a lower current density and proper gloss system. For other mechanical designs, please adjust the equipment manufacturers appropriately. There should be room for improvement.

The magnitude of the current is related to the plating area, which we call current density. The more uniform the current distribution, the better the electroplating quality, and the higher the current density is, the shorter the time for the same copper plating thickness. However, high current density is often accompanied by the problem of poor electrical uniformity. How to balance between productivity and quality is a problem you must think about. Generally speaking, if the line becomes thinner and the copper surface is unevenly distributed, then theoretically it means that the current density that can be used is lower.

When the early high frequency circuit board manufacturers faced the problem of plating uniformity, another more direct thinking was to increase the distance between the cathode and anode. This treatment can reduce the power line repellency to a relatively low level. Uniformity really helps. However, this treatment consumes more energy and is not an appropriate treatment method for pulse electroplating. For circuit electroplating, the dense circuit area will bear relatively uniform current, but the current distribution in the independent circuit area (sparse and uneven area) will be relatively poor. At this time, if possible, some false points should be added to the high-frequency circuit board. Disperse the current, otherwise the plating uniformity will inevitably become worse. The above information is the relevant information provided by ipcb and is for reference only.