Plating process----Multilayer pcb
With the vigorous development of SMT, the future trend of pcb will inevitably move towards thin lines, small holes, multilayer high-density packaging type. However, the manufacture of such high-level circuit board copper plating process will also face some technical bottlenecks. In recent years with the rapid development of the semiconductor and computer industry, the production of printed circuit boards are increasingly complex, the circuit board complex program pointer = the layers of circuit boards * the number of solder lines between the two / two solder joints (inches) Width (mil) For example:
A 16-layer board, the 0.1 inches solder joint spacing, the wire width is 5mils, two welding points between the three wires is the complexity of the index of 96, since the 1980s, the surface of the popular technology driven circuit board industry towards the high-level Multi-layer board forward, so that the rapid rise in complex indicators, from the traditional circuit board 20 rose to the current 100 or higher, in this update, product evolution process, of course, inevitably encounter some technical bottlenecks Copper plating process, for example, I try to giant, micro and microstructure of three aspects to explore its basic principles and to seek response strategies.
In terms of the board surface, the size of a board is usually about 24 "* 18", to make the central and edge coating thickness is not easy, according to Faraday electrolysis law, the thickness of the coating which is proportional to the applied current. Assuming that the density of the coating is a certain value, the thickness distribution of the coating is the distribution of the cathode current. Many of the factors that affect the current distribution include the resistance in the solution, the polarization of the electrode, the geometry of the plating, The distance, the magnitude of the applied current, the rate of mass transfer, etc., we will discuss the effects in the following sections, respectively, when the current distribution on the electrode does not produce polarization or other interference factors in the case of a current distribution that depends entirely on The geometrical shape of the plating tank, when a certain voltage is applied to the two electrodes, the plating bath at every point there is a certain voltage exists, the size between the two electrode voltage, because the metal electrode conductivity is very strong, we can assume that the electrode surface The voltage of each point is equal to the same, in the bath can also find some of the imaginary plane with equal potential, in general, to the location near the electrode, the equipotential plane and the electrode shape is very similar but its shape with the And the distance between the electrode is gradually increased, Figure 1 shows the situation of the equipotential plane distribution, the density of the equipotential surface distribution is relatively dense, and vice versa. By the electric field theory, the equipotential plane And the plane of their stress is perpendicular to each other, and the electrode itself belongs to the equipotential plane, so the current flow into or out of the electrode must be a point with the point where the plane perpendicular to each other. Figure 2 shows the equipotential plane and current flow distribution If the equipotential plane is replaced by a constant conductor or the plane of the stress applied to the equipotential plane is an insulator, it will not affect its electric field. On the other hand, if the equipotential surface is cut by any substitute, the entire electric field Will be subject to the same degree of interference, the current distribution will also change to an example, with A and BB as the electrode and the A and C as the electrode will get the same current distribution, the main reason is the BB plane just The equipotential surface coincides with the original, and it does not affect the electric field. Assuming that the A and C of Figure 1 are moved slightly and deviated from the center position, the distribution of the equipotential lines will be very different from that of the original Affecting the electric field makes the current distribution also changed.