Electroplating process --- multi-layer circuit board (PCB)
With the vigorous development of surface adhesion technology, the future trend of printed circuit boards will inevitably move towards thin lines, small holes, multi-layer high-density packaging type.However, the manufacture of such high-level circuit board copper plating process will also face some technology 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 number of circuit boards * the number of solder lines between the two / two solder joints (inches) Width (mil) For example:
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A 16-layer board, the solder joint spacing of 0.1 inches, the wire width of 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 of complex indicators, from the traditional circuit board 20 or so rose to the current 100 or higher, in this update, product evolution process, of course, can not help but 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.
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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 Each point of the voltage are equal to the same reason, in the bath can also be found in some of the imaginary plane with equal potential, in general, to the location near the electrode, equipotential plane and electrode shape Is similar to the shape of the electrode with the distance gradually increases, the figure shows that the equipotential plane distribution of the situation, in the equipotential surface distribution is more dense local current density is large, otherwise smaller. It is known that the plane of the equipotential and the plane of its stress are perpendicular to each other, and the electrode itself belongs to the equipotential plane, so the current flowing into or out of the electrode must be perpendicular to the plane in which the point is located. The relationship between the equipotential plane and the current flow distribution. If the equipotential plane is replaced by a constant conductor or the plane of the stress plane of the equipotential plane is replaced by an insulator, it will not affect its electric field. On the other hand, if the equipotential is replaced by any The current distribution will be changed, with an example, the A and BB as the electrode and the A and C as the electrode will get the same current distribution , The main reason is that the BB plane coincides with the equipotential surface, and thus 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 bit line will be very large Different because of electricity Modifiers influence the position of the electric field so that the current distribution has also produced a change.