plate surface of the circuit board, usually a board the size of the board is approximately 24 "* 18", to the central and edge coating thickness uniformity is no easy task, according to the Faraday¡¯s law of electrolysis, the coating thickness is proportional to the applied current, assuming that the density of the coating as a certain value, the distribution of coating thickness is the cathode current distribution, affecting many of the current distribution factors, including the resistance of the solution, the polarization of the electrodes, plated pieces of the geometric shape of the anode and cathode distance, plus the current size, mass transfer rapid rate, in the following sections we will discuss the impact when the current distribution on the electrode polarization or other interference factors called current distribution depends entirely on the plated slot geometry When a certain voltage is applied to the two electrodes, each point also certain of the voltage is present in the plating bath, and its size is the range between the two electrode voltage, because of the highly conductive metal electrodes, we can assume that each point of the surface of the electrode voltage to equal Similarly, in the plating bath may also find some of the imaginary plane having an equal potential, generally said, come close to the position of the electrode, such as the ground plane and the electrode shape is very similar, but its shape gradually decreased as the distance to the electrodes increase and change, Figure description of one that the distribution of the condition of the ground plane, the more intensive local current density distribution in the equipotential surface, otherwise smaller. learned by the electric field theory, and so the potential of the plane and the stress The planes are perpendicular to each other, while the electrode itself is equipotential plane, so a certain point of the current flow into or out of the electrode will be with the point where the plane is perpendicular to each other. i.e. instructions distribution relationship of the ground plane and the current flows if the equipotential plane is certain the entire conductor to replace or potential surface stress of the plane on an insulator alternative would not affect its electric field. Conversely, if such as bit-plane is no substitute for cutting off the entire farm will be equal to the degree of interference, the current distribution will change as electrodes and electrode will be the same as the current distribution of A and C as an example, A and BB, mainly due to the the BB plane happens to coincide with the equipotential surface, thus will not affect the electric field, assuming that the A and C slightly mobile, its off-center position, such as the distribution of the bit line and the original are very different impact modifiers because the electrode position of the electric field so that the current The distribution also change.

(A) 1. Change a current distribution method

By said farm basic theory that, once the current distribution is entirely dependent on the geometry of the plating tank, which is also the distance of the anode and cathode, the size, shape will affect the current distribution on the circuit board board its edge most other planes than intensive distribution, it is thicker coating and the central part of the thin To improve this phenomenon must be stressed that the concept of the design, such as increasing the anode and cathode distance, increasing the anode and the area, the use the insulation of shielding material to change the bit planes, auxiliary anode to improve the current distribution of the low current area, dispersed auxiliary cathode current high current area are feasible.

(A) 2. Secondary current distribution

Since the electrode is polarized to change a current distribution in this case, the resultant current is referred to as a secondary current distribution, first, the concept of polarization must be simple descriptions In simple terms, the polarization electrode electrochemical reaction occurs in the vicinity of increasing the resistance of the solution could successfully generate To make the desired reaction applied voltage must be increased this way, will generate additional heat and power consumption electrode voltage level dilute potential difference due to polarization effects, both of the difference is called the voltage in the vicinity of the cathode, the ions participate in the electrode reaction, consume too fast too late supplementary, this time caused by over-voltage, said To make the concentration over-voltage, ion passed some energy barrier to reach the electrode are required to participate in the reaction voltage is called activation voltage, while the total over-voltage is the concentration over-voltage and activated the sum of the voltage, is used to measurement indicators of the degree of polarization of the electrode. inversely proportional to the distance between the current size and the anode and cathode, the electric intraoperative role of representing an increase of the distance of the anode and cathode of the distance double since such effect known as the characteristic length, secondary The current more or less will be able to reduce the current uneven phenomenon.

(A) 3. Polarization parameters

Actual subject to the following two factors swayed by the foregoing basic theory learned current electric field distribution force, respectively, for the solution resistance and polarization resistance and ALKIRE once the polarization The parameter P made the following definitions.

P = R / Rp = acFLj / RgTK (2) wherein ac is the migration coefficient, F is the Faraday constant, L is the anode and cathode distance, j is the average current density, Rg is a gas constant, T is the temperature, K is the conductivity of the solution. if P << 1, on behalf of the polarization effect far exceeding the electric field effect, the current tends to secondary current distribution will be very uniform. if P >> 1, the current tends to primary current distribution depends entirely on the geometry of the plating tank, they additives on the board the macroscopic current distribution force are nothing to get uniform distribution of current shield or auxiliary cathode.

(B) microetch

Here for board plated through hole (PTH) in terms of the past five years, the large number of surface-mount components adopted by the board tend to thin lines, small holes, and more layer of the difficulty level, and thus in the drilling, desmear, copper plating are facing unprecedented challenges, for example, a 0.3 inch thick multilayer drilling 15mils through hole, guillotine aspect ratio up to 20 : 1, so orifice like a capillary having a considerable degree of surface tension, according to theoretical calculations require at least square pressure 0.093psi additional liquid can smoothly pass through a fine double the depth of the hole, the traditional blow stirring method has been unable to meet this requirement. plating tank is bound to make a special design. (B) 1. tertiary current distribution

In the through-hole and its vicinity, There are many factors affecting the current distribution, including the geometry of the plating tank, the plating bath is conductive, the rapid rate of mass transfer, copper ion concentration, etc. Current intricate affect its distribution is called tertiary current distribution, and in this most worth mentioning is the problem of mass transfer within the aperture Xun. night we know, in the aspect ratio high apertures, internal solution through the not easily affected by many factors , plus the rate of the ion bridal veil than ion consumed slower, so the diffusion layer is formed near the hole wall and away from the region of the hole wall of the room. diffusion layer will affect the rate of plating, if desired to increase the plating rate must increase impressed current, but the current is increased coating quality will gradually deteriorate when the current rises to a certain level, the coating was rough, loose unable to accept the current at this time is called the limiting current density, in order to Jlim = nFDCb / ¡Ó (3) wherein n is the number of electrons, F is the Farah constant, Cb is the thickness of the diffusion layer. Generally, if the applied current density to maintain the limit current density, if kept limit electrical Han density is less than 25%, will be obtained a good quality plating if managed improve the limiting current density will also increase the plating rate by the formula (3) can be seen to improve the limiting current density, the method comprising increasing the concentration of copper ions, increase the diffusion constant, and to reduce the thickness of the diffusion layer. elevated temperatures also increase the diffusion constant of effect, while the pulse plating technology uses to reduce the thickness of the diffusion layer has a considerable effectiveness. Basically, the pulse plating is a through different waveforms of the current or voltage of the metal adhered to the substrate plating technique, the waveform can be broadly divided into three categories, respectively, for square wave, sine wave and triangular wave. addition, special needs for the various properties also performances by the three basic waveform shape of the waveform, if we adopt the direct current for impressed current

(B) 3. Use of special mixing method to improve the holes in the plating rate, the metal ion generating electrode reaction must be replenished quickly, usually in two ways, through diffusion, First, by means of convection, the former is by no hole of the copper ion concentration to the hole wall in areas with low movement, the latter by the rapid flow of the bath so that the hole in the fresh bath inflow hole bridal veil consumption of copper ions, when the holes capillarity is very significant, the diffusion layer has a certain thickness diffusion for some hampered by the hole inside and outside convection is good, not only can reduce the thickness of the diffusion layer can also increase the rate of plating , to use the high current electroplating way of, As for what kind of mixing method to enhance the convection There are two possible ways:

(1) impact spray method, is directly vertically ejected through hole of the high-pressure nozzle when the playing of the bath using a pump, and its advantages is to increase hole quality pass rapid rate, but Ordering of the nozzle aperture, the ejection direction, and are to make a special design, thus increasing the device production and management costs.

(2) one-way pressure difference method, its principle is based on the circuit board plating tank is divided into two regions, and you want to be on tight. Then these two regions to produce a pump pressure difference, so the bath will have no choice but was forced from the small hole through the advantages of this method is to exempt high speed nozzle design trouble but the drawback is unable to achieve the goal of mass production.

(B) plating tank design guidelines plated holes are too many factors involved, so that the plating tank design is quite difficult, but kessler and alkire some basic rules as a basis for the design I Reference First, they define two basic parameters N and E, N represents the average current parameter, E represents a current distribution force parameters to the physical sense, the resistance N = solution resistance / mass transfer fast arising

(4) E = solution resistance / polarization resistance

(5) If the value of N is large, on behalf of the current tends to the primary current distribution, relatively uneven, if the value of N is small, there are shown tends to limit mass transfer fast, i.e., plating deterioration of the quality, when E << 1, the polarization effect of the role of the resistor is greater than the solution the current tends secondary current distribution will be very uniform, if the E >> 1 the current distribution uniformity deteriorated, such as N and E at the same time consider summarized in the following two criteria:

(1) E <1 while the panel and a hole to obtain a uniform current distribution.

(2) N> = 64E can be reached between the two relations of the uniformity of the distribution and coating quality of the hole current balance. Micro-structure aspects of

C) high-level multi-layer printed circuit board often used as a military use, its reliability must also objects do not pay attention to the need by the U.S. military specifications such as drift tin or temperature the test cycle, the physical properties of the coating, such as ductility, tensile strength can often determine the success or failure of the test, gloss and additives play a very important role to improve the physical properties of the coating, the basic reaction mechanisms in this special simple descriptions.

(C) 1. Plating the basic reaction institutions metal ion plating with at the cathode substrate is usually divided in two steps, the first step is the solution of metal ions to the cathode movement by an electric double layer i.e. charge migration reaction, a second step is ion reaches the electrode combined with each other or with the original grain Results, together this step is called crystallization, due to the metal ions in the solution is often the number of water molecules ­³ wrong ion is formed, the water molecules must be removed before the metal slowly ions and electrons knot together, because the surface of the substrate lattice planes of varying shapes, several of Curved planar and curved edge voids and holes, like so wrong ions to the water charge transfer reaction first plane ladder curved than directly into the location of the hole-shaped columns can save energy, As regards the formation of crystals.

(C) 2. The role of the additives in the plating so that the surface roughness is reduced or Sik the ductility of the coating often require additives or gloss agents have proposed the projections of the surface smoothness of the reaction mechanism of a section can be adsorbed more gloss agents, thus increasing the resistance, since the current is always toward the low resistance portion, so the current can flow smoothly into the coating recessed part of coarse reduced and because the majority of gloss agents to organic Bockris also proposed a theory described adsorbed on the condition of the electrode surface when the electrode itself with excess negative or positive charge, water molecules will be rendered electrically bipolar morphology of falling or rising, i.e., increase and adsorption between electrodes force this way reduce the force of the adsorption of organic molecules, whereas, if the electrode itself without charge, the rising and falling trend of water molecules cancel one another, the adsorption force is reduced thereby enhancing the adsorption of organic molecules, whereby the basic theory will be available for The different nature of the coating study its place of the additives.

(C) 3. Pulse plating affect on the micro-structure of the pulse wave plating most significant of the function is to change its way to the physical properties of the coating microstructure, many data show, in the The ductility of the coating adhesion than traditional DC pulse current is far greater, and the roughness is reduced through which institutions produce such effects? has still not very clear.

Conclusion

This paper to analyze the basic theory to macroscopic, microscopic and micro-structure of three points of view on the multi-layer printed circuit board copper plating process, the conclusions are summarized as follows: (1) on the circuit board panels, the current distribution is mainly determined by the geometrical shape of the plating tank, such as anode distance arrangement, size, etc., luster agents or additives has little influence on the current distribution. To change the current distribution uneven enables auxiliary devices such as shielding or auxiliary cathode.

(2) on the circuit board through-hole current distribution and coating properties, mainly affected by the resistance of the solution, electrode polarization and mass transfer fast complex factors To get quality distribution and uniform coating, it is bound to emphasize the design concept, for example, the application of special mixing method, the use of pulse plating technology.

(3) Additive or gloss agents may change the physical properties of the coating, such as ductility, tensile strength, etc., but if the amount of excess may also cause pollution of organic matter on the coating quality, in addition also increased management of inconvenience. pulse plating method to improve the physical properties of the coating is worth the effort to study. circuit board industry booming production ranks third in the world in the production of high-level board, however there are still a lot of neck yet to break through the future trends of the copper plating process is the use of specially designed plating tank and coupled with the quest for improvement in the chemical, in order to improve the technical level of a new bright vision.