Foreword
The volume of electronic products has become thinner and shorter, and via holes (viaonHole or Viaonvia) have been designed to obtain high-density interconnects. To make holes, the bottom of the hole should be flat. There are several ways to make a typical flat hole surface. The Via Filling Plating process is a representative one.
The electroplating hole filling process not only can reduce the necessity of additional process development, but also is compatible with the current process equipment, which is favorable for obtaining good reliability.
Electroplated hole filling has the following advantages:
(1) It helps to design Stacked and via.on.Pad:
(2) Improve electrical performance and help high-frequency design;
(3) Helps to dissipate heat;
(4) Plug holes and electrical interconnections are completed in one step;
(5) Blind holes filled with electroplated copper, higher reliability, better conductive properties than conductive adhesive.
Electroplated hole filling is currently a hot topic for PCB manufacturers and drug distributors. Atotech, Shipley, Okuno, Ichterization and Ebara and other well-known pharmaceutical companies have all launched their own products to seize market share.
2 electroplating filling hole influence parameters
Although the electroplating and hole-filling process has been studied a lot, it is still a long time for the real mass production. One of the factors is that there are many factors affecting electroplating and filling holes. As shown in Figure 1, the influencing factors of electroplating and filling holes can be basically divided into three categories: chemical influencing factors, physical influencing factors and substrate influencing factors, among which chemical influencing factors can be further divided into inorganic components and organic additives. The following three factors will be briefly introduced.
2.1 Chemical Influencing Factors
2.1.1 Inorganic Chemical Composition
Inorganic chemical components include copper (Cu2+) ions, sulfuric acid, and chlorides.
(1) Copper sulfate. Copper sulfate is the main source of copper ions in the bath. Copper ions in the bath pass through the Coulomb equilibrium between the cathode and the anode, maintaining the same concentration. Normally the anode material and the plating material are the same, where copper is both an anode and an ion source. Of course, the anode can also be made of insoluble anodes, and Cu2+ can be added in the form of extra-trenches, such as pure copper corners, CuO powder, and CuCO3. However, it should be noted that air bubbles can easily be mixed in by means of extra-supply. In the low-current region, Cu2+ is in the critical state of supersaturation and is not easily precipitated. It is worth noting that increasing the copper ion concentration has a negative effect on the through hole dispersion capability.
(2) Sulfuric acid. Sulfuric acid is used to enhance the conductivity of the bath. Increasing the concentration of sulfuric acid can reduce the resistance of the bath and improve the efficiency of the plating.
However, if the concentration of sulfuric acid is increased during the filling of the hole plating, copper ion supplementation that affects the filling hole will cause poor hole filling. Low-sulfuric acid concentration system is generally used in filling-hole plating in order to obtain better filling effect.
(3) acid-copper ratio. The traditional high-acid low-copper (Cw+:Ccu2+=8~13) system is suitable for the through-hole plating, and the plating and filling hole should use the low acid and high copper (Cw+:Ccu2+=3~10) plating solution system. This is because in order to obtain a good hole filling effect, the plating rate in the microvia hole should be greater than the plating rate on the substrate surface. In this case, the solution formula is made of high acid as compared with the conventional plated through hole plating solution. Low-copper is changed to low-acid and high-copper, which guarantees the supply of copper ions in depressions without any worries.
(4) Chloride ion. The role of chloride ions is mainly to allow copper ions and metal copper to form a stable transition between the double layer of electronic transmission bridge.
In the electroplating process, the chloride ions at the anode can help to uniformly dissolve the phosphor bronze balls and form a uniform anode film on the anode surface. The synergistic action between the cathode and the inhibitor allows the stable deposition of copper ions, reducing the polarization and making the plating fine.
In addition, the conventional chloride ion analysis is performed on a UV-visible spectrophotometer. Since the electroplating filling solution has a stricter requirement on the concentration of chloride ions, and the copper sulfate plating solution is blue, the measurement on the spectrophotometer is very influential. Large, so should consider using automatic potentiometric analysis.
2, 1.2 organic additives
The use of organic additives can refine the plated copper grains, improve the dispersion ability, and make the coating bright and level. There are three types of additives in acid copper plating baths: Carrier, Leveler, and Brightener.
(1) Carriers. Carriers are polymeric polyalcohol compounds. The carrier agent is adsorbed on the surface of the cathode and acts together with chloride ions to suppress the plating rate, so that the difference in the high and low current regions is reduced (ie, the polarization resistance is increased), so that the electroplated copper can be uniformly deposited. The inhibitor can act as a wetting agent at the same time, reducing the surface tension at the interface (reducing the contact angle), allowing the bath to more easily enter the pores and increase the mass transfer effect. In filling-hole plating, the inhibitor can also deposit copper layer uniformly.
(2) Leveling agent. The leveling agent is usually a nitrogen-containing organic material, the main function is to adsorb in the high current density area (raised area or corner), so that the electroplating speed at this place slows down but does not affect the electroplating of the low current density area (depressed area). This flattened surface is an essential additive for electroplating. In general, the use of a high-copper, low-acid system for the electroplated hole filling will make the coating rough. Studies have shown that adding a leveling agent can effectively improve the problem of poor plating.
(3) brightener. Brighteners are usually sulphurous organics. The main role of electroplating in electroplating is to accelerate the reduction of copper ions at the cathode and form new copper plating nucleuses (reducing the surface diffusion deposition energy), so that the copper layer structure becomes more detailed. Another role of brighteners in hole filling electroplating is to help the rapid deposition of electroplated copper within the blind hole if there are more brightener distribution ratios in the holes.
For hole filling of laser blind holes, all three kinds of additives are used, and the amount of leveling agent must be properly increased, so that a higher current area on the plate surface, forming a situation in which the leveling agent competes with Cu2+, stops Copper is long and thick. Correspondingly, there is a chance that the bright spots in the micro-vias with more brighteners will be plated faster. This concept and practice is similar to the Demascene Copper Plating process for IC copper plating.
2.2 Physical influence parameters
The physical parameters that need to be studied are anode type, anode and cathode spacing, current density, agitation, temperature, rectifier, and waveform.
(1) Type of anode. When it comes to anode types, it is nothing more than soluble anodes and insoluble anodes. Soluble anode is usually a phosphorus-containing copper ball, easy to produce anode mud, contaminate the bath, affecting the performance of the bath. Insoluble anodes, also known as inert anodes, are typically composed of a titanium mesh coated with a mixed oxide of cerium and zirconium. Insoluble anodes, good stability, no need for anode maintenance, no anode slime production, pulse or DC plating are applicable; however, additive consumption is large.
(2) Cathode and anode spacing. The design of the gap between the cathode and the anode in the electroplating hole filling process is very important, and the design of different types of equipment is also not the same. However, it should be pointed out that no matter how you design, you should not violate Faraday's law.
(3) Stir. There are many types of stirring, such as mechanical swing, electric shock, air shock, air agitation, and Eductor.
For electroplated hole filling, it is generally preferred to add a jet design based on the configuration of a conventional copper cylinder. However, what is the bottom jet or the side jet, how the layout of the jet tube and the air mixing tube in the cylinder; how much the jet flow per hour; the distance between the jet tube and the cathode; if it is the side jet, the jet is in the anode Front or back; if the bottom jet is used, it will cause uneven agitation, and the bath will be weak and strong; the number, spacing, and angle of jets on the jet tube are all factors that must be taken into consideration when designing the copper cylinder. To conduct a large number of tests.
In addition, the ideal way is to connect the flowmeter to each jet tube so as to achieve the purpose of monitoring the flow. Since the jet flow is large and the solution is prone to heat, temperature control is also important.
(4) Current density and temperature. Low current density and low temperature can reduce the surface copper deposition rate while providing enough Cu2+ and brightener into the hole. Under this condition, the hole filling ability is enhanced, but at the same time, the plating efficiency is also reduced.
(5) Rectifier. Rectifiers are an important part of the electroplating process. At present, the research on electroplated hole filling is mostly limited to full-plate plating. If the electroplated hole filling is taken into consideration, the cathode area will become very small. At this time, high requirements are placed on the output accuracy of the rectifier.
The choice of rectifier output accuracy should be based on the product's line and via size. The finer the lines and the smaller the holes, the higher the accuracy of the rectifier. Rectifiers with an output accuracy of 5% or less are generally preferred. The high accuracy of the selected rectifier will increase the investment in the equipment.
Rectifier output cable wiring, the rectifier should be placed as far as possible on the edge of the plating tank, which can reduce the length of the output cable and reduce the pulse current rise time. The rectifier output cable specification shall be selected to meet the line voltage drop of the output cable within 0.6V when the maximum output current is 80%. The required cable cross-sectional area is usually calculated based on the current-carrying capacity of 2.5 A/mm2. If the cross-sectional area of ​​the cable is too small or the cable length is too long and the line pressure drop is too large, the output current may not reach the current value required for production.
For plating tanks with a groove width greater than 1.6m, double-sided feeding should be considered, and the length of the bilateral cables should be equal. In this way, it can be ensured that the bilateral current error is controlled within a certain range. A rectifier should be connected to both sides of each flying bar on the plating tank so that the currents on both sides of the plated part can be adjusted respectively.
(6) Waveforms. At present, from the waveform point of view, there are two kinds of electroplating filling holes: pulse plating and DC plating. Both of these electroplating methods have been studied. The DC electroplating filling hole adopts the traditional rectifier, which is convenient to operate. However, if the plate is thick, it will be powerless. Pulse plating is used for filling holes. The PPR rectifier has many operating steps, but it has strong processing capability for thicker boards.
2.3 The influence of the substrate
The influence of the substrate on the electroplating and filling holes can not be ignored. Generally, there are dielectric layer materials, hole shape, thickness-to-diameter ratio, chemical copper plating and other factors.
(1) Dielectric layer material. The dielectric layer material has an effect on the filling of the hole. Compared to glass fiber reinforced materials, non-glass reinforced materials are easier to fill. It is worth noting that the hole glass fiber protrusions have an adverse effect on the chemical copper. In this case, the difficulty in electroplating is to increase the adhesion of the electroless seed layer rather than the hole filling process itself.
In fact, electroplating and filling holes on glass fiber reinforced substrates have been applied to practical production.
(2) Hole shape.
(3) Thickness ratio. At present, the hole filling technology for different shapes and sizes of holes is very important to both manufacturers and developers. The hole filling capacity is greatly affected by the ratio of hole diameter to diameter. Relatively speaking, DC systems are used more commercially. In production, the pore size will be narrower, typically 80gm to 120gm in diameter, 40gm to 80gm in depth, and a thickness to diameter ratio of 1:1.
(4) Electroless copper plating. The thickness and uniformity of the electroless copper plating and the time after the electroless copper plating all affect the filling performance. Chemical copper is too thin or uneven in thickness and its hole filling effect is poor. In general, it is recommended to fill the hole when the chemical copper thickness is > 0.3um. In addition, the oxidation of chemical copper also has a negative effect on the pore filling effect.
3 Conclusion
The above are some of the most basic discussions of the influencing factors of electroplating and filling holes. Other factors have not been mentioned. If the plating solution is non-dyed, the non-dye liquid has good stability and is not likely to form harmful by-products. For example, the design of anode baffles is now focused on electroplating filling holes in the whole plate plating, and there are not many studies on the electroplated filling holes. When performing pattern plating, the baffle design is particularly important in order to ensure the uniformity of the plating, and the baffle design is often a patent of the plating equipment manufacturer. In addition, since pattern electroplating involves a dry film, the dry film has an influence on the performance of the plating solution. Therefore, a dissolution test should be performed on the dry film in order to determine the active carbon treatment period.
In any case, for the electroplating hole filling technology, the following conclusions have been accepted by everyone:
(1) Plating solution formulation. The use of high copper and low acid plating bath formulations, while controlling the proportion of additives, can ensure the coating quality and hole filling effect is good, effective monitoring of additives is very important;
(2) Current density and operating temperature. Low current density and low temperature can reduce the surface copper deposition rate while providing enough Cuz' and brightener into the hole. Under this condition, the hole filling ability is enhanced, but at the same time, the plating efficiency is also reduced.
(3) Equipment type. Electroplating holes are very demanding for equipment.
1 The use of soluble anodes - The dissolution of anodes may lead to side reactions of additives. 2 Insoluble anodes One-to-one water electrolysis produces a large amount of oxygen, which consumes organic additives excessively. 3 Stirring one by one should be stable and uniform. Inappropriate agitation not only causes a decrease in the filling ability but also leads to deterioration of the plating quality. 4 The cathode/anode spacing—The cathode/anode spacing and baffle design should be considered together. Otherwise, the distribution of power lines will be uneven.
(4) Monitoring of additive by-products. One of the manifestations of excessive accumulation of byproducts of organic additives is the decrease in the ability to fill holes. The Hull tank or CVS should be used to effectively control the additive content of the bath. When mass-produced, it is very important to effectively remove the degradation byproducts of additives.
(5) Through-hole and blind hole plating at the same time, the plating depth of the through hole will be affected.
In short, the best use of equipment, chemicals, additives and operating parameters will be the key to successful plating.
In the clinical medical experiments usinghuman venous blood as specimensome take the serum from the specimen as the experimental object.The blood collection tubes suitable for this type of medical tests are called serum blood collection tube.
color guide blood collection tubes,collection tubes for blood,tubes for blood collection,blood collection tubes color code
Yong Yue Medical Technology(Kunshan) Co.,Ltd , https://www.yongyuetube.com