Method for forming soldering layer of fiber arrays

#1. Field of the Invention

#The present invention relates to a surface treating method and, more particularly, to a surface treating method suitable for forming a solder layer on the substrate surface of fiber arrays.

#2. Description of Related Art

#FIG. 1 is a top view of the bases having grooves on a silicon wafer of the present invention;

#FIG. 2 is a cross-section view of the silicon wafer used in the method of the present invention.

#The method for forming the grooves of the substrate of the present invention is not limited. Preferably, the grooves of the substrate are formed through dicing, cutting or etching (with reference of FIG. 1). In most cases, bases 110 with a plurality of grooves are formed on a silicon wafer substrate 100 first for mass production. After the formation of metal layer is achieved, the substrate 100 was then diced or cut into fiber array base units 200 (please refer to FIG. 2d). The surface of the groove of the substrate of the present invention is immersed in a solution of 1 g/L (6.4×10−3M) of SnCl2 for 5 to 10 minutes with gently stirring. Through the immersing, Sn2+ ions are adsorbed on the surface of the substrate without any physical abrasions. In most cases, the solution of 1 g/L of SnCl2 is prepared by adding 300 ml of crystalline SnCl2 into 300 g of 18 Ω water and stirring for around 3 minutes to form a clear, colorless SnCl2 solution. This SnCl2 solution is stored under N2 atmosphere before use. The sensitized substrate surface is subsequently immersed into water twice and then subjecting to an activating solution, which contains 6 g/L (3.4×10−2 M) of PdCl2 and 0.02 M HCl, for 1 min with gently stirring.

#For adjusting the sensitization to an optimal condition, the concentration effect of PdCl2 and HCl is considered and studied. The studied results show that high concentration of PdCl2 is beneficial to the sensitization. In contrast, the high concentration of HCl does not result in similar effect. Even though less concentration of HCl does better, the concentration of the HCl should still be kept in sufficient concentration to dissolve PdCl2. Generally speaking, the concentration of Pd of PdCl2 ranging from 2 g/L to 10 g/L can be used. Preferably, the concentration of Pd of PdCl2 is 6 g/L. The other things to be kept in mind is that the Sn2+ ions absorbed on the surface are easily oxidized and deadsorbed when the treated substrate is transferred to PdCl2 solution since Sn2+ competes against the reduction of Pd2+. On the other hand, high-quality nickel-plating layer can be formed when PdCl2 is in a concentration of 6 g/L and HCl is in a concentration of 0.02 to 0.05 M. But only partial nickel layer are formed when HCl is 0.1 M. Therefore, the concentration of HCl should be kept as low as possible but sufficient to dissolve PdCl2.

#Suitable commercial electroless nickel solution used here usually contains two parts, i.e. Solution A and Solution B. They are mixed just before use. Solution A provides Ni2+ ions. Solution A here is solutions containing Ni2+ ions such as nickel chloride, nickel sulfide, and nickel acetate. Solution B is a solution, which provides hypophosphite group, such as sodium hypophosphite. In one example of the nickel plating solution used here, Solution A is a solution containing nickel sulfide and Solution B is a solution containing sodium hypophosphite, sodium hydroxide and acetic acid. The nickel-plating solution is prepared by mixing the Solution A, the Solution B and water together. The adequate pH of the solution ranges from 4.5 to 5.2. The nickel-containing solution used in the metallization process is prepared by mixing Solution A, Solution B and 18 MΩ of water in a ratio of 1:3:16. The solution is then filtrated with Halgne Media-Plus filtering unit (Nylon with 0.2 μm pore size) after it is made. The pH of this solution is about 4.85, and the temperature for plating said nickel layer is about 85° C. The controlling of the temperature here is very important because nickel will plate on the container wall at high temperature spontaneously. On the contrary, the plating rate will dramatically decreases as the plating is achieved at low temperature. The temperature gradient from the top to the bottom of the container is required to be above 1 to 2° C. The spontaneous plating occurs when the gradient is above 10° C. In most cases, the spontaneous plating of nickel will cause rapid accumulation of nickel and production of hydrogen gas. Furthermore, the bubble of the hydrogen gas in the solution will adhere to the substrate surface and prevent the deposition of the nickel layer plating. For controlling the temperature well, a container installed with nickel-containing solution is put into a larger container installed with water at the bottom and equipped a stirring bar. Then the large container is mounted on a fluoroware cage. The water of the water bath surrounding the container installed with nickel containing solution is used to precisely control the temperature of solution. Consequently, the spontaneous plating seldom occurs within 6 hours.