Patent Application
20120094035
The present invention relates generally to a method for preparing plastic particles coated with metal, and particularly to a method for preparing plastic particles coated with metal having enhanced adhesion by special pre-processing of particles using microwave activation.
Owing to technological progresses and requirements for efficient, small-sized, and low-priced electronic products, flip-chip technology has become the main architecture of interconnection in packaging. The interconnection methods in flip-chip technology include metal interconnection, conductive paste interconnection, micro-bump bonding interconnection, anisotropic conductive film (ACF) interconnection, and conductive resin interconnection. Currently, metal interconnection and ACF interconnection are mainly adopted. In the trend of high reliability and fine spacing, the ACF used by flip-chip technology includes conductive particles of polymer plastic powder coated with nickel and gold. The advantage of the conductive particles is their compressibility at the plastic cores, thus increasing the contact areas between electrodes and the conductive particles. The present invention provides an electroless plating process for coating polymer microballs, which are key materials in valuable ACF. The present invention relates to a structure and a manufacturing method of the conductive particles (having a polymer core and a metal shell) in an ACF.
Surface pre-processes on plastic substrates are required in chemical or displacement plating. The steps of chemical plating (chemical nickel, chemical copper) on a substrate according to the prior art include: alkaline degreasing, roughening, reduction, surface adjustment, sensitizing, activating, chemical plating, and other plating. In particular, the pre-processes have to etch and roughen the surface of the plastic substrate to some extent, so that the surface becomes hydrophilic and porous, facilitating subsequent adhesion between the plastic substrate and metal-electroplated layer. The most mature chemical is the mixture of chromate and sulfuric acid. However, chromate produces chromium mists, which are carcinogenic and toxic, endangering the health of operators. Besides, if they are not cleaned or reduced, the activation of palladium-ion solution will be reduced.
Currently, most patents mainly relate to activation (or catalysis) and plating bath recipes in electroless plating processes for nonconductive substrates. Concerning non-chromate etching, U.S. Pat. No. 6,712,948 discloses a process for metallizing a plastic surface. According to its claim, the plastic surface is treated with a metal salt solution comprising at least one salt selected from the grout comprising a cobalt salt, a silver salt, a tin salt, and a lead salt. However, in its embodiment, mild etching solution such as sulfuric acid/aqueous peroxide, sulfuric acid/potassium permanganate, and other peroxides are mentioned. U.S. Pat. No. 5,762,777 discloses a process of directly electroplating onto a nonconductive substrate. Organic hydrocarbons or polymers are selected (such as PTH-102) to enhance adsorption of catalysts. Then, after catalyzing and accelerating, electroplating is performed. However, the etchants for plastic substrate include nitro group, nitroso ions, and their relevant compounds with concentrations no more than 40 wt %. Nevertheless, this type of chemicals has strong corrosiveness, and hence endangering the health of operators. Besides, if they are not cleaned or reduced, the activation of palladium-ion solution will be reduced.
According to the prior art, the pre-processes for the surfaces of plastic substrates include chemical etching, sensitizing, and activating. Then electroless plating is adopted for finishing the process. The sensitizing process is immersing a roughened substrate into a solution contains sensitizer; the surfaces of the substrate attracts a layer of metal ions prone to be oxidized. The activation processes the sensitized surface by means of a metal compound solution having catalytic capability. Activation means immersing the substrate with a reductant into a solution with an oxidant, such that the surface thereof adsorbs certain activation centers. Thereby, the critical step is activation. The processed surface of the substrate contains noble ions (generally silver or palladium). On the surface of the plastic particle, a certain amount of the activation centers is adsorbed thereon for catalyzing the subsequent chemical or displacement plating. Thereby, activation determines not only the property but also the quality of the plated layer.
In order to make the plated metal layer coat the plastic particle completely, the surfaces of the plastic particles have to adsorb more metal palladium uniformly. The sensitizer generally used is stannous chloride (SnCl2), which owns a reducing capability. SnCl2 is used as a reductant for reducing the ion Pd2+ to Pd0 and forming Sn/Pd colloid. However, because the physical adsorption of the Sn/Pd colloid on the surfaces of the plastic particles is inferior, the Sn/Pd colloid tends to aggregate, which retards the adsorption quantity of the Sn/Pd colloid on the surfaces of the plastic particles, and hence making the amount of the activation centers for surface catalysis insufficient. The insufficiency is disadvantageous for adsorption of the plated metal layer on the surfaces of the plastic particles. Thereby, the plated metal layer tends to appear rough and peel off, and its quality cannot be controlled with precision.
Accordingly, the present invention provides a method for preparing plastic particles coated with metal. According to the present invention, the adsorption of plated metal layer on the surfaces of the plastic particles is increased without chemical roughening or etching processes. Thereby, the problems described above can be solved.
An objective of the present invention is to provide a method for preparing plastic particles coated with metal, which adopts microwave to activate a plurality of tin/palladium colloidal particles adsorbed on the surface of a plastic particle for increasing the amount of adsorbed tin/palladium colloidal particles and hence increasing adsorption of the plated metal layer on the surface of the plastic particle. Thereby, roughness and peeling-off of the plated metal layer can be reduced, thus enhancing the quality of the plated layer.
Another objective of the present invention is to provide a method for preparing plastic particles coated with metal, which first mixes a plurality of plastic particles with a stannous chloride/hydrochloric acid solution, then mixes the plurality of plastic particles with a palladium chloride/hydrochloric acid solution such that a plurality of tin/palladium colloidal particles are adsorbed on the surfaces of the plastic particles. Then microwave is adopted to activate the plurality of tin/palladium colloidal particles adsorbed on the surfaces of the plurality of plastic particles for increasing the amount of adsorbed tin/palladium colloidal particles and hence increasing adsorption of the plated metal layer on the surfaces of the plastic particles. Thereby, roughness and peeling-off of the plated metal layer can be reduced, thus enhancing the quality of the plated layer.
The method for preparing plastic particles coated with metal according to the present invention comprises the following steps. First, mix a plurality of plastic particles with a tin/palladium solution to form a first mixed liquid. The plurality of plastic particles adsorb a plurality of tin/palladium colloid particles in the tin/palladium solution. Alternatively, first mix the plurality of plastic particles with a stannous chloride/hydrochloric acid solution such that the plurality of plastic particles adsorb a plurality of stannous ions in the stannous chloride/hydrochloric acid solution. Then mix the plurality of plastic particles adsorbing the plurality of stannous ions with a palladium chloride/hydrochloric acid solution and form the first mixed liquid, such that the plurality of plastic particles adsorb a plurality of palladium ions. Next, microwave the first mixed liquid so that the tin/palladium colloidal particles coat the plastic particles and thus forming first metal particles. Afterwards, mix the first metal particles with an electroless nickel solution and form a second mixed liquid. Metal nickel then coats the first metal particles and forming a plurality of second metal particles. Finally, filter the second mixed liquid and keep the second metal particles. Use microwave to activate the plurality of tin/palladium colloidal particles adsorbed on the surfaces of the plastic particles, and hence increasing the amount of adsorbed tin/palladium colloidal particles and increasing adsorption of the plated metal layer on the surfaces of the plastic particle. Thereby, roughness and peeling-off of the plated metal layer can be reduced, thus enhancing the quality of the plated layer.
In order to make the structure and characteristics as well as the effectiveness of the present invention to be further understood and recognized, the detailed description of the present invention is provided as follows along with embodiments and accompanying figures.
Next, step S2 is executed for microwaving the first mixed liquid such that the plurality of tin/palladium colloidal particles coat the plastic particles 10 and forming first metal particles. Take a certain quantity of first mixed liquid and pout into a microwave reactor. Set the microwave power to 30 to 300 W. Microwave the first mixed liquid in the microwave reactor for 3 to 30 minutes. Thereby, the surfaces of the plastic particles 10 will be coated with a tin/palladium colloid layer 20 having catalyzing capability. After the surfaces of the plastic particles are coated with the tin/palladium colloid layer 20, steps S22 to S26 are executed for filtering, rinsing, and baking the first metal particles. Afterwards, step S3 is executed for mixing the first metal particles with an electroless nickel solution and forming a second mixed liquid. The ratio in weight of the first metal particles to the electroless nickel solution can be 1/200 to 1/500. The first metal particles are coated with metal nickel and forming second metal particles. Oat a metal shell 30 at the outer side of the tin/palladium colloid layer 20, and execute step S32 for heating and stirring the second mixed liquid. The electroless nickel solution is heated and stirred. When the temperature reaches the reaction temperature, add the plastic particles 10 pre-processed by microwave activation. The plastic particles 10 are mixed with the electroless nickel solution with reaction time of 1 to 15 minutes at a stirring rate of 150 to 500 rpm and at a reaction temperature of 40 to 85° C. The mixing proportion is nickel sulfate 30 g/L, sodium hypophosphite 30 g/L, sodium lactate 40 g/L, glycine 10 g/L, and lead nitrate 1.5 mg/L. At last, step S4 is executed for filtering the second metal particles in the second mixed liquid. The methods for filtering the second metal particles include filtering by using an air exhauster or a centrifuge and then separating solids from liquids. Finally, vacuum dry or dry the second metal particles and give the metal particles coated with metal.
According to the present invention, the plastic particles 10 are coated with an extremely thin nickel layer on the surface of the tin/palladium colloid layer 20. Thereby, the outer side of the tin/palladium colloid layer 20 is covered by the metal shell 30 for forming a particle using polymer as the core and metal as the shell. The material of the plastic particles includes PMMA, epoxy resin, or polystyrene. The diameter of the plastic particles 10 can be between 100 nm to 10 μm. The shape of the plurality of plastic particles 10 can be true-ball, ellipsoid, or hollow-ball shaped. The metal shell 30 can contain nickel, old, or copper with a thickness around 30 to 300 nm. The plastic particles 10 and tin/palladium nanometer particles are activated by microwave. The adsorbed nanometer tin/palladium colloid can be the bridge between the plastic particles 10 and the metal shell 30.
Next, step S15 is executed for mixing the plurality of plastic particles 10 adsorbing the plurality of stannous ions with a palladium chloride/hydrochloric acid solution and forming a first mixed liquid, so that the plurality of plastic particles 10 adsorb a plurality of palladium ions. While preparing the palladium chloride/hydrochloric acid solution, palladium dichloride is mixed with concentrated hydrochloric acid at a ratio between 1/2 and 1/4. Use pure water to dilute for preparing a diluted palladium dichloride solution. The ratio of hydrochloric acid to pure water is 0.1%-2%. According to the present embodiment, 0.5 g of palladium dichloride is mixed and stirred with of concentrated hydrochloric acid. Use pure water to dilute to 500 ml for preparing the diluted palladium dichloride solution.
In order to reduce aggregation of the stannous ions adsorbed on the plastic particles 10, the solution with the plastic particle 10 adsorbing the stannous ions is filtered, rinsed, and baked for sensitizing. Then add the sensitized plastic particles 10 into 200 g of the diluted palladium dichloride solution, stir, and make them well mixed. Next, step S16 is executed for stirring the stannous chloride/hydrochloric acid solution at a fixed temperature. The ratio of the plastic particles 10 to the diluted palladium dichloride solution is 1:30 to 1:60. Afterwards, steps the S2 to S4 are executed for preparing second metal particles coated with metal.
To sum up, the method for preparing plastic particles coated with metal according to the present invention comprises the following steps. First, mix a plurality of plastic particles with a tin/palladium solution to form a first mixed liquid. The plurality of plastic particles adsorb a plurality of tin/palladium colloid particles in the tin/palladium solution. Alternatively, first mix the plurality of plastic particles with a stannous chloride/hydrochloric acid solution such that the plurality of plastic particles adsorb a plurality of stannous ions in the stannous chloride/hydrochloric acid solution. Then mix the plurality of plastic particles adsorbing the plurality of stannous ions with a palladium chloride/hydrochloric acid solution and form the first mixed liquid, such that the plurality of plastic particles adsorb a plurality of palladium ions. Next, microwave the first mixed liquid so that the tin/palladium colloidal particles coat the plastic particles and thus forming first metal particles. Afterwards, mix the first metal particles with an electroless nickel solution and form a second mixed liquid. Metal nickel then coats the first metal particles and forming a plurality of second metal particles. Finally, filter the second mixed liquid and keep the second metal particles. Use microwave to activate the plurality of tin/palladium colloidal particles adsorbed on the surfaces of the plastic particles, and hence increasing the amount of adsorbed tin/palladium colloidal particles and increasing adsorption of the plated metal layer on the surfaces of the plastic particle. Thereby, roughness and peeling-off of the plated metal layer can be reduced, thus enhancing the quality of the plated layer.
Accordingly, the present invention conforms to the legal requirements owing to its novelty, nonobviousness, and utility. However, the foregoing description is only embodiments of the present invention, not used to limit the scope and range of the present invention. Those equivalent changes or modifications made according to the shape, structure, feature, or spirit described in the claims of the present invention are included in the appended claims of the present invention.
