TWI472593B - Lead - free conductive adhesive and its preparation method - Google Patents

Description

Lead-free conductive adhesive and preparation method thereof

The invention relates to a conductive adhesive and a preparation method thereof, in particular to a lead-free conductive adhesive and a preparation method thereof.

Compared with traditional coal-fired, gas-fired or nuclear power generation, solar cells use solar power to directly convert solar energy into electrical energy, so they are not accompanied by greenhouse gases such as carbon dioxide, and can reduce the dependence on fossil fuels to provide safety. Autonomous source of electricity. Generally, in the process of solar cell, an aluminum-containing conductive paste (abbreviated as aluminum glue) is coated on a germanium wafer and dried and sintered to form an aluminum-germanium layer for improving the energy of the solar cell. Conversion efficiency.

However, it is well known that aluminum powder is a water-repellent substance because aluminum itself is highly susceptible to violent oxidation reactions and releases hydrogen. The typical solar cell sintering process (Sintering Process) is extremely fast, the highest temperature is between 750-850 ° C, and the reaction time is only 2-10 seconds. Therefore, the aluminum ball particles in the aluminum rubber cannot be completely sintered, only the aluminum ball particles. Partially connected into an aluminum electrode, the conventional solar energy is sintered with aluminum rubber to form an aluminum electrode on the tantalum wafer. The aluminum ball particles lack a complete protective film on the surface, resulting in high heat in the hot water at 75 ° C. The reaction releases a hydrogen bubble that does not meet the boiling water application characteristics of more than 10 minutes.

Accordingly, it is an object of the present invention to provide a lead-free conductive paste which can improve the resistance to boiling of water and a method of preparing the same.

Therefore, the lead-free conductive paste of the present invention comprises, in an amount of 100% by weight based on the total weight of the lead-free conductive paste, 0.1 to 3% by weight of lead-free glass powder, 20% to 25% by weight of an organic vehicle, and an inorganic substance. An additive, and an aluminum powder having an equilibrium amount and a purity of 99.8% or more. Wherein, the inorganic additive comprises vanadium oxide in a weight percentage of 0.02-0.6 wt%, and the average particle diameter of vanadium oxide is 0.05-1.0 μm.

Another object of the present invention is to provide a method of preparing the above lead-free conductive paste.

Therefore, the method for preparing the lead-free conductive paste of the present invention comprises: (a) grinding the vanadium oxide of the inorganic additive to an average particle diameter of 0.05 to 1.0 μm; and (b) preparing the composition of the lead-free glass powder according to an appropriate ratio. Performing atmospheric melting to form a homogeneous glass melt, and obtaining a lead-free glass by a water quenching process, and then grinding to a fineness of 10 μm or less to become the lead-free glass powder; and (c) the inorganic additive, the lead-free glass powder, and the aluminum powder The mixture is uniformly dispersed in the organic medium, and the mixture is stirred and mixed in the mixing tank to form a colloid, and then the colloid is uniformly dispersed to a fineness of 25 μm or less by a three-roller to obtain the lead-free conductive paste.

The effect of the invention is that the lead-free conductive paste can be used in the step of fabricating the wafer electrode of the solar cell in a very short reaction time by using vanadium oxide as an inorganic additive instead of being mixed in the lead-free glass powder. A dense oxide protective film is formed to conform the wafer electrode to the needs of the boiled application characteristics.

A preferred embodiment of the lead-free conductive paste of the present invention comprises, according to the total weight of the lead-free conductive paste, 100% by weight, 0.1% by weight to 1% by weight of lead-free glass powder, and 20% by weight to 25% by weight of an organic vehicle. An inorganic additive and an aluminum powder having an equilibrium amount and a purity of 99.8% or more. Wherein, the inorganic additive comprises vanadium oxide (V ₂ O ₅ ) in a weight percentage of 0.02-0.6 wt%, and the average particle diameter (D ₅₀ ) of vanadium oxide is 0.05-1.0 μm. The aluminum powder has a weight percentage of 70 to 80% by weight, and the aluminum powder has an average particle diameter of 0.5 to 15 μm. Preferably, the aluminum powder has an average particle diameter of 3 to 8 μm.

The lead-free glass powder has an average particle diameter of 0.5 to 5.0 μm, and the lead-free glass powder comprises 0.2 to 4% by weight of aluminum oxide (Al ₂ O ₃ ) based on 100% by weight of the total weight of the lead-free glass powder. 2, 12% by weight of cerium oxide (SiO ₂ ), 10 to 16% by weight of zinc oxide (ZnO), and 6 to 12% by weight of boron trioxide (B ₂ O ₃ ) The weight percentage is 0.1 to 3 wt% of barium oxide (BaO), and the balance amount of antimony trioxide (Bi ₂ O ₃ ).

The organic vehicle includes an organic solvent, an organic binder, and an organic additive. Wherein, the organic solvent comprises 5 to 30% by weight of diethylene glycol monobutyl ether based on 100% by weight of the total weight of the organic vehicle (Butyl Carbitol, BC), 20~45wt% by weight of Butyl Carbitol Aceta (BCA), and a balanced amount of terpineol (Terpineol), the organic binder includes weight percentage 1 to 4 wt% of polyvinyl butyral resin, and 3 to 6 wt% of ethyl cellulose by weight, the organic additive is composed of a surfactant, a lubricant, a thickener, a leveling agent, a stabilizer And at least one of the antifoaming agents is selected.

The following describes the preparation method of the lead-free conductive paste. First, weigh the appropriate amount of vanadium oxide, place it in a ball mill, place it in a yttria ball that is stabilized in yttrium, perform ball milling at 450-600 rpm for 2 to 4 hours, and then place it in an oven at 120 °C. After drying for 2 to 4 hours, the vanadium oxide having an average particle diameter of 0.05 to 1.0 μm is obtained after being taken out and being crushed.

The lead-free glass powder is prepared by weighing 3 wt% of aluminum oxide, 10 wt% of cerium oxide, 11 wt% of zinc oxide, and 6 wt% of trioxide according to the total weight of the lead-free glass powder. Boron, 0.5wt% yttrium oxide, and a balanced amount of antimony trioxide, mixed in a mixer, poured into a white gold crucible and placed in a high temperature furnace at 1000 ° C, until all oxides are completely melted and then held warm After 10 minutes, it is ensured that a homogeneous glass melt is formed, and then the glass melt is poured into water for water quenching process to obtain lead-free glass, which is then ground into the lead-free glass powder to an average particle diameter of 0.5 to 5.0 μm.

The organic medium is prepared by weighing 25% by weight of diethylene glycol monobutyl ether and 25 wt% of diethylene glycol alone, based on 100% by weight of the total weight of the organic solvent plus the organic binder. Butyl ether acetate, an equilibrium amount of terpineol, 2% by weight of polyvinyl butyral resin, 4% by weight of ethyl cellulose, and stirred at 85 ° C in a mixing container to obtain a transparent, uniform A quality organic vehicle (without organic additives).

Then, according to the experimental design requirement, 0.02-0.6 wt% of vanadium oxide, 0.5-2 wt% of lead-free glass powder, and 21-24 wt% of organic medium are weighed according to the total weight of the lead-free conductive paste: 100 wt% (not Containing an organic additive), 0.5% by weight of zinc stearate, 0.5% by weight of a surfactant (zinc stearate and a surfactant are organic additives), and an aluminum powder having an equilibrium amount and a purity of 99.8% or more. After the above ingredients are uniformly stirred in the mixing tank for 40 minutes to form a colloid, the colloid is uniformly dispersed to a fineness of 25 μm or less by using a three-roller, thereby preparing various lead-free conductive pastes of various ratios as shown in Table 1 below. .

Different proportions of lead-free conductive adhesive were applied by screen printing on a 156 mm × 156 mm polycrystalline silicon wafer (the thickness of the tantalum sheet was 180-200 μm, which was coated with the front silver paste and the back silver paste), and dried at 200 ° C. Sintering is performed using an infrared high temperature furnace to complete a wafer electrode. In the infrared high temperature furnace, the highest temperature (Peak Temperature) is 800 °C.

The electrical properties of the wafer electrode were measured to conform to the quality specifications of the tube, and the electrode of the wafer was placed in water at 75 ° C for more than 10 minutes to conduct a boiling resistance test to see if it was blistering.

As shown in Table 1 on the following page, it can be seen from the results of the water resistance test that the addition of vanadium oxide significantly improves the boiling resistance of the wafer electrode, which is improved from less than 1 minute in the control group (without adding vanadium oxide) to more than 10 minutes. bubble. However, as a result of Table 1, it can be found that when the amount of vanadium oxide added is large (0.4 wt% or more), the degree of bowing of the wafer electrode is excessively large.

In addition, if the vanadium oxide is used as one of the components of the lead-free glass to produce a lead-free conductive paste, the lead-free conductive paste cannot pass the boiling resistance test, as described below:

First, a lead-free glass powder containing vanadium oxide (referred to as vanadium-free lead-free glass powder) is prepared, and 6 wt% of vanadium oxide and 2 wt% of aluminum oxide are weighed, based on 100 wt% of the total weight of the vanadium-containing lead-free glass powder. 7 wt% of cerium oxide, 4% by weight of zinc oxide, 4% by weight of boron trioxide, 0.3% by weight of cerium oxide, and a balance of antimony trioxide, mixed uniformly by a mixer, and poured The white gold crucible is placed in a high temperature furnace at 1000 ° C. After all the oxides are completely melted, the temperature is maintained for 10 minutes to ensure the formation of a homogeneous glass melt, and then the glass melt is poured into water for water quenching process to obtain vanadium-free lead-free. The glass is then ground into vanadium-free lead-free glass powder to an average particle size of 0.5 to 5.0 μm. The vanadium-free lead-free glass powder is mixed with the organic medium and the aluminum powder according to the same ratio as described above to obtain a lead-free conductive paste, and is coated on the polycrystalline silicon wafer to complete a wafer electrode, and the wafer electrode is placed in the same manner as described above. The water resistance test was carried out in water at 75 ° C for more than 10 minutes to observe whether or not there was foaming, and the results as shown in Table 2 were obtained.

From the results of Table 2, it is known that the lead-free conductive paste prepared by using vanadium oxide as a component of lead-free glass does not allow the wafer electrode to pass the boiling resistance test. Therefore, vanadium oxide needs to be used as an inorganic additive alone, so that the lead-free conductive paste can pass the boiling resistance test, and as one of the components of the lead-free glass, the effect of improving the boiling resistance of the wafer electrode cannot be achieved.

In summary, the present invention can form a dense electrode in a very short reaction time in the step of fabricating a wafer electrode of a solar cell by using vanadium oxide as an inorganic additive instead of being mixed in a lead-free glass powder. The oxide protective film makes the wafer electrode meet the needs of the water-resistant cooking characteristics, so that the object of the present invention can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent changes and modifications made by the patent application scope and patent specification content of the present invention, All remain within the scope of the invention patent.

Claims (8)

A lead-free conductive paste, comprising 100% by weight of the total weight of the lead-free conductive paste, comprising: a lead-free glass powder, the weight percentage is 0.1 to 3 wt%; an organic vehicle, the weight percentage is 20 to 25 wt%; an inorganic additive, It is a vanadium oxide having a weight percentage of 0.02 to 0.6 wt%, wherein the vanadium oxide has an average particle diameter of 0.05 to 1.0 μm; and an equilibrium amount of aluminum powder having a purity of 99.8% or more. The lead-free conductive paste according to claim 1, wherein the lead-free glass frit has an average particle diameter of 0.5 to 5.0 μm. The lead-free conductive paste of claim 1, wherein the lead-free glass frit comprises 0.2 to 4 wt% of aluminum oxide, and the weight percentage is 2 to 12 wt%, based on 100 wt% of the total weight of the lead-free glass frit. % of cerium oxide, 10 to 16% by weight of zinc oxide, 6 to 12% by weight of boron trioxide, 0.1 to 3% by weight of cerium oxide, and a balance of antimony trioxide. The lead-free conductive paste of claim 1, wherein the organic vehicle comprises an organic solvent, an organic binder, and an organic additive. The lead-free conductive paste according to claim 4, wherein the organic solvent comprises 5 to 30% by weight of diethylene glycol monobutyl ether in a weight percentage of 20% by weight based on the total weight of the organic vehicle. ~45wt% diethylene glycol monobutyl ether acetate, and a balanced amount of terpineol, the organic binder comprises 1~4wt% by weight of poly Vinyl butyral resin, and ethyl cellulose in a weight percentage of 3 to 6 wt%, the organic additive is selected from surfactants, lubricants, thickeners, leveling agents, stabilizers, and defoamers At least one. The lead-free conductive paste of claim 1, wherein the aluminum powder has a weight percentage of 70 to 80% by weight. The lead-free conductive paste according to claim 1, wherein the aluminum powder has an average particle diameter of 0.5 to 15 μm. The lead-free conductive paste according to claim 7, wherein the aluminum powder has an average particle diameter of 3 to 8 μm.