Controllable sintering silver paste and preparation method thereof

Abstract

The invention discloses controllable sintered silver paste and a preparation method thereof, and belongs to the technical field of electronic manufacturing. The controllable sintering silver paste is obtained by grinding a mixture comprising the following components in parts by weight: 58-46 parts of silver powder; 2-14 parts by weight of a silver sintering precursor; 35 to 40 parts by weight of a waterborne polyurethane emulsion; and 0-5 parts by weight of an auxiliary agent. According to the controllable sintering silver paste, a water-based system is adopted, polyurethane is used as dispersion resin, and controllable sintering is achieved through pressure application.

Description

TECHNICAL FIELD

[0001] The application relates to controllable sintering silver paste and a preparation method thereof, and belongs to the technical field of electronic manufacturing. BACKGROUND

[0002] The sintering silver paste is usually used for the connection of electronic components (such as chips, substrates, integrated circuits and the like) to achieve the purposes of electric conduction and heat conduction, and therefore, the sintering silver paste is a basic material in the field of electronic manufacturing, and the composition mainly comprises silver powder, organic solvent, resin, additive and the like. The sintering silver paste is applied between the surfaces of the components to be connected to form a sandwich, and with the drying and sintering process, the effective connection of the components is formed. In the use process of the sintering silver paste, the viscosity and the like of the silver paste change, which is not conducive to construction on the one hand and changes the amount of the silver paste on the other hand, thereby changing the silver paste in the sandwich of the components and reducing the qualified rate of the components. SUMMARY

[0003] In order to solve the problem that the sintering paste is prone to extrusion in the prior art of sintering silver paste, the application provides a controllable sintering silver paste technical scheme of a water-based system, polyurethane is used as a dispersion resin, and pressure application is used to realize controllable sintering.

[0004] The application adopts the following technical scheme: According to the first aspect of the application, a controllable sintering silver paste is provided, and the controllable sintering silver paste is obtained by grinding a mixture containing the following components by weight: Silver powder 58-46 parts by weight; Silver sintering precursor 2-14 parts by weight; Water-based polyurethane emulsion 35-40 parts by weight; Auxiliary agent 0-5 parts by weight.

[0005] The controllable sintering silver paste has the following properties: Optionally, in an air atmosphere, the sintering strength of the controllable sintering silver paste increases with the increase of the sintering pressure. The controllable sintering silver paste between two components can be sintered under heat pressure of 1-20 MPa in an air atmosphere, and the two components form a strong mechanical force connection; when the heat pressure is less than 1 MPa or no pressure is applied, the sintered product of the controllable sintering silver paste between the two components is easy to be crushed, and the two components cannot form a strong mechanical force connection.

[0006] Optionally, the sintering condition of the controllable sintering silver paste comprises that the sintering pressure is 1-20 MPa.

[0007] Optionally, the size of the silver powder is 3-8 μm.

[0008] Optionally, the silver powder is at least one of flaky silver powder and spherical silver powder.

[0009] Optionally, the silver sintering precursor is selected from at least one of silver oxide, silver carbonate, silver oxalate, silver formate, silver citrate.

[0010] Optionally, the water-based polyurethane emulsion is a water-based polyether polyurethane emulsion.

[0011] Optionally, the auxiliary agent includes an antifoaming agent, a wetting dispersant.

[0012] According to the second aspect of the present application, a preparation method of the controllable sintering silver paste is provided, including the following steps: providing a water-based polyurethane emulsion; grinding and mixing a mixture containing silver powder, a silver sintering precursor, an auxiliary agent, and the water-based polyurethane emulsion to obtain the controllable sintering silver paste.

[0013] Optionally, the water-based polyurethane emulsion is prepared by the following steps: a mixture containing a polyether diol, a hydrophilic polyether diol, a prepolymer of diisocyanate, and a catalyst is heated to react (reacted to the theoretical value of NCO) under stirring, and the reaction product is cooled to below 60°C, then water is added to the reaction product, and the water-based polyurethane emulsion is obtained by stirring. Adding water to the reaction product and stirring vigorously is intended to disperse, and the viscosity of the polymer before dispersion increases with the decrease of temperature, which is not conducive to dispersion. Cooling and adding water is to reduce the reaction speed of the remaining NCO and water, so as to avoid the phenomenon that the fast crosslinking groups cannot be dispersed. Through experiments, it is found that adding water below 60°C can disperse smoothly.

[0014] Optionally, the polyether diol is selected from polypropylene glycol with an average molecular weight of 400-3000.

[0015] Optionally, the hydrophilic polyether diol is selected from polyethylene glycol with an average molecular weight of 400-2000.

[0016] Optionally, the prepolymer further includes a chain extender, and the chain extender is selected from at least one of ethylene glycol, propylene glycol, and butanediol.

[0017] Optionally, the diisocyanate is selected from isophorone diisocyanate and / or 4,4'-dicyclohexylmethane diisocyanate, and the NCO / OH value is 1.0-1.3. The NCO / OH value can control the ratio of alcohol and isocyanate, and the use ratio of the polyether diol, the hydrophilic polyether diol, and the diisocyanate can be selected as needed and controlled by the NCO / OH value.

[0018] Optionally, the catalyst is selected from organic bismuth.

[0019] Optionally, the amount of the catalyst is 0.06wt%-0.1wt% of the prepolymer.

[0020] Optionally, the heating reaction condition comprises: the reaction temperature is 80-90°C, and the reaction time is 2-4 h.

[0021] Optionally, the solid content of the aqueous polyurethane emulsion is 30-50%.

[0022] Optionally, the prepolymer is obtained by mixing alcohol raw materials containing polyether glycol and hydrophilic polyether glycol after being heated to melt, vacuum dehydration and cooled to below 60°C with diisocyanate. The conditions for heating to melt and vacuum dehydration can be adjusted as needed, for example, heating to melt at 100°C and vacuum dehydration for 1 h.

[0023] The beneficial effects of the present application include: The controllable sintering silver paste provided by the present application is a water-based system sintering silver paste. After coating, the solvent water of the silver paste dries faster than the silver paste using high-boiling organic solvents in the prior art. After coating into a thin layer, the water evaporates quickly, the coating layer has almost no flowability, and there is almost no problem of sintering paste extrusion when the two connecting pieces are extruded. The silver paste uses polyurethane as a dispersion resin, which makes the silver paste have high viscosity. At the same time, due to the presence of hydrophobic segments and hydrophilic segments, the micron silver powder, silver sintering precursor, etc. can form a relatively stable system, thereby being able to position the connecting pieces. With the application of a certain pressure and heating, the polyurethane is squeezed out and decomposed, and the silver powder is sintered. Under the condition of low pressure, the silver powder is wrapped by polyurethane, which hinders the sintering of silver migration, and cannot form an effective sintered body, which presents an easy-to-crush silver body that can be removed from the coating surface. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Schematic diagram of sintering test connecting pieces.

[0025] BRIEF DESCRIPTION OF DRAWINGS 101 represents a copper sheet; 102 represents a silver paste; 103 represents a chip; and 104 represents a glass sheet. DETAILED DESCRIPTION

[0026] The present application will be described in detail below in conjunction with examples, but the present application is not limited to these examples.

[0027] Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels.

[0028] Unless otherwise specified, the test methods all use conventional methods, and the instrument settings all use the recommended settings of the manufacturer.

[0029] The sintering test method in the examples of the present application is as follows: For example, Figure 1As shown, a copper sheet (approximately 2mm thick) is sanded, cleaned with alcohol, and coated with silver paste to a thickness of 50-100 micrometers. After about 5 minutes, a 1mm x 1mm chip is placed on top of the silver paste, followed by a glass plate. The copper sheet and glass plate are then clamped together with clips and placed in a muffle furnace at 180℃ for 30 minutes. The silver paste layer between the chip and the copper sheet is under pressure, while other parts of the silver paste are not. After sintering, the side of the sintered chip is pushed with a shear head, and the force (N / mm) is recorded using a digital push-pull force meter. 2 As sintering strength.

[0030] Example 1 (1) Preparation of waterborne polyurethane In a three-necked flask equipped with a stirrer and thermometer, 21 g of polypropylene glycol (average molecular weight Mn3000) and 9 g of polyethylene glycol (average molecular weight Mn2000) were added. The oil bath was set to 100°C, and the mixture was heated until melted. Vacuum dehydration was carried out for 1 hour, and the mixture was cooled to below 60°C. 2.8 g of isophorone diisocyanate was added, with an NCO / OH ratio of 1.10. After the temperature of the system stabilized, about 0.04 g of organic bismuth catalyst was added. The oil bath temperature was set to 80°C, and the mixture was stirred for 3 hours. The temperature was then lowered to below 60°C, and 46 g of water was added. The mixture was stirred vigorously to obtain a white, viscous, water-based polyurethane emulsion PU-1 with a solid content of 41%.

[0031] (2) Preparation of controllable sintering silver paste Take 0.3g of micron-sized silver flake powder, 0.06g of silver oxide, and 0.27g of waterborne polyurethane emulsion PU-1, grind and mix them evenly to obtain silver paste.

[0032] The prepared silver paste was subjected to sintering tests, and the results were as follows: using one clip to cover four chips, the average sintering strength was 10 N / mm. 2 In areas not covered by chips, the silver paste can be easily peeled off into powder.

[0033] Example 2 (1) Preparation of waterborne polyurethane In a three-necked flask equipped with a stirrer and thermometer, 21 g of polypropylene glycol (average molecular weight Mn3000) and 9 g of polyethylene glycol (average molecular weight Mn2000) were added. The oil bath was set to 100°C, and the mixture was heated until melted. Vacuum dehydration was carried out for 1 hour, and the mixture was cooled to below 60°C. Then, 0.12 g of 1,3-butanediol and 3.4 g of isophorone diisocyanate were added. The NCO / OH ratio was 1.20. After the temperature of the system stabilized, about 0.04 g of organic bismuth catalyst was added. The oil bath temperature was set to 80°C, and the mixture was stirred for 3 hours. The temperature was then lowered to below 60°C, and 60.5 g of water was added. The mixture was stirred vigorously to obtain a white, viscous, water-based polyurethane emulsion PU-2 with a solid content of 35.6%.

[0034] (2) Preparation of controllable sintering silver paste Take 0.39g of micron-sized silver sphere powder, 0.09g of silver oxide, and 0.19g of waterborne polyurethane emulsion PU-2, grind and mix them evenly to obtain silver paste.

[0035] The prepared silver paste was subjected to sintering tests, and the results were as follows: using two clips to cover four chips, the average sintering strength was 17 N / mm². 2 In areas not covered by chips, the silver paste can be easily peeled off into powder.

[0036] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A controllable sintering silver paste, characterized in that, The controllable sintering silver paste is obtained by grinding a mixture comprising the following components in parts by weight: 58-46 parts by weight of silver powder; 2-14 parts by weight of silver sintering precursor; 35-40 parts by weight of waterborne polyurethane emulsion; Additives: 0-5 parts by weight.

2. The controllable sintering silver paste according to claim 1, characterized in that, The controllable sintering silver paste has the following properties: In an air atmosphere, the sintering strength of the controllable sintering silver paste increases with increasing sintering pressure.

3. The controllable sintering silver paste according to claim 1, characterized in that, The sintering conditions for the controllable sintering silver paste include: a sintering pressure of 1-20 MPa.

4. The controllable sintering silver paste according to claim 1, characterized in that, The silver powder has a size of 3-8 μm; Preferably, the silver powder is at least one of flake silver powder and spherical silver powder.

5. The controllable sintering silver paste according to claim 1, characterized in that, The silver sintering precursor is selected from at least one of silver oxide, silver carbonate, silver oxalate, silver formate, and silver citrate.

6. The controllable sintering silver paste according to claim 1, characterized in that, The aqueous polyurethane emulsion is an aqueous polyether-type polyurethane emulsion.

7. The controllable sintering silver paste according to claim 1, characterized in that, The additives include defoamers and wetting and dispersing agents.

8. The method for preparing controllable sintering silver paste according to any one of claims 1 to 7, characterized in that, Includes the following steps: Provides waterborne polyurethane emulsions; The mixture containing silver powder, silver sintering precursor, additives and the aqueous polyurethane emulsion is ground and mixed to obtain the controllable sintering silver paste.

9. The preparation method according to claim 8, characterized in that, The aqueous polyurethane emulsion was prepared using the following steps: A mixture of a prepolymer containing polyether diol, hydrophilic polyether diol, diisocyanate and catalyst is heated and reacted under stirring conditions. After the reaction product is cooled to below 60°C, water is added to the reaction product and the mixture is stirred vigorously to obtain the waterborne polyurethane emulsion.

10. The preparation method according to claim 9, characterized in that, The polyether diol is selected from polypropylene glycol, with an average molecular weight of 400-3000. Preferably, the hydrophilic polyether diol is selected from polyethylene glycol, with an average molecular weight of 400-2000; Preferably, the prepolymer further includes a chain extender selected from at least one of ethylene glycol, propylene glycol, and butanediol; Preferably, the diisocyanate is selected from isophorone diisocyanate and / or 4,4'-dicyclohexylmethane diisocyanate, with an NCO / OH value of 1.0-1.3; Preferably, the catalyst is selected from organic bismuth; Preferably, the amount of catalyst used is 0.06wt%-0.1wt% of the prepolymer; Preferably, the conditions for the heating reaction include: a reaction temperature of 80-90°C and a reaction time of 2-4 h; Preferably, the solid content of the waterborne polyurethane emulsion is 30-50%; Preferably, the prepolymer is obtained by mixing an alcohol raw material containing polyether diol and hydrophilic polyether diol with diisocyanate after heating to melt, vacuum dehydration and cooling to below 60°C.

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