Ultrathin metal welding layer preparation method based on distributed interval coating and silver soldering paste

Abstract

The invention relates to an ultra-thin metal welding layer preparation method based on distributed interval coating and silver soldering paste. The ultra-thin metal welding layer preparation method comprises the following steps that S1, silk-screen printing is conducted, specifically, the to-be-welded surface of first base metal is coated with the silver soldering paste through a distributed interval silk-screen template; s2, pre-curing treatment is conducted, specifically, preheating is conducted for a period of time within the pre-curing temperature range, so that the silver soldering paste is preliminarily shaped; s3, base material assembling is conducted, specifically, the first base material coated with the silver soldering paste is covered with the second base material, and certain pressure is applied; and S4, brazing forming is conducted, specifically, under the protective atmosphere, heat preservation is conducted for a period of time within the melting temperature range of the silver soldering paste, and an ultrathin welding layer with the thickness not larger than 12 micrometers and the porosity smaller than 0.1% is formed. The invention further discloses the silver soldering paste used for the preparation method. The method is simple and convenient to use, and the welding quality is ensured.

Description

Technical Field

[0001] This application relates to a method for preparing an ultrathin metal solder layer based on distributed spacing coating and a silver solder paste, which is mainly applicable to scenarios requiring ultrathin solder layers (thickness ≤20μm) in electronic packaging, semiconductor chip mounting and high-density interconnect (HDI) device manufacturing. Background Technology

[0002] With the rapid development of electronic technology, the performance requirements for soldering materials are becoming increasingly stringent. Chip mounting requires solder layer thickness controlled within 10-50μm, necessitating high-precision printing technology. Currently, the fabrication of ultra-thin solder layers faces two major technical bottlenecks: 1. Uneven solder extrusion: When traditional pre-coated paste is pressed against the base material, if the flow of the organic solvent inside the paste is uneven before it evaporates, dense bubble clusters will be formed. After cooling, micron-level gaps will be generated, resulting in an increase in the effective solder layer thickness (usually >50μm) and a decrease in soldering reliability. 2. Thickness control limit: Although the traditional flat extrusion method can achieve 50um non-uniform coating, it cannot achieve the 12um uniformity threshold of the solder layer for high-precision electronic packaging applications.

[0003] 3. Traditional screen printing is prone to thickness fluctuations (±10μm) due to powder agglomeration or sagging. Its coarse particles or pores result in low density of the coating surface, reducing the connection strength after welding. Summary of the Invention

[0004] The first technical problem addressed by this application is to overcome the shortcomings of the prior art mentioned in points 1 and 2 above, by providing a "Distributed Intermittent Coating (DIC)" method. This method achieves this by designing a screen template with a specific geometric pattern. Pre-coating stage: Apply silver solder paste only to the coating area, leaving uncoated areas spaced out; Brazing stage: The molten solder spreads autonomously into the uncoated area, reducing the final weld thickness and eliminating bubble defects.

[0005] The second technical problem solved by this application is to address the shortcomings of the prior art mentioned in point 3 above, and to provide a silver solder paste for a method of preparing an ultrathin metal solder layer.

[0006] The technical solution adopted by this application to solve the first technical problem mentioned above includes: a method for preparing an ultrathin metal welding layer based on distributed interval coating, characterized by including the following steps: S1 screen printing: Applying silver solder paste to the surface of the first base material to be soldered using a distributed, spaced screen template; The distributed spaced wire mesh template consists of a coating area for applying silver solder paste arranged at uniform intervals and a non-coating area that cannot be coated with silver solder paste. S2 Pre-curing treatment: Preheat within the pre-curing temperature range (60℃-90℃ in special cases) for a period of time (1-3 minutes) to allow the silver solder paste to initially set; S3 Base Material Assembly: Cover the first base material coated with silver solder paste with the second base material and apply a certain pressure; S4 Brazing Forming: Under a protective atmosphere, the silver solder paste is held at a temperature and pressure within its melting temperature range (meaning the pressure maintained in step S3) for a period of time. The molten silver solder paste flows and fills the uncoated areas, forming an ultra-thin solder layer with a thickness of no more than 12 μm and a porosity of <0.1%. The S4 brazing forming step involves holding the temperature and pressure at 850±10℃ for 8-12 minutes under an argon protective atmosphere, allowing the molten solder to flow and fill the uncoated area, forming an ultra-thin brazing layer with a thickness of 10.1±0.3μm and a porosity of <0.06%.

[0007] The pre-curing temperature is 60℃-90℃; the pressure in step S3 is 0.5-20MPa.

[0008] Both the coated and uncoated areas are fan-shaped or triangular, and the coated and uncoated areas are arranged circumferentially around the same vertex to form a circle or polygon.

[0009] The distributed spaced wire mesh template consists of 12 sectors, of which 6 sectors are coating areas with uniformly arranged wire mesh, and the other 6 sectors are uncoated areas.

[0010] The distributed spaced wire mesh template has a wire mesh thickness of 25 micrometers, and the amount of silver solder paste applied in a single coating area accounts for 70-85% of the coating area capacity.

[0011] The silver solder paste is composed of the following raw materials in the following mass percentages: metal powder accounts for 80-95% of the total mass of the silver solder paste; binder accounts for 5-20% of the total mass of the silver solder paste; wherein, the metal powder has a particle size ≤15 micrometers, and the metal powder is divided into three groups according to particle size: the first group is coarse metal powder, with a particle size of 5 micrometers ≤15 micrometers, and coarse metal powder accounts for 70-75% of the total mass of the metal powder; the second group is fine metal powder, with a particle size of 0.5 micrometers ≤5 micrometers, and fine metal powder accounts for 15-25% of the total mass of the metal powder; the third group is nano-particle metal powder, with a particle size of 50 nanometers ≤200 nanometers, and nano-particle metal powder accounts for 5-10% of the total mass of the metal powder.

[0012] The technical solution adopted by this application to solve the second technical problem mentioned above is as follows: a silver solder paste for the preparation method of the above-mentioned ultrathin metal solder layer, composed of the following raw materials in mass percentage: metal powder accounts for 80-95% of the total mass of the silver solder paste; binder accounts for 5-20% of the total mass of the silver solder paste; wherein, the particle size of the metal powder is ≤15 micrometers, and the metal powder is divided into three groups according to the particle size: the first group is coarse metal powder, with a particle size of 5 micrometers ≤ 15 micrometers, and the coarse metal powder accounts for 70-75% of the total mass of the metal powder; the second group is fine metal powder, with a particle size of 0.5 micrometers ≤ 5 micrometers, and the fine metal powder accounts for 15-25% of the total mass of the metal powder; the third group is nano-particle metal powder, with a particle size of 50 nanometers ≤ 200 nanometers, and the nano-particle metal powder accounts for 5-10% of the total mass of the metal powder. The metal powder used in this application is designed with multi-scale composite particles to control the proportion of coarse, fine, and nano particles, avoiding the "arch bridge effect" caused by a single particle size and ensuring that the solder layer is free of cracks after printing.

[0013] The adhesive is composed of the following raw materials by mass percentage: resin accounts for 5%-10% of the total mass of the adhesive, and organic solvent accounts for 95%-90% of the total mass of the adhesive.

[0014] As a preferred embodiment, the metal powder accounts for 92%-94% of the total mass of the silver solder paste, and the binder accounts for 8%-6% of the total mass of the silver solder paste.

[0015] The metal powder is composed of copper and silver in a mass ratio of 72:28.

[0016] As a preferred embodiment, the adhesive is composed of the following raw materials in weight percentages: resin accounts for 6%-8% of the total weight of the adhesive, and organic solvent accounts for 94%-92% of the total weight of the adhesive.

[0017] The method for preparing the silver solder paste described in this application includes the following steps: S5 Weigh out the resin and organic solvent according to the specified ratio; S6 involves adding resin and organic solvent to the same container, heating to 75℃-90℃, and stirring until completely melted to form an adhesive; S7 adhesive should be cooled to room temperature (20℃-25℃) and stored in a sealed bag at room temperature for later use. S8 weighs the binder and metal powder according to the ratio, pours them into the solder paste mixer, stirs for 5 minutes, and then vacuum stirs for 10 minutes to fully mix the metal powder and binder, thus obtaining a silver solder paste for screen printing.

[0018] Compared with the prior art, this application has the following advantages and effects: the method is simple, easy to use, and ensures welding quality. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a distributed spacer wire mesh template according to this application.

[0020] Figure 2 This is a schematic diagram of the solder flow and filling process of this application, wherein... Figure 2 In this context, 'a' represents the initial coating state, 'b' represents the molten spreading state, and 'c' represents the weld layer.

[0021] Figure 3 This is a schematic diagram of another structure of the distributed spacer wire mesh template of this application.

[0022] Figure 4 for Figure 3 The diagram shows another distributed spacer screen template solder flow filling process, in which... Figure 4 In this context, 'a' represents the initial coating state, 'b' represents the molten spreading state, and 'c' represents the weld layer.

[0023] In the diagram: 1-Coated area; 11-Screen mesh; 2-Uncoated area. Detailed Implementation

[0024] The present application will be further described in detail below with reference to specific embodiments and accompanying drawings. The following embodiments are explanations of the present application, but the present application is not limited to the following embodiments.

[0025] The first embodiment of this application is described in [reference]. Figure 1 , Figure 2 This application discloses a method for preparing an ultrathin metal welding layer based on distributed interval coating, characterized by the following steps: S1 screen printing: Applying silver solder paste to the surface of the first base material to be soldered using a distributed, spaced screen template; The distributed spaced wire mesh template consists of several sectors on a circular base. Some sectors are coating areas 1 (meaning that silver solder paste is allowed to be applied to the base material from the corresponding position of the sector), and the remaining sectors are non-coating areas 2 (meaning that silver solder paste is not allowed to be applied to the base material from the corresponding position of the sector). Coating areas 1 and non-coating areas 2 are arranged alternately. In this specific application, there are 12 equally divided sectors, each sector having a central angle of 30°. Six sectors are coating areas 1, in which uniformly arranged wire mesh 11 is provided, and the other six sectors are non-coating areas 2. S2 Pre-curing treatment: Preheat within the pre-curing temperature range for 1-3 minutes to allow the silver solder paste to initially set; S3 Base Material Assembly: Cover the first base material coated with silver solder paste with the second base material and apply a pressure of 0.5-20MPa; S4 Brazing Forming: Under an argon protective atmosphere, maintain the temperature within the range of 850±10℃ for 8-12 minutes to allow the silver solder paste to melt and spread (flow filling) to the surrounding non-coated area 2, forming an ultra-thin solder layer with a thickness of no more than 12μm and a porosity of <0.1%.

[0026] The distributed spaced screen template described in this application has a screen thickness of 25 micrometers, and the amount of silver solder paste coated in a single coating area accounts for 70-85% of the coating area capacity (it is difficult to completely fill the coating area during screen printing, but it can be relatively accurate and ensures that the height of the solder layer during printing is equal to the screen thickness).

[0027] This application also includes a silver solder paste for the above-mentioned screen printing, which is composed of the following raw materials in weight percentages: metal powder accounts for 92-94% of the total mass of the silver solder paste, binder accounts for 6-8% of the total mass of the silver solder paste, wherein the particle size D90 of the metal powder is less than or equal to 15 μm, wherein coarse metal powder (particle size between 5 μm and 15 μm) accounts for 70-75% of the total metal powder, fine metal powder (particle size greater than or equal to 0.5 μm but less than 5 μm) accounts for 15-25%, and nano-particle metal powder (particle size greater than or equal to 50 nm but less than 200 nm) accounts for 5-10%.

[0028] The adhesive is composed of the following raw materials in weight percentages: 8% resin and 92% organic solvent.

[0029] The preparation method of the above-mentioned silver solder paste includes the following steps: S5 Weigh out the resin and organic solvent according to the specified ratio; S6 involves adding resin and organic solvent to the same container, heating to 75℃-90℃, and stirring until completely melted to form an adhesive; S7 adhesive should be cooled to room temperature (20℃-25℃) and stored in a sealed bag at room temperature for later use. S8 weighs the binder and metal powder according to the ratio, pours them into the solder paste mixer, stirs for 5 minutes, and then vacuum stirs for 10 minutes to fully mix the metal powder and binder, thus obtaining a silver solder paste for screen printing.

[0030] As a preferred embodiment, the mesh count of the screen template in this application is 300, the screen template is a circle with a diameter of 1mm divided into 12 equal parts, the initial printing thickness is 25±1μm, the measured thickness of the solder layer is 10.1±0.3μm, the average bubble porosity is 0.05%, and the silver solder saving rate is 52%.

[0031] The second embodiment of this application is as follows: Figure 3 , Figure 4As shown, the difference between this embodiment and the first embodiment lies only in the pattern presented by the distributed spacer screen template. The distributed spacer screen template of the first embodiment is a circle or a near-circular polygon, while the distributed spacer screen template of the second embodiment is square in general, with the coating area and the non-coating area 2 being rectangular or square. The rest, including the working principle and working method, are the same, and the technical effects are also similar.

[0032] Table 1 shows the main parameter data of the embodiments of this application (wherein the metal powder accounts for 93% of the total mass of the silver solder paste, the binder accounts for 7% of the total mass of the silver solder paste, and the binder is prior art): As can be seen from the table above, this application has fully achieved the goal of controlling the thickness of the weld layer to below 12 micrometers, and the porosity is all below 0.08%, which greatly improves the level of high-precision welding.

Claims

1. A method for preparing an ultrathin metal welding layer based on distributed interval coating, characterized in that... Includes the following steps: S1 screen printing: Applying silver solder paste to the surface of the first base material to be soldered using a distributed, spaced screen template; The distributed spaced wire mesh template consists of a coating area for applying silver solder paste arranged at uniform intervals and a non-coating area that cannot be coated with silver solder paste. S2 Pre-curing treatment: Preheat within the pre-curing temperature range for a period of time to allow the silver solder paste to initially set; S3 Base Material Assembly: Cover the first base material coated with silver solder paste with the second base material and apply a certain pressure; S4 Brazing Forming: Under a protective atmosphere, the silver solder paste is kept at a constant temperature and pressure for a period of time within its melting temperature range. The molten silver solder paste flows and fills the non-coated area, forming an ultra-thin solder layer with a thickness of no more than 12μm and a porosity of <0.1%.

2. The method for preparing an ultrathin metal welding layer based on distributed interval coating according to claim 1, characterized in that: The S4 brazing forming step involves holding the temperature and pressure at 850±10℃ for 8-12 minutes under an argon protective atmosphere, allowing the molten solder to flow and fill the uncoated area, forming an ultra-thin brazing layer with a thickness of 10.1±0.3μm and a porosity of <0.06%.

3. The method for preparing an ultrathin metal welding layer based on distributed interval coating according to claim 1, characterized in that: The pre-curing temperature is 60℃-90℃.

4. The method for preparing an ultrathin metal welding layer based on distributed interval coating according to claim 1, characterized in that: Both the coated and uncoated areas are fan-shaped or triangular, and the coated and uncoated areas are arranged circumferentially around the same vertex to form a circle or polygon.

5. The method for preparing an ultrathin metal welding layer based on distributed interval coating according to claim 1, characterized in that: The distributed spaced wire mesh template has a wire mesh thickness of 25 micrometers, and the amount of silver solder paste applied in a single coating area accounts for 70-85% of the coating area capacity.

6. A silver solder paste for use in the method for preparing an ultrathin metal solder layer according to any one of claims 1 to 5, characterized in that: The silver solder paste is composed of the following raw materials in the following mass percentages: metal powder accounts for 80-95% of the total mass of the silver solder paste; binder accounts for 5-20% of the total mass of the silver solder paste; wherein, the particle size of the metal powder is ≤15 micrometers, and the metal powder is divided into three groups according to particle size: the first group is coarse metal powder, with a particle size of 5 micrometers ≤15 micrometers, and coarse metal powder accounts for 70-75% of the total mass of the metal powder; the second group is fine metal powder, with a particle size of 0.5 micrometers ≤5 micrometers, and fine metal powder accounts for 15-25% of the total mass of the metal powder; the third group is nano-particle metal powder, with a particle size of 50 nanometers ≤200 nanometers, and nano-particle metal powder accounts for 5-10% of the total mass of the metal powder.

7. The silver solder paste according to claim 6, characterized in that: The adhesive is composed of the following raw materials by mass percentage: resin accounts for 5%-10% of the total mass of the adhesive, and organic solvent accounts for 95%-90% of the total mass of the adhesive.

8. The silver solder paste according to claim 6, characterized in that: The metal powder accounts for 92%-94% of the total mass of the silver solder paste, and the binder accounts for 8%-6% of the total mass of the silver solder paste.

9. The silver solder paste according to claim 8, characterized in that: The metal powder is composed of copper and silver in a mass ratio of 72:

28.

10. The silver solder paste according to claim 7, characterized in that: The adhesive is composed of the following raw materials by mass percentage: resin accounts for 6%-8% of the total mass of the adhesive, and organic solvent accounts for 94%-92% of the total mass of the adhesive.

Images