CN105618882A - Packaging method for soldered joint - Google Patents

Abstract

The invention discloses a packaging method of a brazing joint, which is used for solving the technical problem of poor strength of the brazing joint in the prior packaging method. The technical solution is to use a laser to process regular quadrangular prism-shaped microstructure grooves on the surface of the copper plate of electronic components, clean the prefabricated microstructure grooves, and use Sn-Ag-Cu solder to separate the smooth surface of the copper plate and the surface of the microstructure grooves. Carry out wetting experiments to test the wetting angle; observe the filling and dissolution of Sn-Ag-Cu solder under different microstructures; use Sn-Ag-Cu as the solder to implement on the copper plate with prefabricated microstructure grooves Brazing. Due to the existence of regular quadrangular columnar microstructure grooves on the surface of the copper plate, the wetting angle of the Sn-Ag-Cu solder on the surface of the copper plate is reduced from 59.2° in the background technology to 26.3°, which promotes the metallurgical bonding of the brazed joint, brazing The strength of the joint is increased from 72.4±3.8MPa in the background technology to 85±4.5MPa.

Description

Solder joint packaging method

technical field

The invention relates to a packaging method, in particular to a packaging method for brazed joints.

Background technique

With the advancement of science and technology and the emphasis on the hazards of lead elements, electronic products are gradually becoming lead-free, so new requirements are put forward for interconnect materials such as solder. Traditional solder materials such as Sn-Pb binary eutectic alloys, Although it has the characteristics of good solderability, excellent performance, and excellent cost, it is gradually being replaced by lead-free solder. Among all the lead-free solders that have been applied, Sn-Ag-Cu solder is considered to be one of the most promising lead-free solder alloy systems due to its superior reliability and good compatibility with electronic components. one. However, the wetting and spreading ability of Sn-Ag-Cu solder is worse than that of Sn-Pb solder, and the controllability of spreading is poor, which makes it easy to produce defects such as de-soldering, missing soldering and overflowing soldering in precision electronic devices.

Copper has good thermal and electrical conductivity, low thermal expansion coefficient, good brazing and corrosion resistance, good formability, low cost and other advantages, so most of the pin joints and lead frames in electronic components are used Made of copper. However, the wetting angle of the Sn-Ag-Cu solder on the surface of the copper plate is 59.2°, and the strength of the brazed joint is 72.4±3.8MPa. In order to solve the problem of wetting and spreading of Sn-Ag-Cu solder in the brazing process, the literature "D.QYu, JZhao, LWang. Improvement on the microstructure stability, mechanical and wetting properties of Sn-Ag-Culead-free solder with the addition of rare earth elements [J]. 1): 170-175." discloses a packaging method. This method solves the wetting problem of Sn-Ag-Cu solder to a certain extent by adding rare earth elements to the Sn-Ag-Cu solder, but intermetallic compounds are generated at the joint, which increases the defects at the joint interface, which is harmful to the improvement The accuracy and performance of the brazed joint, reducing the size of the joint has a more adverse effect.

Contents of the invention

In order to overcome the disadvantage of poor soldering joint strength in the existing packaging method, the invention provides a packaging method for the soldering joint. In this method, lasers are used to process square prism-shaped microstructure grooves with a height and width of 20±2 μm on the surface of copper plates of electronic components, and pickling and ultrasonic cleaning are performed on the prefabricated microstructure grooves, using Sn-Ag-Cu The wetting test of the solder on the smooth surface of the copper plate and the grooved surface of the microstructure was carried out to test the wetting angle; the filling situation of the Sn-Ag-Cu solder in different microstructures and the dissolution of the microstructure were observed under the light microscope ; Using Sn-Ag-Cu as solder, brazing is carried out on the copper plate with prefabricated microstructure grooves. Due to the existence of square prism-shaped microstructure grooves on the surface of the copper plate of electronic components, the wetting angle of the Sn-Ag-Cu solder on the surface of the copper plate is reduced from 59.2° in the background technology to 26.3°, which promotes the metallurgical bonding of the brazing joint , the strength of the brazed joint is increased from 72.4±3.8MPa in the background technology to 85±4.5MPa.

The technical solution adopted by the present invention to solve the technical problem: a method for encapsulating a brazed joint, which is characterized in that it includes the following steps:

Step 1. Use SiC sandpaper to grind and polish the surface of the copper plate of electronic components, then use ultrasonic cleaning and drying, and use a femtosecond laser to process a microstructure in the shape of a regular prism on the surface of the copper plate, with a width and height of 20±2μm , the groove widths between the quadrangular prisms are respectively 10-40 μm.

Step 2. Put the prefabricated copper plate with regular quadrangular prism microstructure into 30% HNO ₃ and ultrasonically clean it for 1 to 2 minutes to remove surface dirt and oil, then wash it with clean water, and then use absolute ethanol to absorb water and blow it. Dry and set aside.

Step 3. In the O2C wetting angle measurement system, ultrasonically clean the Sn-Ag-Cu solder ball with a diameter of 0.6mm in absolute ethanol for 10-12min to remove surface impurities and oil stains, and the treated Sn-Ag-Cu Ag-Cu solder balls are placed in the center of the microstructure surface of different sizes. After starting the video recording system, the heating rate is rapidly raised to the brazing temperature at a heating rate of 40-50 °C/min. The cooling rate of min is used to quickly cool down, record the video data of the entire melting and wetting process, select the wetting start and end time to take screenshots, and measure the wetting angle.

Step 4: Using Sn-Ag-Cu as solder, brazing is carried out on the copper plate with prefabricated microstructure, and brazing is carried out at 320-330° C. for 5-7 minutes.

The beneficial effects of the present invention are: the method adopts a laser to process regular quadrangular columnar microstructure grooves with a height and width of 20±2 μm on the surface of the copper plate of electronic components, and pickling and ultrasonic cleaning the prefabricated microstructure grooves , using Sn-Ag-Cu solder to conduct wetting experiments on the smooth surface of the copper plate and the grooved surface of the microstructure, and test the wetting angle; observe the filling of Sn-Ag-Cu solder under different microstructures under a light microscope situation and the dissolution of the microstructure; using Sn-Ag-Cu as the solder, brazing is carried out on the copper plate with the prefabricated microstructure groove. Due to the existence of square prism microstructure grooves on the surface of the copper plate of electronic components, the wetting angle of the Sn-Ag-Cu solder on the surface of the copper plate is reduced from 59.2° in the background technology to 26.3°, which promotes the metallurgical bonding of the brazing joint , the strength of the brazed joint is increased from 72.4±3.8MPa in the background technology to 85±4.5MPa.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is an optical microscope photo of microstructures with different groove widths processed by a femtosecond laser on the surface of a copper plate in the packaging method of a brazed joint according to the present invention. Figure 1(a) groove width is 10 μm, Figure 1(b) groove width is 20 μm, Figure 1(c) groove width is 30 μm, Figure 1(d) groove width is 40 μm.

Fig. 2 is a photograph of the wetting angle of microstructures of different sizes in the packaging method of the soldered joint of the present invention. Figure 2(a) smooth surface, Figure 2(b) groove width 10 μm, Figure 2(c) groove width 20 μm, Figure 2(d) groove width 30 μm, Figure 2(e) groove width 40 μm.

Fig. 3 is a variation curve of the wetting angle and the microstructure groove width in the packaging method of the soldered joint of the present invention.

Fig. 4 is a photo of the surface of the microstructure after dissolution in the encapsulation method of the soldered joint of the present invention. Figure 4(a) has a groove width of 10 μm, Figure 4(b) has a groove width of 20 μm, Figure 4(c) has a groove width of 30 μm, and Figure 4(d) has a groove width of 40 μm.

detailed description

Refer to Figure 1-4. The specific steps of the packaging method of the brazed joint of the present invention are as follows:

Step 1. Use SiC sandpaper to grind and polish the surface of the copper plate of electronic components, then use ultrasonic cleaning and drying, and use a femtosecond laser (model HSGQ-20W) to process a microstructure in the shape of a regular square prism on the surface of the copper plate, the width of which is and the heights are both 20±2 μm, and the groove widths between the quadrangular prisms are 10 μm, 20 μm, 30 μm and 40 μm, respectively.

Step 2: The precision of the surface microstructure is extremely high, so operations such as grinding or polishing cannot be performed on it. Wet samples with prefabricated surface microstructures were ultrasonically cleaned in 30% HNO ₃ for 1 to 2 minutes to remove surface dirt and oil, then washed with water, then absorbed with absolute ethanol and dried for use.

Step 3: Observing the processing condition of the microstructure under a light microscope and measuring its size to verify that it meets the experimental precision requirements.

Step 4. In the O2C wetting angle measurement system, use Sn-Ag-Cu solder balls with a diameter of 0.6 mm. Before the experiment, ultrasonically clean them in absolute ethanol for 10-12 minutes to remove surface impurities and oil stains. Placed in the center of microstructure surfaces of different sizes, start the video recording system and quickly heat up to the brazing temperature at a heating rate of 40-50°C/min, and then quickly cool down to the brazing temperature at a cooling rate of 40-50°C/min after holding for 5-6 minutes. At a suitable temperature, record the video data of the entire melting and wetting process, select the wetting start and end time to take screenshots, and measure the wetting angle.

Step 5. Cut the wetted sample along the direction perpendicular to the wetted interface and parallel to the groove, and inlay it into a metallographic sample. It is observed under the light microscope that the microstructure is slightly eroded, and the solder can well fill the microstructure of the interface. structure.

Step 6. Analyze the test results to verify the influence of the microstructure on the wetting and spreading of the Sn-Ag-Cu solder on the surface of the base metal. Through the wetting experiment, it is verified that the microstructure can spread the Sn-Ag-Cu solder on the surface of the copper The wetting angle decreased from 58.2o to 26.3°, demonstrating that the microstructure can promote the wetting and spreading of the solder on the surface of the base metal.

Step 7. Using Sn-Ag-Cu as solder, perform brazing on the copper plate with prefabricated microstructure. The brazing experiment is kept at 320-330°C for 5-7 minutes, and the "lead-free brazing" in the reference standard of lead-free technology is used. "Solder joint tension and shear test method of material" to test the strength of the welded joint, the joint strength increased from 72.4±3.8MPa to 85±4.5MPa, and the joint strength increased by 20%.

Claims (1)

1. A packaging method for a brazed joint, characterized in that it may further comprise the steps: Step 1. Use SiC sandpaper to grind and polish the surface of the copper plate of electronic components, then use ultrasonic cleaning and drying, and use a femtosecond laser to process a microstructure in the shape of a regular prism on the surface of the copper plate, with a width and height of 20±2μm , the width of the grooves between the quadrangular prisms is 10-40 μm; Step 2. Put the prefabricated copper plate with regular quadrangular prism microstructure into 30% HNO ₃ and ultrasonically clean it for 1 to 2 minutes to remove surface dirt and oil, then wash it with clean water, and then use absolute ethanol to absorb water and blow it. dry for use; Step 3. In the O2C wetting angle measurement system, ultrasonically clean the Sn-Ag-Cu solder ball with a diameter of 0.6mm in absolute ethanol for 10-12min to remove surface impurities and oil stains, and the treated Sn-Ag-Cu Ag-Cu solder balls are placed in the center of the microstructure surface of different sizes. After starting the video recording system, the heating rate is rapidly raised to the brazing temperature at a heating rate of 40-50 °C/min. The cooling rate of min is fast, and the video data of the entire melting and wetting process is recorded, and the wetting start and end time are selected to take screenshots, and the wetting angle is measured; Step 4: Using Sn-Ag-Cu as solder, brazing is carried out on the copper plate with prefabricated microstructure, and brazing is carried out at 320-330° C. for 5-7 minutes.