Low-temperature lead-free formic acid solder paste and preparation method and application thereof

Abstract

The invention relates to low-temperature lead-free formic acid solder paste and a preparation method and application thereof, and belongs to the technical field of welding materials. The low-temperature lead-free formic acid solder paste is prepared from the following raw materials in percentage by mass: 85-90% of alloy welding powder and 10-15% of scaling powder, the soldering flux comprises the following raw materials in parts by weight: 10-15 parts of an activating agent, 1-5 parts of a rheological agent, 20-30 parts of an organic solvent, 20-30 parts of a paste forming agent, 3-5 parts of a surfactant and 0.1-0.5 part of a corrosion inhibitor, the activating agent is a composition of hydrogenated dimer acid, glycollic acid and ethylenediaminetetraacetic acid, and the organic solvent is a composition of tetrahydrofurfuryl alcohol and cyclohexanol. The paste forming agent is polyethylene glycol. The solder paste is suitable for a low-temperature welding process at the temperature of 120-150 DEG C, welding energy consumption can be reduced, the residual rate after welding is low, follow-up cleaning is not needed, the production environment can be improved, and the production cost can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of welding materials, and in particular to a low-temperature lead-free formate solder paste and a preparation method and application thereof. Background Art

[0002] With the continuous development of electronic technology, the trend of miniaturization and high performance of electronic equipment is becoming increasingly obvious, which puts higher requirements on the welding quality of electronic components. At the same time, the enhancement of environmental awareness makes lead-free welding an inevitable trend in the development of the industry. Low-temperature lead-free solder paste can effectively avoid damage to heat-sensitive components because it can achieve welding at a lower temperature. It can be used for special chip interconnection and as a chip for medical / special detectors.

[0003] Solder paste, as a key material in electronic welding, is composed of alloy powder and flux. Traditional tin-lead solder is gradually replaced by lead-free solder due to the toxicity of lead, which poses a serious threat to the environment and human health. In the lead-free solder system, low-temperature lead-free solder paste has become a hot spot for research and application due to its unique advantages, such as lowering welding temperature, reducing energy consumption, and protecting sensitive components. However, the existing low-temperature lead-free solder paste still has some problems in practical applications, such as insufficient welding strength, poor wettability, and easy generation of voids, which limits its further application in the manufacturing of high-end electronic products. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a low-temperature lead-free formate solder paste and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a low-temperature lead-free formate solder paste, which is made of the following raw materials in percentage by mass: 85-90% alloy solder powder and 10-15% solder flux; The soldering flux comprises the following raw materials in parts by weight: 10-15 parts of an activator, 1-5 parts of a rheological agent, 20-30 parts of an organic solvent, 20-30 parts of a paste-forming agent, 3-5 parts of a surfactant and 0.1-0.5 parts of a corrosion inhibitor, wherein the activator is a composition of hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid, the organic solvent is a composition of tetrahydrofurfuryl alcohol and cyclohexanol, and the paste-forming agent is polyethylene glycol.

[0006] The activators of the flux are hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid. Among them, hydrogenated dimer acid has a long chain structure and can remain fluid at low temperatures (such as 150-180°C). It can quickly penetrate the pores of the oxide film. The dicarboxylic acid group (-COOH) it contains can adsorb metal oxides at multiple points. The local concentration is high at low temperatures, which accelerates the metal saponification reaction and can effectively improve the activity of the flux at low temperatures. Glycolic acid has a low boiling point (112°C) and can quickly vaporize and release H during low-temperature welding. + , no high-temperature thermal activation is required. The hexadentate coordination structure of ethylenediaminetetraacetic acid (EDTA) can still efficiently chelate metal ions at low temperatures to form a stable water-soluble complex, overcoming the insufficient reaction rate at low temperatures. At the same time, the EDTA complex can be washed with water, which can reduce the risk of residues. Hydrogenated dimer acid, glycolic acid and EDTA significantly improve the oxide layer removal ability and wettability of the flux in low-temperature environments through the synergistic mechanism of low-temperature volatility activation, molecular structure adaptability and efficient chelation of metal ions. This system breaks through the limitation of traditional organic acids relying on high-temperature reactions, and provides key technical support for low-temperature lead-free soldering and precision electronic packaging.

[0007] The organic solvent of the present invention is tetrahydrofurfuryl alcohol and cyclohexanol. The tetrahydrofurfuryl alcohol remains in liquid state in the low temperature range of 80-150°C, ensuring that the activator is evenly dispersed. The tetrahydrofurfuryl alcohol (boiling point 178°C) and glycolic acid (boiling point 112°C) form a boiling point gradient, and the activator is released in stages in the range of 80-150°C to avoid premature exhaustion of the activator in the low temperature stage. The cyclic structure of cyclohexanol can reduce the crystallization tendency, so that the flux still maintains fluidity at -20°C, and avoids the stratification of the flux caused by low temperature crystallization. Therefore, the organic solvent selected by the present invention can improve the spreading rate of the solder paste at low temperature, reduce the residual amount of the solder paste at low temperature, and at the same time can also increase the storage period of the solder paste, reduce the precipitation of crystallization, and improve the storage stability.

[0008] Preferably, the mass ratio of the hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid is 1:(5-8):(2-4).

[0009] Preferably, the mass ratio of tetrahydrofurfuryl alcohol to cyclohexanol is 1:(1-3).

[0010] Preferably, the rheological agent is a polyamide rheological agent.

[0011] Preferably, the hydrogenated dimer acid is C36 hydrogenated dimer acid.

[0012] Preferably, the surfactant is a fluorocarbon surfactant.

[0013] Preferably, the corrosion inhibitor is an imidazoline corrosion inhibitor.

[0014] Preferably, the alloy solder powder comprises the following raw materials in percentage by mass: 25-35% indium, 1-2% silver, 0.8-1% aluminum and 0.5-1% antimony, with the remainder being tin. Indium and tin form a Sn-In eutectic phase (melting point 120-135°C), which is lower than the Sn-Bi eutectic (139°C). Adding silver can increase the surface tension of the molten alloy and improve the wettability of the solder paste. Aluminum and antimony can improve the mechanical properties of the alloy.

[0015] Specifically, the method for preparing the alloy welding powder comprises the following steps: All metal elements are mixed and melted to make solder, which is then centrifuged and sieved to obtain alloy solder powder.

[0016] Preferably, in the method for preparing the alloy welding powder, the melting temperature is 1000-1500° C., and the melting time is 1-3 h.

[0017] Preferably, the particle size of the alloy welding powder is the size of No. 4-6 powder.

[0018] In a second aspect, the present invention provides a method for preparing the low-temperature lead-free formate solder paste described in the first aspect, comprising the following steps: S1. Place the activator, rheological agent, organic solvent, paste-forming agent, surfactant and corrosion inhibitor in a reaction kettle, heat to 40-60° C., start stirring, heat to 90-95° C. while stirring, keep warm, and continue stirring for 5-10 minutes to obtain a mixture, cool the mixture, grind it, refrigerate it and then return it to the temperature to obtain the soldering flux; S2. gradually add alloy solder powder into the soldering flux and stir evenly to obtain the low-temperature lead-free formate solder paste.

[0019] Preferably, the stirring speed of step S1 is 5000-6000 rpm, and the heating time is 3-5 min.

[0020] Preferably, in step S1, the mixture is cooled to 25-30°C, then ground to less than 2 μm, refrigerated at 0-10°C for 12-18 hours, and then allowed to warm to room temperature.

[0021] In a third aspect, the present invention provides a use of the low-temperature lead-free formate solder paste described in the first aspect in packaging chips.

[0022] Specifically, chip packaging includes the following steps: A coating step, coating the chip packaging formate solder paste on the pads of the substrate to form a solder layer; In the welding process, the chip is mounted on the solder layer, and formic acid gas is introduced for reflow welding, so that the chip is welded on the welding pad.

[0023] Preferably, the time for introducing formic acid gas is 120-180 seconds.

[0024] Compared with the prior art, the present invention has the following beneficial effects: The solder paste of the present invention adopts a flux formula that does not contain rosin to avoid the generation of smoke and harmful substances during the welding process. The selection of specific activators and organic solvents realizes gradient activation in a wide temperature range (120-150°C). When the temperature reaches 112°C (the boiling point of glycolic acid), the oxide layer removal is started to meet the requirements of lead-free low-temperature solder. At 140-160°C, tetrahydrofurfuryl alcohol and cyclohexanol are azeotropic, and hydrogenated dimer acid dissolves the oxide sublayer, which ensures the cleaning effect and wettability, so that the spreading area of ​​the alloy solder is improved; at more than 160°C, the residual tetrahydrofurfuryl alcohol forms a film to prevent solder joint voids and reduce residual ion contamination. Therefore, the solder paste of the present invention is suitable for low-temperature welding processes of 120-150°C, which can reduce welding energy consumption, and the residual rate after welding is low, and no subsequent cleaning is required, which improves the production environment and reduces production costs. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0026] The sources of the materials used in the following examples and comparative examples are as follows: C36 hydrogenated dimer acid: the manufacturer is Jasik Commercial Trading (Shanghai) Co., Ltd., the model is dimer acid IPU22; Formic acid: manufacturer is Shanghai MacLean Biochemical Technology Co., Ltd.; Polyamide rheological agent: manufacturer is Shenzhen Xinzhihe New Materials Co., Ltd., model number is 6500; Fluorocarbon surfactant: the manufacturer is Shenzhen Xinzhihe New Materials Co., Ltd., the brand is FS-3100; Imidazoline corrosion inhibitor: 2-methylimidazole, the manufacturer is Shenzhen Jintenglong Industrial Co., Ltd.

[0027] Unless otherwise specified, other materials, reagents, etc. used in the specific embodiments can be obtained from commercial sources.

[0028] Example 1 A low-temperature lead-free formate solder paste is made of the following raw materials in percentage by mass: 87% alloy solder powder and 13% soldering flux; The soldering flux comprises the following raw materials in parts by weight: 12 parts of an activator, 2 parts of a rheological agent, 28 parts of an organic solvent, 23 parts of a paste-forming agent, 4 parts of a surfactant and 0.2 parts of a corrosion inhibitor; the activator is a composition of hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid in a mass ratio of 1:6:3; the organic solvent is a composition of tetrahydrofurfuryl alcohol and cyclohexanol in a mass ratio of 1:2; the paste-forming agent is polyethylene glycol PEG-1000; the rheological agent is a polyamide rheological agent, the hydrogenated dimer acid is C36 hydrogenated dimer acid, the surfactant is a fluorocarbon surfactant, and the corrosion inhibitor is an imidazoline corrosion inhibitor; The alloy solder powder comprises the following raw materials in percentage by mass: 30% indium, 1.5% silver, 1% aluminum and 0.6% antimony, with the balance being tin.

[0029] Specifically, the method for preparing the alloy welding powder comprises the following steps: All metal elements are mixed and melted at 1200°C for 2 hours to prepare solder, which is then centrifuged and sieved to obtain alloy solder powder of size 4.

[0030] The method for preparing the low-temperature lead-free formate solder paste comprises the following steps: S1. Place the formulated amount of activator, rheological agent, organic solvent, paste-forming agent, surfactant and corrosion inhibitor in a reaction kettle, heat to 50°C, start stirring at a speed of 5500 rpm, heat to 95°C at a rate of 5°C / min while stirring, then keep warm, and continue stirring for 8 minutes to obtain a mixture, cool the mixture to 25°C, grind to 2 μm, refrigerate at 5°C for 12 hours, and then return to room temperature to obtain the soldering flux; S2. gradually add alloy solder powder into the soldering flux and stir evenly to obtain the low-temperature lead-free formate solder paste.

[0031] Example 2 A low-temperature lead-free formate solder paste is made of the following raw materials in percentage by mass: 85% alloy solder powder and 15% soldering flux; The soldering flux comprises the following raw materials in parts by weight: 10 parts of an activator, 1 part of a rheological agent, 20 parts of an organic solvent, 20 parts of a paste-forming agent, 3 parts of a surfactant and 0.1 parts of a corrosion inhibitor; the activator is a composition of hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid in a mass ratio of 1:5:2; the organic solvent is a composition of tetrahydrofurfuryl alcohol and cyclohexanol in a mass ratio of 1:1; the paste-forming agent is polyethylene glycol PEG-1000; the rheological agent is a polyamide rheological agent, the hydrogenated dimer acid is C36 hydrogenated dimer acid, the surfactant is a fluorocarbon surfactant, and the corrosion inhibitor is an imidazoline corrosion inhibitor; The alloy solder powder comprises the following raw materials in percentage by mass: 25% indium, 1% silver, 0.8% aluminum and 0.5% antimony, with the balance being tin.

[0032] Specifically, the method for preparing the alloy welding powder comprises the following steps: All metal elements are mixed and melted at 1000°C for 3 hours to form solder, which is then centrifuged and sieved to obtain alloy solder powder of size 4.

[0033] The method for preparing the low-temperature lead-free formate solder paste comprises the following steps: S1. Place the formulated amount of activator, rheological agent, organic solvent, paste-forming agent, surfactant and corrosion inhibitor in a reaction kettle, heat to 40°C, start stirring at a speed of 6000 rpm, heat to 90°C at a rate of 5°C / min while stirring, then keep warm, and continue stirring for 3 minutes to obtain a mixture; cool the mixture to 20°C, grind to 1 μm, refrigerate at 0°C for 12 hours, and then return to room temperature to obtain the soldering flux; S2. gradually add alloy solder powder into the soldering flux and stir evenly to obtain the low-temperature lead-free formate solder paste.

[0034] Example 3 A low-temperature lead-free formate solder paste is made of the following raw materials in percentage by mass: 90% alloy solder powder and 10% soldering flux; The soldering flux comprises the following raw materials in parts by weight: 15 parts of an activator, 5 parts of a rheological agent, 30 parts of an organic solvent, 30 parts of a paste-forming agent, 5 parts of a surfactant and 0.5 parts of a corrosion inhibitor; the activator is a composition of hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid in a mass ratio of 1:8:4; the organic solvent is a composition of tetrahydrofurfuryl alcohol and cyclohexanol in a mass ratio of 1:3; the paste-forming agent is polyethylene glycol PEG-1000; the rheological agent is a polyamide rheological agent, the hydrogenated dimer acid is C36 hydrogenated dimer acid, the surfactant is a fluorocarbon surfactant, and the corrosion inhibitor is an imidazoline corrosion inhibitor; The alloy solder powder comprises the following raw materials in percentage by mass: 35% indium, 2% silver, 1% aluminum and 1% antimony, with the balance being tin.

[0035] Specifically, the method for preparing the alloy welding powder comprises the following steps: All metal elements are mixed and melted at 1500°C for 1 hour to prepare solder, which is then centrifuged and sieved to obtain alloy solder powder with a particle size of 30-40 μm.

[0036] The method for preparing the low-temperature lead-free formate solder paste comprises the following steps: S1: placing the formulated amount of activator, rheological agent, organic solvent, paste-forming agent, surfactant and corrosion inhibitor in a reaction kettle, heating to 60°C, stirring at a speed of 5000 rpm, heating to 95°C at a speed of 5°C / min while stirring, then keeping the temperature, and stirring for 5 minutes to obtain a mixture; cooling the mixture to 30°C, grinding it to 2 μm, refrigerating it at 10°C for 18 hours, and then returning it to room temperature to obtain the soldering flux; S2. gradually add alloy solder powder into the soldering flux and stir evenly to obtain the low-temperature lead-free formate solder paste.

[0037] Example 4 The difference between Example 4 and Example 1 is that the added amount of the activator remains unchanged, and the mass ratio of the hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid is 3:6:1.

[0038] Example 5 The difference between Example 5 and Example 1 is that the added amount of the activator remains unchanged, and the mass ratio of the hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid is 1:3:6.

[0039] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the amount of the activator added remains unchanged, no hydrogenated dimer acid is added, and glycolic acid and ethylenediaminetetraacetic acid in a mass ratio of 2:1 are used to make up for the missing amount.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the amount of the activator added remains unchanged, glycolic acid is not added, and hydrogenated dimer acid and ethylenediaminetetraacetic acid in a mass ratio of 1:3 are used to make up for the missing amount.

[0041] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the amount of the activator added remains unchanged, ethylenediaminetetraacetic acid is not added, and hydrogenated dimer acid and formic acid in a mass ratio of 1:6 are used to make up for the missing amount.

[0042] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the amount of the organic solvent added remains unchanged, tetrahydrofurfuryl alcohol is not added, and an equal amount of cyclohexanol is used to make up the missing amount.

[0043] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the amount of the organic solvent added remains unchanged, cyclohexanol is not added, and an equal amount of tetrahydrofurfuryl alcohol is used to make up the missing amount.

[0044] Performance Testing The solder pastes obtained in Examples 1-5 and Comparative Examples 1-5 were respectively subjected to the following tests: 1. Wettability test: Test according to the standard "IPC-TM-650 Solder Paste-Wettability Test"; 2. Thermal collapse: According to the IPC-TM-650 2.4.35 test method, a thermal collapse test was conducted using a 0.1mm thick template. The test condition was to place the solder paste on a 150℃ metal hot plate for 10 minutes. The qualified standard is: the solder paste edge diffusion does not exceed 20-25% of the original printing width, and the solder paste shape has no obvious collapse or deformation.

[0045] 3. Residual rate of solder flux: Weigh the solder paste with a mass of m1. The proportion of solder flux in the solder paste is ρ. The solder paste is applied on the aluminum substrate pad with a mass of m2 and a size of 30 mm×30 mm×0.1 mm to form a solder layer. Then, the chip is placed on a heating plate at a constant temperature of 120°C for preheating for 15 seconds. Then, the chip is bonded to the solder layer on the surface of the pad. Then, it is placed in a formic acid furnace for soldering, and the oxygen content in the formic acid furnace is controlled below 50 ppm. Formic acid gas is introduced for 180 seconds for reflow soldering. The soldering temperature is 150°C. The solder spreads and forms solder joints, so that the chip is soldered on the pad. After keeping it for 60 seconds, it is removed and then directly weighed to obtain its mass m3. The residual rate f after soldering is calculated according to the following formula: f=[m3-m2-(1-ρ)m1)] / (ρm1). The specific data are shown in Table 1.

[0046] 4. Test method for expansion rate and black spots: After each group of solder paste is automatically printed by SMT, patched, and reflow soldered, the expansion rate test is carried out according to JIS Z 3197 standard. Whether black spots are generated is determined by whether black pollution appears around the solder joints.

[0047] 5. Stability test: Viscosity change is the core parameter for characterizing the stability of solder paste, because it directly reflects the uniformity of components, chemical stability and resistance to environmental interference. Therefore, the smaller the viscosity change, the more stable the solder paste. After storing each group of solder paste at 30°C for 90 days, the viscosity before and after storage was tested using a viscometer, and the viscosity value at 10 rpm was used for comparison to characterize the viscosity change, where the viscosity change % = (viscosity value at 10 rpm after storage - viscosity value at 10 rpm before storage) / viscosity value at 10 rpm before storage. Then, according to the aforementioned wettability test, the wettability data after 90 days of storage was tested, and the results are shown in Table 1.

[0048] Table 1 Performance test data of each group of solder paste

[0049] It can be seen from Table 1, combined with the data of Examples 1-5, that when the mass ratio of hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid is 1:(5-8):(2-4), the wettability, flux residue rate and viscosity change of the solder paste are better, that is, the low temperature resistance of the solder paste is better.

[0050] It can be seen from the data of Example 1 and Comparative Examples 1-3 in Table 1 that when any one of the hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid in the activator is missing, the wettability, expansion rate and thermal collapse performance of the solder paste are significantly reduced, which shows that the three components of the activator have a synergistic effect and can significantly improve the low-temperature performance of the solder paste.

[0051] It can be seen from the data of Example 1 and Comparative Examples 4-5 in Table 1 that when any one of tetrahydrofurfuryl alcohol and cyclohexanol in the organic solvent is missing, the storage stability, wettability and expansion rate of the solder paste are significantly reduced, indicating that tetrahydrofurfuryl alcohol and cyclohexanol can synergistically improve the spreading rate of the solder paste at low temperature, reduce the amount of residual ions at low temperature, and at the same time increase the storage period of the solder paste, reduce the precipitation of crystallization, and improve the storage stability.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A low-temperature lead-free formate solder paste, characterized in that: Made of the following raw materials in mass percentage: 85-90% alloy solder powder and 10-15% flux; The soldering flux comprises the following raw materials in parts by weight: 10-15 parts of an activator, 1-5 parts of a rheological agent, 20-30 parts of an organic solvent, 20-30 parts of a paste-forming agent, 3-5 parts of a surfactant and 0.1-0.5 parts of a corrosion inhibitor, wherein the activator is a composition of hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid, the organic solvent is a composition of tetrahydrofurfuryl alcohol and cyclohexanol, and the paste-forming agent is polyethylene glycol.

2. The low-temperature lead-free formate solder paste according to claim 1, characterized in that: The mass ratio of the hydrogenated dimer acid, glycolic acid and ethylenediaminetetraacetic acid is 1:(5-8):(2-4).

3. The low-temperature lead-free formate solder paste according to claim 1, characterized in that: The mass ratio of tetrahydrofurfuryl alcohol to cyclohexanol is 1:(1-3).

4. The low-temperature lead-free formate solder paste according to claim 1, characterized in that: The raw material is selected from at least one of (I) to (IV): (I) the rheological agent is a polyamide rheological agent; (II) the hydrogenated dimer acid is C36 hydrogenated dimer acid; (III) the surfactant is a fluorocarbon surfactant; (IV) The corrosion inhibitor is an imidazoline corrosion inhibitor.

5. The low-temperature lead-free formate solder paste according to claim 1, characterized in that: The alloy solder powder comprises the following raw materials in percentage by mass: 25-35% indium, 1-2% silver, 0.8-1% aluminum and 0.5-1% antimony, with the balance being tin.

6. The low-temperature lead-free formate solder paste according to claim 5, characterized in that: The method for preparing the alloy welding powder comprises the following steps: All metal elements are mixed and melted to make solder, which is then centrifuged and sieved to obtain alloy solder powder.

7. The low-temperature lead-free formate solder paste according to claim 6, characterized in that: In the preparation method of the alloy welding powder, the melting temperature is 1000-1500° C. and the melting time is 1-3 hours.

8. The method for preparing the low-temperature lead-free formate solder paste according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Place the activator, rheological agent, organic solvent, paste-forming agent, surfactant and corrosion inhibitor in a reaction kettle, heat to 40-60° C., start stirring, heat to 90-95° C. while stirring, keep warm, and continue stirring for 5-10 minutes to obtain a mixture, cool the mixture, grind it, refrigerate it and then return it to the temperature to obtain the soldering flux; S2. gradually add alloy solder powder into the soldering flux and stir evenly to obtain the low-temperature lead-free formate solder paste.

9. Use of the low-temperature lead-free formate solder paste according to any one of claims 1 to 7 in packaging chips.

10. The use according to claim 9, characterized in that Packaging chips includes the following processes: A coating step, coating the chip packaging formate solder paste on the pads of the substrate to form a solder layer; In the welding process, the chip is mounted on the solder layer, and formic acid gas is introduced for reflow welding, so that the chip is welded on the welding pad.

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