A soldering material for chip packaging and a method for preparing the same

Abstract

The application relates to the solder technology field, and particularly discloses a soldering material for chip packaging and a preparation method thereof, and the soldering material for chip packaging comprises the following component raw materials in percentage by weight: Ag 2-6%, Cu 0.4-1%, Al 0.05-0.2%, Cr 0.03-0.08%, CeO2 0.01-0.06%, P 0.0003-0.001% and the rest Sn, and the soldering material for chip packaging prepared by the application has the advantages of improving the solderability and the oxidation resistance of the soldering material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solder, in particular to a solder for chip packaging and a preparation method thereof. BACKGROUND

[0002] Chip packaging is a housing for mounting semiconductor integrated circuit chips, which has the functions of placing, fixing, sealing, protecting the chip and enhancing the electrical and thermal performance. Chip packaging is a bridge between the internal world of the chip and the external circuit. The solder is fused with the metal welding point, and then welded with external components, so as to weld the chip on the circuit board. The solder is an indispensable basic raw material in the production processes of surface treatment, weldability test, thermal stress test and welding. For a long time, people have widely used tin-lead solder alloy with excellent performance, and the eutectic composition is SnPb37. With the proposal of the Lead Ban Act, the development and research of lead-free solder have been increasingly valued. Through extensive research, it is found that the most likely non-toxic alloy to replace Sn-Pb solder is Sn-based alloy, mainly Sn, with the addition of Ag, Zn, Cu, Sb, Bi, In and other elements to form binary or multi-element alloy to improve performance.

[0003] According to many existing technical materials, high-end chips such as mobile phones and computers usually use Sn-Ag-Cu solder for packaging interconnection, so as to realize the function of the chip. However, Sn-Ag-Cu solder is easy to oxidize and not easy to weld. SUMMARY

[0004] In order to improve the oxidation resistance of the solder, the present application provides a solder for chip packaging and a preparation method thereof.

[0005] The present application provides a solder for chip packaging, which adopts the following technical scheme:

[0006] A solder for chip packaging comprises the following components by weight percentage: Ag 2-6%, Cu 0.4-1%, Al 0.05-0.2%, Cr 0.03-0.08%, CeO2 0.01-0.06%, P 0.0003-0.001%, and the balance of Sn.

[0007] By adopting the technical scheme, the Sn-Ag-Cu alloy has good comprehensive performance and can replace the Sn-Pb alloy, the Ag element in the tin-based alloy can improve the spreadability of the alloy solder, but the tin-based lead-free alloy is very easy to form oxide tin slag and cause tin waste and increase production cost in the high-temperature molten state, in order to reduce the oxidation performance of the Sn-Ag-Cu alloy, Cr, Al and CeO2 are added to the Sn-Ag-Cu alloy, the CeO2 is easy to form a sub-grain boundary structure at the grain boundary position of the alloy, which is beneficial to the diffusion of Cr and Al atoms to the surface of the matrix, because the activity of Al is higher than that of Cr, therefore, Al first diffuses to the surface of the alloy to contact oxygen to form an Al2O3 oxidation film, then part of the Cr atoms contact oxygen to form Cr2O3, thereby forming a continuous Al2O3 and Cr2O3 composite film on the surface of the alloy during the alloy melting process, which to some extent inhibits the oxidation behavior inside the alloy, greatly improves the oxidation resistance of the soldering tin, and the addition of phosphorus can improve the thermal fatigue characteristics of the welded part to resist thermal deformation and stress, prevent the crystalline particles from becoming coarse, reduce the possibility of cracks caused by poor welding, and ensure reliable welding.

[0008] Optionally, the following components are included: Ag 2-5%, Cu 0.4-0.65%, Al 0.05-0.1%, Cr 0.03-0.06%, CeO2 0.01-0.04%, P 0.0003-0.0009%, and the balance of Sn.

[0009] By adopting the above technical scheme, the amount of each raw material is optimized, so that each raw material can play a role and improve the oxidation resistance and weldability of the tin solder.

[0010] Optionally, the following components are included: Ag 2-5%, Cu 0.4-0.65%, Al 0.05-0.1%, Cr 0.03-0.06%, CeO2 0.01-0.04%, P 0.0003-0.0009%, and the balance of Sn.

[0011] By adopting the above technical scheme, the optimal amount of each raw material is adjusted to obtain a tin solder with good oxidation resistance.

[0012] In a second aspect, the application provides a preparation method of a soldering tin for chip packaging, which adopts the following technical scheme: a preparation method of a soldering tin for chip packaging, including the following steps:

[0013] Step one, preparing SnAgCu alloy: heating and melting the tin ingot, heating, adding copper and silver materials, melting and stirring uniformly to obtain a liquid SnAgCu alloy;

[0014] Step two, preparation of SnAgCuCrAlPCeO2 alloy: chromium material, aluminum material and cerium oxide powder are added into the liquid SnAgCu alloy prepared in step one, and the temperature is reduced and stirred until completely melted, then phosphorus powder is added and stirred uniformly to obtain liquid SnAgCuCrAlPCeO2 alloy;

[0015] Step three, preparation of finished product: the oxide slag on the surface of the liquid SnAgCuCrAlPCeO2 alloy prepared in step two is removed by a stainless steel scraper, the temperature is reduced, the alloy liquid is poured into a mold, and the mold is cooled to obtain solder material.

[0016] By adopting the technical scheme, the components of the solder are adjusted based on the prepared SnAgCu alloy, Cr, Al and CeO2 are added for melting to prepare a finished product. In high-temperature welding, the solder can maintain an oxidation-free state for a longer time, has good oxidation resistance, has fewer welding defects than ordinary Sn-Ag-Cu alloy during welding, and is more easily to have good affinity with the base material, thereby effectively improving the welding efficiency and welding quality.

[0017] Optionally, in step one, the tin ingot is heated and melted, the temperature is raised to 490-520°C, the copper material and silver material are added and stirred uniformly to obtain liquid SnAgCu alloy.

[0018] By adopting the technical scheme, the tin ingot is first heated and melted, the copper material and silver material are added to be solid-solute in the tin liquid to form Sn-Ag-Cu alloy, which has good mechanical properties and weldability and can replace traditional Sn-Pb alloy.

[0019] Optionally, in step two, the chromium powder, aluminum powder and cerium oxide powder are added into the liquid SnAgCu alloy prepared in step one, and the temperature is reduced to 460-490°C and stirred for 30-40 min until completely melted.

[0020] By adopting the technical scheme, the chromium powder, aluminum powder and cerium oxide powder are added into the liquid SnAgCu alloy, and in the melting process, reducing the temperature can improve the flowability of the solder during welding operation and significantly reduce tin slag, thereby avoiding the increase of solder defects caused by too high temperature and too fast melting.

[0021] Optionally, in step three, the temperature is reduced to 300-330°C, the alloy liquid is poured into a mold, and the mold is cooled to obtain solder material.

[0022] By adopting the technical scheme, when preparing the finished product, the temperature is reduced to cool the alloy liquid in the pouring mold to obtain solder material.

[0023] Optionally, the purity of the chromium powder, aluminum powder and cerium oxide powder is 99.95%-99.99%.

[0024] By adopting the technical scheme, high-purity chromium powder, aluminum powder and cerium oxide powder are adopted, and in the process of metal blending and melting, oxidation of impurities is avoided, and oxidation slag is formed, thereby affecting the welding quality.

[0025] In summary, the present application has the following beneficial effects:

[0026] 1. In the present application, Cr, Al and CeO2 are added to the Sn-Ag-Cu alloy, and CeO2 is easy to form a sub-grain boundary structure at the grain boundary position of the alloy, which is beneficial to the diffusion of Cr and Al atoms to the surface of the matrix. Since the activity of Al is higher than that of Cr, Al first diffuses to the surface of the alloy to contact oxygen to form an Al2O3 oxidation film, and then part of the Cr atoms contact oxygen to form Cr2O3. Thus, a continuous Al2O3 and Cr2O3 composite film is formed on the surface of the alloy during alloy melting, which to some extent inhibits the oxidation behavior inside the alloy, greatly improving the oxidation resistance of the tin solder.

[0027] 2. In the present application, the addition of phosphorus can improve the thermal fatigue properties of the welded part to withstand thermal deformation and stress, prevent the crystalline particles from becoming coarse, reduce the possibility of cracks caused by welding, and ensure reliable welding. DETAILED DESCRIPTION

[0028] The present application will be further described in detail below in combination with examples and comparative examples.

[0029] Examples

[0030] Example 1

[0031] A preparation method of a solder for chip packaging, comprising the following steps:

[0032] Step one, preparing SnAgCu alloy: tin ingot is heated and melted, the temperature is raised to 500℃, copper material and silver material are added and melted and stirred uniformly to obtain liquid SnAgCu alloy;

[0033] Step two, preparing SnAgCuCrAlPCeO2 alloy: chromium material, aluminum material and cerium oxide powder are added to the liquid SnAgCu alloy prepared in step one, the temperature is lowered to 470℃, and stirring is performed for 35 minutes until complete melting, then phosphorus powder is added and stirred uniformly to obtain liquid SnAgCuCrAlPCeO2 alloy, wherein the purity of chromium powder, aluminum powder and cerium oxide powder is 99.99%;

[0034] Step three, preparing finished product: the liquid SnAgCuCrAlPCeO2 alloy prepared in step two is used to remove the oxide slag on the surface of the alloy liquid with a stainless steel scraper, the temperature is lowered to 320℃, the alloy liquid is poured into a mold, and the mold is cooled to get out of the mold to obtain the solder.

[0035] Example 2

[0036] A method for preparing a soldering material for chip packaging, comprising the following steps:

[0037] Step one, preparing SnAgCu alloy: tin ingot is heated and melted, the temperature is raised to 490℃, copper and silver are added and melted and stirred uniformly to obtain liquid SnAgCu alloy;

[0038] Step two, preparing SnAgCuCrAlPCeO2 alloy: chromium, aluminum and cerium oxide powder are added to the liquid SnAgCu alloy prepared in step one, the temperature is lowered to 460℃, and stirring is performed for 30 minutes until complete melting, then phosphorus powder is added and stirred uniformly to obtain liquid SnAgCuCrAlPCeO2 alloy, the purity of chromium powder, aluminum powder and cerium oxide powder is 99.99%;

[0039] Step three, preparing finished product: the liquid SnAgCuCrAlPCeO2 alloy prepared in step two is removed from the surface of the alloy liquid by a stainless steel scraper to remove oxide slag, the temperature is lowered to 300℃, the alloy liquid is poured into a mold, and the mold is cooled to obtain the soldering material.

[0040] Example 3

[0041] A method for preparing a soldering material for chip packaging, comprising the following steps:

[0042] Step one, preparing SnAgCu alloy: tin ingot is heated and melted, the temperature is raised to 520℃, copper and silver are added and melted and stirred uniformly to obtain liquid SnAgCu alloy;

[0043] Step two, preparing SnAgCuCrAlPCeO2 alloy: chromium, aluminum and cerium oxide powder are added to the liquid SnAgCu alloy prepared in step one, the temperature is lowered to 490℃, and stirring is performed for 35 minutes until complete melting, then phosphorus powder is added and stirred uniformly to obtain liquid SnAgCuCrAlPCeO2 alloy, the purity of chromium powder, aluminum powder and cerium oxide powder is 99.95%;

[0044] Step three, preparing finished product: the liquid SnAgCuCrAlPCeO2 alloy prepared in step two is removed from the surface of the alloy liquid by a stainless steel scraper to remove oxide slag, the temperature is lowered to 330℃, the alloy liquid is poured into a mold, and the mold is cooled to obtain the soldering material.

[0045] The raw materials and their corresponding weight percentages of each component in examples 1-3 are shown in Table 1.

[0046] Table 1 Components and their weight percentages (wt%) in examples 1-3,

[0047]

[0048] Example 4

[0049] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that in Step 1, the tin ingot is heated and melted, the temperature is raised to 480°C, the copper material and silver material are added and stirred until they are uniformly melted, and a liquid SnAgCu alloy is obtained.

[0050] Example 5

[0051] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that in Step 1, the tin ingot is heated and melted, the temperature is raised to 530°C, the copper material and silver material are added and stirred until they are uniformly melted, and a liquid SnAgCu alloy is obtained.

[0052] Example 6

[0053] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that in Step 2, the chromium powder, aluminum powder, and cerium oxide powder are added to the liquid SnAgCu alloy prepared in Step 1, the temperature is lowered to 450°C, and stirring is performed for 25 min until complete melting.

[0054] Example 7

[0055] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that in Step 2, the chromium powder, aluminum powder, and cerium oxide powder are added to the liquid SnAgCu alloy prepared in Step 1, the temperature is lowered to 500°C, and stirring is performed for 45 min until complete melting.

[0056] Comparative Example

[0057] Comparative Example 1

[0058] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that the raw materials do not include CeO2.

[0059] Comparative Example 2

[0060] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that the raw materials do not include Al.

[0061] Comparative Example 3

[0062] A method for preparing a soldering material for chip packaging, which is different from Example 1 in that the raw materials do not include Cr.

[0063] Performance Test

[0064] The soldering material samples prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to performance tests.

[0065] The test sample oxide weight gain, under the same heating temperature and time conditions, the less solder weight gain indicates that the less oxide formed on the surface, the better the solder oxidation resistance.

[0066] Table 2 performance test results

[0067]

[0068]

[0069] It can be seen from the combination of Example 1 and Examples 4-5 and Table 2 that the oxidation resistance of Example 1 is better than that of Examples 4-5. By adjusting the appropriate melting temperature, the copper material and the silver material are solid-solved in the tin liquid to form a Sn-Ag-Cu alloy. If the temperature exceeds the appropriate range, too much oxidation slag is generated, and the oxidation resistance is reduced.

[0070] It can be seen from the combination of Example 1 and Examples 6-7 and Table 2 that the oxidation resistance of Example 1 is better than that of Examples 6-7. By adjusting the appropriate temperature, the Al, Cr and CeO2 are improved in the melting process to improve the oxidation resistance of the solder material in operation, and the tin slag is reduced.

[0071] It can be seen from the combination of Example 1 and Comparative Examples 1-3 and Table 2 that the oxidation resistance of Example 1 is better than that of Comparative Examples 1-3. CeO2 is beneficial to the diffusion of Cr and Al atoms to the surface of the matrix. Since the activity of Al is higher than that of Cr, Al first diffuses to the surface of the alloy and contacts oxygen to form an Al2O3 oxidation film. Then, part of the Cr atoms contact oxygen to form Cr2O3. In this way, a continuous Al2O3 and Cr2O3 composite film is formed on the surface of the alloy during the alloy melting process, which inhibits the oxidation behavior inside the alloy to a certain extent, greatly improving the oxidation resistance of the solder material.

[0072] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, and the modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A soldering material for a chip package, characterized by: Comprise the following weight percentage of component raw materials: Ag 2-6%, Cu 0.4-1%, Al 0.05-0.2%, Cr 0.03-0.08%, CeO2 0.01-0.06%, P 0.0003-0.001% and the balance of Sn; The preparation method of the soldering material for the chip package comprises the following steps: Step one, preparation of SnAgCu alloy: tin ingot is heated and melted, the temperature is raised to 490-520 DEG C, copper material and silver material are added and melted and stirred uniformly to obtain liquid SnAgCu alloy; Step two, preparation of SnAgCuCrAlPCeO2 alloy: chromium material, aluminum material and cerium oxide powder are added to the liquid SnAgCu alloy prepared in step one, the temperature is lowered to 460-490 DEG C, stirring is carried out for 30-40 min until complete melting, then phosphorus powder is added and stirred uniformly to obtain liquid SnAgCuCrAlPCeO2 alloy; Step three, preparation of finished product: the liquid SnAgCuCrAlPCeO2 alloy prepared in step two is used to remove oxide slag on the surface of the alloy liquid with a stainless steel scraper, the temperature is lowered to 300-330 DEG C, the alloy liquid is cast in a mold, and the mold is cooled and removed to obtain the soldering material.

2. The solder paste for a chip package according to claim 1, wherein: Comprise the following weight percentage of component raw materials: Ag 2-6%, Cu 0.4-1%, Al 0.05-0.2%, Cr 0.03-0.08%, CeO2 0.01-0.06%, P 0.0003-0.001% and the balance of Sn; 3. The solder paste according to claim 1, wherein: Comprise the following weight percentage of component raw materials: Ag 2-6%, Cu 0.4-1%, Al 0.05-0.2%, Cr 0.03-0.08%, CeO2 0.01-0.06%, P 0.0003-0.001% and the balance of Sn.

4. A method for preparing a solder for chip packaging according to any one of claims 1-3, characterized in that: Comprise the following steps: Step one, preparation of SnAgCu alloy: tin ingot is heated and melted, the temperature is raised to 490-520 DEG C, copper material and silver material are added and melted and stirred uniformly to obtain liquid SnAgCu alloy; Step two, preparation of SnAgCuCrAlPCeO2 alloy: chromium material, aluminum material and cerium oxide powder are added to the liquid SnAgCu alloy prepared in step one, the temperature is lowered to 460-490 DEG C, stirring is carried out for 30-40 min until complete melting, then phosphorus powder is added and stirred uniformly to obtain liquid SnAgCuCrAlPCeO2 alloy; Step three, preparation of finished product: the liquid SnAgCuCrAlPCeO2 alloy prepared in step two is used to remove oxide slag on the surface of the alloy liquid with a stainless steel scraper, the temperature is lowered to 300-330 DEG C, the alloy liquid is cast in a mold, and the mold is cooled and removed to obtain the soldering material.

5. The method for preparing a solder for chip packaging according to claim 4, characterized in that: The purity of the chromium material, the aluminum material and the cerium oxide powder is 99.95%-99.99%.

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