JP4677849B2 - Solder joining method - Google Patents

Description

  The present invention relates to a solder bonding method, and more particularly to a solder bonding method for bonding semiconductor wafers using a lead-free solder material that does not contain lead.

  A tin (Sn) -based solder material based on lead has a characteristic that it can be easily formed into a foil having a thickness of several to several tens of μm because it contains soft lead. For this reason, this solder material has been conventionally used for soldering semiconductor devices. However, in order to suppress environmental pollution due to lead, it is said that in 2007, usable solder materials will be completely switched to lead-free solder materials, that is, lead-free solder materials. Materials are being developed.

  In general, Sn-Ag (silver) solder materials and Sn-Sb (antimony) solder materials are known as lead-free solder materials. In order to use these lead-free solder materials as solder materials for producing a wafer laminated body in which a plurality of semiconductor wafers are joined together by soldering, it is necessary to make the solder materials into foil. However, since these solder materials do not contain lead, it is difficult to form a foil. Accordingly, the present applicant has previously filed a method for joining wafers using a solder material that is obtained by sintering a fine powder raw material of a solder material that does not contain lead as a thin plate (for example, a patent document). 1). The solder material used here is a sintered body of metal powder.

  Further, a method has been proposed in which electronic components or semiconductor chips and tabs are joined using a solder foil made by rolling a material containing copper (Cu) or silver particles and tin particles (for example, (See Patent Document 2). The solder foil used here is not alloyed. Further, the present applicant relates to a method for bonding wafers by heating an aluminum layer or an aluminum layer and a nickel layer between wafers and heating in a pressurized state when producing a wafer laminate. Have been filed earlier (see, for example, Patent Document 3).

JP 2004-146462 A JP 2004-247742 A Japanese Patent Application Laid-Open No. 11-97618

  However, the solder joining method disclosed in Patent Document 1 or 2 requires a step of pulverizing the solder material and the metal that is the raw material thereof, which is not preferable because the manufacturing cost of the solder material increases. The same applies when the solder material is pulverized into a solder cream. Moreover, the joining method disclosed in Patent Document 3 is not a method for joining semiconductor wafers using a lead-free solder material formed into a foil.

  Further, generally known Sn—Ag solder materials and Sn—Sb solder materials have a solidus temperature as low as 216 to 250 ° C., so that, for example, a chip is cut out from a wafer laminate, and 260 to the chip. If heating at 10 ° C. for 10 seconds is repeated three times (solder heat treatment), the solder material is completely melted and the chip is bent. Therefore, there is a problem that the subsequent assembly as a semiconductor device is hindered.

  In order to eliminate the above-mentioned problems caused by the prior art, the present invention uses a thin sheet-like lead-free solder material and has a solder heat resistance equivalent to or higher than that of a conventional solder material containing lead. It aims at providing the soldering method which can perform soldering so that it may have.

  In order to solve the above-described problems and achieve the object, in the solder joining method according to the present invention, a sheet-like solder material formed by rolling an alloy containing tin, silver, copper as a main component and not containing lead is used. Use. Then, the solder material and the semiconductor wafer are alternately laminated, and in this state, the solder material is melted by heating while pressing from a direction perpendicular to the wafer surface.

  For example, a sheet-like solder material formed by rolling an alloy containing tin, 10 wt% or more and 20 wt% or less silver and 3 wt% or more and 5 wt% or less copper as main components and not containing lead is used. Then, the solder material and the semiconductor wafer are alternately laminated, and in this state, the solder material is melted by heating while pressing from a direction perpendicular to the wafer surface.

  At that time, the pressing pressure is controlled to 1 MPa or more and 10 MPa or less, preferably 3 MPa or more and 7 MPa or less, and the heating temperature is set so that the low melting point component in the melted solder material is pushed out from the bonded portion between the wafers. 30 ° C. higher than the solidus temperature of the material (hereinafter referred to as solder solidus temperature + 30 ° C.) or higher and 30 ° C. lower than the liquidus temperature of the solder material (hereinafter referred to as solder liquidus) The temperature is controlled below. For example, the temperature is controlled at 250 to 330 ° C.

  Then, the melted solder material is solidified to join the wafers together. Further, when the solder material is melted, the solder material and the semiconductor wafer which are stacked and pressed are put into a chamber of a soldering apparatus, and the inside of the chamber is replaced with an inert gas atmosphere, for example, 4 Torr or less. A vacuum atmosphere may be used. According to this invention, since the low melting point component in the solder material melted by heating is pushed out from the joint between the wafers, the solder heat resistance is equal to or higher than that when using a conventional solder material containing lead. A solder joint having the following is obtained.

  According to the solder joining method of the present invention, a thin sheet-like lead-free solder material is used so that the solder heat resistance is equal to or higher than that of a conventional solder material containing lead. There is an effect that can be performed.

  Exemplary embodiments of a solder joining method according to the present invention will be explained below in detail with reference to the accompanying drawings. The lead-free solder material used in the soldering method according to the present invention is an alloy mainly composed of tin, silver, and copper. The silver content is suitably 10% by weight or more and 20% by weight or less, preferably 20% by weight. The copper content is suitably 3% by weight or more and 5% by weight or less, preferably 5% by weight. All or most of the rest is tin. As an example, there are Sn-10Ag-5Cu solder material containing 10% by weight silver and 5% by weight copper, Sn-20Ag-5Cu solder material containing 20% by weight silver and 5% by weight copper, and the like. .

  The solder material is rolled into a sheet shape. Although the thickness is not specifically limited, For example, they are 40 micrometers or more and 120 micrometers or less. This range of thicknesses means that when manufacturing a wafer laminate in which a plurality of semiconductor wafers are joined via a solder material, the thickness per wafer, the number of wafers to be laminated, and a predetermined number of wafers are soldered. It depends on the thickness when they are joined to each other via a material. Further, the shape and size of the solder material may be the same shape and the same size as the member to be joined. For example, when the member to be joined is a semiconductor wafer, it is preferable that the member has a disk shape having the same diameter as the wafer.

  FIG. 1 and FIG. 2 are diagrams for explaining an outline of a process for manufacturing a wafer laminate by the soldering method according to the present invention, and show a cross-sectional configuration of the wafer laminate. As shown in FIG. 1, first, a plurality of wafers 11 and lead-free solder materials 12 are alternately laminated to form a wafer-solder material laminate 10.

  Next, the lead-free solder material 12 is melted by heating the wafer-solder material laminate 10 under pressure, and the wafer 11 is solder-bonded via the solder bonding layer 22 as shown in FIG. The laminate 20 is obtained. The joining temperature at this time is in the range of the solder solidus temperature + 30 ° C. to the solder liquidus temperature −30 ° C.

  This is a solder heat resistance test in which a chip is cut out from the wafer laminated body 20 and then heated at 260 ° C. for 10 seconds three times while supporting both ends of the chip in the wafer lamination direction. This is because the minimum temperature that passes in this case is the solder solidus temperature + 30 ° C. Further, at a temperature higher than the solder liquidus temperature of −30 ° C., the homogenization of the melted solder proceeds, so that the soldering liquid of the low melting point liquid phase is pushed out of the joint by pressurization and the solder heat resistance of the joint is increased. This is because the effect of improving the performance is lost. Although there are some deviations depending on the composition of the solder material, specifically, it is about 250 to 330 ° C.

  Moreover, the pressure which pressurizes the wafer-solder material laminated body 10 at the time of solder joining is 1-10 Mpa. The reason is that if the pressure is 1 MPa or more, the entire wafer can be bonded, and if it exceeds 10 MPa, the wafer is easily broken. In order to produce a wafer laminate with a high yield rate more reliably, it is preferably 3 to 7 MPa. By this pressurization and heat treatment, the heat resistance of the solder joint layer 22 is improved.

  In obtaining the wafer laminate 20 shown in FIG. 2, for example, as shown in FIG. 3, a heat and pressure soldering apparatus 160 is used. The wafer-solder material laminate 10 is sandwiched between the upper surface uniform heating and pressing plate 162 of the upper press body 161 and the lower surface uniform heating and pressing plate 164 of the lower press body 163 of this apparatus. Then, the upper press body 161 is lowered by the press arm 165 to pressurize the wafer-solder material laminate 10. In this state, the wafer-solder material laminate 10 is heated by the heaters 166 and 167 embedded in the upper and lower press bodies 161 and 163, respectively. This heating may be induction heating.

  Alternatively, in order to pressurize the wafer-solder material laminate 10, a pressurization laminating jig 170 may be used as shown in a plan view and a side view in FIGS. 4 and 5, respectively. In this case, the wafer-solder material laminate 10 is sandwiched between the bottom plate 171 and the top plate 172 of the jig 170. Then, the nut 174 screwed into the threaded portion at the top of the plurality of rod-like members 173 serving as columns connecting the bottom plate 171 and the top plate 172 is tightened to pressurize the wafer-solder material laminate 10.

In the case of using the pressure lamination jig 170 described above, for example, as shown in FIG. 6, the pressure lamination jig in a state where the wafer-solder material laminate 10 is pressurized on the belt 191 of the belt conveyor furnace 190. 170 may be arranged and heated by moving under the heater 193 by feeding the belt 191 by the rotating body 192. Alternatively, as shown in FIG. 7, using a vacuum heater 200, a pressure lamination jig 170 in a state where the wafer-solder material laminate 10 is pressurized is placed on the sample stage 202 in the vacuum chamber 201. The chamber 201 is evacuated by the ion pump 203 and the cryopump 204 and heated by the heater 205. At this time, an inert gas such as H ₂ or N ₂ may be introduced into the chamber 201.

When the vacuum heater 200 shown in FIG. 7 is used, an inert gas such as H ₂ or N ₂ is introduced into the chamber 201 and the atmosphere in the chamber is replaced with an inert gas atmosphere. The chamber 201 may be evacuated to Torr or lower by the cryopump 204 and then heated by the heater 205. In this way, since the solder surface can be prevented from being oxidized, the bondability between the wafer and the solder is improved. Further, since the degree of vacuum in the chamber is 4 Torr or less, the low melting point liquid phase solder liquid in the melted solder material can be efficiently pushed out of the joint.

  The present inventors conducted a test for examining the rollability using solder materials of various compositions, produced a wafer laminate 20 as shown in FIG. 2, and used the chips cut out from the wafer laminate 20 for solder heat resistance. A test was conducted to investigate. The result will be described. The composition of the solder material, the solidus temperature and the liquidus temperature, and the temperature and pressure when producing the wafer laminate 20 are as shown in Table 1.

  With respect to the rolling test of the solder material, ingots of solder alloys having various compositions were prepared, and it was examined whether each ingot could be rolled into a sheet having a diameter of 100 mm and a thickness of 40 μm. The results are shown in Table 1. In the column of rollability in Table 1, the symbol “◯” indicates that rolling was possible, and the symbol “x” indicates that rolling was not possible. From Table 1, it can be seen that if the silver content is 5 wt% or more and 20 wt% or less and the copper content is 1 wt% or more and 5 wt% or less, the rollability is good. These solder materials having good rolling properties have the same or higher rolling properties as conventional tin-based solder materials based on lead. On the other hand, when the silver content was 25% by weight or 30% by weight, the rollability deteriorated and could not be rolled to a desired size and thickness.

  For the solder heat resistance test, the solder material that has been rolled into the desired sheet shape in the rolling property test is used, the solder material and 20 wafers are stacked on top of each other, and soldering is performed under various temperature and pressure conditions. It was. Then, the obtained wafer laminated body was cut into approximately 0.5 mm square chips with a wire saw, and as shown in FIG. Heating at 10 ° C. for 10 seconds was repeated 3 times. After heating, the bending amount x at the center of the chip 31 was measured, and it was examined whether x was a predetermined value, for example, 50 μm or less. The results are shown in Table 1. In the solder heat resistance column of Table 1, a circle indicates that x is 50 μm or less, and a cross indicates that x is greater than 50 μm.

  From Table 1, using a solder material having a silver content of 10 wt% or more and 20 wt% or less and a copper content of 3 wt% or more and 5 wt% or less, the soldering temperature is set to a solder solid line. It is good by setting it to the range from the temperature + 30 ° C. (here 260 ° C.) to the temperature of the solder liquidus temperature−30 ° C. (here 320 ° C.) and the soldering pressure 1 to 10 MPa. It can be seen that solder heat resistance is obtained. These solder materials having good solder heat resistance have the same or higher solder heat resistance as conventional lead-based tin-based solder materials.

  On the other hand, even when the solder material has good rolling properties, when the silver content is 5% by weight or the copper content is 1% by weight, the soldering temperature When the temperature is lower than the solder solidus temperature + 30 ° C. or higher than the solder liquidus temperature −30 ° C., good solder heat resistance cannot be obtained. In addition, the present inventors manufactured a wafer laminated body with a soldering condition having excellent heat resistance using a solder material having a solder composition having excellent rolling properties, and a semiconductor device using a chip cut out from the wafer laminated body. When assembled, initial electrical characteristics and reliability equivalent to those obtained when a tin-based solder material based on a conventional lead was used were obtained.

  As described above, according to the embodiment, the low-melting-point component in the melted solder material can be pushed out from the bonded portion between the wafers by controlling the pressurizing pressure and the heating temperature at the time of soldering. As a result, it is possible to obtain a solder joint having a solder heat resistance equal to or higher than that of a conventional solder material containing lead. In addition, since the solder alloy is excellent in rollability, a sheet-like thin solder material can be easily obtained by rolling an ingot of the solder alloy.

  As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the numerical values such as the content ratio, dimensions, temperature, and pressure described in the embodiments are examples, and the present invention is not limited to these values.

  As described above, the solder joining method according to the present invention is useful for a solder joining method using a lead-free solder material, and in particular, by joining a plurality of semiconductor wafers using a lead-free solder material. It is suitable for a solder bonding method when manufacturing a wafer laminate.

It is sectional drawing which shows the structure in the manufacture stage of the wafer laminated body produced by applying the soldering method concerning this invention. It is sectional drawing which shows the structure in the manufacture stage of the wafer laminated body produced by applying the soldering method concerning this invention. It is sectional drawing which shows typically the heat-pressure soldering apparatus used when applying the soldering method concerning this invention and producing a wafer laminated body. It is a top view which shows typically the pressurization lamination jig | tool used when producing the wafer laminated body by applying the solder joining method concerning this invention. It is a side view of the pressurization lamination jig | tool shown in FIG. It is sectional drawing which shows typically the belt conveyor furnace used when applying the soldering joining method concerning this invention and producing a wafer laminated body. It is sectional drawing which shows typically the vacuum heater used when applying the soldering method concerning this invention and producing a wafer laminated body. It is a schematic diagram for demonstrating a solder heat resistance test.

Explanation of symbols

11 To-be-joined member 12 Lead-free solder material 201 Vacuum chamber

Claims (4)

Sheet-shaped solder material and semiconductor wafer formed by rolling an alloy containing tin, 10% by weight to 20% by weight silver and 3% by weight to 5% by weight copper, the main component of which is not containing lead A first step of laminating to,
A second step of melting the solder material by heating while pressing from a direction perpendicular to the wafer surface in a state where the solder material and the semiconductor wafer are laminated;
A third step of solidifying the melted solder material and joining the wafers;
Only including,
A solder joining method, wherein a soldering temperature is in a range from 260 ° C. to 320 ° C., and a soldering pressure is 1 to 10 MPa . In the second step, the melted as low melting point component in the solder material is forced out from the joint between the wafer, according to claim 1, characterized in that to control the applied pressure heating temperature Solder joining method. In the second step, the solder material and the semiconductor wafer are stacked and pressurized, placed in a chamber, the chamber is replaced with an inert gas atmosphere, and then heated to a vacuum atmosphere. The soldering method according to claim 1 or 2 , characterized in that The soldering method according to claim 3 , wherein the chamber is heated with a degree of vacuum of 4 Torr or less.

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