JP2018511482A - Hybrid alloy solder paste - Google Patents

Abstract

The solder paste comprises an amount of the first solder alloy powder between 44 wt% and less than 60 wt%, an amount of the second solder alloy powder of more than 0 wt% to 48 wt%, and a flux, The 1 solder alloy powder includes a first solder alloy having a solidus temperature of greater than 260 ° C., and the second solder alloy powder includes a second solder alloy having a solidus temperature of less than 250 ° C. It is what. In another aspect, the solder paste comprises an amount of first solder alloy powder between 44% and 87% by weight, an amount of second solder alloy powder between 13% and 48% by weight, and a flux. Become. [Selection figure] None

Description

  The present invention relates generally to the composition of hybrid alloy solder (solder) pastes, and in particular, in some embodiments, to the composition of each alloy component within the solder paste for application in high temperature solder joint formation.

[Description of related technology]
Lead generated by the disposal of electronic assemblies is believed to be harmful to the environment and human health. Laws are increasingly prohibiting the use of Pb (lead) containing solder in the electronic interconnection and electronic packaging industries. Pb-free solders that replace conventional eutectic Pb-Sn have been extensively studied. SnAg, SnCu, SnAgCu and SnZn solders have become mainstream solders for mutual coupling in the semiconductor and electronics industries. However, development of conventional high-lead-containing solders, that is, high-temperature Pb-free solders as a substitute for Pb-5Sn or Pb-5Sn-2.5Ag, is still in its initial stage. High temperature solder is utilized to maintain internal bonding within components within an assembly when the assembly is “soldered” onto a printed wire board (printed wiring board; PWB).

  A common use of high temperature solder is for die bonding. In one exemplary process, the assembly is formed by soldering a silicon die onto a lead frame using high temperature solder. The encapsulated or unencapsulated silicon die / lead frame assembly is then attached to the PWB by soldering or by mechanical fixation. The board (PWB) can also be exposed to a few reflow processes to surface (surface mount) other electronic devices on the board. During the further soldering process, the internal bond between the silicon die and the lead frame must be well maintained. This requires that the high temperature solder resist multiple reflows without causing any malfunction. Therefore, in order to be compatible with the solder reflow profile (solder reflow characteristics) used in the industry, the main requirements for high temperature solder are (i) a melting temperature (melting point) of about 260 ° C. or higher (typical) A typical solder reflow profile), (ii) good thermal fatigue resistance, (iii) high thermal / electrical conductivity, and (iv) low cost.

  Currently, there are no drop-in lead-free substitutes available in the industry. In recent years, however, a few lead-free solder candidates for high temperature die bonding applications such as (1) Sn—Sb, (2) Zn-based alloys, (3) Au—Sn / Si / Ge and (4) Bi-Ag and the like have been proposed.

  Sn—Sb alloys containing less than 10 wt% Sb maintain good physical properties without forming large amounts of intermetallic compounds. However, because the solidus temperature does not exceed 250 ° C, the need for 260 ° C for reflow resistance cannot be met.

  A Zn main component alloy containing eutectic Zn—Al, Zn—Al—Mg, and Zn—Al—Cu has a melting point exceeding 330 ° C. However, the high affinity of Zn, Al and Mg for oxygen provides extremely poor wetting (wetting, wettability) for various metallized surface finishes. Zn- (20-40 wt%) Sn solder alloy, which has been proposed as one of high temperature lead-free alternative solders, has a liquidus temperature exceeding 300 ° C., but its solidus temperature is only about 200 ° C. It is believed that a semi-solid state of Zn—Sn solder as high as 260 ° C. maintains good mutual bonding between components during subsequent reflow. However, problems arise when the semi-solid solder is compressed in an encapsulated package and the semi-solid solder is forced out. This creates an unexpected risk of malfunction. The Zn-based solder alloy also forms a large IMC layer between the metallized surface and the solder. The presence of the IMC layer and its rapid growth during subsequent reflow and operation also raises reliability problems.

  Eutectic Au-Sn composed of two kinds of intermetallic compounds has an experimentally reliable high temperature due to its melting point of 280 ° C, good physical properties, high electrical and thermal conductivity, and excellent corrosion resistance. It was shown to be a solder. However, due to extremely high costs, their use is limited to areas where consideration of the importance of reliability outweighs costs.

  A Bi—Ag alloy with a solidus temperature of 262 ° C. meets the melting point conditions for a high temperature die bond solder. However, there are several important problems: (1) poor wetting for various surface finishes, and (2) weak joint interface (contact surface) associated with poor wetting.

  Melting point conditions for high melting point lead-free solders make Sn-Sb and Zn-Sn solders ineligible. The extremely high cost of Au-rich solders limits acceptance by industry. Zn-Al and Bi-Ag meet melting point conditions and are acceptably low cost. However, due to high affinity for oxygen (which is in the Zn-Al solder system) or (even in Bi-Ag solder systems or lead-containing solders such as Pb-Cu and Pb-Ag systems) Due to the weak binding force due to the wetting properties due to the poor reaction chemistry between the solder and the base metal coating, these poor wettings make these high melting solders difficult to use in industry ( Due to weak binding due to poor wetting). However, the desirable high melting points of BiAg and ZnAl still qualify them as candidates for high temperature lead-free solders.

  As noted above, poor solder wetting results from (1) poor reaction chemistry or (2) solder oxidation. Weak binding is always related to poor wetting. For example, poor wetting of Bi-based solder on different metallized surfaces is mainly due to poor reaction chemistry between Bi and the substrate material (ie Cu) or due to Bi oxidation during reflow. . Ge-doped BiAg has been developed for the purpose of preventing excessive formation of metal flotation on the alloy surface during melting. However, this doping will not change the reaction chemistry between Bi and the metallized surface finish of the substrate. Bi and Cu will not form IMC at the Bi / Cu interface (interface). This is the main reason for poor wetting and weakly bonded interfaces. Bi and Ni will form an IMC layer at the Bi / Ni interface, but the brittle IMC because cracks continually expand along the interface between Bi3Ni and the solder matrix, or the interface between BiNi and Ni substrate. (Bi3Ni or BiNi) weakens the bond strength. Thus, the reaction chemistry between Bi and the substrate material results in poor wetting and weak cohesion.

  Attempts have been made to modify the reaction chemistry between the solder alloy and the metallized surface finish by alloying additional elements within the solder. However, alloying usually involves some unexpected loss of properties. For example, Sn has better reaction chemistry characteristics than Bi. However, when Sn is directly alloyed in BiAg (Ag is intended to increase thermal / electrical conductivity), (1) a significant decrease in melting point, or (2) formation of Ag3Sn IMC in the alloy, May be encouraged. If there is not enough time to dissolve them in the molten solder during reflow, this will not improve the reaction chemistry between Sn and the base metal. Therefore, even if the element is alloyed directly in the solder, for example, Sn is alloyed directly in the Bi-Ag alloy, only a minimal improvement is shown.

(nothing special)

[A brief summary of embodiments of the invention]
The present invention provides a novel technique for designing and preparing hybrid alloy solder pastes, providing combined benefits from constituent alloy powders. In some embodiments, such hybrid alloy solder pastes are suitable for high temperature solder applications such as die bonding. Because the components included improved reaction chemistry with the second alloy, better controlled IMC layer thickness and enhanced reliability, high melting temperature and good thermal / electrical conductivity with the first alloy Because it provides the desired benefits. The present invention also provides a method for preparing a hybrid alloy solder paste and a method for bonding electronic components or mechanical components with a hybrid alloy solder paste.

  The technique of the present invention provides a method for designing a hybrid alloy powder paste in which additional powder is present in the paste to improve reaction chemistry at relatively low temperatures or with dissolution of the first alloy solder powder. . In some embodiments, the hybrid alloy powder paste includes a plurality of alloy powders and a flux. The alloy powder in the paste consists of one kind of solder alloy powder, which occupies the majority, and an additional small amount of alloy powder. Addenda provides superior chemical properties for wetting the various metallized surface finishes of the substrate, specifically the commonly used Cu and Ni surface finishes, and so on.

  In some embodiments, the additive will dissolve prior to or with the dissolution of most solder. The molten add-on will wet and adhere onto the substrate prior to, or with, the first alloy that partially melts or completely melts. The addendum dominates the formation of IMC along the substrate metallization surface finish and is designed to be completely converted to IMC during the reflow process. Thus, because of the dominant role played by addenda in IMC formation, the thickness of the IMC layer will be well managed by the amount of addenda in the paste. In some embodiments, the first alloy solder will have a strong affinity for the IMC layer formed between the additive and the substrate. This strong affinity will enhance the bond strength between the solder body and the IMC. Thus, the desired reaction chemistry and well-controlled thickness of the IMC layer not only improves the wetting performance, but also enhances the bond strength associated with the wetting performance.

  Other features and aspects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example features according to embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined only by the claims.

  The present invention in accordance with one or more various embodiments is described in detail with reference to the following drawings. The drawings are provided for purposes of illustration only and merely illustrate exemplary or exemplary embodiments of the invention. These drawings are provided to facilitate the understanding of the reader and should not be taken as limiting the breadth, scope and applicability of the present invention. For clarity and ease of explanation, these drawings are not necessarily drawn to scale.

FIG. 1 illustrates a reflow solder process performed in accordance with one embodiment of the present invention. FIG. 2 shows the wetting performance of an exemplary solder paste consisting of 90 wt% Bi10.02Ag3.74Sn + 10 wt% flux on a Cu coupon (cut specimen) and an Alloy 42 coupon. FIG. 3 shows the wetting performance of an exemplary hybrid alloy powder solder paste consisting of 84 wt% Bi11Ag + 6 wt% Bi42Sn + 10 wt% flux on Cu coupon and Alloy 42 coupon. FIG. 4 shows the wetting performance of an exemplary hybrid alloy powder solder paste consisting of 84 wt% Bi11Ag + 6 wt% Bi52In48Sn + 10 wt% flux on Cu coupon and Alloy 42 coupon. FIG. 5 is a DSC chart of a hybrid alloy powder solder paste composed of 84 wt% Bi11Ag + 6 wt% Sn15Sb + 10 wt% flux. FIG. 6 is a DSC chart of a hybrid alloy powder solder paste composed of 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux. FIG. 7 is a DSC chart of a hybrid alloy powder solder paste composed of 84 wt% Bi11Ag + 6 wt% Bi42Sn + 10 wt% flux. 8a and 8b are cross-sectional images of a joint made of a hybrid alloy powder solder paste on a Cu coupon and a Ni coupon. This hybrid alloy powder solder paste consists of 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux. 8a and 8b are cross-sectional images of a joint made of a hybrid alloy powder solder paste on a Cu coupon and a Ni coupon. This hybrid alloy powder solder paste consists of 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux.

  These drawings are not intended to limit the invention to only them or to the form as disclosed. It should be understood that the invention can be practiced with modification and alteration and that the invention be limited only by the claims and the equivalents thereof.

Detailed Description of Embodiments of the Invention
The present invention relates to a solder paste containing a mixture of different solder alloys in a flux. Multiple solder alloys or metals are incorporated into the flux material. The first solder alloy or metal ("first alloy") will form the body of the solder joint during reflow. The remaining second solder or metal, ie, another additional solder alloy or metal (“second alloy”), is selected based on the reactive chemical properties with the metal substrate or the affinity for the first alloy. The melting temperature (melting point) Tm (B) of the second alloy is lower than the melting point Tm (A) of the first alloy. During reflow, the second alloy first melts and spreads on the substrate. As the first alloy melts, the presence of the second alloy facilitates hardening of the molten first alloy on the substrate. The second alloy is designed to generate a low temperature melt phase that is fully converted to IMC and is present to a minimum or absent in the final bond.

  Addenda in the paste modify the reaction chemistry during reflow, improve wetting, control the thickness of the IMC, and thus increase the bond strength. In addition to the solder for high temperature lead free soldering with the desired wetting and reliability, the design process can be applied to many other soldering applications whenever a solder with poor wetting performance is used. For example, Pb—Cu alloys have a high melting point, but poor wetting performance on various metal substrates. They are therefore difficult to use for soldering. In the present invention, small amounts of additives such as Sn alloys or Sn-containing alloys help Pb-Cu to wet various metal surfaces. However, if Sn is simply alloyed in Pb-Cu, Cu6Sn5IMC formation will degrade the reaction chemistry from Sn. Alloying a large amount of Sn in the solder will greatly reduce the melting point of Pb-Cu, but this is not preferred.

  FIG. 1 illustrates a reflow process using a hybrid solder paste according to one embodiment of the present invention. The hybrid solder paste includes first alloy solder particles 118 and second alloy solder particles 115 suspended in the flux. In some embodiments, the second alloy is selected according to excellent reaction chemistry characteristics for the substrate or for a range of normal substrates. The hybrid solder paste is applied to the substrate 124. (For the sake of explanation, the flux is not shown in the drawing)

  During reflow, the temperature of the assembly rises above the melting point Tm (B) of the second alloy. The second alloy 112 melts and spreads on the base material 124 and the first alloy particles 118 that remain in a solid state. The superior surface reaction chemistry of the second alloy will facilitate wetting of the molten solder alloy 112 on the substrate 124. Thus, the IMC layer 109 is formed between the molten second alloy 112 and the base material 124. Thus, the IMC layer is controlled primarily by the amount of second alloy 115 in the original paste.

  Furthermore, the second alloy is designed to have a good affinity for the first alloy. This affinity is either due to (1) the negative mixing enthalpy between the first alloy and the second alloy, or (2) the formation of a eutectic phase composed of constituent elements from the first alloy and the second alloy. Can be determined by. In some embodiments, this affinity results in the dissolution of a portion of the first alloy 118 within the molten second alloy 112 and forms a hybrid 106 of the first alloy and the second alloy.

  As the temperature rises above the melting point Tm (A) of the first alloy, the first alloy terminates melting, forms a solution 103 of the first alloy and the second alloy, and wets the IMC layer 109. With the assembled part maintained above Tm (A), the second alloy is removed from the solution 103, increasing the IMC layer 109, leaving the molten first alloy 100. In some embodiments, in addition to forming the IMC layer 109, excess constituents from the second alloy are incorporated into the IMC along with constituents from the first alloy. The affinity between the first alloy and the second alloy contributes to improved wetting of the first alloy 100 on the IMC layer 109 and enhances the bond strength.

  When the assembly part is cooled, the solder bump 121 or the joint is formed by the base material 124 bonded to the IMC 109 and bonded to the solidified first alloy. After solidification, a homogeneous solder joint with an improved adhesive interface has been achieved.

  Solder joints resulting from the use of a hybrid solder paste show a significant improvement in the use of a solder paste containing one solder alloy, where the single solder alloy is composed of elements of the first and second alloys Even better. FIG. 2 illustrates solder bumps 201 and 207 formed using a solder paste of 86.24 wt% Bi10.02Ag3.74Sn + 10 wt% flux on Cu substrate 200 and Alloy 42 substrate 205, respectively. As these results show, large dewetting 202 and 206 occurs with the use of one (single) solder alloy. On the other hand, FIG. 3 illustrates solder bumps 211 and 216 formed using a hybrid solder paste of 84 wt% Bi11Ag + 6 wt% Bi42Sn + 10 wt% flux on Cu substrate 210 and Alloy42 substrate 215, respectively. As these results show, the use of hybrid solder paste shows little or no visible dewetting.

  In one embodiment, the hybrid solder paste includes BiAg as the first alloy and SnSb as the second alloy. In the second alloy, Sn has been selected for its excellent reaction chemistry over Bi with various substrates. SnSb has a lower melting point than BiAg. Sn and Bi exhibit a negative mixing enthalpy and form a eutectic phase over a wide composition range according to the binary phase diagram. Sb and Bi also exhibit negative mixing enthalpy and mutual infinite solubility. During reflow, SnSb is first dissolved to form a Sn-containing IMC layer on the substrate surface. When the temperature exceeds the melting point of BiAg, all the alloy powder in the paste is dissolved. Good affinity between Bi and Sn / Sb ensures good adhesion of molten Bi on the Sn-containing IMC layer. Furthermore, the presence of Ag in the first alloy converts surplus Sn into Ag3SnIMC present in the solder body. Thus, the least low temperature dissolved BiSn phase is left, or no low temperature dissolved BiSn phase remains. This is because Sn is completely consumed by (1) forming an IMC layer between the solder and the metal substrate and (2) forming Ag3Sn inside the BiAg solder bump.

  FIG. 5 illustrates the DSC curve of the joint resulting from the use of 84 wt% Bi11Ag + 6 wt% Sn15Sb + 10 wt% flux. The top curve shows the heat flow profile after reflow on the ceramic coupon. Spikes around 138 ° C indicate the presence of the second alloy. The bottom curve shows the heat flow profile of the paste after reflow on the Cu coupon. The absence of this spike in the bottom curve demonstrates the disappearance of the low temperature dissolved phase in the BiAg + SnSb system. FIG. 6 shows the disappearance of the low temperature dissolution phase in the BiAg + SnAg system. The experiment of FIG. 6 used 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux on the ceramic coupon and Cu coupon as shown in FIG. FIG. 7 shows the disappearance in the BiAg + BiSn system. The experiment of FIG. 7 used 84 wt% Bi11Ag + 6 wt% Bi42Sn + 10 wt% flux on the ceramic coupon and Cu coupon as in FIGS. In FIG. 7, the top curve showing the heat flow profile after solder reflow on the ceramic shows the lack of a cold melt phase. This may be due to the small amount of reactive agent Sn in the mixed solder paste and the high affinity between Sn and Ag, and as a result, the second alloy Sn is in the first alloy to the IMC in the final solder bump. Results in incorporation with a portion of the Ag.

  FIG. 8a is a micrograph of a solder joint resulting from the use of a hybrid solder paste consisting of 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux. In this example, a hybrid solder paste was applied to the Cu coupon 300. The IMC 301 is formed between Cu 300 and the second alloy. The size of the IMC 301 mainly depends on the amount of the second alloy in the paste. In the example shown, 6% by weight of the second alloy Sn3.5Ag resulted in an IMC that was only a few microns thick. Most of the solder joints are composed of Ag 303 in the Bi rich phase 302. Aging at 150 ° C. for 2 weeks did not increase the IMC thickness significantly. On the other hand, Bi and Cu do not form an intermediate metal, and since no IMC layer exists between the solder and the base material, only Bi11Ag forms a weak bond (force).

  In one embodiment of the present invention, a method of designing a hybrid solder paste selects a first alloy according to the desired properties of a finished solder joint, followed by an applicable substrate and a selected first Selecting the second alloy based on the affinity with the one alloy. The relative amounts of the first alloy, the second alloy and the flux can be determined based on conditions such as the desired IMC layer thickness, the required application conditions and the reflow process. The IMC layer thickness is related to the amount of the second alloy in the solder paste, the reflow profile, and the aging conditions after application. The acceptable IMC layer thickness can vary with different application conditions and different IMC compositions. For example, for a Cu6Sn5 / Cu3SN IMC layer, 10 microns is an acceptable thickness.

  As the amount of the second alloy in the paste increases, a cold melt phase will remain in the final bond. If the amount of the second alloy is reduced in the solder paste, the desired wetting performance will be difficult to achieve. As the amount of the second alloy decreases, good wetting requires the use of a higher total amount of paste printed or provided on the substrate. However, an increase in the total amount of paste may interfere with geometric constraints from the soldered package.

  For high temperature solder applications, the first alloy must be selected from a variety of high temperature melting solder alloys. In some embodiments, Bi-rich alloys having a solidus temperature of about 258 ° C. or higher, ie Bi—Ag, Bi—Cu, and Bi—Ag—Cu are used. The second alloy (additive) is selected from alloys that exhibit excellent chemical properties to wet and adhere on various metallized surface finishes and good affinity for molten Bi.

  In these embodiments, the second alloy will dissolve prior to or with the Bi-rich alloy and will then be easily wetted and bonded onto the substrate. On the other hand, a good affinity between Bi and the second alloy will provide good wetting. Therefore, Sn, Sn alloy, In and In alloy are selected as the second alloy. Three groups are classified based on the melting point of the selected second alloy. Group A is an additional alloy with a solidus temperature of about 230 ° C. to 250 ° C., ie Sn, Sn—Sb, Sn—Sb—X (X = Ag, Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt and Zn) alloys, and the like. Group B is a solder alloy having a solidus temperature of about 200 ° C. to 230 ° C., Sn—Ag, Sn—Cu, Sn—Ag—X (X = Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb and Zn), Sn—Zn alloys, and the like. Group C is a solder alloy with a solidus temperature below 200 ° C., ie Sn—Bi, Sn—In, Bi—In, In—Cu, In—Ag and In—Ag—X (X = Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb, Sn and Zn), Sn-Bi-X (X = Ag, Al, Au, Co, Cu, Ga, Ge, In) , Mn, Ni, P, Pd, Pt, Sb or Zn), Sn-In-X (X = Ag, Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn), and Bi-In-X (X = Ag, Al, Au, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn) alloys, etc. . In these alloys, Sn and / or In are alloy-based reactants.

  In one embodiment of the invention, the first alloy is an alloy from the Bi—Ag system and has a solidus temperature of about 260 ° C. or higher. In one particular embodiment, the first alloy comprises 0 to 20 wt% Ag with the balance being Bi. In yet another embodiment, the first alloy includes 2.6 to 15 wt% Ag with the balance being Bi.

  In the second embodiment of the present invention, the first alloy is selected from a Bi—Cu system and has a solidus temperature of about 270 ° C. or higher. In one particular embodiment, the first alloy comprises 0 to 5 wt% Cu with the balance being Bi. In yet another embodiment, the first alloy includes 0.2 to 1.5 weight percent Cu with the balance being Bi.

  In the third embodiment of the present invention, the first alloy is selected from the Bi—Ag—Cu system and has a solidus temperature of about 258 ° C. or higher. In one particular embodiment, the first alloy comprises 0 to 20 wt% Ag and 0 to 5 wt% Cu with the balance being Bi. In yet another embodiment, the first alloy includes 2.6 to 15 wt% Ag and 0.2 to 1.5 wt% Cu with the balance being Bi.

  In a fourth embodiment of the invention, the second alloy is selected from the Sn—Sb system and has a solid line temperature of about 231 ° C. to about 250 ° C. In one particular embodiment, the second alloy includes 0 to 20 wt% Sb, with the remainder being Sn. In yet another embodiment, the second alloy includes 0 to 15 wt% Sb, with the remainder being Sn.

  In the fifth embodiment of the present invention, the second alloy is Sn—Sb—X (X = Ag, Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt and Zn. And has a solidus temperature of about 230 ° C. to about 250 ° C. In one particular embodiment, the second alloy comprises 0 to 20 wt% Sb and 0 to 20 wt% X with the remainder being Sn. In yet another embodiment, the second alloy includes 0 to 10 wt% Sb and 0 to 5 wt% X with the remainder being Sn.

  In the sixth embodiment of the present invention, the second alloy includes Sn—Ag and has a solidus temperature of about 221 ° C. or higher. In one particular embodiment, the second alloy comprises 0 to 10 wt% Ag with the balance being Sn. In another embodiment, the second alloy comprises 0 to 5 wt% Ag with the balance being Sn.

  In the seventh embodiment of the present invention, the second alloy includes Sn—Cu and has a solidus temperature of about 227 ° C. or higher. In one particular embodiment, the second alloy comprises 0 to 5 wt% Cu with the balance being Sn. In another embodiment, the second alloy includes 0 to 2 wt% Cu with the balance being Sn.

  In the eighth embodiment of the present invention, the second alloy is Sn—Ag—X (X = Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb and Zn) and has a solidus temperature of about 216 ° C. or higher. In one particular embodiment, the second alloy comprises 0 to 10 wt% Ag and 0 to 20 wt% X with the balance being Sn. In another embodiment, the second alloy comprises 0 to 5 wt% Ag and 0 to 5 wt% X with the balance being Sn.

  In the ninth embodiment of the present invention, the second alloy contains Sn—Zn and has a solidus temperature of about 200 ° C. or higher. In one particular embodiment, the second alloy comprises 0 to 20 wt% Zn with the remainder being Sn. In another embodiment, the second alloy includes 0 to 9 wt% Zn with the balance being Sn.

  In the tenth embodiment of the present invention, the second alloy includes a Bi—Sn alloy and has a solidus temperature of about 139 ° C. or higher. In one particular embodiment, the second alloy includes 8 to 80 wt% Sn with the balance being Bi. In another embodiment, the second alloy includes 30 to 60 wt% Sn with the balance being Bi.

  In the eleventh embodiment of the present invention, the second alloy includes a Sn—In alloy and has a solidus temperature of about 120 ° C. or higher. In one particular embodiment, the second alloy comprises 0 to 80 wt% In and the rest is Sn. In another embodiment, the second alloy includes 30 to 50 weight percent In and the remainder is Sn.

  In a twelfth embodiment of the present invention, the second alloy includes a Bi—In alloy and has a solidus temperature of about 100 ° C. to about 200 ° C. In one particular embodiment, the second alloy contains 0 to 50 wt% In with the remainder being Bi. In another embodiment, the second alloy includes 20 to 40 weight percent In and the balance is Bi.

  In a thirteenth embodiment of the present invention, the second alloy includes an In—Cu alloy and has a solidus temperature of about 100 ° C. to about 200 ° C. In one particular embodiment, the second alloy comprises 0 to 10 wt% Cu with the balance being In. In another embodiment, the second alloy includes 0 to 5 weight percent Cu with the balance being In.

  In a fourteenth embodiment of the invention, the second alloy comprises an In—Ag alloy and has a solidus temperature of about 100 ° C. to about 200 ° C. In one particular embodiment, the second alloy comprises 0 to 30 wt% Ag with the remainder being In. In another embodiment, the second alloy contains 0 to 10 wt% Ag with the remainder being In.

  In the fifteenth embodiment, the second alloy includes In—Ag—X (X = Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb, Sn, and Zn). Having a solidus temperature of about 100 ° C to 200 ° C. In one particular embodiment, the second alloy comprises 0 to 20 wt% Ag and 0 to 20 wt% X, with the remainder being In. In another embodiment, the second alloy includes 0 to 10 wt% Ag and 0 to 5 wt% X, with the remainder being In.

  A further embodiment of the present invention provides a method for producing a hybrid solder paste. In some embodiments, particles of the first alloy are formed and particles of the second alloy are formed. The particles of the first alloy and the second alloy are then mixed with the flux to form a solder paste. The final paste includes the first alloy powder, the second alloy powder, and the remaining flux. In some embodiments, the first alloy particles are made of an alloy having a solidus temperature of at least about 260 ° C.

  In yet another embodiment, the second alloy is an alloy having a solidus temperature between about 230 ° C. and about 250 ° C., an alloy having a solidus temperature between about 200 ° C. and about 230 ° C., or And alloys having a solidus temperature of less than about 200 ° C. In some embodiments, the paste includes between about 60% and about 92% by weight of the first alloy powder, the amount of the second alloy powder is greater than 0% but not more than 12% by weight, with the remainder being flux It is. In yet another embodiment, the second alloy powder is a mixed solder paste between 2% and 10% by weight.

  In one particular embodiment, the first alloy includes a Bi—Ag alloy, a Bi—Cu alloy, or a Bi—Ag—Cu alloy. In yet another embodiment, the alloy having a solidus temperature of about 230 ° C. to about 250 ° C. is Sn alloy, Sn—Sb alloy, or Sn—Sb—X (X = Ag, Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt and Zn) alloys. In another embodiment, the alloy having a solidus temperature of about 200 ° C. to about 230 ° C. is Sn—Ag alloy, Sn—Cu alloy, Sn—Ag—X (X = Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb and Zn) alloys or Sn—Zn alloys are included. In yet another embodiment, the alloy having a solidus temperature less than about 200 ° C. includes a Sn—Bi alloy, a Sn—In alloy, or a Bi—In alloy.

  In still another embodiment, the second alloy powder includes a powder including a plurality of alloy powders. For example, the second alloy powder can include a mixture of different alloys selected from the alloys described herein. In some embodiments, the relative amounts of the first alloy and the second alloy in the hybrid solder paste are determined according to the solder application form. In some embodiments, as the amount of the second solder alloy in the paste increases beyond a predetermined threshold, the probability of maintaining some low temperature melt phase in the final solder joint will increase. In some cases, wetting to the substrate will decrease when the amount of the second solder alloy in the paste falls below a predetermined threshold. In one embodiment, the amount of the second solder alloy in the paste is determined so that the low temperature melt phase can be completely converted to high temperature melt IMC after reflow. In another embodiment, the second alloy in the paste varies between an amount greater than 0 wt% and an amount less than about 12 wt%. In one particular embodiment, the second alloy in the paste is greater than about 2% by weight but less than about 10% by weight.

  In addition to various normal impurities, a small amount of different elements, other elements can be added or incorporated into the alloy so long as the reaction characteristics of Sn are maintained.

  In some embodiments, the reflow profile used for soldering with the hybrid solder paste is designed to be quickly heated to a temperature above the melting point of the first alloy. In this case, a short immersion time at a low temperature causes a reactant such as Sn to flow quickly to the substrate side, and reacts with the substrate in the complete dissolution pool rather than the semi-solid dissolution pool. The dissolution of both the first alloy and the second alloy will facilitate the diffusion of the second alloy element from the molten solder into the substrate and parts, as well as “sinking” onto the surface.

Example
Various hybrid alloy powder solder pastes covering the ranges described herein were tested to confirm solder performance.

  Table 1 illustrates the composition of an exemplary hybrid solder paste made using a first alloy containing Bi11Ag or Bi2.6Ag, a second alloy containing Sn10Ag25Sb or Sn10Ag10Sb, and a flux.

  Table 2 shows an exemplary hybrid solder paste made using a first alloy containing Bi11Ag, a second alloy containing Sn3.8Ag0.7Cu, Sn3.5Ag, Sn0.7Cu, or Sn9Zn, and a flux. The composition of is described.

  Table 3 illustrates the composition of an exemplary hybrid solder paste made using a first alloy containing Bi11Ag, a second alloy containing Bi42Sn, Bi33In or In48Sn, and a flux.

Each paste described by Table 1, Table 2 and Table 3 was prepared and printed on the coupon using a 3 hole stainless steel stencil. Cu, Ni, Alloy 42 and alumina coupons were used. Each paste was printed on each coupon. The holes were 1/4 inch (about 0.635 cm) in diameter. The printed coupon was reflowed through a reflow oven with a profile designed for hybrid alloy powder solder paste. Reflow was performed in a three-zone reflow oven at 380 ° C., 400 ° C. and 420 ° C. under a N ₂ atmosphere at a belt speed of 13 inches (about 33 cm) / min.

  The wetting performance on Cu and Ni coupons was visually inspected. All of the hybrid solder alloys showed improved wetting performance compared to the single BiAg solder paste. 3 and 4 are photographs showing typical results. FIG. 3 shows an example of the wetting performance of a hybrid alloy powder solder composed of 84 wt% Bi11Ag + 6 wt% Bi42Sn + 10 wt% flux. The left image shows the reflowed paste on the Cu coupon, and the right image shows the reflowed paste on the Alloy 42 coupon. FIG. 4 shows the wetting performance of an example of a mixed alloy powder solder paste composed of 84 wt% Bi11Ag + 6 wt% Bi52In48Sn + 10 wt% flux. The image on the left shows the paste 401 reflowed on the Cu coupon 400, and the image on the right shows the paste 402 reflowed on the Alloy 42Cu coupon 405.

  The reflowed solder balls were peeled from the alumina coupon for DSC testing. Solder bumps formed on the Cu coupon and Ni coupon were also removed with a punch for DSC testing. DSC measurements were performed using a differential scanning calorimeter at a heating rate of 10 ° C / min. Representative DSC curves are shown in FIGS. FIG. 5 shows the DSC curve for the joint obtained using 84 wt% Bi11Ag + 6 wt% Sn15Sb + 10 wt% flux. The top curve illustrates the heat flow profile after reflow on the ceramic coupon. A spike at about 138 ° C indicates the presence of the second alloy. The bottom curve shows the heat flow profile of the paste after reflow on the Cu coupon. The absence of this spike in the bottom curve confirms the disappearance of the low temperature dissolved phase in the BiAg + SnSb system. FIG. 6 shows the disappearance of the low temperature dissolution phase in the BiAg + SnAg system. The experiment of FIG. 6 used 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux on the ceramic coupon and Cu coupon as in FIG. FIG. 7 shows the disappearance in the BiAg + BiSn system. The experiment of FIG. 7 used 84 wt% Bi11Ag + 6 wt% Bi42Sn + 10 wt% flux on the ceramic coupon and Cu coupon, as in FIGS. In FIG. 7, the top curve illustrating the heat flow profile after solder reflow on the ceramic shows the lack of a low temperature dissolved phase. This may be due to the high affinity between Sn and Ag, and Sn in the second alloy will result in incorporation into the IMC in the final solder bump.

  A cross section of the sample was imaged to determine the IMC thickness at the interface between the solder bump and the Cu coupon or Ni coupon. A representative image is shown in FIG. FIG. 8a is a cross-section of a solder bump using 84 wt% Bi11Ag + 6 wt% Sn3.5Ag + 10 wt% flux on a Cu coupon. FIG. 8b is a cross section of a solder bump using the same solder paste on a Ni coupon. As these results show, the IMC layer thickness was regulated to a few μm on both coupons.

  In an embodiment, the second solder alloy is a Bi—Sb—Sn alloy consisting of greater than 0 wt% to 40 wt% Sb, greater than 0 wt% to 40 wt% Sn, and Bi.

  In an embodiment, the second solder alloy is a Bi—Sb—Sn—X alloy, where X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt or Zn. In the implementation of these examples, the Bi-Sb-Sn-X alloy is composed of more than 0% to 40% Sb, more than 0% to 40% Sn, more than 0% to 5% by weight. X and Bi.

  In an embodiment, the first solder alloy is a Bi—Ag—Y alloy, a Bi—Cu—Y alloy, or a Bi—Ag—Cu—Y alloy, where Y is Al, Au, Co, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb, Sn, or Zn. In the implementation of these examples, Y is in the range of greater than 0% to 5% by weight of the first solder alloy.

  In further embodiments, the solder paste comprises a higher weight percent second alloy powder, a lower weight percent first alloy powder, or some combination thereof. In one such embodiment, the solder paste comprises 44 wt% and less than 60 wt% of the first alloy powder, greater than 0 wt% and less than 48 wt% of the second alloy powder, 0 wt% and 15 wt%. Consisting of a flux between. In one particular form of this example, the amount of the second alloy powder may be greater than 2 wt% and less than 40 wt%.

  In another such embodiment, the solder paste comprises between 44 wt% and 87 wt% first solder alloy powder, between 13 wt% and 48 wt% second solder alloy powder, and 0 wt%. And 15% by weight flux. In one particular form of this embodiment, the amount of the second alloy powder may be between 26% and 40% by weight.

  In these alternative embodiments, a higher weight percent of the second alloy powder, a lower weight percent of the first alloy powder, or a combination thereof increases the homogeneity of the solder paste. This improved homogeneity allows the hybrid alloy solder paste to be applied to the formation of even smaller joints, at least for both wetting and high temperature performance, whether bonding of just 0.2 mm diameter joints. provide. Furthermore, this combination of solder alloy powders allows even higher solder joint temperatures after reflow. For example, in one such form, the remelting temperature of the formed bond can exceed 270 ° C. In another such form, the remelting temperature of the formed bond can be up to 280 ° C. or higher.

  Although various embodiments / examples of the present invention have been described above, it should be understood that they have been provided by way of example only and are not intended to be limiting. Similarly, the various drawings illustrate exemplary configurations or other forms of the invention, which are intended to assist in understanding the features and functionality that may be included in the invention. The present invention is not limited to the configurations and configurations shown and described, and desirable features can be implemented using various other configurations and configurations. In fact, it will be apparent to those skilled in the art how alternative functional, logical or physical divisions and forms can be utilized to implement the desired features of the present invention. In addition, many different components other than those described here can be applied to various division forms. In addition, with respect to flow diagrams, operational descriptions, and method claims (claims), the order in which the implementation steps are provided therein, unless otherwise noted, the various embodiments have the same specified functionality. Does not require to be performed in order.

  Although the present invention has been described above by various exemplary embodiments and aspects, the various features, forms and functionality described in one or more individual embodiments are not limited to those specific embodiments described. It is not limited to the applicability of the invention, whether specifically described, or whether such features are part of the described embodiment, either alone or in various combinations. It should be understood that other embodiments of the present invention are applicable. Accordingly, the breadth and scope of the present invention should not be limited to any of the above-described exemplary embodiments.

  The terms and expressions used herein, and their variations, unless otherwise expressly stated, are open-ended and not limiting. For example, the term “includes” means “including without limitation”, etc., and the term “example” provides a representative example of what is being described, including a depleted or limited list thereof. What is not intended to be provided, and what is not specifically mentioned in the number, means “at least one”, “one or more”, etc., “conventional”, “traditional”, “normal”, “ “Standard”, “known” and similar expressions are not to be understood as being limited to what is available at a given time or at a given time, but can be used at any time, now or in the future It should be read to cover any known, ordinary, traditional, ordinary or standard techniques. Similarly, when this specification refers to techniques that are obvious or known to a specialist in the field, such techniques are known or known to the expert at any time, now or in the future. It covers what is being done.

  Terms such as “one or more”, “at least”, “non-limiting”, etc. mean that if a broadening term is absent, a narrower case is envisaged or required. It should not be understood. The use of the term “module” does not mean that all components or functionality described or claimed as part of the module are designed to fit within a common package. In fact, the various components of the module, whether control logic or other components, can be combined in one package or can be maintained separately, and can be grouped or grouped together. It is possible to distribute to the package or to multiple locations separately.

  Additionally, the various embodiments described herein are described in the form of representative block diagrams, flowcharts, and other diagrams. As will be apparent to those skilled in the art upon reading this specification, the embodiments described and illustrated, and various variations thereof, can be practiced without limitation to the described embodiments. is there. For example, block diagrams and the accompanying description should not be construed as requiring a particular configuration or configuration.

“Dewetting” in FIG. 2 is dewetting (or non-wetting).
“Alloy 42” in FIGS.
“Solder” in FIGS. 8a and 8b is solder.
“Bi-rich phase” is a Bi-rich phase.
“IMC” is an intermetallic compound.

Claims (32)

Solder paste (solder paste)
An amount of first solder alloy powder of 44 wt% to less than 60 wt%;
An amount of second solder alloy powder of greater than 0% by weight and up to 48% by weight;
Consisting of flux,
The first solder alloy powder includes a first solder alloy having a solidus temperature exceeding 260 ° C.,
The second solder alloy powder is a solder paste containing a second solder alloy having a solidus temperature of less than 250 ° C.   The solder paste according to claim 1, wherein the second solder alloy has a solidus temperature between 230C and 250C.   The second solder alloy is a Sn alloy, a Sn—Sb alloy, or a Sn—Sb—X alloy (where X is Ag, Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, The solder paste according to claim 2 containing Pd, Pt or Zn).   The solder paste according to claim 1, wherein the second solder alloy has a solidus temperature between 200C and 230C.   The second solder alloy is Sn—Ag alloy, Sn—Cu alloy, Sn—Ag—X alloy (where X is Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd). , Pt, Sb or Zn), or a Sn—Zn alloy.   The solder paste according to claim 1, wherein the second solder alloy has a solidus temperature of less than 200C.   The second solder alloy is Sn—Bi alloy, Sn—In alloy, Bi—In alloy, Sn—Bi—X alloy (where X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb or Zn), Sn—In—X alloy (X is Ag, Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb) Or Zn), or a Bi—In—X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn). Solder paste as described.   The solder paste of claim 1, wherein the amount of the second solder alloy powder is between 2 wt% and 40 wt%.   The said 2nd solder alloy is a Bi-Sb-Sn alloy which consists of Sb exceeding 0 to 40 weight%, Sn exceeding 0 to 40 weight%, and Bi. Solder paste.   The second solder alloy includes Bi-Sb composed of Sb exceeding 0 wt% up to 40 wt%, Sn exceeding 0 wt% to 40 wt%, X exceeding 0 wt% to 5 wt%, and Bi. The solder paste according to claim 1, which is a Sn-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt or Zn).   The solder paste according to claim 1, wherein the first solder alloy includes a Bi—Ag alloy, a Bi—Cu alloy, or a Bi—Ag—Cu alloy.   The first solder alloy includes a Bi—Ag—Y alloy, a Bi—Cu—Y alloy, or a Bi—Ag—Cu—Y alloy, where Y is Al, Au, Co, Ga, Ge, In, 2. The solder paste according to claim 1, wherein Mn, Ni, P, Pd, Pt, Sb, Sn, or Zn, and Y is in the range of more than 0 wt% and up to 5 wt%. The first solder alloy is
The remaining part contains Bi with an Ag exceeding 0% by weight up to 20% by weight,
More than 0 wt.% And up to 5 wt.% Cu with the balance containing Bi, or
The solder paste according to claim 1, wherein more than 0% by weight of Ag and 20% by weight of Ag and more than 0% by weight of up to 5% by weight of Cu, with the remainder comprising Bi. The first solder alloy is
2.6% to 15% by weight of Ag with the remainder containing Bi
0.2 wt% to 1.5 wt% Cu with the balance containing Bi, or
The solder paste according to claim 1, wherein 2.6% to 15% by weight of Ag and 0.2% to 1.5% by weight of Cu, with the remainder containing Bi. Solder paste (solder paste)
An amount of first solder alloy powder between 44 wt% and 87 wt%;
An amount of second solder alloy powder between 13% and 48% by weight;
Consisting of flux,
The first solder alloy powder includes a first solder alloy having a solidus temperature exceeding 260 ° C.,
The second solder alloy powder is a solder paste containing a second solder alloy having a solidus temperature of less than 250 ° C.   The solder paste of claim 15, wherein the second solder alloy has a solidus temperature between 230 ° C. and 250 ° C.   The second solder alloy is a Sn alloy, a Sn—Sb alloy, or a Sn—Sb—X alloy (where X is Ag, Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, The solder paste according to claim 16 containing Pd, Pt or Zn).   The solder paste of claim 15, wherein the second solder alloy has a solidus temperature between 200 ° C. and 230 ° C.   The second solder alloy is Sn—Ag alloy, Sn—Cu alloy, Sn—Ag—X alloy (where X is Al, Au, Bi, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd). , Pt, Sb or Zn) alloy or Sn-Zn alloy.   The solder paste according to claim 15, wherein the second solder alloy has a solidus temperature of less than 200 ° C.   The second solder alloy is Sn—Bi alloy, Sn—In alloy, Bi—In alloy, Sn—Bi—X alloy (where X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb or Zn), Sn—In—X alloy (X is Ag, Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb) Or Zn), or a Bi—In—X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn). Solder paste as described.   The solder paste according to claim 15, wherein the amount of the second solder alloy powder is between 26 wt% and 40 wt%.   The second solder alloy is a Bi-Sb-Sn alloy composed of Sb exceeding 0 wt% to 40 wt%, Sn exceeding 0 wt% to 40 wt%, and Bi. Solder paste.   The second solder alloy includes Bi-Sb composed of Sb exceeding 0 wt% up to 40 wt%, Sn exceeding 0 wt% to 40 wt%, X exceeding 0 wt% to 5 wt%, and Bi. Item 16. The solder paste according to Item 15, which is a Sn—X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, or Zn).   The solder paste according to claim 15, wherein the first solder alloy includes a Bi—Ag alloy, a Bi—Cu alloy, or a Bi—Ag—Cu alloy.   The first solder alloy includes a Bi—Ag—Y alloy, a Bi—Cu—Y alloy, or a Bi—Ag—Cu—Y alloy, where Y is Al, Au, Co, Ga, Ge, In, The solder paste according to claim 15, wherein Mn, Ni, P, Pd, Pt, Sb, Sn, or Zn, and Y is in the range of more than 0 wt% and up to 5 wt%. The first solder alloy is
The remaining part contains Bi with an Ag exceeding 0% by weight up to 20% by weight,
More than 0 wt.% And up to 5 wt.% Cu with the balance containing Bi, or
16. A solder paste according to claim 15, wherein more than 0% by weight of Ag and 20% by weight of Ag and more than 0% by weight of up to 5% by weight of Cu, the balance being Bi. The first solder alloy is
2.6% to 15% by weight of Ag with the remainder containing Bi
0.2 wt% to 1.5 wt% Cu with the balance containing Bi, or
16. The solder paste according to claim 15, wherein 2.6% to 15% by weight of Ag and 0.2% to 1.5% by weight of Cu, with the remainder containing Bi.   The solder paste according to claim 1, wherein the solidus temperature of the first solder alloy is less than 320C. The first solder alloy is a Bi—Ag alloy, a Bi—Cu alloy, a Bi—Ag—Cu alloy, or a Bi—Ag—Cu—Y alloy, where Y is Al, Au, Co, Ga, Ge. In, Mn, Ni, P, Pd, Pt, Sb, Sn or Zn,
The second solder alloy includes a Bi—Sn alloy, a Bi—In alloy, a Bi—Sb—Sn alloy,
Sn-Bi-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb or Zn),
Sn-In-X alloy (X is Ag, Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn),
Bi-In-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn), or
The solder paste according to claim 1, which is a Bi-Sb-Sn-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt or Zn). .   The solder paste according to claim 15, wherein the solidus temperature of the first solder alloy is less than 320 ° C. The first solder alloy may be a Bi—Ag alloy, a Bi—Cu alloy, a Bi—Ag—Cu alloy, or a Bi—Ag—Cu—Y alloy (Y is Al, Au, Co, Ga, Ge, In, Mn Ni, P, Pd, Pt, Sb, Sn or Zn),
The second solder alloy includes a Bi—Sn alloy, a Bi—In alloy, a Bi—Sb—Sn alloy,
Sn-Bi-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt, Sb or Zn),
Sn-In-X alloy (X is Ag, Al, Au, Bi, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn),
Bi-In-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, Mn, Ni, P, Pd, Pt, Sb or Zn), or
The solder paste according to claim 15, which is a Bi-Sb-Sn-X alloy (X is Ag, Al, Au, Co, Cu, Ga, Ge, In, Mn, Ni, P, Pd, Pt or Zn). .

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