JP2013035046A - Soldered joined structure of metal film and lead, and its heat treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the time deterioration of a solder fillet, and to improve the reliability of a soldered joined structure.SOLUTION: A lead member 10 with a solder material has a double-structure in which the surface of a lead wire 11 is coated with a Cu-soldered foundation layer 12, and an Sn-system soldered layer 13 containing Sn whose density is not lower than a prescribed value is laminated on the foundation layer. The soldered joined structure is characterized in that: an electronic element 20 such as a semiconductor and a piezoelectric vibrator is joined to the lead wire 11 by using the Sn-system soldered layer 13; the time deterioration is suppressed by bringing a diffusion reaction into a balanced state by applying prescribed heat treatment to the solder fillet after being soldered, and a metal composition of the solder fillet is changed to higher-resistance high-temperature solder. At this time, the Cu-soldered foundation layer 12 coated on the lead wire 11 is imparted with a sufficient thickness in advance, and the Cu-soldered foundation layer 12 is made not to vanish even if the mutual diffusion of Cu and Sn is progressed up to the balanced state.

Description

  The present invention relates to a bonding structure in which terminal leads of electronic components are soldered to a metal film on an insulating substrate, and in particular, a terminal lead in which an Sn alloy solder material is formed on a Cu plating lead wire is connected to an electrode metal film formed on an insulating substrate. The present invention relates to a solder joint structure of a metal film and a lead, and a heat treatment method thereof.

In an assembly structure of an electronic component in which an electronic element such as a semiconductor or a crystal resonator is arranged in a package, a package terminal lead is usually bonded to an electronic element electrode provided on an insulating substrate. For example, there is a case where an electronic device provided on an electrode metal film on an insulating substrate is subjected to reflow using a Sn-based high-temperature solder material as a lead Cu plating lead. At that time, mutual diffusion due to contact between the Cu and Sn alloy occurs due to the high-temperature solder material, and an intermetallic compound Cu ₃ Sn layer (Cu side) and Cu ₆ Sn ₅ layer (Cu side) between the Cu layer and the Sn-based solder layer ( It is known that delamination occurs at the interface between the Cu layer and the Cu ₃ Sn layer. This phenomenon is attributed to the accumulation of Kirkendall voids, and in order from the upper layer of the solder joint interface, intermetallic compounds (Cu ₆ Sn ₅ and Cu ₃₎ formed by mutual diffusion of Sn of the solder material and plated Cu on the lead. Depending on Sn), it causes peeling. In particular, Cu ₆ Sn ₅ layer (η phase) hardly grows at the time of reflow, and Cu ₃ Sn layer (ε phase) is generated and grown, so that Cu diffuses faster and in large quantities than Sn, so Cu ₃ Sn layer and Cu layer Kirkendall voids grow on the interface with the difference in diffusion rate of both atoms, develop into cracks, break the solder joints and cause failure. Here, regarding the generation of Kirkendall void, in the interdiffusion of Cu and Sn, the Cu atom has a faster diffusion rate than the Sn atom, and the Cu ₃ Sn layer of the generated intermetallic compound contains Cu atoms and Sn atoms. The difference in diffusion rate is large and Cu atoms preferentially diffuse, so that Kirkendall voids are generated at the interface between the Cu ₃ Sn layer and the underlying Cu layer, while the diffusion process in the Cu ₆ Sn ₅ layer of the intermetallic compound Then, since there is no big difference in the diffusion rate of Cu atom and Sn atom, the generation of Kirkendall void is not seen at the interface.

For this reason, various measures have been proposed for the purpose of ensuring the bonding reliability between the base Cu material and the Sn-based solder layer, and the Ni material has a slower reaction with Sn than Cu between the base Cu material and the Sn-based solder layer. Measures such as providing a diffusion barrier layer made of For example, Patent Document 1 relates to a conductive member, in which the area coverage of the Cu ₃ Sn layer with respect to the Ni-based underlayer is 60% or more, and the ratio of the convex portion to the concave portion of the Cu—Sn intermetallic compound layer is 1.2 to 5 Furthermore, by making the average thickness of the Cu ₃ Sn layer 0.01 to 0.5 μm, Kirkendall void is prevented, and the Ag ₃ Sn layer is provided on the Sn-based plating layer to improve the heat resistance of the plating material. I am letting. Further, in the crystal resonator of Patent Document 2, a Cu plating layer for forming an intermetallic compound with Sn and adhesion with a base metal, a Sn plating layer mainly responsible for hermetic sealing by plastic deformation at the time of press-fitting, A metal plating layer for forming an intermetallic compound with Sn, suppressing a reaction between Sn and Au, and wire bonding is provided, and the Sn plating layer is made into an intermetallic compound by heat treatment to increase the melting point.

JP 2011-026667 A JP 2010-010940 A

  As described above, when an Sn-based solder layer is applied directly to the underlying Cu material, various measures are taken to ensure the reliability of solder bonding. However, interdiffusion of Cu and Sn easily proceeds even in a temperature environment of about room temperature, so that solder bonding deteriorates with time after being supplied to the final consumer, which is a problem. In addition, an Sn—Pb alloy solder layer has been applied on the Cu base plating layer so far, and the lead terminal and the electrode of the mounted element are bonded under heat treatment conditions that do not cause mutual diffusion as much as possible. In addition, the 3 μm pure Cu plating layer completely disappeared in about 320 days, and it was also experienced that the bonding strength was significantly reduced at that time. Therefore, when the Sn-based solder layer is applied directly on the underlying Cu material, even if heat treatment is performed so that the diffusion reaction does not proceed in the manufacturing process, the joint strength deteriorates early and avoids a decrease in reliability. I couldn't. The problem to be solved by the present invention is to prevent the generation of Kirkendall voids known as interlayer growth voids generated by coalescence and growth of atomic vacancies generated by imbalance in mutual diffusion, It is to prevent the plating layer from being peeled off, to make it possible to use a solder material having a low Sn working temperature and a high Sn concentration as a high-temperature solder material.

As a result of intensive studies focusing on the interfacial reaction due to mutual diffusion of various lead members, the inventor has found that a Sn-based solder containing a predetermined concentration of Sn on a Cu lead member or a Cu plating layer applied to the lead member. The layer is pre-coated, the Sn-based solder layer is melted and soldered at the first melting temperature on the lower temperature side, and then the solder fillet formed in the soldering process is further heat-treated in the solid state. The alloy composition of the solder fillet can be changed to a high-temperature solder fillet having a second melting temperature on the higher temperature side, and this can be applied to high-temperature solder joints inside electronic device packages such as semiconductors and crystal resonators. I found that I can do it. That is, when performing melt soldering using an Sn-based solder layer containing a predetermined concentration of Sn on the underlying Cu material, the solid-state of the Sn-based solder layer that has become a liquid phase at the soldering operation temperature and the underlying Cu material is fixed. In liquid diffusion, a Cu ₃ Sn layer (ε phase) and a Cu ₆ Sn ₅ layer (η phase) of intermetallic compounds are generated at the solid-liquid interface between the molten Sn-based solder and the solid base Cu material. , Cu ₃ Sn layer (ε phase) is rarely generated, and Cu ₆ Sn ₅ layer (η phase) is preferentially generated and formed at the solid-liquid interface at the interface between the Cu—Sn intermetallic compound layer and the underlying Cu material. It has been found that the solder fillet has no generation of harmful Kirkendall void. Since this solder fillet is formed only from a coating film and has a limited Sn stoichiometry, when the solder fillet is subjected to heat treatment and solid phase diffusion is achieved until it reaches an equilibrium state, Sn contained in the solder rapidly Diffusion consumption is consumed and the diffusion supply of Sn to the base Cu side decreases, and all of the Cu ₆ Sn ₅ layers change into Cu ₃ Sn layers. Cu diffusion from the Cu material is eliminated and the generation of Kirkendall void is suppressed. In addition, when the Cu material is composed of a coating layer such as plating, the Cu plating underlayer and the Sn-based solder layer will not be lost due to the erosion phenomenon in the soldering process and heat treatment after soldering. By preliminarily adjusting the amount of Cu, the mechanical strength of the Cu—Sn intermetallic compound layer can be prevented from being deteriorated.

  According to the present invention, the aforementioned Cu material may be a Cu plating underlayer obtained by applying a Cu plating underlayer to a lead wire, and an Sn-based solder layer containing Sn in a predetermined concentration range is formed on the Cu plating underlayer. A solder joint structure of a laminated lead member and an electrode metal film on an insulating substrate having an electronic element, wherein the Sn-based solder layer is melted at a predetermined temperature to connect the lead member and the electrode metal film to a solder fillet The metal fillet and the lead are characterized in that the solid phase diffusion of Cu—Sn is progressed by heat treatment of the solder fillet by heat treatment to obtain an equilibrium intermetallic compound in which the pure metal Sn component is a predetermined concentration or less. A solder joint structure is provided. In the case where the Sn-based solder layer is a Sn—Pb alloy solder material, it is desirable to contain Sn in the range of 10 to 30 mass% in the composition, and in the case of Sn or Sn—Cu alloy solder material, the composition thereof In Sn, it is desirable to contain in the range of 85-100 mass%. That is, by performing a predetermined heat treatment, the diffusion reaction is brought into an equilibrium state to suppress a change with time, and the metal composition of the initial solder fillet is changed to a high-temperature solder fillet having a higher melting temperature. A new and improved solder joint structure and heat treatment method thereof are provided.

  Here, the Cu plating underlayer has the Sn series to such an extent that the Cu phase of the Cu plating underlayer does not disappear even after the Cu phase mutually diffuses with the Sn phase of the Sn series solder layer and reaches an equilibrium state. An excessive amount of Cu is previously applied as a base layer to the total amount of Sn contained in the solder layer. That is, in a lead member in which a Cu plating base layer applied to a lead member such as a lead wire of an electronic component and a Sn-based solder layer containing Sn in a predetermined concentration range are laminated on the Cu plating base layer, a sufficient thickness is previously provided. A new and characterized in that the Cu plating underlayer is provided and the mutual diffusion of Cu and Sn proceeds to an equilibrium state so that the Cu plating underlayer does not disappear even if the pure metal Sn component is below a predetermined concentration. An improved solder joint structure is provided. Specifically, a high-temperature solder fillet is disclosed as a solder joint structure of a metal film and a lead having an Sn content of 1% by mass or less as a pure metal excluding an Sn alloy of an intermetallic compound.

  According to another aspect of the present invention, a step of procuring a lead member in which a Cu plating base layer is applied to a lead wire and an Sn-based solder layer containing Sn in a predetermined concentration range is laminated thereon, and an insulation having an electronic device A step of forming an electrode metal film on the substrate, a soldering step of melting the Sn-based solder layer and joining the lead member and the electrode metal film via a solder fillet, and heat-treating the solder fillet by Cu-Sn A heat treatment method for a solder joint structure of a metal film and a lead is proposed, which includes a heat treatment step in which solid phase diffusion of the metal is progressed to form an intermetallic compound in an equilibrium state. That is, a predetermined amount of Sn is contained on the underlying Cu material of the lead member so that it can be melted at a lower temperature in the step of joining the metal film for an electrode of an electronic element such as a semiconductor or piezoelectric element to the lead member with a solder material. The Sn-based solder layer is coated in advance, the Sn-based solder layer is melted and soldered at the first melting temperature on the lower temperature side, and then the initial solder fillet is heat-treated in a solid-phase state. A solder heat treatment method for a lead member with a solder material, wherein the metal composition of the fillet is changed to a high temperature solder fillet having a second melting temperature on the higher temperature side.

  In the electronic component to which the lead member with a solder material of the present invention is applied, since the mutual diffusion of Sn and Cu is in an equilibrium state in the heat treatment after soldering, there is no fear that the high-temperature solder fillet after the product is deteriorated with time. Reliability is improved. Moreover, after joining the electronic element with a Sn-based solder layer having a higher Sn concentration at a lower working temperature, a predetermined heat treatment is applied to the initial solder fillet where the lead member and the electronic element are joined, and the pure fill in the solder fillet is applied. By setting the metal Sn component to a low equilibrium concentration equal to or lower than a predetermined concentration, the melting temperature of the solder fillet can be shifted to the high temperature side and used as a heat resistant high temperature solder fillet. Furthermore, the lead member with a solder material of the present invention has a solid-phase line and a liquid-phase line that are open like conventional Sn-Cu alloy solder materials, and it has been difficult to achieve both heat resistance of the solder fillet. A crystalline Sn alloy can also be used as a heat-resistant high-temperature solder by performing a predetermined heat treatment after soldering to change the phase of the solder fillet.

It is a fragmentary sectional view which shows the arrangement | positioning state of the lead member 10 and the electronic element 20 in the soldering process of the solder joint structure which concerns on this invention. It is a fragmentary sectional view according to each process in the solder processing of FIG. 1 is an exploded perspective view of a hermetic terminal for a cylindrical crystal resonator according to an embodiment of the present invention. It is a junction partial sectional view of a lead member which has Cu plating foundation layer and a Sn-Pb solder layer in a manufacturing process of a solder joint structure concerning the present invention. It is an equilibrium state figure explaining the state change of the Sn-Pb alloy at the time of soldering and a diffusion process regarding the solder joint structure concerning the present invention. It is a partial expanded sectional view of the junction part of the lead member which has Cu plating foundation layer and Sn solder layer in the manufacturing process of the solder joint structure concerning the present invention. It is an equilibrium state figure of Cu-Sn alloy about Sn solder material.

  As shown in FIG. 1, the solder joint structure according to the present invention is configured by arranging a lead member 10 and an electronic element 20 and soldering them together. The lead member 10 has a multilayer structure in which a surface of a lead wire 11 serving as a base material is provided with a Cu plating base layer 12 and an Sn-based solder layer 13 containing Sn in a predetermined concentration range is laminated on the Cu plating base layer 12. Have The lead member 10 with a solder material is soldered to a planar electrode 25 made of a metal film to connect an electronic element 20 such as a semiconductor or a piezoelectric vibrator mounted on an insulating substrate or the like, as shown in FIG. Bonding and heat treatment are performed through three steps. That is, the solder layer 23 of the lead member and the planar electrode 25 of the electronic element are arranged as shown in FIG. 2A, and the electronic element electrode and the solder material are attached as shown in FIG. An initial solder fillet 26 bonded to the lead member by the molten solder layer is formed, and then a solid state diffusion by a heat treatment process is performed as shown in FIG. Here, by performing a predetermined heat treatment on the initial solder fillet 26 immediately after soldering, the diffusion reaction proceeds, and the concentration of the pure metal Sn component contained is brought to an equilibrium state of 1% by mass or less to suppress the change over time, The metal composition of the solder fillet is changed to a heat-resistant high-temperature solder fillet 27. Further, at this time, the Cu plating underlayer 12 applied to the lead wire 11 is provided with a sufficient thickness so that the Cu plating underlayer 12 does not disappear even if the mutual diffusion of Cu and Sn proceeds to the equilibrium state. ing. An excessive amount of the Cu plating underlayer 12 is provided in advance with respect to the total Sn amount of the Sn-based solder layer 13 and is set so that the Cu plating underlayer 12 does not disappear even if the mutual diffusion of both elements reaches an equilibrium state. Is done. In particular, when the lead wire 11 is made of an Fe-based alloy material such as Kovar alloy or Ni-Fe alloy, the Cu-based underlayer 12 disappears because the Fe-based alloy material lead wire and the Sn-based solder material are difficult to diffuse each other. If this is done, the bonding allowance is lost and the plating film may be peeled off at the interface. However, the interfacial peeling can be prevented by holding the Cu plating base layer 12.

  As described above, the solder processing method of the solder joint structure according to the present invention is an Sn-based solder whose Sn content is adjusted so that the solder material shown in FIG. 2B can be melted at a low temperature after the predetermined arrangement of the joining members. The solder layer 23 is coated on the Cu plating base layer 22, and the Sn-based solder layer 23 is melted at the first melting temperature on the low temperature side. As shown in FIG. 2C, the initial solder fillet 26 is further heat-treated in a solid phase to change the alloy composition of the fillet to a high-temperature solder fillet 27 having a higher melting temperature. That is, the Sn solder layer 23 of the lead member with solder material and the planar electrode 25 of the electronic element 24 are brought into contact with each other and heated, and only the Sn solder layer 23 of the outermost layer is melted to form the initial solder fillet 26. Thereafter, the initial solder fillet 26 is heat-treated in a solid phase until the diffusion reaction reaches an equilibrium state, and the solder fillet 26 is phase-changed to a heat-resistant high-temperature solder fillet 27.

In the embodiment according to the present invention, an airtight terminal of a cylindrical crystal unit is applied to a solder joint structure and a heat treatment method thereof. As shown in FIG. 3, the cylindrical crystal resonator includes a metal cap 30, a crystal resonator 32, and an airtight terminal 33, and the lead wire 31 of the airtight terminal 33 and the planar electrode 35 of the crystal resonator 32 are The metal cap 30 is press-fitted and hermetically sealed by soldering. Further, as shown in the partially enlarged cross-sectional view of FIG. 4, a Cu plating base layer 42 is applied on the metal lead wire 41 of the airtight terminal 33 made of Kovar alloy, 42Ni-Fe alloy or the like, and Sn is further contained thereon. A lead member with a Sn—Pb alloy solder material having a rate of 10 to 30% by mass and the remaining Pb of the Sn—Pb alloy solder layer 43 is provided. Here, regarding the composition of the Sn—Pb alloy solder layer 43, when the Sn content is less than 10% by mass, the total diffusion amount of Sn in the solder material into the Cu plating material is too small. In the soldering process, the Cu ₃ Sn layer (ε phase) is preferentially generated, and the generation of Kirkendall voids becomes significant due to the large difference in the diffusion rates of Cu and Sn. On the other hand, if the Sn content exceeds 30% by mass, the formed solder fillet has too much Sn content, and even if heat treatment is applied to the initial solder fillet after soldering, it cannot be changed to the desired high-temperature solder fillet. .

As shown in FIG. 4A, the lead member with the Sn—Pb alloy solder material comes into contact with a planar electrode 45 such as Au applied to the crystal resonator and is reflow soldered. The thickness of the Cu plating underlayer 42 is such that the thickness of the Cu layer is at least 0.5 with respect to the film thickness ratio 1 of the Sn—Pb alloy solder layer 43, and the mutual diffusion is balanced in the heat treatment after soldering. A sufficient Cu film thickness is ensured so that the Cu plating underlayer 42 does not disappear even if it is advanced to the state. The lead member with a Sn—Pb alloy solder material performs reflow soldering at a relatively low temperature of 230 to 280 ° C. At this working temperature, a solid Cu-plated underlayer 42 and a molten Sn—Pb alloy solder 70 at the solid-liquid interface have Cu ₃ Sn on the Cu plated underlayer 42 side as shown in FIG. 4B. A layer (ε phase) 48 and a Cu ₆ Sn ₅ layer (η phase) 49 are formed on the molten solder side. At this time, when the Sn concentration in the Sn—Pb alloy solder material is within a range of 10 to 30 mass%, Cu ₆ Sn ₅ layer (η phase) 49 is preferentially generated in reflow soldering, and Cu ₃ Sn. Since the generation of the layer (ε phase) 48 is small and the thickness is extremely thin, an initial solder fillet 70 having no Kirkendall void is formed at the interface between the Cu—Sn intermetallic compound and the Cu plating underlayer 42. After soldering, the initial solder fillet 70 that has become solid is heat-treated at a temperature of 150 ° C. or higher and lower than 183 ° C. as shown in the state diagram of FIG. 5B, and the pure metal Sn remaining in the solder fillet 70 The phase is solid-phase diffused to an equilibrium state to grow a Cu ₆ Sn ₅ layer (η phase) 49. When the Sn concentration of the solder fillet 70 is 1 mass% or less, the diffusion reaction reaches an equilibrium state, the diffusion of Sn from the solder fillet 70 is saturated, and the Cu diffusion from the Cu plating underlayer 42 is also eliminated, so Cu ₆ Sn ₅ The layer 49 changes into the Cu ₃ Sn layer 48 shown in FIG. 4C, and becomes a high-temperature solder fillet 71 having no Kirkendall void. As shown in FIG. 4C, the cross-sectional structure of the high-temperature solder fillet 71 includes a Cu plating underlayer 42, a Cu ₃ Sn layer (ε phase) 48 of an intermetallic compound, and an initial Sn concentration of 10 to 30 mass. %, A high temperature solder having a heat resistance of 320 ° C. or higher.

  According to another aspect of the present invention, as shown in the enlarged sectional view of FIG. 6A in which the lead element before soldering and the electronic element are in contact with each other, it is made of Kovar alloy, 42Ni-Fe alloy or the like. A Cu plating base layer 62 is applied on the metal lead 61 of the airtight terminal, and a solder layer 63 made of Sn or Sn—Cu alloy containing 85% by mass or more of Sn is applied thereon. Here, regarding the Sn—Cu alloy solder layer 63, when the content of the Sn composition is less than 85% by mass, there are too many solid phase components in the solder material in the molten soldering process, and the solder material does not melt. It becomes sufficient, and the fluidity of the solder material becomes poor at the working temperature, and the electronic element cannot be soldered.

The lead member with the Sn or Sn—Cu alloy solder material is brought into contact with the planar electrode 65 such as Au applied to the crystal resonator 64 and is reflow soldered. The film thickness of the Cu plating underlayer 62 is such that the Cu layer thickness is at least 1.3 with respect to the film thickness ratio 1 of the Sn or Sn—Cu alloy solder layer 63, and interdiffusion in the heat treatment after soldering. Sufficient Cu film thickness is ensured so that the Cu plating underlayer 62 does not disappear even if the process proceeds to an equilibrium state. The lead member with Sn solder material is subjected to reflow soldering at 232 ° C. At this working temperature, a solid-liquid interface between the solid Cu plating underlayer 62 and the molten Sn solder 70 has a Cu ₃ Sn layer (ε phase) 68 on the Cu plating underlayer 62 side as shown in FIG. A Cu ₆ Sn ₅ layer (η phase) 69 is generated on the molten solder 70 side, but when the Sn concentration in the Sn or Sn—Cu alloy solder material is 85 mass% or more, Cu ₆ Sn is used in reflow soldering. Since the Sn ₅ layer (η phase) 69 is preferentially generated, the Cu ₃ Sn layer (ε phase) 68 is generated little and the thickness is very thin, the Cu plating underlayer 62 and the Cu ₃ Sn layer (ε phase) 68 An initial solder fillet 70 having no Kirkendall void is formed at the interface (see FIG. 6B). The initial solder fillet 70 that has become solid after soldering is heat-treated at a temperature of 150 ° C. or higher and lower than 227 ° C., as shown in the state diagram of FIG. 7, to solidify the Sn solder fillet 70 and the Cu plating underlayer to an equilibrium state. Phase diffusion is performed to grow intermetallic compound layers 68 and 69. When the diffusion reaction reaches the equilibrium state, the concentration of the pure metal Sn component contained in the Sn solder fillet 70 is 1% by mass or less, and there is no Cu diffusion from the Cu plating underlayer 62. Therefore, Cu ₆ Sn _{The fifth} layer 69 changes into a Cu ₃ Sn layer 68 shown in FIG. 6C and becomes a high-temperature solder fillet 68 having no Kirkendall void. The cross-sectional structure of the high temperature solder fillet 68 is a Cu plating underlayer 62 and an intermetallic compound Cu ₃ Sn layer (ε phase) 68 as shown in FIG. Change to solder.

  In Example 1, a lead member with a Sn—Pb alloy solder material is applied to a cylindrical crystal resonator, and as shown in the enlarged sectional view of FIG. 4A, a Kovar lead wire having a diameter of 0.15 mm. 41 is a hermetic terminal for a crystal resonator in which a Cu plating base layer 42 is applied by electroplating 41 and an Sn-Pb alloy solder layer 43 comprising an Sn content of 20% by mass and the balance Pb is applied thereon by electroplating. . The Cu plating underlayer 42 has a sufficient film thickness so that the underlayer does not disappear even if the mutual diffusion proceeds to an equilibrium state. That is, in the case of the Sn—Pb alloy solder layer 43, the Cu layer is applied at least to a film thickness ratio of 0.5 or more with respect to the film thickness ratio 1 of the Sn—Pb alloy solder layer 43. Therefore, the plating thickness of the Cu plating base layer 42 is set to 5 μm, and the Sn—Pb alloy solder layer 43 having a plating thickness of 10 μm is further formed thereon. The electrode terminal with the Sn—Pb alloy solder material of Example 1 is in contact with the Au electrode 45 provided on the crystal resonator 44 and is reflow soldered.

Next, reflow soldering and heat treatment of the lead member with the Sn—Pb alloy solder material of Example 1 will be described with reference to FIG. First, as shown in FIG. 4A, the soldered electrode terminal is heated while being in contact with the Au electrode 45 of the crystal unit 44, and only the Sn—Pb alloy solder layer 43 is melted to perform reflow soldering. I do. The electrode terminal with the Sn—Pb alloy solder material of Example 1 has a solder material composed of the Sn-Pb alloy plating layer 43 with an Sn content of 20% by mass and the remaining Pb on the Cu plating base layer 42. Reflow soldering is possible at an extremely low temperature of 230 to 280 ° C. In the reflow soldering step, as shown in FIG. 4B, an intermetallic compound Cu ₆ Sn ₅ layer (η phase) is formed at the solid-liquid interface between the molten Sn—Pb alloy solder 70 and the solid Cu plating underlayer. 49 is preferentially produced, and the Cu ₃ Sn layer (ε phase) 48 is generated little and the thickness is very thin. Therefore, a Kirkendall void is formed at the interface between the Cu ₃ Sn layer (ε phase) 48 and the Cu plating underlayer 42. A missing initial solder fillet 70 is formed. Next, the pure metal Sn component remaining in the initial solder fillet 70 under the temperature condition of 150 ° C. or more and less than 183 ° C. is used to convert the initial solder fillet 70 in the solid phase into the equilibrium high-temperature solder of FIG. When solid phase diffusion is performed until the fillet 71 is obtained, a Cu ₆ Sn ₅ layer (η phase) 49 grows first, and then when the Sn concentration in the high-temperature solder fillet 71 reaches a thermal equilibrium of 1% by mass or less, the high-temperature solder fillet The diffusion of Sn from 71 is saturated and the Cu ₆ Sn ₅ layer 49 changes to the Cu ₃ Sn layer 48. The initial solder fillet 70 is composed of a Sn-Pb alloy solder layer 43 of a thin plating material and is limited in terms of the total amount. Therefore, the solid phase diffusion reaches an equilibrium state in a very short time, but has reached thermal equilibrium at this point. Therefore, apparently, Cu is not diffused from the Cu plating underlayer 42, the generation of Kirkendall void is suppressed, and the high temperature solder fillet 71 without void accumulation is formed. The cross-sectional structure of the high-temperature solder fillet 71 formed after the heat treatment is as shown in the enlarged cross-sectional view of FIG. 4C. The base Cu plating layer 42 of 1.0 μm and the intermetallic compound Cu ₃ Sn of 5.1 μm are used. Layer (ε phase) 48 and an Sn—Pb alloy layer in which the Sn concentration is initially reduced from 10 to 20 mass% to 1 mass% or less by solid phase diffusion, and is shown in the Sn—Pb alloy phase diagram of FIG. Thus, the high-temperature solder fillet 71 having a heat resistance of 320 ° C. or higher is hermetically sealed.

  In Example 2, a lead member with Sn solder material is applied to a cylindrical crystal resonator, which will be described with reference to FIG. In Example 2, as shown in the enlarged cross-sectional view of FIG. 6A, a Cu plating base layer 62 is applied by electroplating to a Kovar lead wire 61 having a diameter of 0.15 mm, and Sn solder is further formed thereon by electroplating. This is a hermetic terminal for a crystal resonator provided with a layer 63. The Cu plating underlayer 62 has a sufficient film thickness in advance so that the underlayer does not disappear even if the mutual diffusion proceeds to an equilibrium state. That is, in the case of the Sn solder layer 63, the Cu layer is applied at least to a film thickness ratio of 1.3 or more with respect to the film thickness ratio 1 of the Sn solder layer 63. Accordingly, the plating thickness of the Cu plating base layer 42 is set to 16 μm, and the Sn solder layer 63 having a plating thickness of 10 μm is further formed thereon.

The electrode terminal with Sn solder material of Example 2 is in contact with the Au electrode 65 provided on the crystal resonator 64 and reflow soldered as shown in FIG. Since the Sn solder layer 63 has a melting temperature of 232 ° C., reflow soldering can be performed at a relatively low temperature. Also when reflow soldering is performed using the Sn solder layer 63 as a solder material, in the melting process, as shown in FIG. Cu ₆ Sn ₅ layer (η phase) 69 of an intermetallic compound is preferentially generated at the solid-liquid interface between the solid Cu plating underlayer 62 and the Cu ₃ Sn layer (ε phase) 68 and the thickness is small. Very thin. Accordingly, the initial solder fillet 70 is free of the occurrence of Kirkendall void. In the heat treatment process shown in FIG. 6C, the initial solder fillet 70 is heat-treated at a temperature of 150 ° C. or higher and lower than 227 ° C. until the Sn layer completely disappears to grow a Cu ₆ Sn ₅ layer (η phase) 69. . The initial solder fillet 70 is composed of an Sn solder layer 63 of a thin plating material, and the total amount is limited, so that the solid phase diffusion reaches an equilibrium state in a very short time. If the initial solder fillet 70 is completely changed to the Cu ₆ Sn ₅ layer (η phase) 69 by this heat treatment, the supply of Sn diffusing from the solder fillet is lost, so the Cu ₆ Sn ₅ layer (η phase) 69 changes to a Cu ₃ Sn layer (ε phase) 68, but since thermal equilibrium is reached at this point, generation of a new Kirkendall void is suppressed and a high-temperature solder fillet 71 without voids can be formed. . As shown in FIG. 6C, the high-temperature solder fillet 71 includes a 0.8 μm Cu plating underlayer 62 and a 18.9 μm Cu ₃ Sn layer (ε phase) in which the solder fillet 70 is completely changed to an intermetallic compound. 7 and changes to a high-temperature solder fillet 71 having a heat resistance of 640 ° C. or higher as shown in the Cu—Sn alloy phase diagram of FIG.

  Example 3 is a lead member with an Sn—Cu alloy solder material in which the Sn solder layer is changed to an Sn—Cu alloy solder layer in the modification of Example 2, and this is applied to a cylindrical crystal resonator. . Example 3 will be described using the enlarged cross-sectional view of FIG. A Kovar lead wire 61 having a diameter of 0.15 mm is subjected to an electroplating with a Cu plating underlayer 62 of 13 μm, and further subjected to electroplating with an Sn 85 mass% and the remaining Cu of an Sn—Cu alloy solder layer 63 of 10 μm to produce crystal vibration It is a hermetic terminal for a child.

The electrode terminal with the Sn—Cu alloy solder material of Example 3 is in contact with the Au electrode 65 applied on the crystal resonator 64 and reflow soldered as shown in FIG. Since Sn-Cu alloy solder layer 63 of Sn 85 mass% and the remaining Cu starts melting by Sn-Cu eutectic phase at 227 ° C. or higher, reflow soldering can be performed at a relatively low temperature. Even when reflow soldering is performed using the Sn—Cu alloy solder layer 63 as a solder material, in the melting process shown in FIG. 6B, the solid-liquid interface between the Sn—Cu alloy solder 70 and the solid Cu plating underlayer 62 is formed. Since the intermetallic compound Cu ₆ Sn ₅ layer (η phase) 69 is preferentially generated and the Cu ₃ Sn layer (ε phase) 68 is generated little and the thickness is very thin, the initial solder with no generation of Kirkendall void Fillet 70 is obtained. Next, heat treatment is performed until the Sn phase in the Sn—Cu alloy solder 70 is completely diffused at a temperature of 150 ° C. or higher and lower than 227 ° C., and the Cu ₆ Sn ₅ layer (η phase) 69 and initial solder in FIG. The fillet 70 is changed to a Cu ₃ Sn layer (ε phase) 68 to be mutated into a high-temperature solder fillet 71 shown in FIG. The high-temperature solder fillet 71 is composed of only a 1.2 μm Cu plating underlayer 62 and a 16.5 μm Cu ₃ Sn layer (ε phase) 71 changed to an intermetallic compound, and has a heat resistance of 640 ° C. or higher. It becomes a fillet 71 and hermetically sealed.

  The present invention is used for a lead member of an electronic component package, and is particularly effective for a heat-resistant and high-temperature solder joint member used inside the package.

10 ... Lead member with solder material 20, 24, 34 ... Electronic element,
30 ... Metal cap, 32, 44, 64 ... Quartz crystal,
33 ... Airtight terminal 11, 31, 41, 61 ... Lead wire,
12, 22, 42, 62 ... Cu plating underlayer,
13, 23, 43, 63 ... solder layer, 25, 35, 45, 65 ... planar electrodes,
48, 68 ... Cu ₃ Sn layer (ε phase), 49, 69 ... Cu ₆ Sn ₅ layer (η phase),
26, 70 ... initial solder fillet, 27, 71 ... high temperature solder fillet.

Claims (10)

  A solder joint structure comprising a lead member in which a Cu plating base layer is applied to a lead wire and an Sn-based solder layer containing a predetermined concentration of Sn is laminated thereon, and an electrode metal film on an insulating substrate having an electronic element. The Sn-based solder layer is melted at a predetermined temperature, and the lead member and the electrode metal film are joined via a solder fillet. The solder fillet is subjected to heat treatment to cause solid-phase diffusion of Cu-Sn to proceed. A metal film and lead solder joint structure characterized by using an intermetallic compound in an equilibrium state of a fillet.   After the Cu phase of the Cu plating underlayer interdiffuses with the Sn phase of the Sn-based solder material and reaches an equilibrium state, the Cu plating underlayer has a Cu content with respect to the total amount of Sn contained in the Sn-based solder layer. The metal film and lead solder joint structure according to claim 1, wherein an excessive amount of Cu is applied in advance so that the phase does not disappear.   The metal film and lead solder joint structure according to claim 1, wherein the Sn-based solder layer is a Sn—Pb alloy containing Sn in a range of 10 to 30 mass% in composition.   2. The solder joint structure of a metal film and a lead according to claim 1, wherein the Sn-based solder layer is Sn or Sn—Cu alloy containing Sn in a range of 85 to 100 mass% in composition.   The metal film and lead solder joint structure according to claim 1, wherein the high-temperature solder fillet has a pure metal Sn component content excluding intermetallic compounds of 1 mass% or less.   A step of procuring a lead member on which a lead plating layer is provided with a Cu plating base layer and an Sn-based solder material containing Sn of a predetermined concentration or more is laminated thereon, and an electrode metal film on an insulating substrate having an electronic element is formed A step of melting the Sn-based solder layer and joining the lead member and the electrode metal film through a solder fillet; and a solid phase diffusion of Cu—Sn is advanced by heat-treating the solder fillet. A heat treatment method for a solder joint structure of a metal film and a lead, including a heat treatment step for forming an intermetallic compound in an equilibrium state.   The Sn-based solder layer is a Sn—Pb alloy containing Sn in the range of 10 to 30% by mass, and the Cu plating underlayer has a film thickness ratio of the Sn—Pb alloy. 7. The heat treatment method for a solder joint structure of a metal film and a lead according to claim 6, wherein the thickness of the Cu plating underlayer is at least 0.5 or more with respect to 1.   In the heat treatment step, the solid phase diffusion of the pure metal Sn phase remaining in the solder fillet is performed in a solid state under a temperature condition of 150 ° C. or higher and lower than 183 ° C. until a solid state is reached. The method for heat-treating a solder joint structure of a metal film and a lead according to claim 7.   The Sn-based solder layer is Sn or Sn—Cu alloy containing Sn in a range of 85 to 100 mass% in composition, and the Cu plating underlayer has a film thickness that is the Sn or Sn—Cu alloy. The heat treatment method for a solder joint structure of a metal film and a lead according to claim 6, wherein the thickness of the Cu plating underlayer is at least 1.3 or more with respect to the film thickness ratio of 1. The heat treatment step is characterized in that the solid phase diffusion of the pure metal Sn phase remaining in the solder fillet under a temperature condition of 150 ° C. or higher and lower than 227 ° C. is performed until the solder fillet in a solid phase is in an equilibrium state. A heat treatment method for a solder joint structure of a metal film and a lead according to claim 9.

Images