JP2000052027A - High temperature resistant metal jointing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out soldering at comparatively low temperature by inserting only Sn as a solder alloy filler between metals to be jointed, rising the temperature of the jointed part to more than the melting temperature of the filler, and carrying out the liquid phase dispersion till the solder alloy filler phase in a metal component is vanished. SOLUTION: Sn is powdered, and a filler paste 10 with which a flux is kneaded, is applied on a jointed part of a printed base material 4, namely a metallic foil pattern 5. Then, a jointed part of an electronic part 6, namely a lead 7 is put on the metallic foil pattern 5, and a bottom part 9 of a press heating device 8 is put on the lead 7. The bottom part 9 is heated by a heating wire 11. Thereby, the filler paste 10 is fused for adhering the lead 7 on the metallic foil pattern 5. Furthermore, in a process that the filler paste 10 is fused, heated, and held, the pressure of 0.001-3.0 kg/mm2 is applied to the jointed part by the bottom part 9 of the press heating device 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining at a temperature lower than the heat resistance required by a solder joint, and for sufficiently joining the solder joint at a predetermined heat resistance required for use. The present invention relates to a high-temperature resistant metal bonding method that can be used.

[0002]

2. Description of the Related Art Conventionally, as a solder alloy, (1) Sn is 60% by weight, Pb is 40% by weight, and the melting temperature is 1%.
90 ° C. low temperature solder alloy, (2) 10% by weight of Sn,
Two types of high-temperature solder alloys having a Pb content of 90% by weight and a melting temperature of 300 ° C. are widely used. Recently, Pb-free has been called out due to environmental problems. However, in the case of the low-temperature solder alloy (1), Pb-free is achieved by using a Sn-based alloy whose main component is Sn. As for the high-temperature solder alloy of the above (2), there is no prospect of solving Pb-free at present. Recently, there is a case where a thermoelectric element is attached in order to utilize waste heat of an incinerator. As a high-temperature solder alloy for this attachment, the melting temperature of the high-temperature solder alloy of (2) is 300.
A solder alloy that can withstand a high temperature of over ℃ has been demanded. From this point of view, 300
There are no solder alloys that can be used at high temperatures up to 400 ° C. The reason will be described later.

[0003]

At present, as a high-temperature solder alloy, a solder alloy containing 10% by weight of Sn and 90% by weight of Pb and containing a large amount of Pb is widely used.
However, Pb-free, which has been demanded from the viewpoint of environmental problems of high-temperature solder alloys containing as much as 90% by weight of Pb, seems to be completely impossible at present. This is because there is no useful metal corresponding to Pb as a main component of the solder alloy when the melting temperature is between 300 ° C and 400 ° C. Cd exists at a melting temperature of 321 ° C., but cannot be used as a solder alloy because Cd is a harmful metal of Pb or more. The above-described solder alloy containing 10% by weight of Sn and 90% by weight of Pb and containing a large amount of Pb has been used in a considerable amount in mounting a printed circuit board. Conventionally, alloys that have been widely used as filler metals include brass braze, silver braze, and phosphor copper braze, and are mainly used at 800 ° F. (426 ° C.) or higher. According to the rules of the American Institute of Metals (ASM), 8
Brazing a joint of 00 ° F (426 ° C) or more (brazi
ng), and bonding at 800 ° F. (426 ° C.) or less is defined as soldering (Soldering). Therefore,
The present invention can perform soldering at a relatively low temperature, and furthermore, a solder alloy structure is lost by liquid phase diffusion, and a specially-bonded part can withstand a high temperature higher than a soldering temperature. Used in applications, and in some cases, P
It is an object of the present invention to provide a high-temperature resistant metal bonding method capable of performing high-temperature resistant metal bonding even with a b-free solder alloy.

[0004]

According to the present invention, only Sn is used.
Inserted as a solder alloy filler between the metals to be joined, raise the temperature of the part to be joined of the metal to be joined to 232 ° C. or higher, which is the melting temperature of the solder alloy filler, and observe the portion to be joined with a microscope. A high-temperature resistant metal bonding method characterized in that liquid phase diffusion is performed until the solder alloy filler phase in the metal structure disappears. Further, the present invention provides a method of manufacturing a semiconductor device according to the present invention, wherein the Sn is added with 0.001 to 80% by weight of one or more additional elements that form a eutectic with the Sn.
The high-temperature resistant metal bonding method uses an alloy as the solder alloy filler.

[0005] Further, the present invention provides the above-mentioned additive element,
Ag, Au, Bi, Ca, Ce, Cu, Ge, In, L
a, Li, Ma, Na, P, Pb, Zn; here,
If the purpose is to make Pb free, Pb is excluded.
Further, the present invention provides the above-mentioned joined portion in an amount of 0.1 mm ² .
This is a high-temperature resistant metal bonding method in which a pressure of 001 to 3.0 Kg is applied to promote the liquid phase diffusion.

Further, the present invention is characterized in that the Sn or the Sn alloy is powdered, and a filler paste in which a flux is kneaded is applied on a metal foil pattern which is the portion to be joined of a printed circuit board, so that the electronic component is covered with the filler paste. A lead, which is a bonding portion, is mounted on the metal foil pattern, a lower end portion of a pressing and heating device is mounted on the lead, and the filler paste is melted by heating the lead, so that the lead is made of the metal foil. In the process in which the filler paste fixed to the pattern and applied to the metal foil pattern is melted and continuously heated and held, a pressure of 0.001 to 3.0 kg per 1 mm ² is applied to the portion to be joined. And a high-temperature resistant metal bonding method. Further, according to the present invention, a projection is provided on the side where the lead is in contact with the metal foil pattern, and the projection is formed on the part to be joined in a range of 0.2 mm / mm ² .
Immediately before applying a pressure of 001 to 3.0 Kg, the above-mentioned metal joining method for high temperature resistance can be performed immediately before the liquid phase diffusion can be promoted. Further, the present invention is the above-described high-temperature resistant metal bonding method performed in a reducing gas atmosphere or an inert gas atmosphere.

According to the present invention, the filler is heated to a uniform liquid phase or a state in which the liquid phase and the solid phase are mixed at the time of bonding. Accompanied by a facilitation phenomenon. Originally, the reason why the bonding strength of the soldered joint is not so strong, and when the melting temperature is reached again, the two are separated from each other is because the filler phase remains there. As shown in FIGS. 1 and 2, when the gap between the joined parts 1 and 2 of the two joined metals due to the solder alloy filler 3 is defined as a gap part t, the strength of the joined part decreases in a parabolic manner. When the gap t is widened to the right side, the bonding strength becomes substantially constant and reaches the same strength as the solder alloy filler 3 itself. Here, in the present invention, the gap t is almost disappeared by diffusing the filler phase until the filler phase disappears, and the interatomic bonding near the vertical axis in FIG. 1 is enabled. For this reason, the bonding strength at this time is
This will far exceed the strength of the solder alloy filler 3 itself. In such actual joining work, it is a problem how to shorten the diffusion time.The degree of disappearance of the solder alloy filler phase can be determined by observing the contact cross section of the test piece after the test with a microscope. However, by measuring the change over time of the electrical resistance value of the joint, the progress can be continuously observed and determined.

[0008] The following conditions can be cited as points at which the diffusion at the junction is advanced. (1) A liquid phase exists in at least a part of the filler at the joining heating temperature; (2) the thickness of the filler is made as thin as possible, and the amount of the filler used is reduced as much as possible; (4) The diffusion temperature is to increase the temperature within the heatable temperature range of the material to be joined, and (5) The diffusion temperature is (6) Diffusion treatment should be performed in an inert gas atmosphere,
It is desirable to be in a reducing gas atmosphere or in a vacuum.

[0009] As a filler composition which is one of the diffusion factors, if the purpose is to be Pb-free, Pb-free
It is assumed that the base material is a Sn metal base containing no.
Moreover, since the diffusion temperature lowers the melting temperature, it is wise to select a metal having an appropriate eutectic composition. With regard to the eutectic alloy with Sn at this time, a multi-element eutectic alloy of ternary, quaternary,... Can be produced by combining these additional elements, and the melting point can be lowered. Become.
At this time, the elements capable of forming the Sn-based eutectic alloy include Ag, Au, B
i, Ca, Ce, Cu, Ge, In, La, Li, M
g, Na, P, Pb, Zn and the like. When the filler composition is determined by the above composition, the diffusion temperature is defined as the temperature range in which the liquid phase or the liquid phase and the solid phase can coexist in the solder alloy. Originally, diffusion is a function of time and temperature when the external conditions are constant in the same composition, and thus the required diffusion time is determined.

In the diffusion, it is important that no voids exist between the metals to be joined. For this reason, pressing is an important condition for the diffusion. For example, it is possible to press with a pressing and heating device shown in FIG.
In the case of the P mounting method or the like, the element's own weight itself such as an LSI also exerts a pressing effect. As the heating atmosphere, it is preferable to diffuse in an inert atmosphere in consideration of the tendency of the filler metal used to be oxidized. For example, a case where a Sn-Ag-Li-based Sn-based ternary eutectic alloy is used as a filler corresponds to this. Next, as treatment of the diffusion surface of the article to be joined, it is desirable to remove the oxide in advance, but in consideration of the material of the metal to be joined, for example, as a Sn-based filler composition, Ag, Au, B
i, Ca, Ce, Cu, Ga, Ge, In, La, L
One or more of i, Mg, Na, P, Pb, Zn and the like are selectively added. Next, as a diffusion accelerator, it is effective to apply a thin zinc chloride as an inorganic substance and a rosin-based organic substance to a metal to be joined in advance, which helps to shorten the diffusion time. Make it possible. It is also effective to coat such an accelerator in advance on the filler alloy itself.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on its embodiments with reference to the drawings.

EXAMPLE 1 A solder alloy filler composed of 50% by weight of In and 50% by weight of Sn and coated with a zinc chloride solution as a flux on both sides of a thin piece having a thickness of 0.05 mm was inserted between copper plates. A solder alloy filler phase of a metal structure observed by a microscope is heated by applying a pressure of 0.001 kg / mm ^{2 to the} joint of the metal to be joined so that a load of 0.001 kg per 1 mm ² is applied to the joint of the metal to be joined and heated at 135 ° C. for 50 minutes. Liquid phase diffusion was performed until disappeared. The heating was conducted in an N ₂ atmosphere. As a result, a peel strength of 15 kgf / mm ² was obtained as a result of performing a peel test on the bonded copper plate. The presence of an In-Sn alloy layer was not observed in the cross-section microstructure. Also, at 300 ° C., 2
As a result of performing a peeling test under a load of 50 g, no peeling occurred. This is considered to be due to the fact that the In-Sn alloy layer does not remain in the structure of the joint that can be seen with a microscope.

[0012]

Example 2 30% by weight of In and the balance of Sn
Using a solder alloy foil having a thickness of 0.07mm as the solder alloy filler, 1 mm ² per 1.5 at the junction of the joined metal
A load is applied and pressed so that a load of Kg is applied to the joint of the metal to be joined, and the soldering temperature is set to 150 ° C.
While maintaining the temperature for 0 minute, the liquid phase diffusion was performed until the solder alloy filler phase of the metal structure observed by a microscope disappeared to prepare a test piece. The test piece was subjected to a peel test at 300 ° C., and as a result, no peeling occurred. This seems to be due to the fact that the In-Sn alloy layer does not remain.

Embodiment 3 Using a solder alloy filler of a foil made of only Sn having a thickness of 0.01 mm, a 1 m
Pressure is applied so that a load of 1.5 kg per m ² is applied to the joint of the metal to be joined, the soldering temperature is set to 250 ° C., the temperature is maintained for 50 minutes, and the soldering of the metal structure observed by a microscope is performed. As a result of performing a peeling test at 300 ° C. on a test piece prepared by performing liquid phase diffusion until the alloy filler phase disappeared, no peeling occurred.
This seems to be due to the fact that the metal Sn layer does not remain.

[0013]

Example 4 A foil having a chemical composition of 95.2% by weight of Sn, 2.5% by weight of Ag, 2.0% by weight of Bi and 0.3% by weight of Cu and having a thickness of 0.03 mm was prepared. A Bi / Te thermoelectric element plated with Cu and used as a solder alloy filler was soldered at a temperature of 220 ° C. on a metal foil pattern made of Cu on a printed circuit board. After maintaining the diffusion time for 60 minutes and performing liquid phase diffusion until the solder alloy filler phase of the metal structure observed by the microscope disappeared, the mixture was air-cooled. The test piece was subjected to a peel test at 300 ° C., and as a result, no peeling occurred. Also, no solder alloy filler phase remained at the joint.

Embodiment 5 A solder alloy filler consisting of 2.5% by weight of Na, 0.10% by weight of Ce and the balance of Sn was added to a thickness of 0.1%.
10 mm, inserted between the Cu plate and the Cu plate, 23
Heat diffusion was performed at 5 ° C., and liquid phase diffusion was performed until the solder alloy filler phase of the metal structure observed by a microscope disappeared, and the bonding was completed after heating and holding for 30 minutes. This work
The test was performed in a nitrogen gas atmosphere. About this test piece, 3
As a result of performing a peeling test at 00 ° C., no peeling occurred.

[0014]

Embodiment 6 Using a solder alloy filler consisting of 1.5% by weight of Ge, 5% by weight of Zn and the balance of Sn, 23
Soldering was performed at 0 ° C., the temperature was maintained for 60 minutes, and liquid phase diffusion was performed until the solder alloy filler phase in the metal structure observed by a microscope disappeared. About this test piece,
As a result of performing a peeling test at 300 ° C., peeling did not occur. It is considered that the diffusion was promoted by the addition of Zn.

EXAMPLE 7 A solder alloy filler consisting of 1.3% by weight of Mg, 0.003% by weight of P, 0.01% by weight of Ca, and the balance of Sn was made 0.10 mm in thickness. It was inserted into a space between the plates and was heated and diffused at 218 ° C. in a hydrogen atmosphere. The liquid phase was diffused until the solder alloy filler phase in the metallographic structure observed by a microscope disappeared, and heated and held for 40 minutes. When the solder alloy filler contains a metal such as Mg which is easily oxidized, it is particularly preferable to perform the reduction in a reducing atmosphere. About 300 ° C
As a result of the peel test, no peeling occurred.

[0015]

Example 8 Pb was 3% by weight, P was 0.001% by weight,
A solder alloy filler made of 0.02% by weight of Li, 0.02% by weight of La, and the balance of Sn is made 0.50 mm in thickness, inserted between Cu plates, and placed in an argon atmosphere. At 210 ° C., liquid phase diffusion was performed until the solder alloy filler phase of the metal structure observed by a microscope disappeared, and the mixture was heated and held for 45 minutes. The test piece was subjected to a peel test at 300 ° C., and as a result, no peeling occurred.

Embodiment 9 A solder alloy filler consisting of 1.5% by weight of Au and the balance of Sn was made 0.01 mm thick, and inserted between Cu plates. Heat diffusion was performed at 232 ° C., which is 15 ° C. higher than the eutectic temperature with Sn at 217 ° C., and liquid phase diffusion was performed until the solder alloy filler phase in the metal structure observed by a microscope disappeared, and the mixture was heated and held for 50 minutes. The test piece was subjected to a peel test at 300 ° C., and as a result, no peeling occurred.

[0016] Hereinafter, used in the method of the present invention, per 1 mm ² to the joint portion of the bonding metal 0.001.
The high-temperature resistant metal bonding method of the present invention in which a pressure of 0 kg is applied will be described with reference to FIG. Filler paste 10 in which Sn or an Sn alloy is powdered and flux is kneaded is applied on metal foil pattern 5 which is a portion to be joined of printed circuit board 4. Next, the lead 7 which is the part to be joined of the electronic component 6 is mounted on the metal foil pattern 5, and the lower end 9 of the pressing and heating device 8 is mounted on the lead 7. The lower end 9 is heated by the heating wire 11. Next, the filler paste 10 is melted by heating the lead 7 with the heating wire 11, and the lead 7 is fixed on the metal foil pattern 5. Further, in a process in which the filler paste 10 applied to the metal foil pattern 5 is melted and heated and held, the lower end 9 of the pressing and heating device 8 applies 1 m to the portion to be joined.
pressure per m ² 0.001~3.0Kg is added. Further, as shown in FIG. 4, by providing a convex portion 7 a on the side where the lead 7 is in contact with the metal foil pattern 5, the bonded portion has 0.001 to 3.0 K per 1 mm ² .
A pressure of g is applied. At this time, the liquid phase diffusion may be promoted by the pressurizing effect at the joint.

[0017]

As described above, according to the present invention, soldering can be performed at a relatively low temperature, the solder alloy structure is lost by liquid phase diffusion, and the joined part is heated to a high temperature higher than the soldering temperature. In addition, in some cases, a high-temperature resistant metal bonding can be performed even with a Pb-free solder alloy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a bonding interval of metal to be bonded and a bonding strength in a high-temperature resistant metal bonding method of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a bonding interval of metal to be bonded and a bonding strength in the high temperature resistant metal bonding method of the present invention.

FIG. 3 is a configuration diagram of a pressing and heating device for enhancing a pressing effect used in the metal joining method for high temperature resistance according to the present invention.

FIG. 4 is a partial configuration diagram of a pressing and heating device for intensively increasing a pressing effect used in the metal joining method for high temperature resistance according to the present invention.

[Explanation of symbols]

 Reference numerals 1, 2 and 3 to be joined 3 Solder alloy filler 4 Printed circuit board 5 Metal foil pattern 6 Electronic component 7 Lead 7a Convex portion 8 Pressing / heating device 9 Lower end portion 10 Filler paste 11 Heating wire

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H05K 3/34 507 H05K 3/34 507N 512 512C // C22C 13/00 C22C 13/00 F term (reference) 4E067 AA14 AB06 BA05 DB03 DB04 DC02 EA04 EC03 5E319 AA03 AC01 BB01 BB05 CC33

Claims (7)

[Claims] 1. A method according to claim 1, wherein only Sn is inserted between the joined metals as a solder alloy filler, and the temperature of the joined portion of the joined metal is raised to a melting temperature of the solder alloy filler or higher. A high-temperature resistant metal bonding method, wherein liquid phase diffusion is performed until the solder alloy filler phase in the metal structure observed by a microscope disappears. 2. A method for forming a eutectic on said Sn with said Sn.
2. The high-temperature resistant metal bonding method according to claim 1, wherein an Sn alloy to which 0.001 to 80% by weight or more of additional elements are added is used as the solder alloy filler. 3. The method according to claim 1, wherein the additive element is Ag, Au, Bi,
Ca, Ce, Cu, Ge, In, La, Li, Mg, N
The high-temperature resistant metal bonding method according to claim 2, wherein one or more types are selected from a, P, Pb, and Zn. 4. The method according to claim 1, wherein the joint is 0.001 per mm ^2.
The high-temperature resistant metal bonding method according to any one of claims 1 to 3, wherein a pressure of ~ 3.0 kg is applied to promote the liquid phase diffusion. 5. The method according to claim 5, wherein the Sn or the Sn alloy is powdered, and a filler paste obtained by kneading the powdered Sn or the Sn alloy with a flux is formed on a metal foil pattern which is the portion to be joined of a printed circuit board. The lead which is applied and the part to be joined of the electronic component is mounted on the metal foil pattern, the lower end of the pressing and heating device is placed on the lead, and the filler paste is melted by heating the lead. Then, the leads are fixed on the metal foil pattern, and the filler paste applied to the metal foil pattern is melted, and in the process of being continuously heated and held, 0 mm / mm ^{2 is applied to the} portion to be joined. 5. A pressure of 0.001 to 3.0 kg is applied.
The metal joining method for high temperature resistance according to any one of the above. 6. The liquid phase by applying a pressure of 0.001 to 3.0 kg per 1 mm ^{2 to the} joint to be joined by providing a projection on the side where the lead is in contact with the metal foil pattern. The high-temperature resistant metal bonding method according to claim 5, wherein diffusion can be promoted. 7. The high-temperature resistant metal bonding method according to claim 1, which is performed in a reducing gas atmosphere or an inert gas atmosphere.