JP2587014B2 - Lead mounting structure of ceramic substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead mounting structure for connecting a terminal of a circuit pattern on a surface of a ceramic base such as a ceramic package or a ceramic base to a lead end by brazing.

[Prior Art] In a conventional lead mounting structure, as shown in FIG. 2, a terminal 2 of a circuit pattern made of metallization on the surface of a ceramic substrate 1 is electrically connected to a terminal 2 and an electric circuit of an external device. A metal thin rod-shaped lead 3 made of 42 alloy (iron-nickel alloy) or kovar (iron-nickel-cobalt alloy) for connection is directly brazed using a brazing material 4 such as silver brazing. Connected.

By the way, in recent years, the integration of the semiconductor element has been further advanced, and the semiconductor element mounted or housed in the ceramic base 1 has been increasing in size. Along with this, due to the difference in the coefficient of thermal expansion between the semiconductor element and the ceramic base 1, an excessive thermal stress is applied to the semiconductor element which has been increased in size from the ceramic base 1, and the influence of breakage of the semiconductor element is becoming a problem. .

Therefore, in recent years, the ceramic base 1 has a thermal expansion coefficient of 3 × 10 ⁻⁶ / ° C. instead of a base made of alumina ceramic having a high thermal expansion coefficient formed by ordinary high-temperature firing.
A base made of mullite ceramic or the like formed by low-temperature baking with a low coefficient of thermal expansion, which is close to the coefficient of thermal expansion of a semiconductor element made of silicon (hereinafter referred to as a base having a small coefficient of thermal expansion)
Has been developed, and semiconductor devices using the base are being put into practical use.

[Problems to be Solved by the Invention] However, a substrate having a low heat and an expansion coefficient made of mullite ceramic or the like formed by the above-described low-temperature sintering is, compared with a substrate made of alumina ceramic formed by ordinary high-temperature sintering, There was no mechanical strength and it was brittle.

That is, a substrate made of alumina ceramic has a transverse rupture strength of 30 to 40 kg / cm ² , whereas a base body made of mullite ceramic or the like having a low coefficient of thermal expansion has a transverse rupture force of 20 kg / c.
m ² only.

In addition, while the coefficient of thermal expansion of a substrate having a small coefficient of thermal expansion such as mullite ceramic is 4 to 7 × 10 ⁻⁶ / ° C.,
The coefficient of thermal expansion of the silver solder is 18 to 20 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of the silver solder is 4 to 5 times the coefficient of thermal expansion of the substrate having a small coefficient of thermal expansion.
About twice as large.

Therefore, as shown in FIG. 2, when the ends of the leads 3 are brazed to the terminals 2 of the circuit pattern formed on the surface of the substrate 1 having a low coefficient of thermal expansion using a brazing material 4 such as silver brazing. In addition, a brazing filler metal 4 having a large coefficient of thermal expansion, such as silver brazing,
On the surface of the base 1 having a low coefficient of thermal expansion made of the mullite ceramic or the like described above, the base 1 is cooled while greatly shrinking.
Solidified. Excessive heat shrinkage stress is applied to the base 1 from the brazing material 4 such as silver brazing, which cools and solidifies while largely shrinking on the surface of the base 1, causing cracks in the fragile base 1 made of mullite ceramic or the like. Was. And
The airtightness of the base 1 was impaired, and cracks formed in the base 1 made the connection strength of the ends of the leads 3 brazed to the terminals 2 on the surface of the base 1 unstable.

The present invention has been made in order to solve such a problem, and a lead end portion is formed from a brazing material such as a silver brazing material on a terminal of a circuit pattern on a substrate surface having a low coefficient of thermal expansion. It is an object of the present invention to provide a ceramic substrate lead mounting structure (hereinafter referred to as a lead mounting structure) that can be brazed and connected without applying excessive heat shrinkage stress to the substrate.

Means for Solving the Problems In order to achieve the above object, a lead mounting structure according to the present invention provides a circuit pattern provided on a ceramic substrate, in which a terminal provided on the surface of the substrate has a brazing filler metal terminal. A member formed separately from the lead inside the brazing material between the end of the lead and the terminal, wherein the outer diameter of the terminal is equal to or A member having an outer diameter slightly smaller than the outer diameter of the terminal and having a smaller coefficient of thermal expansion than the brazing material is interposed.

In the lead mounting structure of the present invention, it is preferable that the member is made of molybdenum, tungsten or titanium oxide whose surface is plated with metal.

[Function] In the lead mounting structure of the present invention, when the lead end is brazed to the terminal of the circuit pattern on the surface of the ceramic base using a brazing material such as silver brazing material, the brazing material having a large coefficient of thermal expansion is used. Many parts can be replaced by members interposed inside the brazing material between the lead ends and the terminals and having a smaller coefficient of thermal expansion than the brazing material.

Further, since the member interposed between the lead end and the terminal has the same outer diameter as the terminal or slightly smaller than the outer diameter of the terminal, the member extends between the periphery of the member and the terminal. The amount of brazing material adhered in a meniscus shape can be extremely reduced.

Therefore, when the lead ends are brazed to the terminals, the amount of brazing material that cools and solidifies on the surface of the ceramic base is extremely small, and the heat shrinkage stress applied to the ceramic base from the brazing material is greatly reduced. it can.

In addition, since the member is formed separately from the lead, the member interposed inside the brazing material is not a member made of the same material as the lead, but a member having a thermal expansion coefficient close to that of the ceramic base or a brazing material is cooled. A member having a coefficient of thermal expansion close to zero that can reduce the heat shrinkage stress during solidification can be selected. Then, when the lead end is connected to the terminal by brazing, the heat shrinkage stress applied to the ceramic base from the member interposed inside the brazing material is appropriately reduced, or the brazing material is interposed inside the brazing material. Heat shrinkage stress during cooling and solidification can be reduced.

Example Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a preferred embodiment of the lead mounting structure of the present invention, and is a partially broken front view thereof. less than,
This lead mounting structure will be described.

In the lead mounting structure shown in the figure, a ceramic substrate 1 having a low coefficient of thermal expansion was formed of mullite ceramic having a coefficient of thermal expansion of 4.5 × 10 ⁻⁶ / ° C.

On the surface of the base 1, a circular terminal 2 made of tungsten metallized was provided in series with a circuit pattern (not shown) made of tungsten metallized provided inside or on the surface of the base 1.

Nickel plating 6 was applied to the surface of the terminal 2 by an electroless plating method. And the wettability of the brazing material 4 on the surface of the terminal 2 was improved.

On the upper surface of the terminal 2 on which the nickel plating 6 is applied,
As shown in FIG. 1, a member 5 made of molybdenum having a coefficient of thermal expansion smaller than the coefficient of thermal expansion of silver braze and having a coefficient of thermal expansion close to the coefficient of thermal expansion of the substrate 1 made of mullite ceramic is mounted. .

The surface of the member 5 was subjected to metal plating such as nickel plating 6 and gold plating. Then, the wettability of the brazing material 4 on the surface of the member 5 is improved so that the brazing material 4 such as silver brazing can be accurately adhered to the surface of the member 5.

The member 5 was formed in a disk shape having an outer diameter equal to or slightly smaller than the outer diameter of the terminal 2 having a circular shape. Then, the member 5 was mounted on the upper surface of the terminal 2.

On the upper surface of the member 5 mounted on the upper surface of the terminal 2, the thin columnar lead 3 made of Kovar described above was mounted so as to rise above the member 5 with its lower end abutting on the upper surface of the member 5. .

Next, the end of the lead 3, the member 5 and the terminal 2 are
Preheating was performed at about 800 ° C. together with the substrate 1 around the terminal 2. At the same time, the silver solder 4a was heated and melted. Then, the molten silver solder 4a was attached to the periphery of the member 5 around the end of the lead 3 and the terminal 2. Then, the silver solder 4a was cooled and solidified on the surface of the base 1 around the terminal 2.

The lead mounting structure shown in FIG. 1 was configured as described above.

 Next, the operation of the lead mounting structure will be described.

In the above-described lead mounting structure, as shown in FIG. 1, many parts of the silver solder 4a in which the ends of the leads 3 are brazed and connected to the terminals 2 on the surface of the base 1 are connected to the ends of the leads 3 and the terminals 2. The member 5 interposed between the silver brazes 4a and having a coefficient of thermal expansion smaller than that of the silver solder 4a could be replaced.

Also, since the member 5 interposed between the end of the lead 3 and the terminal 2 has the same outer diameter as the terminal 2 or slightly smaller than the outer diameter of the terminal 2, as shown in FIG. The amount of the silver solder 4a adhered in a meniscus shape between the periphery of the member 5 and the terminal 2 could be extremely reduced.

A silver solder 4a for brazing and connecting the end of the lead 3 to the terminal 2 is used. The amount of the silver solder 4a to be cooled and solidified on the surface of the substrate 1 is extremely small, and the silver solder is used.
From 4a, the heat shrinkage stress applied to the base 1 was significantly reduced.

Also, the member 5 is formed separately from the lead 3, and the silver solder 4a is formed.
A member 5 made of molybdenum having a thermal expansion coefficient close to that of the base 1 made of mullite ceramic and having a material different from the material constituting the lead 3 made of 42 alloy, Kovar, etc. Because of the selection, when the end of lead 3 was soldered to terminal 2
4a, the heat shrinkage stress applied to the base 1 from the member 5 interposed in the inside 4a was able to be appropriately reduced.

In addition, the surface of the member 5 is plated with metal so that the silver solder 4a is in close contact with the surface of the member 5 accurately.
When the end is soldered to the terminal 2, the silver solder 4 a comes into close contact with the surface of the member 5, and the lead 3
The end was brazed to the terminal 2 with high connection strength and high reliability.

As a result, when the ends of the leads 3 are brazed to the terminal 2 using the silver solder 4a, the heat shrinkage stress applied to the base 1 from the silver solder 4a that cools and solidifies on the surface of the base 1 around the terminal 2 causes mullite. Fragile substrate 1 made of ceramic
The generation of cracks was surely prevented. Then, it is ensured that the airtightness of the base 1 is impaired and that the cracks formed in the base 1 make the connection strength of the ends of the leads 3 brazed to the terminals 2 on the surface of the base 1 unstable. Could be prevented.

Also, the terminal 2
When the tensile strength of the lead 3 brazed to the terminal 2 was measured, the lead 3
It was confirmed that the connection strength was sufficiently high for practical use.

In the lead mounting structure, the brazing material 4
Instead of the silver solder 4a, a eutectic solder of silver and copper or a gold germanium solder may be used. Further, as the base 1, a base made of low-temperature fired alumina ceramic may be used instead of the mullite ceramic. Further, the terminal 2 may be formed by silver metallization which does not require metal plating for improving the wettability of the brazing material 4 on its surface. And even in such a case, a lead mounting structure having substantially the same operation as the above-described lead mounting structure can be achieved.

Further, the member 5 may be formed using tungsten or titanium oxide having a coefficient of thermal expansion close to that of the base 1, in addition to molybdenum. Alternatively, the member 5 may be an inorganic member whose surface having a smaller coefficient of thermal expansion than that of the silver solder 4a is metallized, and the brazing material 4 is accurately adhered to the surface. And even in such a case, a lead mounting structure having substantially the same operation as the above-described lead mounting structure can be configured.

Further, the member 5 may be formed using a member having a thermal expansion coefficient smaller than the base 1 and close to zero. By interposing the member 5 inside the brazing material 4, the heat shrinkage stress when the brazing material 4 is cooled and solidified may be reduced by the member 5. Then, the heat shrinkage stress applied to the base 1 from the brazing material 4 may be reduced by the member 5.

Also, when the lead 3 is brazed and connected to the terminal 2 on the surface of the base 1 made of aluminum nitride, which is tougher than the alumina ceramic but has a larger difference in thermal expansion coefficient from the brazing material 4 than the alumina ceramic, 1 and the brazing material 4, the difference in the coefficient of thermal expansion between the brazing material 4 and the base 1
In some cases, excessive heat shrinkage stress may be applied to the substrate 1 to cause cracks. Therefore, even in such a substrate 1, an excessive heat shrinkage stress is applied to the substrate 1 from the brazing material 4 by brazing and connecting the leads 3 to the terminals 2 on the surface of the substrate 1 using the lead mounting structure of the present invention. In addition, the occurrence of cracks in the base 1 can be reliably prevented.

FIG. 1 shows a lead mounting structure in which leads 3 are brazed and connected to terminals 2 on the surface of a substrate 1 in the form of a substrate. The present invention is also applicable to a case where the terminal of the input / output circuit pattern is brazed to the lead end. Then, the base 1 having such a package shape is also provided with the lead mounting structure of the present invention,
By connecting the leads 3 to the terminals 2 on the surface of the packaged base 1 by brazing, it is possible to reliably prevent the base 1 from being cracked.

[Effects of the Invention] As described above, according to the lead mounting structure of the present invention, the amount of brazing material for brazing the lead end to the terminal on the surface of the base can be extremely reduced.

At the same time, a member having a coefficient of thermal expansion close to that of the base, or a thermal expansion close to zero that can reduce the thermal contraction stress when the brazing material cools and solidifies, is added to the member interposed inside the brazing material. You can select a member with a ratio.

Then, when the lead ends are connected to the terminals by brazing, the heat shrinkage stress applied to the base from the brazing material that cools and solidifies on the base surface can be greatly reduced.

As a result, when the lead end is brazed to the terminal on the surface of the ceramic substrate, it is possible to reliably prevent the substrate from cracking. In addition, it is possible to prevent the airtightness of the base from being impaired, and to prevent the cracks formed in the base from destabilizing the connection strength of the ends of the leads brazed to terminals on the surface of the base.

[Brief description of the drawings]

FIG. 1 is a partially broken front view of a lead mounting structure of the present invention, and FIG. 2 is a partially broken front view of a conventional lead mounting structure. 1 ... Base, 2 ... Terminal, 3 ... Lead, 4 ...
Brazing material, 4a: silver brazing, 5: members.

Claims (2)

(57) [Claims] 1. A ceramic base having a lead end connected to a terminal provided on the surface of the base of a circuit pattern provided on the ceramic base by brazing using a brazing material. Inside the brazing material, a member formed separately from the lead, having an outer diameter equal to or slightly smaller than the outer diameter of the terminal, and having a smaller coefficient of thermal expansion than the brazing material. A lead mounting structure for a ceramic base, wherein a member is interposed. 2. The lead mounting structure for a ceramic substrate according to claim 1, wherein the member is made of molybdenum, tungsten or titanium oxide whose surface is metal-plated.