JP2630281B2 - Ceramic package and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic package on which a semiconductor element such as an infrared sensor is mounted and a method of manufacturing the same, and more particularly, to a ceramic package in which the mounting strength of a lead frame to an electrode pad on a package substrate is improved. And a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view showing a structure of a lead connection portion of a conventional ceramic package of this kind. First,
Front surface (or back surface) of ceramic package substrate 1
Next, the electrode pad 6 for external connection is formed by a thick film printing technique or by performing partial electrolytic plating on the thin film metallization layer using a photolithography technique.
Then, on this electrode pad 6, Pb / Sn solder or Au
An external lead 3 of a lead frame using copper, Kovar or the like is connected via a brazing material 7 such as / Sn. Further, in order to enhance the connection reliability, the connection portion is sealed with an epoxy-based sealing resin 8 to reinforce the connection strength.

[0003]

In the above-described conventional connection structure, a substrate, an electrode pad, a brazing material, a lead frame,
Since the sealing resin of the connection part is made of a different material,
In the temperature cycle at the time of the reliability evaluation test, a stress singularity field was formed in the connection portion due to inconsistency of the coefficient of thermal expansion in the connection portion, and a connection failure such as crack generation or breakage was sometimes caused.

In a semiconductor device such as a cooling type infrared sensor, the temperature is from room temperature to a temperature of liquid nitrogen of 77 K in use.
Because of the inconsistency of the coefficient of thermal expansion in the joints made of dissimilar materials, relative tensile stress due to shrinkage deformation is formed, and at the same time the material of the joints becomes brittle, However, there is a problem that poor connection such as crack generation or breakage occurs.

Further, in the conventional external lead connection structure, although reinforced with a sealing resin, the mechanical strength is not high, and there is also a problem that the external leads and electrode pads are easily peeled off by external force. Was. The present invention has been made in view of such circumstances, and its purpose is to have a high resistance to a mechanical external force, and to cause a crack or break due to a temperature cycle in an evaluation test or cooling during use. It is to be without.

[0006]

According to the present invention, a semiconductor chip mounting portion is provided in a central portion, and a plurality of lead fixing portions are provided in a peripheral portion.
The electrode pad connected to the electrode of the semiconductor chip is
A ceramic package substrate provided with
A plurality of external leads fixed to the lead fixing portions of the package substrate, the external leads having linear portions in the fixing portions; and the depth of each of the lead fixing portions of the ceramic substrate is substantially equal to the thickness of the external leads. A rectangular cavity having a constant width deeper than that is formed, and an external lead whose design value width at the linear portion is larger than the design value width of the rectangular cavity is press-fitted into the rectangular cavity, and the electrode pad is formed.
A ceramic package, wherein the external leads are pressed against the ceramic package.

Further, according to the present invention, a semiconductor chip mounting portion is provided in the central portion, the shape cavity towards a certain width in the peripheral portion becomes the lead fixing portion is formed, and the lead fixing portion
A method of manufacturing a ceramic package, comprising: fixing external leads having a design value width larger than a design value width of a rectangular cavity of the package substrate to a package substrate provided with an electrode pad connected to an electrode of a semiconductor chip. And heating the package substrate to increase the width of the rectangular cavity, insert or press-fit the external lead into the rectangular cavity, and insert the external lead into the electrode pad.
The method of manufacturing a ceramic package, characterized in that for pressing the parts lead, is provided.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a view showing a first embodiment of the present invention. FIG. 1A is a plan view of the entire package, and FIG.
(B) is an enlarged exploded perspective view of the part circled. As shown in FIG. 1A, a semiconductor element 2 such as an infrared sensor is mounted at the center of a package substrate 1, and electrodes on the semiconductor element and terminals on the package substrate are connected by bonding wires. I have. External leads 3 separated from the lead frame are fixed to the outer peripheral portion of the package substrate 1.

As shown in FIG. 1 (b), the cross-sectional shape of the fixing portion of the external lead 3 of the package substrate is similar to that of the external lead 3, the width thereof is slightly smaller than that of the external lead 3, and the depth thereof is Are provided with a first cavity 4 which is equal to or deeper than the thickness of the external lead 3, and a second cavity 5 which is connected to the first cavity and has a circular shape.

[0010] The second cavity 5 has an inner diameter larger than the width of the first cavity and an equal depth.
This depth may be greater than the depth of the first cavity. An electrode pad 6 is provided on the bottom surface of the first cavity 4.
Are formed. The electrode pad 6 is connected to a terminal formed around the semiconductor element mounting portion by a wiring (not shown). The external lead 3 is press-fitted into the first cavity 4, and at this time, the external lead 3 comes into surface contact with the electrode pad 6 so as to be electrically connected.

FIG. 2 is an explanatory view showing a process when the external lead is press-fitted into the first cavity. The dimensions before and after the external lead press-fitting between the first cavity 4 and the external lead 3 and the connection after press-fitting. The contraction force acting on the part and the clamping force of the spring effect are shown.

The width of the first cavity before the press-fitting of the external lead is d ₁ , and the width d _{2 of the} external lead 3 before the press-fitting and the width d after the press-fitting are d ₂ >d> d ₁ . When the external leads 3 are pressed and contracted by an external lead 3 [delta] ₂ by elastic deformation, the first cavity 4 similarly spread by [delta] _1. A contraction tightening force proportional to the elastic deformation acts on the external lead 3.

At the same time, as the width of the first cavity 4 is increased, the opening forming the connection portion with the first cavity 4 is expanded in the second cavity 5, and a leaf spring with an arc is formed.
A tightening force is generated by a spring effect, which is similar to the shape of the retaining ring and is proportional to the spread of the opening, and tightens the outer lead 3.

The tightening force P is given by the following equation (1). P = {2 (δ ₁ + δ ₂ ) / d} [[(1 + ν ₁ ) / E ₁ ｝ −｝ (ν ₂ -1) / E ₂ ｝] ⁻¹ (1) E ₁ , ν ₁ : Package Young's rate and Poi of substrate 1
Sson ratio E ₂ , ν ₂ : Young's ratio and Poiss of external lead 3
on ratio δ ₁ , δ ₂ : half width of deformation amount of first cavity 4 and external lead 3

Here, aluminum nitride is used for the package substrate 1 and Kovar is used for the external leads 3. The width d ₁ of the first cavity before press-fitting is 399.5 μm, and the width d ₂ of the external leads 3 is 400.5 μm. And the width d after press-fitting
Is set to 400 μm, and the aluminum nitride and Kovar Yo
ung ratio, Poisson's ratio, aluminum nitride: 313.8 GPa, 0.24, Kovar: 138.3 GPa, 0.3 From the formula (1), P ≒ 500 MPa can be obtained from the equation (1). . This is a sufficiently large value as the connection strength.

The operation of press-fitting the external leads into the package substrate can be performed at room temperature by appropriately setting the width of the cavity and the external leads. However, by heating the package substrate to reduce the dimensional difference to about half, a smoother operation becomes possible. Aluminum nitride,
The thermal expansion coefficient of each of Kovar is 0.46 × 10 ^-5 ,
0.615 × 10 ^-5 [From the Japan Society of Mechanical Engineers 70th National Convention Lecture Paper Collection (B1992, pp. 549-551, Matsuura / Kawakami)]. The temperature difference required to increase the width of the first cavity is required to be about 200 ° C. Since the tightening force of 500 MPa is a sufficiently large value, if this is halved, about 100 ° C. is sufficient. In this operation, the package substrate may be heated and the external leads (lead frames) may be cooled. Alternatively, the lead frame may be fixed in a state where there is no dimensional difference by sufficiently increasing the temperature difference between the two.

In the package configured as described above, since the external leads are firmly held by the package substrate, the external leads do not peel off even when a mechanical external force is applied, and the package shown in FIG. As in the case of the conventional example, the brazing filler metal and the sealing resin are not used, and the stress singularity field due to the mismatch of the coefficient of thermal expansion is hardly generated.
Even if a temperature cycle is applied, occurrence of connection failure due to cracking or breakage in the connection portion is suppressed. In addition, there is an advantage that the structure is simplified and the material cost can be reduced.

Next, the second embodiment of the present invention will be described with reference to FIGS.
An example will be described. FIG. 3 is an exploded perspective view showing a structure of a connecting portion according to a second embodiment of the present invention, and FIG.
FIG. 9 is an explanatory view showing a process when the external lead 3 is press-fitted into the first and second cavities 4 and 5, and shows dimensions of the first and second cavities 4 and 5 and the external lead 3 before and after press-fitting the external lead. The relationship and the contraction clamping force and the clamping force of the spring effect acting on the connection after press-fitting are shown.

In this embodiment, the external lead 3 is
and a C-shaped retaining ring portion 3b having a C-shaped retaining ring shape at the end of the connecting portion, and a clamping force due to a spring effect proportional to the compression elastic deformation of the opening of the C-shaped retaining ring portion 3b. Is advantageous in that the tightening force is further increased as compared with the case of the first embodiment. The shape of the retaining ring portion 3b can be made into an E-shape instead of the C-shape. The dimensions of the first cavity 4, the second cavity 5, and the linear portion 3a of the external lead 3 are the same as those in the first embodiment, as shown in FIG. Therefore, the contraction and tightening relationship between the first cavity 4 and the linear portion 3a of the external lead is the same as in the first embodiment, and the tightening force is the same.

There is a relation of D ₂ >D> D ₁ between the inner diameter D _{1 of} the second cavity 5 before the press-fitting of the external lead 3 and the outer diameter D _{2 of the} C-shaped retaining ring 3b and the outer diameter D after the press-fitting. The relationship holds.
Here, assuming that the elastic deformation of the C-shaped retaining ring portion 3b caused by the press-fitting is δ, a force P ′ for pressing the inner wall of the second cavity of the C-shaped retaining ring portion 3b is given by the following equation (2). . P ′ = E ₂ · 2δ · k / 3p (2) where E ₂ : Young's ratio of C-shaped retaining ring 3b k: Shape factor of C-shaped retaining ring 3b, in this case 0.0
3p: Width of C-shaped retaining ring 3b

As in the case of the first embodiment, the package substrate 1 is formed by using aluminum nitride, the external leads 3 are formed by using Kovar, D ₁ is 599.0 μm, D _{2 is}
Is 600.0 μm, and the plate width p of the C-shaped retaining ring portion 3b is 1
If it is 00 μm, δ will be 1.0 μm, so that the spring effect tightening force P ′ is obtained from the equation (2) as P ′ ≒ 28 MPa. Therefore, in the second embodiment, the connection strength is higher by the amount of the pressing force than in the first embodiment.

While the preferred embodiment has been described above,
The present invention is not limited to these embodiments, but can be appropriately modified within the scope described in the claims. For example, the package substrate and the lead frame can be formed using materials other than the examples,
Further, the package according to the present invention can be applied to semiconductor elements other than the infrared sensor.

[0023]

As described above, the ceramic package according to the present invention has a rectangular cavity having a width slightly smaller than the width of the external lead provided on the outer peripheral portion of the package substrate, and the external lead is pressed into the rectangular cavity. As a result, the external leads are firmly held by the shrinkage tightening force of the package substrate, and therefore, peeling of the external leads and the electrode pads due to the mechanical external force is suppressed. In addition, since it is not fixed by a brazing material or a sealing resin, a stress singular point does not occur at the time of cooling use, and the occurrence of a crack or a connection failure due to a breakage due to the passage of a temperature cycle is suppressed.

Further, by providing a circular second cavity connected to the first cavity in the package substrate, a tightening force is applied to the external lead by a spring action of the circular cavity, and the circular lead is further applied to the external lead. According to the embodiment in which the C-shaped retaining ring portion or the E-shaped retaining ring portion is press-fitted into the second member, the second action of the retaining ring portion is caused by the spring action.
Since a pressing force is applied to the inner wall of the cavity, the connection structure of the external leads can be further strengthened. In addition, materials for connection can be reduced, and material costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a first embodiment of the present invention and an exploded perspective view of a connection portion thereof.

FIG. 2 is a view for explaining an assembling process, a dimensional change of each part, and a contraction tightening force after assembling in the first embodiment of the present invention.

FIG. 3 is an exploded perspective view of a connecting portion according to a second embodiment of the present invention.

FIG. 4 is a view for explaining an assembling process, a dimensional change of each part, and a contraction tightening force after assembling in a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a connection portion of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Package board 2 Semiconductor element 3 External lead 3a Linear part 3b C-shaped snap ring part 4 1st cavity 5 2nd cavity 6 Electrode pad 7 Brazing material 8 Sealing resin d the linear portion) width D external leads pressed after the second cavity inner and outer leads of the C-shaped snap ring portion outer diameter d ₁ first cavity of the external lead press-fitting previous width D ₁ second cavity of the external lead press-fitting previous Inner diameter d ₂ Width before press-fitting of external lead straight part D ₂ Outer diameter before press-fitting of external lead retaining ring p Plate width of C-shaped retaining ring δ Deformation amount of C-type retaining ring after external lead press-fitting δ ₁ Change in width of first cavity after press-fitting external lead δ ₂ Change in width (of linear portion) of external lead after press-fitting external lead

Claims (5)

(57) [Claims] 1. A semiconductor chip mounting portion is provided in the central portion, the fixing portion a plurality of leads on the peripheral portion is provided, the lead
The electrode pad connected to the electrode of the semiconductor chip is
The provided ceramic package substrate, and a plurality of fixed to the lead fixing portion of the package substrate ,
In a ceramic package having an external lead having a straight portion in a fixing portion, a square cavity having a constant width is formed in each lead fixing portion of the package substrate at a depth approximately equal to or greater than the thickness of the external lead. And
An external lead whose design value width at the linear portion is larger than the design value width of the rectangular cavity is press-fitted into the rectangular cavity, and the external lead is pressed against the electrode pad.
Ceramic package, characterized by being. 2. The package substrate has a circular cavity connected to the rectangular cavity and having an inner diameter larger than a width of the rectangular cavity and a depth equal to or deeper than a depth of the rectangular cavity. 2. The ceramic package according to claim 1, wherein an inner tip of said external lead projects into said circular cavity. 3. An inner lead of the external lead has a shape of a C-shaped retaining ring or an E-shaped retaining ring, and
3. The ceramic package according to claim 2, wherein an outer shape of the retaining ring portion is set larger than an inner diameter of the circular cavity. 4. A semiconductor chip mounting portion is provided in a central portion, and a rectangular cavity having a fixed width to be a lead fixing portion is formed in a peripheral portion , and an electrode of the semiconductor chip is formed in the lead fixing portion.
A step of fixing external leads having a design value width larger than a design value width of a rectangular cavity of the package substrate to a package substrate provided with electrode pads connected to the package substrate, wherein the package substrate is heated. The width of the rectangular cavity is increased to insert or press-fit the external lead into the rectangular cavity, and the external lead is inserted into the electrode pad.
A method for manufacturing a ceramic package, comprising: 5. The method of manufacturing a ceramic package according to claim 4, wherein the external leads are cooled when the external leads are inserted or press-fitted.