JP2005101073A - Stem of semiconductor device package and cladding material therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cladding material which is suitable as material of a stem used for a semiconductor device package and capable of improving the semiconductor device in heat dissipation and cooling performance. <P>SOLUTION: The cladding material for the stem of the semiconductor device is equipped with a base layer 1 formed of iron steel material, a copper layer 2 formed of pure copper or a copper-based copper alloy and laminated on the base layer 1, and an iron coating layer 3 which is formed of soft steel and laminated on the copper layer 2. The iron coating layer 3 has an average hardness of Hv 180 to 230. A surface-hardened layer can be formed on the surface of the iron coating layer 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a stem of a semiconductor element package and a clad material suitable as a material for coining molding of the stem.

  A semiconductor element package enclosing a semiconductor element such as a laser diode includes a stem on which the semiconductor element is mounted and a cap provided to cover the semiconductor element mounted on the stem.

  As shown in FIG. 4, the stem includes a base portion 21 made of low carbon steel and a heat sink 22 provided on the base portion 21. The heat sink 22 includes a flat portion 23 laminated on the base portion 21 and a mount portion 24 erected integrally from the flat portion 23. The flat portion 23 and the core portions 23a and 24a of the mount portion 24 are formed of copper having excellent heat dissipation or a copper alloy containing copper as a main component, and resistance weldability is improved on the surfaces of the core portions 23a and 24a. Therefore, a resistance welding layer 25 made of low carbon steel is coated.

  A semiconductor element S is mounted on a side surface (elevation surface) of the mount portion 24, and through holes (not shown) for attaching the electrodes of the semiconductor element S in an insulated state are appropriately opened in the base portion 21 and the flat portion 23. The After the semiconductor element S is mounted, the mount portion 24 is covered with a cap 26 made of low carbon steel, and the peripheral edge of the opening is resistance welded to the resistance weld layer 25 at the outer peripheral edge of the flat portion 23. .

As described in Japanese Patent No. 2880048 (Patent Document 1), such a stem for a semiconductor element package includes a base layer that is a base of the base portion 21, a core portion of the flat portion 23 and the mount portion 24. A press working material having a diameter of about 3 to 5 mm is collected from a clad material in which the copper layer that is the basis of 23a and 24a and the iron coating layer that is the basis of the resistance welding layer 25 are laminated in the same order. It is integrally formed by coining. During coining, the flat portion 23 and the mount 24 of the stem are integrally formed with the resistance weld layer 25 from the copper layer and the iron coating layer of the clad material. The clad material is sufficiently softened and annealed at a high temperature of about 1000 ° C. so that the iron coating layer smoothly spreads together with the copper layer and bulges the mount 24 during coining.
Japanese Patent No. 2880048 (Claim 2, FIG. 2)

  As described in Patent Document 1, by performing coining molding using a three-layer clad material, it is possible to easily integrally mold a stem in which a mount portion projects from a flat portion. However, during coining molding, a resistance weld layer is inevitably formed on the surface of the mount portion. When a semiconductor element is mounted on the mount portion via this resistance weld layer, the resistance weld layer is a steel material, so the thermal conductivity is low, and the thermal conductivity from the semiconductor element to the core portion of the mount portion deteriorates.

  In recent years, high-capacity optical disk systems compatible with high-speed and large-capacity broadband have been replaced by conventional blue semiconductor lasers instead of red semiconductor lasers. Such semiconductor devices are required to have higher heat dissipation. Further, the thermal conductivity deterioration due to the resistance weld layer cannot be overlooked.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a stem of a semiconductor element package excellent in heat dissipation and cooling performance of a semiconductor element and a clad material suitable as a material thereof.

  The clad material for the stem of the semiconductor element of the present invention is formed of a base layer made of a steel material, pure copper or a copper alloy containing copper as a main component, a copper layer laminated on the base layer, and a mild steel, And an iron coating layer laminated on the copper layer, and the average hardness of the iron coating layer is Hv 180 to 230, preferably Hv 210 to 230.

  When coining to make the mount part bulge locally using this clad material, the copper layer easily plastically flows to bulge the mount part, while mild steel adjusted to a relatively high hardness The iron coating layer consisting of cannot follow the plastic flow of the copper layer, and on the side surface (elevation surface) of the mount part, the expanded iron coating layer (resistance welding layer) is cracked and divided, The core part of the mount part is exposed partially or entirely. For this reason, when a semiconductor element is mounted on the side surface of the mount part bulged by coining molding, the semiconductor element and the copper material of the core part of the mount part exposed from the gap between the welding resistance layers are in direct contact. For this reason, it is excellent in the thermal conductivity with respect to a semiconductor element, and cooling property. The average hardness of the iron coating layer is preferably Hv210-230. As a result, the exposed area of the core portion of the mount portion can be increased more than when the average hardness of the iron coating layer is less than Hv210.

  In the clad material, the base layer is preferably formed of mild steel. By forming the base layer from mild steel, during coining molding, the bottom surface of the base layer located below the mount part is molded so as to be pushed upward, so that the plastic flow of the copper layer is prevented when the mount part is bulged. It is promoted to improve the moldability of the mount part.

  In the clad material, a hardened surface layer may be formed on the surface of the iron coating layer. Since this surface hardened layer is the starting point of cracking during coining molding, the iron coating layer that has spread during coining bulge molding is likely to crack and break, and the core of the mount The exposed area of the copper part can be increased, and the thermal conductivity is further improved.

  The thickness of the iron coating layer of the clad material may be about 100 to 200 μm, and the thickness of the copper layer is preferably about 500 to 1000 μm. When the thickness of the iron coating layer of the clad material is 100 μm or less, the resistance weldability of the cap is lowered. On the other hand, when the thickness exceeds 200 μm, it is difficult to bulge and form a copper layer having a thickness of about 500 to 1000 μm during coining molding. .

The stem of the semiconductor device package of the present invention includes a base portion formed of a steel material and a heat sink formed on the base portion, and the heat sink includes a flat portion stacked on the base portion and the flat portion. The flat portion and the mount portion are covered with a resistance weld layer made of mild steel on a core portion made of pure copper or a copper alloy containing copper as a main component. The resistance weld layer is formed and divided at the side surface of the mount portion, and the core portion of the mount portion is partially or entirely exposed.
According to this stem, by mounting the semiconductor element on the mount portion where the copper material is exposed, the semiconductor element is in direct contact with the core portion of the mount portion formed of the copper material. Excellent in properties.

  According to the clad material of the present invention, since the hardness of the iron coating layer formed of mild steel is adjusted to Hv 180 to 230, when coining molding is performed using the clad material of the present invention, the iron coating layer is compared with the copper layer. Since the layer is difficult to plastically flow, the iron coating layer (resistance weld layer) extended on the side of the mount part swelled from the copper layer is cracked and divided, and the core copper material of the mount part is partially Or it will be exposed entirely. For this reason, since the semiconductor element mounted in the mount part is in direct contact with the exposed copper material of the core part, it is possible to obtain excellent thermal conductivity and cooling performance as the whole stem. Further, the stem of the semiconductor element package of the present invention is such that the resistance weld layer on the side surface of the mount part on which the semiconductor element is mounted is divided, and the core part formed of copper material is partially or entirely exposed. The stem as a whole has excellent thermal conductivity and cooling performance.

  FIG. 1 shows a partial cross section of a clad material according to an embodiment of the present invention, in which a copper layer 2 is diffusion bonded on a base layer 1, and an iron coating layer 3 is diffusion bonded thereon. In this embodiment, both the base layer 1 and the iron coating layer 3 are made of mild steel.

  As the mild steel forming the iron coating layer 3 and the base layer 1, basically, low carbon steel or stainless steel having good pressure contact property and press formability and having a C content of about 0.2 mass% or less is suitable. . On the other hand, the copper layer 2 is formed of pure copper having a high thermal conductivity and spreadability or a copper alloy mainly composed of copper. The purity of pure copper or the copper content of the copper alloy is 98 mass% or more, preferably 99 mass%, more preferably 99.9 mass% or more.

  When the press formability is not required, the base layer 1 is not limited to mild steel but may be carbon steel or alloy steel having a higher C content. However, when coining is formed, the plastic layer 2 is made to flow smoothly by forming the lower surface of the base layer 1 to be pushed upward below the mount portion, and the mount portion can be formed easily. Thus, when making the base layer 1 participate in shaping | molding of a mount part, it is preferable to form the base layer 1 also with mild steel like this embodiment.

  The copper layer 2 has a hardness of about Hv 80-100 and has good press formability. On the other hand, the hardness of the iron coating layer 3 is adjusted so that the press formability is rather lowered. In the present invention, as will be apparent from Examples described later, the average hardness of the iron coating layer 3 is set to Hv 180 to 230. If the average hardness of the iron coating layer 3 is less than Hv180, the spreadability is too good, so that the iron coating layer 3 spread on the side surface of the mount part is difficult to crack during the coining molding, and it is difficult to split, and the core of the mount part The exposed amount of the copper part becomes too small. On the other hand, if it exceeds Hv230, it is too hard as compared with the copper layer 2, so that it is difficult to bulge the mount portion 14 during coining molding, and the bondability with the copper layer 2 is lowered, and it is easy to peel off.

  2 and 3 are cross-sectional explanatory views of a stem coined by using the clad material. When the clad material is coined and the mount portion 14 of the heat sink 12 is bulged, the resistance weld layer 15 formed by spreading the iron coating layer 3 is formed on the mount portion 14 as shown in FIG. The core part 14a of the mount part 14 formed by cracking at the side face (elevation face) and being divided by plastic flow of the copper layer 2 is partially exposed. By setting the average hardness of the iron coating layer 3 as high as Hv 210 to 230, the interval between the cracks increases, and depending on the molding conditions, the core portion is entirely formed on the side surface of the mount portion 14 as shown in FIG. 14a comes to be exposed. On the other hand, the base layer 1 is molded so as to push up toward the mount portion 14 during coining molding, and a concave portion 16 is formed in the base portion 11 of the stem, and is laminated on the base portion 11 accordingly. Similarly, the flat portion 13 is pushed up toward the mount portion 14.

The iron coating layer 3 preferably has a surface hardened layer formed on the surface thereof. By forming the hardened surface layer, the iron coating layer (resistance welding layer) spread when the mount portion 14 is bulged and formed by coining molding is easily cracked, and the resistance welding layer 15 is formed on the side surface of the mount portion 14. Is more easily divided, the exposed area of the core part 14a of the mount part 14 is increased, and the contact area with the semiconductor element is increased, so that the thermal conductivity is further improved.
The thickness of the surface hardened layer may be about 7% or more of the thickness of the iron coating layer 3, and the hardness may be higher than the average hardness of the iron coating layer 3 by about Hv10 or more. The surface hardened layer can be easily formed by polishing the surface of the iron coating layer 3 with a wire brush or a grindstone, or by applying sand blasting, shot blasting or bead blasting.

  The thickness of each layer of the clad material may be such that the copper layer 2 can be plastically flowed and the mount portion 14 of the heat sink 12 can be bulged by coining. In general, the thickness of the copper layer 2 may be about 500 to 1000 μm, and the iron coating layer 3 formed thereon may be about 100 to 200 μm. The layer thickness of the base layer 1 may be approximately the same as that of the copper layer 2.

Next, a method for manufacturing the clad material will be described.
First, on the front and back surfaces of the copper sheet that is the basis of the copper layer 2, a mild steel sheet sheet that is the basis of the base layer 1 and the iron coating layer 3, for example, JIS standard SPCC, SPCD, SPCE, is overlaid and passed through a pair of rolls. After that, the obtained pressure contact sheet is subjected to diffusion annealing. After the diffusion annealing, finish rolling can be performed as necessary, and thereby the thickness of the plate and the iron coating layer 3 can be adjusted.

  The roll reduction ratio at the time of the press contact may be about 50 to 70%, and as the press contact method, cold press contact under the atmosphere is sufficient. In order to prevent surface oxidation, the diffusion annealing is preferably performed in an inert gas atmosphere such as nitrogen or a reducing gas atmosphere such as hydrogen gas. The annealing temperature is about 750 to 650 ° C. which is lower than usual (about 1000 ° C.), and the annealing time may be about several minutes. If annealing is performed at a temperature higher than 750 ° C. or if the annealing time is longer than necessary, the iron coating layer 3 is excessively softened, and the desired hardness cannot be ensured. The clad material manufactured as described above is slit into an appropriate width and wound.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limitedly interpreted by this Example.

A soft steel sheet of SPCC (C amount: 0.12 mass% or less) is superposed on both sides of a copper sheet made of pure copper and cold-welded at a rolling reduction of about 60%, and an iron sheet (170 μm) / copper sheet ( A pressure contact sheet having a structure of 800 μm) / iron sheet (800 μm) was obtained. This pressure contact sheet was held in various atmospheres within the range of 600 to 1000 ° C. for 2 minutes in a hydrogen gas atmosphere to perform diffusion annealing. Then, finish rolling (cold rolling) is performed at a reduction ratio of about 10% for thickness adjustment and hardness adjustment, and the clad materials of sample Nos. 1-12 and 21-32 having a final plate thickness of 1.6 mm are obtained. It was. The structure of this clad material was iron coating layer (160 μm) / copper layer (720 μm) / iron base layer (720 μm). Sample No. 12 is a conventional example in which the diffusion annealing temperature is 1000 ° C.
Further, for Sample Nos. 21 to 32, after manufacturing the clad material, the surface of the iron coating layer of the clad material was brushed with a wire brush to form a hardened surface layer.

  The average hardness of the iron coating layer and the copper layer of the sample clad material was measured as follows. Take a hardness test piece from the clad material, embed the test piece in resin so that the thickness cross section along the rolling direction is the measurement surface, grind the embedded test piece so that the cross section is exposed, and coat with iron The Vickers hardness (additional load 200 gf at the time of measurement) at the center of the thickness of the layer and the copper layer was measured. Moreover, about sample No. 21-32, the Vickers hardness (additional load 25gf at the time of a measurement) of the surface of an iron coating layer was measured. Samples Nos. 21 to 32 correspond to Nos. 1 to 12, and the annealing temperatures of the corresponding samples are the same. For this reason, the average hardness of the iron coating layer and the copper layer of the corresponding samples is the same. ing.

  Further, a bending test piece having a length of 50 mm and a width of 10 mm was taken from each sample of the clad material along the rolling direction, and a bending test was performed using this. The bending test was performed using a V-shaped mold (bottom bend radius = 1.6 mm) with a bending angle of 30 °, and placing the clad material so that the iron coating layer is on the molding surface side of the female mold. Further, a male mold (bending radius at the tip = 1.6 mm) was hit with a hammer, and the sample was bent along the V-shaped molding surface. Further, a bending test was also performed in which the test piece was bent at 90 ° and then bent by a vise so that the angle formed by the two sides was 0 °. The outer side (iron coating layer side) of the test piece after the bending test was observed with an optical microscope (25 times magnification). Less than 100%, 90% or more of which discontinuous cracks occurred "○○", less than 90% of the total width, 50% or more of those where discontinuous cracks occurred "○", The case where a discontinuous crack occurred over less than 50% and 20% or more of the full width was evaluated as “Δ”, and the case where no crack occurred over the full width was evaluated as “x”.

  Further, the bonding strength was examined using each sample of the clad material. As the bonding strength, the load P (N) required to peel the iron coating layer and copper layer in the bonded state in the opposite direction from the base layer at 10 mm / min is divided by the plate width W (mm). The peel strength was sought. This value indicates the bonding strength between the copper layer and the base layer (soft steel), and at the same time indicates the bonding strength between the copper layer and the iron coating layer (soft steel). When the bonding strength was 30 N / mm or more, there was no problem in handling, so that a pass (◯) and a value less than 3 ON / mm were evaluated as a failure (×). These measurement results are also shown in Table 1.

  From Table 1, in the invention examples of sample Nos. 2 to 12, the average hardness of the iron coating layer is in the range of Hv 180 to 230, and 20% by bending with a V-shaped mold having a bending angle of 30 °. The occurrence of the above cracks was observed, and cracks occurred in more than 50% of the total width especially at 0 ° bending. In addition, in the inventive example, the bonding strength was obtained with no problem in handling. Furthermore, in the invention example (Sample Nos. 22 to 28) in which the hardened surface layer was formed, cracks occurred in 50% or more of the entire width even at 30 ° bending, and cracks occurred in the region of 90 to 100% at 0 ° bending. did. The bulge molding of the mount part by coining molding is a severe process that is subject to large deformation compared to the bending process described above. Therefore, according to the clad material of the invention example, the bulge molding of the mount part is performed during the bulge molding process. It is expected that the iron coating layer (resistance welding layer) is cracked and easily divided to expose the core copper material of the mount portion.

It is a fragmentary sectional view of the clad material concerning the embodiment of the present invention. It is a section explanatory view of a stem coining-molded using the clad material of the present invention as a raw material, and the core copper material is partially exposed in the mount portion. FIG. 4 is a cross-sectional explanatory view of a stem that is coined and formed using the clad material of the present invention as a raw material having an iron coating layer having a relatively high hardness, and the core copper material is entirely exposed in the mount portion. It is sectional explanatory drawing of the stem coining-molded using the conventional clad material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base layer 2 Copper layer 3 Iron coating layer 11 Base 12 Heat sink 13 Flat part 14 Mount part 15 Resistance welding layer

Claims (6)

  A base layer formed of a steel material, a copper layer formed of pure copper or a copper alloy containing copper as a main component and laminated on the base layer, and an iron coating layer formed of mild steel and laminated on the copper layer A clad material for a stem of a semiconductor device package, wherein the iron coating layer has an average hardness of Hv 180 to 230.   The clad material according to claim 1, wherein the iron coating layer has an average hardness of Hv210 to 230.   The clad material according to claim 1 or 2, wherein the base layer is formed of mild steel.   The clad material according to any one of claims 1 to 3, wherein a hardened surface layer is formed on a surface of the iron coating layer.   5. The clad material according to claim 1, wherein the iron coating layer has a thickness of 100 to 200 μm, and the copper layer has a thickness of 500 to 1000 μm. A base formed of a steel material, and a heat sink formed on the base,
The heat sink is composed of a flat portion laminated on the base portion and a mount portion formed integrally with the flat portion,
The flat part and the mount part are coated with a resistance welding layer made of mild steel on a core part made of pure copper or a copper alloy containing copper as a main component,
The stem of the semiconductor device package, wherein the resistance weld layer is divided on a side surface of the mount portion, and a core portion of the mount portion is partially or entirely exposed.

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