The disclosure of Japanese Patent Application No. 2010-261874 filed Nov. 25, 2010 including specification, drawings and claims is incorporated herein by reference in its entirety.
The present invention relates to a lead frame for an electronic component and a method of manufacturing the same, the lead frame including at least two stacked metal plates.
In the case where a lead frame for an electronic component is fabricated by joining at least two metal plates, the metal plates are bonded by caulking. The at least two metal plates may be joined by other methods such as welding and bonding but these joining methods require a welding material or a bonding material, whereas caulking does not particularly require any other members, achieving low production cost.
As shown in
Alternatively, a protrusion may be formed beforehand on one of the lead frames and a hole may be formed on the other lead frame. In this case, the lead frames are set in a mold so as to insert the protrusion into the hole and then the protrusion is flattened with a working punch, so that a caulked joint is completed.
As shown in
In the lead frame for an electronic component according to the related art shown in
As has been discussed, in the lead frame for an electronic component according to the related art, one metal plate is simply pressed with a punch and is stacked on the other metal plate. Disadvantageously, the metal plates are joined by caulking with a small strength and may be separated from each other. Moreover, it is quite difficult to align the at least two metal plates with parts in a mold in a caulking process, causing a misalignment when a caulked joint is made. Thus a desired joint may not be obtained, resulting in a lower caulking strength. Furthermore, in the laminated structure of the multiple metal plates, the protrusion 36 for caulking is left in the lead frame for an electronic component after the caulked joint is made, increasing the thickness of the lead frame for an electronic component. Thus the electronic component may not be reduced in thickness, leading to problems in packaging.
An object of the present invention is to improve a bonding strength while securing a reduction in size and thickness with a simple method.
In order to attain the object, a method of manufacturing a lead frame for an electronic component according to the present invention includes: a first placing step of placing a first metal plate on a die, the first metal plate having a hole; a second placing step of placing a second metal plate on a surface of the first metal plate with the hole formed on the surface; and a processing step of inserting a punch into the hole from above the second metal plate, wherein the second metal plate is extended into the hole and an intermetallic bond is formed between the first metal plate and the second metal plate on the inner surface of the hole.
Preferably, the punch contains first protrusions capable of protruding from the side of the punch and an operation pin used for protruding the first protrusions, the first protrusions are protruded from the side of the punch by the operation pin after the processing step, so that the second metal plate is protruded into engagement with the first metal plate.
Moreover, a plurality of protruding shapes may be formed on the side of the punch so as to be inserted into the hole and a plurality of projecting portions are formed on the second metal plate by the protruding shapes such that the second metal plate is engaged into the first metal plate.
Furthermore, second protrusions capable of protruding are retracted on a surface of the die with the first metal plate placed on the surface, and after the processing step, the intermetallic bond may be accelerated by protruding the second protrusions to form a recessed portion around a region directly below the hole on the contact surface of the first metal plate with the die.
Moreover, a lead frame for an electronic component according to the present invention includes: a first metal plate having a hole on a first major surface; and a second metal plate joined in contact with at least the inner surface of the hole and a part of the first major surface, wherein an intermetallic bond is formed between the first metal plate and the second metal plate on the inner surface of the hole.
Preferably, the second metal plate is protruded on the inner surface of the hole into engagement with the first metal plate.
The lead frame for an electronic component may further include a recessed portion formed around a region directly below the hole on the contact surface of the first metal plate with the die.
The hole may be formed by penetrating the first metal plate.
Generally, a lead frame for an electronic component includes a stepped member, on which only a heat dissipation part has a large thickness, to obtain a heat dissipation function. However, the stepped member in a special form has to be fabricated in a larger number of steps with higher production cost as compared with an ordinary plate. For this reason, two metal plates varied in thickness are prepared such that one of the metal plates has a large thickness to obtain a heat dissipation function and the other metal plate has a function other than heat dissipation. The two metal plates are joined by caulking, so that a lead frame for an electronic component with the heat dissipation function can be formed in a smaller number of steps and with lower production cost than in the fabrication of the stepped member.
Moreover, a lead frame for an electronic component with various functions may be formed by joining two different metal plates by caulking. For example, in the case where heat dissipation and insulation are necessary on a lead frame for an electronic component in a package containing two chips, it is difficult to obtain heat dissipation and insulation from a single material. For this reason, a metal plate having excellent heat dissipation and a metal plate having high insulation are prepared and the two metal plates are joined by caulking, so that a lead frame for an electronic component can be fabricated with heat dissipation and insulation. The multiple metal plates having different functions are joined thus by caulking, so that a lead frame for an electronic component can be fabricated with multiple functions.
Additionally, in the case where only a region of a lead frame for an electronic component requires a different function from the other region, multiple metal plates can be effectively used. For example, in the case where a region of a lead frame for an electronic component requires plating and the other region does not require plating in the fabrication of the lead frame composed of a single metal plate, plating has to be selectively performed or plating has to be removed in the undesired region after the overall lead frame is plated. However, in the case where two metal plates are separately fabricated and are joined by caulking, only one of the metal plates is entirely plated and the other metal plate is not plated in the fabrication of the metal plates. The two metal plates are joined by caulking to fabricate a lead frame for an electronic component such that the plated metal plate is disposed in a region to be plated. Thus an undesired area is not plated and the cost of plating materials can be reduced.
The present invention provides a lead frame for an electronic component, the lead frame being formed by joining multiple metal plates. A feature of the present invention is that at a joint of the metal plates, one of the metal plates is extended into a hole formed on the other metal plate and the metal plates are joined on the inner surface of the hole, which can improve a bonding strength while keeping the small size and thickness of the lead frame with a simple method.
The following will specifically describe examples of a configuration for joining two lead frames that are metal plates. The number of metal plates constituting the lead frame for an electronic component is not limited to two as long as two of the metal plates are joined as described below.
First, referring to
In
Next, as shown in
In the present invention, the hole is not formed like the hole of the lead frame 23 shown in
At this point, the thickness of the lead frame after a caulked joint is made is equal to the total thickness of the two lead frames. The second lead frame 3 is moved by the punch 5 while the depth of the punch is properly adjusted to prevent the second lead frame 3 from protruding from a contact surface with the die 1 and leading to a larger thickness.
The punch 5 and the hole 4 may have any shapes but it is preferable that the punch 5 is cylindrical and the hole 4 has a circular opening. Furthermore, the diameter of the punch 5 is determined by subtracting the total required thickness of the metal plate extended on the inner surface of the hole 4 from the inside diameter of the hole 4.
In the lead frame for an electronic component and the method of manufacturing the same according to the present invention, the lead frame being formed by joining the at least two lead frames that are metal plates, one of the metal plates is extended by the punch into the hole formed on the other metal plate and the two metal plates are connected on the inner surface of the hole. The joint surface of the metal plates is formed thus on the inner surface of the hole by the punch, so that a stress on the joint surface forms an intermetallic bond between the metal plates so as to improve the bonding strength. At this point, the metal plates do not have to be aligned with each other, thereby easily improving the bonding strength. Although a protrusion is formed in the related art, a protrusion forming process is not necessary in the formation of the metal plates according to the present invention, thereby more easily improving the bonding strength. Since the joint surface is formed in the hole, the small size and thickness of the lead frame can be kept without affecting the outside shape of the lead frame for an electronic component. Moreover, a higher bonding strength facilitates handling in a downstream process. In a region where the at least two metal plates are joined, the metal plates are joined without forming any gap, so that an electrical resistance decreases at the joint and electrical conductivity can be improved on a caulked lead.
The lead frames 2 and 3 are metal plates, each having at least one terminal portion or element mounting portion according to the shape of the lead frame for an electronic component.
In the present embodiment, instead of the punch 5 of the first embodiment, a punch 11 is used that includes at least one protrusion 8 capable of protruding from the side of the punch and an operation pin 7 that protrudes the at least one protrusion 8. Before a manufacturing process, the at least one protrusion 8 is retracted in the punch 11 so as to be flush with the side of the punch 11. The at least one protrusion 8 can be protruded from the side of the punch 11 by the operation pin 7. The punch 11 has a hollow part that exposes the inside of the at least one protrusion 8. The operation pin 7 is stored in the hollow part so as to move in parallel with the lowering direction of the punch 11. The operation pin 7 has a tapered end at a contact point with the at least one protrusion 8. The operation pin 7 is moved down in the punch 11, so that the tapered portion can press the at least one protrusion 8.
The same process as in the first embodiment is performed until the state of
The at least one protrusion 8 contained in the punch 11 is protruded thus to engage the lead frame 3 like a wedge into the lead frame 2 on the joint surface of the inner surface of the hole 4, achieving an anchor effect; meanwhile, the small size and thickness of the lead frame is kept with a simple method. Thus the bonding strength of the lead frames 2 and 3 can be more improved than in the first embodiment.
As shown in
Finally, the punch 12 is pulled out, so that the lead frame for an electronic component is formed with the asperities shaped like grooves on the joint surface of the lead frames.
In the present embodiment, the die 1 of the first embodiment is replaced with a die 13 that includes protrusions 10 capable of protruding in a region surrounding a hole 4 on the contact surface of the die with a lead frame 2.
First, as shown in
As has been discussed, the contact surface of the lead frame 2 with the die 13 is deformed by the protrusions 10, so that an intermetallic bond is accelerated on the joint surface of the lead frames and the bonding strength between the lead frames can be easily improved without extending outside dimensions. Furthermore, asperities like wedges on the joint surface can further improve the bonding strength between the lead frames.
In this explanation, the protrusions are formed from the back side of the lead frame 2 in the joining of the first embodiment. The protrusions may be formed from the back side of the lead frame 2 in the joining of the second and third embodiments.
In the explanation of the embodiments, the hole 4 formed on the lead frame 2 penetrates the front and back sides of the lead frame 2. The hole may be closed on the back side of the lead frame 2 with respect to the contact surface of the lead frame 2 with the lead frame 3.
Number | Date | Country | Kind |
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2010-261874 | Nov 2010 | JP | national |