JP3173328B2 - Lead frame for semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame for a semiconductor device in which a metal plate is bonded to a lead frame via an insulating layer, and more particularly to a device for preventing a short circuit between the metal plate and the lead frame.

[0002]

2. Description of the Related Art In recent years, as the density and speed of elements have been increased, the development of lead frames for semiconductor devices with improved heat dissipation has been active. A metal plate that functions as a heat spreader is laminated in the thickness direction of the lead frame in order to enhance heat radiation.In particular, recently, a metal plate coated with an adhesive in advance has been prepared, and it has a predetermined shape with a mold. Attention has been paid to a method of bonding to a lead frame while punching. According to this, there is an advantage that the metal plate can be bonded to the lead frame at low cost.

FIG. 3 shows a typical example of a lead frame structure for a semiconductor device bonded in such a manner. The lead frame 1 having a device hole 5 at the center is shown in FIG.
A metal plate 3 coated with an adhesive 2 so as to cover the device hole 5 is bonded to the inner lead portion 1a.
The semiconductor chip is bonded in the device hole 5 on the metal plate 3.

[0004]

A particular problem in a lead frame for a semiconductor device in which a metal plate for heat dissipation is bonded to a lead frame is an electrical short between the metal plate and the lead. As shown in FIG. 4, which is an enlarged view of the portion C in FIG. 3, the portion A in the figure where the lead frame 1 and the metal plate 3 with adhesive overlap has a high electrical insulation property with respect to the adhesive 2 to be interposed. For example, the problem can be solved by using a thermoplastic polyimide adhesive.

However, at a point B in the figure where the outer peripheral portion 3a of the metal plate 3 faces the lead frame 1, the shortest insulating distance between the two is inevitably the thickness of the adhesive 2, but Since the thickness is generally as thin as about 20 μm, the following problems occur.

(1) Conductive foreign matter generated by punching out of a metal stamped metal plate generated by punching a metal plate with an adhesive is placed between the outer peripheral portion of the metal plate and the lead frame, and the like. Short between the metal plate and the lead frame.

(2) A lead frame for a semiconductor device is packaged after mounting a semiconductor chip. An interface between the adhesive and the package resin is formed at a position B in the drawing,
At this interface, the moisture absorbed by the resin condenses and migrates along the interface to dendrites (dendrites)
There is a concern that this will occur. Dendrites tend to occur particularly when both the lead frame and the metal plate are made of copper, and due to the potential applied to the lead frame side, they are generated from the lead frame side toward the metal plate side, Short between leads.

An object of the present invention is to provide a lead frame for a semiconductor device which can solve the above-mentioned problems of the prior art and can prevent a short circuit between an outer peripheral portion of a metal plate and a lead frame. is there.

[0009]

[0010]

Means for Solving the Problems A first invention is a lead frame.
Both the arm and the metal plate are made of copper, and
The adhesive precoated metal plate via the adhesive while punching into a predetermined shape to a lead frame for a semiconductor device was bonded to the lead frame, bonded to a lead frame that
The adhesive and the package are attached to the outer peripheral portion of the joined metal plate.
A semiconductor device formed to have an interface with a resin.
In the mounting lead frame, on the outer peripheral portion of the metal plate,
A bent portion bent in a direction away from the lead frame is provided to increase the insulation distance between the outer peripheral portion of the metal plate and the lead frame.

In a second aspect based on the first aspect , the height of the edge of the bent portion from the lead frame is 20 to
The thickness was set to 500 μm.

[0012]

According to the first aspect of the present invention, when the bent portion is provided on the outer peripheral portion of the metal plate, when the bent portion is not provided, the outer peripheral portion of the metal plate which has been only the thickness of the insulating layer until then is provided. The insulation distance to the lead frame increases by the height of the bent portion. Therefore, the risk that the metal plate and the lead frame are short-circuited by the conductive foreign matter is reduced. Further, by bending the outer peripheral portion of the metal plate, the interface between the adhesive and the package resin extends by the length of the bent portion, so that it is possible to prevent the occurrence of dendrite which causes a short circuit.

In the case where a metal plate with an adhesive is punched and bonded to a lead frame as in the first invention, a conductive flash such as a punched flash generated at the time of punching is used.
Although it is brought in as it is at the time of bonding, a short circuit between the metal plate and the lead frame due to conductive burrs can be effectively avoided because the bent portion is provided on the outer peripheral portion of the metal plate.

Here, as in the second invention, the height of the bent portion from the lead frame is preferably 20 to 500 μm. If it is less than 20 μm, a short circuit due to a conductive substance or short circuit due to dendrite may not be effectively avoided. Because.

[0015]

FIG. 1 is a cross-sectional view showing the state of bonding a metal plate of a lead frame for a semiconductor device according to an embodiment of the present invention. For this, a metal plate 3 is prepared in which an adhesive 2 serving as an insulating layer is previously applied to one surface. As the adhesive 2, for example, a thermoplastic polyimide adhesive having high electric insulation is used. Further, copper having high thermal conductivity is used for the metal plate 3. The metal plate 3 is stamped out with a die to form a metal plate 3 having a predetermined shape, and the stamped and formed metal plate 3 is continuously bonded to the lead frame 1 as it is. The bonding position of the metal plate 3 is the inner lead portion 1a adjacent to the device hole 5. The same copper as the material of the metal plate 3 is used for the lead frame 1.

As shown in the figure, an outer peripheral portion 3a of a metal plate 3 bonded to the lead frame 1
A bent portion 4 bent in a direction away from the bent portion is provided. By providing the bent portion 4, a gap 7 is formed between the lead frame 1 and the outer peripheral portion 3a of the metal plate 3, and the insulation distance between the outer peripheral portion 3a of the metal plate and the lead frame 1 is increased.

In this embodiment, the height of the edge 3b of the bent portion 4 of the outer peripheral portion 3a of the metal plate from the lead frame 1 is h = 100 μm. With such a height, a conductive beam such as a punching beam which is usually generated when a metal plate is punched out may be attached to the lead frame 1 and the metal plate 3 at the time of bonding.
Short-circuiting due to contact with the outer peripheral portion 3a of the first embodiment can be effectively avoided. The angle of inclination of the bent portion 4 is set to about 45 ° with respect to the plane of the metal plate. With such an inclination angle, the bent portion 4 can be easily formed by using a bending process by a conventional downset method.

By providing the bent portion 4 on the metal plate 3 as described above, the insulation distance 6 between the lead frame 1 and the metal plate 3 along the interface between the adhesive 2 and the resin can be reduced by the conventional method having no bent portion. While the shortest length is 20 μm corresponding to the thickness of the adhesive 2, in the case of the present embodiment, the insulation distance = the thickness of the adhesive 20 μm + the distance of the bent portion is approximately 140 μm (100 / sin45 °) = 160 μm. Increase significantly.

When the lead frame 1 and the metal plate 3 are both made of copper as in this embodiment, migration is likely to occur due to the moisture absorption of the package resin. Since the insulation distance 6 at the interface to the outer peripheral portion 3a of the plate is about 160 μm or more, it can be said that copper dendrite precipitation due to migration which causes a short circuit hardly occurs. Even if it occurs, the distance is about eight times as long as the conventional one, that is, the life is eight times longer, so it can be said that there is almost no problem in practical use.

[0020]

By the way, the bent portion of the outer peripheral portion of the metal plate is formed by performing a chamfering process on the end face of a punch used at the time of punching and bonding, which has substantially the same size as the shape of the bent portion at the time of punching and bonding. Can be processed simultaneously. Therefore, without changing the process of obtaining a normal lead frame at all,
Since the bent portion can be processed only by changing the punch end surface of the mold, there is no increase in manufacturing cost.

FIG. 2 shows a modification in which the tip of the bent portion 8 is further bent so as to be parallel to the metal plate 3. this is,
This is a structure obtained by forming a part of the metal plate 3 in advance and bonding it while punching the outer peripheral portion 3a. According to this, there is an advantage that machining accuracy can be easily obtained as compared with the embodiment of FIG.

[0023]

According to the first aspect of the present invention, the bent portion is provided on the outer peripheral portion of the metal plate, and the insulation distance from the outer peripheral portion of the metal plate to the lead frame is added to the thickness of the insulating layer. Since the height is increased by the height of the curved portion, the risk of a short circuit between the metal plate and the lead frame can be reduced. Further, by bending the outer peripheral portion of the metal plate, the interface between the adhesive and the package resin is extended, so that the occurrence of dendrite which causes a short circuit can be prevented.

According to the first aspect of the present invention, since the present invention is applied to a lead frame having a structure in which a metal plate with an adhesive is bonded to a lead frame while being punched, conductive foreign matter which is generated at the time of punching and carried as it is at the time of bonding. The short circuit between the metal plate and the lead frame can be effectively avoided.

According to the second aspect of the present invention, since the height of the bent portion of the outer peripheral portion of the metal plate from the lead frame is defined within a predetermined range, a short circuit between the lead frame and the metal plate is more effectively avoided. It can be easily processed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a bonding state of a metal plate with an adhesive for explaining an embodiment of a lead frame for a semiconductor device of the present invention.

FIG. 2 is a cross-sectional view illustrating a bonding state of a metal plate with an adhesive for explaining a modified example.

FIG. 3 is a cross-sectional view showing a bonding state of an adhesive-attached metal plate of a conventional lead frame for a semiconductor device.

FIG. 4 is an enlarged view of a portion C in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead frame 2 Adhesive (insulating layer) 3 Metal plate 3a Outer peripheral part 4 Bend part 6 Insulation distance 8 Bend part h Height

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeharu Takahagi 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Systems, Ltd. System Materials Research Laboratories (56) References JP-A-3-161957 (JP, A) JP Hei 7-86458 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 23/50

Claims (2)

(57) [Claims] 1. A lead frame and a metal plate are both made of copper.
Metal plate that is pre-coated with an adhesive that is an insulating layer
The lead frame is punched through the adhesive while punching
Lead frame for semiconductor devices
The outer periphery of the metal plate bonded to the lead frame
Has an interface between the adhesive and the package resin.
-Formed lead frame for semiconductor device
A bending portion which is bent in a direction away from the lead frame on an outer peripheral portion of the metal plate to increase an insulation distance between the outer peripheral portion of the metal plate and the lead frame. Lead frame. 2. An edge at a bent portion of an outer peripheral portion of the metal plate.
Height of the lead frame from 20 to 500 μm
A lead frame for a semiconductor device according to claim 1 .