JP2539432B2 - Resin-sealed semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing the occurrence of cracks in an electronic device, in particular, a resin-sealed package, and, for example, a semiconductor integrated circuit provided with a surface mount type plastic package. The present invention relates to a technology effectively used for a circuit device (hereinafter referred to as IC).

[Conventional technology]

As an IC for high-density mounting, a resin-sealed package in which the tab to which pellets are bonded has a relatively large planar area (for example, 5 mm □ or more) and the outer leads are surface-mounted I have something to prepare.

As an example of describing such an IC, there is "IC implementation technology" issued by the Industrial Research Institute Co., Ltd., January 10, 1980, P135 to P155.

[Problems to be solved by the invention]

However, in an IC equipped with such a surface mount plastic package, the heat of the silicon forming the pellet, the 42 alloy or copper forming the lead frame, and the resin forming the package is Due to the large difference in expansion coefficient, the IC is bonded to the pellet and the tab of the lead frame by being heated in the temperature cycle test, thermal shock test, etc., and in the solder dip or reflow soldering process during mounting. It has been clarified by the present inventor that peeling occurs at the interface, and as a result, a crack occurs in the resin package starting from the back surface of the tab.

An object of the present invention is to provide an electronic device that can prevent the occurrence of cracks in a resin-sealed package.

The above and other objects and novel features of the present invention are as follows.
It will be apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

The typical ones of the inventions disclosed in the present application will be outlined as follows.

That is, a plurality of substantially oval first through holes formed along a first direction in a tab that is a mounting portion of a resin-sealed pellet, and a second direction orthogonal to the first direction. The resin-sealed semiconductor device has a plurality of substantially oval-shaped second through holes formed along the above.

[Action]

According to the above-mentioned means, even if a force for peeling the interface between the lower surface of the tab and the package or the interface between the tab and the pellet acts due to the repeated stress due to the thermal stress, it is filled in the through hole. Since the resin of the package exerts the anchoring effect, the peeling force can be sufficiently resisted, so that the peeling is surely prevented. When peeling does not occur, even if stress concentrates near the outer edge on the back surface of the tab inside the package, cracks originating from the stress do not occur.

Further, since the through hole is formed in the tab, the cross-sectional area of the tab is reduced, so that the elongation amount due to the thermal expansion of the tab is reduced. As a result, the magnitude of the concentrated stress generated due to the difference in thermal expansion between the tab and the package resin on the outer edge of the tab is suppressed to a small level. The generation of cracks from the starting point will be prevented.

[Embodiment 1] FIG. 1 is a longitudinal sectional view showing an IC equipped with a surface mount type resin-sealed package which is an embodiment of the present invention, and FIG. 2 is an enlarged partial plan view showing its tab. FIG. 4 is a plan view showing the manufacturing process, and FIG. 4 is a stress distribution diagram inside the package for explaining its operation.

In the present embodiment, the IC 1 equipped with the surface mount type resin-sealed package is equipped with the lead frame 2, and the lead frame 2 is configured as shown in FIG. 3 before packaging. That is, the lead frame 2 is integrally connected to each of the inner leads 4 and a plurality of inner leads 4 arranged in a substantially cross shape so that a substantially square space 3 remains at the intersection. A plurality of outer leads 5, a dam 6 installed between adjacent outer leads 5 and 5, a pair of outer frames 7 connected to a pair of outer leads 5 group, and arranged in the void 3 The tab 8 is formed in a slightly smaller, substantially square flat plate shape, and the holding member 9 is provided to project from the four corners of the dam 6 and suspends the tab 8.

The tab 8 is formed in a substantially square flat plate shape, and a through hole 10 is concentrically arranged in the central portion thereof so as to be penetrated in the thickness direction. The through hole 10 has a cross-sectional shape that is a perfect circle, and a vertical cross-section that has a taper shape in which the diameter of the pellet bonding surface side (hereinafter referred to as the upper surface) gradually increases. An annular groove 11 is formed on the upper surface of the tab 8 as a through hole.
It is arranged and engraved so as to surround 10. The lead frame 2 is formed by punching press work. Therefore, for example, the through hole 10 is formed in the blade of the press die for punching out the tab 8.
By forming the teeth for punching, the through hole 10 can be formed at the same time as the tab 8 is punched. Further, the through hole 10 can be formed even if the tab 8 is subjected to etching processing, and the annular groove 11 can be similarly formed.

A pellet 12 in which an integrated circuit is formed is bonded on the tab 8 with an adhesive layer 13 made of silver paste or the like, and each inner lead 4 is attached to an electrode pad of the pellet 12.
Wires 14 are respectively bonded between and.
The integrated circuit of the pellet 12 is electrically drawn to the outside through the electrode pad, the wire 14, the inner lead 4 and the outer lead 5.

Here, in the bonding operation of the pellet 12 to the tab 8 using the adhesive, the adhesive 13a is scattered to the outside of the annular groove 11 on the upper surface of the tab 8 as shown by an imaginary line in FIG. Applied to. Then, the pellet 12 is placed on the tab 8 and slid in all directions with a minute stroke. This sliding causes the adhesive material 13a to be spread over a wide range, but there is a risk of protruding into the through hole 10. However, in the present embodiment, since the annular groove 11 is arranged so as to surround the through hole 10, the adhesive material 13a is restrained in this groove 11 and therefore does not protrude into the through hole 10.

And the wire-bonded IC1 is package 1
5 is integrally molded into a substantially square flat plate shape using a transfer molding method using resin. By this package 15, a part of the lead frame 2, the pellet 12, the wire 14 and the tab 8 are hermetically sealed. Ie tab 8
The outer lead groups 5 other than the above are respectively projected from the four side surfaces of the package 15, and the outer lead group 5 is bent downward outside the package 15 and then further bent outward in the horizontal direction. Incidentally, after the package 15 is molded, the outer frame 7 and the adjacent outer leads 5, 5 are formed.
The spaces are cut off.

 Next, the operation will be described.

The IC according to the above configuration is subjected to a sampling inspection before shipping. Environmental tests including temperature cycle tests and thermal shock tests are carried out as sampling inspections. Moreover, when this IC is mounted on a printed wiring board or the like, the IC is heated by solder dipping or reflow soldering.

When such environmental test or mounting, heat stress is
When applied to FPPIC, stress is generated inside the package 15 due to the difference in the coefficient of thermal expansion of the constituent materials.

By the way, when the outer peripheral edge of the tab is formed at a sharp right angle, the internal stress of the package is concentrated near the outer edge on the back surface of the tab 8, as shown in FIG. However, cracks in the package do not occur at this concentration of stress. However, when peeling occurs at the interface between the tab lower surface and the package or the tab and the pellet due to repeated stress due to repeated thermal stress, excessive stress acts on the stress concentration point, and a crack occurs from that point. To do. Furthermore, in the storage process after the package is completed, if moisture enters the gap between the bottom surface of the tab and the package due to peeling, the moisture expands due to heating, causing even greater stress. It has been clarified by the present inventor that there is a problem that cracks originating from the stress concentration points are more likely to occur.

A similar study is published in Japan Science and Technology Federation
Annual Reliability Symposium Proceedings "May 29, 1984
Published in P303-P306.

And, when the lead frame made of 42 alloy is used, peeling at the interface between the tab lower surface and the package, and when the lead frame made of copper is used, peeling at the interface between the pellet and the tab, When each occurs, the stress at the bottom of the tab increases significantly,
The package cracks. In particular, even when a lead frame made of copper, whose coefficient of thermal expansion is almost the same as that of the resin used in the package, is used, if peeling occurs at the interface between the pellet and the tab, the resin portion of the package that contacts the side surface of the tab Opens, and excessive stress acts to cause cracks.

When such a crack occurs in an IC equipped with a surface mount type package, the package is made thin due to the need for surface mounting, so the crack easily reaches the package surface, and the intrusion of moisture through the opening. Therefore, the moisture resistance is sharply reduced.

However, in this embodiment, since the through hole 10 is formed in the tab 8, the pellet 14 is not cracked.

That is, the lower surface of the tab 8 and the package 15, or the tab 8 is repeatedly subjected to the thermal stress as described above.
Even if a force for peeling this is applied to the interface between the pellet 12 and the pellet 12, the resin of the package filled in the through hole 10 exerts an anchoring effect, so that the peeling force Since it can sufficiently resist, peeling is surely prevented. As described above, when the peeling does not occur, even if the stress is concentrated near the outer edge of the back surface of the tab 8, the crack originating from the stress does not occur. By the way, if the through hole 10 is formed as a tapered hole having a large diameter on the pelletizing surface side, the anchoring effect is further enhanced.

Further, since the cross-sectional area of the tab 8 is reduced by forming the through hole 10 in the tab 8, the amount of expansion due to the thermal expansion of the tab is reduced accordingly. As a result, the magnitude of the concentrated stress generated due to the difference in thermal expansion between the tab and the package resin on the outer edge of the tab 8 is suppressed to a small level, so that the above peeling may occur inside the package 15. Also, the occurrence of cracks originating from the stress concentration point is prevented.

 According to the above embodiment, the following effects can be obtained.

(1) By opening the through hole in the tab so as to penetrate in the thickness direction, it is possible to prevent the tab and the package from being separated from each other due to the stress generated by the thermal stress. It is possible to prevent the occurrence of cracks in the package starting from.

(2) Since the generation of cracks in the package can be prevented by the above (1), the surface mount type package can be made thinner and smaller.
It is possible to further increase the integration density and mounting density of the IC having the surface mount type package.

(3) By forming the through hole in a tapered hole having a large diameter on the pelletizing surface side, the anchoring effect of the solid portion of the resin filled in the tapered hole can be enhanced,
By reliably preventing the tab and the package from peeling off, it is possible to more reliably prevent the occurrence of cracks originating from the outer edge of the tab in the package.

(4) By disposing the annular groove outside the through-hole, it is possible to prevent the adhesive from protruding into the through-hole during pellet bonding, so that the through-hole can be reliably filled with the resin.

(5) Since the through hole can be formed at the same time as the tab at the time of punching and pressing the lead frame, it is possible to suppress deterioration in workability.

[Embodiment 2] FIG. 5 shows Embodiment 2 of the present invention and is an enlarged partial plan view corresponding to FIG.

The second embodiment differs from the first embodiment in that it has five through holes.
The tabs 10A are provided along the center line of the tab 8A so as to be arranged on the four sides and substantially in the center, respectively, and the action and effect thereof are substantially the same as those in the first embodiment.

[Embodiment 3] FIG. 6 shows Embodiment 3 of the present invention and is an enlarged partial plan view corresponding to FIG.

The third embodiment differs from the first embodiment in that the through hole 10B is concentrically arranged in the central portion of the tab 8B and has a large diameter.

According to the third embodiment, since the through hole 10B is largely formed in the tab 8B, the elongation due to the thermal expansion of the tab 8B becomes extremely small. Therefore, the stress generated therewith is also suppressed to a small level.

[Embodiment 4] FIG. 7 shows Embodiment 4 of the present invention and is an enlarged partial plan view corresponding to FIG.

The fourth embodiment is different from the first embodiment in that four substantially oval through-holes 10C are arranged along the center line at the center of the four sides of the tab 8C, so that the tab 8C is largely cut away. The point is that it has been opened.

According to the fourth embodiment, the influence of the thermal expansion of the tab 8C is extremely suppressed as in the case of the third embodiment, so that the stress generated therewith is also suppressed to be small.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Nor.

For example, the through hole is not limited to be formed in a circular cross section,
It may be formed in a regular polygonal shape such as a regular quadrangle or a regular hexagon.

The through hole is not limited to the tapered hole, and the annular groove may be omitted.

Further, in order to disperse the stress concentrated on the pellet, it is desirable to form a chamfered portion at the end of the pellet. Further, since stress is generated by peeling between the tab and the pellet, it goes without saying that it is desirable to enhance the adhesiveness between the two.

In the above description, the invention mainly made by the present inventor has been described as applied to an IC having a surface mount type resin-sealed package, which is the field of application of the invention, but is not limited thereto. Also, the present invention can be applied to general electronic devices such as ICs provided with other resin-sealed packages.

〔The invention's effect〕

The following is a brief description of an effect obtained by the representative one of the inventions disclosed in the present application.

By opening a through hole in the tab that is the pellet mounting part so as to penetrate in the thickness direction, it is possible to prevent peeling that occurs between the resin-sealed package and the tab due to thermal stress. It is possible to prevent the occurrence of package cracks starting from.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an IC equipped with a surface mount type resin-sealed package according to an embodiment of the present invention, FIG. 2 is an enlarged partial plan view showing its tab, and FIG. FIG. 4 is a plan view showing the stress distribution inside the package for explaining the action, and FIGS. 5, 6, and 7 show Examples 2, 3 and 4, respectively. It is each expanded partial plan view corresponding to a figure. 1 ... IC equipped with surface mount type resin sealing package
(Electronic device), 2 ... Lead frame, 3 ... Vacancy, 4
…… Inner lead, 5 …… Outer lead, 6 …… Dam,
7 ... Outer frame, 8 ... Tab, 9 ... Holding member, 10, 10A, 1
0B, 10C ... through hole, 11 ... annular groove, 12 ... pellet, 13
...... Adhesive layer, 14 ...... Bonding wire, 15 …… Package

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sumio Okada 111 Nishi-Yokotemachi, Takasaki City Takasaki Plant, Hitachi, Ltd. (72) Inventor Toru Nagamine 15 Asahidai, Moroyama-cho, Iruma-gun, Saitama Hitachi Eastern Semiconductor Co., Ltd. (56) References Actually open Sho 60-118252 (JP, U) Actually open 57-44551 (JP, U)

Claims (2)

(57) [Claims] 1. A resin-encapsulated semiconductor device having a tab and a semiconductor pellet adhered to the tab, wherein a plurality of substantially elliptical first first electrodes are formed on the tab along a first direction. Through holes and a plurality of substantially oval second through holes formed along a second direction orthogonal to the first direction, and the semiconductor pellets are bonded onto this tab. A resin-encapsulated semiconductor device characterized in that 2. A plurality of substantially oval first through holes and second through holes are formed on a straight line centering on an intersection of the first direction and the second direction. The resin-encapsulated semiconductor device according to claim 1, which is characterized in that.