JP2607576B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a semiconductor device, particularly for surface mounting in which a large number of resin-sealed devices are simultaneously mounted on a substrate or the like, and furthermore, a semiconductor package. The present invention relates to a semiconductor device having a large external shape, a large number of pins, and a thin shape.

(Prior Art) Conventionally, as shown in FIGS. 12 to 14, a surface-mounted encapsulated semiconductor device is a flat plate having four corners (four or two corners or two sides in some cases) supported by a tie bar 12. The semiconductor element 3 is mounted on the upper surface of the die pad 2 in a shape of a circle.
After bonding as shown in FIG. 1, a semiconductor package P is generally formed by resin sealing with a mold resin 6.

At this time, the tie bar length L between the corner of the die pad 2 and the tip of the tie bar 1 had a value determined by the outer dimensions of the semiconductor package P.

However, with the recent high-density mounting, FP (flat package), PLCC (chip carrier with plastic lead), SOJ (small outline J)
The use of thin resin-encapsulated packages for surface mounting such as bend packages) is progressing, and when performing surface mounting on the base of such a semiconductor package, unlike the additional heat applied to the individual leads alone, A system in which the whole is exposed to a high temperature of 200 ° C. or more has been adopted.

For this reason, the moisture absorbed inside the mold resin 6 tends to explosively vaporize at the interface between the semiconductor element 3 and the mold resin 6 or at the interface between the die pad 2 and the mold resin 6. In addition, as shown in FIG. 14, cracks 7 are generated in the mold resin 6 on the lower surface around the die pad 2 and in the mold resin 6 on the upper surface around the semiconductor element 3 (not shown). There was a problem that there was.

The crack 7 not only impairs the appearance but also significantly reduces the moisture resistance reliability of the semiconductor element 3.

Further, with the increase in the number of pins of the semiconductor package, the size of the semiconductor package and the size of the semiconductor element have been increasing, while the thickness of the semiconductor package has been reduced, contrary to the thickness of the semiconductor package.

Therefore, as shown in FIG. 15 and FIG. 16, the tie bar 1 supporting the die pad 2 becomes longer and longer, while the size of the die pad 2 becomes larger.
The phenomenon that the die pad 2 and the semiconductor element 3 are pushed up from a normal position (FIG. 15) or pushed down (FIG. 16) due to the flow pressure P of the molten thermosetting resin filled at the time of resin molding. Will happen. This phenomenon not only damages the wire bonding portion due to the vertical movement of the die pad 2, but also causes the resin layer on the upper side or the lower side of the semiconductor element 3 to be extremely thin, and particularly, remarkable moisture resistance after solder reflow. This leads to deterioration of the quality.

In order to prevent the above cracks from occurring, for example,
As No. -208847, a cylindrical or polygonal hole is made in the mold resin portion on the back surface of the semiconductor element to form an extremely thin portion or a portion without mold resin. There has been proposed a means for releasing a gas due to evaporation of water.

(Problems to be Solved by the Invention) However, the one disclosed in Japanese Patent Application Laid-Open No. 60-208847 has a die pad on which a semiconductor element is mounted because a hole is formed in a mold resin on the back surface of the semiconductor element. Not only is the lower surface of the semiconductor package exposed to the outside, but also the entire semiconductor package is exposed to high temperatures, causing the adhesiveness between the mold resin and the die pad to decrease and to peel off radially. May be adversely affected.

In addition, if the flux used during mounting or the processing liquid used in the cleaning process after mounting enters through the holes, these easily contaminate the entire back surface of the die pad. It is considered that there is a problem of causing deterioration of performance.

Furthermore, no countermeasures have been taken against upward or downward displacement of the die pad and the semiconductor element (hereinafter referred to as floating or sinking of the die pad) due to the resin mold.

In view of the above, the present invention eliminates the generation of internal resin cracks at the time of mounting, does not have a problem with moisture resistance reliability even if solder mounting is performed by total heating after moisture absorption, and can adversely affect semiconductor elements. Not only that, it is possible to deal with an increase in the size of the package itself, and furthermore, it is possible to eliminate the occurrence of floating or sinking of the die pad, and to eliminate the problem of moisture resistance reliability in this regard as well. The purpose is to provide.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, a die pad having a semiconductor element mounted on its upper surface is supported by tie bars extending from four corners of the die pad, and the semiconductor element is sealed with a molding resin. In the semiconductor device, at least one of a front surface and a back surface of the mold resin, for example, only one or more holes or notches reaching the tie bar are provided on only the back surface of the mold resin, or both corresponding front and back surfaces of the mold resin. It is provided.

(Operation) By effectively discharging the moisture present inside the mold resin, particularly in the vicinity of the interface between the mold resin and the die pad as vapor at a high temperature during mounting from the perforations or notches to the outside. By forming this outlet in advance to prevent the generation of cracks due to the steam, and by providing this perforation or notch so as to reach the tie bar,
This perforation or notch prevents the semiconductor element from being adversely affected, copes with an increase in the size of the package, and further forms the perforation or notch at opposing positions on the front and back surfaces of the mold resin, respectively. By providing, by pressing the tie bar from above and below via the protrusion of the mold corresponding to the perforation or notch at the time of resin molding and fixing it, the floating or sinking of the die pad can be reliably prevented. It can also be.

(Embodiment) FIGS. 1 and 2 show a first embodiment of the present invention, in which four corners of a flat die pad 2 are supported by tie bars 1 extending from four corners to four sides. The semiconductor element 3 is mounted on the upper surface. The semiconductor element 3 and the lead wire 4 are bonded by bonding wires 5 as shown in FIG.

The semiconductor element 3 and its periphery are resin-sealed with a short mold resin 6 to form a semiconductor package P.

Holes 6a reaching the tie bar 2 are provided at four positions on the back surface of the mold resin 6 opposite to the tie bar 2 on the diagonal line.

By providing the perforations 6a in this manner, when mounting the semiconductor device on a substrate or the like by exposing the entire semiconductor package P to a high temperature of 200 ° C. or more, it is present particularly at the interface between the semiconductor element 3 and the die pad 2 and evaporates. By transmitting the moisture to the die pad 2 through the tie bar 1 continuous to the die pad 2 and discharging the moisture to the outside from the perforations 6a, it is possible to prevent a crack from being generated inside the mold resin 6 due to the pressure of the evaporation.

In addition, when a normal crack occurs, the arc progresses toward the four sides of the mold resin 6 starting from a position corresponding to the center of the four sides of the die pad 2 as a starting point. Since it is difficult to proceed, even if the perforations 6a are provided in this manner, there is little possibility that cracks will be generated from the perforations 6a.

Further, by providing the perforations 6a in this manner, the distance l between the corner of the die pad 2 and the perforations 6a is made shorter than the tie bar length L determined by the outer shape of the semiconductor package P, and the occurrence of cracks is reduced. The size of the semiconductor package is substantially the same as the size of the semiconductor package in the range enclosed by the line connecting the lines, so that the smaller the size of the semiconductor package, the smaller the occurrence of cracks. This is to prevent the occurrence of as much as possible.

85% RH at 85 ° C.
In an accelerated atmosphere, let the moisture content inside the semiconductor package become saturated, and after immersing the solder at 215 ° C for 2 minutes,
As a result of examining the occurrence of cracks, none of the 10 had cracks. On the other hand, as a result of the experiment of the conventional device in the same manner as above, cracks occurred in all of the ten samples.

FIGS. 3 and 4 show the second embodiment. The difference from the above embodiment is that the tie bar 1 is provided at one position on the back surface of the mold resin 6 opposite to the tie bar 1 on the diagonal line. In that the notch 6b is provided.

In this way, the entire semiconductor package P is heated to 200 ° C.
When exposed to the above atmosphere, the moisture evaporated inside the mold resin 6 is discharged from the notch 6b.

Note that, as described above, the perforations 6a
The reason for providing these is mainly to prevent the aesthetics from being impaired, and it is also possible to provide perforations 6 a from the surface of the mold resin 6.

In addition, a junction coating resin (JCR) or polyimide may be applied to the upper surface of the semiconductor element 3 to further improve the moisture resistance reliability.

FIG. 5 and FIG. 6 show a third embodiment, in which four locations on a diagonal line facing the tie bar 1 and from above and below both the front and back surfaces of the mold resin 6 and face each other. Holes 6a, 6a 'reaching the tie bar 1
Are provided respectively.

In this way, the perforations 6a, 6a 'are respectively located from the upper and lower sides facing each other.
In addition to the effects provided from only one of the front surface and the back surface, the following effects are provided.

That is, as shown in FIG. 7, when performing resin molding, the molding die 8, 8
The tie bar 2 fixed by the projections 8a, 8a at the intermediate position (distance 1 (<L))
The die pad 2 and the semiconductor element 3 supported by the tie bar 1 are pushed up from a normal position by the flow pressure of the molten thermosetting resin. , Or being pushed down.

In addition, by reliably preventing the die pad 2 and the semiconductor element 3 from floating or sinking, the resin thickness on the upper side or the lower side of the semiconductor element 3 can be maintained at an appropriate value.
As a result, particularly in a large and thin semiconductor package, it is possible to obtain good moisture resistance reliability especially after solder reflow.

In this embodiment, the perforations 6a and 6a 'formed on both the front and back surfaces of the molding resin 6 are formed in a tapered shape that becomes smaller as approaching the tie bar 1. It is possible to facilitate the molding at the time of molding.

FIG. 8 shows the embodiment of FIG. 4, in which the tie bars 1 extending from the center on the left and right sides of the die pad 2 support the die pad 2 and at two places on the left and right opposite to the tie bar 1. Perforations 6a and 6a 'reaching the tie bar 1, respectively, are provided from both the front and back surfaces and at positions facing each other.

In the above embodiment, as shown in FIG. 9, by forming a large-sized portion 1a having a large area at a part of the tie bar 1 located at a position corresponding to the perforation 6a, the tie bar 1 is generally thin and wide. Because of this, this perforation 6a is surely
, And the appearance can be improved.

FIG. 10 and FIG. 11 show a fifth embodiment, in which two locations on the diagonal line facing the tie-bar 1 from above and below both the front and back surfaces of the mold resin 6 and face each other. Notches 6 reaching the above tie bar 1 in position
b, 6b '.

As described above, the perforations 6a, 6a 'or the notches 6b, 6b'
If provided at more than two places and from the positions facing the front and back surfaces of the mold resin 6, respectively, the effect of preventing the die pad 2 and the semiconductor element 3 from floating or sinking can be exhibited.

In addition, polyimide or the like may be applied to the upper surface of the semiconductor element 3 to further improve the moisture resistance reliability.

〔The invention's effect〕

Since the present invention is configured as described above, when the entire semiconductor package is exposed to a high temperature of 200 ° C. or more at the time of solder mounting, moisture present inside the mold resin becomes steam and is easily discharged to the outside. Thus, generation of cracks due to the steam can be prevented.

Moreover, even in a large semiconductor package, the occurrence of cracks is substantially the same as that of a small semiconductor package due to the positions of perforations and the like, and this occurrence is prevented, and the clutch is usually provided at the four corners of the mold resin. Is difficult to generate, so even if a perforation or notch is provided so as to reach the tie bar hanging the tie pad from the four corners, this perforation or notch does not impair the reliability of the semiconductor element, and is an effective means for deriving steam. Become.

Further, since the lower surface of the die pad on which the semiconductor element is mounted is not exposed to the outside, there is no possibility that the die pad will be corroded. In addition, since the hole from the perforation to the die pad is connected by a thin tie bar, intrusion of contaminants from the outside can be suppressed. Therefore, the semiconductor element is not adversely affected by the perforation or the like.

In addition, by providing perforations or notches that reach the tie bars at positions facing the front and back surfaces of the mold resin, respectively, it is possible to reliably prevent the die pad and the semiconductor element from being vertically displaced (lift or sink) due to the resin mold. Accordingly, there is an effect that it is possible to eliminate the problem of the moisture resistance reliability due to the floating or sinking particularly in a large and thin semiconductor package.

[Brief description of the drawings]

FIGS. 1 and 2 show a first embodiment of the present invention.
FIG. 2 is a sectional view taken along line II of FIG. 2, FIG. 2 is a rear view, FIGS. 3 and 4 show a second embodiment, and FIG.
4 is a rear view, FIGS. 5 to 7 show a third embodiment, FIG. 5 is a cross-sectional view taken along the line VV in FIG. 6, and FIG. FIG. 7 is a cross-sectional view in the manufacturing process, FIG. 8 is a back view (front view) showing the fourth embodiment, FIG. 9 is a back view showing a modification of the tie bar,
10 and 11 show a fifth embodiment, and FIG.
11 is a rear view (front view), FIG.
FIGS. 14 to 14 show a conventional example, FIG. 12 is a rear view, FIG. 13 is a sectional view taken along line XIII-XIII in FIG. 12, and FIG.
FIG. 15 and FIG. 16 are sectional views showing other different conventional examples. 1 ... tie bar, 2 ... die pad, 3 ... semiconductor element, 6 ... mold resin, 6a, 6a '... perforation, 6b, 6b'
…… Notch.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiichi Hirata 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Inside the Toshiba Tamagawa Plant Co., Ltd. (56) References JP-A-58-79739 (JP, A) JP-A-59-121959 (JP, A) JP-A-60-128646 (JP, A) (JP, U)

Claims (2)

(57) [Claims] 1. A semiconductor device in which a tie pad having a semiconductor element mounted on an upper surface is supported by tie bars extending from four corners thereof and the semiconductor element is resin-sealed with a mold resin. Piercing or notch reaching the tie bar with 1
A semiconductor device comprising at least two semiconductor devices. 2. The semiconductor device according to claim 1, wherein a hole or a notch reaching the tie bar is provided at a position facing the front surface and the back surface of the mold resin, respectively.