JP2555428B2 - Lead frame and method of manufacturing semiconductor device using the same - Google Patents

Description

The present invention relates to a lead frame and a semiconductor device manufacturing technique using the same, and is particularly effective when applied to a semiconductor device having an ultrathin package structure. It is about technology.

[Conventional technology]

Regarding the lead frame, for example, Japanese Patent Laid-Open No. 52-9517
No. 3 and JP-A No. 55-21128.

In JP-A-52-95173, thermal stress is applied to a die pad due to a difference in thermal expansion coefficient between a semiconductor pellet (hereinafter referred to as a pellet) and a lead frame, and the pellet is cracked, or the pellet is broken. In order to solve the problem of peeling from the die pad, a technique of absorbing thermal stress by forming a square hole or a plurality of round holes in the die pad is described.

Further, JP-A-55-21128 discloses a technique in which, in order to improve the strength of the suspension leads that support the die pad, the suspension leads are arranged at the four corners of the die pad to support the die pad. .

By the way, in recent years, along with the widespread use of IC cards and ultra-thin electronic devices, development of semiconductor devices having an ultra-thin package structure to be mounted on these is proceeding.

The ultra-thin package structure is described, for example, in "TRIPLE A No. 18" issued by Mitsubishi Electric Corporation, December 1987.

The ultra-thin package structure described in the above document is VS
It has an OP (Very Small Outline Package) type package structure, and the package thickness is 1 mm, which is less than half of the conventional SOP.

Further, a pellet having a thickness of 400 μm is sealed in the package, and the pellet and the inner lead are connected via a wire. Further, in order to prevent the upper end of this wire from being exposed from the upper surface of the package, the die pad on which the pellet is mounted is arranged below the lead.

[Problems to be Solved by the Invention]

However, according to the study by the present inventor, it has been found that the package structure described in the above document has the following problems.

That is, when the ultra-thin package with a thickness of 1 mm or less described in the above-mentioned document (“TRIPLE A No. 18”) is formed by the transfer mold method,
Since the cavity of the mold is extremely narrow, the fluidity of the resin injected into the cavity is lowered, and voids are easily generated at the interface between the die pad and the resin.

In order to prevent this, it is necessary to use a low-viscosity resin to improve its fluidity and to make the flow rate of the resin flowing in the cavity equal on the pellets and below the die pad.

However, in the case of forming an ultrathin package using the lead frame described in JP-A-55-21128, the die pad is arranged to be exposed from the inner lead surface in order to prevent the wire upper end from being exposed from the package. Since the lead frame has to be arranged below, when the lead frame is inserted into the mold during molding, the gap between the die pad and the lower mold becomes narrower than the gap between the pellet and the upper mold.

For this reason, the resin injected into the cavity flows into the pellets with a large gap more than under the die pad with a narrow gap. That is, the resin flowing over the pellet flows faster than the resin flowing under the die pad, and the pressure of the resin flowing over the pellet and under the die pad becomes non-uniform. Then, the resin that flows over the pellets pushes the die pad downward, which stops the flow of resin under the die pad, causing voids under the die pad and exposing the die pad from the bottom surface of the package. However, the manufacturing yield of the package is reduced.

On the other hand, in the technique of Japanese Patent Laid-Open No. 52-95174, since the holes are formed in the die pad and the lower surface of the pellet is exposed, the thickness of the die pad is reduced and the resin flow in that portion is improved. However, this technology does not consider the fluidity and filling of the resin flowing under the pellets, so as the package becomes thinner, the flow velocity and pressure of the resin flowing over the pellets and under the die pad during molding will be the same. It becomes difficult to obtain the effect of doing.

Then, such a problem becomes more remarkable when the pellet size is large.

The present invention has been made in view of the above problems, and an object thereof is to provide a technique capable of improving the manufacturing yield of a semiconductor device having an ultrathin package structure. .

Another object of the present invention is to provide a technique capable of improving the reliability of a semiconductor device having an ultrathin package structure.

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 the problem]

The following is a brief description of the outline of the typical invention disclosed in the present application.

That is, the invention according to claim 1 has a lead frame structure in which at least the die pad is divided along the direction in which the resin injected from the gate into the cavity at the time of molding the pellet flows.

A second aspect of the present invention is a method of manufacturing a semiconductor device using the lead frame of the first aspect.

[Action]

According to the first aspect of the present invention, when the lead frame is molded using the lead frame, the flow path of the resin flowing below the pellet divides the die pad along the flow direction of the resin injected from the gate into the cavity. Since it is ensured by the above, the fluidity of the resin flowing below the pellet is improved, and the gap between the lower surface of the pellet and the lower die exposed from the opening, and the gap between the upper surface of the pellet and the upper die. Can be approximately equal.

As a result, when the pellets are molded, the flow velocity and pressure of the resin flowing above and below the pellets become substantially equal, so that the occurrence of voids and the deformation of the die pad can be effectively prevented.

According to the second aspect of the present invention, when the pellet is molded using these lead frames, the flow path of the resin flowing below the pellet is ensured by the opening portion, so that the fluidity of the resin flowing below the pellet is secured. Since the gap between the lower surface of the pellet exposed from the opening and the lower die and the clearance between the upper surface of the pellet and the upper die can be made substantially equal, the upper and lower portions of the pellet can be improved. It is possible to make the flow velocity of the resin flowing through and the pressure almost equal,
As a result, generation of voids and deformation of the die pad are effectively prevented, and the manufacturing yield of semiconductor devices can be improved.

[Embodiment 1] FIG. 1 (a) is a plan view showing a main part of a lead frame used in a method of manufacturing a semiconductor device according to an embodiment of the present invention.
FIG. 2B is a cross-sectional view taken along line IB-IB in FIG. 1A showing the opening portion of the lead frame, and FIG. 2A shows a case where pellets are mounted on the lead frame. 2A is a sectional view taken along line II A-II A of FIG. 1A, and FIG. 2B is a sectional view taken along line IB-IB of FIG. 1A showing a case where pellets are mounted on the lead frame. Figure 3 (a) ~ (d)
Is a cross-sectional view of a main part of a mold used in a method for manufacturing a semiconductor device,
FIG. 4 is a sectional view taken along the line IB-IB in FIG. 1A showing a semiconductor device manufactured using this lead frame.

The lead frame 1a used for manufacturing the semiconductor device of the first embodiment shown in FIGS. 1A and 1B is, for example, a QFP (Qua
d Flat Package) type semiconductor device.

The lead frame 1a has, for example, a rectangular die pad 3 on which the pellets 2 are mounted, suspension leads 4 that are disposed at the four corners of the die pad 3, support the die pad 3, and are radially disposed around the die pad 3. Multiple leads 5
And a dam piece 6 arranged so as to connect the respective leads 5 and surround the die pad 3, and a frame portion 7 composed of an outer frame portion 7a and an inner frame portion 7b surrounding these.

The suspension lead 4 is bent so that the die pad 3 is arranged below the lead 5, as shown in FIG. This is to prevent the upper end of the wire 8 described below from being exposed from the upper surface of the package.

The outer side of the dam piece 6 is called the outer lead, and the inner side is called the inner lead. The lead 5 is sealed in the mold portion 9 at the time of being a product, and the outer lead is from the side surface of the mold portion 9. The external terminals projecting outward are configured.

In the outer frame portion 7a, a guide hole 10 serving as a guide when the lead frame 1a is transported or positioned is punched out by a press or the like.

The lead frame 1a is formed by integrally forming a plurality of unit frames composed of the above-mentioned respective parts in the extending direction of the outer frame part 7a, for example, seven continuous ones by a press or the like. For example, it is made of 42 alloy, and its thickness is, for example, 150 μm.

The opening portion 11 is formed in the die pad 3 of the lead frame 1a.
The hole a is formed, and the die pad 3 is divided into two by the hole. This opening 11a is filled with resin injected from the gate (shown in FIG. 3 (b)) G into the cavity K (shown in FIG. 3 (a)) during the step of forming the mold portion 9 described later. It extends along the direction of flow. Then, the opening portion 11a secures a flow path of the resin flowing below the pellet 2 as shown in FIG. 1 (b).

Further, since the opening portion 11a divides the die pad 3 into two parts, for example, when moisture in the resin forming the mold portion 9 vaporizes and expands during solder reflow, the stress generated in the die pad 3 due to this vaporization expansion It can be made as small as the case of molding a 1/2 size pellet of 2.

Next, a method of manufacturing the semiconductor device according to the first embodiment will be described with reference to FIGS. 2 (a) and 2 (b) and FIGS. 3 (a) to 3 (d).

First, the pellet 2 is bonded onto the die pad 3 in which the openings 11a are formed by using the adhesive 12 made of, for example, silver paste, and the adhesive 12 is cured at 180 ° C., for example (FIG. 2 (a)). At that time, for example, if a curing method of gradually heating in an open furnace installed in a clean room is used,
The film thickness of the adhesive 12 can be reduced to, for example, about 10 to 30 μm. The thickness of the pellet 2 is, for example, 400 μm, and the upper surface thereof is an integrated circuit forming surface. Further, the adhesive 12 is selected from a material having a low foaming property because it is necessary to reduce the film thickness.

Then, using a wire bonding device (not shown), for example, a diameter of 25 μm is provided between the pellet 2 and the lead 5.
The wire 8 made of the gold wire is bonded (FIG. 2 (b)). At that time, in order to prevent the upper end of the wire from being exposed from the package 1 in the molding step described later,
Height from top of pellet 3 to top of wire 8 (h)
Must be at a predetermined height.

Then, although not shown, an extremely thin polyimide resin is applied to the upper surface of the pellet 2. This is the mold part 9
This is for the purpose of preventing water in the resin forming the resin from entering the integrated circuit, and preventing the filler in the resin from damaging the surface of the integrated circuit.

Next, a process of forming the mold portion 9 on the lead frame 1a on which the pellet 2 is mounted will be described with reference to FIGS.

First, the lead frame 1a on which the pellets 2 are mounted is set at a predetermined position of the transfer molding die 13. The upper mold 13a and the lower mold 1 inside the cavity K of the mold 13.
The gap with 3b is, for example, 1 mm.

At this time, since the die pad 3 is perforated with the opening 11a, the gap A between the upper portion of the pellet 2 and the upper die 13a and the gap B between the lower portion of the pellet 2 exposed from the opening 11a and the lower die 13b. And are almost equal.

Next, the pre-heated tablet resin 15 is placed in the pot 14.
Input. The resin 15 is, for example, a resin obtained by filling a filler such as silica in a silicone-modified epoxy resin so that its thermal expansion coefficient is close to that of silicon, and the viscosity at the time of molding is, for example, 1 × 10 ² P. (Poise) A low-viscosity resin having the following.

Then, the plunger 16 is lowered and the molten resin 15
Is injected into the cavity K through the runner 17 and the gate G (FIG. 3 (b)).

At this time, as described above, since the gap A between the upper part of the pellet 2 and the upper mold 13a and the gap B between the lower part of the pellet 2 exposed from the opening 11a and the lower mold 13b are almost equal, FIG.
As shown in, the flow rate of the resin 15 flowing above the pellet 2 and the flow rate of the resin 15 flowing below the pellet 2 exposed from the opening 11a become substantially equal.

That is, the resin 15 flowing above and below the pellet 2
Since the pressure is substantially uniform, the die pad 3 is not pushed down or pushed up by the resin 15, and the resin is sufficiently filled.

In this way, the resin 15 is sufficiently injected into the cavity K and is cured by heating for a predetermined time (FIG. 3 (c)).

Then, after the resin 15 injected into the cavity K is hardened, the mold 13 is opened, the lead frame 1a is taken out, and the mold portion 9 having a length and width of each side of, for example, 14 mm and a thickness of, for example, 1 mm is formed. It is completed (Fig. 3 (d)).

After that, a predetermined portion of the lead frame 1a is cut, and the lead 5 is bent into, for example, a gull wing shape, whereby the QFP type semiconductor device 18 shown in FIG. 4 is manufactured.

As described above, according to the first embodiment, the following effects can be obtained.

(1). Since the die pad 3 of the lead frame 1a is formed with the opening portion 11a extending along the direction in which the resin 15 injected from the gate G into the cavity K flows when forming the mold portion 9, the opening portion is formed. The fluidity of the resin 15 flowing under the pellet 2 exposed from 11a is improved.

(2). When forming the mold part 9, the gap A between the upper part of the pellet 2 and the upper mold 13a and the gap B between the lower part of the pellet 2 exposed from the opening part 11a and the lower mold 13a become substantially equal. The flow velocities of the resin 15 flowing in the upper part and the lower part are substantially equal, and the pressure of the resin 15 is also substantially uniform.

(3). Due to the above (1) and (2), when forming the mold part 9, unlike the conventional technique, the resin 15 flowing above the pellet 2 pushes down the die pad 3, and voids are generated, or the die pad 3 is formed. It can be effectively prevented from being exposed from the lower surface of 9.

(4). By the above (1) and (2), the filling property of the resin is improved.

(5). Since the die pad 3 is divided into two via the opening 11a, the thermal stress applied to the die pad 3 is dispersed,
It is possible to effectively prevent cracks in the mold portion 9 due to this thermal stress.

(6). According to the above (1) to (4), the thickness is, for example,
1mm mold part 9 can be formed with good yield,
The manufacturing yield of semiconductor devices is improved.

(7). From the above (1) to (5), a highly reliable semiconductor device including the ultra-thin mold portion 9 can be obtained.

[Embodiment 2] FIG. 5 is a plan view of essential parts of a lead frame used in a method of manufacturing a semiconductor device according to another embodiment of the present invention.

In the lead frame 1b of the second embodiment, the die pad 3 and the suspension lead 4 are divided by the opening portion 11b extending along the direction in which the resin 16 injected from the gate G flows when forming the mold portion 9. ing. That is, the die pad 3 and the suspension lead 4 are formed by the opening 11b, respectively.
Divided into 4b.

According to the second embodiment, the resin 15 injected from the gate G into the cavity K during the formation of the mold portion 9 extends between the suspension leads 4a and 4b and between the die pads 3a and 3b.
Since the flow path of the resin 15 is guided by 11b and sufficiently secured without being hindered by the suspension leads 4, the fluidity of the resin 15 flowing below the pellet 2 is further improved.

Other than this, the same operation and effect as those of the first embodiment can be obtained.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the first and second embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the shapes of the openings formed in the die pad described in the first embodiment and the openings for dividing the die pad described in the second embodiment are not limited to those in the first and second embodiments. Alternatively, other shapes may be used as long as holes are formed along the direction in which the resin flows during molding.

That is, for example, it may be comb-teeth like the opening 11c of the die pad 3 of the lead frame 1c shown in FIG.

Also, the die pad 3 of the lead frame 1d shown in FIG.
It may have a rectangular shape like the opening 11d for dividing the.

Further, the material of the lead frame in the above-mentioned embodiment is 42 alloy, but the material is not limited to this, and may be, for example, a tin-nickel plated copper alloy.

In the above description, the case where the invention made by the present inventor is mainly applied to the manufacturing method of the QFP type semiconductor device which is the field of application which is the background has been described, but the invention is not limited to this, for example, TQFP (Thin Quad
Flat Pachage) type or TSOP (Thin Small Outline)
Package) and SOJ (Small Outline J-lead Package)
The present invention can also be applied to a method for manufacturing a semiconductor device of the shape.

〔The invention's effect〕

The effects obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows.

(1). That is, in the lead frame according to claim 1, at least the die pad on which the pellet is mounted is
When the pellet mounted on the die pad is molded, the flow of the resin flowing below the pellet is caused by the division along the flow direction of the resin injected into the cavity from the mold gate when molding the pellet. Since the passage is secured and the exposed gap between the lower pellet and the lower mold and the gap between the upper pellet and the upper mold can be made almost equal, the flow velocity and pressure of the resin flowing above and below the pellet are equal. Therefore, the die pad is prevented from being pushed down by the resin flowing above the pellets, and voids and deformation of the die pad are prevented.

(2). Therefore, according to the semiconductor device manufacturing method of the second aspect, which uses the lead frame of the first aspect,
The manufacturing yield of a semiconductor device having an ultrathin package structure can be improved.

[Brief description of drawings]

FIG. 1 (a) is a plan view of a main part of a lead frame used in a method for manufacturing a semiconductor device according to an embodiment of the present invention, and FIG. 1 (b) is a first part showing an opening of the lead frame. FIG. 2A is a cross-sectional view taken along line IB-IB in FIG. 2A, and FIG. 2A is a cross-sectional view taken along line II A-II A in FIG. 2 (b) is a sectional view taken along line IB-IB of FIG. 1 (a) showing a case where pellets are mounted on this lead frame, and FIGS. 3 (a) to 3 (d) are semiconductor device manufacturing methods. Sectional drawing which shows the principal part of the metal mold | die used for each manufacturing process order, FIG. 4 is a sectional view of the IB-IB line of FIG. 1 (a) which shows the semiconductor device manufactured using this lead frame. 5 to 7 are plan views of a main part of a lead frame used in a method of manufacturing a semiconductor device according to another embodiment of the present invention. 1a to 1d ...... lead frame, 2 ... semiconductor pellet, 3
…… Die pad, 4 …… Suspension lead, 5 …… Lead, 6
...... Dam piece, 7 ...... frame part, 7a …… outer frame part, 7b …… inner frame part, 8 …… wire, 9 …… mold part, 10 …… guide hole, 11a to 11d …… opening part , 12 …… adhesive, 13 …… mold,
13a …… upper mold, 13b …… lower mold, 14 …… pot, 15 …… resin, 16 …… plunger, 17 …… runner, 18 …… semiconductor device, K …… cavity, G …… gate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Obata 5-20-1 Kamimizuhonmachi, Kodaira-shi, Tokyo Inside the Musashi Factory, Hitachi, Ltd.

Claims (2)

(57) [Claims] 1. A lead frame comprising a die pad for mounting a semiconductor pellet on which a predetermined integrated circuit is formed, and a suspension lead for supporting the die pad, wherein at least the die pad is a gate when the semiconductor pellet is molded. The lead frame is characterized in that the resin injected from the cavity into the cavity is divided along the flowing direction. 2. A method of manufacturing a semiconductor device, wherein the lead frame according to claim 1 is used.