JP2544371B2 - Semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to a resin-sealed type suitable for preventing cracks or the like due to stress received during die bonding or surface mounting on a substrate. The present invention relates to a semiconductor device.

[Conventional technology]

In the resin-sealed semiconductor device, a surface mounting type in which leads are directly soldered to a substrate is becoming the mainstream instead of the conventional pin insertion type. In such a package, when stored in a high temperature and high humidity environment, the resin absorbs moisture, and when heat is applied to the solder (during reflow), moisture becomes vapor at the interface between the tab and the resin portion, and cracks occur at the corners on the lower surface of the tab. Is likely to occur.
This crack is commonly called a reflow crack because it occurs during solder reflow.

As a conventional technique for preventing such a reflow crack, there is a method of making a hole in the back surface of the package and letting the generated vapor escape, as described in JP-A-60-208847.

Further, as a technique for improving the adhesive strength at the interface between the resin portion and the tab and preventing the clearance, as a method of providing unevenness on the anti-element mounting surface of the tab, there is disclosed in JP-A-58-199548 and 60-18.
There is a technique disclosed in JP-A-6044 and a technique described in JP-A-59-16357 in which holes are formed in tabs.

[Problems to be solved by the invention]

Among the above-mentioned conventional techniques, the method of forming a hole in the lower surface of the package can prevent the reflow crack, but creates a moisture passage inside and outside the package, which may lead to corrosion of the chip electrode.

Further, although the method of providing a simple unevenness on the anti-element mounting surface of the tab has the effect of restraining the displacement within the bonding surface between the tab and the resin, the displacement in the direction separating the two causes the resin portion that has entered the concave portion to The effect cannot be expected because it is easily removed.

In JP-A-59-16357, a part of the tab is removed,
By filling this portion with resin, peeling due to thermal stress is prevented, and the thickness of the resin portion is equivalently increased, so that the moisture resistance can be improved to some extent. However, due to the vapor pressure generated during reflow soldering, the stress at the point where maximum stress occurs due to the deformation that occurs when the resin part separates from the tab is not much different from the case where part of the tab cannot be removed. The effect of cracking the resin part during soldering cannot be expected.

In order to prevent element destruction due to temperature history during or after damboning, conventional methods such as using a lead frame material with a low expansion coefficient or using a die bonding agent with a low elasticity coefficient limit the selection range of materials, It causes high cost, and almost no effect can be expected for solder reflow crack.

The dimple processing to prevent cracking of the resin at the bottom edge of the tab due to the temperature cycle test is often effective, but if there is a large difference in the linear expansion coefficient between the lead frame material and the resin material, the dimple processing hole is used. There is a problem in that resin cracks are likely to occur at the roots of the protrusions of the resin protrusions filled in.

As a measure to prevent solder reflow cracks, the method of opening a small hole from the package surface to the side opposite to the element of the tab is because the moisture easily reaches the adhesive interface between the tab / resin part and the element surface through the small hole. If it is used for a certain period of time, there is a problem that the moisture resistance is lowered, such as the risk of aluminum (Al) wiring corrosion and other failures. No effect can be expected on the resin crack at the lower end of the tab due to the temperature cycle.

It is an object of the present invention to prevent a semiconductor element from being damaged by a temperature history during or after dampening, to be resistant to a resin crack at a lower end of a tab by a temperature cycle test, and to have a high solder reflow crack resistance. To provide.

[Means for solving problems]

The above object is achieved by using a lead frame in which the tab is composed of an adhesive mounting portion, an element supporting portion and leads connecting the both, and adhering the tab and the semiconductor element only in the adhesive mounting portion.

A first invention of the present application includes a semiconductor element, a tab on which the semiconductor element is mounted, and a lead group including a tab suspension lead connected to the tab, which are sealed with resin and exposed from a resin portion. In the surface mounting type with the tip of the lead bent, the tab is divided into a peripheral annular part and a central island part, and the island part is integrally connected at a part of the annular part to prevent it from interfering. The semiconductor element is indirectly mounted on the island portion via an adhesive, while the semiconductor element is directly mounted on the element mounting surface of the annular portion or via a gap portion (space portion).

Further, in the second invention of the present application, on the same premise as in the first invention, the tab is divided into a semiconductor element bonding adhesive application portion (in short, an island portion) and other portions (annular portion, lead group, etc.). It is characterized by

Furthermore, the third invention of the present application is characterized in that, on the same premise as in the first invention, the adhesive application region of the tab is made smaller than the semiconductor bottom face.

In any case, in the present invention, it is preferable to form the taper in the plate thickness direction of the tab so that the surface area of the tab on the element side is smaller than the surface area on the non-element side. Further, it is preferable to form a groove for preventing the outflow of the bonding agent around the island portion.

Further, it is a preferable aspect that the island portion is recessed more than the annular portion on the element mounting surface side of the tab. In other words, it is desirable that the surface of the adhesive mounting portion is recessed with respect to the surface of the element supporting portion to form a step.

It is also desirable to make the element-side surface of the inner element mounting portion of the annular portion recessed from the other annular-element-side surface. In other words, it is preferable that the element support portion of the tab has a recess formed in a portion that supports the element.

The island portion is not limited to one, and may be divided into a plurality.
Furthermore, it is preferable that the thickness of the island portion is thinner than that of the other lead portions.

It is also possible to combine the above-mentioned aspects appropriately.

[Action]

According to the present invention, since the element and the tab are adhered only to a part of the center of the element, the stress generated in the element is substantially equal to the value corresponding to the length of the adhered portion, which is generated when the element is entirely adhered. For this reason, element cracking does not occur even for large-sized elements.

With respect to the resin crack at the lower end of the tab by the temperature cycle test, there is an opening between the annular part of the tab and the island part, and the resin filled in this part prevents relative slip between the tab anti-element surface and the resin. To be done. Therefore, the stress generated at the lower end of the tab can be suppressed to a low level, so that resin cracking can be prevented.

Since the linear expansion coefficient of the resin is larger than that of the tab, the resin in the holed portion is pressed against the side surface of the tab under high temperature during solder reflow. Moreover, due to the unevenness formed on the side surface of the tab, the side surface of the tab prevents the resin under the tab from bulging even if the adhesive force between the resin and the element is insufficient and vapor pressure is applied. Here, the side surface of the island portion acts as a fixed fulcrum. Therefore, compared with the conventional tab, the generation suppressing force is further reduced, and the reflow crack resistance is improved.

Countermeasures against reflow cracks are especially important for surface mount type. Therefore, if the adhesion area between the tab and the element is reduced, the generated stress is reduced according to the area even if vapor pressure is applied. Therefore, peeling from the resin and cracking of the resin can be prevented.

As described above, according to the present invention, it is possible to provide a semiconductor device that is resistant to element breakdown due to temperature history during and after die bonding, and is resistant to resin crack at the lower end of the tab due to a temperature cycle test, and has excellent reflow resistance. it can.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

 It will be described below.

In calculating the effect of the embodiment, as a conventional technique,
Hypothetical 256KDRAM package, element size 4.0mm × 9.0mm,
It is assumed that the tab size is 4.2 mm × 9.3 mm, the lead frame made of copper (Cu) alloy, and die bonding by soldering.

The semiconductor element 1 is fixed onto the tab 2 with an adhesive or the like, and the terminals on the semiconductor element 1 are electrically connected to the leads 3 arranged around the tab 2 by metal wires. There is. Lead frame tabs Leads including suspension leads 3
And the tab 2, and after being sealed by the resin portion 5, it is separated from the connected outer frame.

Silicon (Si) is used for the semiconductor element 1,
Its linear expansion coefficient α is about 3 × 10 ^-6 / ° C. The lead frame material is usually 42 alloy (α = 5 × 10 ^-6 /
C.) or a copper alloy (.alpha. = ^{17.times.10.sup.-6} / .degree. C.) is used, and .alpha. Of the resin portion 5 is 20 to 30.times.10.sup.- ⁶ / .degree. In this embodiment, the tab 2 is further divided into a central island portion 2a and a peripheral annular portion 2b. The code
Reference numeral 2c is a lead connecting the island portion 2a and the annular portion 2b.
Further, as is clear from FIG. 2, the adhesive 6 is the island portion.
Only applied on 2a.

In the conventional semiconductor device, since the linear expansion coefficient α of the material configured as described above is different, it occurs due to the temperature history during die bonding or after die bonding for joining the element and the tab as the size of the element increases. Problems such as element cracks and resin cracks at the lower end of the tab that occur during cooling after the resin sealing of the semiconductor device and in the temperature cycle test have become problems. Further, when a semiconductor device left in the air for a long period of time is surface-mounted on a substrate, a resin crack (called a resin clerk during solder reflow) may occur. The contents of each failure mode will be described below.

At the time of die bonding, since the linear expansion coefficient of the semiconductor element and the linear expansion coefficient of the tab material are different, thermal stress is generated, and when the adhesive yields, tensile stress is generated on the element surface due to the temperature history after die bonding.

[Reference I Shida, Sakamoto, Yasukawa, VLSI package design software, electronic materials 1982 supplement, 29] This tensile stress is the first in the case of a copper (Cu) lead frame and 95Pn-5Sn solder material.
It becomes as shown in Fig. 5. The tensile stress increases as the element size increases, and in some cases, the fracture strength of the element is exceeded. For this reason, measures such as using a Fe-Ni lead frame material having a low expansion coefficient and reducing stress generated in the element by using an ultra-low elasticity die bonding agent are taken.

Due to the difference in the linear expansion coefficient between the lead frame material and the resin material,
The stress is concentrated on the lower end of the tab. Especially, when the anti-element side and the resin side of the tab are separated from each other, the stress at the lower end of the tab increases stepwise as shown in an example in FIG. Rapidly increases as the tab size (chip size) increases, causing resin cracks. As a method for preventing the resin crack at the lower end of the tab, as described above, for example, a hole is provided on the side opposite to the element of the tab (referred to as dimple processing).
A measure is taken to prevent the relative slip due to the peeling between the tab and the resin portion by filling the hole with resin.

When mounting the semiconductor device on the actual board, the solder connection part of the lead and the connection part of the board are temporarily attached with solder paste, etc., and the entire board is heated in an infrared reflow furnace or vapor reflow furnace, for example, 200 to 250 ° C. By heating for several tens of seconds to several minutes, solder joining is performed and mounting on the board is completed. This is called a solder reflow process.

However, after the semiconductor device is manufactured, if the reflow is performed using a semiconductor device that has been left in an atmospheric environment for a long period of time, or even for a short period of time, the semiconductor device stored in an environment of relatively high humidity, Resin cracks may occur during the solder reflow process.

This is for the following reason. That is, the resin absorbs moisture in the air during storage of the semiconductor device, and moisture accumulates in the resin or in a slight gap between the resin portion and the tab bonding interface. When a semiconductor device that has absorbed moisture is put into a solder reflow process, the water on the resin / tab interface expands into steam due to rapid heating, and a large resin stress is generated due to the steam pressure. Even if there is no water at the adhesive interface, the water in the resin diffuses and is concentrated at the adhesive interface, so that similar resin stress occurs.

FIG. 13 is a sectional view of a resin-sealed semiconductor device using a general lead frame. In Fig. 13, the stress generated when the vapor pressure is acting on the resin bonding interface 15 on the anti-element mounting surface of the tab 2 is shown in Reference II [Southern, Ishiguro, Development of heat-resistant thin film plastic package, Oki Electric R & D ,
No. 128, VOL, 52, No. 4, P75],
It can be obtained by modeling with a uniformly distributed load of a rectangular plate whose four sides are fixed as shown in the figure. The maximum stress σ _{max at} that time occurs at the center of both ends of the long side, and its value is given by the following equation.

Here, P is a uniformly distributed load, a is the length of the short side of the tab, h is the thickness of the resin, and β is a coefficient given by the ratio of the length of the long side to the short side. As is clear from the equation (1), the generated stress increases with the square of the tab size a. Therefore, as the element size increases, the solder reflow cracks shown in FIG. 13 are likely to occur.

However, in the embodiment of the present invention, as shown in FIGS. 1 and 2, the tab 2 is divided into the island portion 2a and the annular portion 2b. Therefore, at the time of die bonding, the adhesive is applied only to the island portion 2a, and the annular portion 2b serves as a stabilizer for stably mounting the element on the tab 2. First, the improvement effect on element cracking will be examined. Element breakage often occurs at the center of the long side of the chip, so assuming the dimension of the long side to be 9 mm □ as a typical value of the element size, and assuming that only 2 mm □ at the center is used for bonding, The stress generated in the element can be reduced to 60% as shown in FIG.

After die bonding, a package is manufactured through a molding process. Next, a resin crack at the lower end of the tab by a temperature cycle test will be examined. Since the resin crack at the bottom of the tab often occurs at the center of the short side of the tab, the tab width
Use 4.2 mm. In FIG. 16, considering a tab width of 4.2 mm, if there is relative slip between the element opposite the side of the tab and the resin as in the prior art, or if there is no relative slip according to this embodiment, the resin stress at the lower end of the tab is 38 Can be%.

Finally, we will try to calculate the effect on solder reflow.
In contrast to the tab size of 4.3 mm x 9.3 mm of the conventional technology, in this example, assuming that the back surface of the element and the resin interface are peeled off, and the short side length of the peeled portion is 2.4 mm and the long side length is 2.6 mm. , (1)
The value of the formula is β = 0.5 α = 4.2 mm in the conventional tab and β = 0.33 α = 2.4 mm in the tab of the present embodiment, and the maximum stress σ _max of the semiconductor device according to the present embodiment is about 22% that of the conventional device. Fall to. If the breaking strength of the resin does not change, the breakdown voltage will increase by 4.6 times.

As described above, according to the present embodiment, it is possible to significantly improve the strength against cracking of the element, resin crack at the lower end of the tab by the temperature cycle test, and solder reflow crack.

As described above, with respect to the resin crack at the lower end portion of the tab by the temperature cycle test, the resin filled in the portion where the tab is removed in FIG. 2 prevents relative slip between the anti-element side of the tab and the resin. Therefore, the stress generated at the lower end of the tab can be suppressed to a low level, and resin cracking can be prevented.

Since the linear expansion coefficient of the resin is larger than that of the tab, the resin filled in the perforated portion shown in FIG. 2 is pressed against the tab side surface 8 when the temperature becomes high during solder reflow. In addition, since the tab side surface is uneven during the formation, even if the adhesive force between the resin and the element of FIG. 2 is insufficient and vapor pressure is applied, the tab side surface of FIG. Prevent the bulge of. 2 FIG. 8 acts as a fixed fulcrum. Therefore, a in the formula (1) is sufficiently smaller than that of the conventional tab, so that the generated stress is further reduced and the reflow crack resistance is improved.

Another embodiment is shown in FIGS. In FIG. 3, a taper 10 in the plate thickness direction of the tab is provided to more firmly prevent the resin tab from bulging. FIG. 4 shows a structure in which a groove is provided on the outer periphery of the adhesive mounting portion to prevent the adhesive from flowing out. The groove may have a width of 0.2 mm and a depth of 0.2 mm, for example.

5 and 6 show steps 12 and δ provided on the surface of the element supporting portion and the surface of the adhesive mounting portion. The thickness of the adhesive can be controlled while minimizing the gap between the element and the element supporting portion. δ is preferably about 10 μm to 50 μm.

FIG. 7 and FIG. 8 show an element supporting portion provided with a recess 13 in a portion for supporting the element to facilitate positioning of the element.

In FIG. 9, the lead thickness 14 of the adhesive mounting portion is made thinner than that of the supporting portion. As a result, the stress generated in the element can be further suppressed.

11 and 12 show two element mounting portions provided. As described above, a plurality of element mounting portions may be provided if necessary.

These examples may be carried out individually or in combination.

According to each of the above embodiments, in die bonding for joining the element and the tab, only a part of the element central portion is joined, so that the element generated stress due to the die bonding or the temperature history generated thereafter can be reduced and the element can be prevented from being broken. .

Since the hole formed in the tab is filled with the resin to form the convex portion, relative slippage of the adhesive portion between the resin on the opposite side of the tab and the resin does not occur. Therefore, the resin stress at the bottom of the tab can be reduced,
The temperature cycle life can be greatly improved.

Further, the side surface of the hole formed in the tab prevents the resin from bulging due to vapor pressure during solder reflow, so that the reflow crack resistance can be greatly improved.

〔The invention's effect〕

As described above, according to the present invention, the semiconductor element is less likely to be damaged by the temperature history during or after die bonding, is resistant to the resin crack at the lower end of the tab by the temperature cycle test, and has high solder reflow crack resistance. There is an effect that a semiconductor device having is obtained.

[Brief description of drawings]

1, 4, 6, 8, 10 and 12 are plan views of a semiconductor device tab according to an embodiment of the present invention and FIG.
1 is a sectional view of FIG. 1, FIG. 5 is a sectional view of FIG. 6, FIG. 7 is a sectional view of FIG. 8, FIG. 9 is a sectional view of FIG. 10, and FIG. 11 is a sectional view of FIG. Sectional view, FIG. 3 is a sectional view of a semiconductor device tab according to an embodiment of the present invention, FIG. 13 is a sectional view of a conventional resin-encapsulated semiconductor device, FIG. 14 is a model diagram of a semiconductor package which receives internal pressure, FIG. 15 is a diagram showing element stress, and FIG. 16 is an explanatory diagram showing under-tab resin stress. 1 ... semiconductor element, 2 ... tab, 2a ... island part,
2b ... annular part, 2c ... island part-annular part joining lead, 3 ... lead, 4 ... metal thin wire, 5 ... resin part, 6
…… Adhesive, 7 …… Resin-filled part, 8 …… Tab side, 9…
… Element / resin interface, 10 …… tapered part, 11 …… groove, 12 ……
Step δ, 13 …… Dimple, 14 …… Island thickness, 15 ……
Tab / resin interface, 16 …… Solder reflow crack, 17 ……
Thickness of resin under the tab.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Tachimichi 502 Jinritsucho, Tsuchiura-shi, Hitachi Ltd. Machinery Research Laboratory (72) Inventor Hideo Miura 502 Jinchocho, Tsuchiura-shi Hitachi, Ltd. Machinery Research In-house (56) Reference JP-A-59-16357 (JP, A) Actually developed S57-4226 (JP, U)

Claims (7)

(57) [Claims] 1. A semiconductor element, a tab on which the semiconductor element is mounted, and a lead group including a tab suspension lead connected to the tab, the lead group being sealed with a resin, and the lead exposed from the resin portion. In a surface-mounting type semiconductor device with a bent tip, the tab is divided into a peripheral annular portion and a central island portion, and a part of the annular portion is supported by the annular portion to support the island portion. A semiconductor device, which is integrally connected, wherein the semiconductor element is indirectly mounted on the island portion via an adhesive while the semiconductor element is mounted directly on the element mounting surface of the annular portion or via a gap. . 2. The semiconductor device according to claim 1, wherein a taper is formed in the plate thickness direction of the tab so that the element-side surface area of the tab is smaller than the anti-element-side surface area. 3. The semiconductor device according to claim 1, wherein a groove for preventing the flow of the bonding agent is formed around the island portion. 4. The semiconductor device according to claim 1, wherein the island portion is recessed from the annular portion on the element mounting surface side of the tab. 5. The semiconductor device according to claim 1, wherein the element-side surface of the inner element mounting portion of the annular portion is recessed more than the other element-side surface of the annular portion. 6. The semiconductor device according to claim 1, wherein the island portion is divided into a plurality of parts. 7. The semiconductor device according to claim 1, wherein the island portion is thinner than the other lead portions.