JPH10294404A - Resin sealed electronic device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable resin sealed type electronic device by relieving the stresses applied between a primary sealing resin and a secondary sealing resin. SOLUTION: An IC package body 5 is constituted in such a way that a silicon chip 2 is mounted on a lead frame 1 and electrically connected to a lead frame 1a through a bonding wire 3. In addition, the wire 3 and chip 2 are molded with a primary sealing resin 4. Then the lead frame and chip 2 are molded with a secondary sealing resin 8. Between the primary and secondary sealing resins 4 and 8, a stress relaxing coating film 9 is arranged. Since the film 9 is made of rubber 10 containing scattered bubbles 11, the film 9 relaxes the stresses caused by the resins 4 and 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resin-sealed electronic device and a method of manufacturing the same.

[0002]

2. Description of the Related Art As shown in FIG. 10, an electronic component 41 such as a silicon chip is mounted on a lead frame 40, and the electronic component 41 is molded with a primary sealing resin 42 to form an IC package 43. The IC package 43 is molded with a secondary sealing resin 44 such as epoxy. That is, the secondary molding (transfer molding, potting molding) of the IC package 43 is performed.

In this resin-sealed electronic device, there is a possibility that the electronic component 41 receives an excessive stress due to a curing shrinkage stress or a thermal stress after curing, and the function thereof is deteriorated.
That is, as shown in FIG. 10, when the IC package 43 is covered with the secondary sealing resin 44, the temperature becomes high as shown in FIG. 11 or the temperature becomes low as shown in FIG. Think. When the coefficient of thermal expansion of the primary sealing resin 42 is αM and the coefficient of thermal expansion of the secondary sealing resin 44 is αE, αE>
When αM is satisfied, when the temperature rises as shown in FIG. 11, the secondary sealing resin 44 expands in a direction away from the IC package body 43. When the temperature becomes low as shown in FIG. 12, the secondary sealing resin 44 contracts in a direction of pressing the IC package body 43. Thus, the IC package 4
3 will be stressed.

In order to alleviate the stress, structural measures such as lowering the stress of the secondary sealing resin itself such as epoxy and reducing the volume of the secondary sealing resin have been made. There were limitations in terms of flexibility and ensuring the reliability of other parts.

[0005] On the other hand, as one method of reducing the stress generated between two members, rubber is generally sandwiched between two members. If this technique is used in a resin-sealed electronic device, rubber is interposed between the primary sealing resin 42 and the secondary sealing resin 44. In this case, the rubber is originally an incompressible substance (Poisson). The ratio is almost 0.
For 5), the IC package 43 is replaced with the secondary sealing resin 44.
In the resin-encapsulated electronic device completely covered with, there is no effect of stress relaxation because it has a structure without deformation voids. That is, the secondary sealing resin 44 generates a contraction force at the time of curing and generates a large amount of stress when subjected to a cooling / heating cycle after the curing. However, the rubber material has the effect of dispersing the external stress. This is limited to the case where a space where the rubber can be deformed is secured.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a highly reliable resin-sealed electronic device by relaxing the stress applied between the primary sealing resin and the secondary sealing resin. is there.

[0007]

According to the first aspect of the present invention, an elastic body (for example, rubber) is used as a base material as a stress buffer coating film disposed between a primary sealing resin and a secondary sealing resin. ), And a material in which air bubbles are scattered in the base material is used.

Accordingly, when stress is applied between the primary sealing resin and the secondary sealing resin due to a temperature change or the like, the elastic body serving as the base material of the stress buffer coating film is deformed, and scattered bubbles are generated. Changes in volume. The stress between the primary sealing resin and the secondary sealing resin is absorbed by the change in the volume of the bubbles, and the stress applied to electronic components such as semiconductor chips is reduced.

That is, when a stress is applied between the primary and secondary sealing resins due to a temperature change or the like, the bubbles in the stress buffer coating film become deformation allowances (crush allowances), thereby relaxing the stress. .

According to the second aspect of the present invention, in the first step, the electronic component disposed on the substrate is molded with the primary sealing resin. Then, in the second step, the surface of the primary sealing resin is coated with a stress buffer coating film in which bubbles are dispersed in an elastic body as a base material. Further, in a third step, the base material and the electronic component are molded with a secondary sealing resin on the outer peripheral side of the stress buffer coating film.

As a result, the resin-sealed electronic device according to the first aspect is manufactured. Here, as described in claim 3, in the second step, it is practically preferable to coat a solution in which a hollow sphere filler is mixed with a liquid elastic material on the surface of the primary sealing resin.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a resin-sealed electronic device according to the present embodiment. In this device, an ignition coil and an ignition circuit of a gasoline engine are resin-molded.

In FIG. 1, a silicon chip 2 as an electronic component is mounted on a lead frame 1 as a base material, and the silicon chip 2 and the lead frame 1a are electrically connected by bonding wires 3. I have. The bonding wire 3 and the silicon chip 2 are connected to a primary sealing resin 4.
Molded at Thus, the IC package body (mold body) 5 is configured.

In addition, a circuit board (printed board) using an alumina substrate other than the silicon chip 2 may be embodied as a package mounted on the lead frame 1.
On the other hand, an ignition coil 7 is arranged at a lower portion inside a housing (housing) 6 of the resin-encapsulated electronic device, and the IC package 5 is provided above the ignition coil 7 inside the housing 6. Is arranged. Case 6
Is filled with a secondary sealing resin 8, and the ignition coil 7 and the aforementioned IC package body 5 are molded with the secondary sealing resin 8. Cast epoxy resin is used for the secondary sealing resin 8. In this cast epoxy, the IC package body 5 receives an excessive stress due to the curing shrinkage stress or the thermal stress after curing, and the function may be deteriorated. Since this has been described with reference to FIGS. 10 to 12, the description is omitted here. In short, when the temperature becomes high as shown in FIG. 11, the secondary sealing resin 8 expands in a direction away from the IC package body 5, When the temperature becomes low as shown in FIG. 12, the secondary sealing resin 8 contracts in a direction of pressing the IC package body 5. Thus, a stress is applied to the IC package body 5 due to the temperature change.

Therefore, as shown in FIG. 1, between the primary sealing resin 4 and the secondary sealing resin 8, a stress buffer coating film 9 for relaxing the stress applied between both sealing resins is provided. Are located. As shown in FIG. 2, the stress buffer coating film 9 is an elastic body as a base material, and in this embodiment, the rubber 1
0 is used and air bubbles 11 are scattered in the base material. The thickness of the stress buffer coating film 9 is about 0.5 mm.

The stress buffer coating film 9 is formed as shown in FIG.
In FIG. 0 to FIG. 12, a buffer region is provided, and its volume changes with the thermal deformation of the IC package body 5 and the secondary sealing resin 8.

That is, since thermal deformation of each part is deformed by a constant displacement amount when there is no constraint, for example, if the buffer region does not restrict the deformation at all, if the primary sealing resin 4 and the secondary sealing resin 4 No thermal stress occurs due to the mismatch of the coefficient of thermal expansion with the resin 8. The relaxation layer that satisfies this requires that the volume can be changed.

That is, as shown in FIG. 3, when the stress buffer coating film 9 is not provided, a force F proportional to the strain amount δ is applied to the IC package body 5 as shown by the characteristic line P1, but the stress F is applied. The provision of the buffer coating film 9 causes the air bubbles 11 to be a crushing allowance, and almost no force F is applied to the IC package body 5 up to a predetermined amount of distortion δ1 as shown by the characteristic line P2.

As shown in FIG. 1, the lead frame 1a is connected to a lead terminal 12 penetrating through the housing 6, and the lead terminal 12 is connected to the outside. The lead frame 1 is connected to a lead terminal 7a of the ignition coil 7. And the lead terminal 12
, A battery voltage is supplied to a circuit formed in the silicon chip 2, a high voltage is generated by the ignition coil 7 at a predetermined ignition timing, and the high voltage is supplied to the ignition plug.

Next, the manufacturing method will be described. As shown in FIG. 4, a silicon chip 2 is mounted on a lead frame 1, and the silicon chip 2 and the lead frame 1 are connected by wires 3.
a is bonded. And bondig wire 3
And the silicon chip 2 are molded with the primary sealing resin 4 to form an IC package 5.

Subsequently, as shown in FIG. 5, the IC package 5 is covered with a coating film 9 for stress buffering.
The coating process using the stress buffer coating film 9 is as follows.
It comprises three steps shown in FIG.

First, a liquid silicone resin as a liquid elastic material is prepared, and a hollow sphere filler (capsule) 20 shown in FIG. 7 is prepared. The hollow sphere filler 20
The fine particles have a diameter D of about 80 μm. As the liquid silicone resin, for example, CY52-227 manufactured by Toray Industries, Inc. is used, and as the hollow sphere filler 20, for example, DU-80 manufactured by Nippon Philite Co., Ltd. is used. Then, the liquid silicone resin and an appropriate amount of the hollow sphere filler 20 are mixed. Here, the mixing ratio of the hollow sphere filler 20 to the liquid silicone resin is about 40 vol%.

Then, the IC package 5 is dipped in a solution in which the hollow sphere filler 20 is mixed into the liquid silicone resin, and coated on the surface of the primary sealing resin 4 (coating process shown in FIG. 6). Subsequently, at 150 ° C., 20
The resin is cured by heating for a minute (a thermal curing step shown in FIG. 6).
As a result, the hollow sphere filler 20 is solidified while being dispersed in the liquid silicone resin. It is confirmed from the cross-sectional photograph of the stress buffer coating film 9 that the bubbles 11 are scattered in the rubber 10 in the stress buffer coating film 9.

By mixing the hollow sphere filler 20 with the liquid resin to form a coating film, the following effects can be obtained. (1) By adjusting the addition amount of the hollow sphere filler 20, the total amount of the bubbles 11 in the stress buffer coating film 9 can be adjusted, and appropriate stress relaxation can be achieved.

Thus, by selecting the content and the particle size of the hollow sphere filler 20, the volume change rate of the target coating film can be set, and the stress relaxation effect can be easily controlled by mixing the materials. (2) Since it is a coating film using a liquid resin (for example, because of coating by a dipping method), a portion of the lead terminal 1a of the IC package body 5 and the like can be completely coated. That is, when the IC package 5 is covered with the cap material 30 having elasticity as shown in FIG. 8 instead of the dipping method, the lead terminals 1 a of the IC package 5 are hardly covered with the cap material 30. However, if the dipping method is used, the portion of the lead terminal 1a can be completely covered. This means that, for example, when the liquid resin potting during the subsequent molding is vacuum-injected,
The buffering effect can be secured without the resin entering the inside of the coating film 9.

As described above, the structure to be coated can form a coating on a required portion. (3) Since it is a coating film using a liquid resin (for example, because of coating by a dipping method), the IC package body 5 having a corner can also be formed with a gentle curved surface at the corner. From this, stress concentration can be reduced,
Cracking of the secondary potting material can be suppressed.

Thus, the structure to be coated can be formed regardless of its shape. (4) Since the air bubbles 11 in the coating film are present alone, the air bubbles 11 will not be buried even in a subsequent step such as epoxy impregnation.

The dip material does not need to be a liquid silicone resin, but may be a liquid soft epoxy agent (for example, EP-001 manufactured by Cemendyne). In this case, when the secondary potting material is epoxy, the chemical adhesion can be ensured because the material is a common material, and further excellent in terms of heat conduction and stress dispersion.

Returning to the description of the manufacturing process, after the IC package body 5 is coated with the stress buffer coating film 9, as shown in FIG. The body 5 is placed. Further, the housing 6 is filled with a liquid epoxy resin 8 and cured (solidified).

The coating of the stress buffer coating film 9 may be performed by spraying, casting, liquid injection molding or the like in addition to dip coating. Next, the effect of reducing the curing shrinkage stress of the epoxy resin 8 will be described with reference to FIG.

First, as shown in FIG. 9A, when the stress buffer coating film 9 is not provided, the surface strain ε generated by the stress applied to the IC package body 5 is -2.
00 μs. Here, the surface strain ε refers to the amount of change in the length of a material having a unit length when the temperature of the material changes from 20 ° C. to 150 ° C. That is, when the length L at 20 ° C. changes to the length L ′ at 150 ° C., it is defined by ε = (L−L ′) / L.

As shown in FIG. 9 (b), a silicone rubber 35 containing no hollow sphere filler is coated with a thickness of 0.5 m.
When m coatings are formed, the surface strain ε is −120 μs.

Further, as shown in FIG. 9 (c), when a silicone rubber (coating film 9) containing a hollow sphere filler was applied to a thickness of 0.5 mm, the surface strain ε was reduced.
Is 0 to −10 μs.

As described above, a cured product obtained by curing the above-mentioned liquid silicone resin usually exhibits rubber elasticity, and its mechanical properties include inelastic deformation and incompressible deformation. Although the rubber elastic body is required to change in volume, the incompressibility of the rubber elastic body cannot sufficiently exert the stress relaxation property, but the stress can be relaxed by scattering the bubbles 11. That is, when an incompressible substance such as silicone rubber is used as the buffer layer, the hollow sphere filler 20 that seals the gas is mixed in, so that the rubber elasticity is maintained and the compressive property is provided as the buffer layer. It becomes excellent as a relaxation layer.

As described above, this embodiment has the following features. (A) As a stress buffer coating film 9 disposed between the primary sealing resin 4 and the secondary sealing resin 8, rubber 10 was used as a base material, and bubbles 11 were dispersed in the base material. When a stress is applied between the primary sealing resin 4 and the secondary sealing resin 8 due to a temperature change or the like,
Rubber 1 as a base material in the stress buffer coating film 9
0 is deformed, and the volume of the scattered bubbles 11 changes. The stress between the primary sealing resin 4 and the secondary sealing resin 8 is absorbed by the change in the volume of the bubbles 11, and the stress applied to the silicon chip 2 is reduced. That is, when a stress is applied between the primary and secondary sealing resins 4 and 8 due to a temperature change or the like, the bubbles 11 in the stress buffer coating film 9 become deformation allowances (crushing allowances) and stress relaxation occurs. Is achieved. (B) The silicon chip 2 placed on the lead frame 1 is molded with the primary sealing resin 4,
Is coated with a stress buffer coating film 9 in which bubbles 11 are dispersed in rubber 10 as a base material,
Further, the lead frame 1 and the silicon chip 2 are molded with the secondary sealing resin 8 on the outer peripheral side of the stress buffer coating film 9. As a result, the resin-sealed electronic device (a) is obtained. (C) As a process of forming the stress buffer coating film 9,
When the surface of the primary sealing resin 4 is coated with a solution in which the hollow sphere filler 20 is mixed in the liquid elastic material, it becomes practically preferable as described above.

In addition, although heating was used for curing the sealing resin,
It may be performed by a method such as ultraviolet irradiation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a resin-sealed electronic device according to an embodiment.

FIG. 2 is a cross-sectional view of a stress buffer coating film.

FIG. 3 is a diagram illustrating a relationship between a strain amount and a force.

FIG. 4 is a cross-sectional view for explaining a manufacturing process of the resin-sealed electronic device.

FIG. 5 is a cross-sectional view for explaining a manufacturing process of the resin-sealed electronic device.

FIG. 6 is a process chart for explaining a manufacturing process of the resin-sealed electronic device.

FIG. 7 is a sectional view of a hollow sphere filler.

FIG. 8 is a cross-sectional view of a resin-sealed electronic device for comparison.

FIG. 9 is a cross-sectional view illustrating stress applied by a sealing resin.

FIG. 10 is a sectional view for explaining stress applied by a sealing resin.

FIG. 11 is a cross-sectional view illustrating stress applied by a sealing resin.

FIG. 12 is a cross-sectional view for explaining stress applied by a sealing resin.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lead frame, 2 ... Silicon chip, 4 ... Primary sealing resin, 8 ... Secondary sealing resin, 9 ... Stress buffer coating film, 10 ... Rubber, 11 ... Bubbles

Claims (3)

[Claims] A first sealing resin that molds an electronic component disposed on a base material; a second sealing resin that molds the base material and the electronic component molded with the primary sealing resin; A resin sealing type electronic device comprising: a primary sealing resin and a secondary sealing resin; and a stress buffer coating film for relaxing stress applied between the two sealing resins. A resin-encapsulated electronic device, wherein an elastic body is used as a base material as the buffer coating film, and air bubbles are scattered in the base material. 2. A first step of molding an electronic component disposed on a base material with a primary sealing resin, wherein air bubbles are scattered on an elastic body as a base material on the surface of the primary sealing resin. A second step of coating with a stress buffer coating film, and a third step of molding the substrate and the electronic component with a secondary sealing resin on the outer peripheral side of the stress buffer coating film.
And a method of manufacturing a resin-sealed electronic device. 3. The resin-encapsulated electronic device according to claim 2, wherein the second step is to coat a solution in which a hollow sphere filler is mixed into a liquid elastic material on the surface of the primary sealing resin. Production method.