JP2720864B2 - Resin-sealed electronic components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-sealed electronic component having a circuit board on which a thick film conductor, a thick film resistor and the like are formed.

[0002]

2. Description of the Related Art A circuit board on which a thick-film conductor or a thick-film resistor is formed and, if necessary, a semiconductor element are separately disposed on a metal support plate also serving as a heat sink, and these are sealed with a resin coating. Stopped electronic components (hybrid ICs) are known. Generally, in this type of electronic component, the upper surface of the thick film conductor, the thick film resistor, and other circuit components is coated with a protective resin (coating material) in order to prevent a decrease in reliability due to intrusion of impurities into the circuit board. Then, the upper portion is further sealed with a resin coating (mold resin). Conventionally, a polyimide resin having excellent adhesion to a circuit board has been used as the protective resin, thereby uniformly covering the thick film conductor, the thick film resistor, and other circuit components. Even if it is formed in this way, if the adhesion between the protective resin and the circuit board is good, the intrusion of impurities from the interface between them can be prevented well.

[0003]

However, a protective resin having excellent adhesion to a circuit board generally has excellent adhesion to a thick film resistor and also has excellent adhesion to a resin coating (mold resin). ing. On the other hand, the adhesion between the thick film resistor and the circuit board is inferior to the adhesion between the thick film resistor and the protective resin.
For this reason, when thermal expansion or the like occurs in the resin sealing body, a pulling force is applied to the thick film resistor from the resin substrate via the protective resin from the circuit board, and peeling or disconnection may occur in the thick film resistor. Since the thickness of the thick-film resistor is wider than that of the thick-film conductor, such a problem is likely to occur.

Accordingly, an object of the present invention is to provide a resin-sealed electronic component in which peeling or disconnection of a thick-film resistor hardly occurs.

[0005]

According to the present invention, there is provided a circuit board having a thick film resistor formed on a part of an upper surface thereof, and a first circuit board covering the upper surface of the thick film resistor. A second protective resin layer, which covers a portion other than the thick film resistor, and is arranged so as to surround the first protective resin layer in plan view; A resin coating covering the first protective resin layer and the second protective resin layer, wherein an adhesive force of the first protective resin layer to the resin coating is equal to that of the second protective resin layer. The present invention relates to a resin-sealed electronic component having a lower adhesive strength to the resin coating. As described in claim 2, the adhesive strength B of the first protective resin layer to the resin coating is reduced based on the adhesive strength A of the resin coating to the circuit board, and the second protective resin layer It is desirable to increase the adhesive force C to the resin coating.

[0006]

According to the invention of each claim, the first aspect is as follows.
Since the adhesive force of the protective resin layer to the resin coating is lower than the adhesive force of the second protective resin layer to the resin coating, the first protective resin layer is pulled upward by the resin coating, Thus, when the thick film resistor is also pulled upward, the thick film resistor is not pulled so strongly by the first protective resin layer.
For this reason, peeling or disconnection of the thick film resistor from the circuit board hardly occurs. Even if the adhesive strength of the first protective resin layer to the resin coating is weak, the adhesive strength of the second protective resin layer disposed so as to surround the first protective resin layer in a plan view is small. Since it is high, it is possible to prevent water and impurities from entering the region where the thick film resistor is formed. Further, since the separation between the resin coating and the protective resin layer easily proceeds from the outer peripheral side to the inner peripheral side, the occurrence and progress of the separation can be prevented by providing the second protective resin layer having a strong adhesive force on the outer peripheral side. Can be suppressed.
According to the invention of claim 2, protection of the circuit board device can be achieved more rationally.

[0007]

1 and 2, a hybrid IC as a resin-sealed electronic component according to an embodiment of the present invention will be described. This hybrid IC includes a metal support plate 1 also serving as a heat sink, an insulating circuit board 2 made of alumina (Al ₂ O ₃ ) or the like, a first protective resin layer 3, a second protective resin layer 4, and a resin cover 5. It has. In addition, external lead leads and the like connected to the electrode metal formed on the circuit board 2 via the lead wires 6 are also provided, but are not shown. Further, a semiconductor element or the like may be further fixed to the metal support plate 1 as necessary. Further, the resin coating 5 may cover the back side of the support plate 1.
Further, a power semiconductor element may be arranged on the metal support plate 1, and the resin coating 5 may cover the power semiconductor element.

The circuit board 2 has a rectangular planar shape, and a thick film resistor 7, a thick film conductor 8, a thick film electrode 9 and the like are formed on one main surface thereof. A region 10 where the thick film resistor 7 and the like are not formed is provided outside one main surface of the circuit board 2. In addition, on one main surface of the circuit board 2,
In addition, other circuit components are fixed, but are not shown. The thick film resistor 7 is formed, for example, by screen printing and firing a thick film resistor paste composed of a ruthenium oxide-based glass powder as a resistance material and an organic binder. The thick-film conductor 8 and the thick-film electrode 9 are screen-printed and fired with a thick-film conductor paste made of, for example, metal powder of Ag (silver) or Ag and Pd (palladium), glass as an inorganic binder and an organic binder. Consisting of As shown, the thick film resistor 7 is formed in a bridge shape so as to overlap a part of the thick film conductor 8. On the other hand, the thick film electrode (bonding pad) 9 is formed integrally with the thick film conductor 8 as this extended wide portion. As shown in FIG. 2, the wiring portion of the thick film conductor 8 is formed narrower than the thick film resistor 7. The thick film resistor 7 has a larger area 10 than the thick film conductor 8 and the thick film electrode 9.
It is formed inside. The other main surface of the circuit board 2 is fixed to one main surface of the support plate 1 with an adhesive.

The first protective resin layer 3 selectively covers substantially only the upper surface of the thick film resistor 7, and covers portions other than the thick film resistor 7, such as the thick film conductor 8 and the thick film electrode 9. The upper surface is an annular region 10 outside the broken line in FIG. 2 where the thick film resistor 7 is not formed.
Is covered with a second protective resin layer 4 different from the first protective resin layer 3 including the upper surface. That is, the second protective resin layer 4 is disposed so as to surround the first protective resin layer 3 when viewed in plan. The first protective resin layer 3 is formed by applying a varnish-like silicone resin and solidifying it. The second protective resin layer 4 is formed by applying and solidifying a varnish-like polyimide resin. In addition, the resin cover 5 and the circuit board 2
When the adhesive strength of the two when they are directly bonded (the force required to peel them off) is Akgf / cm ² ,
Adhesion Bkgf between first protective resin layer 3 and resin coating 5
/ Cm ² and the adhesion Ckgf / cm ² between the second protective resin layer 4 and the resin coating 5 have a relationship of B <A <C. Advantages of this relationship will be described later.

A thin lead wire 6 is connected to the thick film electrode (bonding pad) 9, and the second protective resin layer 4 also covers the upper surface of the thin wire 6. First protective resin layer 3
The second protective resin layer 4 is covered with a resin coating 5. The resin coating 5 is made of, for example, an epoxy resin (including a filler), and also covers a portion of the fine lead wire 6 that is not covered with the protective resin layer 4 and a portion of an external lead (not shown). The adhesion (adhesion) between the first protective resin layer 3 and the resin coating 5 is inferior to the adhesion (adhesion) between the second protection resin layer 4 and the resin coating 5.

As described above, by making the adhesive strength between the first protective resin layer 3 and the resin coating 5 lower than the adhesive strength between the second protective resin layer 4 and the resin coating 5, a thick film is formed. Resistance 7
No peeling or disconnection occurs. The reason will be described below.
Even if the resin coating 5 rises from the main surface of the circuit board 2 due to thermal expansion or the like as in the conventional example, the adhesiveness between the resin coating 5 and the first protective resin layer 3 is poor in this embodiment. In addition, the first protective resin layer 3 is not lifted by being pulled by the resin coating 5. Therefore, the thick film resistor 7 does not peel off. On the other hand, other than the upper surface of the thick film resistor 7, the second protective resin layer 5 has better adhesion to the resin coating 5 than the first protective resin layer 3.
Is protected by the protective resin layer 4, peeling of the thin lead wire 6 from the thick film electrode 9 and intrusion of impurities into the upper surface of the circuit board 2 are also prevented. Even if the connection portion between the thick film electrode 9 and the thin lead wire 6 and the annular region 10 are uniformly covered with the first protective resin layer 3, peeling and disconnection of the thick film resistor 7 can be similarly prevented. However, if this is done, peeling is likely to occur at the interface between the first protective resin layer 3 and the resin coating body 5 near the connection portion of the lead thin wire 6, and if peeling occurs, the stress accompanying the peeling will occur. Is added to the lead wire 6,
The thin lead wire 6 may be peeled off from the thick film electrode 9. In addition, since the separation between the protective resin layer and the resin coating body 5 proceeds from the peripheral side thereof, that is, from the outer peripheral side of the circuit board 2 toward the inside,
If the adhesiveness of the protective resin layer on the outer peripheral side of the circuit board 2 to the resin coating body 5 is poor, the progress of the peeling occurs early, and the peeling of the thin lead wires 6 is likely to be caused early. Also, the circuit board 2
If the adhesion of the protective resin layer covering almost the entire surface including the outer peripheral side of the protective resin layer to the circuit board 2 is not good, peeling of the circuit board 2 and the protective resin layer easily occurs, which is an original function of the protective resin layer. The effect of preventing impurities from entering is impaired. In this embodiment,
Almost the entire surface of the circuit board including the connection portion of the lead thin wires 6 and the outer peripheral side of the circuit board 2 has a second adhesive layer which is more excellent in adhesion to the resin coating 5 and the circuit board 2 than the first protective resin layer 3. Such a problem does not occur because the resin is covered with the protective resin layer 4.

The object of the present invention can be achieved if the first protective resin layer 3 covering the thick film resistor 7 has lower adhesiveness to the resin coating 5 than at least the second protective resin layer 4. Although it is conceivable, in practice, the first protective resin layer 3
Between the resin coating 5 and the circuit board 2
If the adhesiveness is not lower than the adhesiveness, the function and effect of the present invention cannot be sufficiently exhibited. That is, if the adhesion between the first protective resin layer 3 and the resin coating 5 is at the same level as the adhesion between the resin coating 5 and the circuit board 2, the circuit board 2 is directly covered with the resin coating 5. Until the peeling of both occurs
This is because the first protective resin layer 3 and the resin coating 5 maintain good adhesiveness, and during this time, a tensile force may be applied to the thick film conductor. Therefore, it is desirable that B <A <C as described above.

[0013]

[Modifications] The present invention does not relate to the above-described embodiment, and for example, the following modifications are possible. (1) Both the first and second protective resin layers 3 and 4 can be formed of polyimide varnishes having different adhesive strengths. (2) The thick film resistor 7 may be formed of an Ag-Pd resistor paste or the like.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a part of a hybrid IC according to an embodiment of the present invention.

FIG. 2 is a plan view for explaining the circuit board of FIG. 1 and a thick film resistor and a thick film conductor on the upper surface thereof.

[Explanation of symbols]

 Reference Signs List 2 circuit board 3 first protective resin layer 4 second protective resin layer 5 resin coating 7 thick film resistor 8 thick film conductor

Claims (2)

(57) [Claims] 1. A circuit board having a thick film resistor formed on a part of its upper surface, a first protective resin layer covering the upper surface of the thick film resistor, and covering a portion other than the thick film resistor. A second protective resin layer disposed so as to surround the first protective resin layer when viewed in a plan view, and on the first protective resin layer and the second protective resin layer. Wherein the adhesive strength of the first protective resin layer to the resin coated body is lower than the adhesive strength of the second protective resin layer to the resin coated body. Sealed electronic components. 2. The adhesive strength of the resin coating to the circuit board is A, the adhesive strength of the first protective resin layer to the resin coating is B, and the adhesive strength of the second protective resin layer to the resin coating is 2. 2. The resin encapsulation according to claim 1, wherein when the adhesive strength is C, the adhesive strength of the first and second protective resin layers is determined so as to satisfy B <A <C. Shaped electronic components.