JPH0683868B2 - Lead bending method for semiconductors - Google Patents

Description

The present invention relates to a method of bending an external lead of a resin-molded semiconductor.

[Conventional technology]

An outline of a conventional semiconductor package manufacturing method and a semiconductor lead bending method in the semiconductor package manufacturing process will be described with reference to FIGS.

FIG. 5 is a plan view of a semiconductor package, and FIG. 6 is a plan view of a lead frame punched with a pattern in the initial manufacturing step of the semiconductor package. As shown in FIG. 6, a lead frame material (for example, a thin metal plate of 2% Sn-Cu alloy) is punched into a predetermined pattern by a press to obtain a lead frame 1 as shown in FIG. The lead frame 1 is
External lead 2, internal lead 3, tab 4, dam 5
A range surrounded by a chain double-dashed line in the figure is a molding range to be molded in a later step. Then, before the molding step, a semiconductor pellet (not shown) manufactured in a separate step is mounted and adhered on the tab 4 of the lead frame 1 to connect the semiconductor pellet and the internal lead 3, and thereafter, semiconductor resin sealing The molding range of the lead frame 1 is molded by a casting metal fitting for. FIG. 7 is a perspective view showing a state after the molding step. As shown in FIG. 7, the semiconductor pellet on the tab 4 and the inner lead 3 are resin-sealed in the molding portion 7 by the molding resin. Then, after cutting the dam burr 6 of the mold resin and the dam of the lead frame 1 protruding from the casting mold for semiconductor resin encapsulation, the outer lead 2 is bent downward, and through the above manufacturing process, The semiconductor package 8 shown in the sectional view of the semiconductor package in the figure is obtained.

By the way, in such a lead bending process, if the bending process is performed without mechanically restraining the outer lead 2, the bending process force is transmitted to the inner lead 3 and the mold part 7, and as a result, the local part of FIG. As shown in the enlarged portion, the mold portion 7
In some cases, tensile stress acts on the interface between the inner lead 3 and the upper surface of the inner lead 3 to cause peeling, resulting in the formation of a gap 9 between the inner lead 3 and the molded portion 7. The gap 9 has a gap δ of several μm to several tens of μm and a depth l ₁ of several hundred μm. When such a gap 9 is generated, moisture enters from the outside into the gap 9 and corrodes the internal wiring of the semiconductor package. ∙ Disconnection may occur and cause malfunction.

Therefore, conventionally, in order to prevent the occurrence of gaps in the semiconductor package, as shown in, for example, Japanese Patent Publication No. 49-49107, mechanically restraining the vicinity of the external lead to be bent at the time of bending the lead from above and below. I was taking measures such as.

FIG. 9 shows a local sectional view of a conventional lead bending process for preventing the occurrence of such a gap, and the same parts as those in FIG. 8 described above are designated by the same reference numerals. That is, 2 is an outer lead, 3 is an inner lead, and 7 is a mold part. Conventionally, at the time of lead bending processing, the lead bending portion of the outer lead 2 is machined by the upper surface restraining jig 10 and the lower surface restraining jig 11. The bending force P _M downwardly (lead bending load) P _M to the outer lead 2 with the constant constraining force P applied from above and below, so that the bending work force P _M changes the inner lead 3 and the mold part. 7 to prevent the formation of a gap at the interface between the inner lead 3 and the mold 7.

[Problems to be solved by the invention]

In such a lead bending method, the lead member 2
Since the lead bending load P _M required for the lead bending process varies depending on the material, shape, size, etc. of the lead, the lead bending load P _M
It is also necessary to change the mechanical restraining force P applied to the restraining jigs 10 and 11 according to the size of the above. However, there is a limit to the magnitude of this type of restraint force P, and if the restraint force P becomes too large, the restraint site of the external lead 2 may be damaged. In particular, the force to prevent the working force P _M bending the mold inside 7 from being transmitted, the lead holding width l ₂ of the restraining jigs 10, 11
(See FIG. 9) and the constraint force P,
When it is attempted to set the value of the lead pressing width l ₂ small during lead bending, the restraining force P must be increased in inverse proportion to that, and as a result, the surface pressure applied to the restraining surface of the lead 2 is reduced. If the limit value is exceeded, yield stress occurs in the lead 2 and damage (indentation) occurs in the lead 2. Therefore, the lead pressing width l ₂ cannot be made sufficiently small, and there is a problem in that the lead pressing width can be made small and the lead bending process requiring a large bending load P _M cannot be performed accurately.

An object of the present invention is to provide a lead bending method capable of effectively preventing the occurrence of a gap at the interface between the mold portion and the internal lead during lead bending processing while solving the above problems.

[Means for solving problems]

The above-mentioned object is to support the external leads protruding from both left and right sides of the mold part for molding a semiconductor at the lead bending point by supporting only the lower surface of the mold part during the lead bending process. Can be achieved by applying a load that generates a bending moment that cancels the bending moment inside the mold portion caused by the lead bending load during the lead bending process.

[Action]

The operation of the present invention having the above structure will be described with reference to FIGS.
Description will be given based on the principle diagram of the present invention shown in I).

In the same figure (I), the lower surface of the lead bending points b and e of the external lead 2 protruding from the mold portion 7 is supported via a support member 22,
This figure shows a state in which only the lead bending load P _M is applied. In this state, as shown in the bending moment distribution of FIG. 4 (IV) during the lead bending process, the mold portion 7 shown in the range of symbols c to d is shown. A negative bending moment M ₁ is generated inside (c and d are the ends of the mold portion 7), and the bending moment M originally required from the bending points b and e to the surface ends a and f of the outer lead 2 is generated.
₁ 'occurs.

In the figure (II), a predetermined pressing load P is applied to the upper surface of the mold portion 7.
_It represents the state where _S is added uniformly. In this state,
A positive bending moment M ₂ is generated inside the mold portion 7 as shown in the bending moment distribution of FIG.

The present invention is such that the lead bending load P _M shown in FIG. 1I is applied to the external lead 2 and the pressing load P _S shown in FIG. Figure (II
(State of I)), in this case, as shown in FIG. 6 (VI), both bending moments M ₁ and M ₂ of (IV) and (V) are combined,
In the inside of the mold part 7, the bending moments M ₁ and M ₂ cancel each other out and become a state of almost zero. Therefore, the bending moment becomes zero near the ends c and d of the mold part. On the other hand, since the negative bending moment M ₁ ′ of the lead bending load P _M is generated from the bending points b and e of the outer lead 2 to the lead end portions a and f without being canceled, the outer lead 2 is bent. It is bent from b and e in a predetermined direction (downward in the principle diagram in FIG. 1).

Therefore, according to the present invention, the lead bending process of the external lead 2 can be performed, and the bending moment is canceled inside the mold portion 7 during the lead bending process. ) It is possible to suppress P _M from reaching the inside of the mold portion 7 and prevent a gap or a crack from being generated at the interface between the internal lead 3 of the semiconductor and the mold portion 7.

Furthermore, according to the present invention, the lead bending processing force P _M is applied to the inside of the mold part 7 by the pressing load P _S applied to the mold part 7.
In order to prevent this, it is not necessary to press the upper and lower surfaces of the external lead 2 with a restraining jig as in the conventional case.

As a result, it is possible to adopt a method in which each of the external leads 2 is supported by only the lower surface by freeing the pressing of the leads 2 at the lead bending points b and e, so that there is no room for yield stress to occur in the external leads 2, The lead 2 is not damaged, and it is possible to eliminate the limitation of reducing the lead holding width l ₂ due to the existence of the restraining jig as in the conventional case, and the width of the lead supporting portion 22 corresponding to the holding width can be eliminated. Since l ₂ can be further reduced, lead bending accuracy can be improved.

Incidentally, the pressing load P _S of the mold section 7 is set so that canceling the moment M ₁ bending occurs in advance in the mold section 7. Further, in FIG. 6 (VI), some reverse bending moment M ₂ ′ may remain inside the mold portion 7, but this value is in an extremely small range, and the bending rigidity of the mold portion 7 is small. Since it is large, it is hardly affected by lead bending deformation.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS.

FIG. 2 is a front view of essential parts showing a concrete example of a lead bending apparatus for carrying out the lead bending method of the present invention, and FIG. 3 is a front view showing a state after the lead bending processing of the lead bending apparatus. FIG. 4 is a partially omitted perspective view showing an enlarged part A of FIG.

In FIG. 2, reference numeral 20 denotes a lower die that is set when the semiconductor package 8 is bent. The lower die 20 is provided with an accommodation groove 21 for accommodating the lower mold portion 7a of the semiconductor package 8, and both side edges of the accommodation groove 21 are provided. Is provided with a supporting portion 22 for supporting the lower surface side of the bending point of the outer lead 2. 23 is a semiconductor package 8
Is an upper mold for applying a pressing load P _S to the upper surface of the mold part 7, and the upper mold 23 is set to generate a pressing load P _S under the pressing force of the air cylinder 24. This upper mold 23
Is driven by the air cylinder 24 and is located at the lowest point,
Not be subjected to loads P _S presser before the lead bending, and is considered so reverse bending deformation does not occur in the external leads 2. FIG. 4 shows the structure of the upper die 23 provided with the above-mentioned reverse bending deformation preventing means. That is, as shown in FIG. 4, the upper die 23 has the semiconductor package 8
In addition to having the pressing surface 25 that presses the upper surface of the mold portion 7, a plurality of concave portions 26 and convex portions 27 are alternately provided on the side edge of the pressing surface 25 so that when the upper die 23 reaches the lowest point, the concave portion is formed. 26
Is positioned so as to face the upper surface of the outer lead 2 in a non-contact state with the upper surface, that is, to maintain a space, and the convex portion 27 is a lower mold.
When the convex portion 27 comes into contact with the support portion 22, it serves as a stopper so that the pressing surface 25 comes into contact with the surface of the mold portion 7 without pressing. before the lead bending in this way, it is not splash the pressing load P _S.

28 is a bending roller mechanism added bending load (vertical load) P _M to external leads 2, bent roller mechanism 28 along connexion to the left and right side surfaces of the pair of roller members 28a, 28b are upper die 23 and lower die 20 The roller member is mounted so that it can move up and down.
A lead bending load P _M is generated by the descending force of 28a and 28b.

Next, a lead bending process using the lead bending apparatus of this embodiment will be described.

When performing the lead bending process, first, the semiconductor package 8 is placed on the lower die 20, and the lower surface side of the bending point of the external lead 2 is positioned on the support portion 22. Next, the air cylinder 24 lowers the upper mold 23. When the upper mold 23 goes down to the lowest point, the upper mold
The convex portion 27 of 23 comes into contact with the support portion 22 of the lower mold 20, and the pressing surface
25 contacts the upper surface of the mold part 7. In this state,
Each of the roller members 28a and 28b of the bending roller mechanism 28 is indicated by an arrow B.
When it is lowered in the direction, a vertical bending load P _M is applied to the outer lead 2 downward, and the outer lead 2 bends. At the time of this lead bending process, the bending moment M ₁ of the bending load P _M tends to be generated inside the mold portion 7 as shown in the principle diagram of FIG. 1 (I) described above.
In this case, since the upper surface of the lead 2 is free due to the presence of the recess 23 of the upper die 23, the force of the lead bending load P _M acts to lift the outer lead 2 upward in the mold portion 7, acting load P _S presser through the pressing surface 25 of the upper mold 23 in the mold section 7, by connexion Figure 1 to (VI)
Bending moment M ₂ of the load weight P _S presser and the bending moment M ₁ of the lead bending load P _M as shown in cancel each other. Therefore, the bending moment distribution inside the mold part 7 becomes substantially zero, and as a result, the bending processing force P _M of the lead bending load is not transmitted to the interface between the mold part 7 and the semiconductor inner lead 3, and Prevents the formation of gaps at the interface. FIG. 4 shows the state of the semiconductor package 8 and the lead bending apparatus after the lead bending processing.

The lead bending process is performed as described above. However, when bending is performed with the bending radius of the external lead 2 being approximately the same as the lead plate thickness as in this embodiment, a lead member (metal) that is normally used is used. Since the bending moment M ₁ does not change much from the start of plastic deformation to the completion of bending deformation, the pressing load P _S for canceling this bending moment M ₁ may be kept constant during lead bending. Further, the pressing load _{P S}
The material of the lead member and the mold part, because the optimum for the position of the dimensions and the lead lower surface support points are different, by changing the load P _S presser before bending performs bending pressure experiments, no occurrence of clearance The pressing load P _S may be obtained from an experimental value.

As described above, according to the present embodiment, it is possible to prevent the formation of a gap at the interface between the inner lead and the inside of the mold portion during the lead bending process. Further, the gap prevention molding portion 7 of the read bending is not performed by adding binding to the prior restraint jig as, because performed by applying a load P _S pressing the mold section 7, the external lead It is not necessary to give a large mechanical restraining force to the lead wire 2, and as a result, the lead damage can be prevented from occurring without the yield stress occurring in the outer lead 2 itself. Moreover, since the supporting member 22 does not need to impose the role of preventing the transmission of the bending force P _M unlike the conventional restraint jig, the lead supporting portion 22 corresponding to the conventional lead pressing width l ₂ can be used. This has an advantage that the value of the width l ₂ can be set arbitrarily small. For example, whereas the conventional lead pressing width l ₂ can be reduced to only about 0.4 mm, the width l ₂ can be set to about 0.2 to 0.1 mm in this embodiment.

In this embodiment, the air cylinder 24 is used as the pressing load applying means, but a constant load spring, a hydraulic cylinder or the like may be used instead, and the same effect can be obtained.
Further, convex portion (a stop) 27 provided in the upper die 23 for pressing the molded part 7, by the convex portion 27, but to prevent lead before bending the holding force P _S is applied to the mold section 7, Instead of the convex portion 27, a stopper may be attached to the air cylinder 24 to perform the same operation.

〔The invention's effect〕

As described above, according to the present invention, it is possible to solve the problem that the outer lead itself is damaged during the lead bending process, and it is possible to prevent a gap from being formed at the interface between the mold portion and the inner lead.

[Brief description of drawings]

FIGS. 1 (I) to (VI) are schematic diagrams showing the principle of the lead bending method of the present invention, and FIG. 2 is a front view of the main parts of a lead bending apparatus used in the lead bending method of the present invention. FIG. 3 is a front view of a main portion of the lead bending apparatus shown in FIG. 2 after bending, FIG. 4 is a partial perspective view showing an enlarged portion A of FIG. 2, and FIG. 5 is a semiconductor package. Manufacturing process diagram of
FIG. 6 is a partially omitted plan view of a lead frame used for lead bending of the present invention, FIG. 7 is a partially omitted perspective view showing a state of a semiconductor package during a manufacturing process, and FIGS. It is a principal part sectional view of the semiconductor package after performing a lead bending process by the conventional lead bending process method. 2 ... External lead, 3 ... Internal lead, 7 ... Mold part, 8 ... Semiconductor package, 22 ... Lead support part, b,
e ...... lead bending point, _{P M} ...... lead bending load, _{P S} ...
… Pressing load, M ₁ …… Bending moment due to lead bending load, M ₂ …… Bending moment due to pressing load.

Front page continued (72) Inventor Gen Murakami 1450, Kamisuihonmachi, Kodaira-shi, Tokyo Inside the Musashi Factory, Hitachi, Ltd. (56) Reference JP-A-60-189244 (JP, A)

Claims (1)

[Claims] 1. A lead bending method in which a bending load is applied to an external lead of a semiconductor which is resin-sealed with a mold resin to perform a bending process.
Each of the external leads protruding from both the left and right sides of the mold part for resin-sealing the semiconductor is supported by the lower surface only by holding the external lead free at the lead bending points, and the lead part is attached to the mold part. A method for bending a lead of a semiconductor, characterized in that a bending load for canceling a bending moment inside the mold portion caused by a load is applied during the lead bending process, and the lead bending process is performed.