JPH07211846A - Lead frame - Google Patents

Abstract

PURPOSE:To prevent superfluous solder which has flown into a dummy lead from flowing into a lead, by forming a wide part for sucking the superfluous solder and a narrow part where solder is hard to flow, in the dummy lead. CONSTITUTION:In a dummy lead 32, a first wide part 34 is formed in a unified body in the part to be soldered to a corner part 22 of a package substrate 2, and a second wide part 35 is formed in a unified body between the first wide part 34 and a lead tie bar 33. A narrow part 36 is formed in a unified body between the first wide part 34 and the second wide part 35. A narrow part 37 is formed in a unified body between the second wide part 35 and the lead tie bar 33. Hence the greater part of superfluous solder sucked by the wide part 34 of each dummy lead 32 is blocked by the first wide part 34. When the superfluous solder goes across the first wide part 34, the solder passes the narrow part 36, and is sucked and blocked by the next second wide part 35. Thereby the solder can be prevented from going across the second wide part 35 and flowing into the narrow part 37.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has an integrated circuit mounted thereon,
The present invention relates to a lead frame used in an integrated circuit package mounted on a printed wiring board or the like, and particularly to a lead frame having dummy leads for absorbing excess brazing material.

[0002]

In Japanese Patent Publication No. 62-56665, a lead frame formed by arranging a plurality of leads as external connection terminals is provided with dummy leads for absorbing excess brazing material, and an integrated circuit is mounted thereon. There is disclosed an integrated circuit package in which a lead frame is brazed to a conductor pattern formed on a package base for cutting the dummy frame and the dummy lead absorbing the excess brazing material is cut off.

In this conventional integrated circuit package, as shown in FIGS. 6 and 7, a plurality of conductor patterns 1 for brazing a plurality of leads 101 to a package substrate 100.
Forming 02. The lead frame 103 formed corresponding to each of the conductor patterns 102 has a lead tie bar 104 that connects the plurality of leads 101, and is arranged via a brazing material 105 formed in a square ring shape. Here, dummy leads 106 for absorbing excess brazing material are formed on both outer sides of the lead 101 row of the lead frame 103.

[0004]

However, in the conventional integrated circuit package having the above structure, the package substrate 100 is used.
Excess brazing filler metal from the core flows along the dummy leads 106 to the lead tie bar 104, and then the lead tie bar 104
And flow into the lead 101 or the dummy lead 1
There is a risk that it may flow directly into the lead 101 from 06.

As described above, when the excess brazing material flows into the leads 101, the excess brazing material adheres to the leads 1
01 is caused by stains, or the thickness of the excess brazing material causes bending of the leads 101 using a jig in the process of completing the integrated circuit package, and cutting of the lead tie bar 104 for separating each lead 101. , The accurate dimensional accuracy cannot be obtained, and each lead 101
There was a problem that was not uniform.

An object of the present invention is to provide a lead frame capable of preventing excess brazing filler metal from flowing along dummy leads and lead tie bars into the leads. Also,
An object of the present invention is to provide a lead frame capable of preventing a dummy lead from directly flowing into the lead. And to provide a lead frame that prevents the formation of a bridge between adjacent leads to prevent the occurrence of a short circuit, suppresses the occurrence of stains on the leads, and easily obtains leads with accurate dimensional accuracy. is there.

[0007]

According to a first aspect of the present invention, there is provided a lead row having a plurality of leads as external connection terminals, a dummy lead for absorbing an excess brazing material, and the lead mutual. And a lead tie bar connecting the lead row and the dummy lead, wherein the dummy lead has at least one wide portion having a width wider than other portions in the vicinity, and a width wider than the wide portion. The technical means consisting of at least one narrow portion is adopted.

According to a second aspect of the present invention, in addition to the lead frame according to the first aspect, the width of the wide portion of the dummy lead is twice the width of the narrow portion adjacent to the wide portion. The above technical means was adopted. The width of the narrow portion may be substantially the same as the lead width of the lead.

According to a third aspect of the present invention, in addition to the lead frame according to the first or second aspect, a technical means in which the wide portion is provided at the tip portion of the dummy lead is adopted.

The invention described in claim 4 employs a technical means in which, in addition to the lead frame described in claim 3, the wide portion is provided also in a substantially middle portion of the dummy lead.

According to a fifth aspect of the present invention, in addition to the lead frame according to the third or fourth aspect, two of the sides forming the outer shape of the tip portion of the dummy lead are connected to the lead frame. The technical means formed so as to correspond to the outer side of the circuit board to be brazed was adopted.

[0012]

According to the first aspect of the present invention, when brazing a plurality of leads as external connection terminals, the surplus brazing material that has been left over for brazing the plurality of leads flows into the dummy leads. The excess brazing material that has flowed into the dummy lead flows into the wide portion more than the narrow portion, and the excess brazing material from the wide portion to the narrow portion is blocked. As a result, the surplus brazing material does not flow into the lead tie bar along the dummy leads.

According to the second aspect of the present invention, the width of the wide portion of the dummy lead is 2 times the width of the narrow portion adjacent to the wide portion.
Since it is doubled or more, the performance that the surplus brazing material is sucked into the wide portion rather than the narrow portion and the performance of suppressing the inflow of the surplus brazing material from the wide portion to the narrow portion become more remarkable.

According to the third aspect of the invention, the surplus brazing material is attracted to the wide portion at the tip of the dummy lead.
Since the width of the narrow portion is narrower than that of the wide portion of the tip portion and it is difficult to flow, most of the surplus brazing material that has flowed into the wide portion of the tip portion is blocked by the wide portion of the tip portion, There is no excess brazing material that flows over the narrow portion and the lead tie bar beyond the wide portion of the tip portion and flows into the lead.

According to the fourth aspect of the invention, the surplus brazing material is attracted to the wide portion at the tip of the dummy lead.
Since the narrow portion is narrower or more difficult to flow than the wide portion of the tip portion, most of the surplus brazing material that has flowed into the wide portion of the tip portion is blocked by the wide portion of the tip portion.
Nevertheless, when the surplus brazing material exceeds the wide portion at the tip portion, it passes through the narrow portion and is attracted to the next wide portion at the substantially middle portion to be dammed. As a result, there is no excess brazing material that flows along the lead tie bar over the wide portion of the substantially middle portion and flows into the lead.

According to a fifth aspect of the present invention, by aligning two of the sides forming the outer shape of the tip portion of the dummy lead with the side forming the outer shape of the circuit board, the tip portion of the dummy lead and the circuit board are formed. Is aligned with.

[0017]

According to the invention described in claims 1 to 5, since the dummy lead is provided with the wide portion for sucking the excess brazing material and the narrow portion where the excess brazing material is hard to flow, the dummy lead is provided. Since the surplus brazing material that has flowed in is blocked by the wide portion, it is possible to prevent the surplus brazing material that has flowed into the dummy leads from flowing through the dummy leads and the lead tie bars to the leads.

Therefore, since the surplus brazing material is attracted to the wide portion of the dummy lead, the surplus brazing material is provided adjacently.
It is possible to prevent the occurrence of a short circuit due to the formation of a bridge between the two leads, and it is possible to suppress the occurrence of stains on the leads due to the adhesion of the excess brazing material. Further, when bending or cutting a plurality of leads, it is possible to obtain leads with accurate dimensional accuracy, and it is possible to reduce product defects of each lead. According to the invention described in claim 5, it is very easy to align the tip portion of the dummy lead with the circuit board.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the lead frame of the present invention will be described with reference to FIGS. FIG. 1 shows an integrated circuit package that employs one embodiment of the present invention. Reference numeral 1 denotes an integrated circuit package (hereinafter referred to as an IC package). The IC package 1 includes a rectangular ceramic package base 2 made of multilayer ceramics, a lead frame 3 as an external connection terminal which is brazed to the package base 2, and a brazing material for brazing the package base 2 and the lead frame 3 together. 4 is provided.

The package board 2 is a circuit board,
As shown in FIG. 2, tungsten (W) or molybdenum (M
Conductive paste such as o) is screen-printed, each green sheet is laminated by thermocompression bonding, and then fired at a high temperature in a hydrogen furnace in a humidified atmosphere. Further, conductor patterns 21 as a plurality of terminals are formed on the surface of the package substrate 2 by high temperature firing. The conductor pattern 21 includes wire bonding for electrically connecting an integrated circuit (hereinafter referred to as an IC chip) to the outside, and the lead frame 3
Nickel plating is applied to enable brazing. After brazing the lead frame 3, the package base 2 prevents corrosion and securely mounts and wire bonds an IC chip, and further improves the characteristics as an IC by using nickel and gold electricity. Plated.

As shown in FIG. 4, the lead frame 3 is formed of a plurality of rows of leads formed by etching.
31, a plurality of dummy leads 32 protruding inward from both outer sides of the 31 rows, and each lead 31 and each dummy lead 32
It is composed of a square annular lead tie bar 33 that connects the two.

Each lead 31 has a conductor pattern 21 on the package base 2 whose inner end (tip) corresponds to each lead 31.
The outer end (the other end) is brazed to the lead tie bar 33.
It is connected to the dummy lead 32 via. Also lead
In the final step after mounting the IC chip, the connection portion of the lead tie 31 with the lead tie bar 33 is cut off.

The dummy lead 32, as shown in FIG.
The inner edge (tip) is the corner 22 of the package base 2.
The outer end (the other end) is brazed to the lead tie bar 33.
Is connected to each lead 31 via. Further, the dummy lead 32 has a first wide portion 34 as a surplus brazing material absorbing portion for absorbing the surplus brazing material, which is formed at a portion brazed to the corner portion 22 of the package base 2. Furthermore, the first
A second wide portion 35 is formed between the wide portion 34 and the outer end portion as a surplus brazing material absorbing portion for absorbing the surplus brazing material.

The first wide portion 34 is provided at the inner end portion of the dummy lead 32, and is formed in a square and flat plate shape wider than the narrow portions 36 and 37. In the first wide portion 34 of the dummy lead 32 on the left side of the figure and the first wide portion 34 of the dummy lead 32 on the right side of the figure, two of the sides forming the outer shape of the first wide portion 34 are package bases. It is located on each corner portion 22 of the package base 2 so as to coincide with the side forming the outer shape of 2. The first wide portion 34 of the dummy lead 32 on the left side of the drawing is formed so as to protrude from the narrow portion 36 only to one side in the left direction of the drawing. Further, the first wide portion 34 of the dummy lead 32 on the right side of the drawing is formed so as to protrude from the narrow portion 36 only to one side in the right direction of the drawing.

The second wide portion 35 is provided at a substantially middle portion of the dummy lead 32, has the same width as the first wide portion 34, and has the same shape. The second wide portion 35 of the dummy lead 32 on the left side and the right side in the drawing is formed so as to protrude from the narrow portion 37 in the left and right directions in the drawing by the same amount. The width of the first wide portion 34 and the second wide portion 35 is
The lead width of each lead 31, the narrow portion 36 of the dummy lead 32,
It is desirable that the width is at least twice as wide as 37.

The narrow portions 36 and 37 have the same width as the lead width of each lead 31 and are extended from the first and second wide portions 34 and 35 in the direction away from each corner portion 22 of the package base 2. ing. The narrow portion 36 connects the first wide portion 34 and the second wide portion 35, and is inclined from the direction orthogonal to the extending direction of one side of the lead tie bar 33, that is, the lead 31.
It is arranged so as to be inclined in a direction away from the leads 31 on both outer sides of the row. The narrow portion 37 connects the second wide portion 35 and one side of the lead tie bar 33.
They are arranged in a direction (vertical) orthogonal to the extension direction of one side of 33. Here, in the present embodiment, in order to prevent waste of gold in the gold plating process, only the dummy leads 32 are cut after the lead frame 3 is brazed to each conductor pattern 21 of the package base 2.

In the lead tie bar 33, each lead 31 and each dummy lead 32 are provided in a comb shape so as to protrude inward.
The brazing material 4 uses silver brazing filler metal having a melting point of 780 ° C. or higher,
To facilitate the handling of the brazing material 4, as shown in FIG. 3, the brazing material 4 is formed in a rectangular ring shape so as to correspond to the brazing portion of the lead 31.

The operation of the IC package 1 of this embodiment is shown in FIG.
5 to FIG. The lead frame 3 is arranged on the conductor pattern 21 of the package base 2 formed in a rectangular shape with the brazing material 4 formed in a square ring shape. At this time, by aligning two of the sides forming the outer shape of the first wide portion 34 of each dummy lead 32 with the side forming the outer shape of the package base 2, the position of each dummy lead 32 and the package base 2 is adjusted. Matching can be easily performed.

As a result, 31 rows of leads are provided as dummy leads.
Since they are integrally molded via the 32 and the lead tie bar 33, when each dummy lead 32 and the package base 2 are aligned, each lead 31 and the conductor pattern 21 of the package base 2 are easily aligned. be able to.

Then, a jig is used to press and hold. After that, the brazing filler metal 4 is melted by heating to the melting point of the brazing filler metal 4 (for example, 800 ° C.), and capillarity occurs between the inner end of the nearest lead 31 and one pattern (terminal) of the conductor pattern 21. The brazing material 4 invades. Then, the lead frame 3 is integrally brazed to the conductor pattern 21 of the package base 2 by cooling and solidifying the brazing material 4.

Here, the brazing material 4 formed in a square annular shape for easy handling becomes excessive at each corner 22 of the package base 2 where the inner end of the lead 31 is not brazed, but the lead frame Since the dummy leads 32 are formed on the wiring board 3, the excess brazing filler metal that has become excessive at each corner portion 22 of the package base 2 is completely formed on each dummy lead 32.
Flows into the first wide portion 34 of. Therefore, it is possible to prevent the excess brazing material from forming a bridge between two adjacent leads 31 and flowing toward the tip end of the lead 31.

Further, the dummy lead 32 has a first wide portion at a portion brazed to the corner portion 22 of the package substrate 2.
34, and the second wide portion 35 is integrally formed between the first wide portion 34 and the lead tie bar 33. A narrow portion 36 is integrally formed between the first wide portion 34 and the second wide portion 35, and a narrow portion 37 is integrally formed between the second wide portion 35 and the lead tie bar 33. For this reason, most of the surplus brazing material attracted to the first wide portion 34 of each dummy lead 32 is narrower in the narrow portion 36 than in the first wide portion 34, and the brazing material is less likely to flow. The first wide portion 34 blocks the dam.

However, even when the surplus brazing material exceeds the first wide portion 34, the narrow portions 36 and 37 are narrower than the second wide portion 35 and the brazing material is less likely to flow. It is sucked up to the next second wide portion 35 through the portion 36 and is dammed.
As a result, there is no excess brazing material that flows into the narrow portion 37 beyond the second wide portion 35, so that the narrow portion of each dummy lead 32 is removed.
It is possible to prevent excess brazing material from flowing into each lead 31 along the 37 and the lead tie bar 33.

Then, in order to prevent wasteful use of gold in the gold plating process, only the dummy lead 32 is cut. Further, the package base 2 and the leads 31 are electroplated with nickel and gold. At this time, the surplus brazing material is the first
The dummy lead 32 is formed by the rectangular portion 34 and the second rectangular portion 35.
Further, since it is prevented from flowing through the lead tie bar 33 into the lead 31, it is possible to prevent the stain on the lead 31 due to the adhesion of the surplus brazing material after the electroplating of nickel and gold.

In addition, the bending process of the leads 31 using a jig in the process of completing the IC package 1 and the cutting process of the connecting portion of the leads 31 for separating the leads 31 from the lead tie bar 33 can be easily performed. You can Therefore, it is possible to obtain the lead 31 with accurate dimensional accuracy, and each lead 31
It is possible to reduce product defects.

[0036]

[Modification] In this embodiment, a lead frame in which a plurality of leads and dummy leads are provided so as to project inward from two sides of the rectangular lead tie bar is used. A lead frame in which a plurality of leads and dummy leads are protruded inward from at least one side may be adopted, and a plurality of leads and dummy leads are protruded inward from a lead tie bar having a linear shape or a circular shape. A lead frame provided may be used.

The shape of the dummy lead for absorbing the excess brazing material does not need to be limited to the shape of this embodiment, and can be variously changed within the range not departing from the present invention.
Further, in this embodiment, the dummy brazing material is provided with the excess brazing filler metal absorbing portions (wide portions) at two places, but the dummy leads may be provided with one or more extra brazing filler metal absorbing portions (wide portions).

[Brief description of drawings]

FIG. 1 is a plan view showing a state in which a lead frame is brazed to a package base.

FIG. 2 is a plan view of a package board (circuit board).

FIG. 3 is a plan view of a brazing material.

FIG. 4 is a plan view of a lead frame.

FIG. 5 is a perspective view showing a main part of a lead frame brazed to a package base.

FIG. 6 is a plan view showing a state in which a conventional lead frame is brazed to a package base.

FIG. 7 is a plan view of a package base used for brazing a conventional lead frame.

[Explanation of symbols]

 1 IC package (integrated circuit package) 2 Package board (circuit board) 3 Lead frame 4 Brazing material 21 Conductor pattern 31 Lead 32 Dummy lead 33 Lead tie bar 34 First wide part 35 Second wide part 36, 37 Narrow part

Claims (5)

[Claims] 1. A lead row formed by arranging a plurality of leads as external connection terminals, a dummy lead for absorbing excess brazing material, a lead tie bar connecting the leads to each other and the lead row to the dummy lead. In the lead frame, the dummy lead includes at least one wide portion having a width wider than other portions in the vicinity, and at least one narrow portion having a width narrower than the wide portion. Lead frame characterized by. 2. The lead frame according to claim 1, wherein the width of the wide portion of the dummy lead is twice or more the width of the narrow portion adjacent to the wide portion. flame. 3. The lead frame according to claim 1 or 2, wherein the wide portion is provided at a tip portion of the dummy lead. 4. The lead frame according to claim 3, wherein the wide portion is also provided in a substantially middle portion of the dummy lead. 5. The lead frame according to claim 3 or 4, wherein two of the sides forming the outer shape of the tip portion of the dummy lead form the outer shape of a circuit board to which the lead frame is brazed. A lead frame characterized by being formed so as to match the sides.