JP3421207B2 - Wiring board with lead - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board with leads on which a semiconductor integrated circuit chip is mounted, and more particularly to the structure of an insulating tie bar used in a flat type integrated circuit package.

[0002]

2. Description of the Related Art First, an outline of a flat type integrated circuit package will be described with reference to FIG. The substantially square wiring board 2 on which the semiconductor integrated circuit chip is mounted is made of ceramics, and a large number of pad portions are formed around the four sides of its upper surface by a metallizing technique. A large number of external lead terminals 4 extending in four directions from the wiring board 2 made of ceramic, a lead frame body 6 surrounding the peripheral edges of the external lead terminals 4, and tie bar holders 8 arranged at the four corners are all 42 alloy and kovar. It is made of a thin plate of iron / nickel alloy, and is integrally formed by pressing or etching one thin plate. The large number of external lead terminals 4 and the central wiring board 2 are fixed to each other by brazing. Four insulating tie bars 10 are arranged near the inside of the lead frame body 6, and are fixed to the tie bar holders 8, respectively. The insulating tie bar 10 is made of ceramic, and a large number of brazing pad portions for electrically and independently brazing and fixing the external lead terminals 4 are formed on the surface of the insulating tie bar 10 by a metallizing technique. As shown in FIG. 3, the brazing pad portion 12 has a tungsten (W) layer 14 formed on the surface of an insulating tie bar 10 made of ceramic made of alumina by a metallizing technique, and plated with nickel (Ni) on the layer. 16 is formed. One external lead terminal 4 is brazed and fixed to each pad portion 12.

The external lead terminals 4 are brazed by a silver brazing thin plate 18 on the brazing pad 12 as shown in FIG.
Is placed, the external lead terminal 4 is placed thereon, and the silver brazing thin plate 18 is melted by heating at 800 ° C. or higher in a furnace to perform brazing. At this time, due to the surface tension of the molten silver brazing material and the wettability with the nickel plating layer 16 of the brazing pad portion, the molten silver brazing material gathers on the brazing pad portion 12, and the external lead terminals 4 are fixed by brazing. Done.
Here, a large number of long holes 2 provided in the lead frame body 6
0 and the two triangular holes 22 provided in the tie bar holder 8 prevent the lead frame body 6 and the like from being distorted due to thermal expansion and contraction when heated to a high temperature. The function of preventing the inclination of a large number of external lead terminals 4 and maintaining the flatness.

Then, after mounting the semiconductor integrated circuit chip on the substantially square wiring board 2, the lead frame body 6 is separated and each external lead terminal 4 is electrically isolated, and the semiconductor integrated circuit chip and the external lead are separated. Conduct a continuity test with terminal 4. Then, when the integrated circuit is used, the four insulating tie bars 10 and the tie bar holder 8 are separated and the external lead terminals 4 are separated and mounted on a printed circuit board or the like.

Here, the shape of each brazing pad portion 72 of the insulating tie bar 10 of the conventional wiring board with leads is rectangular as shown in FIG. 7 (Japanese Patent Laid-Open No. 4-209564).
issue). However, in recent years, the wiring board 2 has been downsized due to the higher density and higher integration of the integrated circuit, and the number of external lead terminals 4 for connecting the integrated circuit to the outside has been increased. Therefore, the pitch P of the external lead terminals 4 is reduced, and the width A of each external lead terminal 4 and the gap B between the adjacent external lead terminals 4 are also reduced. As a result, the width W and the gap G of each brazing pad portion 72 of the insulating tie bar 10 are reduced. For example, when the pitch P of the external lead terminals 4 is 0.381 mm and the width A is 0.152 mm, the width W of each brazing pad portion 72 is 0.279 m.
m, the gap G between the adjacent brazing pad portions 72 is 0.102
It was set to mm.

Thus, the adjacent brazing pad portions 72
If the gap G is small and linear, there is a problem that the adjacent brazing pad portions 72 may be short-circuited by the silver brazing and a defect may occur. On the other hand, if the gap G between the adjacent brazing pad portions 72 is increased and the width W of the brazing pad portions 72 is reduced in order to prevent a short circuit failure, the brazing margin C becomes smaller and the insulation of the external lead terminals 4 becomes smaller. There is a problem that brazing strength to the tie bar 10 may not be secured.

[0007]

Therefore, the invention according to claim 1 of the present invention prevents short-circuiting between adjacent brazing pad portions of the insulating tie bar even if the pitch of the external lead terminals is small. An object of the present invention is to provide a wiring board with leads that can secure brazing strength between external lead terminals and an insulating tie bar. The invention according to claim 2 is
It is an object of the present invention to provide a leaded wiring board in which the effect of the invention of claim 1 is further ensured by making the width of the narrow portion and the width of the wide portion of the brazing pad portion appropriate. . According to a third aspect of the present invention, a leaded wiring board capable of more reliably preventing a short circuit between adjacent brazing pad portions by making the gap between the adjacent brazing pad portions as wide as possible over its entire length. The purpose is to provide. In the invention according to claim 4, a short circuit is prevented by shortening the length of the portion where the gap between the adjacent brazing pad portions is narrow as much as possible, and the effect of the invention according to claim 1 is further enhanced. An object is to provide a wiring board.

[0008]

In order to achieve the above object, the invention according to claim 1 of the present invention is such that one lead terminal is electrically brazed and fixed to the surface of an insulating tie bar. It has a large number of brazing pad portions for carrying out, and the shape of each brazing pad portion is a concavo-convex shape having alternating wide portions and narrow portions. With this structure, when the lead terminal is brazed to the brazing pad portion of the insulating tie bar, sufficient strength can be secured in the wide convex portion of the brazing pad portion. And
In the narrow concave portion, the gap between the adjacent brazing pad portions becomes large, and the risk of short circuit during brazing is reduced.

According to the second aspect of the present invention, the width of the narrow portion of the brazing pad portion is 1 to 1.5 times the width of the external lead terminal, and the width of the brazing pad portion is wide. It is possible to make the width of the portion 2 to 3 times the width of the external lead terminal. If formed in this way, the lead terminals can be brazed over the entire length of the brazing pad portion, and the necessary and sufficient brazing margin can be secured in the wide portion and the necessary and sufficient brazing strength can be secured. If the width of the narrow portion is less than or equal to one time the width of the external lead terminal, the brazing margin of the narrow portion cannot be secured, and the brazing strength will be reduced. When the width of the narrow portion is 1.5 times or more the width of the external lead terminal, the gap between the adjacent brazing pad portions in the narrow portion becomes small, and the risk of short circuit increases. In addition, the width of the wide portion of the brazing pad portion is 2 times the width of the external lead terminal.
If it is twice or more, a sufficient brazing strength can be obtained at that portion, and if it is three times or more, the gap between the adjacent brazing pad portions becomes small and the risk of short circuit increases.

According to the third aspect of the present invention, the shapes of the plurality of brazing pad portions are arranged such that the wide portions and the narrow portions of the adjacent brazing pad portions are staggered. It can be shaped. When formed in this way, the gap between adjacent brazing pad portions increases over the entire length of the brazing pad, further reducing the risk of short circuit during brazing.

Further, as in the invention described in claim 4, the shape of the brazing pad portion can be an arc shape in the wide portion thereof. By forming in this way, it is possible to further shorten the length of the section where the gap between the adjacent brazing pad portions is narrow, and it is possible to further reduce the risk of short circuit during brazing. is there.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a flat type integrated circuit package which is a wiring board with leads. The substantially square wiring board 2 on which the semiconductor integrated circuit chip is mounted is made of ceramics, and a large number of pad portions are formed around the four sides of its upper surface by a metallizing technique. A large number of external lead terminals 4 extending in all directions from the wiring board 2 made of ceramic, a lead frame body 6 surrounding the peripheral edges of the external lead terminals 4, and tie bar holders 8 arranged at the four corners are all iron / nickel alloys. It is made of Kovar's thin plate, and is integrally formed by pressing one thin plate. The large number of external lead terminals 4 and the central wiring board 2 are fixed to each other by brazing. Four insulating tie bars 10 are arranged near the inside of the lead frame body 6, and are fixed to the tie bar holders 8, respectively. The insulating tie bar 10 is made of ceramic, and the external lead terminals 4 are brazed and fixed by silver brazing to the many brazing pad portions 12 formed by the metallizing technique on the surface thereof.

FIG. 2 is a plan view showing the insulating tie bar 10. The body of the insulative tie bar 10 is made of a ceramic made of alumina, and the external lead terminals 4 are formed on the surface thereof.
A large number of brazing pad portions 12 for electrically and independently brazing and fixing are formed by a metallizing technique.
The brazing pad portion 12 is formed by forming a tungsten (W) layer 14 on the surface of a ceramic made of alumina by a metallizing technique and applying nickel (Ni) plating 16 thereon. The shape of each brazing pad portion 12 is an uneven shape having a wide portion 24 and a narrow portion 26,
The wide portion 24 has a convex arc shape. Further, three or four wide portions 24 are arranged in one brazing pad portion 12, and the wide portions 24 and the narrow portions 26 are arranged alternately in adjacent brazing pad portions 12. It is made into a shape. By doing so, the gap between the brazing pad portions 12 adjacent to each other can be made as large as possible, and the length of the interval where the gap is small can be shortened. It is possible to minimize the short circuit failure of the above. Also, one brazing pad 12 has a wide portion 2
Since at least 3 of 4 are secured, brazing strength of the external lead terminal 4 to the insulating tie bar 10 can be sufficiently secured in this portion. In addition, the width of the narrow portion 26 of the shape of each brazing pad portion 12 is set to 1.5 times the width of the external lead terminal 4, and the wide portion 2 of the arc shape is formed.
The maximum width of 4 is set to 2.55 times the width of the external lead terminal 4. By setting in this way, the risk of short circuit can be avoided and the brazing strength of the external lead terminal 4 can be secured.

FIG. 3 is a sectional view showing a step of brazing the external lead terminal 4 to the insulating tie bar 10. The main body of the insulating tie bar 10 is made of ceramic made of alumina. A large number of brazing pad portions 12 have a tungsten (W) layer 14 formed on the surface of a ceramic made of alumina by a metallizing technique, and a nickel (N) layer 14 is formed thereon.
i) It is formed by plating 16. A silver brazing thin plate 18 is placed on a large number of brazing pad portions 12, and external lead terminals 4 are placed thereon, and the temperature is set to 800 ° C. in a furnace.
The thin plate 18 of silver solder is melted by heating as described above, and the external lead terminals 4 are brazed.

FIG. 4 is a plan view of an essential part of the insulating tie bar 10 showing the second embodiment. In this embodiment,
A large number of brazing pad portions 42 on the surface of the insulating tie bar 10.
Is a semi-circular wide part 4 that projects laterally.
4 and a linear narrow portion 46. Then, in the brazing pad portions 42 adjacent to each other, the wide portion 44 and the narrow portion 46 are arranged so as to be staggered. In this way, by forming the wide portion 44 to have a shape protruding to only one side, one brazing pad portion 42 has a larger width portion 44.
Can be provided, and the brazing strength of the external lead terminal 4 is improved.

FIG. 5 is a plan view of an essential part of the insulating tie bar 10 showing the third embodiment. In this embodiment,
The shape of the wide portion 54 of the brazing pad portion 52 is substantially rectangular, and the wide portion 54 and the narrow portion 56 of the adjacent brazing pad portions 52 are arranged so as to be staggered. There is.

FIG. 6 is a plan view of an essential part of the insulating tie bar 10 showing the fourth embodiment. In this embodiment,
The shape of the brazing pad portion 62 is a continuous shape of triangles protruding on both sides, the protruding portion of the triangle constitutes the wide portion 64 of the brazing pad portion 62, and the recessed portion of the triangle is narrow. It constitutes part 66. Further, in the brazing pad portions 62 adjacent to each other, the wide portion 64 and the narrow portion 66 are arranged so as to be staggered. With such a shape, it is possible to increase the area of the wide portion 64 while ensuring the space between the adjacent brazing pad portions 62, and thus the external lead terminal 4 can be formed.
The brazing strength is improved.

In the embodiment described above, the insulating tie bar 10 is made of a ceramic made of alumina, but it is obvious that a ceramic other than alumina may be used.

[0019]

As described above, according to the present invention, since the shape of the brazing pad portion on the surface of the insulating tie bar is an uneven shape having a wide portion and a narrow portion, the external lead terminal Even if the pitch is small, there is an excellent effect that the brazing strength between the external lead terminal and the insulating tie bar can be secured while preventing a short circuit between the adjacent brazing pad portions of the insulating tie bar.

[Brief description of drawings]

FIG. 1 is a plan view of a flat type integrated circuit package which is a wiring board with leads.

FIG. 2 is a plan view showing an insulating tie bar.

FIG. 3 is a cross-sectional view showing a step of brazing an external lead terminal to an insulating tie bar.

FIG. 4 is a plan view of a main part of an insulating tie bar showing a second embodiment.

FIG. 5 is a plan view of a main part of an insulating tie bar showing a third embodiment.

FIG. 6 is a plan view of a main part of an insulating tie bar showing a fourth embodiment.

FIG. 7 is a plan view of a main part of a conventional insulating tie bar.

[Explanation of symbols]

2 wiring board 4 External lead terminal 10 Insulating tie bar 12 Brazing pad 18 Silver brazing sheet 24 wide part 26 Narrow part

Claims (4)

(57) [Claims] 1. A wiring board for mounting an integrated circuit,
A leaded wiring board, comprising: a large number of external lead terminals fixed to the wiring board; and an insulating tie bar to which the large number of external lead terminals are electrically and independently brazed and fixed, The insulative tie bar has a large number of brazing pad portions for brazing and fixing the lead terminals one by one electrically and independently on the surface thereof, and the shape of each brazing pad portion is a wide portion. And a wiring board with leads, wherein the wiring board has leads and recesses. 2. The width of the narrow portion of the brazing pad portion on the surface of the insulating tie bar is 1 to the width of the external lead terminal.
2. The leaded wiring board according to claim 1, wherein the width is 1.5 times, and the width of the wide portion of the brazing pad portion is 2 to 3 times the width of the external lead terminal. 3. The shape of the plurality of brazing pad portions is a shape in which a wide portion and a narrow portion are arranged alternately in adjacent brazing pad portions. A wiring board with leads according to item 1 or 2. 4. The wiring board with leads according to claim 1, wherein the brazing pad portion has an arc shape in its wide portion.