JPH088510A - Leadless chip carrier - Google Patents

Abstract

PURPOSE:To provide a leadless chip carrier which has a mounting pad capable of improving solder adhesiveness between a mother board and the leadless chip carrier, and enables mounting with high continuity reliability. CONSTITUTION:In a leadless chip carrier having an electrode edge conductor 3 provided on a lateral side 2 of a printed wiring board 1 and a mounting pad 6 linked with the electrode edge conductor 3 and formed on a back side 5 of the printed wiring board 1, the minimum distance from every point on a curve 7 formed by a lateral side 4 of the electrode edge conductor 3 and the back side 5 to an end part 21 of the mounting pad 6 surrounding the curve 7 is not more than 0.6mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leadless chip carrier used for mounting electronic parts such as semiconductor chips and electric parts.

[0002]

2. Description of the Related Art Conventionally, as shown in FIGS. 4 and 5, a recess 8 for mounting a semiconductor chip is formed on the surface of a printed wiring board 1.
There is known a leadless chip carrier (hereinafter, referred to as LCC) configured by providing an electrode edge conductor 3 formed by cutting a through hole in an axial direction and remaining on the side surface 2. Such an LCC 9 includes a printed wiring board 1, a recess 8 for mounting a semiconductor chip on a surface 10 of the printed wiring board 1,
A signal circuit 11 formed around the recess 8; an electrode edge conductor 3 that is electrically connected to the signal circuit 11 and is exposed on the side surface 2;
Further, a mounting pad 6 formed on the back surface 5 of the printed wiring board 1 is provided so as to be connected to the electrode edge conductor 3.

When the LCC is mounted on a mother board made of a printed wiring board, the mounting pads formed on the back surface of the LCC and the connecting pads on the mother board are connected by using solder as a connecting material, and the mother board is connected. It is known how to implement.

As shown in FIG. 3, a method of mounting this LCC on a mother board is to apply a fixed amount of solder cream 14 to a connecting pad 13 formed on the mother board 12 and superimpose the LCC 9 on the mother board 12. A method is known in which heating is performed to melt the solder cream 14, and then the heat is removed to re-solidify the solder for welding.

However, as shown in FIG. 7, the LCC described above is used.
When using the method of welding the motherboard with the LCC
The shortest distance from all points of the mounting pad 6 of No. 9 on the ridge line 7 formed by the side surface 4 and the back surface 5 of the electrode edge conductor 3 to the edge portion 21 of the mounting pad 6 surrounding the ridge line 7. L
1 is 1 mm to 1.5 mm, and the area of the mounting pad 6 is large. Therefore, when the solder cream 14 applied to the connection pad 13 is melted, the solder flowing along the surface of the mounting pad 6 of the LCC 9 is used. Is larger than the amount of solder flowing along the side surface 4 of the electrode edge conductor 3, and the rise of the molten solder due to the surface tension of the side surface 4 of the electrode edge conductor 3 is small, and Connection pad 1
In some cases, the solder fillet 15 formed at the boundary portion with 3 was not sufficiently formed. Further, when the thickness of the gold plating 16 of the mounting pad 6 becomes 0.5 μm or more,
When the solder applied to the connection pad 13 is melted, gold diffuses and transfers into the melted solder, a so-called solder erosion phenomenon occurs, the performance of the solder deteriorates, and the fluidity of the melted solder increases. In some cases, the solder fillet 15 formed at the boundary between the electrode edge conductor 3 and the connection pad 13 is not sufficiently formed, and the solder fillet 15 having a surface substantially parallel to the mother board 12 may be formed. It was In this way, the solder fillet 15 having a small amount of solder lifted to the electrode edge conductor 3 and having a surface substantially parallel to the mother board 12 has a low adhesive force for bonding the LCC 9 and the mother board 12, resulting in poor connection. However, there is a problem that the reliability of conduction is impaired.

[0006]

The present invention has been made in view of the above circumstances, and its object is to:
An object of the present invention is to provide a leadless chip carrier which has a mounting pad capable of improving the solder adhesive force between the mother board and the leadless chip carrier and which can be mounted with high conduction reliability.

[0007]

A leadless chip carrier according to claim 1 of the present invention has an electrode edge conductor 3 on a side surface 2 of a printed wiring board 1 and is connected to the electrode edge conductor 3 for printing. In a leadless chip carrier having a mounting pad 6 formed on the back surface 5 of the wiring board 1,
From all points on the ridge line 7 formed by the side surface 4 and the back surface 5 of the electrode edge conductor 3, the mounting pad 6 surrounding the ridge line 7 is formed.
The shortest distance at the edge portion 21 is within 0.6 mm.

Further, in the leadless chip carrier according to claim 2 of the present invention, the thickness of the gold plating 16 of the mounting pad 6 formed on the back surface 5 of the printed wiring board 1 is
It is characterized by being 0.05 μm to 0.1 μm.

[0009]

The leadless chip carrier according to the present invention has the electrode edge conductor 3 on the side surface 2 of the printed wiring board 1, is connected to the electrode edge conductor 3, and is formed on the back surface 5 of the printed wiring board 1. In the leadless chip carrier having the mounting pads 6, from all points on the ridge line 7 formed by the side surface 4 and the back surface 5 of the electrode edge conductor 3, the ridge line 7 is formed.
The shortest distance at the edge portion 21 of the mounting pad 6 that surrounds the.
Since the distance is within 6 mm, for example, when the leadless chip carrier is bonded to the mother board 12 formed of a printed wiring board, the connecting pad 13 of the mother board 12 is used.
When the solder cream 14 applied to is melted, the melted solder more remarkably flows along the side surface 4 of the electrode edge conductor 3 than the surface of the mounting pad 6. Further, the thickness of the gold plating 16 of the mounting pad 6 formed on the back surface 5 of the printed wiring board 1 which constitutes the leadless chip carrier is set to 0.05 μm to 0.1 μm.
When m, the amount of gold diffused in the molten solder is small,
It is possible to reduce the performance deterioration of the molten solder and maintain the fluidity of the molten solder.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0011]

FIG. 4 is a perspective view of the back surface of a leadless chip carrier according to an embodiment of the present invention, and FIG. 5 is a perspective view of the front surface of this leadless chip carrier.

On a surface 10 of a printed wiring board 1 which constitutes a leadless chip carrier (hereinafter referred to as LCC) of one embodiment of the present invention, a recess 8 for mounting a semiconductor chip, a signal circuit 11, and a side surface 2 are formed. Is provided with an electrode edge conductor 3 and a back surface 5 with a mounting pad 6. This signal circuit 11 is
One end is provided side by side around the recess 8 for mounting the semiconductor chip, and the other end is provided continuously with the electrode edge conductor 3 formed on the side surface 2 of the printed wiring board 1. The electrode edge conductor 3 is formed, for example, by cutting a plated through hole that penetrates the front and back of the printed wiring board 1 in the axial direction and remains, and a signal circuit 11 formed on the front surface of the printed wiring board 1.
And the mounting pad 6 formed on the back surface 5 are electrically connected by plating, and there are a combination of a plurality of through holes and a rectangular top surface with a cutout end.

As the printed wiring board 1, an insulating resin substrate obtained by hardening a resin of a prepreg obtained by impregnating a base material with a resin varnish and drying it, or a ceramic insulating substrate such as alumina is used. The base material of the insulating resin substrate is not particularly limited, but an inorganic material such as glass fiber or aramid fiber is preferable because it is excellent in heat resistance and moisture resistance. Also, a cloth of organic fibers having excellent heat resistance or a mixture thereof can be used as a substrate. The resin in the varnish to be impregnated into the base material is an epoxy resin,
Polyimide resin, fluororesin, phenol resin, polyester resin, polyphenylene oxide resin, etc. alone,
Modified products and mixtures are used.

The signal circuit 11 and the mounting pad 6
May be formed by etching a metal foil attached to the printed wiring board 1 or may be formed by metal plating on the surface 10 of the printed wiring board 1. The method is not particularly limited.

The feature of the present invention resides in the mounting pad formed on the back surface of the above-mentioned printed wiring board. As shown in FIG. 1, the mounting pad is provided on one side of the rectangular mounting pad 6 with an electrode edge conductor. 3 is formed and the open ends 17, 17
Is formed on the back surface 5 of the printed wiring board 1 and has an edge portion 21 surrounding the ridge line 7 formed by the side surface 4 of the electrode edge conductor 3 and the back surface 5 of the printed wiring board 1. . The mounting pad 6 is formed by cutting a through hole having a diameter of 0.35 mm in the axial direction and remaining, and from the ridge line 7 formed by the side surface 4 of the electrode edge conductor 3 and the back surface 5 of the printed wiring board 1, An edge portion 18 parallel to the side surface 2 of the printed wiring board 1 is provided at a position 0.3 mm in the vertical direction from the side surface 2 of the printed wiring board 1. At a distance from each other, the edges 18 and 20 are parallel to each other in a direction perpendicular to the edge 18 and face each other.

From all points on the ridge line 7 formed by the side surface 4 of the electrode edge conductor 3 of the mounting pad 6 and the back surface 5 of the printed wiring board 1, the edge of the mounting pad 6 surrounding the ridge line 7 The shortest distance L2 to the portion 21 is preferably within 0.6 mm, and its shape is the electrode edge conductor 3
Shape, and the connecting pad 13 of the motherboard 12
Is determined by the shape of. In addition, two parallel sides 1 facing each other from the open end 17 of the electrode edge conductor 3 are parallel to each other.
Even if the dimension between 9 and 20 is the same as the width of the open end 17,
Large leadless chip carrier 9
The width is determined by the width of the connection pad 13 of the motherboard 12 on which is mounted.

The gold plating 16 plated on the surface of the mounting pad 6 has a plating thickness of 0.07 μm. This plating thickness prevents gold from diffusing and transferring to the molten solder when the solder is welded. 0.1 μm or less is preferable, and in addition, 0.05 μm or more is preferable in order to improve adhesiveness.

Next, an LCC which is an embodiment of the present invention is
As shown in FIG. 6, a method of mounting on a mother board made of a printed wiring board having signal circuits and connection pads formed on the surface will be described.

First, a predetermined amount of solder cream 14 is applied to the connection pads 13 formed on the mother board 12 by a dispenser. Next, as shown in FIG. 3, the LCC 9 is superposed so that the connection pad 13 of the mother board 12 and the mounting pad 6 of the LCC 9 face each other. next,
The portion coated with the superposed solder cream 14 is heated to melt the solder cream 14. As shown in FIG. 2, the melted solder cream 14 flows along the side surface 2 of the electrode edge conductor 3 formed on the side surface 2 of the LCC 9 through the mounting pad 6 of the LCC 9, so that the solder cream 14 is on the surface. The tension rises along the side surface 4 of the electrode edge conductor 3 to form a solder fillet 15 at the boundary between the electrode edge conductor 3 and the connection pad 13. Further, heat is removed to re-solidify the solder and weld the LCC 9 to the mother board 12.

The method of applying the solder to the connection pads 13 may be the method of applying the solder cream 14 with the dispenser as described above, the method of forming the solder bumps, or the method of dipping in the reflow bath. Is not limited.

Thus, using the LCC of the present invention,
The solder that is heated and melted is easily lifted to the side surface 4 of the electrode edge conductor 3, and the surface of the solder is the mother board 1
Solder fillet 1 that has an inclined surface at an angle of about 45 ° to 2
5 can be stably formed, and strong mounting can be performed.

[0022]

As described above, according to the leadless chip carrier of the present invention, the mounting pads constituting the leadless chip carrier are formed by the side surface 4 and the back surface 5 of the electrode edge conductor 3. From all points on ridge line 7,
Since the shortest distance at the edge portion 21 of the mounting pad 6 surrounding the ridge line 7 is formed within 0.6 mm, and the plating thickness of the mounting pad is 0.05 μm to 0.1 μm, for example, When mounting on a mother board such as a printed wiring board, the solder melted by heating rises to the side surface of the electrode edge conductor due to surface tension, and the surface of the solder has an inclined surface at an angle of about 45 ° to the mother board. Since the solder fillet can be formed in a stable manner, it is possible to mount the solder fillet with high strength, improved solder adhesion, and high conduction reliability.

[Brief description of drawings]

FIG. 1 is a side view of a main part of a leadless chip carrier according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part of a leadless chip carrier according to an embodiment of the present invention mounted on a motherboard.

FIG. 3 is a cross-sectional view of essential parts in which a leadless chip carrier is overlaid on a mother board.

FIG. 4 is a perspective view of the leadless chip carrier of the present invention with the surface thereof facing upward.

FIG. 5 is a perspective view of the leadless chip carrier of the present invention with the back surface facing upward.

FIG. 6 is a perspective view illustrating a method of mounting the leadless chip carrier of the present invention on a motherboard.

FIG. 7 is a cross-sectional view of essential parts in which a conventional leadless chip carrier is mounted on a motherboard.

[Explanation of symbols]

 1 printed wiring board 2 side surface 3 electrode edge conductor 4 side surface 5 back surface 6 mounting pad 7 ridge line 8 recess 9 leadless chip carrier 10 surface 11 signal circuit 12 motherboard 13 connection pad 16 gold plating

Claims (2)

[Claims] 1. An electrode edge conductor (3) is provided on a side surface (2) of a printed wiring board (1), and the electrode edge conductor (3) is provided.
In a leadless chip carrier having a mounting pad (6) formed on the back surface (5) of a printed wiring board (1), the side surface (4) and the back surface (5) of an electrode edge conductor (3). From all points on the ridgeline (7) formed by
The edge portion (2) of the mounting pad (6) surrounding this ridge (7)
A leadless chip carrier characterized in that the shortest distance to 1) is within 0.6 mm. 2. A back surface (5) of the printed wiring board (1).
Of the mounting pad (6) formed on the
The leadless chip carrier according to claim 1, wherein the thickness of 6) is 0.05 μm to 0.1 μm.