JPH11298125A - Surface mounting land - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface mounting land for preventing occurrence of a bridge between leads related to a surface mounting integrated circuit such as QFP(quad flap package). SOLUTION: A land 102 comprises a land main body 206 and first and second wide parts 208 and 210 which are wider than the land main body 206, with the land main body 206 provided at center, while the first and second wide parts 208 and 210 are provided on the both ends. When a lead 204 is jointed with solder to the land 102, a part from a tip end part 212 of the lead 204 to a first clinch part 214 is made to hit the land main body 206 of the land 102 and the first wide part 208, with a melted solder concentrating on the tip end part 212 and the first clinch part 214, resulting in expansion to the first wide part 208 and second wide part 210 for solidification to form a front fillet and a back fillet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a surface mounting land provided on a circuit board for mounting a surface mounting integrated circuit such as a quad flat package (QFP).

[0002]

2. Description of the Related Art FIG. 6 shows an arrangement of a conventional surface mounting land 60 provided on a circuit board surface corresponding to a lead of a quad flat package (QFP) which is one of surface mounting integrated circuits. It is a top view showing an example. The conventional land 60 for surface mounting has a large number of lands 62 arranged in parallel on the circuit board surface, and has a long and narrow rectangular shape. In addition, each land interval is QFP
In many cases, the distance is very narrow, about 1 mm or less.

FIG. 7 is an explanatory view showing a state in which a lead 70 of a QFP is joined to each land 62 by solder 72. Hereinafter, a method of soldering the lead 70 to the land 62 will be described.

[0004] First, cream solder is printed and applied to each land 62 at a constant thickness, and the lands 6 are applied via the cream solder.
The lead 70 of the QFP is placed on 2. Thus QF
In the state where P is placed, reflow heating is performed by passing the whole through a reflow furnace. Then, the solder in the reflow-heated cream solder is melted, and the land 62 and Q
The lead 70 of the FP is soldered.

[0005] However, during soldering, the surface mounting lands 60 of the above-mentioned conventional example have a very narrow land spacing of 1 mm or less. Therefore, FIG. 8 shows a case where a large amount of cream solder is applied. As described above, there is a problem that the bridge 80 is generated between the lands 62 when the cream solder is melted. In particular, at the clinch portion 74 of the lead 70 where the solder 72 collects most, the bridge 80 is likely to occur because the surface tension of the solder 72 remains large.

In order to prevent the occurrence of such a bridge, a surface mounting land provided with a wide portion as disclosed in JP-A-6-268360 and JP-A-7-147479 has been proposed. Proposed. The land disclosed in Japanese Patent Application Laid-Open No. 6-268360 has a circular wide surface provided in a part of the land body.
The land disclosed in 147479 has a land in a teardrop shape, and the lands having the teardrop shape are alternately arranged.

[0007]

However, even in the land disclosed in the above publication, the occurrence of bridges cannot be completely prevented due to the surface tension of the solder. Therefore, a surface mounting land capable of preventing bridges between leads from being realized with higher accuracy than the conventional technology and further improving the reliability of solder bonding is desired.

The present invention has been made in view of the above circumstances, and in a surface mount integrated circuit such as a quad flat package (QFP), a bridge generated between leads can be prevented with higher accuracy than in the prior art. An object of the present invention is to provide a surface mounting land capable of improving the reliability of solder bonding.

[0009]

According to a first aspect of the present invention, there is provided a surface mounting land to which a lead of a surface mounting integrated circuit is soldered, the land corresponding to the shape of the lead. A land body that is elongated in shape and at least one wide portion that is wider than the land body, and the tip of the lead that comes into contact with the land body when the surface-mount integrated circuit is mounted. The bent portion on the portion side is the surface mounting land located on the wide portion side from the boundary between the land main body and the wide portion.

In the above configuration, since the solder concentrates on the wide portion side of the bent portion located at the boundary between the land body and the wide portion,
Bridges between the leads are prevented. In addition, high reliability is obtained in the solder bonding between the lead and the land for surface mounting.

The invention according to claim 2 is the land for surface mounting according to claim 1, wherein a first wide portion and a second wide portion are located at both ends of the land body as the wide portion.

In the invention according to a third aspect, the bent portion is located at a boundary between the land main body and the second wide portion, and a portion from the distal end portion of the lead to the bent portion is the land. The surface mounting land according to claim 2, wherein the land is joined over the main body and the first wide portion.

In the above configuration according to the second and third aspects of the present invention, when the molten solder flows, it flows in the two directions of the first wide portion and the second wide portion, and the first wide portion and the second wide portion. Since the solder is concentrated around the wide portion 2, there is no risk of bridging, and the solder is securely joined.

According to a fourth aspect of the invention, there is provided the surface mounting land according to the first aspect, wherein the width of the wide portion is 1.2 to 1.4 times the width of the land body.

In the above configuration, the molten solder flows naturally to the wide portion due to surface tension.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention relating to a surface mounting land on a circuit board used for solder bonding will be described below with reference to the drawings. FIG. 1 is a plan view showing an arrangement of surface mounting lands 10 corresponding to leads of a quad flat package (QFP) which is one of surface mounting integrated circuits according to an embodiment of the present invention.

The surface mounting lands 100 are provided on the surface of a circuit board such as a printed wiring board.
Are arranged in parallel on the circuit board surface so as to draw a square, and the interval between the lands 102 depends on the lead interval of the QFP mounted on the surface mounting land 100, and is about 1 mm or less in many cases. And is very narrow.

FIG. 2 is an explanatory view showing the relative position between the shape of the land 102 of the QFP 200 and the lead 204 extending from the QFP main body 202. The land 102 includes a land main body 206 and a first wide portion 208 and a second wide portion 210 formed at both ends of the land main body 206 and wider than the land main body 206. However, in the present embodiment, the wide portion on the outer side in FIG.
8. The wide portion on the inner side in FIG. 1 is referred to as a second wide portion 210. Further, the width of the land body 206 is formed to be equal to or narrower than the width of the lead 102, and the first wide portion 208 is formed.
The second wide portion 210 is formed wider than the land body 206.

More specifically, the width of the land body 206 is approximately 0.25 to 0.3 mm, and the width of the first wide portion 208 and the second wide portion 210 is approximately 1. It is 2 to 1.4 times.

The lead 204 of the QFP 200 is a gull-wing type, and has a first bent portion 214 (hereinafter, referred to as a first clinch portion) on the tip portion 212 side of the lead 204 and a second bent portion on the QFP main body 202 side. A portion 216 (hereinafter, referred to as a second clinch portion) is provided. When the lead 204 and the land 102 are soldered, the first clinch portion 214
, The land main body 206 of the land 102 and the first wide portion 208 are joined so as to be in contact with each other.

At this time, as shown in FIG. 2, the first clinch portion 214 is located at the boundary between the land main body 206 and the second wide portion 210, and the distal end portion 212 is located at the middle of the first wide portion 208. I do.

Next, in the surface mounting of the QFP 200,
The step of soldering the land 102 and the lead 204 will be described. FIG. 3 is a sectional view showing a state before the land 102 and the lead 204 are joined by soldering, and FIG.
FIG. 5 is a cross-sectional view showing a state where the lead wire 02 and the lead 204 are soldered, and FIG. 5 is a top view of FIG.

The lead 20 is placed on the land 102 on which the cream solder 302 is applied by printing at a constant thickness at the position shown in FIG.
The QFP 200 is mounted so that the QFP 4 is arranged. This state is shown in FIG. The circuit board 30 in the state of FIG.
4 and the QFP 200 are passed through a reflow furnace and heated by reflow, whereby the cream solder 302 is melted. At this time, the molten solder is applied to both ends of the contact portion between the lead 204 and the land 102 due to surface tension, that is, the lead 204
In the vicinity of the front end portion 212 and the first clinch portion 214.

However, in this specification, the solder concentrated at the tip 212 of the lead 204 is applied to the front fillet 404,
The solder concentrated around the first clinch portion 214 is called a back fillet 406.

As shown in FIGS. 4 and 5,
The solder that has been melted and concentrated on the tip portion 212 and the first clinch portion 214 is subjected to the first wide portion 208 by surface tension.
After spreading to the second wide portion 210 and solidifying, the lead 204 is firmly soldered to the land 102 by the solidified solder 402, and the circuit board 304 and the Q
The FP 200 is electrically and mechanically connected.

As described above, since the surface tension in the first wide portion 208 and the second wide portion 210 is eliminated, the rate of occurrence of bridges generated between the lands 102 is drastically reduced. Further, since the soldering reliability of the QFP is determined by the back fillet 406 having the largest amount of solder, the back fillet 406 is formed around the first clinch portion 214 of all the leads 204 and the lead 2 is formed.
In the present invention where the land 04 and the land 102 are joined,
High reliability can be obtained in solder joining.

The front fillet 404 is used not only for the purpose of firmly joining the lead 204 and the land 102 with solder, but also for confirming the solder joint by image inspection or the like. Considering the flow characteristics of the solder, when the solder is melted, the first wide portion 208 and the second wide portion 2
10, the front fillet 404
Is confirmed to be present, it is expected that the back fillet 406 also exists with a high probability. Therefore, when performing an image inspection on the quality of soldering, the bonding state can be checked by checking the front fillet 404.

In the description of the embodiments of the present invention, QFP is taken as an example of the surface mount integrated circuit. However, SOP (Small Outline Package) and QFJ (Q
It may be applied to a land for surface mounting on which a uad Flat J-leaded Package) is mounted.

[0029]

As described above, according to the surface mounting land of the present invention, the land body and the wide portions formed wider than the land body at both ends are provided, and the bent portion of the lead of the surface mounting integrated circuit is provided. Is positioned at the boundary between the land body and one of the wide portions, and the leads and the surface mounting lands are joined by solder. Therefore, there is an effect that a solder defect is eliminated and a bridge generated between the leads can be prevented. This greatly contributes to improving the reliability of the solder joint between the solder and the lead of the QFP.

[Brief description of the drawings]

FIG. 1 is a plan view showing an arrangement of surface mounting lands according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relative position between a land shape and a lead.

FIG. 3 is a sectional view showing a state before a land and a lead are joined by soldering.

FIG. 4 is a cross-sectional view showing a state where a land and a lead are joined by soldering.

FIG. 5 is a top view of FIG. 4;

FIG. 6 is a plan view showing an arrangement of conventional surface mounting lands.

FIG. 7 is an explanatory view showing a state where leads are joined to lands by soldering.

FIG. 8 is an explanatory view showing a bridge generated between lands of a conventional surface mounting land.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Surface mounting land 102 Land 200 QFP 202 QFP main body 204 Lead 206 Land main body 208 First wide portion 210 Second wide portion 212 End portion 214 First clinch portion 216 Second clinch portion 302 Cream solder 304 Circuit board 402 Solder 404 Front fillet 406 Back fillet

Claims (4)

[Claims] 1. A surface mounting land to which a lead of a surface mounting integrated circuit is soldered, wherein: a land body elongated in correspondence with a shape of the lead; and at least one land formed wider than the land body. A bent portion on the tip end side of the lead abutting on the land body in a state where the surface mounting integrated circuit is mounted, the bent portion being wider than a boundary between the land body and the wide portion. A land for surface mounting, characterized in that it is formed so as to be located on the side of a part. 2. The surface mounting land according to claim 1, wherein a first wide portion and a second wide portion are located at both ends of the land body as the wide portion. 3. The bent portion of the lead is located at a boundary between the land main body and the second wide portion, and a portion from the tip to the bent portion of the lead is formed between the land main body and the first wide portion. The land for surface mounting according to claim 2, wherein the land is formed so as to be joined to the wide portion of the land. 4. The width of the wide portion is 1.2 to 1.4 times the width of the land body.
Land for surface mounting as described.