JP3047228U - Printed board - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When a flat package type electronic component is mounted on a printed circuit board by a dipping method, a bridge is generated between leads. Therefore, conventionally, a large-sized discard land is provided at the end of the land row of the printed circuit board to prevent the occurrence of a bridge. However, the conventional discard land cannot completely eliminate the bridge. SOLUTION: The size of the conventional discarded land is 7 to 8 times the land area of one land in the land row. In the present invention, the area of the discarded land is set to be 10 times or more of one land area of the land row.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention is intended for mounting flat package electronic components such as QFPs and SOICs having a large number of leads on the side surface of the main body, particularly flat package electronic components having a narrow lead pitch of less than 0.8 mm. Regarding suitable printed circuit boards.

[0002]

[Prior art]

 In recent years, as electronic devices have become smaller, electronic components used in electronic devices have also become smaller and more sophisticated. In order to enhance the functions of electronic components, it is necessary to install a large number of leads. To reduce the size, the number of leads must be thin and the lead pitch must be narrow. The mounting of such miniaturized and highly functional electronic components on a printed circuit board is performed by soldering the leads of the electronic component to the lands of the printed circuit board.

In general, there are a soldering method, an immersion method, and a reflow method as a soldering method for mounting an electronic component on a printed circuit board.

[0004] The ironing method is a technique in which a worker holds a greased wire solder in one hand, and holds a greased wire solder on the lead of an electronic component mounted on a printed circuit board with the other hand holding a iron. And soldering the leads and lands by placing a trowel on it and heating it with a trowel to melt the wire solder. This ironing method is not suitable for soldering such as a flat package type electronic component having a large number of leads because soldering must be performed for each soldering portion. The ironing method is a method for removing uneven soldered parts that cannot be soldered by other soldering methods, retrofitting of electronic parts without heat resistance, or defects such as bridges generated by other soldering methods. This is a suitable method for correction.

The immersion method is a method of soldering with an automatic soldering device provided with a fluxer, a preheater, a jet solder bath, a cooler, and the like. In an automatic soldering machine, flux is applied to a printed circuit board with a fluxer, preheated with a preheater, solder is applied in a jet solder bath, and cooled with a cooler. This immersion method is extremely excellent in productivity because many soldered parts can be soldered in one process. Therefore, it is widely used in the production of so-called home appliances such as televisions, videos, and audios, which must be produced in mass production and whose production costs must be reduced. However, in the immersion method, the entire soldering surface of the printed circuit board is brought into contact with the molten solder, so in flat-package electronic components with a narrow lead pitch, a bridge occurs in which the solder spreads and adheres. there were.

[0006] In the reflow method, a solder paste composed of powder solder and flux is printed and applied to a soldering portion of a printed circuit board, electronic components are mounted on the applied portion, and then a reflow furnace, an infrared irradiation device, a laser device, This is a method of soldering electronic components and printed circuit boards by heating with a heating device such as a high-temperature steam device to melt the solder paste. This reflow method applies solder paste only to the necessary parts, so that solder does not adhere to unnecessary parts and it does not cause bridging even in narrow-pitch flat-package electronic components. A soldered part is obtained. However, in the reflow method, it is necessary to use good-quality powdered solder with uniform grain size and use a heating device that is precisely adjusted so that the temperature distribution is uniform. However, it was economically problematic in that it became expensive. For this reason, the reflow method is not suitable for inexpensive home appliances and is intended for high-grade electronic devices such as computers and communication devices that require reliability and precision.

By the way, since a flat package type electronic component has a large number of leads arranged at narrow intervals, the only way to mount the flat package type electronic component on a printed circuit board is by a reflow method with less occurrence of a bridge. Was. In recent years, home appliances have been using flat package type electronic components due to the trend of miniaturization.In order to manufacture home appliances using flat package type electronic components at low cost, they must be mounted by the immersion method. Have to be. However, when the flat package type electronic component is mounted by the immersion method, there has been a problem that a large number of bridges are generated as described above.

Therefore, recently, when a flat package type electronic component is soldered by an immersion method, a measure for suppressing a bridge has been taken. As a countermeasure against bridging in a flat package type electronic component, for example, as shown in FIG. 1, one end of a row of leads 4... A land was installed, or the flat package type electronic component 2 was mounted at an angle of 45 degrees with respect to the traveling direction (large arrow) of the automatic soldering apparatus.

[0009]

[Problems to be solved by the invention]

 Measures such as placing a discard land at one end of the lead row of the flat package type electronic component or mounting it at an angle of 45 degrees are very effective in preventing the bridge, but the bridge still occurred. A printed circuit board with a bridge requires a great deal of work by an operator to correct it with a trowel, so that the economic merit of the immersion method cannot be realized. The purpose of this invention is to improve the abandoned land, which is a measure to prevent bridges, and to further suppress the occurrence of bridges.

[0010]

[Means for Solving the Problems]

 The present inventors have conducted intensive studies on the causes of bridges when flat package type electronic components are mounted on a printed circuit board and soldered by the immersion method.As a result, there are many causes of bridges. As one of the reasons, we found out that the size of abandoned land also affects the occurrence of bridges, and completed the present invention.

The present invention provides a printed circuit board on which a flat lead type electronic component having a narrow lead pitch is mounted, wherein the area of a discarded land is at least 10 times the area of another land. is there.

By the way, a discarded land is formed at the final end (final end in the traveling direction of the printed circuit board) of a large number of land rows in a printed circuit board for a flat package electronic component to be soldered by an immersion method. This is a large land. The area of the conventional land was 7 to 8 times that of other lands.

[0013] The bridge preventing action of the discarded land is considered as follows. When a small amount of molten solder comes into contact with a large amount of molten solder, it is drawn into a large amount of molten solder. In other words, when the printed circuit board is separated from the molten solder while being in contact with the molten solder in the jet solder bath, the rows of lands installed on the printed circuit board gradually separate from the molten solder from the front. When the land rows are in contact with the molten solder, there is molten solder between all the lands, and when the printed circuit board separates, a small amount of molten solder that was Is drawn into the large amount of molten solder existing in the land row behind it. When the tail of the land row separates from the molten solder, if there is no land row behind it, the molten solder attached to the tail returns to the front and forms a bridge. Therefore, if a large-area waste land is installed further behind the last land in the land row, a large amount of molten solder attached to the waste land draws in the molten solder attached to the last land and forms a bridge. Not to form.

However, if the size of the discarded land is not a certain size or more, the amount of the molten solder adhering to the discarded land does not increase. Is formed. The inventors of the present invention have conducted intensive studies on the size of the land that can completely draw the molten solder between the leads. As a result, the size of the discarded land is at least 10 times the area of the land in the land row, preferably It turned out that an area 12 times or more was necessary.

In the present invention, the disposal land is installed at a position separated from the last land of the land row, or is integrated with the last land.

[0016]

[Embodiment of the invention]

 The printed circuit board targeted by the present invention is a printed circuit board on which a flat package type electronic component having a narrow lead pitch of less than 0.8 mm is mounted. When the lead pitch of the flat package type electronic component is 0.8 mm or more, the bridge can be sufficiently suppressed even if the area of the discarded land is 7 to 8 times as large as the other land.

In the present invention, the area of the discarded land is set to be at least ten times larger than the area of the other land, that is, the area of one of the lands on which the leads of the flat package type electronic component are mounted. If the area of the discarded land is less than 10 times the area of the other land, a bridge will be generated. The reason for this is that if the area of the discarded land is less than 10 times the area of the other lands, the amount of molten solder adhering to the discarded land is small, and as a result, the force to draw in the molten solder adhering to the land row becomes weak. This is because bridging is likely to occur.

The relationship between the discarded lands and the land rows on the printed circuit board of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a printed circuit board of the present invention and a flat package type electronic component mounted on the printed circuit board. A plurality of rows of lands 4 are provided on the printed board 1 at positions corresponding to the leads 3 of the flat package type electronic component 2. As shown in the figure, the flat package type electronic component 2 is mounted at an angle of 45 degrees with respect to the traveling direction (large arrow) of the printed board during soldering. Behind the last land 4y, 4y of the upper left land row 4a and the upper right land row 4a in the figure, there are rectangular discarded lands 5m, 5m, and the lower left land row 4b, the lower right land in the figure. In the rear of the last land 4z, 4z of the land row 4b, a circular discard land 5n is provided.

[0019]

【Example】

The embodiment is a printed circuit board on which a QFP having a lead pitch of 0.5 mm and 100-pin leads is mounted. The size of the land in the land row is 2.0 mm × 0.3 mm (0.6 mm ² ), and the size of the land is 2. A rectangular discard land of 0 mm x 3.6 mm (7.2 mm ² : 12 times the other land area) is installed. In addition, a discarded land with a diameter of 3.4 mm (9.0 mm ² : 15 times the size of other land) is installed behind the last land of the left and right land rows. Four QFPs were mounted on the printed circuit board of the example and soldered by the dipping method. After soldering, the defect rate was measured. As a result, the defect rate was 0.02%. Here, the failure rate is obtained by dividing the number of bridges generated by the total number of pins.

[0020]

[Comparative example]

This is a printed circuit board on which the same QFP as in the embodiment is mounted, and the size of the land in the land row is 2.0 mm × 0.3 mm (0.6 mm ² ). End of the land and spaced rearwardly 2.0 mm × 2.4 mm of land row on the left and right: Yes installed a rectangular discarded land (4.8 mm ² 8 times the other land area), also left under At the back of the land row, which is separated from the last land, there is a 2.4 mm diameter discard land (4.5 mm ² : 7.5 times the area of the other land). Four QFPs were mounted on the printed circuit board of the comparative example, and soldering was performed by an immersion method. After soldering, the defective rate was measured, and as a result, the defective rate was 1.2%.

[0021]

[Effect of the invention]

 It was thought that when soldering flat-package electronic components with a narrow pitch by the immersion method, no matter how bridging prevention measures were taken, the occurrence of bridges was considered unavoidable. By merely making the size of the land more than five times the size of the lands in the land row, the occurrence of bridges can be suppressed to a very low level, which has a great effect in contributing to the electronic equipment industry.

[Brief description of the drawings]

FIG. 1 is an explanatory view of mounting a flat package type electronic component on a printed circuit board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Flat package type electronic component 3 Lead 4 Land 4a Land row 4y, 4z Last land 5m, 5n Discard land

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Chiaki Komori 1-2-11 Ikenohata, Taito-ku, Tokyo (72) Inventor Hideaki Fukuda 1-2-11 Ikenota, Taito-ku, Tokyo In Aiwa ( 72) Inventor Takashi Usaba 1-2-11 Ikenohata, Taito-ku, Tokyo Inside Aiwa Co., Ltd.

Claims (3)

[Utility model registration claims] 1. A printed circuit board on which a flat-package electronic component having a narrow lead pitch is mounted, wherein the area of a waste land is at least 10 times the area of another land. 2. The printed circuit board according to claim 1, wherein the waste land is provided apart from the last land of the land row. 3. The printed circuit board according to claim 1, wherein the waste land is integrated with the last land in the land row.