JP3027187U - Printed circuit board for immersion soldering - Google Patents

Abstract

(57) Abstract: When an electronic component having a large number of leads such as QFP is soldered by a dipping method, a bridge is generated between the leads. Conventionally, there has been a printed circuit board in which the land rows are arranged so as to be inclined, or a discard land is arranged behind the land rows, but the bridge is not completely eliminated. The present invention is a printed circuit board that eliminates the occurrence of bridges. SOLUTION: A rectangular land row is arranged to be inclined, and a circular discard land is arranged so as to be spaced from or in contact with the last land of the land row.

Description

[Detailed description of the device]

[0001]

[Technical field to which the device belongs]

 The present invention relates to a printed circuit board on which electronic components are mounted, and particularly to a printed circuit board suitable for soldering electronic components having a large number of leads on all sides.

[0002]

[Prior art]

 With the recent miniaturization of electronic devices, the electronic components used for them are also becoming smaller and more multifunctional.

As a method of soldering these electronic components to a printed circuit board, there are a trowel method, a reflow method, a dipping method and the like.

The troweling method is a method in which an operator holds a greasy wire solder and a trowel and solders a land, which is a soldering portion of a printed circuit board, and a lead of an electronic component, one by one. Since this troweling method is extremely inferior in productivity, it is not suitable for a method having a large number of soldered parts. Therefore, the troweling method is used for repairing defects caused by other soldering methods, or for separately mounting heat-sensitive electronic components after soldering by another soldering method.

The reflow method is a method of soldering with a solder paste composed of powdered solder and paste-like flux with a heating device. In this method, solder paste is applied to the land of the printed circuit board by a printing machine or a discharge machine, then electronic parts are mounted on the solder paste application part, and then reflow oven, infrared ray, laser beam, hot air device, high temperature steam etc. The solder paste is melted and soldered by heating with a heating device.

In the reflow method, the solder paste is applied only to the necessary portions, so that if a high quality solder paste is used, no bridge will be formed that adheres between adjacent lands. Therefore, it is very suitable for soldering an electronic component (hereinafter simply referred to as “multi-lead component”) having a large number of leads such as QFP-IC and SOP-IC.

However, the reflow method requires the use of a solder paste that is time-consuming to manufacture, and requires expensive equipment such as a metal mask for precise printing, a printing machine, and a discharge machine. Initial cost and running cost are both high, which is not economically preferable. Further, in the reflow method, there was a problem that if a solder paste that changed over time was used, bridges, minute solder balls, etc. were generated.

The immersion method is to solder a printed circuit board on which electronic components are mounted by an automatic soldering device. The automatic soldering device is equipped with a soldering device such as a fluxer, preheater, solder bath, and cooler.The flux is applied to the printed circuit board by the fluxer, preheated by the preheater, and soldered by the solder bath. Soldering, and the solder attached to the cooler is completely solidified for soldering.

Since this dipping method allows the solder to be attached to the entire surface of the printed circuit board by one dipping soldering, it is a method that is far superior to other soldering methods in terms of productivity. Also, since the solder used in the dipping method may have a simple shape such as a rod shape or a lump shape, wire drawing like the greasy wire solder used in the trowel method or the solder paste used in the reflow method can be used. It also has the economical advantage that it does not require a great deal of time and effort to manufacture powdered solder.

Therefore, most of the printed circuit boards are soldered by the dipping method, which has excellent economical efficiency and productivity. Even recently, even printed circuit boards with multi-lead components that can be soldered only by the reflow method. Has also been adopted.

However, when a multi-lead component is soldered by the dipping method, a problem occurs that a bridge occurs if the lead pitch, that is, the distance between the centers of adjacent leads is 0.8 mm or less. was there. Recently, multi-lead parts have a so-called fine pitch with lead pitches of 0.5 mm and 0.65 mm. In the electronic equipment industry, even fine-pitch multi-lead parts do not generate bridges by the dipping method. The advent of printed circuit boards has been desired.

Conventionally, many printed circuit boards have been proposed which have an effect of preventing bridging against multi-lead components. For example, a so-called "discard land", which is not a land for soldering leads, may be installed at the end of the arranged land row (Actual No. 54-1 24174, No. 62-65876). (No. 64-2470, No. 2-86175), or at the time of immersion soldering, all the arranged land rows are inclined with respect to the traveling direction of the printed circuit board (Actual number). No. 62-116579, No. 1-116476).

[0013]

[Problems to be solved by the device]

 The effect of preventing land from bridging is to eliminate the bridging between lands by drawing in a large amount of molten solder that has adhered to the land with the molten solder of the large-capacity discarded land. In other words, in immersion soldering, the printed circuit board is carried by the carrier device, contacts the molten solder jetted in the solder bath, and causes the molten solder to adhere to the land, and then separates from the molten solder. When the board is separated by melting, the molten solder of the large-capacity waste land arranged at the end of the land row pulls in the molten solder adhering to the land row to eliminate the bridge between the lands. It has become.

In addition, the effect of preventing bridges in a land row arranged at an angle with respect to the traveling direction of the printed circuit board (hereinafter, simply referred to as “traveling direction”) is that the land adhered to the land row but not to the land behind the land row. This is to make a transition. In other words, in the land rows arranged in the direction parallel to the traveling direction (hereinafter referred to as "parallel land rows"), the solder attached to the land in the front direction of the traveling direction is drawn to the rear lands one after another. Gather on the last land. If there is an abandoned land further behind this rearmost land, bridges are less likely to occur in the parallel land row. However, the land rows arranged laterally in the traveling direction (hereinafter referred to as “lateral land rows”) do not have lands behind the land rows with respect to the traveling direction. The molten solder remains attached and many bridges occur.

By the way, in a printed circuit board on which a multi-lead component is soldered, if the multi-lead component is mounted in parallel with the traveling direction, two sides can be arranged in parallel to the traveling direction. Bridges are unlikely to occur in this parallel land row, but the other two sides are lateral land rows with respect to the traveling direction, and bridges occur in this lateral land row. Therefore, all land rows are arranged so that bridges are unlikely to occur, which is a land row inclined with respect to the traveling direction (hereinafter referred to as “tilted land row”).

In the inclined land row, all the land rows are inclined at 45 degrees with respect to the traveling direction, so that all the land rows have the same soldering condition, and the parallel land rows have the same bridge Although the occurrence cannot be suppressed, the occurrence of bridges is less than that in the lateral land row.

Therefore, if the land rows of the printed circuit board are arranged in a slanted land row, it is possible to perform soldering with almost no bridge to a multi-lead component having a lead pitch of 0.8 mm or more. However, for fine-pitch multi-lead components such as 0.65 mm and 0.5 mm pitch, which have been used in recent electronic devices, the slanted land row alone cannot completely eliminate the bridge. An object of the present invention is to provide a printed circuit board which does not generate a bridge even by immersion soldering of a multi-lead component having a fine pitch of 0.5 mm.

[0018]

[Means for Solving the Problems]

 The present inventors have completed the present invention by focusing on the fact that bridges can be completely eliminated by strengthening the pulling force of the solder on the discarded land, in addition to the effect of preventing bridges in the inclined land row and the discarded land. Let

According to the present invention, in a printed circuit board for soldering an electronic component in which a large number of leads are installed on four sides, the land rows on the four sides are inclined with respect to the printed circuit board traveling direction, and are further forward in the printed circuit board traveling direction. A circular discard land is arranged in contact with the rearmost land or the rearmost land of the arranged two-sided front land row, and is arranged rearward in the traveling direction of the printed circuit board. Immersion characterized in that a circular discard land is arranged so as to be separated from the last land of the rear land rows on the two sides provided, or in contact with either one of the last land. Printed circuit board for soldering.

[0020]

[Embodiment of device]

 In the present invention, a rectangular land row for soldering a multi-lead component is an inclined land row. To describe the inclined land row in more detail, it is a front land row on the front two sides in the traveling direction, that is, a land row on the two sides in which two adjacent land rows are arranged in a divergent shape in the traveling direction. The rear land rows on the two rear sides in the traveling direction, that is, the land rows on the two adjacent sides are land rows on the two sides arranged in a narrow end.

Further, the discard land is disposed at a distance from the rearmost land of the front land row, or is disposed so as to be slightly in contact with the land. Further, the waste land is disposed at a position slightly separated from the rearmost land of the rear land row or slightly contacted with the land.

The waste land provided in the present invention should be a circle larger than the land. If the waste land is circular, as shown in Figs. 2 and 3, the solder S attached to the waste land becomes spherical due to the surface tension, so the center of the circle has the highest height, and a large amount of solder is placed at the center of the circle. Concentrates. In this way, the solder in a large amount adheres strongly to the solder adhered to the rearmost land, and the circular pulling land has the maximum pulling force in the central part. Moreover, since the center of the circular discard land is close to the tail land, a large amount of solder attached to the tail land is strongly pulled by the circular waste land.

On the other hand, when the discarded land is rectangular, the solder S attached to the rectangular discarded land is attracted by the flow of the solder as shown in FIGS. Is the highest height, and the pulling force of this part becomes stronger. However, the maximum height behind the rectangular discard land is far from the rearmost land, which weakens the pulling force of the solder attached to the rearmost land. FIG. 4 is an enlarged view of the rectangular land, and FIG. 5 is a sectional view taken along line BB of FIG.

[0024]

【Example】

 The present invention will be described below with reference to the drawings. FIG. 1 is a land row on a soldering surface of a printed circuit board of the present invention, FIG. 2 is an enlarged view of a circular waste land, and FIG. 3 is a sectional view taken along line AA of FIG.

On the printed circuit board 1, a large number of lands 2 ... Which match the leads of a multi-lead component (not shown) are arranged to form a rectangular land row. The land rows are a front land row X, X arranged forward in the traveling direction and a rear land row Y, Y arranged rearward in the traveling direction. The front land rows X, X and the rear land rows Y, Y are all arranged at an angle of 45 degrees with respect to the traveling direction of the printed circuit board 1 (arrow P).

Discrete lands 3 and 3 are arranged further rearward of the lands 2d and 2d at the rear of the front land rows X and X in the traveling direction. The abandoned lands 3 and 3 shown in the embodiment are arranged slightly apart from the rearmost lands 2d and 2d, but even if the rearmost lands 2d and the abandoned lands 3 are partially in contact with each other. Good.

A circular discard land 4 is arranged further rearward than the rearmost lands 2e, 2e of the rear land row Y, Y. In the embodiment, the abandoned land 4 is also arranged apart from the rearmost lands 2e 1 and 2e, but the abandoned land is partially formed with the rearmost land 2e on either one of the rear land rows Y, Y. It may be in contact with each other.

Next, experimental results of soldering in Examples and Comparative Examples of the present invention will be described. The multi-lead component to be mounted is a QFP-IC with a lead pitch of 0.5 mm, a lead width of 0.5 mm and a number of leads of 100, and 2,000 soldering points on the printed circuit board.

Example 1 As shown in FIG. 1, a rectangular land row is inclined at 45 degrees in the traveling direction, and is spaced apart from the rearmost land of the front land row and the rearmost land of the rear land row. When soldering was performed on the printed circuit board on which the circular waste land was arranged, no bridge was found.

Comparative Example 1 When soldering was performed on a printed circuit board in which rectangular land rows were arranged laterally parallel to the traveling direction, a bridge was generated in all of the lateral land rows.

Comparative Example 2 A rectangular land row is inclined at 45 degrees in the traveling direction, and a rectangular waste land is arranged apart from the last land of the front land row and the last land of the rear land row. When the provided printed circuit board was soldered, the number of generated bridges was 32.

[0032]

[Effect of device]

 As described above, in the conventional printed circuit board with abandoned lands or a printed circuit board with a tilted land row, the generation of bridges could not be eliminated. The bridge can be completely eliminated with a simple structure of land combinations. Therefore, the printed circuit board of the present invention does not require the trouble of correcting the bridge after soldering, and also has an unprecedented excellent feature that the reliability after soldering is extremely good. .

[Brief description of drawings]

FIG. 1 Land line of soldering surface of printed circuit board of the present invention

FIG. 2 is an enlarged view of a circular waste land of the printed circuit board of the present invention.

FIG. 3 is a sectional view taken along line AA of FIG.

FIG. 4 is an enlarged view of a rectangular discard land of a conventional printed circuit board.

5 is a sectional view taken along line BB of FIG.

[Explanation of symbols]

 1 printed circuit board 2 land 2d front land row last land 2e rear land row last land 3 abandoned land 4 abandoned land X front land row Y rear land row S solder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chiaki Komori 1-2-11 Ikenohata, Taito-ku, Tokyo Aiwa Co., Ltd. (72) Inventor Hideaki Fukuda 1-2-11 Ikenohata, Taito-ku, Tokyo Aiwa Co., Ltd. (72) Inventor Takashi Usaba 1-2-1 Ikenohata, Taito-ku, Tokyo Aiwa Co., Ltd.

Claims (1)

[Scope of utility model registration request] 1. A printed circuit board for soldering an electronic component having a large number of leads arranged on four sides, wherein land lines on four sides are inclined with respect to the traveling direction of the printed circuit board and are arranged in front of the traveling direction of the printed circuit board. A circular discard land is arranged in contact with the rearmost land of the front land row of the formed two sides, or in contact with the rearmost land, and is arranged rearward in the printed board traveling direction. For dipping soldering, characterized in that a circular discard land is arranged so as to be spaced apart from the rearmost land of the rear land rows on two sides or to be in contact with either of the rearmost land. Printed board.