JPH07254774A - Printed wiring board - Google Patents

Abstract

PURPOSE:To reinforce the electrical and mechanical coupling between lead terminals and conductor lands while avoiding the solder bridging in the soldering step. CONSTITUTION:Within the printed wiring board, the first soldering resistor layer 16 is formed on the lower surface of an insulating substrate while taper protrusions 16a are point symmetrically formed on the through holes 15 respectively extending in the two orthogonal directions to the arrayal direction of the conductor lands 12 on the other hand, almost semispherical notch parts 16c, 16d are symmetrically formed along the arrayal direction of the conductor lands 12 centered on the through holes 15 as if running on to the conductor lands 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board suitable for soldering an electronic component such as an integrated circuit component provided with continuous lead terminals at an extremely small pitch.

[0002]

2. Description of the Related Art Generally, in this type of printed wiring board, a conductive pattern is formed by a conductive foil or the like around a through hole for inserting a lead terminal of an electronic component, and the lead terminal of the electronic component is inserted into the through hole. The surface of the conductive pattern is immersed in the molten solder layer or the jet solder layer in this state, so that the lead terminals and the conductive pattern are electrically and mechanically coupled by solder.

In the first conventional printed wiring board, a silk printing layer was formed on the surface of the adjacent and opposing portions of the adjacent lands (Japanese Utility Model Laid-Open No. 62-26074). As shown in FIGS. 4 and 5, the silk-printed layers 2 and 2 are provided at intervals of 180 degrees along the land juxtaposition direction and cover the conductive foil surface of the land 1. When the lead terminal a of the electronic component A is inserted into the terminal hole 4 of the printed wiring board 3 and then its conductive pattern surface is immersed in the molten solder in the solder bath, the solder 5 adheres only to the surface of the land 1 and the lead terminal a a is fixed by soldering, and the electronic component A is mounted on the printed wiring board 3. At this time, the amount of solder that adheres to the land 1 is reduced to the minimum necessary and sufficient for securely soldering and fixing the lead terminal a by forming the silk printing layers 2 and 2. Moreover, at the time of solder dipping, the solder 5 that tries to get over the adjacent land from the adjacent portions through the layer of the resist 6 is blocked by the resist 6 and the silk printing layer 2. Therefore, a solder bridge is less likely to occur between the adjacent lands 1 and 1.

In the second conventional printed wiring board, a soldering resistance layer having a pointed symmetrical acute pointed protruding portion centered on the through hole is formed in a direction perpendicular to the land direction arranged in a line. (Japanese Patent Laid-Open No. 61-140193). As shown in FIGS. 6 and 7, two layers of soldering resistance layers 7 and 8 are applied, and the shape of the soldering land portion 9 has a tapered protruding portion 10 having an acute angle in a direction perpendicular to the direction in which the lands are arranged. In addition, when the electronic component B is soldered, the solder is pulled by the protruding portion 10, so that the occurrence of solder bridges is significantly reduced.

[0005]

However, in the first conventional printed wiring board, the silk printing layer is formed on the surfaces of the adjacent and opposing portions of the circular lands.
The silk-printed layer reduces the area of the land in the center, and when soldering, most of the solder is attracted to the lead terminals or the land with a large area other than the center due to surface tension. There is a problem that the amount of solder in the land is small, the solder between the lead terminal and the land is likely to be insufficient, a tunnel phenomenon occurs, and the bonding force between the lead terminal and the land becomes extremely weak.

Further, since the land is circular and the solder spreads in the arrangement direction of the land, the solder bridging cannot be prevented unless the silk printing layer is largely projected into the land, and therefore the through hole is made small. I tried to increase the land area even a little. Therefore, as shown in FIG. 5, the diameter of the lead terminal and the diameter of the through hole are the same, and it takes a lot of time and effort to insert the lead terminal into the through hole. There was a problem that the workability was poor to implement.

In the second conventional printed wiring board, the conductor land has a tapered shape, and the molten solder is pulled in the orthogonal direction in which the conductor lands are arranged.
In the arrangement direction of the conductor lands, since the adjacent conductor lands are close to each other, there is a problem that a solder bridge occurs.

The present invention solves such a conventional problem, and can strengthen the electrical and mechanical coupling between the lead terminal and the conductive land and prevent the solder bridge between the adjacent lands. It is intended to provide an excellent printed wiring board.

[0009]

In order to achieve the above object, the present invention provides an insulating substrate in which a plurality of through holes are formed along the arrangement direction of the lead terminals of the electronic component, and the lower surface of the insulating substrate. A plurality of conductor lands each formed around the through hole, and tapered projections are formed point-symmetrically about the through hole so as to extend in two directions orthogonal to the arrangement direction of the conductor lands, and substantially. A semi-circular cutout portion is provided with a soldering resistance layer symmetrically formed around the through hole along the arrangement direction of the conductor lands.

[0010]

According to the present invention, therefore, when soldering, the tapered protrusions pull the molten solder and the notches facilitate this pulling, so that solder bridges between adjacent lands are prevented and the central portion is prevented. Has a large land area, it strengthens the electrical and mechanical coupling between the lead terminal and the conductor land.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of an essential part showing an embodiment of the printed wiring board of the present invention, FIG. 2 is a side sectional view of the essential part of the printed wiring board of the present invention, and FIG. It is explanatory drawing which compared.

In FIGS. 1 and 2, 11 is an insulating substrate formed of a synthetic resin laminated plate or the like, and 12 is an insulating substrate 11.
Conductor lands formed in an oval shape so as to be long in the direction orthogonal to the array direction of the through holes 15 around the through holes on the lower surface of the lead terminal 15 for inserting the lead terminal 14 of the electronic component 13. Is a plurality of through holes formed along the arrangement direction of.

Reference numeral 16 denotes a solder resistor, which is an insulating substrate 1.
1 is formed on the lower surface of the taper 1 and has tapered projections 16a, 1
The notch portions 16c and 16d each having a substantially semicircular shape are formed in point symmetry with the through hole 15 as a center so that 6b extends in two directions orthogonal to the arrangement direction of the conductor lands 12.
Is a first soldering resistance layer formed so as to be symmetrical with respect to the through hole 15 along the arrangement direction of the conductor lands 12 and to ride on the conductor lands 12.

When an electronic component having a pitch of 1.78 mm is used as an example, the first soldering resistance layer 16 has a thickness of 10 to 20 .mu.
The distance between a and 16b is 2.5 mm, the notch 16c,
The diameter of 16d is 0.2 mm, the distance between the notches 16c and 16d is 1.4 mm, and the diameter of the through hole is 0.8 mm.

Reference numeral 17 denotes a second solder layer formed around the conductor land 12 on the first soldering resistance layer 16 of the insulating substrate 11.
The second soldering resistance layer 17 is a soldering resistance layer.
Are tapered protrusions 17a and 17b having the same size and shape as the first soldering resistance layer 16 and cutouts 17c and 17b.
d is formed.

The first soldering resistance layer 16 and the second soldering resistance layer 17 may be formed by silk printing.

Next, the operation of soldering an electronic component to the printed wiring board of the above embodiment will be described.

In FIGS. 1 and 2, the lead terminals 14 of the electronic component 13 are conveyed in a molten solder bath or a jet solder bath with the lead terminals 14 inserted into the through holes 15, and the lower surface on which the conductor land 12 is formed is the solder bath. Once inside, the lead terminals 14 and the conductor lands 12 are electrically and mechanically coupled by the solder S.

In this case, when the lower surface of the printed wiring board is put in the solder bath and conveyed in the arrangement direction of the conductor lands 12 or in the direction orthogonal thereto, the taper protrusions 16a and 16b of the first soldering resistance layer 16 are formed. , Second soldering resistance layer 1
7. The tapered protrusions 17a and 17b of 7 pull the solder S toward the tapered protrusions, and the notches 16c and 16
d, 17c, and 17d promote the pulling of the solder S toward the tapered protrusion, so that the solder S between the adjacent conductor lands 12 is broken, and the solder S adheres between the adjacent conductor lands 12. (Solder bridge) can be prevented.

Further, the notches 16c, 16d, 17
Even if c and 17d are provided, since the area of the conductor land 12 in the central portion is large, most of the solder is spread on the lead terminals inserted into the through holes when soldering as in the first conventional example. It is possible to prevent the tunnel phenomenon due to the solder being applied only to a part of the land, and to strengthen the electrical and mechanical coupling between the lead terminal 14 and the conductor land 12.

FIG. 3 shows the above embodiment shown in FIGS. 1 and 2.
FIG. 8 is an explanatory diagram showing the number of occurrences of solder bridges tested in the second conventional example shown in FIGS. 6 and 7.

In this experimental example, the electronic component is 1.78.
Arrangement of conductor lands using 20 printed wiring boards (the total number of experiments between conductor lands is 1240) each mounted with a DIP type LSI of 64 terminals with a pitch interval of mm (62 between terminals). Direction and its orthogonal direction, solder temperature is 248 ℃, conveyor speed (conveyance speed of printed wiring board) is 1m / min, solder dipping width is 50mm, solder dipping time is 3 seconds, by flow soldering method. Soldering was done.

As shown in FIG. 3, when the printed wiring board is conveyed in the arrangement direction of the conductor lands, the generation rate of solder bridges can be made "0", while the arrangement direction of the conductor lands is orthogonal. When it was conveyed in the direction, the rate of occurrence of solder bridges could be reduced to about 1/6 that of the second conventional example.

In the above embodiment, the case of a single-sided printed circuit board was described, but it goes without saying that it can be applied to a double-sided printed circuit board.

[0026]

According to the present invention, as is apparent from the above-mentioned embodiment, the tapering protrusions are orthogonal to the arrangement direction of the conductor lands.
The soldering resistance layer is formed symmetrically about the through hole so as to extend in each direction, and the substantially semicircular notch is formed symmetrically about the through hole along the arrangement direction of the conductor lands. Since, when soldering, the tapered protrusion pulls the molten solder, and the notch facilitates this pull, and the solder between adjacent lands is cut off. This has the effect of strengthening the electrical and mechanical coupling between them and preventing solder bridges between adjacent conductor lands.

[Brief description of drawings]

FIG. 1 is a plan view of an essential part showing an embodiment of a printed wiring board according to the present invention.

FIG. 2 is a side sectional view of a main part of the printed wiring board according to the embodiment.

FIG. 3 is an explanatory diagram comparing the present invention with a conventional printed wiring board.

FIG. 4 is a plan view of a main part showing a printed wiring board of a first conventional example.

FIG. 5 is a side sectional view of a main part of the printed wiring board of the conventional example.

FIG. 6 is a plan view of an essential part showing a printed wiring board of a second conventional example.

FIG. 7 is a side sectional view of a main part of the printed wiring board of the conventional example.

[Explanation of symbols]

 11 Insulating Substrate 12 Conductor Land 13 Electronic Component 14 Lead Terminal 15 Through Hole 16 First Soldering Resistance Layer 17 Second Soldering Resistance Layer 16a, 16b, 17a, 17b Tapered Protrusion 16c, 16d, 17c, 17d Notch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoichi Kawamura 4-3-1, Tsunashima-higashi, Kohoku-ku, Yokohama-shi, Kanagawa Matsushita Communication Industrial Co., Ltd.

Claims (2)

[Claims] 1. An insulating substrate having a plurality of through holes formed along an arrangement direction of lead terminals of an electronic component, and a plurality of conductor lands formed around the through holes on a lower surface of the insulating substrate, respectively. The tapered projections are formed point-symmetrically with respect to the through holes so as to extend in two directions orthogonal to the arrangement direction of the conductor lands, and substantially semicircular cutout portions are formed in the arrangement direction of the conductor lands. A printed wiring board having a soldering resistance layer symmetrically formed around the through hole. 2. The printed wiring board according to claim 1, wherein the soldering resistance layer is formed by silk printing.