JPH0760931B2 - Wiring board and soldering method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board and a soldering method thereof, and more particularly to a wiring board for mounting electronic components having a narrow lead interval and a soldering method thereof.

[0002]

2. Description of the Related Art Quad Fl in a conventional wiring board
As the electrode pad 8 for connecting the lead of a semiconductor package such as at package, the electrode pad 8 of the same length is most commonly arranged in a horizontal row as shown in FIG. 3A. Moreover, in the soldering, as shown in FIG.
As shown in (b), a method is generally used in which the cream solder 9 is individually printed according to the shape of the electrode pad 8, then the package is mounted, and the solder paste is passed through a reflow oven or the like for soldering. However, as the demand for high-density packaging has increased and the pitch of the leads of the package has become narrower, printing has become more difficult. As shown in FIG. 3C, the cream solder 10 crosses each electrode pad 8 The method of printing on is also used. In terms of pad arrangement, the electrode pads 11 are arranged in a staggered pattern as shown in FIG.
Wiring board has been proposed. In this case, the number of adjacent portions between the electrode pads 11 is small, and individual printing for each electrode pad becomes easy.

Next, the conventional soldering method is shown in FIG.
The case where the cream solder 10 of (c) is printed in one character across each electrode pad 8 will be described as an example. First, the cream solder 10 is applied in a letter shape on the electrode pad 8 of the wiring board (FIG. 5A), and the leads 13 of the electronic component are aligned and mounted on the electrode pad 8 on which the cream solder 10 is printed. After that (FIG. 5 (b)), by heat treatment using a reflow furnace or the like, the molten solder 14 wets and spreads on the electrode pad 8 and the lead 13 to form a bonded state (FIG. 5).
(C)). Here, when the amount of the printed cream solder 10, the wettability of the melted solder 14 to the electrode pad 8, the reflow condition, etc. are not adequately adequate, it is called the bridge 12 in which the solder 14 remains connected between the leads 13. Defects occur.

[0004]

The above-described conventional wiring board and the soldering method thereof have the following drawbacks.

When the cream solder is individually printed with the electrode pads arranged in a horizontal row (FIG. 3 (b)), printing becomes difficult especially when the pitch is narrowed, and therefore the printing accuracy varies, so that a bridge occurs after reflow. Or, so-called unsolder may occur in which sufficient bonding cannot be obtained because the printing amount is too small. In addition, the solder that is printed when the leads are mounted collapses and is connected to the adjacent pads, which easily causes a defect that becomes a bridge after reflow.

When the cream solder is printed in a single letter on the electrode pads arranged in a horizontal row (FIG. 3 (c)), printing is easy, but since the pads are originally connected to each other to print the cream solder, the bridge is not formed. It is more likely to occur than individual printing.
For this reason, a special technique is required such as raising resin or the like between the pads so that the connected solder is easily broken.

When the pad is staggered as shown in FIG. 4,
It is necessary to make the leads of the package to be mounted in a zigzag pattern in accordance with the electrode pads, which makes it difficult to control the lead formation and causes a cost increase.

[0008]

The wiring board of the present invention includes a plurality of pad pairs each including a linear electrode pad and a dummy pad arranged near one end of the electrode pad and having a length shorter than that of the electrode pad. The pad rows are arranged in parallel and alternately so that the straight lines passing through the dummy pads of the pad pairs in the same direction pass through the ends of the electrode pads of the pad pairs in the opposite direction.

According to the soldering method of the present invention, after the cream solder is printed in a letter shape on both ends of the pad row passing over the dummy pads of the wiring board, the leads of the electronic component are mounted on the electrode pads. Then, the electrode pad and the lead of the electronic component are soldered by heating.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1A is a perspective view of an embodiment of the wiring board of the present invention. A linear electrode pad 2 and a dummy pad 3 arranged near one end of the electrode pad 2 and having a shorter length than the electrode pad 2 form a pad pair, and a plurality of pads are arranged in parallel and alternately turned. Here, the straight line A or B passing through the dummy pad on one side needs to pass through the end portion of the electrode pad 2 of the pad pair facing in the opposite direction. In this embodiment, the pads are arranged so that both ends of the alternately arranged pads are aligned.

1 (b) to 1 (d) are perspective views showing an embodiment of the soldering method of the present invention in the order of steps. First,
On the wiring board described above (FIG. 1A), the cream solder 4 is printed in one character on both ends of the pad row so as to pass through the ends of the dummy pad 3 and the electrode pad 2 (see FIG. 1A).
(B)) Positioning and mounting the lead 5 of the electronic component on the electrode pad 2 (FIG. 1C), and then heating by a reflow furnace to solder the electrode pad 2 and the lead 5 of the electronic component. To form a bonded state (Fig. 1
(D)).

Next, FIGS. 2A to 2C are plan views for explaining in detail the movement of the cream solder 4 in the reflow process of this embodiment. Note that the lead 5 is omitted for the sake of simplification of the description. The cream solder 4 printed on both ends of the pad row is melted by heating (FIG. 2A), and the solder 6 wets and spreads on the adjacent electrode pad 2 and dummy pad 3 (FIG. 2B).
At this time, since the dummy pad 3 has a smaller wetted area than the electrode pad 2, the solder 6 is attracted to the electrode pad 2 by the action of the surface tension, and the solder 6 between the electrode pad 2 and the dummy pad 3 is very easily broken. . Therefore, the bridging due to the lump of solder between the electrode pads as in the past is unlikely to occur. Further, a large amount of the solder 6 is attracted to one electrode pad 2 and the amount of solder does not become uneven, so that the solder 6 is uniformly supplied to each electrode pad 2.

Further, the presence of the dummy pad 3 can prevent the molten solder 6 from moving in the longitudinal direction of the electrode pad 2 with the molten solder 6 being connected to generate a bridge between the adjacent electrode pads 2. Further, in the electrode pads 2 adjacent to each other, the solder 6 wets and spreads from the opposite direction as shown by an arrow C in FIG. In addition, even after the bridge 7 is generated as shown in FIG. 2C after the soldering of the electrode pad 2 and the lead 5 of the electronic component is completed, the gap between the adjacent pair of the electrode pad 2 and the dummy pad 3 can be increased. The bridge 7 does not cause a short circuit between the leads of the electronic component.

As described above, the wiring board and the soldering method according to the present embodiment are easy to print because one character is printed even when a component having a narrow lead interval is mounted. Compared with this, the number of defective products due to the bridge between adjacent leads and pads is significantly reduced, and the product yield is improved. The dummy pad 3 may have a length equal to or less than the width of the electrode pad 2 because the cream solder is less likely to break when reflowing if the area of the dummy pad 3 is large.

[0016]

According to the wiring board and the soldering method thereof of the present invention, since dummy pads are alternately provided at one end and the other end of each electrode pad, a bridge is less likely to occur and each electrode pad is The solder can be supplied uniformly.

Furthermore, in the wiring board of the present invention, there is no need to modify the leads to be mounted, and the conventional semiconductor package can be used as it is.

As described above, the wiring board and the soldering method of the present invention can significantly reduce wiring defects due to bridges in the conventional process, improve the reliability of soldering, and improve the product yield.

[Brief description of drawings]

1A to 1D are perspective views showing an embodiment of the present invention.

2A to 2C are plan views showing a usage example of the present invention.

3A to 3C are plan views showing a first conventional example.

FIG. 4 is a plan view showing a second conventional example.

5A to 5C are perspective views showing a conventional usage example.

[Explanation of symbols]

 2,8,11 Electrode pad 3 Dummy pad 4,9,10 Cream solder 5,13 Lead 6,14 Solder 7,12 Bridge A, B Straight line C Arrow

Claims (4)

[Claims] 1. A semiconductor integrated circuit having a plurality of external connection electrode leads, each extending substantially in a horizontal direction and in a plane in a plane direction substantially parallel to each other. A plurality of electrode pads each formed with a predetermined length in the vertical direction at intervals and widths corresponding to the lateral intervals so that the electrode leads are soldered to the electronic components such as devices. A printed wiring board having a surface on which the plurality of electrode pads are arranged substantially linearly in the lateral direction, and each of the electrode pads has a separating portion for forming a corresponding dummy pad; The printed wiring board characterized in that, for a pair of adjacent electrode pads, the separated portions are symmetrically arranged at both ends in the vertical direction of the corresponding electrode pad. Board. 2. The electrode pads each have an elongated rectangular shape in the longitudinal direction, and each of the separation portions has the same width as the rectangular shape and a length significantly smaller than the rectangular shape. 1 printed wiring board. 3. A solder member, which is arranged across the both longitudinal ends of the electrode pad in the lateral direction so as to cover each of the separated portions of the plurality of electrode pads, is melted by heating. 2. The printed wiring board according to claim 1, wherein the width of the electrode pad and the length of the separated portion are selected so that the molten solder gathers toward the electrode pad by the surface tension of the molten solder. 4. A semiconductor integrated circuit having a plurality of external connection electrode leads each extending substantially in the same horizontal direction and in the same plane in a vertical direction substantially parallel to each other. A plurality of electrode pads each formed with a predetermined length in the vertical direction at intervals and widths corresponding to the lateral intervals so that the electrode leads are soldered to the electronic components such as devices. A printed wiring board having a surface on which the plurality of electrode pads are arranged substantially linearly in the lateral direction, and each of the electrode pads has a separation portion for forming a corresponding dummy pad, A step of preparing a printed wiring board in which the separated portions of the pair of electrode pads adjacent to each other are symmetrically arranged at both ends of the corresponding electrode pad in the vertical direction; Selectively placing cream solder across the longitudinal ends of the electrode pad in the lateral direction so as to cover the separated portion; and aligning the electrode lead with the electrode pad to provide the electronic component A method for soldering an electronic component to a printed wiring board, comprising: mounting the printed wiring board on the printed wiring board; and heating the electrode lead, the electrode pad, and cream solder to solder the lead to the electrode pad.