JPS6364916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead bonding structure for bonding leads of electronic components such as tape carrier devices onto a single-layer or multi-layer wiring board on which wiring conductors are patterned, and particularly relates to a lead bonding structure for bonding leads of electronic components such as tape carrier devices onto a single-layer or multi-layer wiring board on which wiring conductors are patterned. This is a manufacturing technology that is effective when soldering leads using the solder method.

A basic configuration for bonding outer leads of electronic components such as circuit elements onto a component mounting board having wiring conductors will be explained with reference to FIGS. 1 and 2. FIG. The inner lead bonded tape carrier device 1 with the outer leads 2 attached is cut from the conveying tape as shown in FIG. 1, and the outer leads 2 are formed (molded) as shown in FIG. 2 to form the tape carrier device. A bonding portion is formed that is substantially flush with the bottom surface (attachment surface) of 1. Next, the tape carrier device 1 is mounted on the wiring board 3 by making the bonding part of the outer lead 2 face the bonding pad 4 that constitutes a part of the wiring conductor on the wiring board 3 and bonding the two together. Configure the energizing circuit. As a result of the above, tape carrier device 1
Outer lead bonding is performed.

Furthermore, the reflow soldering method means that when performing outer lead bonding, a solder paste containing a solder material and a solvent is layered by a printing method or the like in a partitioned area where band-shaped bonding pads 4 are arranged in parallel. By melting the paste in a reflow oven or infrared irradiation and evaporating the solvent, the solder is focused by surface tension onto each bonding pad 4 of the metal film with affinity, and the solder can be bonded to the bonding pad 4 without using a bonding tool. A plurality of outer leads 2 facing this are connected simultaneously. This reflow soldering method allows solder paste to be applied individually to each bonding pad 4 because (1) solder can be easily applied using a printing method, and (2) the self-alignment effect due to the surface tension of solder can be used. It has the advantages that it is not necessary to apply solder paste, and it is sufficient to apply a uniform layer of solder paste over the entire array section area of the bonding pad 4, and (3) it is possible to bond a large number of devices at the same time. This is a very useful technology for mounting various circuit elements such as ICs and LSIs on wiring boards.

When forming the outer leads 2 of the tape carrier device 1 mounted on the wiring board 3, the forming shape is as follows to prevent the leads 2 from coming into contact with the upper edge of the tape carrier device 1 and becoming an edge. As shown in Fig. 3, the leads 2 extending in two or four directions from near the upper edge of the tape carrier device 1 are bent upward and lifted to separate them from the edge, and then the leads are removed at a position away from the edge. A bent structure of the lead 2 is adopted in which the lead 2 is bent downward and the end thereof is formed flat so as to be substantially flush with the bottom surface (placing surface) of the tape carrier device 1. By using this structure, even if the lead 2 bends during the inner lead bonding process and almost comes into contact with the edge portion of the tape carrier device 1, the bending of the lead 2 can be corrected and a stable lead bonding structure can be obtained.

However, in this vent structure that lifts up the leads 2, there is a risk that the molded parts of the outer leads 2 may be unevenly distributed in the vertical direction, as shown in FIG. When using the reflow soldering method, the outer lead 2 is bonded onto the bonding pad without being pressed by a tool, etc., which causes an open defect where the outer lead and solder are not bonded sufficiently. A poor connection between the lead 2 and the bonding pad significantly reduces production yield.

In view of the above-mentioned problems, the present invention makes full use of technical means to construct an outer lead bonding structure having a forming shape with little variation in the vertical direction, thereby preventing open defects even when using the reflow soldering method. It is an object of the present invention to provide a new and useful lead bonding structure that can reliably connect an outer lead and a bonding pad without any problems.

The cause of the vertical level fluctuation of each formed part that occurs when the outer lead is formed to have a central structure will be analyzed based on FIGS. 5A and 5B. Fifth
Figure A is a plan view of an outer lead formed into a vent structure, and Figure 5B is a front view of Figure 5A.

The outer leads 2 extending outward from near the upper end of the tape carrier device 1 are arranged in rows at a predetermined pitch at the upper end of the tape carrier device 1. On the other hand, since the bonding pads are arranged on the substrate at a wider pitch than this, the outer leads 2 extending from the tape carrier device 1 are obliquely formed in the lateral direction to enlarge the pitch, and then each bonding pad is A bonding portion facing parallel to the pad will be formed. The vent structure is made by bending the outer lead 2 upward from near the upper edge of the tape carrier device 1, then bending it horizontally at the broken line position in the figure, and then bending it downward at a distance of a certain length. It consists of: When a part of the bent portion constituting this bend structure is formed in a fan-out area A that is obliquely formed to enlarge the arrangement pitch of the outer leads 2, each outer lead 2 has a different cross-sectional shape and angular position. This results in vertical level fluctuations due to differences in forming conditions. It is thought that this level fluctuation can be eliminated if the forming conditions of the outer leads 2 are set to be the same for each outer lead. The present invention is constructed based on such a viewpoint, and will be described in detail below with reference to the drawings according to embodiments.

FIG. 6A is a plan view of an outer lead illustrating an embodiment of the present invention, and FIG. 6B is a front view of FIG. 6A.

The outer leads 2 extending outward from the vicinity of the upper end of the tape carrier device 1 are arranged in a row at a predetermined pitch near the upper end of the tape carrier device 1, and the vent structure of this embodiment Each outer lead 2 is bent upward, and all outer leads 2 are bent horizontally in area B immediately before the obliquely formed fan-out area, and then bent downward at the straight part outside the fan-out area. It is bent to form a bonding part. Therefore, all the bending parts are bent at bending positions that cross the center line of the outer leads 2 at right angles in the direction perpendicular to the extending direction of the outer leads 2, and the forming condition is set between all the outer leads 2. are the same. Therefore, vertical level fluctuations between the outer leads 2 are suppressed, and the bonding surfaces of the outer leads 2 are arranged on substantially the same plane.

The tape carrier device lead-formed as described above is placed on a wiring board, and the bonding part of each outer lead is placed facing the bonding pad on the wiring board on which solder paste has been printed, and then infrared rays are irradiated. Heat with etc. By this heating, the solvent in the solder paste evaporates and it becomes molten solder, which is transferred and placed on each bonding pad by the self-alignment effect.
As the molten solder solidifies, the bonding pad and the outer lead are reliably bonded, and no open defects or the like occur. If the level fluctuation of the outer lead is suppressed in this way, a highly reliable lead bonding structure without connection failure can be obtained even in a bonding structure using the reflow soldering method.

Note that the bonding pad and the outer lead are not limited to soldering using the reflow soldering method.

As explained in detail above, according to the present invention, it is possible to prevent contact between leads and device edges by using the vent structure of the lead, and at the same time solve the problem of open failures that the vent structure has, thereby dramatically increasing the yield in production. can be improved.

[Brief explanation of drawings]

FIGS. 1 and 2 are explanatory diagrams illustrating the basic configuration of a lead bonding structure. FIGS. 3 and 4 are explanatory diagrams illustrating the basic structure of a lead bonding structure having a vent structure. Fifth
Figures A and B are a plan view and a front view of forming shapes for analyzing and explaining the causes of vertical level fluctuations of the outer leads. FIGS. 6A and 6B are a plan view and a front view of the forming shape of an outer lead, explaining one embodiment of the present invention. 1... Tape carrier device, 2... Outer lead, 3... Wiring board, 4... Bonding pad.

Claims (1)

[Claims] 1. A lead bonding structure in which a group of leads arranged at a predetermined pitch on a circuit element and extending outward and a group of bonding pads arranged on a substrate at a pitch different from the pitch are bonded by forming the group of leads. In the lead group, the lead group has a base extending straight in an extending direction from a fixed end to the circuit element, an end portion arranged facing each other corresponding to the pitch of the bonding pad group, and the end portion and the lead group. It is characterized by having a bent structure that has a diagonal molded part that connects the root part, and separates the lead group and the circuit element by bending the lead group upward and horizontally at the root part. Lead bonding structure.