JPH0969385A - Electronic part - Google Patents

Abstract

(57) Abstract: In batch reflow soldering for mounting an electronic circuit board, it is possible to prevent unmelting of the solder in a lead joint portion of an electronic component having a large heat capacity such as a large QFP and to achieve good solder joint. SOLUTION: A distance a between a bottom surface 13 of a main body portion 12 of a QFP and a lead installation portion of a substrate 14 after mounting the QFP is 1 mm
The length of the lead 11 is set so as to be the above. For this reason, a spatial gap is provided and the soldered joint 15
Since the heat conduction from the QFP to the main body portion 12 is prevented and the temperature rises sufficiently, the joint failure due to the unmelted solder can be eliminated. Further, by providing a cylindrical or conical projection 21 on the bottom surface 13 of the QFP, it is possible to prevent the lead 11 from being deformed by an external force and to secure the holding stability of the QFP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic component soldered onto an electronic circuit board.

[0002]

2. Description of the Related Art When an electronic component is soldered on a board, first, cream solder is printed on a printed circuit board, the electronic component is mounted on the printed circuit board, and this is passed through a reflow furnace. Then, the cream solder is melted and solidified, and the soldering is completed. A conventional printed circuit board has a uniform flat surface on which electronic components are mounted. Various large and small electronic components are mounted and heated by hot air or far infrared rays in a furnace to melt the solder. .

[0003]

However, due to the difference in size and heat capacity of each electronic component, temperature distribution varies on the same substrate during heating in the reflow furnace. For example, the conventional large QFP (Quad Flat Package) has a large heat capacity of the component body and the distance between the component bottom surface and the substrate is close to 0.5 mm or less, so it should be added to the leads to be soldered. The heat is absorbed by the component body, and the temperature of the lead does not rise easily. For this reason,
In the soldered joint portion of the large QFP, the solder remains unmelted without increasing the temperature up to the melting point, which causes a problem of joint failure. Further, if sufficient heating is performed to melt the solder, the temperature of other components excessively rises, and there is a problem that defects such as life deterioration and breakage easily occur.

In view of the above problems, the present invention eliminates unmelted solder by appropriately blocking heat conduction from the soldering portion of the lead to the component body in an electronic component having a large heat capacity such as a large QFP. The purpose is to enable the leads to be bonded to the substrate with high quality.

[0005]

In order to solve the above problems, according to the present invention, the lead length is set so that the distance from the lead installation portion to the bottom surface of the component body when mounted on the substrate is 1 mm or more. It is a thing.

According to this structure, since a sufficient spatial gap is formed between the lead soldering joint portion of the board and the component body, heat conduction from the substrate to the component body is reduced. For this reason, it is possible to secure a sufficient temperature rise for melting the solder in the substrate. If the distance is less than 1 mm, the amount of heat absorbed by the component body increases as described above, which is not appropriate.

According to the present invention, the protrusion projects from the bottom surface of the component body, and the protrusion length of this protrusion is equal to the distance from the lead installation portion when the component is mounted on the substrate to the bottom surface of the component body. Alternatively, it can be configured so that it is shorter than this distance and the difference from this distance is 0.5 mm or less.

With such a structure, the projections play a role of supporting the component main body. Therefore, although the lead length is set long so that the distance is 1 mm or more as described above, It is possible to prevent the lead from being deformed due to the force from, and thus it is possible to stably hold the component body. If the protruding length is longer than the above distance, the leads will not contact the substrate. If the difference between the protrusion length and the above distance exceeds 0.5 mm, the protrusion cannot serve to support the component body.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cross-section after mounting a QFP on a substrate according to a first embodiment of the present invention. Conventionally, the distance a between the bottom surface of the main body of the QFP and the substrate has been 0.5 mm or less.
The bottom surface 13 of the body portion 12 of the
The length of the lead 11 is set so that the lead 11 is lifted by at least mm. By providing the space in which the distance a is 1 mm or more, the heat conduction from the soldering joint portion 15 to the main body portion 12 of the QFP becomes small, and a sufficient temperature rise in the soldering joint portion 15 can be secured. become.

Table 1 shows the bottom surface 13 of the component body 12 and the substrate 1.
4 shows the results of actually producing a plurality of QFP samples in which the distance a with respect to 4 was changed and measuring the temperature of each lead portion. As is clear from Table 1, the distance a is set to 1
By setting the thickness to be equal to or greater than mm, it is possible to secure an increase in temperature required for the solder of the joint portion 15 to be completely melted.

[0011]

[Table 1]

In the structure of the QFP based on the present invention as described above, the distance a becomes larger than that of the conventional structure, so that the lead 11 can be deformed by external force due to contact with foreign matter during mounting or after soldering. There is a nature. Therefore, in order to prevent this, it is more preferable to add an auxiliary structure as in the second to sixth embodiments described below.

FIG. 2 shows the appearance of a QFP which is an electronic component based on the second embodiment of the present invention, and FIG. 3 shows this QFP.
The cross section when the FP is mounted on the substrate is shown. FIG. 2 is a bottom view of the QFP, in which a small-diameter cylindrical protrusion 21 projects from the center of the bottom surface 13 of the main body portion 12. This projection 2
No. 1 was formed at the same time when the QFP was resin-molded by the mold. As is apparent from FIG. 3, the length of the protrusion 21 is set to be substantially the same as the distance a between the substrate 14 and the bottom surface 13 of the main body portion 12 of the QFP.

By doing so, even if some external force is applied to the main body portion 12 of the QFP after mounting on the substrate 14,
It is possible to prevent the lead 11 from being deformed. Moreover, QF
Most of the bottom surface 13 of the main body portion 12 of P is the substrate 1
Since it is separated from 4 by 1 mm or more, as in the first embodiment, the temperature rise of the soldering joint portion 15 is secured.

A third embodiment, which will be described next, is a further development of the second embodiment. Its appearance is shown in FIG. 4, and its cross section after it is mounted on a substrate is shown in FIG. As shown in FIG. 4, the number of protrusions 21 is four or at least three.
By using a plurality of the QFPs or more, it is possible to secure the stable holding property of the QFP when mounted on the substrate 14. In FIGS. 4 and 5, the QFP body portion 1 is
2 is formed in a rectangular parallelepiped shape, and the bottom surface 13 thereof is formed in a rectangular shape, and the protrusions 21 are provided corresponding to the four sides 17 constituting the bottom surface 13. That is,
Each protrusion 21 is provided close to each side 17, and each protrusion 21 is arranged such that the distance from each side 17 is, for example, 5 mm or less. In order to ensure stable holding of the QFP in which the bottom surface 13 of the main body portion 12 is formed in a rectangular shape, as shown in FIG. 6 which is the fourth embodiment, the four corner portions 18 on the bottom surface 13 are projected. Two
It is more preferable that 1 is provided.

A fifth embodiment is shown in FIGS. 7 and 8.
A sixth embodiment is shown in FIGS. 9 and 10. All of these are developments of the third embodiment described above, and are configured such that the protrusion 21 has a pointed shape such as a conical shape so that the contact with the substrate 14 becomes a point contact. . With such a configuration, heat conduction to the main body portion 12 of the QFP through the tips of the protrusions 21 is more reliably reduced as compared with the third and fourth embodiments, which is more preferable. Considering the stable holding property of the QFP, for the same reason as in the case of the third and fourth embodiments, as shown in FIGS. 7 and 8, four rectangular bottom surfaces 13 of the main body 12 are formed. Rather than providing protrusions 21 corresponding to the respective sides 17, as shown in FIGS. 9 and 10, the protrusions 21 are formed on the four corners 18 of the bottom surface 13.
Is more preferable.

A reflow experiment was conducted using the conventional type QFP and the QFP based on the above-described embodiment of the present invention. As a result, when the reflow equipment was set to the same, unmelted solder was generated in the conventional type QFP. However, in the QFP of the embodiment of the present invention, under the same temperature condition, the solder was completely melted in any of the first to sixth embodiments, and good soldering could be performed.

[0018]

As described above, according to the present invention, the lead length is set so that the distance from the lead installation portion to the bottom surface of the component body when mounted on the substrate is 1 mm or more. A sufficient spatial gap can be formed between the solder joint and the component body, reducing heat transfer from the board to the component body, thus ensuring a sufficient temperature rise on the board to melt the solder. As a result, good soldering can be performed.

Further, according to the present invention, by projecting the projection from the bottom surface of the component body and setting the projection length to an appropriate value, the lead is deformed by an external force after the mounting on the substrate. This can be prevented, and thus the component body can be stably held.

[Brief description of drawings]

FIG. 1 is a Q for a substrate according to the first embodiment of the present invention.
It is sectional drawing which shows the mounting state of FP.

FIG. 2 is an external view of a QFP based on a second embodiment of the present invention.

3 is a cross-sectional view showing a state in which the QFP shown in FIG. 2 is mounted on a substrate.

FIG. 4 is an external view of a QFP based on a third embodiment of the present invention.

5 is a cross-sectional view showing a state in which the QFP shown in FIG. 4 is mounted on a substrate.

FIG. 6 is an external view of a QFP based on a fourth embodiment of the present invention.

FIG. 7 is an external view of a QFP based on a fifth embodiment of the present invention.

8 is a sectional view showing a state in which the QFP shown in FIG. 7 is mounted on a substrate.

FIG. 9 is an external view of a QFP based on a sixth embodiment of the present invention.

10 is a sectional view showing a state in which the QFP shown in FIG. 9 is mounted on a substrate.

[Explanation of symbols]

 11 Lead 12 Main Body 13 Bottom 14 Substrate 15 Joint 21 Protrusion a Distance

Claims (6)

[Claims] 1. An electronic component, wherein a lead length is set so that a distance from a lead installation portion to a bottom surface of a component body when mounted on a substrate is 1 mm or more. 2. A protrusion protrudes from the bottom surface of the component body, and the protrusion length of this protrusion is equal to or equal to the distance from the lead installation portion when the component is mounted on the substrate to the bottom surface of the component body. Shorter than this distance is 0.5
The electronic component according to claim 1, wherein the electronic component has a size of not more than mm. 3. The electronic component according to claim 2, wherein the shape of the protrusion is a cylindrical shape or a conical shape. 4. The electronic component according to claim 2, wherein the number of protrusions is three or more. 5. The electronic component according to claim 4, wherein the bottom surface is formed in a rectangular shape, and the protrusions are provided corresponding to each of the four sides forming the bottom surface. 6. The electronic component according to claim 4, wherein the bottom surface is formed in a rectangular shape, and the protrusions are formed at four corner portions of the bottom surface.