JPH05226557A - Parts for soldering - Google Patents

Abstract

PURPOSE:To solder electronic parts, electrical parts, etc., on a substrate with an excellent bonding strength while suppressing the generation of solder bridge by applying insulative coating partly on the surface of a terminal. CONSTITUTION:A tip of terminal 20 protruding from the body side face of electronic parts, electrical parts, etc., is set as a horizontal section 23 being parallel to the body surface. A rising section 22 on the section 23 is partly treated with insulative coating 24. When it is assumed that the height of the section 22 treated with no coating 24 from the section 23 is H and the thickness of the section 23 is t, respectively, the relation shall be represented by the equation, 1<=H/t<=2. Thus the melting solder is supplied efficiently into a bonding boundary between the section 23 and a land section 31, thereby preventing the melting solder from spreading to the body side through the surface of the terminal 20. Therefore, even the electronic parts, electrical parts, etc., in which many terminals are arranged in narrow clearance can be soldered without causing solder bridge, and correction works after soldering can be also reduced to a great extent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a component which can be soldered to a substrate such as a printed wiring board without forming a solder bridge between terminals.

[0002]

2. Description of the Related Art Electronic parts such as QFP and DIP are mounted on a printed circuit board or the like by a surface mounting method in which a main body is temporarily attached to the surface of the board with an adhesive or the like and soldered. As a method of soldering the terminals of the electronic component to the land portion of the substrate, a dipping method, a jet method, a reflow method, a light beam method or the like is adopted instead of the conventional manual soldering.

For example, when molten solder is supplied by the dipping method, the molten solder permeates the interface between the terminal and the land portion and solidifies to bond the terminal to the land portion. However, the supplied molten solder spreads toward the component body side on the terminal surface due to the capillary phenomenon in addition to the bonding interface between the terminal and the land portion.

The molten solder spread on the surface of the terminal is not effectively utilized for the original solder joining, but also remains and solidifies as a bridge between adjacent terminals. Solder bridges are more prominent in high-density integrated electronic components in which a large number of terminals are provided at narrow intervals, and thus have been a bottleneck in automating the soldering work.

When adjacent terminals are connected by a solder bridge, a short circuit occurs, and the soldered electronic parts cannot exert their original functions. Therefore, a correction work for removing the generated solder bridge is required, but depending on the case, the correction work takes a lot of time and labor, which lowers the productivity.

Therefore, many proposals have hitherto been made on a method of soldering while preventing the formation of a solder bridge, a method of removing the formed solder bridge, and the like. However, there is no practical solution, and in particular, electronic components in which a large number of terminals are arranged at narrow intervals have to rely on soldering by hand. Of course, manual soldering does not guarantee high productivity,
It is not possible to guarantee constant quality due to work variations and difficulty levels.

[0007]

The solder bridge generated between the adjacent terminals is removed by applying the tip of a heated soldering iron to melt the solder and letting it flow down to the land portion or by wiping with the soldering iron. ing. This solder bridge removal work is performed by hand using a soldering iron.

When the solder bridge is removed, the chip of the soldering iron may hit the terminal and the terminal shape may be deformed. Also, the chip heated to high temperature contacts the wiring part of the substrate,
The wiring pattern may be destroyed. Therefore, the work of removing the solder bridge with the soldering iron requires a skilled technique, a long-term concentration, and the like, which imposes a great burden on the operator.

Further, in recent electronic parts, since various functions are built in, a large number of terminals are arranged at narrow intervals, for example, 0.8 mm or less. The solder bridge generated between the terminals arranged at such narrow intervals is difficult to remove even by a manual work using a soldering iron. Therefore, the rate of disposal as defective products is high,
It becomes a factor that reduces the yield.

The present invention has been devised to solve such a problem, and by coating the solder resist on the surface of the terminal under specific conditions, the molten solder is melted along the surface of the terminal to the component body side. Capable of suppressing capillary phenomenon and solder wettability that flow in the air, and suppressing the occurrence of solder bridges even when using an automatic soldering device such as a dipping type, jet type, reflow type, and terminals for electronic parts, electric parts, etc. Is satisfactorily soldered to the land portion of the substrate.

[0011]

In order to achieve the object, a soldering component of the present invention is an electronic component or an electrical component having a plurality of terminals protruding from a main body, wherein the terminals are
A horizontal part in contact with the substrate; a standing part rising from the horizontal part; and an insulating coating applied to the standing part,
A relation of t ≦ H ≦ 2t is maintained between a thickness t of the terminal in the horizontal portion and a height H of the standing portion not covered with the insulating coating from the horizontal portion. And

For the insulating coating, an insulating material such as a thermosetting resin, a thermosetting adhesive, a solder resist, a silk screen ink or a photoresist is used. The insulating coating can be formed, for example, by covering the exposed portion of the terminal with a masking tape or the like and then applying an appropriate insulating material using a dispenser, a brush, a spray or the like. The masking tape used at this time is peeled off immediately before the soldering work. Therefore, the surface of the terminal does not have an oxide film, and the wettability with respect to the molten solder is maintained in a good state.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. As the electronic component mounted on the printed board, a QFP type integrated circuit having a large number of terminals arranged on four sides as shown in FIG. 1 was used. The main body 10 of the integrated circuit has a flat rectangular shape with a length of 20 mm, a width of 20 mm, and a thickness of 4 mm. The width of 0.
A large number of terminals 20 having a thickness of 5 mm and a thickness of 0.3 mm are projected laterally. The gap p between the adjacent terminals 20, 20 is 0.6.
It was 5 mm.

The terminal 20 is connected to the main body 10 as shown in FIG.
The projecting portion 21 projecting from the side surface is bent to form a standing portion 22, and the tip of the standing portion 22 is further bent to form a horizontal portion 23 having a length of 2 mm. The horizontal portion 23 is parallel to the surface of the main body 10 and contacts the land portion 31 formed on the surface of the printed board 30 on which the copper foil is stretched. Standing part 22
A thermosetting epoxy resin was applied as an insulating coating 24 to a part of the above and the protruding portion 21.

In mounting the integrated circuit on the printed circuit board 30, the bottom surface of the main body 10 was adhered to the surface of the printed circuit board 30, and electronic parts were temporarily attached to the printed circuit board 30. The solder bath was passed through in the posture of FIG. 2 in which the integrated circuit is located below the printed circuit board 30, and the terminals 20 were soldered to the land portions 31. As the solder bath, Pb-Sn solder held at a temperature of 250 ° C was used.

When the terminal 20 after soldering was observed, it was found that the adhesion state of the solder to the terminal 20 was greatly influenced by the insulating coating 24. Also,
A large number of solder bridges were formed on the terminals 20 without the insulating coating 24 so as to fill all the terminal gaps.

Therefore, the conditions for forming the insulating coating 24, which does not cause a solder bridge and can achieve soldering with a good joint strength, were obtained. The height H (see FIG. 3) of the standing portion 22 to which the insulating coating 24 is applied from the horizontal portion 23 was variously changed, and the relationship between the height H and the bridge generation rate was investigated. As a result, the height H that suppresses the occurrence of bridges
Has a close relationship with the thickness t of the terminal 20 in the horizontal portion 23 (t = 0.3 mm in this embodiment as described above).

When the rate of occurrence of bridge was arranged by the relationship between the height H and the thickness t, the relationship shown in FIG. 4 was established between H / t and the rate of bridge occurrence. The bridge generation rate was obtained by visually observing the adjacent terminals after soldering, and expressing the ratio of the solder bridge generated to the number of terminal gaps as a percentage.

As is clear from FIG. 4, an extreme difference was observed in the bridge generation rate at the boundary of H / t = 2. That is, when H / t ≦ 2, the generation of solder bridges is completely suppressed, whereas when H / t> 2, the gaps between adjacent terminals are filled with a large number of solder bridges.

The reason why the bridge generation rate sharply changes at the boundary of H / t = 2 is presumed as follows. H / t> 2
In other words, the exposed surface of the terminal 20 which is not covered with the insulating coating 24 has a thickness t of the horizontal portion 23 of 2
When the size of the terminal 20 is increased more than twice,
Supplied on the surface of. The molten solder permeates the interface between the horizontal portion 23 and the land portion 31 and is consumed by the original soldering action, and spreads along the surface of the horizontal portion 23 and the rising portion 22 having good wettability.

When being immersed in the solder bath, the molten solder is continuously supplied. Moreover, the adjacent terminal 2
Since the gap of 0 is small, the main body 1
The molten solder that has spread to the 0 side gathers with the molten solder that has spread to the main body 10 side along the adjacent terminals 20 and at a location near the main body 10 side. The gathered molten solder exhibits the action of sucking the molten solder from the horizontal portion 23 to the main body 10 side by the surface tension. As a result, the amount of molten solder that gathers in the vicinity of the main body 10 increases, and a solder bridge is formed.

On the other hand, when H / t ≦ 2, the surface of the rising portion 24 having good wettability to the molten solder is the horizontal portion 2
It is suppressed to twice the thickness t of 3 or less. Therefore, the amount of molten solder supplied by immersion in the solder bath is
It is limited to only a part of the horizontal portion 23 and the standing portion 22. Further, the molten solder adhering to the surface of the standing portion 22 near the horizontal portion 23 is sucked by the molten solder that permeates the interface between the horizontal portion 23 and the land portion 31. Therefore, the amount of the solder that tries to spread to the main body 10 side along the surface of the terminal 20 is limited, and the solder bridge does not occur.

As described above, the molten solder on the joint interface side exerts a larger suction force than the molten solder on the main body 10 side, and the boundary for sucking the molten solder adhering to the surface of the standing portion 22 is H.
It is considered that / t = 2. This tendency is due to the terminals 20,
The same was true as shown in FIG. 4 when soldering an integrated circuit in which the gap p between the 20 was 0.8 mm.
In this case, since the gap p is relatively large, the bridge generation rate did not rise sharply even if H / t slightly exceeded 2.

From the above, it can be seen that when H / t ≦ 2 is maintained, electronic parts and the like are soldered without generating a solder bridge. However, the height H of the exposed surface of the standing portion 22 without the insulating coating 24
Is smaller than the thickness t of the terminal 20 in the horizontal portion 31, that is, when the insulating coating 24 is applied to a portion that affects the horizontal portion 20, the molten solder supplied to the bonding interface between the horizontal portion 23 and the land portion 31. The amount of is reduced. As a result, the horizontal portion 2 is attached to the land portion 31 with good strength.
3 cannot be soldered. Therefore, the lower limit of H / t was set to 1.

Further, even for electronic parts and electric parts having a large number of terminals 20 with a narrow pitch of less than 0.5 mm, individual terminals 2 can be formed without forming a solder bridge.
It was possible to securely solder 0 to the land portion 31. H / t is 1 at a narrow pitch p of less than 0.5 mm.
It is preferable to be as close to 1 as possible within the range of to 1.5.

[0026]

As described above, according to the present invention, by applying an insulating coating to a part of the terminal under a specific condition, the molten solder is efficiently joined when it is contacted with the solder bath or the molten solder. Supplied at the interface. Then, the spread of the molten solder to the main body side, which causes the solder bridge, is suppressed by the insulating coating. As a result, even in an electronic component, electric component, or the like in which a large number of terminals are arranged at narrow intervals, soldering can be performed with good joint strength without causing a solder bridge. In addition, the automatic soldering device such as the dipping method, the jet method, the reflow method, and the light beam method can be used for soldering, and the repair work after soldering can be greatly reduced, so that the mounting work on the printed circuit board etc. can be made more efficient. Is planned.

[Brief description of drawings]

FIG. 1 is a QFP type integrated circuit soldered in an embodiment of the present invention.

FIG. 2 shows a state in which a QFP type integrated circuit is temporarily attached to a printed circuit board.

FIG. 3 Solder joint

FIG. 4 is a graph showing the effect of an insulating coating on the solder bridge occurrence rate.

[Explanation of symbols]

10 Main body of QFP type integrated circuit 20 Terminal
22 Standing part 23 Horizontal part 24 Insulation coating 30 Printed circuit board 31 Land part

Claims (1)

[Claims] 1. An electronic component or electric component having a plurality of terminals protruding from a main body, wherein the terminals have a horizontal portion in contact with a substrate, an upright portion rising from the horizontal portion, and an insulating coating applied to the upright portion. Between the thickness t of the terminal in the horizontal portion and the height H of the standing portion from the horizontal portion that is not covered with the insulating coating,
A soldering part characterized in that the relationship of t ≦ H ≦ 2t is maintained.