JPH11284318A - Electronic component mounting substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electronic component mounting substrate on which soldering can be performed in such a state that defective contact hardly occurs between the lead pins of electronic component and a soldered wiring pattern and even when the interval between the lead pins becomes narrower. SOLUTION: An electronic component mounting substrate is formed in such a way that a rectangular recessed section 1 is formed in the area which comes into contact with the lead pins 12 of electronic component on a substrate 10, on the surface of which the electronic component are mounted, and the bottom face 13a and at least two facing side faces 13b of the recessed section 17 are coated with conductors which are connected to a wiring pattern 14. Alternatively, the bottom face 13a of the recessed section 17 is coated with conductors which are connected to the wiring pattern 14 and through holes are bored through the bottom 13a of the recessed section 17 and the substrate 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic component mounting board, and more particularly, to a contact failure between a lead pin and a soldering wiring pattern area even when a distance between terminal pins (lead pins) of a flat package IC becomes narrow. The present invention relates to a flat package IC mounting board that can be hardly soldered.

[0002]

2. Description of the Related Art IC devices are classified into various types according to the shapes of packages and lead pins. DI
The P-type (Dual Inline Package) is an insertion type in which lead pins drawn out from both side surfaces are bent downward and their tips are inserted into through holes of a wiring board and soldered, or inserted into a connector or the like. SOP used for VLSI
In the (Small Outline Package) type, the lead pins on both sides are bent downward, and the tip is bent outward at a right angle.
This is an imposition type (surface mounting type) in which this portion is used as a soldering surface for the wiring pattern of the substrate. In addition, QFP (Qu
The ad Flat Package) type has four lead pins on the side, and is also an imposition type. The latter type is usually called a flat package.

In each IC device, if the lead pin is bent in a shape different from the normal shape, the tip may not be inserted into the through hole in the insertion type, and the soldering surface may not contact the wiring pattern in the imposition type. In either case, the soldering is incomplete or impossible, resulting in defective products. In particular, flat package ICs tend to have an increasing number of pins, and as a result, the pin spacing has become narrower, and therefore has the following problems. FIG.
FIG. 5 is a cross-sectional explanatory view of a relationship between a lead pin and a solder wiring pattern area (land) for soldering a lead pin provided on a substrate side. (A) is the case where the number of pins is not large and the pin interval is taken to some extent, and the height of the lead pins is uniform. This depends on the length of one side of the flat package.
And the number of pins is relatively small. However, when the number of pins becomes more than 40 pins, the interval becomes about 0.05 mm or less, and the pin width and the pin interval become narrow. To that extent, variations in the height of the pins greatly affect each other, causing a contact failure in which the lead pin 2 floats with respect to the land 3 as shown in (b), or an adjacent lead pin as shown in (c). In this case, a bridge occurs in which the solders are connected to each other, or a problem such as an increase in the inter-pin coupling capacitance C occurs as shown in FIG. In the drawing, 1 is a substrate, 2 is a lead pin, 3 is a land,
4 is solder.

[0004]

FIG. 5 shows a technique described in JP-A-5-191027 "Land pattern on printed circuit board" as one of the prior arts of the present invention. This is an example of the invention in which a semiconductor device 6 of the type) prevents a solder bridge at the lead pin 7 and takes good contact. As an outline, a bathtub-shaped concave portion 5 corresponding to a land pattern is formed on the substrate 1.
By forming the lead pins 7 in the recesses 5 and soldering, the above-described bridge in FIG. 4C is particularly prevented. However, the soldering connection in this case is such that solder is applied to the bathtub-shaped concave portion 5 and then the lead pin 7 is inserted into the bathtub-shaped concave portion 5 for solder connection, and the lead pin 7 is inserted on the solder. Therefore, there is a high risk that the solder will overflow during soldering depending on the amount of solder.

The arrangement shown in FIG. 5 is effective when a certain interval between lead pins is provided as shown in FIG. 4A, but solder must be provided in the bathtub recess 5 in advance. Unlike FIG. 5, when the solder is supplied from above, the interval between the lead pins is actually reduced, and when the interval is reduced to about 0.05 mm or less, the area of the bathtub-shaped recess 5 becomes smaller. Since it becomes narrow and small, the problem described with reference to FIGS. 4B to 4D occurs due to variations in the height of the lead pins. One of the reasons is that the solder supplied from above does not rise or turn to the bottom due to the relationship between the narrow gap between the lead pin and the bathtub and the surface tension of the solder.
The reason is that as soon as the amount of solder increases, the solder overflows from the recess. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and it is difficult to generate a contact failure between a lead pin and a soldering wiring pattern area even when a distance between lead pins of an electronic component is reduced. It is an object of the present invention to provide an electronic component mounting substrate capable of performing the above.

[0006]

A feature of the electronic component mounting board of the present invention that achieves the above object is that a rectangular concave portion is formed on a surface of the board on which the electronic component is mounted in contact with the lead pins of the electronic component. It is formed, and a side surface at least facing the bottom surface of the concave portion is covered with a conductor, and the conductor is connected to the wiring pattern. Further, as another invention, the bottom surface of the concave portion is covered with a conductor and the conductor is connected to the wiring pattern, and the bottom surface is provided with a hole penetrating to the back surface side of the substrate.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, a rectangular concave portion is provided in a region in contact with a lead pin on a substrate, and the bottom surface and opposing side surfaces are covered with a conductor. , The solder from above can be wrapped around. Hole that penetrates to the back of the board on the bottom (through hole) even if the conductor is not provided on the side
By supplying from the top of the solder,
Air can be vented (degassed) to the back side of the substrate through the space formed according to the height variation of the lead pins, so that the solder supplied from the top in response to the degassing can be used to remove the solder between the bottom of the recess and the lead pin. It can penetrate through the space to the through hole. This allows the solder supplied from above to penetrate into the space between the bottom surface of the concave portion and the lead pin even if the height of the lead pin varies, so that poor connection between the lead pin and the wiring pattern hardly occurs. Further, since the solder flowing to the outside of the concave portion is suppressed by the permeation to the bottom surface, the coupling between adjacent lead pins by the solder bridge is suppressed, and the coupling capacitance between the pins does not increase.

[0008]

FIG. 1 is a cross-sectional view of an embodiment in which the electronic component mounting board of the present invention is applied to a flat package IC mounting board. FIG. 2A is an enlarged view of a connection portion with a lead pin. (B) is an explanatory view of the soldering state, FIG.
FIG. 3 is a schematic diagram showing a relationship between a QFP and a flat package IC mounting board. In FIG. 3, reference numeral 10 denotes a mounting board for a flat package IC, and reference numeral 11 denotes a QFP. A bathtub recess 13 formed as a land corresponding to the tip 12a of each lead pin 12 of the QFP 11
It is formed on the substrate 10 along each side of P11. As shown in FIG. 1, the relationship between each lead pin 12 and the bathtub recess 13 is such that the tip 12 a is at a depth where the bathtub recess 13 is immersed in the bathtub recess 13.
The conductor and the wiring pattern 14 are coated as an extension on the four sides 13a and 13b. The conductor is, for example, a metal conductor such as copper or aluminum similar to the wiring pattern 14, and the bathtub coating portion 15 is formed thereby. Further, a through hole 16 is formed in the center of the bottom surface 13a, and penetrates to the back surface of the substrate 10.

The QFP 11 also has a QFP
A recess 17 slightly larger than the shape of 11 is formed,
The depth of the concave portion 17 corresponds to the depth of the bathtub concave portion 13, and the depth is such that a gap 18 is formed between the bottom surface and the side surface of the QFP 11. Thus, in addition to the bottom surface 13 a of the bathtub recess 13, the four side surfaces 13
The solder 4 supplied from the upper part of the bathtub recess 13 is guided by the side conductor and penetrates to the bottom surface 13a even if the gap between the lead pin 12 and the lead pin 12 becomes small because the conductor 4 is coated with the conductor b. Further, since the through hole 16 is provided on the bottom surface, the air in the bathtub recess 13 escapes to the back surface of the substrate 10 in accordance with the supply from the upper part of the solder 4, so that so-called degassing is performed. In addition, the through holes 16 have a function of allowing the solder 4 to escape to the rear surface of the substrate 10 without overflowing the solder 4 unnecessarily to the upper surface.
The dimensions of such a through hole 16 and the bathtub recess 13
FIG. 2 (a) shows the relationship with the size. That is, if the thickness of the substrate 10 is about 2 mm to 3 mm, the depth of the bathtub recess 13 is about 0.35 mm ± 10%, and the length of the bathtub recess 13 in the extension direction of the lead pin is 1.5 mm. It is about ± 20%. The diameter of the through hole 16 is about 0.2 mm to 0.5 mm.

The substrate 1 having such a bathtub recess 13
In the case where the solder 4 is supplied from above to the solder 0 and soldered, the solder 4 enters the bottom surface 13a along the side wall of the bathtub recess 13b, and as shown in FIG. A connection layer 4a of the solder 4 is formed between the back surface of the tip 12a and the bottom 13a of the bathtub recess 13. Further, a part of the connection layer 4a escapes to the through hole 16.
As a result, the swelling of the solder 4 to the upper portion is reduced, and the thickness required between the back surface (bottom portion) of the front end portion 12a of the lead pin 12 and the bottom portion 13a of the bathtub recess 13 according to the height variation of the lead pin 12. Since the connection layer 4a is formed, sufficient contact between the lead pin 12 and the wiring pattern 14 can be obtained regardless of the variation in the height of the lead pin 12. Furthermore, since the contact includes the bottom surface and the peripheral surface, the contact resistance is reduced. As a result, a solder connection in which a contact failure hardly occurs can be performed.

Next, a method of forming the bathtub recess 13 having the conductor coding 15 on the bottom surface 13a and the four side surfaces 13b will be briefly described. The multilayer substrate is laminated on the surface as a layer having a rectangular hole corresponding to the position where the bathtub recess 13 is formed, and laminated. Next, the bathtub recess 13 is formed together with the wiring pattern by sputtering or electroplating using a perforated mask for forming a pattern forming portion including the bathtub recess 13. Thereafter, the bathtub recess 13 is edged with a mask having a hole slightly smaller than the rectangular shape of the bathtub recess 13 to form the bathtub recess 13 with the bottom surface 13a and the four side surfaces 13b left.

Bathtub recess 1 thus formed
3 and then by drilling each bottom 13a
A through hole 16 is formed by making a hole in the center of the hole. The through-hole 16 may be formed simultaneously with the wiring pattern as a through-hole 16 for connecting each layer in a normal multilayer substrate. In such a case, a metal layer can be formed inside the through-hole 16. In the case of a multilayer wiring, the through hole 16 is not connected to any wiring pattern except the wiring pattern 14.
The wiring pattern connected to the wiring pattern 14 connected to the bathtub recess 13 is an exception.

Incidentally, it is desirable that there is a space between the bottom surface and the side surface between the concave portion 17 provided on the lower side of the main body of the QFP 11 and the bottom portion of the QFP 11. This is because the formation of these spaces allows the heat generated by the QFP 11 to escape upward due to the chimney effect. Thereby, the substrate 1
0 temperature rise can be prevented.

As described above, in the embodiment, the QFP
However, it is needless to say that the present invention can be applied not only to the QFP but also to various surface-mounted electronic components. The conductors coated on the bottom and side surfaces of the bathtub recess are not limited to metal conductors, and the side surfaces need only be guided so that solder can enter the bottom surface. The conductor may be coated on the side surface and the bottom surface. Further, the wiring pattern 14 connected to the bathtub recess of the embodiment is provided on the surface layer, but is a pattern provided on a middle layer of the multilayer substrate and connected to the bathtub recess. Of course, it is good.

[0015]

As described above, according to the present invention, even if the height of the lead pins varies, the solder supplied from above can be permeated into the space between the bottom surface of the recess and the lead pins. As a result, poor connection between the lead pins and the wiring pattern is unlikely to occur. Further, since the solder flowing to the outside of the concave portion is suppressed by the permeation to the bottom surface, the coupling between adjacent lead pins by the solder bridge is suppressed, and the coupling capacitance between the pins does not increase.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment in which an electronic component mounting board of the present invention is applied to a flat package IC mounting board.

FIG. 2A is an enlarged view of a portion connected to a lead pin, and FIG. 2B is an explanatory view of a soldering state.

FIG. 3 is a schematic diagram showing a relationship between a QFP and a flat package IC mounting board.

FIGS. 4A and 4B are cross-sectional views illustrating a relationship between a lead pin provided on a substrate side and a wiring pattern area for soldering, wherein FIG. 4A is a view illustrating a normal connection state, and FIG. ,
FIG. 7C is an explanatory view of a contact failure, FIG. 7C is an explanatory view of a bridge state, and FIG.

FIG. 5 is an explanatory view of the prior art of the present invention which prevents bridging by solder bonding and obtains good contact.

[Explanation of symbols]

1,10 ... substrate, 2,12 ... lead pin, 3 ... land,
4 solder, 4a solder layer, 11 QFP, 12a tip of lead pin, 13 bathtub recess, 13a bottom surface,
13b ... side surface 14 ... wiring pattern, 15 ... bathtub coating part,
16 ... through-hole, 17 ... recess, 18 ... gap.

Claims (3)

[Claims] 1. A rectangular recess is formed in a region on a surface of a substrate on which an electronic component is mounted, the area being in contact with a terminal pin of the electronic component, and at least a side surface facing a bottom surface of the recess is covered with a conductor. Electronic component mounting board connected to the wiring pattern. 2. A rectangular concave portion is formed in a region on a surface of a substrate on which an electronic component is mounted and in contact with a terminal pin of the electronic component, a bottom surface of the concave portion is covered with a conductor, and the conductor is connected to a wiring pattern. An electronic component mounting board, wherein the bottom surface is provided with a hole penetrating to the back surface side of the board. 3. A rectangular recess is formed in a region on a surface of a substrate on which a flat package IC is mounted and which is in contact with a terminal pin of the flat package IC, and a bottom surface and each side surface of the recess are covered with a conductor, and the conductor is covered with a conductor. An electronic component mounting board connected to a wiring pattern, wherein the bottom surface is provided with a hole penetrating to the back side of the board.