JP2001085827A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board which can reduce the temperature difference between different parts, while maintaining the electrical characteristics of the parts. SOLUTION: A printed wiring board 10 is provided with an insulating substrate 11, and pads 12 are provided on the substrate 11. A lead-out patter 16 connected with a via hole 18 is connected to the pad 12C but is disconnected halfway. Consequently, since the heat generated in the soldering of a semiconductor package 14 does not escape to the via hole 18 side and the temperature of the pad 12C becomes higher within a short time, the peak temperature in the soldering of the package 14 can be made nearly equal to those of other pads 12A and 12B. Therefore, parts can be soldered without damaging the components, even when lead-free solder having a high melting point is used, because not only can be temperature difference between identical parts be reduced, but also the temperature difference between the board 10 and substrate 11 can be reduced also.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board, and more particularly to a printed wiring board on which electronic components are soldered by lead-free solder.

[0002]

2. Description of the Related Art In recent years, due to an increase in interest in environmental issues, activities for eliminating harmful lead from solder used in the manufacture of printed wiring boards for electronic devices and the like have been activated. Such lead-free solder (hereinafter referred to as lead-free solder (SnAgCu)) has been proposed, but since its melting point is higher than that of conventional SnPb eutectic solder, thermal damage to components during soldering is suggested. Will increase,
There was a problem.

[0003] For example, as shown in FIG.
b The difference between the melting point of the eutectic solder and the component heat resistance temperature, that is, the allowable temperature range Δt1 in which the component can be soldered without causing thermal damage is about 52 ° C., but the melting point is high in the case of lead-free solder. Therefore, the allowable temperature range Δt2 is about 14 °
C and much smaller than conventional SnPb eutectic solder.

Further, as shown in FIG. 7, there are a wide variety of types of components mounted on a printed wiring board, and the respective components have different heat capacities. In other words, components with a large heat capacity do not easily rise in temperature, and components with a small heat capacity tend to rise in temperature.Therefore, when soldering the entire board at a fixed heating time, such as reflow soldering, As shown in FIG. 7, the peak temperature at the time of soldering differs depending on the component. Therefore, a QFP (Quad Flat Package) having a large heat capacity without increasing the temperature of an aluminum electrolytic capacitor having a small heat capacity and a low heat resistance.
And CBGA (Ceramic Ball Grid A)
(rray), it is very difficult to raise the temperature of the terminal portion of the semiconductor package to a temperature required for melting the solder.

Further, even in the same component, as shown in FIG. 8, there is a difference in heat capacity depending on whether or not a conductive lead pattern 52 is provided on a pad 50 to which a terminal of the component is connected. That is, as shown in FIG. 9, in a case where the pad has a lead pattern 52 and the tip is connected to the ground layer 56 via the via hole 54, the pad is soldered by the solder paste (cream solder) 60. In this case, heat escapes to both the semiconductor package 58 and the ground layer 56 having a large heat capacity along a path indicated by a dotted line in the drawing. As a result, a temperature difference occurs between the pad 50B without the lead pattern 52 and the pad 50C with the lead pattern 52.

To solve this problem, a dummy lead pattern is provided on a pad having no lead pattern and a small heat capacity to connect lands and via holes, thereby increasing the heat capacity and lowering the peak temperature at the time of soldering. A technique has been proposed to reduce the variation in peak temperature between terminals by matching the heat capacity of the pad with that of JP-A-8-64953 and JP-A-8-236913.

However, in the above-mentioned prior art, since the heat capacity of a pad having a small heat capacity is merely adjusted to the heat capacity of a pad having a large heat capacity, as shown in FIG. 10, even if the temperature difference in the same part can be reduced. , Different parts,
That is, it is not possible to reduce the temperature difference between a component having a small heat capacity such as an aluminum electrolytic capacitor.

As shown in FIG. 11A, a constricted portion 50A is provided in a pad 50 having a large heat capacity to which terminals of components such as a semiconductor package are connected.
A technique has been proposed in which a corrugated portion 50B is provided to prevent heat from escaping, reduce the heat capacity, and reduce the temperature difference between terminals (Japanese Patent Laid-Open No. 10-1782).
No. 48)

[0009]

However, in the above prior art, although the temperature difference between the terminals can be reduced, the high-speed operation is required because the cross-sectional area of the wiring is locally reduced and the wiring distance is long. However, there is a problem that the transmission becomes difficult and the current capacity becomes small.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can reduce the temperature difference between different components at the time of soldering and can prevent the deterioration of electrical characteristics. An object is to provide a printed wiring board.

[0011]

According to a first aspect of the present invention, there is provided a printed wiring board in which components are mounted on a board on which a circuit pattern is formed by soldering. The circuit pattern includes a first wiring pattern having a first heat capacity at the time of soldering the component, and a second wiring pattern having a second heat capacity larger than the first heat capacity, It is characterized in that a heat interrupting portion is provided by cutting the middle of the second wiring pattern.

The printed wiring board has a structure in which a circuit pattern is formed on an insulating substrate by using a highly conductive member such as copper. The components constituting the electronic circuit are soldered to the printed wiring board to function as an electronic circuit. The components include, for example, a semiconductor package such as an IC, a resistor, a capacitor, and a diode.

In such a printed wiring board, the circuit pattern includes a first wiring pattern having a first heat capacity. The heat capacity varies depending on the shape and length of the wiring and the components to be soldered to the wiring pattern. When the heat capacity is large, the temperature does not easily rise when heated, and when the heat capacity is small, the temperature tends to rise when heated. Further, the circuit pattern has more members than the first wiring pattern to increase the heat capacity at the time of soldering, and has a second heat capacity larger than the first heat capacity at the time of soldering the components. Wiring pattern.

The member for increasing the heat capacity at the time of soldering is, for example, a connection portion to which components are soldered (for example, due to the heat capacity of a component to be soldered by a pad or the like), or a configuration in which a plurality of substrates are stacked. A pattern formed of an interlayer connection portion (for example, a via hole or a through hole) for connecting each layer to a layer having a large area of a conductive portion (a so-called solid layer), that is, a power supply pattern or a ground pattern, is heated. It is a member that sometimes becomes difficult to raise the temperature. In the middle of the second wiring pattern, a cut-off heat interrupting portion is provided.

The soldering of the components is performed, for example, by applying paste-like solder to a portion to be soldered and heating the portion to which the solder has been applied. When there are many members that increase the heat capacity, the temperature is hard to rise, and the time until the solder reaches the melting point becomes long. In the present invention, by providing the heat blocking portion in the middle of the second wiring pattern, the heat capacity of the second wiring pattern can be reduced, and the temperature tends to increase. Therefore, it is possible to quickly reach the melting point of the solder.

Therefore, for example, the heat capacity of the first wiring pattern and the heat capacity of the second wiring pattern can be made uniform, and the temperature difference at the time of soldering the entire board, that is, the melting point of the solder and the heat resistance temperature of the component can be reduced. Can be reduced and averaged. Therefore, even when lead-free solder having a high melting point is used for soldering, it is possible to perform soldering without damaging the components.

Further, since the heat interrupting portion is configured by simply cutting the wiring pattern, it is difficult to transmit at high speed without locally reducing the cross-sectional area of the wiring or increasing the wiring distance. And the current capacity is not reduced. That is, the electrical characteristics do not deteriorate. Further, the cut allows the heat to be surely shut off, so that the temperature at the time of soldering can be quickly increased. The wiring pattern may be cut after the circuit pattern is formed on the substrate, or the circuit pattern cut from the beginning may be formed on the substrate.

According to a second aspect of the present invention, there is provided a printed wiring board in which components are mounted by soldering on a substrate on which a circuit pattern is formed, wherein the circuit pattern increases a heat capacity when the components are soldered. , And a heat cut-off portion provided by cutting a halfway of the wiring pattern.

The circuit pattern includes a wiring pattern which is connected to a member which increases the heat capacity at the time of soldering the above-mentioned components, and is provided with a heat cut-off portion which is cut in the middle of the wiring pattern. For this reason, when the components are soldered, the side to which the member for increasing the heat capacity is not connected is not affected by the side to which the member for increasing the heat capacity is connected. For this reason, it is possible to independently perform thermal design with the heat blocking portion as a boundary.

According to a third aspect of the present invention, in the wiring pattern, a connection portion for soldering the component and a member for increasing the heat capacity are connected.

In the wiring pattern, a connection portion for soldering a component and a member for increasing the heat capacity are connected, and a part of the wiring pattern is cut off. For this reason,
The heat capacity of the connection portion is reduced, and the component can be quickly soldered at the time of soldering the component.

The connecting portion may be, for example, a conductive pad for connecting electronic components surface-mounted on the substrate. Here, electronic components mounted on the surface include, for example, I
Semiconductor packages such as C and LSI, chip components, connectors and the like are included. ICs and LSIs have terminals, that is, a plurality of connection portions. As described above, the connection portions connected to the wiring pattern having many members that increase the heat capacity have a large heat capacity, and the temperature of the connection portions does not easily increase. The time until the solder reaches the melting point becomes longer. In such a case, a temperature difference is generated between different connection parts depending on the wiring pattern during soldering. However, by cutting the middle of the wiring pattern having many members that increase the heat capacity, the heat capacity can be reduced. The number of members to be increased can be made close to the heat capacity of the connection portion connected to the wiring pattern with a small number, and the temperature difference within the same component can be reduced.

In general, a semiconductor package such as an IC or an LSI has a large heat capacity, and a chip component such as a chip resistor has a small heat capacity. However, it is necessary to cut the middle of a wiring pattern connected to a connection portion of the semiconductor package. Thereby, the temperature of the connection portion of the semiconductor package can be quickly increased. Therefore, it is possible to reduce the temperature difference between components having different heat capacities during soldering, that is, within the substrate.

Further, the connection portion may be a conductive land for connecting an electronic component inserted into the substrate. Here, the electronic components inserted into the substrate include axial components such as resistors and diodes, and axial components such as capacitors.

As described above, the components include a semiconductor package such as an IC and components constituting an electronic circuit such as a resistor, a capacitor, and a diode, but a component that does not constitute an electronic circuit, for example, shields a substrate. Shield members and the like are also included.

The cut wiring pattern must be reconnected in order to finally function as an electronic circuit. For example, after the components are soldered to the board, the cut portions may be reconnected by manual soldering using a soldering iron or the like, but this increases the number of steps.

According to a fourth aspect of the present invention, the member for increasing the heat capacity includes at least one of a connection portion for soldering the component, an interlayer connection portion, a power supply pattern, and a ground pattern. It is characterized in that the interrupting part is electrically connected to the component by means of a conductive member having a heat capacity smaller than the heat capacity of the member that increases the heat capacity by being soldered simultaneously with the component.

The components for increasing the heat capacity include at least one of the components described above, and the thermal cutoff is soldered simultaneously with the component by means of a conductive member. It is preferable to provide a conductive pad in a cut portion before soldering. Thereby, the parts can be soldered and the easily cut wiring patterns can be automatically electrically reconnected.

At the time of soldering parts, the conductive member
Since the heat capacity is smaller than the heat capacity of the member that increases the heat capacity, the cut off part can be soldered easily and quickly, and the heat of the connection part at the time of soldering is connected to the other side through the heat cut off part. Therefore, the component is absorbed by the component side of the connection portion and is soldered, not by the component side that increases the heat capacity to be performed. Therefore, the temperature difference in the substrate at the time of soldering can be reduced.

The conductive member is preferably a member having a sufficiently low resistance value such as a resistance value of substantially zero in order to prevent deterioration of the electrical characteristics, and for example, a jumper wire or a chip resistor can be used. . Thereby, the cut portion can be reconnected with an inexpensive configuration. Note that an insertion member having a lead wire may be used as long as the resistance value is low and the conductivity is high.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a printed wiring board 10 according to the present embodiment. The printed wiring board 10 includes an insulating substrate 11, and the pad 1 is provided on the substrate 11.
2A to 12C are provided corresponding to positions where the terminals 14A of the semiconductor package 14, which are surface mount components such as ICs, are soldered. Semiconductor package 1
4 terminals 14A are connected to corresponding pads 12A to 12A, respectively.
C, and soldered by, for example, reflow soldering.

Of these pads 12A to 12C, the leading pattern 16 is connected to the pad 12A, the leading pattern 16 is not connected to the pad 12B, and the leading pattern 16 is connected to the pad 12C. A via hole 18 is connected to the lead pattern 16. Furthermore, drawer pattern 1
As shown in FIG. 1, the wire 6 is disconnected in the middle, and pads 12D and 12E are connected to ends of the disconnected lead patterns 16A and 16B, respectively.

As shown in FIG. 2, the printed wiring board 10 is a multilayer board in which a plurality of boards 11A and 11B are stacked, and a ground layer 20 is provided between the boards in a so-called solid pattern. The ground layer 20 and the lead pattern 16B are connected by a via hole 18.

Next, the operation of the first embodiment will be described.

First, a solder paste (cream solder) 22 made of lead-free solder (SnAgCu) is printed on the printed wiring board 10 by a solder printing device (not shown). Thereby, the solder paste 22 is applied on the pads 12A to 12C. In the present embodiment, the solder paste 22 is not applied on the pads 12D and 12E provided at the ends of the disconnected lead pattern 16.

Then, the semiconductor package 14 is placed at a predetermined position on the printed wiring board 10 by a component inserter (not shown), that is, the semiconductor package 14
Are mounted so that each of the terminals 14A is placed on the corresponding pad 12.

Then, the printed wiring board 10 on which the semiconductor package 14 is mounted passes through a reflow furnace (heat furnace), whereby the solder paste 22 is melted. At this time, since the extraction pattern 16 is disconnected,
As shown in FIG. 2, heat when the solder paste 22 is melted escapes only to a path indicated by a dotted line in the figure, that is, to the semiconductor package 14 having a large heat capacity. For this reason, the temperature of the pad 12C quickly rises, and the solder paste 22 can be dissolved in the same short time as the other pads 12A and 12B.

After fixing the semiconductor package 14 in this way, the disconnected lead patterns 16A, 16A
B is connected by, for example, a 0 ohm resistor (not shown) having a resistance value of 0 or a jumper wire. Thereby, the terminal 14A
Is connected to the ground layer 20. This may be performed manually by using a soldering iron or the like, or may be performed automatically. Also, soldering may be performed using a known soldering device such as a heating device using a light beam or a partial hot air heating device.

As described above, the lead-out pattern 16 connected to the ground layer 20 is disconnected in advance, and then the semiconductor package 14 is mounted on the printed wiring board 10 by reflow soldering. The peak temperature of the pad 12C increases, and becomes almost the same as the peak temperatures of the pads 12A and 12B.

FIG. 3 shows a conventional drawing pattern 1.
6 shows the peak temperature of each of the pads and the aluminum electrolytic capacitor (not shown) when each of the printed wiring board in which the wiring pattern 6 is not disconnected and the printed wiring board 10 in which the lead-out pattern 16 in the present invention has been disconnected are passed through a reflow furnace. As shown in FIG. 3, since the temperature of the pad 12C in which the extraction pattern 16 is disconnected becomes high in a short time, the peak temperature of the pad 12C without the extraction pattern is increased.
Is almost the same as Therefore, the temperature difference between the terminals, that is, the temperature difference in the same component can be reduced, and
The temperature difference between different components, that is, the temperature difference in the substrate can be reduced, and even when lead-free solder having a high melting point is used, the components can be soldered without being damaged.

Further, since it is not necessary to change the width and length of the extraction pattern 16, it is possible to prevent the deterioration of the electrical characteristics, that is, the inability to transmit at high speed and the reduction in current capacity. it can.

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIG.

FIG. 4 shows a printed wiring board 10 according to the present embodiment. The same parts as those of the printed wiring board 10 in the first embodiment are denoted by the same reference numerals.

The printed wiring board 10 shown in FIG. 4 is different from the printed wiring board 10 shown in FIG. 1 in that the semiconductor package 14 is mounted and, at the same time, the printed wiring board 10 is provided at the ends of the disconnected lead patterns 16A and 16B. Pad 1
The point is that the conductive member 24 is mounted on 2D and 12E. The conductive member 24 is formed of a member having an extremely small electric resistance such as a 0 ohm resistance and having a heat capacity smaller than the heat capacity of the semiconductor package 14 and the ground layer 20. Further, as the structure of the conductive member 24, a structure in which a core member such as copper or nickel is sealed with ceramic, epoxy resin, or the like is preferable.

Next, the operation of the second embodiment will be described.

First, a solder paste (cream solder) 22 made of lead-free solder (SnAgCu) is printed on the printed wiring board 10 by a solder printing device (not shown). Thereby, the solder paste 22 is applied on the pads 12A to 12E.

Then, the semiconductor package 14 is placed at a predetermined position on the printed wiring board 10 by a component insertion machine (not shown), that is, the semiconductor package 14
Are mounted so that each of the terminals 14A is placed on the corresponding pad 12. In addition, the conductive member 2
4 are placed on the pads 12D and 12E.

Then, the printed wiring board 10 on which the semiconductor package 14 and the conductive member 24 are mounted passes through a reflow furnace (heat furnace).
Dissolves. At this time, since the heat capacities of the semiconductor package 14 and the ground layer 20 are both larger than the heat capacities of the conductive members 24, the heat of the pads 12C escapes only to the semiconductor package 14 side, and the heat of the pads 12D escapes only to the conductive member 24 side. Absent. Further, the heat of the pad 12E is applied to the conduction member 24,
It escapes only to the ground layer 20. Therefore, the pad 12
The temperature of the portions C, 12D, and 12E quickly rises, and the solder paste 22 can be melted in almost the same short time as the other pads 12A and 12B, and the temperature difference in the substrate is reduced as shown in FIG. Can be.

Further, since the conductive member 24 is also soldered simultaneously with the soldering of the semiconductor package 14, the step of connecting the conductive member 24 becomes unnecessary, and the man-hour load can be reduced.

[Third Embodiment] A third embodiment of the present invention will be described with reference to FIG. In the first and second embodiments, the case where surface mount components are mounted on the printed wiring board 10 has been described. However, in the third embodiment, axial components such as resistors and diodes, and components such as capacitors and the like are mounted on the printed wiring board 10. The present invention is applied to a case where a radial component, that is, an insertion component is mounted.

As shown in FIG. 5, the printed wiring board 10
The lead 26A of the capacitor 26 has a lead-free solder 2
8, the lead pattern 16 connected to the pad 12D to be soldered is disconnected. Thereby, when soldering, heat is generated in the via hole 1.
8, the temperature difference in the substrate can be reduced.
As in the first and second embodiments, the conductive member 24 may be soldered manually using, for example, a soldering iron or the like, or may be automatically soldered.

As described above, it is more preferable to apply the present invention to a portion where the temperature does not easily rise, but there is no problem if the present invention is applied to other portions.

[0054]

As described above, according to the present invention,
The temperature difference in the substrate at the time of soldering can be reduced, and even when lead-free solder having a high melting point is used, the components can be soldered without damaging the components.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a printed wiring board according to a first embodiment.

FIG. 2 is a cross-sectional view of the printed wiring board according to the first embodiment.

FIG. 3 is a diagram showing a peak temperature of each component.

FIG. 4 is a cross-sectional view of a printed wiring board according to a second embodiment.

FIG. 5 is a cross-sectional view of a printed wiring board according to a third embodiment.

FIG. 6 is a diagram showing a relationship between a melting point of solder and a peak temperature of a component.

FIG. 7 is a diagram showing a peak temperature of each component.

FIG. 8 is a plan view of a conventional printed wiring board.

FIG. 9 is a cross-sectional view of a conventional printed wiring board.

FIG. 10 is a diagram showing a conventional peak temperature of each component.

FIG. 11 is a view showing a conventional pad.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Printed wiring board 11 Substrate 12 Pad 14 Semiconductor package 16 Lead pattern 18 Via hole 20 Ground layer 22 Solder paste 24 Conductive member

Claims (4)

[Claims] 1. A printed wiring board in which components are mounted by soldering on a substrate on which a circuit pattern is formed, wherein the circuit pattern has a first wiring pattern having a first heat capacity when the components are soldered. And a second wiring pattern having a second heat capacity larger than the first heat capacity, wherein a heat interrupting portion is provided by cutting off the middle of the second wiring pattern. substrate. 2. A printed wiring board in which components are mounted by soldering on a substrate on which a circuit pattern is formed, wherein the circuit pattern is connected to a member that increases heat capacity when the components are soldered. A printed circuit board provided with a thermal cut-off portion cut in the middle of the wiring pattern. 3. The printed wiring board according to claim 2, wherein the wiring pattern is connected to a connection portion for soldering the component and a member that increases the heat capacity. 4. The member for increasing the heat capacity includes a connection portion for soldering the component, an interlayer connection portion, a power supply pattern,
And at least one of a ground pattern and the heat interrupting portion is electrically connected to the component by soldering simultaneously with the component by a conductive member having a heat capacity smaller than a heat capacity of the member for increasing the heat capacity. The printed wiring board according to claim 2 or 3, wherein: