JP2013045919A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an unmelted solder paste from occurring and securely join a surface mounted component and a printed wiring board to each other when the surface mounted component is joined to the printed wiring board with reflow soldering.SOLUTION: A surface mounted component 100 is mounted on a printed wiring board 1 with reflow soldering using a solder paste. The printed wiring board 1 includes vent holes 4 which are formed immediately below the surface mounted component 100 surface-mounted on a first surface 1a and allows gases to pass from a second surface 1b to the first surface 1a.

Description

  The present invention relates to a printed wiring board.

  In recent years, many surface mount components (SMD: Surface Mount Device) are mounted on printed wiring boards. Such surface mount components are, for example, reflow soldering in which solder paste is melted by placing the surface mount components on a printed wiring board via a solder paste containing powdered solder and flux. To be bonded to the printed wiring board.

  By the way, in the reflow soldering, the solder paste is melted in a uniform temperature environment equal to or lower than the heat-resistant temperature of the surface mount component or the like. However, if the surface mount component has a large heat capacity such as a large electrolytic capacitor, the surface mount component loses heat, and as a result, the heating efficiency of the solder paste decreases. That is, the temperature of the solder paste varies depending on the location where it is placed, and a partially unmelted solder paste may be generated.

  In order to prevent such unmelted solder paste from occurring, it is conceivable to take measures to increase the heating temperature of the solder paste. Such countermeasures cannot be used. Therefore, Patent Document 1 proposes a printed wiring board having a through via hole connected to a land. In such a printed wiring board, hot melt is supplied from the opposite side of the mounting surface of the surface mount component, and the land is locally heated by the hot air passing through the through via hole, thereby causing unmelting of the solder paste. It is intended to suppress.

JP 10-229273 A

  However, in the printed wiring board disclosed in Patent Document 1, hot air supplied from the opposite side of the mounting surface of the surface mounting component and passing through the through via hole blows through without staying in the vicinity of the land. For this reason, in the printed wiring board disclosed by patent document 1, the temperature of a solder paste cannot fully be raised and the unmelting of a solder paste cannot be prevented reliably.

  The present invention has been made in view of the above-described problems, and prevents the solder paste from being unmelted when the surface mount component is joined to the printed wiring board by reflow soldering. The object is to join the mounting component and the printed wiring board.

As means for solving the above problems, the present invention adopts the following configuration.
A first invention is a printed wiring board on which a surface mount component is mounted by reflow soldering using a solder paste, and is formed immediately below the surface mount component to be surface mounted on the first surface. A configuration is adopted in which a ventilation hole is provided to allow gas to pass from the second surface to the first surface.
According to a second aspect, in the first aspect, the air hole is formed only directly below a surface-mounted component having a heat capacity exceeding a predetermined threshold value.
According to a third invention, in the second invention, a configuration is adopted in which a heat conduction preventing member is disposed between a surface mount component having a heat capacity lower than the threshold value and the vent hole.
According to a fourth invention, in any one of the first to third inventions, a configuration is provided in which a conductive layer is provided which is connected to a pad on which a solder paste is placed and covers an inner wall surface of the vent hole.
In a fifth aspect of the present invention, in any one of the first to fourth aspects, the plurality of vent holes are provided, and the arrangement pattern of the vent holes coincides with the arrangement pattern of the plurality of connection terminals of the dip component. adopt.

In the present invention, a vent hole that allows gas to pass from the second surface side opposite to the first surface on which the surface-mounted component is mounted is provided to the first surface side. It is formed directly under the mounting component. For this reason, in reflow soldering, hot air that has passed through the vent hole from the second surface side to the first surface side is blown to the surface-mounted component. By blowing hot air onto the surface-mounted component in this way, the surface-mounted component is heated to the same temperature as the ambient temperature in a short time even when the heat capacity of the surface-mounted component is large. For this reason, it is possible to prevent the heating efficiency of the solder paste from being reduced due to the amount of heat taken by the surface mount component.
Moreover, since the hot air that has passed through the ventilation holes is blown onto the surface-mounted component as described above, the hot air stays between the surface-mounted component and the printed wiring board, and ensures a long heat exchange time between the hot air and the solder paste. And the solder paste can be heated more efficiently.
Thus, according to the printed wiring board of the present invention, it is possible to efficiently heat the solder paste when mounting the surface-mounted component by reflow soldering. For this reason, generation | occurrence | production of an unmelted solder paste can be prevented and a surface mount component and a printed wiring board can be joined reliably.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram of the printed wiring board concerning 1st Embodiment of this invention, (a) is a top view, (b) is a typical enlarged view containing an electrolytic capacitor, (c) is (b) It is an AA line longitudinal cross-sectional view of). It is a schematic diagram which shows the process of mounting an electrolytic capacitor on the printed wiring board which concerns on 1st Embodiment of this invention. It is a figure which shows typically schematic structure of the printed wiring board which concerns on 2nd Embodiment of this invention, and is the longitudinal cross-sectional view which expanded a part containing an electrolytic capacitor.

  Hereinafter, an embodiment of a printed wiring board according to the present invention will be described with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size.

(First embodiment)
FIG. 1 is a schematic configuration diagram showing a printed wiring board 1 of the present embodiment, where (a) is a plan view, (b) is a schematic enlarged view including an electrolytic capacitor 100, and (c) is a schematic view. It is a longitudinal cross-sectional view of (b).
As shown in FIG. 1A, the printed wiring board 1 of the present embodiment is a substrate on which a large number of electronic components including a surface mount type electrolytic capacitor 100 (surface mount component) are mounted. In FIG. 1A, a part of the mounted component is shown, and the wiring pattern of the printed wiring board 1 is omitted. As shown in FIG. 1C, the printed wiring board 1 includes an insulating substrate 2, a wiring pattern 3, and a vent hole 4. In the following description, the upper surface (first surface) of the printed wiring board 1 in FIG. 1C is referred to as a front surface 1a, and the lower surface (second surface) of the printed wiring board 1 in FIG. This is referred to as back surface 1b.

  The insulating base material 2 is a plate-like member made of an insulating material such as a glass epoxy material or a glass composite material, and is provided with via holes for connecting the inner layer patterns to each other in addition to the vent holes 4.

  The wiring pattern 3 is a conductive layer made of copper. In this embodiment, the surface pattern 3a formed on the surface 1a of the insulating base material 2, the back surface pattern 3b formed on the back surface 1b of the insulating base material 2, and the inner layer pattern formed inside the insulating base material 2 3c and 3d are wiring patterns 3. The inner layer pattern 3c and the inner layer pattern 3d are formed in different layers at a predetermined interval in the thickness direction of the insulating base material 2. These front surface pattern 3a, back surface pattern 3b, and inner layer patterns 3c and 3d are connected to each other through a copper plating layer formed on the inner wall surface of a via hole provided at a predetermined location.

Further, the surface pattern 3a includes a pad 3a1 to which the first terminal 101 of the electrolytic capacitor 100 is bonded via the solder H1, and a pad 3a2 to which the second terminal 102 of the electrolytic capacitor 100 is bonded via the solder H2. Is provided. These pads 3a1 and 3a2 are also places where the solder paste P (see FIG. 2) is disposed when the electrolytic capacitor 100 is soldered by the reflow method.
Further, in the printed wiring board 1 of the present embodiment, the inner layer patterns 3c and 3d are provided so as to avoid being directly below the pads 3a1 and 3a2, as shown in FIG. For this reason, only the insulating base material 2 with low thermal conductivity exists below the pads 3a1 and 3a2.

  The vent hole 4 is a through hole penetrating from the front surface 1 a to the back surface 1 b of the printed wiring board 1, and two vent holes (the vent hole 4 a and the vent hole 4 b) are provided immediately below the electrolytic capacitor 100. Such a vent 4 allows gas to pass from the back surface 1b side of the printed wiring board 1 to the front surface 1a side (or vice versa). The term “directly below the electrolytic capacitor 100” as used herein means a region covered with the electrolytic capacitor 100 of the printed wiring board 1 (a region overlapping the electrolytic capacitor 100 when viewed from the surface 1a side). As will be described in detail later, these vent holes 4 allow hot air blown from the back surface 1b side to vent to the front surface 1a side when the electrolytic capacitor 100 is surface-mounted on the printed wiring board 1 by reflow soldering. The arrangement positions of these vent holes 4 are arbitrary as long as they are directly under the electrolytic capacitor 100, but the heat transfer to the solder paste P (see FIG. 2) used when soldering the electrolytic capacitor 100 is efficiently performed. It is preferable to form in the position. Specifically, it arrange | positions as close as possible to the pads 3a1 and 3a2 by which the solder paste P is arrange | positioned. Or it arrange | positions in the position where the hot air which passes through the ventilation hole 4 and collides with the electrolytic capacitor 100, and changes a flow direction is sprayed on pad 3a1, 3a2.

  Moreover, as shown in FIG.1 (c), the inner wall face of the vent hole 4 is covered with the copper foil 5 (electroconductive layer). The copper foil 5 is formed by plating, for example, and is connected to the pads 3a1 and 3a2 as shown in FIG. The copper foil 5a covering the inner wall surface of the vent hole 4a is connected to the pad 3a1, and the copper foil 5b covering the inner wall surface of the vent hole 4b is connected to the pad 3a2. These copper foils 5a and 5b are not shown in FIG. 1, but are connected to the back surface pattern 3b on the back surface 1b of the printed wiring board 1, and electrically connect the front surface pattern 3a and the back surface pattern 3b. doing. For this reason, copper foil 5a, 5b functions as a part of wiring.

  Further, of the two vent holes 4, one vent hole 4a (the vent hole 4 disposed on the upper side in FIG. 1B) and another vent hole 4b (disposed on the lower side in FIG. 1B). The distance D from the vent hole 4) is set to be the same as the distance between connection terminals of commonly used dip components (for example, a capacitor and a diode). That is, the arrangement pattern of the two (plurality) vent holes 4 matches the arrangement pattern of the connection terminals of the predetermined dip component. Since copper foils 5a and 5b functioning as wiring are provided on the inner wall surface of the vent hole 4, if the printed wiring board 1 of the present embodiment is used for other purposes, these vent holes 4 are used. It is also possible to mount dip parts.

As shown in FIG. 1 (c), in the printed wiring board 1 of the present embodiment, when the electrolytic capacitor 100 is soldered, it passes through on the back surface 1b side so that hot air flows smoothly into the vent hole 4. No electronic components are arranged in the vicinity of the pores 4.
As shown in FIG. 1A, three electrolytic capacitors 100 are installed on the printed wiring board 1 of the present embodiment, and vent holes 4 are provided directly below each electrolytic capacitor 100. .

  Next, a soldering method for mounting the electrolytic capacitor 100 on the printed wiring board 1 of the present embodiment will be described with reference to FIG. In the following description, it will be described that the electrolytic capacitor 100 is soldered to the printed wiring board 1, but in reality, other electronic components are also bonded to the printed wiring board 1 simultaneously in the soldering process described below. Is done.

  In the present embodiment, the electrolytic capacitor 100 is joined to the printed wiring board 1 by reflow soldering. First, as shown in FIG. 2A, a solder paste P containing solder powder and flux is disposed on the pads 3a1 and 3a2. The solder paste P is disposed on the pads 3a1 and 3a2 by, for example, a known printing technique.

  Subsequently, as shown in FIG. 2B, the first terminal 101 contacts the solder paste P1 disposed on the pad 3a1, and the second terminal 102 contacts the solder paste P2 disposed on the pad 3a2. Thus, the electrolytic capacitor 100 is arranged.

  Subsequently, as shown in FIG. 2C, hot air is supplied toward the printed wiring board 1 from each of the front surface 1 a side and the back surface 1 b side of the printed wiring board 1. The temperature of the hot air is set lower than the heat resistance temperature of the electrolytic capacitor 100 and higher than the melting temperature of the solder paste P. For this reason, the solder paste P is heated and melted by the hot air. Thereafter, the supply of hot air is stopped to solidify the molten solder, whereby the above-described solders H1 and H2 are formed, and the mounting of the electrolytic capacitor 100 is completed.

Here, the printed wiring board 1 of the present embodiment is provided with a vent hole 4 immediately below the electrolytic capacitor 100. For this reason, part of the hot air supplied from the back surface 1 b side of the printed wiring board 1 toward the printed wiring board 1 passes through the vent hole 4 and is blown to the electrolytic capacitor 100. By blowing hot air on the electrolytic capacitor 100 in this manner, even when the heat capacity of the electrolytic capacitor 100 is large, the electrolytic capacitor 100 is heated to the same temperature as the ambient temperature in a short time. For this reason, it is possible to prevent the heating efficiency of the solder paste P from being reduced due to the amount of heat taken by the electrolytic capacitor 100.
Further, since the hot air that has passed through the vent hole 4 is blown to the electrolytic capacitor 100 as described above, the hot air stays between the electrolytic capacitor 100 and the printed wiring board 1, and the heat exchange time between the hot air and the solder paste is increased. The solder paste P can be heated more efficiently.
As described above, according to the printed wiring board 1 of this embodiment, when the electrolytic capacitor 100 is mounted by reflow soldering, the solder paste P can be efficiently heated. For this reason, it can prevent that the unmelted solder paste P generate | occur | produces, and can join the electrolytic capacitor 100 and the printed wiring board 1 reliably.
Actually, when reflow soldering is performed in the same environment between the printed wiring board disclosed in Patent Document 1 in which a through-hole is formed in the pad and the printed wiring board 1 of the present embodiment, It was confirmed that the temperature in the vicinity of the solder paste P was higher by about 3 ° C. to 5 ° C. in the printed wiring board 1 of the embodiment.
The unmelted solder paste P is not only the one in which the solder paste P disposed on the pads 3a1 and 3a2 is not melted at all, but the one in which only a part of the solder powder contained in the solder paste P is unmelted. In other words, an electrical or structural joining state between the electrolytic capacitor 100 and the printed wiring board 1 assumed in advance cannot be obtained.

Further, in the printed wiring board 1 of the present embodiment, unlike the printed wiring board disclosed in Patent Document 1, since no holes are provided in the pads 3a1 and 3a2, the solder paste P can be used without worrying about the holes. It is possible to form an optimum fillet.
Moreover, in the printed wiring board disclosed in Patent Document 1, through holes are formed in the pads, the outer shape of the pads must be increased in order to ensure a contact area with the solder. On the other hand, in the printed wiring board 1 of this embodiment, since no hole is provided, it is not necessary to increase the outer shape of the pads 3a1 and 3a2, and the printed wiring board 1 can be downsized.

  Further, the printed wiring board 1 of the present embodiment includes a copper foil 5 that is connected to the pads 3 a 1 and 3 a 2 and covers the inner wall surface of the vent hole 4. For this reason, the heat quantity is transferred by heat conduction from the copper foil 5 heated by the hot air passing through the vent hole 4 to the pads 3a1 and 3a2, and the pads 3a1 and 3a2 can be heated more efficiently.

  Further, in the printed wiring board 1 of the present embodiment, the inner layer patterns 3c and 3d are provided so as to avoid being directly below the pads 3a1 and 3a2. For this reason, it can suppress that the calorie | heat amount of the hot air which passes the ventilation hole 4 is transmitted and diffused by the inner layer patterns 3c and 3d, and can heat the pads 3a1 and 3a2 efficiently.

(Second Embodiment)
Next, a printed wiring board 1A according to a second embodiment of the present invention will be described. In the description of the present embodiment, the description of the same parts as those of the printed wiring board 1 of the first embodiment is omitted or simplified.

  FIG. 3 is a diagram schematically illustrating a schematic configuration of the printed wiring board 1 </ b> A of the present embodiment, and is a partially enlarged longitudinal sectional view including the electrolytic capacitor 100. As shown in this figure, the printed wiring board 1A of this embodiment is close to the electrolytic capacitor 100 of the first embodiment, and a ceramic capacitor 200 (surface mounted component) is surface mounted on the surface 1a of the printed wiring board 1A. Has been. The ceramic capacitor 200 has a smaller heat capacity than the electrolytic capacitor 100 and is joined to the pads 3a3 and 3a4 via the solders H3 and H4.

  Similar to the electrolytic capacitor 100, such a ceramic capacitor 200 is also mounted by reflow soldering. However, since the thermal capacity of the ceramic capacitor 200 is small, the solder paste P disposed on the pads 3a3 and 3a4 melts without being heated by the hot air passing through the vent holes 4 when performing reflow soldering. For this reason, the printed wiring board 1 </ b> A of the present embodiment does not include the vent hole 4 immediately below the ceramic capacitor 200. That is, the printed wiring board 1 </ b> A of the present embodiment includes the vent hole 4 only directly below the electrolytic capacitor 100 having a heat capacity exceeding a predetermined threshold value. This threshold value indicates the heat capacity of the surface-mounted component that can reliably melt the solder paste P, and is a value determined by experiments or the like.

  In the printed wiring board 1A of the present embodiment, the solder resist 6 (heat conduction preventing member) disposed between the electrolytic capacitor 100 and the ceramic capacitor 200 is disposed on the surface 1a. The solder resist 6 regulates the wetting and spreading of the molten solder paste P and prevents heat conduction from the pads 3a1 and 3a2 to the pads 3a3 and 3a4. In such a printed wiring board 1A of the present embodiment, the vent hole 4 is not provided immediately below the ceramic capacitor 200, and heat conduction from the pads 3a1, 3a2 to the pads 3a3, 3a4 can be prevented. The pads 3a3 and 3a4 can be prevented from being unnecessarily heated.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the spirit of the present invention.

For example, when a plurality of surface-mounted components having a large heat capacity are mounted on the printed wiring board 1 of the above-described embodiment, it is preferable to provide the vent holes 4 directly below each surface-mounted component.
In the above embodiment, the surface mount component having a large heat capacity is the electrolytic capacitor 100. However, the surface mount component may be another electronic component such as an IC (Integrated Circuit) chip.
In the above-described embodiment, the configuration in which the two air holes 4 are provided directly below the electrolytic capacitor 100 has been described. However, it is conceivable to provide three or more or a single vent hole directly under the electrolytic capacitor 100.
Further, when a plurality of vent holes 4 are provided immediately below the electrolytic capacitor 100, it is not necessary that all the vent holes 4 have the same diameter. Further, the cross-sectional shape of the vent hole 4 need not be circular.
Furthermore, the diameter of the vent hole 4 can be reduced from the back surface 1b toward the front surface 1a, and the vent hole 4 can be shaped to be narrowed toward the front surface 1a. In such a case, the hot air from the back surface 1b side can be easily taken into the vent hole 4, and the flow rate of the hot air blown from the vent hole 4 to the electrolytic capacitor 100 can be increased. Conversely, the diameter of the vent hole 4 can be increased from the back surface 1b toward the front surface 1a, and the vent hole 4 can be shaped to expand toward the front surface 1a. In such a case, the amount of hot air entering the vent hole 4 from the back surface 1b side can be reduced, and the flow rate of hot air blown from the vent hole 4 to the electrolytic capacitor 100 can be slowed. The shape of the vent hole 4 is selected depending on the position of the pad and the shape of the electrolytic capacitor 100 (surface mount component).
Moreover, in the said embodiment, the structure which the electroconductive layer which covers the inner wall face of the vent hole 4 is the copper foil 5 was employ | adopted. In consideration of the fact that it can be formed simultaneously with the wiring pattern and ease of processing, it is preferable to use copper, but it is also possible to use other conductive layers.
Moreover, in the said embodiment, the structure whose heat conduction prevention member is the soldering resist 6 was demonstrated. However, the present invention is not limited to this, and a separately provided heat insulating material can be used as the heat conduction preventing member. In addition, when providing a heat insulating material separately as a heat conduction prevention member, the said heat insulating material can be easily formed in arbitrary patterns. For this reason, for example, a heat insulating material is formed so as to surround the surface mount component (for example, the electrolytic capacitor 100) having a high heat capacity, or the surface mount component (for example, the ceramic capacitor 200) for low heat quantity is surrounded. A material can be formed.

  DESCRIPTION OF SYMBOLS 1,1A ... Printed wiring board, 1a ... Front surface (1st surface), 1b ... Back surface (2nd surface), 2 ... Insulation base material, 3 ... Wiring pattern, 3a1-3a4 ... Pad 4, 4a, 4b ... vents, 5, 5a, 5b ... copper foil (conductive layer), 6 ... solder resist (heat conduction prevention member), H1-H4 ... solder, P, P1, P2 …… Solder paste, 100 …… Electrolytic capacitor (surface mount component), 200 …… Ceramic capacitor (surface mount component)

Claims (5)

A printed wiring board on which surface-mounted components are mounted by reflow soldering using a solder paste,
A printed wiring board, characterized in that it is formed immediately below a surface-mounted component that is surface-mounted on a first surface, and has a vent hole that allows gas to pass from the second surface to the first surface.   2. The printed wiring board according to claim 1, wherein the vent hole is formed only directly under the surface-mounted component having a heat capacity exceeding a predetermined threshold value.   The printed wiring board according to claim 2, wherein a heat conduction preventing member is disposed between the surface mount component having a heat capacity lower than the threshold and the vent hole.   The printed wiring board according to claim 1, further comprising a conductive layer that is connected to a pad on which the solder paste is placed and covers an inner wall surface of the vent hole.   5. The printed wiring board according to claim 1, wherein a plurality of the air holes are provided, and an arrangement pattern of the air holes is matched with an arrangement pattern of the plurality of connection terminals of the dip component.

Images