JP2007180078A - Printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce poor electrical contacts between components due to scattering or attachment of flux during a reflow process. <P>SOLUTION: The printed circuit board has such a structure that part above a pattern land to which a component formed on an insulation substrate is to be soldered is coated with a solder resist to form a solder resist formed portion. In part of the solder resist formed portion, a concave portion is formed wherein there is no solder resist existing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printed circuit board on which components are mounted using a reflow apparatus, and more particularly to a technique for reducing contact failure due to flux scattering during reflow.

  The component mounting method on a printed circuit board in a small electronic device such as a video camera is such that a solder paste including solder and flux is printed on a pattern land formed on an insulating substrate, and then a soldering terminal of the component is mounted. It is mounted according to the position of the pattern land for joining, the solder is melted by heating by a reflow device, and the part and the pattern land on the printed circuit board are electrically connected by metal joining. The solder also has a role of physically fixing and holding the component on the printed circuit board in addition to electrical bonding between the soldering terminal of the component and the pattern land.

  In addition, the flux contained in the solder paste has the effect of removing the oxide film on the pattern land formed on the insulating substrate and preventing the oxidation, as well as lowering the interfacial tension of the solder to facilitate soldering. Effective and indispensable material for soldering. However, the flux has an electrical insulating property and has a property of flowing out from the solder portion and being scattered in a high temperature environment during soldering. Here, in the case of a small electronic device such as a video camera, it is necessary to use a small component, and a connection terminal may be disposed in the vicinity of the solder portion. Therefore, there is a problem that the scattered flux adheres to the surface of the connection terminal and causes poor contact.

In the conventional technology for reducing such flux outflow / scattering, solder is provided by providing a barrier that is high enough to prevent the flux from flowing out between the electrodes of the circuit board to form a continuous flux coating. A continuous flux residue is not formed between the electrodes of the electronic circuit board after being attached. (For example, see Patent Document 1)
In another conventional technique, when the solder resist film 6 is formed on the upper side of the insulating substrate 1 by silk printing, a flux reservoir recess 8 is provided to prevent spots of flux generated on the solder resist surface. Yes. (For example, see Patent Document 2)
JP 2002-185129 A JP-A-5-13938

  In recent years, as a video camera is miniaturized, a small connection connector for connecting to an external device has been used. In such a connector, in order to cope with the force applied when connecting a cable or the like, mechanical strength is ensured by providing a reinforcing terminal and soldering to the pattern land through the through hole of the printed circuit board. ing. That is, it is common to ensure mechanical strength by soldering solder on a pattern land of a predetermined size so as to swell the solder. Therefore, a solder part becomes high and the flux from a solder part will also flow from a high place. In addition, the distance between the reinforcing terminal and the connecting terminal that comes into contact with the cable has been reduced due to the miniaturization of the connecting connector, and the flux at the time of soldering the reinforcing terminal is likely to adhere to the contact terminal.

  However, the prior art described in Patent Document 1 prevents flux from the solder portion of the chip component, and does not consider flux outflow when solder is raised like a connection connector. That is, since the insulating layer is disposed adjacent to the electrode portion and the cream solder portion, there is a problem that flux outflow cannot be prevented when the solder rises more than the insulating layer. Furthermore, the insulating layer needs to be formed of a separate member such as a resin, which increases the cost of the printed circuit board.

  The problems of the prior art described in Patent Document 2 will be described with reference to FIGS. Here, a case where a connection connector for connecting to an external device as a component is soldered will be described and described.

  FIG. 4 shows a cross-sectional view of a printed circuit board on which components of the prior art are mounted. 1 is an insulating substrate, 2 is a pattern land made of copper foil, 3 is a solder resist formed on the insulating substrate 1 or the pattern land 2, 4 is a solder part, 5 is a flux flowing out of a solder paste (not shown), 6 is a reinforcing terminal of a connection connector to which a cable is connected in order to connect with an external device, 7 is a connection connector, and 8 is in contact with the connection terminal of the cable to make an electrical connection with the external device in the connection connector 7. The connection terminal 11 is a recess where the solder resist 3 is not formed on the insulating substrate 1, 51 is a flux scattered and adhered to the connection terminal 8, and U is the thickness dimension of the solder resist 3. Here, a large amount of solder paste is printed on the pattern land 2 and the reinforcing terminals 6 are mounted through the through holes 12 and then heated by a reflow device. Flux 5 flows out from the elevated position toward the periphery. However, since the height of the wall corresponding to the thickness U (for example, 25 μm) of the solder resist 3 is insufficient, the flow of the flux 5 cannot be stopped so much in the concave portion 11, and the flux 5 exceeds the concave portion 11 and the solder 5 When the resist 3 flows up to the vicinity of the connection terminal 8 and scatters there, the scattering flux 51 may adhere to the connection terminal 8. Due to the electrical insulation of the scattered flux 51, there arises a problem that the external connection by the connection terminal 8 is not made.

  Next, FIG. 5 shows a cross-sectional view of a printed circuit board on which components are mounted when the pattern land 2 is large. Here, the pattern land 2 is enlarged toward the connection terminal 8 in order to ensure physical strength corresponding to the force applied to the connection connector 7 when the cable is connected. Also in this case, similarly to FIG. 4, the flux 5 generated when the solder is melted by the heating by the reflow device flows out from the high position toward the periphery. In this case, since the concave portion 11 is far from the solder portion 4, the height of the flux 5 away from the solder portion 4 is low. Therefore, the flux 5 emitted from the solder portion 4 has a thickness U ( For example, the concave portion 11 having a height of 25 μm) stops as a wall, but the concave portion 11 becomes close to the connection terminal 8, and the scattering flux 51 adheres to the connection terminal 8 due to the scattering of the flux 5. As in the case described, there arises a problem that electrical connection to the outside by the connection terminal 8 is not performed.

  An object of the present invention is to provide a recess that does not form a solder resist in a part of a solder resist formation portion on a pattern land formed on an insulating substrate, thereby stopping the flow of flux and electrically It is providing the printed circuit board which reduces a contact failure.

  In order to solve the above-described problems, the present invention includes a pattern land for soldering a component formed on an insulating substrate, and a solder resist forming portion that covers a part of the pattern land with a solder resist. In the printed circuit board having the structure, a concave portion that does not form a solder resist is provided in a part of the solder resist forming portion. Thereby, the flow of a flux can be stopped and the electrical contact failure by scattering and adhesion of a flux can be reduced. Further, since a separate member for forming the wall is unnecessary, the cost is not increased.

  Further, the pattern land is a pattern land having a predetermined size corresponding to a required mechanical strength. As a result, the distance from the connection terminal can be secured even when the pattern land is large in order to ensure mechanical strength, such as the reinforcing terminal of the connection connector, thus reducing electrical contact failures due to flux scattering and adhesion. Can do.

  According to the present invention, by providing a recess that does not form a solder resist in a part of the solder resist forming portion on the pattern land formed on the insulating substrate, the flow of flux is stopped, and the electrical contact failure due to the scattering and adhesion of the flux Can be reduced.

  Hereinafter, an embodiment of a printed circuit board according to the present invention will be described in detail with reference to FIGS.

  First, an embodiment of a printed circuit board according to this embodiment will be described with reference to FIG. FIG. 1 shows a cross-sectional view of a printed circuit board on which components according to this embodiment are mounted.

  1 is an insulating substrate, 2 is a pattern land made of copper foil, 3 is a solder resist formed on the insulating substrate 1 or the pattern land 2, 4 is a solder part, 5 is a flux from a solder paste (not shown), 6 is a reinforcing terminal of a connection connector to which a cable is connected in order to connect to an external device, 7 is a connection connector, and 8 is a connection in contact with the connection terminal of the cable for electrical connection with the external device in the connection connector. A terminal, 9 is a recess on the pattern land where no solder resist is formed, 12 is a through hole, U is a thickness dimension of the solder resist 3, V is a thickness dimension of the pattern land 2, and L is a distance from the reinforcing terminal 6 of the recess 9 The dimension from an end surface to the connection terminal 8 is shown.

  The printed circuit board according to the present embodiment has a structure in which a concave portion 9 where the solder resist 3 is not formed is provided on the pattern land 2 on the connection terminal 8 side of the pattern land 2 to which the reinforcing terminal 6 is connected. Note that a plurality of the recesses 9 may be provided.

  When the connection connector 7 having the reinforcing terminal 6 is mounted on the printed circuit board having this structure, a large amount of solder paste (not shown) is printed on the pattern land 2 to ensure the mechanical strength. When the solder paste is melted by heating with a reflow device after the solder is mounted through the through hole 12, the flux 5 emitted from the solder paste flows along the solder resist 3 at the same time. When mounting the connection connector 7 having the reinforcing terminal 6, the reinforcing terminal 6 is fixed on the pattern land 2 by the solder portion 4 with a predetermined mechanical strength, so that it is necessary to increase the amount of solder paste. As a result, the height of the solder part 4 increases (rises). Therefore, when the solder paste is melted by the heating by the reflow device, the flux 5 emitted from the solder portion 4 flows out from a high position. Here, according to the printed circuit board according to the present embodiment, the concave portion 9 where the solder resist 3 is not formed is provided on the pattern land 2 having a thickness V (35 μm in the present embodiment). Is the sum of the thickness dimension U of the solder resist 3 (25 μm in this embodiment) and the thickness dimension V of the pattern land 2 (35 μm in this embodiment) (60 μm in this embodiment). The flow of the flux 5 flowing out from the solder portion 4 at the time of melting can be stopped by the wall of the solder resist 3 formed by the recess 9. As a result, the flux 5 stops at the recess 9 and does not approach the connection terminal 8 any more, so that the distance L between the flux 5 and the connection terminal 8 can be increased. Therefore, even if the flux 5 is scattered, it is difficult to reach the connection terminal 8, the adhesion of the flux 5 to the connection terminal 8 can be reduced, and the connection connector due to the adhesion of the flux 5 to the connection terminal 8 generated in the prior art. 7 and electrical connection failures between external devices can be reduced. Further, since the wall is formed by the solder resist concave portion on the pattern land, the cost is not increased.

  Next, an example of a printed circuit board on which the component according to this example is mounted will be further described with reference to FIG. FIG. 2 shows a top view of the printed circuit board according to this embodiment. In addition, the same part as FIG. 1 mentioned above is made into the same number, and description of the same number is abbreviate | omitted here. Reference numeral 10 denotes a direction in which the flux 5 flows to the connection terminal 8 side.

  In the printed circuit board according to this embodiment, the outer periphery of the pattern land 2 is covered with the solder resist 3, the solder paste is melted around the through hole 12 through which the reinforcing terminal 6 is passed, and the pattern on the connection terminal 8 side. On the land 2, there is provided a recess 9 where the solder resist 3 is not formed.

  Here, when the solder paste is melted by heating by the reflow apparatus, the flux 5 flowing out from the solder portion 4 simultaneously flows in the direction indicated by 10, but is provided by the recess 9 that does not form the solder resist 3 on the pattern land 2. Can be stopped by a wall. For this reason, the flux emitted from the solder paste stops at the concave portion 9 and does not approach the connection terminal 8 any more. Therefore, the distance L between the flux 5 and the connection terminal 8 can be increased. Therefore, even if the flux 5 is scattered, it is difficult to reach the connection terminal 8, the adhesion of the flux 5 to the connection terminal 8 can be reduced, and the connection connector due to the adhesion of the flux 5 to the connection terminal 8 generated in the prior art. Etc. and poor electrical connection between the external device and the like can be reduced.

  Next, how to determine the dimensions of the printed circuit board according to this embodiment will be described with reference to FIG. FIG. 3 is a cross-sectional view of the printed circuit board according to this embodiment. P is a pattern land width dimension from the end face of the through hole 12 of the pattern land 2 to the connection terminal 8 side, Q is a pattern A width dimension of the pattern A21 from the end face of the through hole 12 side to the solder resist 3, and R is on the pattern land 2 The resist A width dimension of the solder resist A31, S is the width dimension of the recess 9 and T is the resist B of the solder resist B32 from the end face of the recess 9 far from the reinforcing terminal 6 to the end face of the pattern land 2 far from the reinforcing terminal. Indicates the width dimension.

  In this embodiment, the pattern land width dimension P is set to 0.4 mm as a dimension for fixing the reinforcing terminal 6 to the pattern land 2 with a predetermined mechanical strength. Here, since the height of the flux 5 flowing out from the solder part 4 is lower when the distance is far from the solder part 4, it is more effective to move the recess 9 away from the solder part 4 as much as possible. It is better to make it as small as possible. Further, the wall of the concave portion 9 needs to be formed on the pattern land 2 even if there is a variation in manufacturing the printed circuit board. In this example, since the manufacturing variation in forming the solder resist 3 on the pattern land 2 is 0.05 μm, the resist B width dimension T is set to 0.05 μm as a center value. Further, the recess width dimension S was determined by the amount of solder paste printed on the pattern land 2 for connecting the reinforcing terminal 6 and the length of the recess 9. Since the amount of flux flowing out from the solder paste increases as the amount of solder paste increases, it is necessary to be able to store all the flux flowing out from the solder paste. Further, due to the manufacturing limitation that the solder resist formation width is a minimum value of 0.1 μm, the resist A width dimension R was set to 0.1 μm. As a result, the remaining pattern A width dimension Q was 0.15 μm.

  From the above, by using the structure of the printed circuit board of this embodiment, it is possible to print components such as connectors for connection to external devices having reinforcing terminals for physically fixing the components on the printed circuit board by soldering. When mounting on a substrate, it is possible to secure the distance between the flux flowing out from the solder part and the connection terminal with the external device in the component such as the connection connector, so that the adhesion of the flux to the connection terminal can be reduced, and the connection It is possible to reduce poor electrical connection with external devices such as connectors.

Sectional view of a printed circuit board on which components according to the embodiment are mounted Top view of printed circuit board on which components according to the embodiment are mounted Cross section of printed circuit board according to the embodiment Cross-sectional view of a printed circuit board with conventional parts Sectional view of a printed circuit board on which components are mounted when the pattern land 2 of the prior art is large

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Pattern land, 3 ... Solder resist, 4 ... Solder part,
5 ... flux, 6 ... reinforcing terminal, 7 ... connection connector, 8 ... connection terminal, 9 ... recess,
10 ... direction of flux flow, 11 ... recess, 12 ... through hole, 21 ... pattern A,
31 ... Solder resist A, 32 ... Solder resist B, 51 ... Scattering flux,
L: Distance, P: Pattern land width dimension, Q: Pattern A width dimension,
R: resist A width dimension, S: recess width dimension, T: resist B width dimension,
U: Solder resist thickness dimension, V: Pattern land thickness dimension

Claims (2)

In a printed circuit board comprising a pattern land for soldering a component formed on an insulating substrate, and a solder resist forming part that covers a part of the pattern land with a solder resist,
A printed circuit board, wherein a concave portion that does not form a solder resist is provided in a part of the solder resist forming portion. The printed circuit board according to claim 1, wherein the pattern land is a pattern land having a predetermined size according to a required mechanical strength.

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