JP2006319145A - Metal core circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal core circuit board that minimizes an increase in costs, stabilizes quality easily because the metal core circuit board is manufactured easily, has no worries about an electrical short-circuiting by external moisture and rubbish, prevents warpage from occurring easily, and has superior soldering workability. <P>SOLUTION: The metal core circuit board 4 has a through-hole 14, and a metal layer 3 inside an insulating layer 1. A through-hole 16 is provided near a through-hole 14 of the metal layer 3, the through-hole 16 is filled with resin whose thermal conductivity is lower than that of the metal layer 3, and both the sides of the opening of the through-hole 16 are sealed by the insulating layer 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal core circuit board having a metal layer inside an insulating layer.

  A metal core circuit board is a circuit board in which, for example, a copper or aluminum metal plate is inserted as a metal layer inside an insulating layer of a circuit board such as a printed circuit board. The heat radiated from the circuit and the electronic component is efficiently transmitted to the metal layer, so that the heat radiation characteristic of the entire circuit board can be enhanced, and the temperature uniformity of the entire circuit board can be achieved. As a result, each circuit on the circuit board can be thinned, and a larger current can be passed through the thin circuit.

However, on the contrary, when soldering electronic components on the metal core circuit board, this characteristic is damaged, and the heat of the molten solder when soldering electronic components is diffused and dissipated through the metal layer. As a result, the temperature of the molten solder is lowered, causing a problem in soldering workability (hereinafter referred to as solder workability).
Specifically, the temperature of the molten solder decreases, the surface tension of the solder increases, the viscosity increases, and so on, for example, in a through hole, the solder rising into the through hole becomes worse. Solder workability deteriorated, and in the worst case, soldering failure occurred. In addition, voids may be formed in the through holes, resulting in unstable product quality, that is, reliability may be reduced.

In particular, instead of eutectic solder (Sn-Pb system) with a low melting temperature (soldering temperature) that has been generally used as in the past, that is, solder containing lead, it is lead-free from the viewpoint of environmental problems. As lead-free solders became mainstream, this problem became more serious.
That is, compared with eutectic solder (about 183 ° C.) having a low melting temperature, the melting temperature of lead-free solder is, for example, as high as about 217 ° C. in the case of (Sn—Ag—Cu series), for example, in a flow furnace If the soldering temperature of the solder is about 255 ° C., the difference is only about 38 ° C. in the latter case, so the heat applied for the soldering process diffuses through the metal layer, and the soldering portion Is likely to be around 217 ° C. or lower than when the former eutectic solder is used.
As a result, especially when soldering by inserting the lead of the mounting component into the through hole, the through hole may be close to the metal layer, so the heat applied to melt the solder There is a problem that it is easily taken away by the metal layer and soldering failure as described above is likely to occur.

  A method for solving this problem is disclosed in Patent Document 1. In this method, as shown in FIG. 7, a groove 10 is formed from the surface of the metal core circuit board 4 until the metal core, that is, the metal layer 3 is exposed, and the metal layer 3 is formed on the exposed metal layer 3 at the bottom of the groove 10. When the electronic component 8 is soldered to the surface of the metal core circuit board 4 with the gap 12 penetrating to the lower surface of the metal core circuit board 4, the soldering operation is performed with the gap between the gaps open. A meltable metal 11 such as mercury or fluorinate is poured into the gap 12 so as to eliminate the gap 12 thermally.

In this way, when the electronic component 8 is mounted on the metal core circuit board 4, the gap 12 is provided in the metal layer 3 to prevent the diffusion of heat for soldering, and the soldering can be performed more easily. In addition, after the soldering is completed, the metal core having excellent thermal conductivity, for example, a molten metal 11 is poured into the gap 12 to equalize the temperature of the entire metal core circuit board 4 in a normal use state. The original characteristics of the circuit board 4 can be exhibited.
7, reference numeral 1 denotes an insulating layer, reference numeral 2 denotes a circuit wiring layer, and reference numeral 5 denotes a conductor pad for mounting the electronic component 8 on the metal core circuit board 4. Reference numeral 6 denotes a component main body of the electronic component 8, reference numeral 7 denotes a lead extending from the component main body 6, and reference numeral 9 denotes a bonding material for soldering the conductor pad 5 and the lead 7 of the electronic component 8. Specifically, solder is shown.

JP 2000-183475 A

However, as shown in FIG. 7 of Patent Document 1, when the groove 10 or the gap 12 is provided in the metal core circuit board 4, the following problems may occur.
That is, considerable precision is required to form the grooves 10 and the gaps 12 in the final stage metal core circuit board 4 that is almost a finished product, which causes quality defects and a significant cost increase. There is a fear.
Further, if the formation of the groove 10 or the like fails and the groove 10 or the gap 12 is provided up to an unnecessary portion, the entire metal core circuit board 4 that has already been formed must be discarded, which also increases the cost. Fear is high.

In addition, when used for a long time, moisture, dust and the like are easily mixed in the groove 10 and the gap 12, and in the worst case, there is a possibility of causing an electrical short circuit. In this respect, Patent Document 1 also proposes a method of covering the groove 10 with a cover, but it is impractical to cover the small and narrow groove 10 even if a cover can be provided. It will lead to further cost increase.
Furthermore, when the groove 10 that opens on the surface of the substrate is provided only on one side of the metal core circuit board 4, the metal core circuit board 4 is warped in the long term due to unbalance of distortion generated on both sides of the metal core circuit board 4. There is also a problem of promoting the occurrence.

  Therefore, the object of the present invention is to minimize the cost increase, and to easily stabilize the quality because it is easy to manufacture. There is no fear of an electrical short circuit due to external moisture or dust, and the circuit board. It is an object of the present invention to provide a metal core circuit board that is less likely to warp and is excellent in solder workability.

  In order to achieve the above object, a metal core circuit board according to claim 1 of the present invention is a metal core circuit board having a through hole and a metal layer inside an insulating layer, and penetrating near the through hole of the metal layer. A hole is provided, the resin having a lower thermal conductivity than the metal layer is filled in the through hole, and both sides of the opening of the through hole are sealed with the insulating layer. .

  According to the metal core circuit board according to claim 1, the through hole is provided only in the metal layer embedded in the insulating layer of the metal core circuit board, and the thermal conductivity is lower in the through hole than in the metal layer. For example, when the lead of an electronic component is inserted into the through hole portion of the metal core circuit board and soldered, the heat of the molten solder is passed through the through hole in the vicinity of the through hole in the metal layer. As a result, the heat conduction area is reduced, heat diffusion is prevented, and the temperature of the soldering portion is less likely to be lowered, so that the soldering workability can be improved while maintaining the characteristics of a normal metal core circuit board.

In addition, unlike conventional methods in which grooves and gaps are formed later in a completed metal core circuit board, it is only necessary to provide a through hole in advance in a metal layer that is only one component of the metal core circuit board. It is easy and cost increase is minimized, and errors such as excessive opening of grooves and gaps are unlikely to occur. Therefore, it is easy to stabilize the quality of the metal core circuit board, and it is possible to suppress an increase in cost because it is difficult to cause defects.
Furthermore, since both sides of the resin filled in the through holes are covered with an insulating layer, grooves and gaps are not opened on the surface of the metal core circuit board as in the prior art. Therefore, there is no possibility of electrical short-circuiting, and distortion imbalance is unlikely to occur on both sides of the circuit board. Therefore, there is little risk of warping of the metal core circuit board in the long term.
As described above, according to the metal core circuit board according to the first aspect, the cost increase can be minimized, and the quality is easily stabilized because of easy manufacture, and electrical short-circuiting due to external moisture and dust. Therefore, it is possible to provide a metal core circuit board which is excellent in soldering workability and is free from warping.

The metal core circuit board according to claim 2 of the present invention is characterized in that, in the metal core circuit board according to claim 1, the through hole is an elongated hole.
According to the metal core circuit board according to claim 2 formed in this way, in addition to the effect of the invention according to claim 1 described above, less heat is diffused when the electronic component is soldered to the through hole with the through hole. It is preferable because the number of through holes can be suppressed.

Furthermore, the metal core circuit board according to claim 3 of the present invention is the metal core circuit board according to claim 1, wherein the through holes are a plurality of holes provided at predetermined intervals.
According to the metal core circuit board according to claim 3 formed as described above, the through holes formed in the metal layer are formed by a plurality of holes provided at predetermined intervals around the through holes. In addition to the effect of the present invention, heat diffusion during soldering can be suppressed more uniformly in each direction, so that more stable soldering is possible.

  As described above, according to the present invention, it is possible to minimize the cost increase, and the quality is easy to stabilize because it is easy to manufacture, and there is no fear of an electrical short circuit due to external moisture or dust. In addition, it is possible to provide a metal core circuit board excellent in solder workability in which the circuit board is hardly warped.

The metal core circuit board of the present invention will be described below in detail with reference to the drawings.
FIG. 1 shows an embodiment of a metal core circuit board according to the present invention, and is a partial longitudinal sectional view showing a through hole portion provided in the metal core circuit board.
Specifically, as shown in FIG. 1, the metal core circuit board 4 of the present invention has a prepreg made of an insulating resin containing, for example, a glass cloth on the front and back surfaces of a metal layer 3 made of, for example, a copper plate or an aluminum plate. The insulating layer 1, 1 is formed on both sides of the metal layer 3, and the printed circuit 2 (wiring) is formed on both sides or one side of the insulating layer 1 thus formed by general-purpose technology. Layer). Although not shown in FIG. 1, it is also common to leave a portion (land) necessary for soldering the printed circuit 2 and further provide a solder resist layer on the other surface.

As shown in FIG. 1, the major feature of the metal core circuit board 4 of the present invention is that, in the vicinity of the through hole 14, a through hole 16 is provided in advance in the metal layer 3, and the resin is filled therewith. The both sides of the front surface and the back surface of the substrate are sealed with the insulating layer 1.
Incidentally, the inside of the through hole 16 is filled with a resin having a lower thermal conductivity than the metal layer 3, in this example, as described above, an insulating prepreg resin. The resin of the prepreg flows when a part of the resin constituting the prepreg sandwiching the metal layer 3 is pressed while being heated when the insulating layer 1 is formed on both surfaces of the metal layer 3. Forming the insulating layer 1 using the prepreg resin in this way is preferable because it can simultaneously fill the through-hole 16 with resin during heating and pressurization during the formation of the insulating layer, which helps to reduce costs.

For example, when the metal layer 3 is a copper plate, the thermal conductivity is 400 W / m · ° C., whereas when an epoxy resin is used as the prepreg resin, the thermal conductivity is, for example, 3 ˜5 W / m · ° C. Thus, it can be said that the thermal conductivity of the resin filled in the through hole 16 is sufficiently lower than the thermal conductivity of the metal layer 3.
Of course, the through hole 16 is not filled with the resin of the prepreg forming the insulating layer 1 but with the metal layer 3 or another resin having a lower thermal conductivity than the resin of the prepreg described above. Needless to say, the metal layer 3 may be sandwiched by the insulating layer 1 described above from both sides and integrated by heating and pressing.
Here, in FIG. 1, reference numeral 15 denotes an inner metal plating layer of the through hole 14, and reference numeral 17 denotes a predetermined gap between the inner metal plating layer 15 of the through hole 14 at a position where the through hole 14 of the metal layer 3 is provided. The through-hole for through-holes drilled so as to have an insulation interval is shown.

Various embodiments in which the through hole 16 is provided in the vicinity of the through hole 14 of the metal core circuit board 4 will be described below with reference to FIGS. Incidentally, these figures correspond to the AA sectional view in FIG.
FIG. 2A shows a structure in which a plurality of circular through holes 16 are provided at predetermined intervals on the entire circumference of the through hole 14 in the metal layer 3. In the case of a method of providing a large number of small through-holes 16 as in this example, it is easy to balance the above-described heat diffusion suppression during soldering, heat dissipation from normal electronic components, etc., and soaking, which is preferable. . Of course, it goes without saying that the through-holes 16 may be provided around the through-holes 14 at random rather than at predetermined intervals.

  FIG. 2B shows a case where a rectangular through hole 16 is provided around the through hole 14. When the elongated through holes 16 are provided in this way, heat diffusion during soldering in the through holes 14 can be efficiently suppressed with a small number of through holes 16.

  FIG. 2C shows an example in which intermittent ring-shaped through holes 16 are formed at predetermined intervals around the through hole 14 so as to be substantially concentric with the through hole 14. In this case, similarly to FIG. 2B, it is possible to efficiently suppress the diffusion of heat at the time of soldering in the through hole 14 with a small number of through holes 16, which is preferable.

  Further, FIG. 2D shows a case where through holes 14 are provided at one corner of the four corners of the metal core circuit board 4, and in such a case, not in the entire circumference of the through holes 14, but in two directions, In this figure, about two through-holes 16 that are concentric with the through-hole 14 as shown in FIG. 2C and have an intermittent ring shape may be provided on the right and upper sides of the through-hole 14 in the drawing.

  By the way, the number, shape, and size of the through holes 16 provided in the metal layer 3 are set so that heat for melting the solder is difficult to diffuse when soldering the lead of the electronic component to the through hole 14, that is, soldering. It is determined in consideration of the balance between the two so that the work is easy and the metal core circuit board 4 does not lose its original characteristics such as soaking and heat dissipation.

  FIG. 3 shows an example in which a plurality of through holes 14 are present collectively in the through hole 17 for the through hole of the metal layer 3. When a plurality of through-holes 14 are grouped in this way, the through-holes 16 are not provided around each of the through-holes 14 but collectively around the group of the through-holes 14. Thus, forming the through hole 16 is efficient and preferable in terms of cost reduction. FIG. 3 also corresponds to the AA cross-sectional view in FIG.

  As shown in FIG. 2 and FIG. 3 described above, the meaning that the through-hole 16 is provided in the vicinity of the through-hole 14 in the present invention means the entire circumferential direction of the through-hole 14 and the circumferential direction. It is assumed that there are two meanings in a part direction.

Hereinafter, an example of a method for manufacturing the metal core circuit board 4 of the present invention will be described with reference to FIG. Incidentally, FIG. 4 is a partial longitudinal sectional view showing only the through hole 14 and its vicinity.
As shown in FIG. 4A, a metal plate 3a having a through hole 17 for a through hole 14 in a predetermined position and a through hole 16 in the vicinity thereof is prepared in advance, and this metal plate 3a is used as a center. For example, prepreg sheets 1a made of an insulating resin containing glass cloth inside are laminated on and under the metal plate 3a. At this time, the through hole 16 and the through hole 17 can be formed by a single process, for example, by punching.

Next, as shown in FIG. 4B, the laminated metal plate 3a and the prepreg sheets 1a and 1a are integrated by heating and pressurizing to form a substrate having the metal layer 3 sandwiched between the insulating layers 1 and 1. And the copper foil 2a for circuit formation is affixed on both surfaces of this board | substrate. A part of the resin of the prepreg is filled in the through hole 16 of the metal layer 3 and the through hole 17 for the through hole 14 by the heating and pressurization.
If it is desired to fill the through hole 16 with a resin other than the prepreg resin, for example, a resin having a lower thermal conductivity with respect to the metal layer 3, the metal plate 3a and the prepreg sheets 1a and 1a are heated and pressurized. The resin to be filled in the through hole 16 may be filled in advance.

Subsequently, as shown in FIG. 4C, a through hole 18 for the through hole 14 is formed at a predetermined position by a drill or the like.
Thereafter, after applying an etching resist (not shown) to the substrate surface of FIG. 4C, the copper foils 2a and 2a are etched to form the wiring layer 2 as shown in FIG. 4D. In addition, the inner metal plating layer 15 was applied to the inner surface of the through hole 18 for the through hole 14 to form the through hole 14.

  Here, the application of the etching resist on the copper foil 2a which is omitted in the drawing is not after the through hole 18 for the through hole is formed as shown in FIG. After the copper foils 2a and 2a are attached to the surfaces of the insulating layers 1 and 1, the copper foils 2a and 2a are applied onto the surfaces and etched, and the wiring layer 2 is formed. It may be formed. In any case, the portions other than preparing the metal plate 3a having the through holes 16 and 17 in advance are not limited to the method shown in FIG. 4 and may be formed according to various general-purpose manufacturing methods for the metal core circuit board 4.

FIG. 4 (e) shows a metal core circuit board 4 which is an embodiment of the present invention showing a state in which a solder resist 20 is applied to a desired position on the substrate surface shown in FIG. 4 (d).
On the surface of the metal core circuit board 4 thus completed, electronic components for surface mounting and electronic components whose leads are inserted into the through holes 14 and soldered are usually mixed and mounted.

Here, the terminal plating of the electronic component 8 for surface mounting has been increasingly subjected to lead-free plating, but there are cases in which Sn—Bi system is the main component in the plating. In addition, since such Sn—Bi-based plating has a low melting point (139 ° C.), there is a concern that when normal flow soldering is performed, the plating is remelted and defects such as lift-off occur.
Therefore, in the metal core circuit board 4 of the present embodiment, first, as shown in FIG. 5, the electronic component 8 for surface mounting is soldered to the predetermined position of the metal core circuit board 4 by the solder 9 using the reflow furnace. As shown in FIG. 6, the lead 30 of the electronic component having the insertion type lead 30 is inserted into the through hole 14 of the metal core circuit board 4 by the spot flow process and soldered by the solder 9.
At this time, as shown in FIG. 6, the through hole 16 is interposed between the mounting position of the electronic component 8 to be soldered using a reflow furnace and the soldering position of the lead 30 to be soldered by the flow process. It is formed in a shape.

By doing so, in the metal core circuit board 4 of the present embodiment, the through hole 16 is provided in the metal layer 3 in the vicinity of the through hole 14, and the cross-sectional area of the metal layer 3 is reduced accordingly. When soldering the lead 30 into the through hole 14, the heat of the molten solder is difficult to diffuse through the metal layer 3.
Therefore, it is more difficult to lower the temperature of the molten solder than the conventional one that does not have the through hole 16, the increase in the surface tension of the solder and the increase in the viscosity are suppressed, the soldering operation is facilitated, and the solder rise failure, etc. The problem of deterioration of quality due to soldering failure due to, voids in the through-hole 14 or the like is reduced.

Further, the heat possessed by the molten solder through the through holes 16 is difficult to escape and the temperature of the molten solder is difficult to decrease, so that the soldering operation can be performed in a shorter time, and the thermal load on the surrounding electronic components 8 is reduced. Reduced.
In addition, the fact that the heat of the molten solder is difficult to escape means that the heat is not easily transmitted to the surface mounting electronic component 8 side. In addition, since the through hole 16 is interposed between the electronic component 8 and the lead 30, even if the heat of the molten solder is transmitted to the electronic component 8 side, it is delayed so as to bypass the region of the through hole 16 Communicated.
Further, just because the temperature of the molten solder is excessively lowered as in the prior art, it is not necessary to add a higher temperature to the portion where the flow treatment is performed in advance.
As described above, the thermal load on the surface-mounting electronic component 8 already mounted in the vicinity of the through hole 14 can be kept low, and thermal deterioration of the electronic component 8 can be prevented.

By the way, in order to suppress the thermal load on the surface-mounting electronic component 8 already mounted in the vicinity of the through-hole 14, the surface-mounting electronic component 8 and the lead 30 soldered to the through-hole 14 are provided. There is also a method in which the electronic components are grouped as much as possible, and the circuit design is made in advance so that the mounting positions of both are separated as much as possible.
If it does in this way, the heat | fever at the time of soldering the lead | read | reed 30 of an electronic component to the through hole 14 becomes difficult to exert a thermal influence on the electronic component 8 for surface mounting already mounted, and it is preferable.
If the electronic components 8 for surface mounting and the electronic components with leads 30 to be soldered to the through holes 14 are grouped in this manner, the electronic components with leads 30 that are soldered together are grouped around the group of the grouped electronic components with leads 30 as shown in FIG. As shown in FIG. 4, since it is sufficient to provide the through holes 16 in a lump, there is an advantage that the number of the through holes 16 can be reduced.

  Thus, according to the metal core circuit board of the present embodiment, as shown in FIGS. 1 to 6, the through hole 16 is provided only in the metal layer 3 embedded in the insulating layer 1 of the metal core circuit board 4. Since the resin having a lower thermal conductivity than the metal layer 3 is filled in the through hole 16, for example, when the electronic component lead 30 is inserted into the through hole 14 of the metal core circuit board 4 and soldered, the solder The heat applied to melt the metal layer 3 is reduced by the amount of the through holes 16 in the metal layer 3, the heat conduction area is reduced, heat diffusion is suppressed, and the soldering workability is maintained while maintaining the characteristics of the normal metal core circuit board 4. Can be increased.

Further, unlike the conventional case where grooves and gaps are formed later in the completed metal core circuit board, in the case of the metal core circuit board 4 of this embodiment, the through holes 16 are provided in advance in the metal plate on which the metal layer 3 is formed. Therefore, the cost increase is kept to a minimum, and there is no worry of making an error such as excessive opening of grooves and gaps that impede the product unlike the conventional one. As a result, the quality of the metal core circuit board can be stabilized, and cost can be prevented from being increased due to the difficulty of causing defects.
Furthermore, in the case of the metal core circuit board 4 of the present embodiment, the both sides of the opening of the through hole 16 are sealed with the insulating layer 1 so that grooves and gaps are formed on the surface of the metal core circuit board 4 as in the conventional product. Since there is no opening, there is no risk of moisture and dust accumulating in the grooves and gaps, causing an electrical short circuit, and distortion imbalance is unlikely to occur on both sides of the circuit board. There is little fear of occurrence.

  As described above, according to the present invention, it is possible to minimize the cost increase, and it is easy to manufacture, the quality is easy to stabilize, and there is a fear of an electrical short circuit due to external moisture and dust. In addition, it is possible to provide a metal core circuit board excellent in solder workability, which is free from warping of the board.

It is a partial longitudinal cross-sectional view which shows one Example of the metal core circuit board of this invention. (A)-(d) is the AA cross-section equivalent figure in FIG. 1 of the other Example of the metal core circuit board of this invention. FIG. 6 is still another embodiment of the metal core circuit board according to the present invention, and is a cross-sectional view corresponding to the AA cross section in FIG. 1. (A)-(e) is a partial longitudinal cross-sectional view which shows one Example of the manufacturing method of the metal core circuit board of this invention. It is a partial longitudinal cross-sectional view which shows the state which mounted the electronic component for surface mounting on the metal core circuit board of this invention. It is a partial longitudinal cross-sectional view which shows the state which mounted both the electronic component for surface mounting and the electronic component with an insertion type lead | read | reed on the metal core circuit board of this invention. It is a longitudinal cross-sectional view which shows an example of the conventional metal core circuit board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulation layer 2 Wiring layer 3 Metal layer 4 Metal core circuit board 8 Electronic component for surface mounting 14 Through hole 16 Through hole 30 Lead

Claims (3)

  In a metal core circuit board having a through hole and having a metal layer inside an insulating layer, a through hole is provided in the vicinity of the through hole in the metal layer, and has a lower thermal conductivity than the metal layer in the through hole. A metal core circuit board characterized by being filled with resin and sealed on both sides of the opening of the through hole with the insulating layer.   The metal core circuit board according to claim 1, wherein the through hole is an elongated hole.   The metal core circuit board according to claim 1, wherein the through holes are a plurality of holes provided at predetermined intervals.

Images