JP4776559B2 - Metal core multilayer printed wiring board for electrical junction box of vehicle - Google Patents

Description

The present invention relates to a highly reliable metal core multilayer printed wiring board for an electrical junction box of a vehicle having a metal core therein, having a high mounting density and excellent heat dissipation and mass productivity.

  In recent years, for example, an electrical junction box mounted in an engine room or a room of a vehicle has a thickness including a metal core instead of a bus bar made of a metal conductor bent three-dimensionally to form a high-current electric circuit. A metal core printed wiring board provided with a meat conductor layer is used to reduce the size of an electrical junction box that accommodates these substrates.

Due to the structure of this metal core printed wiring board , via holes (via holes) such as through holes and inner via holes are used as means for connecting arbitrary conductor layers in a printed circuit board in which conductor layers are laminated. (For example, refer to Patent Document 1).

In forming the via hole, through holes (through holes) or non-through holes are formed in the thickness direction of the printed circuit board according to the application, and copper plating with a thickness of 20 to 50 μm is applied to the inner wall surface of these holes. A method of electrically connecting conductor layers is generally used. A thermosetting insulating material in which glass fiber is impregnated with an epoxy resin is used for the printed circuit board, electrolytic copper foil is used for the conductor layer, and the above-described copper plating is applied to the via hole.
JP-A-8-162765 (page 4-5, FIG. 1)

  For example, as the performance of electronic devices mounted on vehicles has improved, the need for heat dissipation has increased due to the increased capacity of electronic components to be mounted and the higher density of the wiring board itself. There is an increasing need for metal core multilayer printed wiring boards having a core. In addition, electronic devices equipped with a metal core multilayer printed wiring board are increasingly used not only in a favorable environment as in the prior art but also in a severe environment exposed from below freezing to a high temperature. Especially for metal core multilayer printed wiring boards that are housed in electrical junction boxes mounted in vehicle engine rooms, etc. and are subjected to severe thermal shock environments, through holes and inner via holes that connect electronic circuits between conductor layers There are the following problems.

  Specifically, since the metal core multilayer printed wiring board is thicker than the multilayer printed wiring board, the contact length between the copper plating layer forming the through hole or the inner via hole and the insulating layer is increased.

  Since the thermal expansion coefficients of the copper plating layer and the insulating layer are different from each other, tensile stress is generated due to the temperature rise in the thermal shock environment at the boundary between the copper plating layer and the insulating layer due to the difference of the thermal expansion coefficient of both. At the same time, compressive stress is generated due to the temperature drop. In this way, the copper plating layer of the through hole or inner via hole is subjected to repeated stress fatigue due to thermal stress due to temperature fluctuations in a thermal shock environment, so that plastic strain accumulates and breaks, resulting in electrical resistance. The increase causes a problem that the metal core multilayer printed wiring board cannot withstand a practical number of thermal cycles.

  In order to avoid such a problem, the following specific measures have been conventionally taken.

  As a first measure, the thermal expansion coefficient of the resin of the insulating layer to be used is matched to the thermal expansion coefficient of the copper plating applied to the through hole or the inner via hole, and the thermal stress of the copper plating at the portion where the insulating layer is in contact is reduced. It is to plan. However, a resin having a low coefficient of thermal expansion is expensive, and since many additives are blended to keep the coefficient of expansion low, the workability is remarkably poor, so such a measure is not an appropriate measure.

  As a second countermeasure, the thickness of the copper plating applied to the through hole or the inner via hole is increased so that the copper plating in contact with the insulating layer can withstand thermal stress. However, it becomes complicated in terms of process management, and the manufacturing cost increases, which is not an appropriate measure.

An object of the present invention is to provide a metal core multilayer printed wiring board for an electric junction box of a vehicle having a low cost and high reliability under a thermal shock environment.

In order to solve the above-mentioned problem, a metal core multilayer printed wiring board for an electrical junction box of a vehicle according to the present invention is:
As a conductor layer in a cross section in the thickness direction of the printed wiring board, it has a metal core inside, one inner layer conductor on each side of the metal core via an inner insulating layer, and an outer side on both sides of the inner layer conductor In the metal core multilayer printed wiring board for an electrical junction box of a vehicle, wherein the conductor layer including the metal core has at least five layers by having one outer layer conductor each through an insulating layer,
The metal core multilayer printed wiring board may be a through hole in which the arbitrary conductor layers are electrically connected by copper plating so as to penetrate the thickness direction of the metal core multilayer printed wiring board and connect to an arbitrary conductor layer. , At least one of inner via holes in which the inner layer conductors are electrically connected by copper plating is formed,
A dummy land electrically insulated from the metal core and the inner layer conductor and connected only to the copper plating is provided in the metal core,
An electric junction box for a vehicle, characterized in that the conductor layers are connected to each other, and the length of the portion where the copper plating and the insulating material in contact with each other are in contact with each other is 0.5 mm or more and 0.8 mm or less. Metal core multilayer printed wiring board.

By metal core multilayer printed wiring board having such a structure, rather short insulating material interposed between the respective insulating layers and the copper plating layer and the conductor layer Shitaga length of a portion in contact in succession in the copper plating Thus, the strain energy accumulated in the copper plating portion by the thermal cycle can be reduced. In other words, even if the copper plating and each insulating layer and insulating material in contact with the copper plating are repeatedly expanded and contracted due to temperature changes, the copper plating is distorted so that the distortion does not accumulate much due to an increase in temperature cycle. Plating fatigue fracture can be made difficult to occur.

In addition, since the metal core multilayer printed wiring board has dummy lands formed on the metal core, the length of each insulating layer and the portion of the insulating material in contact with the copper plating can be shortened more actively, and the thermal cycle Thus, the strain energy accumulated in the copper plating portion can be further reduced. That is, even if the copper plating and each insulating layer in contact with the copper layer undergo repeated expansion and contraction due to temperature changes, the strain does not accumulate due to an increase in the temperature cycle, and the fatigue of the copper plating does not increase. Breakage can be made difficult to occur.
In particular, as in a metal core multilayer printed wiring board used in an electric junction box of a vehicle, it is required to satisfy 3000 cycles of the thermal shock test under the harshest use conditions. It has been found that the thickness of the insulating layer continuously contacting the copper plating of the inner via hole and the insulating material flowing out of the insulating layer must be at least 0.8 mm or less. Therefore, it turned out that the structure of the metal core multilayer printed wiring board which has the structure concerning this invention is excellent.

Moreover, the metal core multilayer printed wiring board for electric junction boxes for vehicles according to claim 2 of the present invention is the metal core multilayer printed wiring board for electric junction boxes for vehicles according to claim 1 ,
The thermal expansion coefficient in the thickness direction of each insulating layer is 45 ppm / ° C. or more.

The function of the present invention is sufficiently exhibited by providing each insulating layer constituting the metal core multilayer printed wiring board for an electrical junction box for a vehicle according to claim 1 with such a thermal expansion coefficient in the thickness direction. Can do.

ADVANTAGE OF THE INVENTION According to this invention, the metal core multilayer printed wiring board for electric junction boxes of a vehicle with high reliability under a thermal shock environment at low cost can be provided.

  Hereinafter, the metal core multilayer printed wiring board 1 concerning the 1st Embodiment of this invention is demonstrated based on drawing. FIG. 1 is a cross-sectional view of the metal core multilayer printed wiring board 1 according to the first embodiment of the present invention cut in the thickness direction of the wiring board along the central axis of a through hole (through conduction hole) 101. In the drawings relating to the present invention, in order to facilitate the understanding of the description, the conductor layer is indicated by hatching in the upper right direction in the drawing, the insulating layer is indicated by hatching in the drawing, and flows out from the insulating layer and is adjacent thereto. The resin material filled in the space is indicated by hatching in the lower right in the figure. Copper plating is indicated by a thick solid line.

  As shown in FIG. 1, the metal core multilayer printed wiring board 1 according to the first embodiment of the present invention has a metal core 111 having a thickness of about 200 μm inside and on both sides of the metal core 111 (upper and lower in the figure). A) having inner conductors 112 and 113 each having a thickness of about 150 μm through inner insulating layers 121 and 122 having a thickness of about 150 μm, and having thicknesses on both sides of the inner layer conductors 112 and 113 (up and down in the figure). A metal core multilayer printed wiring board having a structure in which a conductive layer including the metal core 111 has a five-layer structure by including a structure in which each of the outer layer conductors 114 and 115 is provided via outer insulating layers 123 and 124 having a thickness of about 150 μm. It has become.

  The metal core 111, the inner layer conductors 112 and 113, and the outer layer conductors 114 and 115 are made of copper foil, and the inner insulating layers 121 and 122 and the outer insulating layers 123 and 124 are glass epoxy having a thermal expansion coefficient of 45 ppm / ° C. or more. Made of resin.

  Further, the metal core multilayer printed wiring board 1 is formed with a through hole 101 penetrating in the thickness direction of the printed wiring board. A copper plating 141 having a thickness of about 50 μm is applied to the entire inner surface of the through hole 101, and the upper and lower outer conductors 114, 115 and the upper and lower inner conductors 112 in the figure are electrically connected by the copper plating 141. Further, a part of the through hole 101 penetrates the metal core 111, and a part of the metal core 111 is electrically connected to the copper plating 141 of the through hole 101 as a dummy land 111A. Further, as shown in FIG. 2, the metal core 111 is adjacent to four cutouts having a substantially ¼ arc shape for defining the dummy land 111A with the surrounding metal core body 111B. Four notch holes 111a to 111d are formed in advance by etching or the like in which the ends of the notches are separated from each other by a small distance. The notches 111a to 111d are filled with an insulating material made of an epoxy resin flowing out from the inner insulating layers 121 and 122 (not shown in FIG. 2).

  Further, as shown in FIG. 3, the adjacent end portions of the notch holes 111a to 111d are sized so as to remove the adjacent end portions and connect the end portions of the notch holes 111a to 111d. Non-conducting holes 134 to 137 are formed. The non-conductive holes 134 to 137 are filled with an insulating material made of an epoxy resin that penetrates the inner insulating layers 121 and 122 formed between the metal core 111 and the inner layer conductors 112 and 113 and flows out from the outer insulating layers 123 and 124. ing.

  In this manner, the peripheral portion of the metal core 111 electrically connected to the through hole 101 and the copper plating 141 forms a dummy land 111A. The dummy land 111A is insulated from the surrounding metal core body 111B by the four cutout holes 111a to 111d and the non-conduction holes 134 to 137 of the metal core 111, so that the dummy land 111A is surrounded by the surrounding metal core body. Separately from 111B, a separate circuit is formed electrically.

  The two inner layer conductors 112 and 113 are configured as a predetermined circuit pattern not shown in the cross-sectional view of FIG. 1 and extend between the inner insulating layer and the outer insulating layer, respectively.

  Further, the above-described non-conductive holes 134 to 137 are formed at predetermined positions of the inner layer conductors 112 and 113. In the non-conductive holes 134 to 137, a space is formed between the inner layer conductors 112 and 113 and the outer insulating layers 123 and 124, and this space is filled with an insulating material made of epoxy resin flowing out from the outer insulating layers 123 and 124. Has been.

As is apparent from the fact that the metal core multilayer printed wiring board 1 has the above-described configuration, the lengths of the inner insulating layers 121 and 122 and the outer insulating layers 123 and 124 that are in continuous contact with the copper plating 141 of the through hole 101. The length (see X1 and X2 in FIG. 1) is 150 μm, which is considerably thinner than 0.8 mm (800 μm).

Then, the specific effect | action of the metal core multilayer printed wiring board 1 concerning the 1st Embodiment of this invention is demonstrated. Since the metal core multilayer printed wiring board 1 has such a structure, the length of each insulating layer continuously in contact with the copper plating 141 of the through hole 101 is as thin as 0.8 mm or less. The strain energy accumulated by the thermal cycle in the part can be reduced. That is, even when the copper plating 141 and each insulating layer in contact with the copper layer 141 are repeatedly expanded and contracted due to temperature changes, the copper plating 141 is not strained due to an increase in the temperature cycle. The fatigue fracture of 141 can be made difficult to occur. In the present invention, the reason why the length of the portion continuously in contact with the through hole of each insulating layer is set to 0.8 mm or less will be described in detail in a later embodiment.

  Then, the manufacturing method of the metal core multilayer printed wiring board relevant to the above-mentioned embodiment is demonstrated based on FIG. In the description of the manufacturing method based on FIG. 4, the dummy land 111 </ b> A is common to the above-described embodiment in that the metal core 111 is formed. However, the pattern of the inner layer conductors 112 and 113 near the through hole is as follows. 1 is slightly different from the upper and lower inner layer conductors 112 and 113 shown in FIG.

  When manufacturing this metal core multilayer printed wiring board, as shown in FIG. 4A, first, CCL (Copper clad laminate) which forms the metal core 111 and the inner layer conductor 113 is etched. At this time, in order to form a portion that becomes the dummy land 111A of the metal core 111, notched holes 111a to 111d that are substantially ¼ arc-shaped notches and that have adjacent end portions with a slight interval are formed. Etching is performed as shown in FIG. At this time, the etching is performed while leaving a bridge-like connection portion connecting adjacent notch holes.

  Next, as shown in FIG. 4B, the opposite inner layer conductor, that is, the CCL forming the upper inner layer conductor 112 is laminated and pressed. At this time, the insulating material flowing out from the inner insulating layers 121 and 122 is filled into a space formed between the metal core 111 and the inner insulating layers 121 and 122. Then, the upper inner layer conductor 112 is etched to leave a necessary portion.

  Next, a non-conducting hole 134 to 137 (see FIG. 3) penetrating the upper and lower inner layer conductors is opened with a drill or the like to connect between approximately 1/4 arc-shaped cutout holes of the metal core 111. Remove.

  Next, the upper and lower inner layer conductors 112 and 113 are laminated with CCLs forming outer layer conductors 114 and 115, respectively, and are pressed with pressure. The resin flowing out of the outer insulating layers 123 and 124 by this pressurization is filled in the space formed between the inner layer conductors 112 and 113 and the outer insulating layers 123 and 124.

  Next, a through hole for a through hole is formed by penetrating the upper and lower outer layer conductors with a drill or the like (see FIG. 4C).

  Next, copper plating 141 is applied around the outer layer conductors 114 and 115, and the copper plating 141 is also applied to the inner surface of the through hole for the through hole to complete the through hole 101.

  Thereby, a dummy land of the metal core 111 is formed around the through hole 101. Further, a predetermined pattern is formed on the outer conductors 114 and 115 by etching to complete the metal core multilayer printed wiring board (see FIG. 4D).

  In the case of FIG. 4D, a dummy land 111A is formed in the metal core 111, and the upper inner layer conductor 112 and the upper and lower outer layer conductors 114 and 115 are connected by a through hole. It can be seen that the hole is reinforced.

  Next, a modification of the metal core multilayer printed wiring board according to the first embodiment will be described with reference to FIG. In addition, about the structure equivalent to the above-mentioned metal core multilayer printed wiring board, a corresponding code | symbol is attached | subjected and detailed description is abbreviate | omitted. Unlike the metal core multilayer printed wiring board 1 according to the first embodiment, the metal core multilayer printed wiring board 1 ′ according to this modification has dummy lands formed on the metal core 111 (not shown in FIG. 5). Only the lower inner layer conductor 113 is in contact with the copper plating 141 of the through hole 101.

That is, the copper plating 141 of the through hole 101 is in contact with only one of the inner layer conductors 113, and the other part is applied to the metal core 111 and the inner layer conductors 112 and 113 during the press molding of the metal core multilayer printed wiring board 1 ′. The formed space is filled with insulating materials 131 and 132 made of epoxy resin flowing out from the inner insulating layers 121 and 122 and the outer insulating layers 123 and 124, and this epoxy resin is in contact with the copper plating 141. The through hole 101 is continuous with the copper plating 141 of the through hole 101, which is above the lower inner layer conductor in contact with the copper plating 141 of the through hole 101 and is made of an inner insulating layer, an outer insulating layer, and an insulating material filled between the insulating layers. The length Y1 of the contacted portion is 0.8 mm or less. The lower outer insulating layer 124 has a thickness of about 150 μm.

Since the metal core multilayer printed wiring board 1 ′ has such a structure, the inner insulating layers 121 and 122, the outer insulating layer 123, and the insulating material filled between the insulating layers are stacked above the lower inner conductor 113. consisting of a length Y1 of the portion in contact in succession in the through hole 101 can reduce the strain energy stored in this portion of the copper plating 141 by 0.8mm or less and a short no longer, thermal cycle. That is, even if the copper plating is distorted by repeated expansion and contraction due to temperature changes, the copper plating 141 and the insulating layers 121 to 123 in contact therewith and the insulating material filled between the insulating layers increase the temperature cycle. As a result, the strain does not accumulate so much and fatigue breakage of copper plating can be made difficult to occur.

  Next, the metal core multilayer printed wiring board 2 according to the second embodiment of the present invention will be described. In addition, about the structure equivalent to the above-mentioned metal core multilayer printed wiring board 1, 1 ', the same code | symbol is attached | subjected and detailed description is abbreviate | omitted. FIG. 6 is a cross-sectional view of the metal core multilayer printed wiring board 2 according to the second embodiment of the present invention cut along the central axis of the inner via hole 201 in the thickness direction of the wiring board.

  As shown in FIG. 6, the metal core multilayer printed wiring board 2 according to the second embodiment of the present invention has a metal core 211 with a thickness of 200 μm inside and on both sides (upper and lower in the figure) of the metal core 211. One inner layer conductors 212 and 213 each having a thickness of 150 μm are provided via inner insulating layers 221 and 222 having a thickness of 150 μm, and outer insulating layers 223 and 224 having a thickness of 150 μm are provided on both sides of the inner layer conductors 212 and 213. By providing a configuration having one outer layer conductor 214, 215, the conductor layer including the metal core 211 is a metal core multilayer printed wiring board having a five-layer structure.

  Also, the metal core multilayer printed wiring board 2 is formed with an inner via hole (internal conduction hole) 201 in which inner layer conductors are electrically connected by copper plating 241. The inner via hole 201 is formed of the metal core 211 by the copper plating 241. The dummy land 211A and the upper and lower inner layer conductors 212 and 213 are connected. The dummy land 211A of the metal core 211 connected to the inner via hole 201 and the copper plating 241 is not shown in detail here, but is formed in the metal core and has four notch holes corresponding to FIG. 211, copper plating 241 of the inner via hole 201 by taking insulation by four non-conductive holes (corresponding to the non-conductive holes 134 to 137 in the first embodiment) penetrating the inner layer conductors 212 and 213 and the inner insulating layers 221 and 222. Is separated from the surrounding metal core body (not shown in FIG. 6). An epoxy resin that has flowed out of the glass epoxy resin used as the inner insulating layers 221 and 222 and the outer insulating layers 223 and 224 is formed in the space formed between the dummy land 211A, the surrounding metal core body, and the inner layer conductor. Only filled. The inner layer conductors 212 and 213 are configured as predetermined circuit patterns not shown in the cross-sectional view of FIG. 6 and extend between the inner insulating layer and the outer insulating layer, respectively.

Since the metal core multilayer printed wiring board 2 has such a structure, the length of each insulating layer continuously in contact with the copper plating 241 of the inner via hole 201 is reduced to 0.8 mm or less. The strain energy accumulated by the thermal cycle in the part can be reduced. That is, even if the copper plating 241 and each insulating layer in contact with the copper plating 241 are repeatedly expanded and contracted due to temperature changes, the copper plating 241 is not strained due to an increase in the temperature cycle. It is possible to make it difficult for fatigue fracture of 241 to occur.

Then, the modification of the metal core multilayer printed wiring board concerning this 2nd Embodiment is demonstrated. In addition, about the structure equivalent to the above-mentioned metal core multilayer printed wiring board, a corresponding code | symbol is attached | subjected and detailed description is abbreviate | omitted. As shown in FIG. 7, the metal core multilayer printed wiring board 2 ′ according to this modification differs from the metal core multilayer printed wiring board 2 according to the second embodiment in that a metal core (not shown in FIG. 7). No dummy land is formed, and the upper and lower inner conductors 212 and 213 are in contact with the copper plating 241 applied to the inner via hole 201, and the inner insulating layer 221 made of glass epoxy resin is provided in the other portions. 222 and the metal core multilayer printed wiring board 2 ′ are in contact with an insulating material 231 made of an epoxy resin that flows out from the inner insulating layer and the inner insulating layer and fills a space formed in the metal core during pressure molding. The inner layer conductors 212 and 213 are configured as predetermined circuit patterns not shown in the cross-sectional view of FIG. 7 and extend between the inner insulating layer and the outer insulating layer, respectively. The lengths of the inner insulating layers 221 and 222 in contact with the outer side of the copper plating of the inner via hole and the length of the portion in contact with the copper plating of the through hole made of an insulating material filled between the insulating layers (see U1 in FIG. 7) are as follows. It is 0.8 mm or less.

The metal core multilayer printed wiring board 2 ′ is continuously formed outside the copper plating 241 applied to the inner via hole 201 formed by such a structure, that is, the inner insulating layers 221 and 222 and the insulating material 231 filled between the insulating layers. Thus, the strain energy accumulated in the portion of the copper plating 241 by the thermal cycle can be reduced by reducing the length of the contacting portion to 0.8 mm or less. That is, even if the copper plating 241 and the inner insulating layers 221 and 222 in contact with the copper plating 241 are repeatedly expanded and contracted due to a temperature change, the copper plating 241 may be strained due to an increase in temperature cycle. In addition, fatigue breakage of the copper plating 241 can be made difficult to occur.

  In addition, the metal core multilayer printed wiring board according to the present invention is not necessarily limited to the combination of the components in the above-described embodiments and modifications thereof as long as it exhibits the function of the present invention, and a conductor including a metal core. It goes without saying that a metal core multilayer printed wiring board having a structure of 6 or more layers may be used.

  Moreover, when manufacturing the metal core multilayer printed wiring board concerning this invention, it is not necessary to necessarily use CCL, and it cannot be overemphasized that a copper foil and an insulating resin layer may each be laminated | stacked.

Hereinafter, since the evaluation test which evaluates the usefulness of this invention was done, this test content and a test result are demonstrated. In the evaluation test, among the metal core multilayer printed wiring boards having the following dimensions, the metal core multilayer printed wiring board having the configuration of the present invention is an insulating layer continuously in contact with copper plating of through holes and inner via holes (via holes). The length of 0.5 mm was taken as the first example, and the length of the insulating layer continuously contacting the via hole copper plating was taken as 0.8 mm. On the other hand, a metal core multilayer printed wiring board having a conventional configuration and having an insulating layer length of 1.0 mm continuously in contact with via hole copper plating is used as a first comparative example, and via hole copper plating is used. The insulating layer having a continuous contact length of 2.0 mm was used as the second comparative example.

The specifications in this evaluation test were specifically as follows.
-The thermal expansion coefficient of the insulating material is 45 ppm / ° C in the thickness direction,
・ Land size is the dimension of 0.4mm to 1.0mm added to the diameter of through hole or inner via hole.
・ For copper plating of through holes and inner via holes, use copper sulfate plating with a total thickness of 50μm.
-As the hole diameter of the through hole and inner via hole, the inner diameter after copper plating is 0.3 mm to 1.0 mm,
-The insulation layer thickness between conductors is 0.2 mm,
-The thickness of the metal core is rolled copper foil 0.2 mm to 0.4 mm,
-The thickness of the inner layer conductor is 0.07 mm electrolytic copper foil,
-The thickness of the outer layer conductor is an electrolytic copper foil of 0.07 mm,
-The diameter of the non-conduction hole was set to 0.3 mm to 1.0 mm.

  Under such evaluation specifications, a thermal shock test of −40 ° C. to 120 ° C. was performed as a reliability test condition. And as a criterion, the thing of 10% or less of fluctuation | variation of a via-hole conduction | electrical_connection resistance value was made pass, and the thing exceeding the fluctuation | variation 10% of a via-hole conduction | electrical_connection resistance value was made unacceptable. The change rate of the conduction resistance value represents the ratio between the value before the test and the value after the test.

The evaluation test results are shown in FIGS. As is clear from the evaluation test results shown in the figure, even when the number of thermal shock cycles is significantly increased to 3000 cycles, in the case of a metal core multilayer printed wiring board having an insulating layer length of 0.8 mm or less, the electrical resistivity is It has been found that the change of is suppressed considerably. More specifically, as is apparent from the evaluation test results of FIGS. 8 and 9, the first and second examples have passed the reliability test up to a thermal shock cycle number of at least 3000 cycles. On the other hand, the first comparative example failed when the thermal shock cycle number was 3000 cycles, and the second comparative example failed when the thermal shock cycle number was 1000 cycles.

  Based on the knowledge based on this evaluation test, the metal core multilayer printed wiring board has a through-thickness through-thickness in the thickness direction of the metal core multilayer printed wiring board with respect to the increase or breakage of the electrical resistance value of the through-holes and inner via holes in the thermal shock environment. It has become clear that the length of the insulating layer in contact with the holes and inner via holes is related.

From the above, for example, a metal core multilayer printed wiring board used for an electric junction box of a vehicle is required to satisfy the 3000 cycles of the thermal shock test under the most severe usage conditions. It has been found that the length of the insulating layer continuously contacting the copper plating of the through hole and the inner via hole and the length of the insulating material flowing out from the insulating layer must be at least 0.8 mm. Therefore, it was found that the structure of the metal core multilayer printed wiring board having the configuration according to the modification of the first embodiment and the modification of the second embodiment described above is excellent.

Further, when the length of the insulating layer continuously contacting the copper plating of the via hole or the length of the insulating material flowing out from the insulating layer cannot be 0.8 mm or less, the first embodiment and the second embodiment described above are used. It has been found that if the structure in which the dummy lands are provided on the metal core as in the embodiment is taken, the length can be reduced to 0.8 mm or less, and the increase in electrical resistance and the breakage can be avoided.

  In this case, connecting the metal core and the inner layer conductor forming a part of the electric circuit to the copper plating of the via hole unnecessarily disturbs the electrical connection. It has been found that by providing dummy lands that are not electrically connected to other electrical circuits such as forms, this problem can be avoided and the length of the insulating layer can be reduced to 0.8 mm or less without difficulty.

  As described above, according to the present invention, it is possible to provide a metal core multilayer printed wiring board that is excellent in heat dissipation and can withstand a severe thermal shock environment.

  In addition, a metal core multilayer printed wiring board that can withstand a severe thermal shock environment can be manufactured using an inexpensive resin without applying a resin having a thermal expansion coefficient close to that of copper plating to the insulating layer.

  In addition, a metal core multilayer printed wiring board capable of withstanding a severe thermal shock environment could be manufactured without cumbersome thickening of copper plating for forming through holes and inner via holes.

It is sectional drawing which cut | disconnected the thickness direction of the wiring board along the center axis line of the through-hole of the metal core multilayer printed wiring board concerning the 1st Embodiment of this invention. It is a top view of the metal core of the metal core multilayer printed wiring board shown in FIG. FIG. 3 is a III-III cross-sectional view of the metal core multilayer printed wiring board shown in FIG. 1. It is process drawing explaining the manufacturing process of the metal core multilayer printed wiring board shown in FIG. It is sectional drawing corresponding to FIG. 1 which shows the modification of the metal core multilayer printed wiring board shown in FIG. It is sectional drawing which cut | disconnected the metal core multilayer printed wiring board concerning the 2nd Embodiment of this invention in the thickness direction of a wiring board along the center axis line of an inner via hole. It is a figure which shows the modification of the metal core multilayer printed wiring board shown in FIG. 6 corresponding to FIG. It is a table | surface which shows the evaluation test result which compared the present Example and the comparative example in the evaluation test of this invention. It is a characteristic view which shows the evaluation test result which compared the present Example and the comparative example in the evaluation test of this invention.

Explanation of symbols

1, 1 ', 2, 2' Metal core multilayer printed wiring board 101 Through hole 111 Metal core 111a to 111d Notch hole 111A Dummy land 111B Metal core body 112, 113 Inner layer conductor 114, 115 Outer layer conductor 121, 122 Inner insulating layer 123, 124 Outer insulating layer 134-137 Non-conductive hole 131, 132 Insulating material 141 Copper plating 201 Inner via hole 211 Metal core 211A Dummy land 212 Inner layer conductor 213 Inner layer conductor 214, 215 Outer layer conductor 221, 222 Inner insulating layer 223, 224 Outer Insulating layer 231 Insulating material 241 Copper plating

Claims (2)

As a conductor layer in a cross section in the thickness direction of the printed wiring board, it has a metal core inside, one inner layer conductor on each side of the metal core via an inner insulating layer, and an outer side on both sides of the inner layer conductor In the metal core multilayer printed wiring board for an electrical junction box of a vehicle, wherein the conductor layer including the metal core has at least five layers by having one outer layer conductor each through an insulating layer,
The metal core multilayer printed wiring board may be a through hole in which the arbitrary conductor layers are electrically connected by copper plating so as to penetrate the thickness direction of the metal core multilayer printed wiring board and connect to an arbitrary conductor layer. , At least one of inner via holes in which the inner layer conductors are electrically connected by copper plating is formed,
A dummy land electrically insulated from the metal core and the inner layer conductor and connected only to the copper plating is provided in the metal core,
An electric junction box for a vehicle, characterized in that the conductor layers are connected to each other, and the length of the portion where the copper plating and the insulating material in contact with each other are in contact with each other is 0.5 mm or more and 0.8 mm or less. Metal core multilayer printed wiring board. 2. The metal core multilayer printed wiring board for an electric junction box of a vehicle according to claim 1, wherein a thermal expansion coefficient in a thickness direction of each of the insulating layers is 45 ppm / ° C. or more.

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