JP6444651B2 - Multilayer printed wiring board - Google Patents

Description

  The present invention relates to a multilayer printed wiring board having an asymmetric configuration having a high-frequency substrate and excellent in low warpage.

  In recent years, safety systems have rapidly evolved in the automobile field. Among them, the preventive safety (active safety) system is intended to prevent the occurrence of an accident and reduce the impact at the time of a collision, and is expected to become increasingly popular in the future. For these, millimeter wave radars are mounted as sensors, and high frequency bands such as 24 GHz band and 77 GHz band are widely used because of high weather resistance.

  In the printed wiring board, a high-frequency substrate having a low dielectric constant and a low dielectric loss tangent has been developed to cope with this high frequency band. However, since these high-frequency substrates are very expensive, they should not be used frequently. Therefore, these materials are used only in the high-frequency wiring pattern portion composed of an antenna that transmits and receives radio waves in a high frequency band, a microstrip line, and the like, and in other low-frequency wiring pattern portions, an inexpensive general material (FR Patent Document 1 discloses a multilayer printed wiring board composed of -4 materials. These manufacturing methods and features will be described with reference to FIG.

  First, a base substrate BP2 on which a low frequency wiring pattern is formed is prepared. The base substrate BP2 is manufactured by using a general FR-4 material by a build-up method or the like. At the same time, a high frequency substrate 23 in which metal foils 22a and 22b are attached to both surfaces of the high frequency base material 21 is prepared, and among these, the metal foil 22b of the inner layer IL is etched to form a desired wiring pattern. Thereafter, these two substrates were laminated and integrated using a semi-cured insulating adhesive layer 24 (which becomes the insulating adhesive layer DL when cured), thereby having the high-frequency substrate 23 on one surface of the base substrate BP2. A multilayer printed wiring board Pb is obtained.

  In this way, by replacing only necessary portions with the high-frequency substrate 23, the multilayer printed wiring board Pb having high-frequency characteristics can be manufactured at a lower cost. However, in such a configuration in which different materials are combined, the multilayer printed wiring board itself is warped (see FIG. 15B). This is due to the fact that materials having different characteristics constituting each layer are laminated and integrated in an asymmetrical arrangement.

JP-A-8-181458

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a multilayer printed wiring board having excellent low warpage in a multilayer printed wiring board having an asymmetric configuration having a high-frequency substrate.

The present invention relates to a base substrate obtained by repeatedly laminating a desired number of layers of a conductor layer and an insulating resin layer, and a conductor layer and high frequency characteristics laminated on one surface of the base substrate via an insulating adhesive layer. A multilayer printed wiring board comprising at least a high-frequency substrate having an insulating resin layer excellent in electrical conductivity and having both surfaces thereof conductively connected by blind via holes ,
Insulating resin layer positioned at the outermost layer of the other surface of the base substrate, Ri Do the high frequency substrate from the cured product of the insulating resin layer in a semi-cured state of being laminated in the same process as to laminate on the base substrate, and a multilayer printed wiring board whose both sides, characterized in Rukoto such are conductively connected by the small diameter of the blind via hole from the blind via hole opening diameter of the high-frequency substrate in which the above-mentioned problems are eliminated.

  According to the present invention, in a multilayer printed wiring board having a high-frequency substrate on one side, the high-frequency substrate is disposed on one surface of the base substrate via the semi-cured insulating adhesive layer, and this is laminated and integrated. On the other surface of the substrate, the insulating resin layer that forms the outermost layer of the base substrate is disposed as a semi-cured insulating resin layer, and is laminated and cured at the same timing. Thereby, the influence by the curing shrinkage of the insulating adhesive layer that adheres the high-frequency substrate is offset by the curing shrinkage of the insulating resin layer that forms the outermost layer of the base substrate. Therefore, a multilayer printed wiring board excellent in low warpage can be obtained even in an asymmetric printed wiring board having a high-frequency substrate.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic cross-sectional explanatory drawing of the printed wiring board which concerns on 1st embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional process explanatory diagram illustrating a method for producing a printed wiring board according to a first embodiment of the present invention. FIG. 3 is a schematic cross-sectional process explanatory diagram subsequent to FIG. 2. FIG. 4 is a schematic cross-sectional process explanatory diagram subsequent to FIG. 3. FIG. 5 is a schematic cross-sectional process explanatory diagram subsequent to FIG. 4. FIG. 6 is a schematic cross-sectional process explanatory diagram subsequent to FIG. 5. FIG. 7 is a schematic cross-sectional process explanatory diagram subsequent to FIG. 6. Process explanatory drawing at the time of the through-hole processing in a high frequency board. The schematic cross-section explanatory drawing of a base substrate intermediate body. The schematic cross-sectional process explanatory drawing which shows the manufacturing method of the printed wiring board which concerns on 2nd embodiment of this invention. FIG. 11 is a schematic cross-sectional process explanatory diagram subsequent to FIG. 10. The schematic cross-section explanatory drawing of the improved type of the printed wiring board which concerns on 2nd embodiment of this invention. Schematic cross-sectional process explanatory drawing which shows the manufacturing method of the printed wiring board which concerns on 3rd embodiment of this invention. The schematic cross-section explanatory drawing of the improved type of the printed wiring board which concerns on 3rd embodiment of this invention. Schematic cross-sectional process explanatory drawing which shows the manufacturing method of the conventional printed wiring board.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

A multilayer printed wiring board Pb1 according to a first embodiment of the present invention will be described with reference to FIG.
In the multilayer printed wiring board Pb1 of the present invention, the high frequency substrate 3 is laminated and integrated on one surface of the base substrate BP via the insulating adhesive layer DL1, and the outer layer OL1 of the high frequency substrate 3 has a conductor layer. It has a high-frequency wiring pattern 12 formed by etching (made of a metal foil 2a, a metal film 5, and a metal film 11). On the other hand, on the other surface side of the base substrate BP, an insulating resin layer DL2 constituting the outermost layer of the base substrate BP is made of a cured product of a semi-cured insulating resin layer, and a high frequency via the insulating adhesive layer DL1. It is laminated on the base substrate intermediate BP1 in the same process as the lamination of the substrate 3, and a conductor layer (consisting of the metal foil 8 and the metal film 11) is etched on the outer layer OL2 on the insulating resin layer DL2. Thus, the low-frequency wiring pattern 13 is formed.

  Although the multilayer printed wiring board Pb1 has an asymmetrical structure in which the high-frequency substrate 3 is bonded only to one surface of the base substrate BP, the warpage is suppressed to be small. This is because the curing shrinkage of the insulating adhesive layer DL1 (actually a semi-cured insulating adhesive layer) generated when the high-frequency substrate 3 is laminated on the base substrate BP is caused on the other surface side of the base substrate BP. This is because the semi-cured insulating resin layer of the insulating resin layer DL2 that forms the outermost layer of the base substrate BP laminated in the same process as the lamination is offset by curing shrinkage that occurs when the insulating resin layer is cured.

  Further, since the warpage is reduced, distortion at the interface IF of different materials is also reduced, so that the possibility of delamination can be reduced even when high-temperature processing such as solder reflow is performed. Therefore, the multilayer printed wiring board Pb1 of the present invention has a structure excellent in heat resistance by suppressing warpage.

  Incidentally, the insulating adhesive layer DL1 and the insulating resin layer DL2 are the same in terms of an insulating resin layer, but the insulating adhesive layer DL1 adheres a high-frequency substrate, and the insulating resin layer DL2 is the base substrate BP. Are used for different purposes.

  Next, the manufacturing method of the printed wiring board concerning 1st embodiment of this invention is demonstrated using the schematic cross-sectional process drawing of FIGS.

  First, as shown in FIG. 2A, a high frequency substrate 3 is prepared in which metal foils (a metal foil 2a on the outer layer OL1 side and a metal foil 2b on the inner layer IL side) are attached to both surfaces of the high frequency base material 1. . The high-frequency substrate 1 is not particularly limited as long as it has insulating properties and excellent high-frequency characteristics, but if the relative dielectric constant is 3.0 or less and the dielectric loss tangent is 0.002 or less, the wiring pattern Is not required to be strictly adjusted, and sufficient high frequency characteristics can be obtained in the several GHz band. Examples of such material candidates include liquid crystal polymers and PTFE materials as appropriate. Furthermore, if these materials are mixed with a filler such as alumina or silica, the rigidity and heat dissipation can be improved and the thermal expansion coefficient can be reduced.

  The thickness of the high-frequency substrate 1 may be selected according to the high-frequency wiring pattern formed on the outer layer OL1 side. However, when an antenna (microstrip antenna or the like) is formed in addition to the microstrip line, the antenna Since it is necessary to ensure the gain, the thickness of the high-frequency substrate 1 is set so as to be suitable for the antenna pattern.

  The metal foils 2a and 2b are not particularly limited as long as they can form a circuit by etching in a later step, but copper foils are appropriately used in consideration of conductivity and cost merit.

  Incidentally, as described above, the thickness of the high-frequency substrate 1 greatly affects the high-frequency characteristics of the high-frequency substrate 3. For this reason, if the core material (copper clad laminated board) with which the high frequency base material 1 and metal foil 2a, 2b were integrated is used, a high frequency characteristic will be obtained more stably also at the time of mass production.

  Next, in order to make the metal foils on both surfaces of the high-frequency substrate 3 conductive, the through holes 4 are formed (see FIG. 2B). Although there is no restriction | limiting in particular as a method of forming the through-hole 4, When processing with drill DR, it is preferable to insert from the metal foil 2b side of inner layer IL as a surface into which drill DR is put. That is, when a low-elastic material such as PTFE material is used as the base for the high-frequency base 1, the high-frequency base 1 and the metal foils 2a and 2b on both sides thereof are easily stretched in the direction of pulling out the drill DR (see FIG. 8). . For this reason, the corner part of the metal film 2a arranged on the outer layer OL1 side has a curved shape, and the metal foil 2b on the inner layer IL side has a sharp shape in the drawing direction.

  As a result, this through hole is subjected to a conductive treatment and is finally disposed in the outermost layer OL1 of the multilayer printed wiring board. However, the corner portion has a curved shape, so that the thermal expansion of the high-frequency substrate is performed. Since stress concentration due to (in particular, PTFE material exhibits a high coefficient of thermal expansion) is alleviated, the occurrence of corner cracks can be reduced. On the other hand, since the inner layer IL side has a pointed shape, when it is bonded to the base substrate in a later step, the inner layer IL has a shape that bites into an insulating adhesive layer that bonds them, thereby improving the adhesion.

  Next, the high-frequency substrate 3 is subjected to conductive treatment, and a metal film 5 is formed on the entire surface. Thereby, an interstitial via hole (hereinafter referred to as IVH) 6 in which the metal foils on both sides are conductively connected is formed (see FIG. 2C). There are no particular limitations on the method of conducting the conductive treatment, as long as the metal film 5 can be formed, whether dry or wet, the metal film 5 can be uniformly formed including the inner wall of the IVH 6 by plating. Moreover, in order to improve the adhesiveness to the high frequency base material 1, it is desired to perform a corona treatment or a plasma treatment as a plating pretreatment. The type of the metal film 5 is not particularly limited, but copper is appropriately used in consideration of conductivity and cost merit.

  Next, the conductor layer (consisting of the metal foil 2b and the metal film 5) on the inner layer IL side of the high-frequency substrate 3 is etched to form a desired wiring pattern (see FIG. 3D). Among these, at least the ground pattern GND is formed on the inner layer IL side where the high frequency wiring pattern is formed in the outer layer OL1.

  As described above, since the high-frequency substrate 1 has low adhesion to other insulating materials, it is desired to increase the metal coverage so that the high-frequency substrate 1 is not exposed as much as possible. Specifically, on the inner layer IL side, by setting the solid pattern region including GND, that is, the metal coverage, to 80% or more, the risk of lowering adhesiveness can be further reduced. Furthermore, when the high-frequency base material 1 is, for example, a PTFE material, the surface of the high-frequency base material 1 is activated and the adhesive force can be improved by performing corona treatment or plasma treatment.

  On the other hand, a base substrate intermediate BP1 is manufactured in parallel with the high frequency substrate (see FIG. 4). The base substrate intermediate BP1 is not particularly limited as long as a low-frequency wiring pattern can be formed. A double-sided board, a multilayer board, a metal core board, etc. are made of a general insulating material such as an FR-4 material. What is necessary is just to produce what was comprised with conductor materials, such as material and copper foil. The production method is not particularly limited, and a multilayer board may be produced by a build-up method or the like.

  However, when a thin one-side build-up substrate manufactured by a bonding method or the like is used as the base substrate intermediate BP2, it is preferable that the top TOP side of the BVH face the surface on which the high-frequency substrate is laminated (FIG. 9A )reference). This is because the metal coverage of the bonding surface of the base substrate intermediate BP2 is increased, and the effect of curing and shrinking of the semi-cured insulating adhesive layer when the high-frequency substrate is stacked can be further reduced. Regardless of the above configuration, when there is a difference in metal coverage between the base substrate intermediate (especially, the outermost conductor layer), the surface with the high metal coverage faces the surface on which the high-frequency substrate is laminated. It is desirable to arrange them as follows.

  In addition, when a substrate having a biased conductor layer thickness, such as an even-numbered metal core substrate, is used as the base substrate intermediate BP3, the thick conductor layer TPL is a surface on which high-frequency substrates are stacked. It is desirable to arrange so that the position is close to (see FIG. 9B). This is also the same as the base substrate intermediate BP2, and because the conductor thickness is large, it is possible to reduce the influence of curing and shrinkage of the semi-cured insulating resin layer used when the high frequency substrates are laminated. Also regarding this, regardless of the above configuration, it is desirable that the thick conductor layer be positioned so as to be close to the surface on which the high-frequency substrate is bonded.

  Next, the high-frequency substrate 3 manufactured as described above and the base substrate intermediate BP1 are laminated and integrated. At that time, the high-frequency substrate 3 is disposed on one surface of the base substrate intermediate BP1 via a semi-cured insulating adhesive layer 7a, and the other surface is similarly semi-cured and insulated. The metal foil 8 is disposed via the resin layer 7b (see FIG. 5A). Here, for example, a case in which a high-frequency substrate 3 based on PTFE material is used and an epoxy resin prepreg is used for the semi-cured insulating adhesive layer 7a and the semi-cured insulating resin layer 7b is assumed. To explain, in this configuration, curing shrinkage of the prepreg is a main factor of warpage. For this reason, if the same resin prepreg is disposed in the semi-cured insulating resin layer 7b, the movement with respect to heat becomes the same as that of the insulating adhesive layer 7a. Naturally, the timing of curing shrinkage is the same, so that distortion due to these curing shrinkage differences is eliminated, and warpage can be reduced. Furthermore, at this time, the thicknesses of the insulating adhesive layer 7a and the insulating resin layer 7b are also made the same, so that the amount of expansion and contraction of the entire layer structure can be balanced and the warpage can be further reduced.

  However, in the structure having IVH on the high-frequency substrate as in the present invention, it may be difficult to make the insulating adhesive layer 7a and the insulating resin layer 7b have the same thickness. In order to fill the IVH formed on the high-frequency substrate 3 with an insulating resin, the insulating adhesive layer 7a needs to be thick, and in the other insulating resin layer 7b, the diameter of the BVH for interlayer connection is reduced. The insulating resin layer 7b needs to be thin. For this reason, even in the above configuration, although the warpage can be sufficiently reduced as compared with the conventional configuration, a slight warpage due to the thickness difference occurs. Therefore, in order to cover this thickness difference, a material in which the expansion and contraction of the insulating adhesive layer 7a and the insulating resin layer 7b is adjusted is used.

  As an actual phenomenon, since the insulating adhesive layer 7a is thicker than the insulating resin layer 7b, the influence of this expansion / contraction amount increases, and warping occurs. Therefore, as a countermeasure to be implemented, the insulating adhesive layer 7a is used that has a smaller amount of expansion and contraction when laminated and integrated than the insulating resin layer 7b.

  Specifically, when these materials containing reinforcing fibers such as glass woven fabric are used, the insulating adhesive layer 7a has a larger fiber diameter or number than that contained in the insulating resin layer 7b. May be used (that is, the glass cloth is more tightly packed and uniformly woven in the surface) or contains reinforcing fibers having high strength. Moreover, when the thing containing fillers, such as a silica and an alumina, is used, what contains the filler amount of the insulating contact bonding layer 7a more than the insulating resin layer 7b should just be used.

  By using such a material, even if there is a difference in thickness between the insulating adhesive layer 7a and the insulating resin layer 7b, the difference in the amount of expansion and contraction during the lamination integration can be reduced, so that the warpage can be further reduced. Moreover, electrical characteristics can also be improved by using the material containing many reinforcing fiber and filler contained in the insulating contact bonding layer 7a in this way. In order to reduce variations in electrical properties, it is necessary to use reinforcing fibers with small in-plane variations (that is, clogged and uniformly woven) and have a dielectric constant close to that of reinforcing fibers. This is because it is effective to use a resin (mixing a filler such as silica in the resin). On the other hand, in the insulating resin layer 7b, the use of a material containing few reinforcing fibers or fillers contained in the insulating resin also has an effect of facilitating the formation of BVH formed in a later process (disturbance during laser processing). Because there are few things).

  Furthermore, here, in order to reduce the difference in expansion and contraction, copper foil is used as the metal foil 8 showing a linear expansion coefficient equivalent to that of the high-frequency substrate 1 (for example, CTE of RO3003 manufactured by Rogers (XY direction): 16 to 17 ppm). By disposing the foil (CTE (XY direction): 16 ppm) on the semi-cured insulating resin layer 7b, warpage can be further reduced. The thickness of the copper foil is preferably 5 μm or more and 35 μm or less in consideration of forming a circuit by etching the conductor layer containing the copper foil (if less than 5 μm, the effect of suppressing warpage is small, When it is thicker than 35 μm, it is difficult to form a fine line).

  Next, what is arranged as described above is sandwiched between hot plates and laminated and integrated by a laminating press or the like. As a result, the insulating resin of the semi-cured insulating adhesive layer 7a is melted, and the high-frequency substrate 3 side is filled between the wiring patterns of the base substrate intermediate BP1 and inside the IVH6 to form the insulating adhesive layer DL1 (here) The outer layer on the side is referred to as OL1). On the other hand, the base substrate BP is formed by melting the insulating resin of the semi-cured insulating resin layer 7b on the other surface and forming the insulating resin layer DL2 between the wiring patterns of the base substrate intermediate BP1. (The outer layer on this side is referred to as OL2) (see FIG. 6B).

  At this time, a resin release material is disposed between the high frequency substrate 3 and the hot plate. If it is a resin-based release material, it can be more closely attached to the high-frequency substrate 3 than a metal-based release material, so that the insulating resin filled in the IVH 6 formed on the high-frequency substrate 3 is an outer layer. This is because the amount that oozes out on the surface of OL1 can be reduced.

  Further, before the lamination and integration, in order to improve the adhesion between each substrate and the semi-cured insulating adhesive layer 7a and the semi-cured insulating resin layer 7b, the surfaces of the high-frequency substrate 3 and the base substrate intermediate BP1 are improved. May be roughened. The roughening treatment includes physical etching such as blasting and polishing, but chemical etching can be more efficiently performed on the surface on which the wiring pattern is formed. Specifically, soft etching, blackening treatment, or the like mainly composed of formic acid or an amine complexing agent is used as appropriate.

  Next, in order to remove the insulating resin that has oozed from the IVH 6 onto the outer layer OL1, a surface polishing treatment is performed. The polishing method is not particularly limited, but the surface of the metal film 5 is removed together with the insulating resin that has oozed out on the outer layer OL1, so that the metal is also removed by physical polishing such as buff polishing or belt polishing that can simultaneously remove the metal. That's fine.

  Next, blind via holes 9 (hereinafter referred to as BVH) and through holes 10 (hereinafter referred to as TH) for connecting the respective conductor layers to desired locations are formed. The hole forming method is not particularly limited, but BVH9 may be formed by laser processing and TH10 may be formed by drilling (see FIG. 6C).

  Next, since smear may occur at the bottom of the BVH 9, it is removed by desmear processing. As a method for desmear treatment, it may be immersed in a permanganic acid solution for several minutes. Furthermore, in order to ensure the plating adhesion of the high-frequency base material (particularly PTFE material), it is desired to perform corona treatment, plasma treatment, and the like.

  Next, the metal film 11 is formed on the entire surface including the inside of the BVH 9 and TH 10 by conductor processing (see FIG. 6D). A method for forming the metal film 11 is not particularly limited, whether it is a dry method or a wet method. However, if it is performed by plating, the metal film 11 can be uniformly formed even in complicated holes. The type of the metal film 11 is not particularly limited, but copper is appropriately used in consideration of conductivity and cost merit.

  Next, the conductor layer (consisting of the metal foil 2a, the metal film 5, and the metal film 11) on the outer layer OL1 side and the conductor layer (comprising the metal foil 8 and the metal film 11) on the outer layer OL2 side are etched. The multilayer printed wiring board Pb1 in which the high frequency wiring pattern 12 is formed on the outer layer OL1 on which the high frequency substrate 3 is laminated and the low frequency wiring pattern 13 is formed on the outer layer OL2 on the opposite side is obtained.

  Incidentally, in addition to the high-frequency wiring pattern 12, it is possible to form the low-frequency wiring pattern 13 in the outer layer OL1, so that a multilayer printed wiring board in which these are mixed in the same layer can also be formed ( (Refer FIG.7 (e)).

  Although the multilayer printed wiring board Pb1 manufactured as described above has an asymmetric layer configuration having the high-frequency substrate 3 on one side, the warp can be remarkably reduced as compared with the conventional configuration. . Therefore, defects in the manufacturing process caused by warpage are suppressed, and as a result, defects at the time of component mounting can also be prevented.

Further, since the warpage is reduced, the distortion of the interface IF between the high-frequency substrate 3 and the insulating adhesive layer DL1 can also be reduced, so that the risk of delamination and the like occurring at the interface IF is reduced even when a high-temperature reflow process is performed. Further, heat resistance can be improved.

  Next, a second embodiment of the printed wiring board of the present invention will be described (see FIG. 11 (f)). The point of this configuration is that both surfaces of the high-frequency substrate 3 are conductively connected by BVH.

  In the first embodiment, both surfaces of the high-frequency substrate 3 are conductively connected by IVH6. In this case, since the through hole 4 is opened in advance in the high-frequency substrate 3 and the conductive treatment is performed, the process is somewhat complicated. In addition, the outer layer OL1 on the high frequency substrate 3 side is formed with the metal film 5 in which IVH6 is conductively connected on the metal foil 2a, and further, the metal film 11 that connects TH and the like is overlapped, so that the conductor layer is formed. It becomes thick and is somewhat disadvantageous for high density.

  On the other hand, in the second embodiment, after the high-frequency substrate 3 is laminated on the base substrate BP, both surfaces of the high-frequency substrate 3 are connected by the BVH to be formed. Therefore, since the outer layer OL1 on the high-frequency substrate 3 side can make the conductor layer thinner, the second embodiment can provide a multilayer printed wiring board with a shorter manufacturing process and higher density than the first embodiment. .

  Next, the manufacturing method of this 2nd embodiment is demonstrated using FIG. 10 and FIG. First, a high-frequency substrate 3 having the same configuration as that of the first embodiment is prepared, and a desired wiring pattern is formed by etching the metal foil 2b located in the inner layer IL (see FIGS. 10A and 10B).

  In the next stage, materials are arranged in the same configuration as in the first embodiment, and the layers are integrated (see FIGS. 10C and 10D). As a result, the number of steps for processing the relatively thin high-frequency substrate 3 alone is reduced, so that not only the manufacturing process is shortened but also the yield is improved. Further, in this configuration, since IVH is not formed on the high-frequency substrate, it is not necessary to fill the inside with the insulating resin of the semi-cured insulating adhesive layer 7a. Therefore, the insulating adhesive layer 7a can be made thinner and the multilayer printed wiring board can be made thinner than in the first embodiment. Furthermore, since the semi-cured insulating adhesive layer 7a and the semi-cured insulating resin layer 7b can be of the same thickness, warpage can be further reduced and management during manufacturing can also be simplified.

  Next, BVH and TH for connecting each conductor layer to a desired location are formed (see FIG. 11E). Among these, the BVH 14 is formed on the high-frequency substrate 3. Incidentally, when an antenna corresponding to the millimeter wave number band is formed on the high-frequency substrate 3, the thickness of the high-frequency substrate 1 is often 100 μm or more because of material characteristics. On the other hand, since BVH9 formed on the other surface is formed on the insulating resin layer DL2, it is often 100 μm or less.

  For this reason, it is desirable that BVH14 has a larger opening diameter than BVH9. This is because when the high-frequency base material 1 having a large linear expansion coefficient is taken into account that the expansion amount increases as the thickness increases, the BVH 14 having a large opening diameter leads to an improvement in the reliability of conductive connection. Because. On the other hand, the reduction in the diameter of the BVH 9 leads to an increase in the density of the low frequency wiring pattern. The drilling is the same as in the first embodiment, and BVH9 and BVH14 may be formed by laser processing, and TH10 may be formed by drilling.

  Thereafter, in the same manner as in the first embodiment, the metal film 11 is formed on the entire surface including the inside of the BVH9, the BVH14, and the TH10 by conducting a conductive treatment, and the respective conductor layers (the outer layer OL1 side is a metal foil). 2a and the metal film 11, and the outer layer OL2 side is made of the metal foil 8 and the metal film 11), the high-frequency wiring pattern 12 is formed on the outer layer OL1 on which the high-frequency substrates are laminated, and the low frequency is formed on the outer layer OL2. A multilayer printed wiring board Pb2 on which the wiring pattern 13 is formed is obtained (FIG. 11 (f)).

  Of course, this is also the same as in the first embodiment, and in addition to the high-frequency wiring pattern 12, it is possible to form the low-frequency wiring pattern 13 in the outer layer OL1, so that these are mixed in the same layer. A multilayer printed wiring board can also be obtained.

  In addition, as an applied configuration of the second embodiment, a multilayer printed wiring board Pb3 in which the hole shape of the BVH 15 formed in the high-frequency substrate 3 has a barrel shape is used (see FIG. 12). Thereby, the adhesiveness of the high frequency base material 1 exposed in BVH15 and the metal film 11 can be strengthened also from a hole shape, and more stable conduction | electrical_connection reliability can be obtained.

  As a method for forming this BVH15, when forming a hole by laser processing, it can be easily formed by a conformal method. Incidentally, the conformal method is a method in which a metal foil having the same size as the perforated region is removed by etching, and then the inner insulating adhesive layer is removed by laser irradiation. On the other hand, the large window method is a method in which the metal foil in the region irradiated with the laser is etched and removed larger than the perforated region, and then the laser is irradiated to remove the internal insulating adhesive layer.

  Next, a third embodiment of the printed wiring board of the present invention will be described with reference to FIGS. The point of this configuration is that the metal foil 16 on the semi-cured insulating resin layer 7b provided on the other surface of the high-frequency substrate 3 is used not only as a warp suppressing layer but also as a heat dissipation layer.

  In the multilayer printed wiring board corresponding to the millimeter wave radar, the radar transmission / reception component is naturally mounted on the high frequency substrate. Among these radar transmission / reception components, there are components that easily generate heat. Therefore, providing a heat dissipation layer in the multilayer printed wiring board is an advantageous configuration for stably expressing the function. Therefore, in the third embodiment, a relatively thick metal foil is used as the metal foil provided on the insulating resin layer.

  As a result, the rigidity of the metal foil is increased, so that the influence of curing shrinkage of the insulating adhesive layer can be kept low without strictly controlling the characteristics of the insulating adhesive layer and the insulating resin layer as shown in the first embodiment. And warpage can be reduced. Furthermore, high heat dissipation can be obtained by electrically connecting the thick metal foil and the high-frequency wiring pattern via TH. As a result, it is possible to obtain a multilayer printed wiring board that not only reduces warpage but also has heat dissipation.

  Next, the manufacturing method of this multilayer printed wiring board is demonstrated using FIG. First, the high-frequency substrate 3 having a desired wiring pattern formed on the inner layer IL is disposed on one surface of the base substrate intermediate BP1 via the semi-cured insulating adhesive layer 7a, and at the same time, the base substrate intermediate BP1 On the other surface, a metal foil 16 thicker than the other conductor layers is disposed via a semi-cured insulating resin layer 7b (see FIG. 13A).

  Although there is no restriction | limiting in particular as a kind of metal foil 16, In consideration of heat dissipation and cost merit, copper foil is used suitably. If the thickness of the metal foil 16 is at least 70 μm or more from the viewpoint of rigidity as a warp suppressing layer and heat dissipation, the above effect can be obtained. The upper limit is not particularly limited as long as the circuit is not formed, but if the circuit is formed, the upper limit is preferably 200 μm or less from the viewpoint of etching accuracy.

  Next, this is laminated and integrated, and the multilayer printed wiring board Pb4 is obtained by forming TH10 and the like and conducting a conductive treatment or the like as in the other embodiments (see FIG. 13B).

  This multilayer printed wiring board Pb4 has a high-frequency wiring pattern 12 in the outer layer OL1 on the high-frequency substrate 3 side and a heat radiation pattern 17 (consisting of a metal foil 16 and a metal film 11) in the opposite outer layer OL2 through TH10. Conductive connection. As a result, a multilayer printed wiring board that not only reduces warping but also has heat dissipation properties can be obtained.

  In addition, as an application configuration of the third embodiment, the outer layer OL1 and the outer layer OL2 can be etched in the conductor layers having different thicknesses at the same time, and the outer layer OL2 side can be stably attached to the casing while ensuring heat dissipation. The shape can be fixed (see FIG. 14).

  This manufacturing method is very easy, and the desired configuration can be obtained by simultaneously etching the conductor layer on the outer layer OL2 side under the etching conditions matched to the conductor layer on the outer layer OL1 side. In other words, since the conductor layer on the outer layer OL2 side is half-etched, the insulating resin layer DL2 is not exposed on the entire surface, and the conductor layer can exist. For this reason, for example, as shown in FIG. 14, when a convex pattern 20 is formed on the casing 19, the outer layer OL <b> 2 is etched in accordance with this shape to form a concave pattern 18, thereby forming the casing 19. The contact area can be increased, so that heat can be radiated more efficiently.

  Furthermore, since this convex pattern 20 can be used as a guide pin for alignment, it is possible to improve the position accuracy and workability when the housing is assembled.

  In describing the present invention, a printed wiring board having a seven-layer structure has been described as an example. However, other structures may be used as long as they do not depart from the structure of the present invention.

1: High frequency substrate 2a: Metal foil 2b: Metal foil OL1: Outer layer IL: Inner layer 3: High frequency substrate 4: Through hole 5: Metal film 6: Interstitial via hole (IVH)
GND: ground pattern BP: base substrate BP1: base substrate intermediate TOP: top of blind via hole (BVH) BP2: base substrate intermediate TOL: conductor layer BP3 thicker than other conductor layers: base substrate intermediate 7a: semi-cured Insulating adhesive layer 7b in state: Semi-cured insulating resin layer 8: Metal foil DL1: Insulating adhesive layer DL2: Insulating resin layer OL2: Outer layer 9: Blind via hole (BVH)
10: Through hole (TH)
11: Metal film 12: High frequency wiring pattern 13: Low frequency wiring pattern Pb1: Multilayer printed wiring board DR: Drill 14: Blind via hole (BVH)
Pb2: Multilayer printed wiring board 15: Bride via hole (BVH)
Pb3: Multilayer printed wiring board 16: Metal foil Pb4: Multilayer printed wiring board 17: Heat radiation pattern 18: Concave portion 19: Housing 20: Convex portion Pb5: Multilayer printed wiring board 21: High-frequency substrate 22a: Metal foil 22b: Metal foil 23: High-frequency substrate 24: Semi-cured insulating adhesive layer BP2: Base substrate Pb: Multilayer printed wiring board DL: Insulating adhesive layer IF: Interface

Claims (5)

A base substrate in which a conductor layer and an insulating resin layer are repeatedly laminated in a desired number of layers, and an insulating resin excellent in high frequency characteristics, laminated on one surface of the base substrate via an insulating adhesive layer A multilayer printed wiring board comprising at least a high-frequency substrate having both sides thereof and conductively connected to each other by blind via holes ,
Insulating resin layer positioned at the outermost layer of the other surface of the base substrate, Ri Do the high frequency substrate from the cured product of the insulating resin layer in a semi-cured state of being laminated in the same process as to laminate on the base substrate, and a multilayer printed wiring board whose both sides, characterized in Rukoto such are conductively connected by the small diameter of the blind via hole from the blind via hole opening diameter of the high-frequency substrate.   2. The multilayer printed wiring board according to claim 1, wherein the insulating adhesive layer on the one surface and the insulating resin layer on the other surface are made of the same material.   The multilayer printed wiring board according to claim 1 or 2, wherein the insulating adhesive layer on the one surface and the insulating resin layer on the other surface have the same thickness.   2. The multilayer printed wiring board according to claim 1, wherein the insulating adhesive layer on the one surface is made of a material having a smaller amount of expansion and contraction when laminated than the insulating resin layer on the other surface.   2. The multilayer printed wiring board according to claim 1, wherein the outer layer surface of the cured product of the insulating resin layer has a conductor layer laminated simultaneously with the lamination of the semi-cured insulating resin layer. .