JP2008288356A - Printed circuit board and module structure - Google Patents

Abstract

Provided is a printed circuit board in which a solder protrusion having a height exceeding 250 μm is not formed even when a solder is filled into a through hole by a flow soldering method.
Through holes 3 are formed in laminated base materials 20 and 50, and insulating protective films 42 and 62 having openings for exposing the through holes are formed on the back surface of the laminated base material. The printed boards 1 and 5 were formed by forming the second lands 24b and 25b in the openings of the insulating protective film on the back surface of the laminated base material by applying metal platings 24 and 25 to the exposed surfaces. The through hole was formed in a circular cross section with a radius R ≦ 0.75 mm, and the second land was formed in an annular shape of π (0.6R + 0.09) mm ² or less. Alternatively, the through hole was formed in a circular cross-sectional shape of 0.75 mm <radius R ≦ 1.0 mm, and the second land was formed in an annular shape of π (0.2R + 0.01) mm ² or less.
[Selection] Figure 1

Description

  The present invention relates to a printed circuit board suitable for mounting electronic components by a flow soldering method and a module structure in which the electronic components are mounted on the printed circuit board.

  Conventionally, when mounting a surface mount type electronic component (SMD) or the like on the printed circuit board, an electrode part of the electronic component is placed on a solder paste applied to the printed circuit board to warm the printed circuit board. Many reflow soldering methods have been used in which the electrodes are soldered by heating with wind or infrared rays.

  However, in recent years, many low-heat-resistant electronic components such as LED with polycarbonate lens have appeared, and in the reflow soldering method described above, electronic components are also heated at 250 ° C. to 260 ° C. by hot air or infrared rays. Since it is heated to ° C., there is a problem that it is not suitable for mounting such surface mount type electronic components having low heat resistance.

  On the other hand, as a technique suitable for mounting such a surface mount type electronic component with low heat resistance on the printed circuit board, as shown in Patent Document 1, a through hole is formed in the printed circuit board. A flow soldering method is known in which solder is filled in the through hole to solder the electrode part of the electronic component.

  For example, as shown in FIG. 8A, the printed circuit board 9 used for the flow solder is a plate-shaped insulating substrate 10 and a first surface formed on the surface side on which the electronic components of the insulating substrate 10 are placed. A laminated base material 90 having one conductive layer 91 and a second conductive layer 92 formed on the back surface side of the insulating substrate 10 can be used in which two through holes 93 are formed.

  In these first and second conductive layers 91 and 92, wiring patterns (not shown) are formed by an etching method, and the wiring patterns by the conductive layers 91 and 92 are formed on both surfaces of the insulating substrate 10. The laminated base material 90 is formed with a first insulating protective film 95 having an opening for exposing the through hole 93 on the surface. At the same time, an insulating protective film 96 a is formed on the back surface of the laminated substrate 90 at the center of the surface between the through holes 93.

  Then, on the exposed surface of the laminated base material 90 that is not covered by the first conductive layer 91 and the second conductive layer 92, that is, from the back surface of the laminated base material 90 to the surface of the laminated base material 90 through the through hole 93. By applying copper plating 94 to the exposed surface of the laminated base material 90, the printed board 9 has the first land 94 a formed in the opening of the first insulating protective film 95 on the surface of the laminated base material 90. ing. An insulating protective film 96b is formed on the outer peripheral portion of the back surface of the laminated base material 90 on the copper plating 94 so that the lower surface is positioned horizontally with the insulating protective film 96a. As a result, the printed circuit board 9 has the second insulating protective film 96 having an opening exposing the through hole 93 formed by the insulating protective films 96a and 96b, and the back surface is formed flat. A second land 94 b formed by copper plating 94 is provided in the opening of the second insulating protective film 96.

  Thereby, when the electronic component is mounted by the flow soldering method, the printed circuit board 9 has the main body 80 on the insulating protective film 95 with the electrode portion 81 of the electronic component M positioned on the first land 94a. After being temporarily fixed by 97, the through hole 93 is filled with solder. At that time, as shown in FIG. 8B, the back surface side of the printed circuit board 9 is brought into contact with the molten solder flowing in the surface direction indicated by the arrow in the drawing. Then, the molten solder rises in the through hole 93 toward the surface side of the printed circuit board 9, and gets wet to the electrode portion 81 of the electronic component M on the first land 94a as shown in FIG. After that, it is cooled and solidified. As a result, the printed circuit board 9 is electrically connected to the electronic component M with the electrode 81 fixed on the first land 94a.

  In this way, when the electronic component M is mounted on the printed circuit board 9 by the flow soldering method, the electronic component M is not heated by warm air or infrared rays as in the reflow method. Even the electronic component M can be mounted.

  On the other hand, with the development of various products in recent years, the amount of heat generated by the printed circuit board 9 on which the electronic component M is mounted has been remarkably increased. ), A heat radiating sheet 80 may be attached to the back surface thereof.

  However, in the above-described flow soldering method, the solder protrusion 88 is formed on the back surface of the printed circuit board 9 by partially solidifying it by cooling and solidifying in a state where the solder protrudes from the surface of the second land 94 b on the back surface of the printed circuit board 9. It may be done. Nevertheless, since the solder protrusion 88 does not cause a problem in the assembly structure, the printed circuit board 9 has been used as it is without any device for lowering the solder protrusion 88. In addition, in the printed circuit board 9, the elevating efficiency of the solder by the flow soldering method is more important than the height of the solder protrusion 88, the diameter of the through hole 93 is formed larger, and the second insulating protective film 96 is formed. Is formed with a large opening that exposes the through-hole 93, so that the second land 94 b is formed large. The large-diameter through-hole 93 and the large-area second land 94 b are formed on the solder protrusion 88. It helped increase the size.

  As a result, the printed circuit board 9 in which the solder protrusions 88 are formed at a height exceeding 250 μm from the surface of the second land 94 b can absorb the height of the solder protrusions 88 even by the second insulating protective film 96. In other words, there is a problem that a gap 98 is generated between the second insulating protective film 96 and the heat radiating sheet 80, and the heat radiating effect is lowered.

  Further, the printed circuit board 9 on which the heat radiating sheet 80 is attached has a corrugated surface on the lower surface of the heat radiating sheet 80 because the heat radiating sheet 80 undulates when the solder protrusions 88 are present. When assembling the product while being fixed to other parts, there is a problem that this unevenness hinders the assembly of the product.

JP-A-52-100175

  The present invention has been made in view of such circumstances, and it is intended to provide a printed circuit board in which solder protrusions having a height exceeding 250 μm are not formed even when solder is filled into a through hole by a flow soldering method. It is to be an issue.

That is, the invention according to claim 1 is provided on the insulating substrate formed in a plate shape, the first conductive layer formed on the surface side on which the electronic component of the insulating substrate is placed, and the back surface side of the insulating substrate. The laminated base material having the formed second conductive layer is provided with a through hole for flow solder, and an insulating protective film having an opening exposing the through hole for flow solder is formed on the laminated base material. The laminated base is formed by applying metal plating to an exposed surface of the laminated base that is formed on the back and extends from the opening of the insulating protective film on the back of the laminated base to the surface of the laminated base through the through hole. A printed circuit board in which a first land is formed on the surface of the material and a second land is formed in the opening of the insulating protective film on the back surface of the laminated base material, and the radius of the through hole is R If, the through hole is formed in a circular cross-shaped R ≦ 0.75 mm, the second land, the opening exposing the through holes in the insulating protective film is π (R + 0.3) It is characterized by being formed in a ring shape of π (0.6R + 0.09) mm ² or less by being formed in a size of ² mm ² or less.

  Here, the insulating protective film having an opening exposing the through hole means an insulating protective film having an opening having an outer shape that is at least the same as or larger than the through hole, and the above-described back surface of the laminated base material Since the second land is formed in the opening of the insulating protective film, the opening of the insulating protective film means that the outer shape is formed larger than the through hole so as to form the second land. is doing.

  According to a second aspect of the present invention, in the printed circuit board according to the first aspect, the second land has an inner diameter of 2 Rmm and an outer diameter of (2R + 0.6) mm or less. It is characterized by being.

According to a third aspect of the present invention, there is provided a printed circuit board comprising: an insulating substrate formed in a plate shape; a first conductive layer formed on a surface side on which electronic components of the insulating substrate are placed; and a back surface of the insulating substrate. A through-hole for flow soldering is formed in a laminated base material having a second conductive layer formed on the side, and an insulating protective film having an opening exposing the through-hole for flow soldering is formed on the laminated base. By forming metal plating on the exposed surface of the laminated base material that is formed on the back surface of the material and reaches the surface of the laminated base material from the opening of the insulating protective film on the back surface of the laminated base material through the through hole. A printed circuit board in which a first land is formed on the front surface of the laminated base material and a second land is formed in the opening of the insulating protective film on the back surface of the laminated base material, and the radius of the through hole In the case of R, the through hole is formed in a circular cross section of 0.75 mm <R ≦ 1.0 mm, and the second land is an opening exposing the through hole in the insulating protective film. Is formed in a ring shape of π (0.2R + 0.01) mm ² or less by being formed in a size of π (R + 0.1) ² mm ² or less.

  According to a fourth aspect of the present invention, in the printed circuit board according to the third aspect, the second land is formed in an annular shape having an inner diameter of 2 Rmm and an outer diameter of (2R + 0.2) mm or less. It is characterized by having.

  According to a fifth aspect of the present invention, in the printed circuit board according to any one of the first to fourth aspects, the through hole has a plurality of holes per one electrode part of an electronic component mounted on the printed circuit board. It is characterized by being installed.

  A sixth aspect of the present invention is a module structure in which a surface mount type electronic component is mounted on the printed circuit board according to any one of the first to fifth aspects, wherein the through hole is filled with solder. The electronic component is mounted by electrically connecting the electrode portion of the electronic component to the first conductive layer and / or the second conductive layer.

According to the invention described in claim 1 or 2, when the radius of the through hole is R, the through hole is exposed when the through hole is formed in a circular cross section of R ≦ 0.75 mm. By forming the opening in a size of π (R + 0.3) ² mm ² or less, the second land is formed in an annular shape of π (0.6R + 0.09) mm ² or less.
Even when molten solder is brought into contact with the back surface of the printed circuit board by the flow soldering method, the solder protrusion having a height exceeding 250 μm can be prevented from being formed on the back surface of the printed circuit board.

  For this reason, as in the invention described in claim 2, a printed circuit board in which the second land is formed in an annular shape having an inner diameter of 2 Rmm and an outer diameter of (2R + 0.6) mm or less is preferably used. Can do.

According to the invention described in claim 3 or 4, when the radius of the through hole is R, when the through hole is formed in a circular cross section of 0.75 mm <R ≦ 1.0 mm, The second land is formed in an annular shape of π (0.2R + 0.01) mm ² or less by forming the opening exposing the through hole in a size of π (R + 0.1) ² mm ² or less. Even when molten solder is brought into contact with the back surface of the printed circuit board by the flow soldering method, the solder protrusion having a height exceeding 250 μm can be prevented from being formed on the back surface of the printed circuit board.

  For this reason, as in the invention described in claim 4, a printed circuit board in which the second land is formed in an annular shape having an inner diameter of 2 Rmm and an outer diameter of (2R + 0.2) mm or less is preferably used. Can do.

  Further, according to the invention described in claim 5, even when each through hole and the second land are formed small by drilling a plurality of through holes, it is sufficient for soldering the electrode portion. The amount of solder can be secured. For this reason, it is possible to ensure a sufficient amount of solder while suppressing the formation of solder protrusions.

  Further, the above-mentioned printed circuit board can mount surface mount type electronic components as in the invention described in claim 6, and in particular, surface mount type electronic devices having low heat resistance such as LED with polycarbonate lens. Even a component can be mounted, and can be suitably used as a module structure on which the electronic component is mounted.

  Hereinafter, two embodiments of a printed circuit board according to the present invention, a method for mounting electronic components on each printed circuit board, and a module structure in which the electronic components are mounted on each printed circuit board will be described.

[First Embodiment]
First, a printed circuit board according to the first embodiment, a method for mounting electronic components on the printed circuit board, and a module structure in which electronic components are mounted on the printed circuit board will be described with reference to FIG. FIG. 1 is a schematic diagram of a printed circuit board, in which (a) is a plan view, (b) is a cross-sectional view, and (c) is a bottom view.

  In the printed circuit board 1 of the present embodiment, a first wiring pattern (first conductive layer) 21 is formed on the surface side of the rectangular plate-shaped insulating substrate 10 on which electronic components are placed, and the insulating substrate 10 It has a laminated base material 20 on which a second wiring pattern (second conductive layer) 22 is formed on the back side, and is used for flow solder having a circular cross section with a radius of 1.0 mm or less on the laminated base material 20. A through hole 3 is formed.

  The reason why the radius of the through hole 3 is set to 1.0 mm or less in this way is that the solder protrusion 88 formed when mounting the electronic component as described later becomes larger as the through hole 3 becomes larger. This is to prevent the solder protrusion 88 from being formed to a height exceeding 250 μm.

  The first wiring pattern 21 and the second wiring pattern 22 are configured by forming a pattern on a copper foil fixed to the entire surface of the insulating substrate 10 by etching.

  Further, the printed circuit board 1 has the first insulating protective film 41 directly formed on the outer peripheral portion of the first wiring pattern 21 in a rectangular ring shape so that the first insulating protective film 41 is a laminated base material. A rectangular opening for exposing the through hole 3 is formed on the surface of 20. On the other hand, the second insulating protective film 42 is formed directly and entirely on the back surface of the insulating substrate 10 outside the outer peripheral edge of the second wiring pattern 22. A circular opening that exposes the through hole 3 is formed on the back surface of the laminated base material 20.

  As these insulating protective films 41 and 42, a cover film or a solder resist is used, and the cover film is fixed to the first wiring pattern 21 or the insulating substrate 10, or the solder resist is used for the first wiring pattern 21 or the insulating film. It is formed by being applied to the substrate 10. Further, the opening formed in the insulating protective films 41 and 42 is formed larger than the through hole 3.

Furthermore, the printed circuit board 1 is disposed on the exposed surface of the laminated base material 20 that is not covered with the insulating protective films 41 and 42, that is, through the through hole 3 from the opening of the insulating protective film 42 on the back surface of the laminated base material 20. Copper plating (metal plating) 24 is formed on the exposed surface of the laminated base material 20 reaching the opening of the insulating protective film 41 on the surface of the material 20. As a result, in the printed circuit board 1, the first land 24 a by the copper plating 24 is formed in the opening of the first insulating protective film 41 on the surface of the laminated base material 20, and the second land on the back surface of the laminated base material 20. A second land 24 b is formed by copper plating 24 in the opening of the insulating protective film 42.
In other words, the first land 24 a is patterned by the first insulating protective film 41, and the second land 24 b is patterned by the second insulating protective film 42.

When the radius of the through hole 3 is R, the second land 24b has an opening that exposes the through hole in the second insulating protection film 42 when R ≦ 0.75 mm. Π (R + 0.3) By being formed in a size of ² mm ² or less, it is formed in an annular shape of π (0.6R + 0.09) mm ² or less. Further, when 0.75 mm <R ≦ 1.0 mm, the opening through which the through hole in the second insulating protective film 42 is exposed is formed with a size of π (R + 0.1) ² mm ² or less, It is formed in a ring of π (0.2R + 0.01) mm ² or less.
That is, when R ≦ 0.75 mm, the second land 24 b is formed in an annular shape having an inner diameter of 2 Rmm and an outer diameter of (2R + 0.6) mm or less, and 0.75 mm. When <R ≦ 1.0 mm, the inner diameter is 2 Rmm and the outer diameter is (2R + 0.2) mm or less.

  This is because the back surface side on which the second wiring pattern 22 of the printed circuit board 1 is formed by the flow soldering method is immersed in molten solder by forming the second land 24b to a size equal to or smaller than the above-described upper limit. This is because even if the solder is wetted up to the through hole 3, the solder protrusion protruding downward from the surface of the second land 24b is not formed at a height exceeding 250 μm.

  Next, a method for mounting electronic components on the printed circuit board 1 of the first embodiment described above and a module structure in which the electronic components are mounted on the printed circuit board 1 will be described.

First, the electronic component is temporarily fixed to the printed circuit board 1 with the electrode portion 81 of the electronic component positioned on the first land 24 a of the printed circuit board 1.
Next, the printed circuit board 1 on which electronic components are temporarily fixed is introduced into a flow soldering apparatus filled with molten solder with the back side facing downward.

  Then, the molten solder rises in the through hole 3 from the back surface side of the printed circuit board 1 and is cooled and solidified in a state where it is wetted onto the electrode part 81 of the electronic component on the surface of the printed circuit board 1. As a result, the electronic component has a module structure in which the electrode portion 81 is fixed to the first land 24a of the printed circuit board 1 and is electrically connected to the wiring patterns 21 and 22 of the printed circuit board 1. Then, it is carried out from the flow soldering apparatus.

  As shown in FIG. 2, in this module structure, an electrode part 81 of an electronic component is fixed to the first land 24a of the printed circuit board 1 described above, and the solder protrusion by the solder fixing the electrode part 81 The height of 88 is suppressed to 250 μm or less.

[Second Embodiment]
Next, a printed circuit board according to the second embodiment will be described with reference to FIG. 3A and 3B are schematic diagrams of a printed circuit board, where FIG. 3A is a plan view, FIG. 3B is a cross-sectional view, and FIG. 3C is a bottom view. In addition, about the structure same as 1st Embodiment, description is abbreviate | omitted by using the same code | symbol.

  In the printed circuit board 5 of the present embodiment, a first wiring pattern (first conductive layer) 51 is formed on the surface side of the rectangular plate-shaped insulating substrate 10 on which electronic components are placed. It has the laminated base material 50 in which the 2nd wiring pattern (2nd conductive layer) 52 was formed in the back surface side. A plurality of (four in the present embodiment) through-holes 3 for flow solder having a circular cross section having a radius of 1.0 mm or less are formed in the rectangular laminated base material 50. Each of these through holes 3 is formed on the mounting surface of the electrode part 81 of the electronic component so as to be point-symmetric with respect to the center of the mounting surface, and has the same size as in the first embodiment. It has a caliber.

  Each through-hole 3 may have a different diameter, but preferably has the same diameter. This is because if the diameter of some of the through holes 3 is formed large, the height of the solder protrusion 88 increases only in that through hole 3. Accordingly, each through hole 3 preferably has an equivalent diameter in order to reduce the overall height of the solder protrusion 88.

Further, the first insulating protective film 61 is directly formed on the outer periphery of the first wiring pattern 51 in a rectangular ring shape, so that the first insulating protective film 61 passes through the surface of the laminated substrate 50. A rectangular opening for exposing the hole 3 is formed.
On the other hand, the second insulating protective film 62 is formed directly on the second wiring pattern 52 so as to exclude the periphery of the through hole 3, so that the through hole 3 is formed on the back surface of the laminated substrate 50. Is formed with a circular opening that exposes.

These insulating protective films 61 and 62 are formed of a cover film or a solder resist like the insulating protective films 41 and 42, and the opening for exposing the through hole 3 is formed larger than the through hole 3.
Further, the printed circuit board 5 is laminated on the exposed surface of the laminated base material 50 that is not covered by these insulating protective films 61 and 62, that is, from the back surface of the laminated base material 50 to the surface of the laminated base material 50 through the through hole 3. Copper plating (metal plating) 25 is formed on the exposed surface of the substrate 50. As a result, the printed circuit board 5 has the first land 25a formed by the copper plating 25 on the surface of the laminated base material 50 and the second land 25b formed by the copper plating 25 on the back surface of the laminated base material 50. Yes.

When the radius of the through hole 3 is R and the radius of the through hole 3 is R ≦ 0.75 mm, the second land 25b has an opening that exposes the through hole 3 in the second insulating protective film 62 by π (R + 0. 3) By being formed in a size of ² mm ² or less, it is formed in an annular shape of π (0.6R + 0.09) mm ² or less. Further, when 0.75 mm <R ≦ 1.0 mm, an opening exposing the through hole 3 in the second insulating protective film 62 is formed to have a size of π (R + 0.1) ² mm ² or less. Therefore, it is formed in an annular shape of π (0.2R + 0.01) mm ² or less.
That is, as in the first embodiment, the second land 25b has an annular shape with an inner diameter of 2 Rmm and an outer diameter of (2R + 0.6) mm or less when R ≦ 0.75 mm. In addition, when 0.75 mm <R ≦ 1.0 mm, the inner diameter is 2 Rmm and the outer diameter is (2R + 0.2) mm or less.

  This is because, since the second land 25b is formed to have a size equal to or smaller than the above-described upper limit, the solder protrusion is not formed to have a height exceeding 250 μm, similarly to the second land 24b of the first embodiment. Because.

  Next, a method for mounting electronic components on the printed circuit board 5 of the second embodiment described above and a module structure in which the electronic components are mounted on the printed circuit board 5 will be described.

First, the electronic component is temporarily fixed to the printed circuit board 5 with the electrode part 81 of the electronic component positioned on the first land 24 a of the printed circuit board 5.
Next, the printed circuit board 5 on which the electronic components are temporarily fixed is introduced into a flow soldering apparatus filled with molten solder with the back side facing downward.

  Then, the molten solder rises in the through hole 3 from the back surface side of the printed circuit board 5, and is cooled and solidified in a state where the molten solder is wetted onto the electrode part 81 of the electronic component on the surface of the printed circuit board 5. As a result, the electronic component is flow soldered in a state where the electrode portion 81 is fixed to the first land 25a and is electrically connected to the wiring patterns 51 and 52 of the printed circuit board 5 to form a module structure. It is carried out from the attaching device.

  As shown in FIG. 4, in this module structure, an electrode part 81 of an electronic component is fixed to the first land 25a of the above-mentioned printed circuit board 5, and solder protrusions by solder fixing the electrode part 81 The height of 88 is suppressed to 250 μm or less.

According to the printed boards 1 and 5 of the first and second embodiments described above, the through hole 3 has a radius R ≦ 1.0 mm, and the through hole 3 is formed in a circular cross-sectional shape with R ≦ 0.75 mm. In this case, the second land 24b is formed to have a size of π (0.6R + 0.09) mm ² or less by forming an opening through which the through hole 3 is exposed to a size of π (R + 0.3) ² mm ² or less. When the through hole 3 is formed in a ring shape and has a circular cross section of 0.75 mm <R ≦ 1.0 mm, the opening through which the through hole 3 is exposed is π (R + 0.1) ² mm ^{Since the second} land 24b is formed in an annular shape of π (0.2R + 0.01) mm ² or less by forming it in a size of ² or less, the formation of the solder protrusion 88 having a height exceeding 250 μm is surely prevented. be able to.

  In particular, according to the printed circuit board 5 of the second embodiment, since the plurality of through holes 3 are formed, it is possible to reduce the size of each through hole 3 while securing a sufficient amount of solder. The solder protrusion 88 can be made small.

  The present invention is not limited to the above-described embodiment. For example, the openings of the second insulating protective films 42 and 62 are not circular, but are polygonal such as a square as shown in FIG. 6 may be formed in a circular arc shape by taking a polygonal corner such as a square as shown in FIG. 6, or may be formed in an elliptical shape.

  A printed circuit board No. 1 using the printed circuit board 1 in the first embodiment described above. Six pieces of 1 to 12 were prepared.

These printed circuit boards No. 1 to 12 use a laminated base material 20 in which wiring patterns 21 and 22 are formed on a glass epoxy substrate of FR-4 as an insulating substrate 10, and the through hole 3 is 0.3 mm in the laminated base material 20. ≦ Radius R ≦ 1.0 mm is formed. Further, the second insulating protective film 42 is formed so that the radius of the opening exposing the through hole 3 is 0.4 mm or more and 1.3 mm or less. The two lands 24b have an inner diameter of 2Rmm and are formed in an annular shape having a range of 0.8mm ≦ outer dimension ≦ 2.6mm.
Each printed circuit board No. Table 1 shows the radius of the through hole 3 in 1 to 12 and the radius of the opening formed in the insulating protective film 42.

  Next, printed circuit board No. The six pieces of No. 1 were used as Sample 1 to Sample 6, and the solder was filled into the through hole 3 from the second land 24b under the conditions of the flow solder shown in Table 2, respectively. At that time, using an automatic flow soldering apparatus, the preheating temperature is set to 140 ° C, the molten solder temperature to be jetted is set to 258 ° C, and the time for the second land 24b to contact the molten solder is set to 5 to 6 seconds. did.

Next, the printed circuit board No. Similarly, with respect to Samples 2 to 12, the samples 1 to 6 were soldered under the above-described conditions, and the printed circuit board Nos. The height (μm) of 1 to 12 solder protrusions was measured and shown in Table 3. Also,
The change in the height of the solder protrusion is shown in FIG.

  As can be seen from Table 3 and FIG. 7, as the radius of the through hole 3 increases, the solder protrusion becomes higher, and as the opening of the second insulating protective film 42 becomes larger than the through hole 3, That is, the solder protrusion becomes higher as the second land 42b becomes larger.

Further, when the radius R of the through hole 3 is 0.3 mm ≦ R ≦ 0.75 mm, the radius of the opening of the second insulating protective film is formed to be larger than the radius of the through hole 3 by 0.3 mm. Thus, in other words, the opening size is increased to π (R + 0.3) ² mm ^2, so that the outer diameter of the second land 42b is increased to 0.6 mm rather than the diameter 2R of the through hole. However, it has been found that the height of the solder protrusion can be prevented from exceeding 250 μm.

On the other hand, when the radius R of the through hole is 0.75 mm <R ≦ 1.0 mm, the radius of the opening 42 a of the insulating protective film 42 is larger than the radius of the through hole 3 by 0.1 mm. As a result, it has been found that the height of the solder protrusion may exceed 250 μm.
In other words, it has been found that the height of the solder protrusion can be prevented from exceeding 250 μm even when the outer shape of the second land 42b is formed to be 0.2 mm larger than the diameter 2R of the through hole.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic schematic diagram of the printed circuit board of 1st Embodiment, Comprising: (a) is a top view, (b) is sectional drawing, (c) is a bottom view. It is a cross-sectional schematic diagram which shows the module structure body by which the electronic component was mounted in the printed circuit board of 1st Embodiment. It is a schematic schematic diagram of the printed circuit board of 2nd Embodiment, (a) is a top view, (b) is sectional drawing, (c) is a bottom view. It is a cross-sectional schematic diagram which shows the module structure body by which the electronic component was mounted in the printed circuit board of 2nd Embodiment. It is a bottom view of the printed circuit board concerning the present invention. It is a bottom view of the printed circuit board concerning the present invention. It is a line graph which showed the relationship of the height of a solder protrusion with respect to the through-hole radius and the opening radius of an insulating protective film. It is the side surface schematic diagram which showed the process of mounting an electronic component on the conventional printed circuit board by the flow soldering method.

Explanation of symbols

1, 5 Printed circuit board 3 Through hole 10 Insulating substrate 20, 50 Laminate base material 21, 51 First wiring pattern (first conductive layer)
22, 52 Second wiring pattern (second conductive layer)
24, 25 Copper plating (metal plating)
24a, 25a First land 24b, 25b Second land 42, 62 Second insulating protective film (insulating protective film)

Claims (6)

A laminate having an insulating substrate formed in a plate shape, a first conductive layer formed on the front side on which electronic components of the insulating substrate are placed, and a second conductive layer formed on the back side of the insulating substrate A through hole for flow solder is drilled in the base material, and an insulating protective film having an opening for exposing the through hole for flow solder is formed on the back surface of the laminated base material. The exposed surface of the laminated base material from the opening of the insulating protective film on the back surface to the surface of the laminated base material through the through hole is subjected to metal plating, whereby the first land and the laminated material are formed on the surface of the laminated base material. A printed circuit board in which second lands are respectively formed in the openings of the insulating protective film on the back surface of the substrate,
When the radius of the through hole is R, the through hole is formed in a circular cross section of R ≦ 0.75 mm, and the second land exposes the through hole in the insulating protective film. A printed circuit board characterized in that the opening to be formed is formed in a ring shape of π (0.6R + 0.09) mm ² or less by being formed in a size of π (R + 0.3) ² mm ² or less.   The printed circuit board according to claim 1, wherein the second land has an annular shape with an inner diameter of 2 Rmm and an outer diameter of (2R + 0.6) mm or less. A laminate having an insulating substrate formed in a plate shape, a first conductive layer formed on the front side on which electronic components of the insulating substrate are placed, and a second conductive layer formed on the back side of the insulating substrate A through hole for flow solder is drilled in the base material, and an insulating protective film having an opening for exposing the through hole for flow solder is formed on the back surface of the laminated base material. The exposed surface of the laminated base material from the opening of the insulating protective film on the back surface to the surface of the laminated base material through the through hole is subjected to metal plating, whereby the first land and the laminated material are formed on the surface of the laminated base material. A printed circuit board in which second lands are respectively formed in the openings of the insulating protective film on the back surface of the substrate,
When the radius of the through hole is R, the through hole is formed in a circular cross-sectional shape of 0.75 mm <R ≦ 1.0 mm, and the second land is formed on the insulating protective film. The opening for exposing the through hole is formed to have a size of π (R + 0.1) ² mm ² or less, thereby forming an annular shape of π (0.2R + 0.01) mm ² or less. Printed board.   The printed circuit board according to claim 3, wherein the second land has an annular shape with an inner diameter of 2 Rmm and an outer diameter of (2R + 0.2) mm or less.   5. The printed circuit board according to claim 1, wherein a plurality of the through holes are formed in one electrode part of an electronic component mounted on the printed circuit board. 6.   A module structure in which a surface mount type electronic component is mounted on the printed circuit board according to any one of claims 1 to 5, wherein the through hole is filled with solder, and an electrode portion of the electronic component is formed. A module structure in which the electronic component is mounted by being electrically connected to the first conductive layer and / or the second conductive layer.

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