JP4735538B2 - Electronics - Google Patents

Description

The present invention relates to an electronic apparatus using the circuit board having a through hole, in particular, at an insertion type electronic component lead-free solder by mounting the insertion type electronic component on a circuit board suitable for mounting soldering Relates to electronic equipment.

  Many leadless electronic components are surface-mounted on a circuit board, but some electronic components such as connectors and variable resistors are inserted into through-holes as insertion-type electronic components, Soldered. FIG. 7A is a top view showing a structure of a mounting portion of an insertion type electronic component of a conventional circuit board on which the insertion type electronic component is mounted, and FIG. 7B is a diagram of A in FIG. It is sectional drawing by the -A line. In the present specification, the through hole refers to a through hole in which the wall surface of the through hole is covered with a conductive film, such as a plated through hole.

  A circuit board used for mounting electronic components is usually manufactured through the following steps. A glass cloth base material is impregnated with a resin such as an epoxy resin or a polyimide resin, and a semi-cured prepreg or a paper base material is impregnated with a phenol resin, and a copper foil is pressed on the semi-cured laminate of the prepreg. Using a copper-clad laminate attached by heat treatment, the copper foil is patterned by a photoetching method or the like to produce a wiring board having a predetermined number of inner layer patterns. Then, in order to improve the adhesion to the prepreg, the surface of the copper foil (inner layer pattern) is subjected to a roughening treatment (blackening treatment), and then the copper foil is the outermost layer of the wiring board and the copper-clad laminate. Are laminated through a prepreg and integrated by pressurization and heating to produce a substrate having the inner layer wiring 3 in the resin laminate 2.

  Next, the through hole is opened by drilling, and in order to improve the connectivity between the inner layer wiring and the through hole, the resin of the inner layer wiring part is cleaned (desmear), and then activation treatment, electroless plating, and electrolytic plating are performed. As a result, the through hole 4 is formed. Subsequently, the through hole is protected by a hole filling method or a tenting method, the outermost layer copper layer is patterned to form the outer layer wiring 5, and the land 6 is formed around the through hole on the front and back surfaces of the substrate. The through hole 4, the outer layer wiring 5, and the land 6 can also be formed by a pattern plating method.

  Finally, a solder resist (not shown) is formed in the region excluding the soldered portions on the front and back surfaces of the substrate, and the manufacturing process of the multilayer circuit board 1 is completed.

  The above is the manufacturing process of the multilayer circuit board having the inner layer wiring, but in the case of the double-sided circuit board, it can be formed by performing the process after the through-hole forming process using the double-sided copper-clad laminate as a starting material.

  In FIG. 7, a line passing through the center of the casing of the electronic component after mounting the electronic component is indicated by O. In the conventional circuit board, the through holes 4 are arranged at equal intervals. That is, even in the vicinity of the central through hole 4a where the lead closest to the center of the casing of the electronic component is inserted, and also in the vicinity of the outermost end through hole 4b where the outermost lead of the casing of the electronic component is inserted. They were arranged at an equal pitch.

  The process of soldering an electronic component using the multilayer circuit board 1 manufactured in this way is generally performed after a reflow process of mounting a surface mount type component such as a chip component and a QFP. A flow process for mounting the insertion type electronic component is performed.

  As a solder material for soldering electronic components, tin-lead solder has been used for a long time. Particularly, the concentration ratio (mass%) of Sn and Pb is Sn: Pb = 60 to 63%: 40 to 37. Tin-lead eutectic solder with a percent eutectic composition has been used. Since the tin-lead eutectic solder was a material with high ductility, the stress generated by the difference in thermal expansion and contraction of the multilayer circuit board 1 and the casing of the electronic component during the soldering process was alleviated with tin-lead eutectic solder. It was possible to do.

Japanese Utility Model Publication No. 57-037276 JP 2001-156420 A JP 2003-218534 A JP 08-148790 A Japanese Patent Laid-Open No. 04-261087 Japanese Patent Laid-Open No. 03-009594

  However, in recent years, environmental pollution due to lead has become a problem due to an increase in environmental awareness, and the conversion to lead-free solder containing no lead is rapidly progressing. This lead-free solder contains tin as a main component, and contains silver, copper, zinc, bismuth, indium, antimony, nickel, germanium, and the like as additive components. Compared with Pb), the metal has a metal property that the tensile strength and creep strength of the metal are strong and the ductility is small. Also, the melting temperature of the lead-free solder is as high as 190 ° C. to 230 ° C., compared to 183 ° C. for the tin-lead eutectic solder. As a result, the stress generated by the difference in thermal expansion and contraction between the multilayer circuit board and the electronic component housing during the soldering process is large, and the stress on the circuit board is less likely to be relaxed by the solder itself. In particular, a phenomenon that the outermost end through-hole portion is broken can be seen. Even though the conventional tin-lead eutectic solder had a phenomenon that the through-hole portion was destroyed, this phenomenon became more remarkable by switching to lead-free solder. The situation will be described more specifically with reference to FIGS.

  FIG. 8 is a cross-sectional view showing a state in which an electronic component is soldered to the conventional multilayer circuit board 1 shown in FIG. 7 using lead-free solder. This cross-sectional view shows a circuit board made of FR-4 as a base material, the housing is made of polyamide, and an 8-pin single-row connector is lead-free solder (Sn-3.0 mass% Ag-0.5 mass% Cu). ) Is a drawing based on a cross-sectional photograph when soldering using.

  When the coefficient of linear expansion of the casing material of the electronic component is α and the coefficient of linear expansion of the substrate material of the circuit board is β, in the case of α> β, as shown in FIG. The electronic component lead 8 is electrically and mechanically coupled to the copper layer of the multilayer circuit board 1 by a solder fillet 9. As shown in the figure, the lead 8 inserted into the central through-hole 4a is almost perpendicular to the multilayer circuit board 1, and the center of the central through-hole 4a and the center of the lead 8 substantially coincide with each other. Soldered with. However, the lead 8 inserted into the outermost end through-hole 4b is displaced from the center of the outermost end through-hole 4b in the opposite direction (outward direction) from the center direction of the casing 7 of the electronic component during mounting. It is soldered and soldered in a state bent toward the center of the casing 7 of the electronic component toward the upper side of the figure. The reason for mounting in this way is due to the difference in thermal expansion coefficient due to the difference in material between the casing 7 of the electronic component and the multilayer circuit board 1.

  FIG. 9 is a cross-sectional view showing a state before electronic components are mounted on a circuit board and soldered. Before the soldering process, the centers of all the through holes including the outermost end through hole 4b and the centers of the leads 8 are substantially coincident. When preheating is performed from this state and immersion in a solder bath is performed, if the linear thermal expansion coefficient of the casing portion 7 of the electronic component is larger than the linear thermal expansion coefficient of the multilayer circuit board 1, the casing of the electronic component is The difference between the thermal expansion amounts of the electronic component casing 7 and the multilayer circuit board 1 increases as the body part 7 thermally expands more than the multilayer circuit board 1 and away from the center of the electronic component casing 7. Therefore, the center of the lead 8 at the outermost end is shifted in the direction opposite to the direction from the center of the outermost end through hole 4b toward the center of the casing 7 when the electronic component is mounted. In this state, the inside of the through hole is filled with molten solder, and the multilayer circuit board is pulled up from the solder bath. Immediately after the soldering process, as the temperature decreases, the housing part 7 of the electronic component is more thermally contracted than the multilayer circuit board 1, so that the leads 8 are directed upward in the figure toward the upper part of the housing part 7 when the electronic component is mounted. It is in a state bent in the center direction.

  On the other hand, in the case of α <β, the electronic component is soldered at a position shifted from the center of the outermost end through-hole 4b toward the center of the casing 7 of the electronic component during mounting, and upwards in the figure. Soldered in a state bent in the direction opposite to the center direction of the casing portion 7 of the case.

  10 is an enlarged cross-sectional view of the leftmost outermost through hole 4b in FIG. As shown in FIG. 10A, the lead 8 at the outermost end is soldered by shifting from the center of the outermost end through-hole 4b in the direction opposite to the center direction of the housing part 7 when the electronic component is mounted. For this reason, the amount of solder in the region opposite to the center direction of the electronic component housing portion between the through hole and the lead 8 (A portion: the hatched region in the figure) is reduced. The lead 8 is bent in the center direction of the housing portion 7 upward in the figure. Here, since the lead-free solder has a lower stress relaxation capability than the tin-lead eutectic solder, the effect of absorbing the stress generated by bending the lead 8 with the lead-free solder is remarkably low. For this reason, a large stress is applied to the through-hole corner portion B and the through-hole outer wall surface C of the through-hole portion in the direction opposite to the center of the housing portion when the electronic component of the outermost end through-hole 4b is mounted. Therefore, as shown in FIG. 10 (b), a corner crack 11 is likely to occur in the through-hole corner portion, and as shown in FIG. 10 (c), a through-hole peeling 12 in which the through-hole plating layer is peeled off easily occurs. As a result, poor electrical continuity of electronic components occurs.

  Similarly, when the coefficient of linear expansion of the casing material of the electronic component is α and the coefficient of linear expansion of the substrate material of the circuit board is β, in the case of α <β, the electronic component between the through hole and the lead 8 is used. Since the amount of solder in the region in the center direction of the housing portion is reduced, a large stress is applied to the through hole portion in the center portion of the housing portion when the electronic component is mounted on the outermost end through hole 4b. For this reason, a corner crack is likely to occur in the through-hole corner portion, or through-hole peeling 12 in which the through-hole plating layer is peeled off easily occurs. Due to this corner crack and through-hole peeling 12, an electrical continuity failure of the electronic component occurs.

An object of the present invention, even when the insertion type electronic component mounted with the lead-free solder, an electronic apparatus using a reliable circuit board never through hole corner cracks and through-holes peeling occurs There is.

The electronic device according to the first aspect of the present invention is electrically connected to the through hole into which the lead of the electronic component with the lead is inserted and soldered, and the periphery of the through hole on the front and back surfaces of the substrate through the through hole. With land. In this circuit board, the linear expansion coefficient of the casing material of the electronic component is α, the linear expansion coefficient of the substrate material of the circuit board is β, and the outermost lead of the electronic component of the circuit board is inserted. P ′ is the distance between the center of the outermost through hole and the center of the through hole closest to the outermost through hole, and the center of the central through hole into which the lead closest to the center of the electronic component is inserted Let P be the distance from the center of the nearest through hole.
(Α−β) (P′−P)> 0
Circuit board that meets
An electronic component with a lead is mounted, the lead of the electronic component is inserted into the through hole of the circuit board, and soldered with lead-free solder,
The distance between the center of the casing of the electronic component and the center of the outermost through hole is L, and the difference between the melting point of the lead-free solder and room temperature (25 ° C.) is ΔT.
| P′−P | ≧ | α−β | × L × ΔT
It is characterized by satisfying .

The electronic device according to the second invention of the present application is characterized in that a lead of an electronic component with a lead having leads arranged at equal intervals is inserted and soldered around the through hole on the front and back surfaces of the substrate. And a land electrically connected through the through hole. In this circuit board, the linear expansion coefficient of the casing material of the electronic component is α, the linear expansion coefficient of the substrate material of the circuit board is β, and the outermost lead of the electronic component of the circuit board is inserted. P ′ is the distance between the center of the outermost through hole and the center of the through hole closest to the outermost through hole, and is the distance between the outermost through hole and the through hole closest to the outermost through hole. Let p be the pitch of leads arranged in the direction connecting the leads of the electronic component to be inserted,
(Α−β) (P′−p)> 0
Circuit board that meets
An electronic component with a lead is mounted, the lead of the electronic component is inserted into the through hole of the circuit board, and soldered with lead-free solder,
The distance between the center of the casing of the electronic component and the center of the outermost through hole is L, and the difference between the melting point of the lead-free solder and room temperature (25 ° C.) is ΔT.
| P′−p | ≧ | α−β | × L × ΔT
It is characterized by satisfying .

  According to the present invention, when the linear expansion coefficient of the casing material of the electronic component is α and the linear expansion coefficient of the substrate material of the circuit board is β, in the case of α> β, the electronic component between the through hole and the lead Since it is possible to suppress the amount of solder in the area opposite to the center direction of the casing, it is possible to suppress the stress applied to the through hole in the direction opposite to the center of the casing when mounting the electronic component of the outermost end through hole. Can be reduced. Also, in the case of α <β, it is possible to suppress a decrease in the amount of solder in the region in the central direction of the electronic component casing between the through hole and the lead, so when mounting the electronic component in the outermost end through hole The stress applied to the through hole portion in the central direction of the housing portion can be reduced. For this reason, it is possible to prevent corner cracks occurring in the through-hole corner portion and through-hole peeling occurring in the through-hole plating layer, and maintain electrical conduction of the electronic component.

  According to the present invention, when an electronic component is mounted on a circuit board and soldered, the outermost through hole is filled in a region opposite to the center of the casing of the electronic component from the center of the outermost through hole. The amount of solder to be filled is larger than the amount of solder filled in the region opposite to the center of the casing of the electronic component from the center of the through hole other than the outermost end through hole. As a result, during the soldering process, the outermost end through-hole was filled with thermal stress generated by bending the outermost end lead due to the difference in thermal expansion between the casing of the electronic component and the circuit board. It can be absorbed by solder. For this reason, the stress applied to the corner portion and the inner wall of the through hole opposite to the center of the housing portion of the electronic component of the outermost end through hole is reduced. Thereby, generation | occurrence | production of the through-hole corner crack and through-hole peeling of an outermost end through-hole can be suppressed. Therefore, according to the present invention, even if soldering is performed using lead-free solder, the occurrence of poor electrical conduction of electronic components is suppressed, and soldering with high connection reliability can be performed.

FIGS. 2A and 2B are a top view and a cross-sectional view, respectively, of the multilayer circuit board according to the first embodiment of the present invention. It is sectional drawing which shows the state which mounted the electronic component in the multilayer circuit board of the 1st Embodiment of this invention. FIG. 3 is a partially enlarged view of FIG. 2. It is a top view which shows the multilayer circuit board of the 2nd Embodiment of this invention. It is a top view which shows the multilayer circuit board of the 3rd Embodiment of this invention. It is a top view which shows the multilayer circuit board of 4th Embodiment of this invention. (A) And (b) is the top view and sectional drawing of the conventional multilayer circuit board, respectively. It is sectional drawing which shows the state which mounted the electronic component on the conventional multilayer circuit board. It is sectional drawing which shows the state before mounting an electronic component on the conventional multilayer circuit board, and performing soldering. (A) thru | or (c) is sectional drawing which shows the trouble of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer circuit board 2 Resin laminated board 3 Inner layer wiring 4 Through hole 4a Center part through hole 4b Outermost end through hole 4c, 4d Adjacent through hole 5 Outer layer wiring 6 Land 7 Case part 8 Lead 9 Solder fillet 10 Solder resist 11 Corner Crack 12 Through hole peeling

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment]
FIG. 1A is a top view of the circuit board according to the first embodiment of the present invention as viewed from the component mounting surface side, and FIG. 1B is the AA line in FIG. It is sectional drawing by. Many surface-mounted electronic components or insertion-type electronic components are mounted on the multilayer circuit board, but FIG. 1 shows only a portion where the one-insertion-type electronic component is mounted. The same applies to drawings showing other embodiments. As shown in FIG. 1, a multilayer circuit board 1 is formed using a resin laminate 2 as a substrate, and has an inner layer wiring 3 inside. Through holes 4 (4a to 4d) are formed at the insertion positions of the electronic component leads of the multilayer circuit board 1, and lands 6 are formed around the through holes on the back surface of the substrate. Outer wiring 5 is also formed on the front and back surfaces of the substrate.

  In FIG. 1, a center line O passing through the center of the casing when an electronic component is mounted is indicated by a chain line. Of the through holes 4, the one near the center line O is the central through hole 4 a, the one farthest away is the outermost through hole 4 b, and the adjacent through hole closest to the central through hole 4 a is the adjacent through hole. 4c, the adjacent through hole closest to the outermost end through hole 4b is the adjacent through hole 4d. In the present embodiment, FR-4 is used as the base material of the multilayer circuit board, and the material of the casing of the electronic component is assumed to be polyamide. In this case, if the linear expansion coefficient of the casing material of the electronic component is α (ppm / ° C.) and the linear expansion coefficient of the substrate material of the multilayer circuit board is β (ppm / ° C.), then α> β. According to the present invention, in this case, the interval (pitch) between the through holes is wider at the outermost end than at the center. That is, the distance between the centers of the outermost end through hole 4b and the nearest adjacent through hole 4d is P ', and the distance between the centers of the center through hole 4a and the nearest adjacent through hole 4c is P, P '> P.

Here, since it is desirable that the lead of the electronic component is located closer to the center of the casing of the electronic component than the central portion of the outermost end through hole immediately before the solder solidifies, the center of the casing of the electronic component is desirable. And the center of the outermost through hole 4b is L, the linear expansion coefficient of the casing of the electronic component is α (ppm / ° C.), and the linear expansion coefficient β (ppm / ° C.) of the multilayer circuit board ,
P ′> (α−β) × L × ΔT + P (1)
Is desirable. Here, ΔT is {maximum temperature (about 200 ° C.) − Normal temperature (about 25 ° C.) of the casing of the electronic component during the soldering process}. ΔT may be replaced with (solder melting point−normal temperature). Assuming that the linear expansion coefficient of the casing material of the electronic component is smaller than the linear expansion coefficient of the substrate material of the multilayer circuit board, the above equation is
| P′−P | ≧ | α−β | × L × ΔT (2)
It becomes. Further, in the above formula, instead of P, the pitch of the lead of the electronic component is used to determine the center-to-center distance P ′ between the outermost end through hole 4b and the nearest adjacent through hole 4d, and the central through hole 4a. The distance P between the centers of the adjacent through-holes 4c closest to this may be the lead pitch of the electronic component.

An electronic component is mounted on the multilayer circuit board 1 configured as described above by performing a flow process using lead-free solder. For example, the flow process is performed as follows.
1. Electronic components are mounted at predetermined positions on the multilayer circuit board.
2. Apply flux on the side of the multilayer circuit board that contacts the jet solder,
3. Preheating,
4). Immerse the multilayer circuit board in a solder bath that jets molten lead-free solder.
5. cooling.

Further, main process conditions of the flow process are set as follows, for example, so that lead-free solder can be raised on the component mounting surface side land 6 and a solder fillet can be formed.
Preheating temperature: 100 ° C. to 120 ° C.
Conveyor speed: 0.8 m / min to 1.2 m / min, solder jet: double wave,
Solder bath temperature: 250 ° C. ± 5 ° C.

  FIG. 2 is a cross-sectional view showing a state in which electronic components are mounted on the multilayer circuit board according to the first embodiment shown in FIG. This is because the case 7 is made of a multilayer circuit board using FR-4 (linear expansion coefficient: 10 to 25 ppm) as a substrate material, and a rectangular planar shape as an electronic component and made of polyamide (linear expansion coefficient: 50 to 85 ppm). It is drawing which created based on the cross-sectional photograph which image | photographed the state after soldering the 8-pin connector which has NO using lead-free solder (Sn-3.0Ag-0.5Cu). As shown in FIG. 2, an electronic component having a casing portion 7 and leads 8 is mounted on the multilayer circuit board 1, and solder fillets 9 are formed in the through holes and on the lands 6. As described above, in the present embodiment, among the through holes, the center-to-center distance P ′ between the outermost end through hole 4b into which the outermost end lead of the electronic component is inserted and the adjacent through hole 4d is determined by the electronic component. Since the distance P between the center through hole 4a into which the lead closest to the center of the casing is inserted and the adjacent through hole 4c is larger than the center distance P (that is, P '> P), the outermost end through hole 4b The amount of lead-free solder filled in the region opposite to the center (A portion in the figure) increases. As a result, an effect of relaxing the stress generated by bending the lead of the electronic component during the soldering process with lead-free solder can be obtained. This point will be described in more detail with reference to FIG.

  FIG. 3 is an enlarged cross-sectional view of the leftmost outermost through hole 4b in FIG. Since the center position of the outermost end through-hole 4b satisfies the above formula (1), the lead 8 of the electronic component is placed at the outermost position immediately before the multilayer circuit board is put into the solder bath and the solder is solidified. It is located on the right side from the center of the end through-hole 4b, that is, closer to the center of the casing of the electronic component. In this state, the solder starts to solidify first, and then the multilayer circuit board and the casing portion 7 contract. Here, since the linear thermal expansion coefficient β of the substrate material of the multilayer circuit board is smaller than the linear thermal expansion coefficient α of the casing portion 7 (α> β), the upper portion of the lead is pulled closer to the center portion of the electronic component. Therefore, the lead 8 is fixed with its upper portion inclined to the left side. As a result, the inner wall and the corner portion of the outermost end through hole 4b on the side away from the center of the casing portion 7 are subjected to stress, but the outermost end through hole 4b has a portion in the direction opposite to the center of the casing portion (see FIG. By increasing the amount of lead-free solder filled in the middle A portion), these stresses received by the outermost end through-hole 4b are alleviated. As a result, the occurrence of corner cracks and through-hole separation shown in FIGS. 10B and 10C is suppressed, and high electrical conduction reliability can be ensured.

  In addition, when the linear expansion coefficient of the casing material of the electronic component is α (ppm / ° C.) and the linear expansion coefficient of the substrate material of the multilayer circuit board is β (ppm / ° C.), The central through hole 4a into which the lead P between the outermost end through hole 4b into which the outermost end lead of the component is inserted and the adjacent through hole 4d is closest to the center of the casing of the electronic component is inserted. Is smaller than the center-to-center distance P between the through hole 4c and the adjacent through hole 4c (that is, P '<P). It is located closer to the direction opposite to the center direction of the electronic component casing than the center of the through hole 4b. In this state, first, the solder starts to solidify, and then the multilayer circuit board and the housing part 7 contract. Here, since the linear expansion coefficient β of the substrate material of the multilayer circuit board is larger than the linear expansion coefficient α of the casing portion 7 (α <β), the upper portion of the lead is pulled toward the opposite direction to the central portion of the electronic component. For this reason, the lead 8 is fixed with its upper portion inclined to the left side. As a result, the inner wall and the corner of the outermost end through-hole 4b in the central direction of the casing 7 are subjected to stress, but the lead-free solder filled in the central portion of the casing at the outermost end through-hole 4b By increasing the amount, these stresses received by the outermost end through hole 4b are alleviated. As a result, the occurrence of corner cracks and through-hole separation shown in FIGS. 10B and 10C is suppressed, and high electrical conduction reliability can be ensured.

  When α> β, since P ′> P, that is, (α−β)> 0 and (P′-P)> 0, (α−β) (P′−P)> 0. Further, when α <β, P ′ <P, that is, (α−β) <0 and (P′−P) <0, so that (α−β) (P′−P)> 0 Become. As described above, by satisfying (α−β) (P′−P)> 0, the occurrence of corner cracks and through-hole separation shown in FIGS. It is possible to ensure conduction reliability.

[Second Embodiment]
FIG. 4 is a partial top view of the circuit board according to the second embodiment of the present invention as viewed from the component mounting surface side. 4, parts that are the same as the parts of the first embodiment shown in FIG. 1 are given the same reference numerals, and redundant descriptions are omitted. The multi-layer circuit board of the present embodiment differs from that of the first embodiment shown in FIG. 1 in that the planar shape of the through hole 4 is circular in the first embodiment. Is a long rectangle in the longitudinal direction of the casing of the electronic component to be mounted. In the present embodiment, the center through-hole 4a and the adjacent through-hole into which the lead P closest to the center of the housing part of the electronic component is inserted with the center distance P 'between the outermost end through-hole 4b and the adjacent through-hole 4d. In addition to being larger than the center-to-center distance P with respect to 4c, the planar shape of the through-hole is a rectangle that is long in the longitudinal direction of the housing portion, so that the stress relaxation is higher than in the case of the first embodiment. An effect can be obtained.

  By changing the second embodiment, the planar shape of the through hole may be an ellipse that is long in the longitudinal direction of the casing, a gourd shape, or a shape in which a circle is divided into two and a rectangle is inserted therebetween. Furthermore, it is good also as shapes, such as a square and a regular hexagon.

[Third Embodiment]
FIG. 5 is a partial top view of the circuit board according to the third embodiment of the present invention as viewed from the component mounting surface side. In FIG. 5, the same reference numerals are given to the same parts as those of the first embodiment shown in FIG. The difference between the multilayer circuit board of the present embodiment and that of the first embodiment shown in FIG. 1 is that the center of the outermost through hole 4b and the adjacent through hole 4d is different in the first embodiment. Although only the distance P ′ is longer than the distance between the other through-hole centers, in this embodiment, the distance between the through-holes is gradually increased as the distance from the center of the housing portion when mounting the electronic component is increased. The That is, as shown in FIG. 5, the distance between through holes closest to the center of the casing is P1, the distance between the second and third through holes from the center of the casing is P2,
P1 <P <P2 <P '
Has been made.

[Fourth Embodiment]
FIG. 6 is a partial top view of the circuit board according to the fourth embodiment of the present invention as viewed from the component mounting surface side. 4, parts that are the same as the parts of the first embodiment shown in FIG. 1 are given the same reference numerals, and redundant descriptions are omitted. The difference between the multilayer circuit board of the present embodiment and that of the first embodiment shown in FIG. 1 is that in the first embodiment, the electronic component to be mounted has a planar shape of its casing. In contrast to the rectangular leads arranged in a line, in the electronic component mounted on the circuit board according to the present embodiment, the leads are arranged radially from the center of the casing.

  Also in the present embodiment, the outermost end through-hole 4b and the adjacent through-hole 4d closest to the outermost end through-hole 4b on the radiation connecting the center of the casing of the electronic component and the outermost end lead of the electronic component. The center-to-center distance P ′ is the center-to-center distance between the central through hole 4a and the adjacent through hole 4c closest to the central through hole on the radiation connecting the center of the housing of the electronic component and the outermost lead of the electronic component. By being larger than P, the same effect as in the first embodiment can be obtained. It should be noted that this embodiment can be combined with the second embodiment and the third embodiment.

  According to the present invention, since the occurrence of poor electrical continuity of electronic components is suppressed in soldering with lead-free solder, a circuit board with high connection reliability can be obtained.

Claims (8)

Through-holes into which leads of electronic components with leads are inserted and soldered,
And a land electrically connected through the through hole around the through hole on the front and back surfaces of the substrate,
The linear expansion coefficient of the casing material of the electronic component is α, the linear expansion coefficient of the substrate material of the circuit board is β, and the outermost end through-hole into which the outermost lead of the electronic component of the circuit board is inserted P ′ is the distance between the center of the through hole and the center of the through hole closest to the outermost end through hole, and the center of the central through hole into which the lead closest to the center of the electronic component is inserted is closest to the central through hole Let P be the distance from the center of the through hole.
(Α−β) (P′−P)> 0
To be times circuit board meet,
An electronic component with a lead is mounted, the lead of the electronic component is inserted into the through hole of the circuit board, and soldered with lead-free solder,
The distance between the center of the casing of the electronic component and the center of the outermost through hole is L, and the difference between the melting point of the lead-free solder and room temperature (25 ° C.) is ΔT.
| P′−P | ≧ | α−β | × L × ΔT
An electronic device characterized by satisfying A through-hole into which the lead of the electronic component with lead having leads arranged at equal intervals is inserted and soldered;
Lands electrically connected through the through holes around the through holes on the front and back surfaces of the substrate;
Have
The linear expansion coefficient of the casing material of the electronic component is α, the linear expansion coefficient of the substrate material of the circuit board is β, and the outermost end through-hole into which the outermost lead of the electronic component of the circuit board is inserted The distance between the center of the through hole and the center of the through hole closest to the outermost end through hole is P ′, and the distance between the outermost end through hole and the through hole closest to the outermost end through hole Let p be the pitch of the leads arranged in the direction connecting the leads,
(Α−β) (P′−p)> 0
To be times circuit board meet,
An electronic component with a lead is mounted, the lead of the electronic component is inserted into the through hole of the circuit board, and soldered with lead-free solder,
The distance between the center of the casing of the electronic component and the center of the outermost through hole is L, and the difference between the melting point of the lead-free solder and room temperature (25 ° C.) is ΔT.
| P′−p | ≧ | α−β | × L × ΔT
An electronic device characterized by satisfying The distance between the centers of the through holes adjacent to each other is from the central through hole into which the lead closest to the center of the electronic component is inserted toward the outermost end through hole into which the outermost lead of the electronic component is inserted. The electronic apparatus according to claim 1, wherein the electronic apparatus changes gradually. The lead of the electronic component is arranged in a line shape or a radial pattern from the center of the casing of the electronic component when the electronic component is mounted. The electronic device as described in. 5. The planar shape of the through hole is a circle, an ellipse, a square, a rectangle, or a shape in which a rectangle is sandwiched between two semicircles. 6. Electronic equipment . 6. The electronic device according to claim 1, wherein the circuit board has a multi-layer configuration using at least one prepreg and a laminated board on which copper is pasted. 6. . Lead-free solder exists on the entire outer surface of the lead between the inner wall of the outermost through hole of the circuit board and the lead of the electronic component inserted into the through hole. The electronic device according to any one of claims 1 to 6 . The outer through-hole has a larger amount of solder in the through-hole than the through-hole in the center of the electronic component, and solder exists around the entire periphery of the lead inserted into the through-hole. The electronic device according to claim 1 , wherein the electronic device is an electronic device.

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