JP5381987B2 - Wiring board, chip component mounting structure, and chip component mounting method - Google Patents

Description

  The present invention has a structure in which a chip component is mounted on a wiring board using a conductive member, and particularly when lead-free solder is used for the conductive member, the chip component in the fillet cross-sectional shape of the conductive member in the longitudinal direction of the chip component Chip component mounting structure in which the distance from the bottom surface of the electrode to the outside of the fillet is increased to increase the crack propagation distance until electrical conduction failure and the electrical conduction reliability is improved, and the wiring board used therefor In addition, the present invention relates to a chip component mounting method.

  FIG. 1A shows an example of a chip component mounting structure (hereinafter also referred to as a related structure) related to the present invention. This is a mounting structure of a chip component called 2012R, 3216R, 5025R, etc., whose shape in the wiring board plane direction is rectangular. FIG. 1B is an enlarged view of the mounting structure cross section around the fillet.

  In the related structure shown in FIG. 1, the electrodes 5 provided at both ends of the body part 6 of the chip component and the mounting pads 4 provided on the wiring substrate 1 are connected via the conductive member 3. . Since the solder resist 2 exists on the outer peripheral portion of the mounting pad 4, the conductive member 3 exists outside the area of the mounting pad 4 except for cases such as excessive supply of the conductive member 3. Not.

  The shape of the mounting pad 4 is a shape corresponding to the electrode 5 of the chip component, and is generally rectangular or square. Note that, as in the invention described in Patent Document 1, the mounting pad may be divided in order to minimize voids in the conductive member.

  “Solder” is mainly used as the material of the conductive member 3, and in particular, lead-tin solder (Sn: Pb = 60 to 63%: 40 to 37) in which the mass ratio% of Sn and Pb is close to the eutectic composition. %) Is often used. In the following description, the conductive member 3 is assumed to be solder and is also referred to as solder 3.

  For chip parts that have poor continuity due to cracks in the solder after mounting, especially when high-cost multilayer wiring boards are used, instead of discarding the entire wiring board, use a soldering iron Only defective parts are repaired using hot air, heaters, etc.

  Chip components solder-mounted on a wiring board generate heat and generate heat in the usage environment, and thus thermally expand during use. Similarly, since the wiring board is heated by the heat generated by the wiring pattern, chip component, and other electronic components, it expands thermally. The amount of thermal expansion depends on the coefficient of thermal expansion of the material, and the amount of thermal expansion increases as the material has a larger coefficient of thermal expansion even if the dimensions are the same.

In general, the material of the body part of the chip component is ceramic (thermal expansion coefficient α = 11 to 5 ppm), whereas the material of the wiring board is FRP (Fiber Reinforced Plastic) material (thermal expansion coefficient) such as FR-4. (α = 10 to 50 ppm), the material of the wiring board has a larger thermal expansion coefficient.
For this reason, stress is applied to the solder joint between the electrode 5 of the chip component and the mounting pad 4 due to the difference between the thermal expansion amount of the body portion 6 of the chip component and the wiring board 1. Since this stress is repeatedly applied to the solder joint, the rigidity of the solder 3 is lowered, so that a crack is generated in the solder joint.

  In general, cracks in a chip component are more often generated on the lower surface portion of the electrode 5 of the chip component than in the solder fillet portion. This is because the solder 3 has a smaller amount of solder than the solder fillet portion at the lower surface portion of the electrode 5 of the chip component, so that the solder 3 is less effective in relieving stress by itself.

  When the shape in the wiring board plane direction is rectangular like a chip part such as 3216R or 5025R, the difference in thermal expansion / contraction between the chip part and the wiring board 1 is maximum in the longitudinal direction, and this occurs at the lower surface of the electrode. It is presumed that the cracks easily propagate along the solder portion on the lower surface of the electrode 5 in the longitudinal direction. Thereafter, the crack reaches the solder fillet portion and finally penetrates the solder fillet portion. When the crack penetrates the solder fillet portion, the electrode 5 of the chip component and the mounting pad 4 are completely separated, and an electrical conduction failure occurs.

  In addition, high-density packaging is required as electronic devices become more functional and smaller. For this reason, the area of the mounting pad 4 is reduced, and the protruding dimension (Yf in FIG. 1B) of the mounting pad 4 is also shortened. For this reason, the distance from the lower surface of the electrode 5 of the chip component to the outside of the solder fillet in the cross-sectional shape of the solder fillet in the longitudinal direction of the chip component (the portion indicated by the double arrow in FIG. 1 (b)) is also shortened. It is easy to penetrate.

In addition, in response to environmental regulations, the transition from lead-tin solder to lead-free solder is progressing. Lead-free solder is mainly composed of tin and is composed of silver, copper, zinc, bismuth, indium, antimony, nickel, germanium, etc. It has the properties of high strength and creep strength and low ductility. For this reason, the lead-free solder has a smaller effect of absorbing stress by the solder itself than the tin-lead solder, and if a crack occurs at the solder joint, the crack is likely to progress.
Moreover, the melting temperature of lead-tin eutectic solder is 183 ° C., whereas the melting temperature of lead-free solder is as high as 190 to 230 ° C. For this reason, in order to repair a chip component having a poor electrical continuity, it is necessary to heat the solder joint to a higher temperature than when lead-tin eutectic solder is used. Therefore, as the heating temperature increases, the thermal load applied to other electronic components existing around the defective component increases, and the warpage of the wiring board itself increases, so that the possibility of failure of the peripheral components increases.

  Many parts such as lead parts such as QFP (Quad Flat Package) and TSOP (Thin Small-Outline Package), chip parts, surface mount parts such as CSP (Chip Size Package) and BGA (Ball Grid Array), and flip chip parts Wiring boards that are mounted at high density are expensive, so it is essential to repair only defective parts, but there is an adverse effect on peripheral parts due to the thermal load during repair, so electronic parts including chip parts There is a need for a mounting structure that improves the reliability of electrical conduction.

As a method for improving the reliability of the electrical continuity of the chip component, as in the invention described in Patent Document 1, the mounting pads on the wiring board corresponding to the electrodes of the electronic component are divided and voids in the solder are obtained. The method of suppressing generation | occurrence | production of a crack by reducing as much as possible is mentioned.
Further, as in the invention described in Patent Document 2, there is a method of suppressing the generation of cracks such as dividing the electrodes of the electronic component and relaxing the stress at a place where the solder does not adhere, thereby suppressing the generation of cracks. It is done.

Japanese Patent Laid-Open No. 10-075042 JP 2000-261131 A

  However, in the current situation where high-density mounting is required, since the area of the mounting pad is reduced, if the mounting pad is divided, the amount of solder at the joint is further reduced. In this case, since the stress applied to the solder itself becomes large, it is difficult to suppress the occurrence of cracks by the method described in the above patent document, and it is estimated that the effect of improving the reliability of electrical conduction of the chip component is small. .

  In addition, since the mounting pads are not filled with resin or the like and are empty, the effect of suppressing the progress of cracks is small, and the distance from the bottom surface of the chip component electrode to the outside of the solder fillet is Since there is no change from the conventional mounting structure, if a crack occurs in the solder joint, there is a problem that it rapidly develops and leads to poor electrical conduction.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a chip component mounting structure in which the reliability of electrical conduction of the chip component is improved, a wiring board used therefor, and a chip component mounting method. .

  In order to achieve the above object, as a first aspect of the present invention, a chip component having an electrode provided at an end is mounted on a mounting pad formed at a position corresponding to the electrode via a conductive member. A wiring board having an auxiliary pad formed on an insulating material adjacent to the mounting pad on the side where the distance from the electrode is increased, and when the chip component is mounted, the electrode and the mounting pad In addition, the present invention provides a wiring board in which a fillet made of a conductive member is formed between the auxiliary pad and the auxiliary pad.

  In order to achieve the above object, the present invention provides, as a second aspect, a chip component mounting structure comprising the wiring board according to the first aspect of the present invention and a chip component. Is.

  In order to achieve the above object, according to a third aspect of the present invention, there is provided a chip component having an electrode provided at an end, a mounting pad formed at a position corresponding to the electrode, and a distance from the electrode. A chip component mounting method for mounting via a conductive member on a wiring board having an auxiliary pad formed on an insulating material so as to be adjacent to a mounting pad on the larger side, comprising an electrode, a pad, and an auxiliary pad A chip component mounting method is provided, wherein the chip component is mounted such that a fillet of a conductive member is formed between the two.

  ADVANTAGE OF THE INVENTION According to this invention, the chip component mounting structure which improved the reliability of the electrical continuity of a chip component, the wiring board used for this, and a chip component mounting method can be provided.

It is a figure which shows the chip component mounting structure relevant to this invention. It is a figure which shows the structure of the wiring board applied to the chip component mounting structure which concerns on 1st Embodiment which implemented this invention suitably. It is a figure which shows the chip component mounting structure which concerns on 1st Embodiment. It is a figure which shows the state which the crack progressed in the chip component mounting structure which concerns on 1st Embodiment. It is a figure which shows the state which the crack advanced in the chip component mounting structure relevant to this invention. It is a figure which shows the state which the crack advanced in the chip component mounting structure relevant to this invention. It is a figure which shows the shape of the electrically-conductive member fillet at the time of lengthening an auxiliary pad. It is a figure which shows the state in which the fillet was formed including the electrode upper surface part. It is a figure which shows the structure of the wiring board applied to the chip component mounting structure which concerns on 2nd Embodiment which implemented this invention suitably. It is a figure which shows the chip component mounting structure which concerns on 2nd Embodiment. It is a figure which shows the state which provided the wiring in the vicinity of the mounting pad in the chip component mounting structure relevant to this invention. It is a figure which shows another structure of the wiring board applied to the chip component mounting structure which concerns on 2nd Embodiment.

[First Embodiment]
A first embodiment in which the present invention is suitably implemented will be described. In the following description, a chip part having a rectangular shape in the wiring board plane direction is used as an example, but the chip part to be applied is provided with an electrode for electrical connection at the end of the body. As long as the structure is mounted on the pads on the wiring board via the conductive member, other shapes may be used.

FIG. 2A shows a configuration of a wiring board applied to the chip component mounting structure according to the present embodiment. The wiring board 11 has mounting pads 14 formed at positions corresponding to the electrodes provided at the end of the chip component. An auxiliary pad 17 is formed on the solder resist 12 outside the mounting pad 14.
As shown in FIG. 2B, when the chip component is mounted, a fillet made of the conductive member 13 is formed between the electrode 15 formed on the end portion of the body portion 16 and the mounting pad 14 and the auxiliary pad 17. It is formed.

FIG. 3 shows a chip component mounting structure according to this embodiment. 3A is a cross-sectional view in the longitudinal direction of the chip component, and FIG. 3B is an enlarged cross-sectional view of the periphery of the fillet.
A chip component composed of the body portion 16 and the electrode 15 formed on the end portion of the body portion 16 includes a mounting pad 14 provided on the wiring board 11 corresponding to the electrode 15, and a mounting pad 14. It is mounted and mounted on the wiring substrate 11 via the auxiliary pad 17 provided on the upper surface of the solder resist 12 on the outer side in the chip component longitudinal direction and the conductive member 13. Note that the upper surface of the auxiliary pad 17 is lower than the mounting height of the chip component.

  In a chip component (2012R, 3215R, 5025R, etc.) having a rectangular shape in the planar direction of the wiring substrate 11, the direction connecting the electrodes 15 provided at the end of the body part 16 of the chip part is the body part 16 of the chip part. In the longitudinal direction. In other words, the electrodes 15 are provided at both ends in the longitudinal direction of the body portion 16 of the chip component.

  The conductive member 13 is solder or conductive resin. Examples of solder materials include Sn-Pb, Sn-Ag-Cu, Sn-Ag, Sn-Cu, Sn-Sb, Sn-Zn, and Sn-In. It will never be done.

  As a material of the auxiliary pad 17, a metal (Cu or the like), a conductive resin, or the like can be applied. However, the material is not limited to any material as long as the material has wettability with respect to the conductive member 13. Further, even if the material does not have wettability with respect to the conductive member 13, it can be applied as the auxiliary pad 17 by performing surface treatment (Au plating or the like) on the surface so as to get wet with the conductive member 13. . Needless to say, the material having wettability with respect to the conductive member 13 may be subjected to surface treatment in order to further improve wettability.

  The effect of the chip component mounting structure according to the present embodiment will be described in a state where a crack generated in the conductive member 13 existing between the lower surface portion of the electrode 15 and the mounting pad 14 progresses through the fillet portion. FIG. 4 shows the progress of cracks in the chip component mounting structure according to the present embodiment, and FIGS. 5 and 6 show the progress of cracks in related structures represented by the above-mentioned patent documents. The length of the crack that has advanced the fillet portion is the same in any mounting structure, but in the chip component mounting structure according to the present embodiment, the crack 18 stays in the fillet, whereas in the related structure, A crack 8 penetrates the fillet portion. For this reason, in the chip component mounting structure shown in FIGS. 5 and 6, the chip component is in a state of poor electrical conduction.

  The reason why the crack 18 stays in the fillet in the chip component mounting structure according to the present embodiment is that the distance from the lower surface of the electrode 15 to the outside of the fillet in the fillet cross-sectional shape in the longitudinal direction of the chip component is the chip according to the present embodiment. This is because the component mounting structure is longer.

In the chip component mounting structure according to the present embodiment, a fillet is formed between the side surface portion of the electrode 15 of the chip component, the mounting pad 14 and the auxiliary pad 17. In the fillet cross-sectional shape in the longitudinal direction of the chip component, the distance from the lower surface of the electrode 15 to the outside of the fillet is the mounting height H ′ of the chip component, the protruding dimension Yf of the mounting pad 14, and the chip component longitudinal direction of the auxiliary pad 17. H ′ = Yf + Yd so that the distance from the lower surface of the electrode 15 to the outside of the fillet is the longest.
As shown in FIG. 7A, it seems that the distance from the lower surface of the electrode 15 to the outside of the fillet increases as Yd increases. However, as shown in FIG. Since the center of the bottom of the fillet has a downwardly convex curved shape, the distance from the lower surface of the electrode 15 to the outside of the fillet is shortened. Therefore, Yd is preferably set to a value in the vicinity of (H′−Yf).

  On the other hand, in the chip component mounting structure shown in FIG. 5, the fillet is formed only between the chip electrode 5 and the mounting pad 4. With the recent high-density mounting, the protruding dimension Yf of the mounting pad 4 has become smaller, and generally H ′> Yf. Therefore, as shown in FIG. 6, the distance from the lower surface of the electrode to the outside of the fillet also tends to be short.

  The crack generated in the lower surface portion of the electrode of the chip component advances the conductive member on the lower surface of the electrode in the longitudinal direction of the chip component and reaches the fillet portion. After that, when the fillet portion is developed and the crack penetrates the fillet portion, the electrode of the chip component and the mounting pad are completely separated, and an electrical conduction failure occurs. For this reason, the longer the distance from the lower surface of the electrode to the outside of the fillet, the more difficult the crack penetrates the fillet portion, so the life of electrical continuity becomes longer.

As described above, in the chip component mounting structure according to the present embodiment, the fillet is formed between the electrode 15 of the chip component and the auxiliary pad 17 in addition to between the electrode 15 of the chip component and the mounting pad 14. The distance from the bottom surface of the electrode to the outside of the fillet is increased in the fillet cross section with respect to the longitudinal direction, and the reliability of electrical conduction of the chip component is improved.
In particular, when a lead-free solder having a stress relaxation performance lower than that of lead-tin solder and having a high melting point is used as the conductive member 13, this effect is remarkably obtained.

  In the above description, the case where the dimension Yd of the auxiliary pad 17 satisfies H ′ = Yf + Yd has been described as an example. However, by providing the auxiliary pad 17, the distance from the lower surface of the electrode 15 to the outside of the fillet may be increased. In this case, the same effect can be obtained.

  Further, in the above description, the case where the fillet is formed between the side surface portion of the electrode 15 of the chip component, the mounting pad 14 and the auxiliary pad 17 is exemplified. However, as shown in FIG. Even in the structure in which the fillet is formed between the electrode 15 of the chip component, the mounting pad 14 and the auxiliary pad 17 including the upper surface of the electrode 15 of the component, the distance from the lower surface of the electrode 15 to the outside of the fillet is long. Therefore, the same effect can be obtained.

  In this embodiment, the size of the chip component is not particularly limited. However, the larger the body part 16 of the chip component (the longer the length in the longitudinal direction), the conductive member between the electrode 15 and the pad of the chip component. The stress applied to the joint is increased, and cracks are likely to be generated and propagated. In particular, for a chip component larger than a chip component generally called 5025R (the shape in the wiring board plane direction is rectangular, the length in the longitudinal direction is about 5 mm, and the length in the short direction is about 2.5 mm), Since the crack is easily generated in the conductive member joint portion and is also easily developed, the above-described effect can be obtained particularly remarkably.

  Further, in this embodiment, the amount of the conductive member in the fillet portion is larger than that in the related structure, so that the stress applied to the conductive member joint portion between the chip component electrode 15 and the mounting pad 14 is relieved by itself. It is easy to be done, and the effect which suppresses the crack generation under an electrode is also anticipated.

  As described above, in the chip component mounting structure according to the present embodiment, cracks hardly penetrate the conductive member fillet portion, and the reliability of electrical conduction of the chip component is improved.

[Second Embodiment]
A second embodiment in which the present invention is suitably implemented will be described.
FIG. 9 shows a configuration of a wiring board applied to the chip component mounting structure according to the present embodiment. FIG. 10 shows a chip component mounting structure according to this embodiment. 10A is a cross-sectional view in the longitudinal direction of the chip component, and FIG. 10B is an enlarged cross-sectional view of the periphery of the fillet.
In the chip component mounting structure and the wiring board used therefor according to the present embodiment, at least a part of the wiring 19 is formed on the wiring board 11 immediately below the auxiliary pad 17, and between the auxiliary pad 17 and the wiring 19. This is different from the first embodiment in that the solder resist 12 is interposed.

When the wiring is provided in the vicinity of the mounting pad, it is necessary to provide the wiring at the outer side in the component longitudinal direction of the mounting pad 4 in the structure as in the patent document. However, as shown in FIG. 11A, when the wiring 9 is provided with the length of the mounting pad 4 as it is, the area on which the chip component can be mounted on the surface of the distribution board 1 is reduced by the provision of the wiring 9. This hinders high-density mounting. On the other hand, when the mounting pad 4 is shortened and the wiring 9 is provided there as shown in FIG. 11B, high-density mounting can be realized, but the distance from the lower surface of the electrode to the outside of the fillet is shortened. The reliability of electrical continuity is reduced.
In other words, in the related structure, when the wiring 9 is provided in the vicinity of the mounting pad 4, the realization of high-density mounting and the reliability of electrical conduction of the chip component are in a trade-off relationship.

  In the chip component mounting structure according to the present embodiment, as in the first embodiment, the distance from the lower surface of the electrode 15 of the chip component to the outside of the fillet is longer than the structure as in the patent document. The reliability of electrical continuity is improved. Furthermore, since the auxiliary pad 17 and the wiring 19 are three-dimensionally arranged via the solder resist 12, a high-density wiring formation / mounting structure can be realized.

  In the chip component mounting structure according to the present embodiment, wirings and pads are formed directly below the auxiliary pad 17 via an insulating member such as a solder resist 12, so that high-density mounting is realized. Needless to say, the same effect as in the first embodiment in which cracks hardly penetrate the fillet portion of the conductive member 13 and the reliability of electrical conduction of the chip component is improved.

Here, the structure in which the solder resist 12 is interposed between the auxiliary pad 17 and the wiring 19 is taken as an example, but any material is interposed as long as it is a material that does not allow conduction between the auxiliary pad 17 and the wiring 19. The same effect can be obtained.
In the present embodiment, the wiring 19 is provided immediately below the auxiliary pad 17. However, the present invention is not limited to the wiring, and as shown in FIG. 12, a via hole that is electrically connected to the wiring layer 22 inside the wiring substrate 11. 20 may be provided, and in any case, high-density mounting is possible.

  As described above, the chip component mounting structure according to the present embodiment can achieve both high-density component mounting / wiring formation and improved electrical continuity reliability of the chip components.

  Each of the above embodiments is an example of a preferred embodiment of the present invention, and the present invention is not limited to these, and various modifications are possible.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2008-184590 for which it applied on July 16, 2008, and takes in those the indications of all here.

DESCRIPTION OF SYMBOLS 1,11 Wiring board 2,12 Solder resist 3,13 Conductive member 4,14 Mounting pad 5,15 Electrode 6,16 Body part 8,18 Crack 9,19 Wiring 17 Auxiliary pad 20 Via hole 21 Pad 22 Wiring layer

Claims (8)

A chip component provided with an electrode at an end is a wiring board mounted via a conductive member on a mounting pad formed at a position corresponding to the electrode,
An auxiliary pad formed on an insulating material provided adjacent to the mounting pad on the side where the distance from the electrode increases,
When the chip component is mounted, a fillet made of the conductive member is formed between the electrode, the mounting pad, and the auxiliary pad.   The wiring board according to claim 1, wherein an upper surface of the auxiliary pad has wettability to the conductive member. The wiring board according to claim 1, wherein the conductive member is lead-free solder.   The sum of the length of the protruding portion of the mounting pad from the end of the electrode and the length of the auxiliary pad is substantially the same as the mounting height of the chip component. 4. The wiring board according to any one of 3 above. 5. The wiring board according to claim 1, wherein at least a part of the wiring is formed immediately below the auxiliary pad with the insulating material interposed therebetween.   5. At least a part of a pad connected to an internal wiring layer through a via hole is formed immediately below the auxiliary pad through the insulating material. Wiring board according to item.   A chip component mounting structure comprising the wiring board according to claim 1 and the chip component. The chip component electrodes are provided on the end portion, and a mounting pad formed at a position corresponding to the electrode, on the insulation material you adjacent the mounting pad in distance increases the side from the electrode A chip component mounting method for mounting via a conductive member on a wiring board provided with a formed auxiliary pad,
A chip component mounting method, wherein the chip component is mounted such that a fillet of the conductive member is formed between the electrode, the mounting pad, and the auxiliary pad.

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