JP2015126182A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress occurrence of cracks at a solder joint part with a ceramic electronic component in a printed wiring board on which the ceramic electronic component is mounted.SOLUTION: Disclosed is a printed wiring board 100A with a multilayer structure which is equipped integrally with a laminate material 120 on at least one surface of a core base material 110 and in which a ceramic electronic component 10 containing a ceramic material as a base material is mounted on the laminate material 120. A raw material of the laminate material 120 is low in elasticity, lower than a general purpose rigid material and having elastic modulus of less than 20 GPa, and which is rich in flexibility, and a recess 150 is formed by removing a part or the whole of base material specific points included in a mounting region MS of the ceramic electronic component 10 out of the core base material 110.

Description

  The present invention relates to a printed wiring board, and more particularly to a technique for improving connection reliability with a ceramic electronic component having a multilayer structure.

  Ceramic electronic components, particularly large-sized ceramic electronic components such as sensors used in digital cameras and the like, have one side exceeding 50 mm. The heat cycle test is performed as a test for evaluating connection reliability with components mounted on a printed wiring board. Especially, the heat cycle test is performed on a printed wiring board mounted with large-sized ceramic electronic components. If the soldering is performed, cracks may occur in the solder joints, and in the worst case, disconnection may occur due to solder cutting or the like.

  The heat cycle test is one of the accelerated tests used for the reliability test of the printed wiring board. The conditions are different for each set maker, but the environment of low temperature and high temperature is alternately repeated, and this is performed for a predetermined number of cycles. As an example, the low temperature is set to −40 ° C., the high temperature is set to 125 ° C., the low temperature 30 minutes and the high temperature 30 minutes are set as one cycle, and this is performed for 500 cycles or more and the disconnection does not occur. Yes.

  Here, an example of a printed wiring board for mounting a ceramic electronic component will be described with reference to FIG. The printed wiring board 200 is a printed wiring board having a structure in which a laminated material 220 (including an upper laminated material 220a and a lower laminated material 220b) is integrally laminated on both surfaces of a core base 210 serving as an inner layer. (For example, refer to Patent Document 1 regarding the manufacturing method).

  In this example, inner layer circuits 211 are formed on both surfaces of the core substrate 210, and lands 221 for soldering the ceramic electronic component 10 are formed on the upper laminated material 220a side. The land 221 and the inner layer circuit 211 are connected to each other through a conductor plated in the via hole 240. Generally, the portions other than the soldering lands of the upper laminated material 220a and the lower laminated material 220b are formed by a solder resist 230. It is covered.

  As shown in FIG. 5A, the ceramic electronic component 10 to be mounted includes a lead terminal mold 10A in which a plurality of lead terminals 12 are drawn out from a flat package 11 in a gull wing shape, for example, and FIG. As shown in FIG. 2, there is a leadless type 10B in which a plurality of electrode terminals 13 are formed in an L shape from the side surface to the bottom surface of the flat package 11. In some leadless types 10B, the electrode terminals 13 are arranged only on the bottom surface of the flat package 11.

  At present, the lead terminal type 10A is the mainstream, but the leadless type 10B is increasing due to progress toward higher density. In any case, the lead terminal 12 or the electrode terminal 13 is joined to the land 221 on the laminated material 220 (in this example, the upper laminated material 220a) by soldering, but in the heat cycle test, the solder joint has cracks. In order to prevent the occurrence of such a problem, attempts have been made to use high-performance rigid materials having a small thermal expansion coefficient for the core base material 210 and the laminated material 220 (220a, 220b).

  The thermal expansion coefficient of the ceramic material that is the base material of the ceramic electronic component 10 is about 4 to 7 ppm / ° C., whereas the thermal expansion coefficient of the general-purpose rigid material is about 12 to 16 ppm / ° C., which is large in the thermal expansion coefficient. There is a difference. On the other hand, the thermal expansion coefficient of the high-performance rigid material is as low as about 3 to 10 ppm / ° C.

  Examples of general-purpose rigid materials currently on the market include FR-4 (Frame Regentant Type 4) formed by impregnating an epoxy resin into a glass fiber cloth and performing a thermosetting treatment. Generally, a general-purpose rigid material is a highly rigid material having a high elastic modulus (approximately 20 to 30 GPa). On the other hand, the highly functional rigid material is a very rigid material having a higher elastic modulus (approximately 25 to 35 GPa).

  As an example, the thermal expansion coefficient of the ceramic electronic component 10 is 7 ppm / ° C., the length of one side is 50 mm, the thermal expansion coefficient of FR-4 (general purpose rigid material) is 14 ppm / ° C., and the heat cycle test conditions are low temperature − When 40 degreeC and high temperature 125 degreeC are set, the difference of thermal expansion-contraction will be 0.06 mm.

  Referring to FIG. 5B, in the case of the lead terminal mold 10A, the difference in thermal expansion and contraction is absorbed by deformation of the lead terminal 12, and the mechanical stress concentration on the solder material S is relieved to some extent. If the allowable limit that can be absorbed by the terminal 12 is exceeded, cracks will occur in the solder material S.

  In the case of the leadless type 10B, it is more serious. As shown in FIG. 6B, since the mechanical stress due to the difference in thermal expansion and contraction is directly applied to the solder material S, cracks are likely to occur. .

  In addition, the cause of cracks in the solder material S includes the occurrence of warpage due to expansion and contraction of the printed wiring board 200 itself due to the high and low heat applied in the heat cycle test, and swell due to the wiring shape.

  The problem of crack generation and progression becomes more prominent as the size of the ceramic electronic component 10 to be mounted becomes larger. As an example, due to the recent enhancement in functionality of digital cameras and the like, the sensor as the ceramic electronic component 10 mounted on the digital camera becomes, for example, a large size having a side exceeding 50 mm. Has become a serious problem.

JP 2010-56373 A

  Accordingly, an object of the present invention is to effectively suppress the occurrence of cracks in a solder joint with a ceramic electronic component and improve the connection reliability in a printed wiring board on which the ceramic electronic component is mounted.

In order to solve the above-described problems, the present invention has a basic configuration in which a laminated material is integrally provided on at least one surface of a core substrate, and a ceramic electronic component using the ceramic material as a substrate is soldered on the laminated material. In the multilayer printed circuit board to be mounted,
The laminated material is made of a low elasticity and flexible material having a lower elastic modulus than a general-purpose rigid material and having a low elastic modulus of 20 GPa or less, and is included in a component mounting region of the ceramic electronic component in the core base material. It is characterized in that a part or all of the base material specific part is removed.

  Preferably, the elastic modulus of the laminated material is 0.2 to 6 GPa, and a flexible substrate is optimal as such a low elastic substrate.

  As an aspect of the present invention, in an aspect in which a component mounting region of the ceramic electronic component is set on the surface of the laminated material disposed on the outer surface side of the printed wiring board, the laminated material is at least It is preferable that a reinforcing copper foil is provided on the back side of the component mounting region.

  Further, as another aspect, in the aspect in which the component mounting area of the ceramic electronic component is set on the back surface side of the laminated material, the base material specific portion is arranged so that the component mounting area on the back surface side is exposed. A concave portion formed by removing all of the ceramic electronic components is provided in the concave portion.

  In the present invention, the core substrate is preferably made of a highly elastic material having a low thermal expansion coefficient substantially equal to or less than that of the ceramic material of the ceramic electronic component. As this type of material, a highly functional rigid material having a thermal expansion coefficient of 3 to 10 ppm / ° C. and an elastic modulus of 25 to 35 GPa is preferably employed.

  The present invention is particularly suitable when the ceramic electronic component mounted on the laminated material is a leadless type, but it is a matter of course that a general chip component may be mounted.

  According to the present invention, in a printed wiring board having a multilayer structure, a laminated material is integrally provided on at least one surface of a core substrate, and a ceramic electronic component based on the ceramic material is mounted on the laminated material by soldering. The material is lower elasticity than general-purpose rigid material, and the elastic modulus is 20 GPa or less and low elasticity and a flexible material (preferably a flexible substrate), which is included in the component mounting area of the ceramic electronic component in the core substrate By removing a part or all of the specific part of the base material, the laminated material can easily follow the thermal shrinkage of the ceramic electronic component during the heat cycle test, etc. in the component mounting area, and it is mechanically applied to the solder joint Since the stress is reduced, the occurrence of cracks in the solder joints is effectively suppressed, and the connection reliability with ceramic electronic components It is enhanced.

  It is undeniable that the rigidity (mechanical strength) of the printed wiring board itself will be reduced by removing part or all of the specific part of the substrate, but at least the back side of the mounting area of the laminated material By providing the copper foil for reinforcement in the case, the lack of rigidity can be compensated for more or less.

  Further, the core base material is a highly elastic material having a low thermal expansion coefficient substantially equal to or less than that of the ceramic material of the ceramic electronic component. Specifically, the thermal expansion coefficient is 3 to 10 ppm / ° C., and the elastic modulus is 25 to 25. Similarly, by using a highly functional rigid material of 35 GPa, the lack of rigidity of the printed wiring board itself can be compensated.

  In addition, the high-performance rigid material has a high content of inorganic filler and high thermal conductivity, so heat easily escapes when mounting ceramic electronic components, but the flexible base material used as a laminate is more inorganic than the high-performance rigid material. Since the filler content is low and the thermal conductivity is low, heat at the time of mounting becomes difficult to escape, and the mountability is improved.

  In terms of manufacturing costs, flexible base materials are cheaper than high-performance rigid materials, so the core material and the laminated material are both high-performance rigid materials because the laminated material is a flexible base material. Can lower the cost. Furthermore, although a flexible base material is used as the laminate material, the core base material is a rigid material, so the printed wiring board has high rigidity, so there is no need to change the component mounting process, etc. It can be handled by the production equipment for wiring boards.

  In addition, when the component mounting area of the ceramic electronic component is set on the back surface side of the laminated material, that is, the concave portion formed by removing all of the above-mentioned base specific portions so that the component mounting area on the back surface side of the laminated material is exposed Since the ceramic electronic component is disposed in the recess, the height of the ceramic electronic component can be absorbed in the wiring board (in the recess).

Sectional drawing which shows the printed wiring board of the multilayer structure which concerns on 1st Embodiment of this invention. Sectional drawing which shows the printed wiring board of the multilayer structure which concerns on another aspect of the said 1st Embodiment. Sectional drawing which shows the printed wiring board of the multilayer structure which concerns on 2nd Embodiment of this invention. Sectional drawing which shows the conventional printed wiring board for ceramic electronic component mounting. (A) Perspective view which shows lead terminal type | mold ceramic electronic component, (b) The expanded sectional view which shows the solder joint part. (A) The perspective view which shows a leadless type | mold ceramic electronic component, (b) The expanded sectional view which shows the solder joint part.

  Next, some embodiments of the present invention will be described with reference to FIGS. 1 to 3, but the present invention is not limited thereto.

  First, referring to FIG. 1, a printed wiring board 100A according to a first embodiment of the present invention includes a core substrate 110 serving as an inner layer, and a laminated material 120 (upper laminated material 120a) integrally laminated on both surfaces thereof. , Including the lower laminated material 120b).

  In the first embodiment, the upper laminate material 120a and the lower laminate material 120b are connected via a conductor plated in the via hole 140, and the ceramic electronic component 10 is soldered to the upper laminate material 120a side. Lands 121 for this purpose are formed.

  Similar to a normal printed wiring board, the portions other than the soldering lands of the upper laminated material 120a and the lower laminated material 120b are covered with a solder resist 130 as in the case of a general printed wiring board. In the printed wiring board 100A, the lower laminated material 120b may be omitted as necessary.

  The core base material 110 is preferably made of a highly elastic (high rigidity) material having a low thermal expansion coefficient substantially equal to or less than that of the ceramic material of the ceramic electronic component 10 such as a highly functional rigid material. According to this, generation | occurrence | production of curvature, a wave | undulation, etc. of printed wiring board 100A itself is suppressed by highly functional rigid material.

  On the other hand, the laminated material 120 (120a, 120b) has a lower elasticity (lower rigidity) and more flexibility than a general-purpose rigid material having an elastic modulus of about 20 to 30 GPa, preferably a polyimide resin, TPI ( A flexible base material containing an adhesive mainly composed of an amorphous polyimide resin), an LCP (liquid crystal polymer), or an epoxy resin blended to lower the elastic modulus is used.

  The elastic modulus of the high-performance rigid material used as the core base material 110 is about 25 to 35 GPa, and the rigidity (mechanical strength) of the entire printed wiring board 100A is carried by this high rigidity. On the other hand, it is preferable that the elastic modulus of a flexible base material is 0.2-6GPa. The measured value of the elastic modulus is based on the DMA method (rigid material: bending mode, flexible base material: tensile mode). Note that a general-purpose rigid material (an elastic modulus of about 20 to 30 GPa) may be used as the core substrate 110.

  The ceramic electronic component 10 mounted on the printed wiring board 100A may be either the lead terminal type 10A shown in FIG. 5 (a) or the leadless type 10B shown in FIG. 6 (a).

  Further, in the case of the lead terminal type 10A, the lead terminal 12 is soldered onto the land 121 by the solder material S in the manner shown in FIG. 5B, and in the case of the leadless type 10B, the electrode terminal 13 thereof. 6B is soldered onto the land 121 by the solder material S in the embodiment shown in FIG. 6B, but it is known that lead-free solder is more susceptible to cracking than eutectic solder.

  As described above, the thermal expansion coefficient of the ceramic material that is the base material of the ceramic electronic component 10 is about 4 to 7 ppm / ° C., whereas the core base material made of a general general-purpose rigid material is used. The coefficient of thermal expansion is approximately 12-16 ppm / ° C. Further, the printed wiring board itself is warped or swelled by high and low heat repeatedly applied in the heat cycle test.

  Due to these factors, mechanical stress is intensively applied to the solder material S shown in FIGS. 5B and 6B during the heat cycle test, which causes cracks in the solder joints. Will do.

  In order to prevent the occurrence of such cracks, in the first embodiment, only the upper laminated material 120a is left in the component mounting area MS of the ceramic electronic component 10, and the core substrate 110 included in the component mounting area MS is left. Part or all and a corresponding part of the lower laminated material 120b are removed. Thereby, in the component mounting region MS, a recess 150 is formed below the upper laminated material 120a.

  According to this, in the component mounting region MS, the upper laminate material 120a can easily follow the thermal contraction of the ceramic electronic component 10 during a heat cycle test or the like, so that the mechanical stress applied to the solder joint is reduced, The occurrence of cracks in the solder joint is effectively suppressed, and the connection reliability with the ceramic electronic component 10 is improved.

  Along with the removal of a part or all of the core base material 110 corresponding to the component mounting region MS and the corresponding part of the lower laminated material 120b (hereinafter also referred to as “base material specific portion”). Therefore, it is undeniable that the rigidity of the printed wiring board 100A is weakened, but by leaving the reinforcing copper foil 122 on at least the back surface side of the component mounting region MS of the upper laminated material 120a made of a flexible base material, The lack of rigidity can be compensated for somewhat.

  Moreover, as shown by the imaginary line in FIG. 1 without removing all of the base material specific portions, a part 110a on the upper laminated material 120a side of the core base material 110 may be left. Various embodiments are also included in the present invention.

  In order to remove the base material specific portion, the laminated material 120 may be integrally bonded to the core base material 110 and then removed by counterboring by cutting, or the core base material 110 or the lower laminated material may be removed in advance. The printed wiring board 100A may be constructed by window-cutting and laminating portions corresponding to the component mounting region MS of the material 120b.

  In any case, the core base material 110 and the laminated material 120 may be integrally laminated by a prepreg or an adhesive material blended for decreasing the elastic modulus according to a conventional method.

  In the first embodiment, the laminated material 120 is provided as one layer on each side of the core base material 110. As another example of the printed wiring board 100A, FIG. A printed wiring board having an eight-layer build-up (2 + 4 + 2) configuration in which two layers of the laminated material 120b and four layers of the core substrate 110 are shown is shown. As described above, the laminated material 120 may have two layers (two or more) on one side, and the core substrate 110 may have a multilayer structure (three or more layers).

  In addition, as shown in FIG. 2, an inner layer circuit 111 can be appropriately formed in the core substrate 110, and the via hole 140 of the via hole 140 penetrating between the upper laminated material 120 a and the lower laminated material 120 b can also be formed. In addition, an interstitial via hole 140a, a laser via hole 140b, or the like that connects the inner layer circuits 111 may be employed, and all of those using existing via formation techniques and via connection methods can be used.

  Next, a printed wiring board 100B according to a second embodiment of the present invention will be described with reference to FIG.

  This printed wiring board 100B has the same layer configuration as the eight-layer build-up (2 + 4 + 2) illustrated in FIG. 2, but FIG. 3 shows the printed wiring board 100A of FIG. . Therefore, the positions of the upper laminated material 120a (two layers) and the lower laminated material 120b (two layers) are interchanged as compared with FIG.

  As shown in FIG. 3, in the printed wiring board 100 </ b> B according to the second embodiment, unlike the first embodiment, the ceramic electronic component is formed in the recess 150 formed by removing all the base material specific portions of the core base material 110. 10 is implemented.

  For this reason, of the two laminated upper layers 120a1 and 120a2, the inner layer upper laminate 120a2 is formed with a soldering land 121 on the back side which is the bottom surface of the recess 150. Thus, the ceramic electronic component 10 is soldered by the solder material S. In the second embodiment, the upper laminated material 120a and the lower laminated material 120b may both have a single layer (one sheet) configuration.

  According to this, as in the first embodiment, in the component mounting region MS, the upper laminated material 120a2 can easily follow the thermal contraction of the ceramic electronic component 10 during a heat cycle test or the like, and the machine is applied to the solder joint portion. Stress is reduced, the occurrence of cracks in the solder joint is effectively suppressed, the connection reliability with the ceramic electronic component 10 is improved, and the height of the ceramic electronic component 10 is accommodated in the recess 150. Can do.

  In each of the above embodiments, when there are a plurality of component mounting regions MS, the recess 150 is provided for each component mounting region MS and is not only mounted on the portion where the upper laminated material 120a is left, It can also be mounted on the lower laminate 120b.

  3, the ceramic electronic component 10 is mounted in the recess 150, but the ceramic electronic component 10 can also be mounted on the surface of the upper laminated material 120a1 corresponding to the recess 150.

10 Ceramic electronic parts 10a Ceramic electronic parts (lead terminal type)
10b Ceramic electronic components (leadless type)
DESCRIPTION OF SYMBOLS 100 Printed wiring board 110 Core base material 111 Inner layer circuit 120 (120a, 120b) Laminated material 121 Land 130 Solder resist 140 Via hole MS Component mounting area S Solder material

Claims (7)

In a printed wiring board having a multilayer structure in which a laminated material is integrally provided on at least one side of a core substrate, and a ceramic electronic component based on a ceramic material is mounted on the laminated material by soldering,
The laminated material is made of a low elasticity and flexible material having a lower elastic modulus than a general-purpose rigid material and having a low elastic modulus of 20 GPa or less, and is included in a component mounting region of the ceramic electronic component in the core base material. A printed wiring board, wherein a part or all of a base material specific portion is removed.   The printed wiring board according to claim 1, wherein an elastic modulus of the laminated material is 0.2 to 6 GPa.   The printed wiring board according to claim 1, wherein the laminated material is made of a flexible base material.   A component mounting area of the ceramic electronic component is set on the surface of the laminated material arranged on the outer surface side of the printed wiring board, and the laminated material is reinforced at least on the back side of the component mounting area. The printed wiring board according to any one of claims 1 to 3, further comprising a copper foil for use.   A component mounting area of the ceramic electronic component is set on the back surface side of the laminated material, and a recess formed by removing all of the base material specific portion is exposed so that the component mounting area on the back surface side is exposed. The printed wiring board according to claim 1, further comprising: a printed wiring board according to claim 1.   7. The print according to claim 1, wherein the core base material is made of a highly elastic material having a low thermal expansion coefficient substantially equal to or less than that of the ceramic material of the ceramic electronic component. Wiring board.   The printed wiring board according to claim 6, wherein the core substrate is made of a highly functional rigid material having a thermal expansion coefficient of 3 to 10 ppm / ° C. and an elastic modulus of 25 to 35 GPa.

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