JP5085306B2 - Resin composition for underfill, printed circuit board, and electronic device - Google Patents

Description

  The present invention relates to a technology for obtaining a printed circuit board by flip-chip mounting an electronic component such as an IC chip on a printed wiring board, and in particular, a resin composition for underfill applied between the electronic component and the printed wiring board. The present invention relates to a printed circuit board improved by using the same, and an electronic apparatus such as a semiconductor device.

  In flip chip mounting of semiconductor elements, in an electronic device in which an LSI such as a ball grid array (BGA), which is an IC package in which solder balls are arranged in a grid shape, is mounted on a motherboard, the motherboard and BGA due to vibration, shock, and temperature change Stress may occur due to the difference in thermal expansion coefficient between the solder balls, and the solder ball joint may break. For this reason, in order to prevent breakage of the solder ball joint, to fix the joint, and to relieve stress applied to the solder ball joint, an underfill is provided between the motherboard and the BGA (for example, Patent Document 1, (See Patent Document 2 and Patent Document 3).

In this underfill material, for example, a filler (filler) such as silica particles for suppressing thermal expansion of the epoxy resin is dispersed in a thermosetting resin such as an epoxy resin. When the filler is uniformly dispersed in the epoxy resin, the stress applied to the solder ball joint portion is improved. However, the underfill applied between the motherboard and the BGA package tends to settle the dispersed filler when the viscosity is lowered by heating. When the cross section of the underfill thermally cured in that state was observed with an SEM, the filler was distributed on the substrate side and was hardly present on the BGA side. Thus, when the distribution of the filler is not uniform, the stress is not sufficiently relaxed, and the solder ball joint may break.
JP 2007-5477 A JP 2006-73777 A JP 2005-330881 A

  The present invention has been made in view of the above circumstances, and by applying an underfill that can sufficiently relieve stress generated in the solder ball joint due to vibration, impact, and temperature change, the solder ball joint is broken. It is an object of the present invention to obtain a circuit board having a connection structure which is difficult and has high reliability.

The underfill resin composition of the present invention is characterized by containing a nonmagnetic filler containing at least one inorganic filler and an elastomer among a liquid epoxy resin, silica, and alumina , and a magnetic filler.

The printed circuit board of the present invention is provided between a printed wiring board having a connection terminal, an electronic component joined to the connection terminal of the printed wiring board via a solder ball, and between the printed wiring board and the electronic component, It is characterized by comprising an epoxy resin, a nonmagnetic filler containing at least one inorganic filler of silica and alumina dispersed in the epoxy resin and an elastomer , and an underfill containing a magnetic filler.

An electronic device according to the present invention includes a printed wiring board having a connection terminal, an electronic component joined to the connection terminal of the printed wiring board via a solder ball, an epoxy component provided between the printed wiring board and the electronic component, A printed circuit board having a resin, a nonmagnetic filler containing at least one inorganic filler and an elastomer among silica and alumina dispersed in the epoxy resin, and an underfill containing a magnetic filler is provided. And

  When the underfill according to the present invention is used, the stress of the solder ball joint caused by vibration, impact, temperature change, etc. can be sufficiently relaxed, the solder ball joint is not easily broken, and a highly reliable connection is obtained. It is done.

  The underfill composition of the present invention is a liquid epoxy resin and an underfill composition containing a filler, and the filler includes a nonmagnetic filler and a magnetic filler.

  Further, the printed circuit board of the present invention is an application of the above underfill composition, and includes a printed wiring board having connection terminals, an electronic component joined to the connection terminals of the printed wiring board via solder balls, and a printed circuit board. A printed circuit board having an underfill containing an epoxy resin and a filler dispersed in the epoxy resin, which is provided between the wiring board and the electronic component, and the filler contains a nonmagnetic filler and a magnetic filler.

  Furthermore, the electronic device of the present invention is also obtained by applying the above-mentioned underfill composition between a printed wiring board and an electronic component and thermally curing the printed wiring board having a connection terminal, and the printed wiring board. An electronic component joined to a connecting terminal of the printed circuit board via a solder ball, a printed circuit board having an underfill including an epoxy resin and a filler dispersed in the epoxy resin provided between the printed wiring board and the electronic component This filler contains a nonmagnetic filler and a magnetic filler.

  According to the present invention, when a nonmagnetic filler and a magnetic filler are used together as fillers for underfill, the characteristics of the nonmagnetic filler that tends to settle down in the underfill, that is, the substrate side, and the magnetic filler that tends to be attracted by magnetic force. Due to the difference, the distribution of the filler in the underfill can be controlled so as to exist in both the substrate side region and other regions such as the electronic component side region.

  FIG. 1 is a model diagram schematically showing the distribution of fillers in the underfill according to the present invention.

  As shown in the drawing, the underfill 11 is applied between a printed wiring board 1 provided with connection terminals 2 and an electronic component such as a semiconductor chip 3 provided with wiring 4. The magnetic filler 7 contained in the underfill 11 is attracted to, for example, the upper wiring 4 and distributed in a large amount in the electronic component side region. On the other hand, the nonmagnetic filler 6 settles downward and is distributed in a large amount in the substrate side region.

  When the present invention is used, as described above, the filler distribution becomes more homogeneous, so that the stress relaxation of the underfill is exerted on the solder ball 5, particularly the junction with the electronic component and the junction with the printed wiring board. It becomes more homogeneous, and these solder ball joints are less likely to break and a highly reliable connection is obtained.

  The nonmagnetic filler can contain at least one inorganic filler of silica and alumina as a main component.

  Here, the main component refers to an element or a group of elements having the largest component ratio among the components constituting the substance.

  In the nonmagnetic filler, a part of the inorganic filler can be replaced with an elastomer.

  In FIG. 2, the model figure which represents typically distribution of the filler in the other example of the underfill concerning this invention is shown.

  This underfill 12 has the same configuration as in FIG. 1 except that it further includes an elastomer 8. As shown in the figure, unlike the inorganic filler 6, such an elastomer can be selected and used in a liquid epoxy resin. As a result, the elastomer 8 is largely distributed in the region above the lower portion of the underfill 12 where a large amount of the precipitated inorganic filler 6 is present. Even when the epoxy resin expands due to heating, the elastomer contracts due to its elasticity, so that the stress generated by the thermal expansion of the epoxy resin can be relieved. In this manner, the filler distribution becomes more homogeneous, so that the stress relaxation action of the underfill 12 becomes more uniform than that in FIG. 1, and the solder ball 5 joint is less likely to break and has high reliability. Is obtained.

  Further, the distribution of the elastomer 8 can be controlled by selecting materials that attract each other as the magnetic filler 7 and the magnetic elastomer 8 by, for example, partially applying a magnetic material to the elastomer.

  As the elastomer, for example, at least one of a silicone resin and a urethane resin can be used.

  The filler used in the present invention has a size of, for example, 500 nm to 20 μm. Within this range, good fluidity and filling performance can be obtained.

  The filler can be added in an amount of 50 to 90% by weight with respect to the liquid epoxy resin. Within this range, the stress relaxation action of the underfill is good.

  Among the fillers, the nonmagnetic filler can be added in an amount of 30 to 80% by weight based on the liquid epoxy resin. Within this range, the stress relaxation action of the underfill is good.

  The magnetic filler can be added in an amount of 10 to 60% by weight based on the liquid epoxy resin. Within this range, the stress relaxation action of the underfill is good.

  Examples of the magnetic material used for the magnetic filler include ferrite. Ferrite can be used alone or in combination with silica or the like. Examples of combinations with silica and the like include, for example, those obtained by mixing ferrite in melted silica and miniaturized by spraying, and those obtained by attaching ferrite to the silica surface. Moreover, what applied the magnetic body to the elastomer can be used as a magnetic filler as needed.

  The elastomer material can be added in an amount of 0 to 70% by weight with respect to the nonmagnetic filler. Within this range, the stress relaxation action of the underfill is good.

  As the epoxy resin used in the present invention, for example, bisphenol A type, bisphenol F type liquid epoxy resin, and the like can be used, and they can be mixed and used as necessary.

  To the underfill composition of the present invention, for example, a curing agent comprising an acid anhydride such as dodecenyl succinic anhydride, methyltetrahydrophthalic anhydride, methyl nadic anhydride, and the like can be further added.

  The acid anhydride can be added in an amount of 15 to 25% by weight based on the total amount of the underfill composition. Within this range, there is an effect that the effect as a polymerization catalyst is improved in terms of reaction rate.

  Carbon black can be further mixed into the underfill composition of the present invention. By using carbon black, the underfill can be visualized after coating by coloring it black.

  3 and 4 are views showing an example of the manufacturing process of the printed circuit board of the present invention.

  After the printed circuit board of the present invention is mounted by providing an electronic component 3 such as an IC bare chip via a solder ball 5 on the connection terminal 2 on the printed wiring board 1 on which the wiring is printed, and then performing heat connection. The underfill composition 13 is potted in a gap between the printed wiring board 1 and the electronic component 3 with, for example, a dropper-like member, injected into the gap using a capillary phenomenon, and then cured by heating to form an underfill. Can be obtained. In addition, the clearance gap between the printed wiring board 1 and the electronic component 3 is about 150 micrometers thru | or 30 micrometers normally.

  This underfill can be provided in the gap between the printed wiring board and the electronic component, or can be provided around the gap. The underfill composition can also be applied directly to the joint on the printed circuit board before mounting.

  Next, an example of the electronic device of the present invention will be described with reference to FIGS.

  As shown in FIG. 5, a portable computer 110 as an electronic device includes a flat rectangular box-shaped device main body 112 and a flat rectangular display unit 13. The device main body 112 includes a housing 114 made of, for example, synthetic resin. The housing 114 includes a rectangular base portion 115 having an open top surface and a top cover 116 joined to the base portion so as to cover the opening of the base portion.

  As shown in FIGS. 5 and 6, the base portion 115 of the housing 114 integrally includes a rectangular bottom wall 114 a, left and right side walls erected around the bottom wall, a front wall, and a rear wall. Yes. The top cover 116 is opposed to the bottom wall 114 a and constitutes the upper wall of the housing 114. In the housing 114, a keyboard placement unit 20 is provided at the center of the top cover 116, and the keyboard 22 is placed on the keyboard placement unit. Speakers 24 are respectively exposed on the left and right of the rear end of the top cover 116. The top front end portion of the top cover 116 constitutes a palm rest portion 26, and a touch pad 25 and a click button 27 are provided substantially at the center of the palm rest portion.

  As shown in FIG. 5, the display unit 13 includes a flat rectangular box-shaped housing 28 and a liquid crystal display panel 30 accommodated in the housing. The display surface 30 a of the liquid crystal display panel 30 is exposed to the outside through a display window 31 formed in the housing 28. The housing 28 has a pair of leg portions 32 protruding from one end thereof. These leg portions 32 are rotatably supported on the rear end portion of the housing 114 via a hinge portion (not shown). As a result, the display unit 13 can rotate between a closed position where the keyboard 22 is tilted so as to cover the keyboard 22 from above and an open position where the keyboard 22 stands up behind the keyboard 22.

  In the apparatus main body 110, an optical disk drive, a hard disk drive (HDD), a card slot, a battery pack, and other various electronic components (not shown) are arranged. As shown in FIGS. 6 and 8, a circuit board device 34 is disposed on the bottom wall 114a in the housing 114. The circuit board device 34 is electrically connected to an electronic component such as a drive disposed in the keyboard 22, the liquid crystal display panel 30, and the housing 114.

  The circuit board device 34 includes a printed circuit board 36 disposed on the bottom wall 114a. The printed circuit board is disposed on the bottom wall 114a on the side opposite to the first surface 36a and the first surface 36a located on the top cover 116 side. It has the 2nd surface 36b which opposes. As shown in FIG. 7, the printed circuit board 36 is disposed on a boss 37 formed on the inner surface of the bottom wall 114 a of the housing 114. As shown in FIGS. 6 to 7, on the first surface 36a of the printed circuit board 36, a plurality of electronic components including a plurality of semiconductor elements 38 including an MPU 38a made of BGA, a connector 41, and the like are mounted. The underfill of the present invention is applied at least between the MPU 38a and the printed circuit board 36. Further, as will be described later, a plurality of electronic components are also mounted on the second surface 36b.

  The MPU 38a functioning as the first electronic component generates heat as it operates. Therefore, a cooling unit 40 for cooling the MPU 38 a is provided on the first surface side of the printed circuit board 36. The cooling unit 40 includes a heat radiating plate 42 that functions as a heat radiating member that radiates heat from the MPU 38a, and a stop plate 44 that presses the heat radiating plate against the MPU 38a.

  The heat radiating plate 42 is formed in a substantially rectangular shape with a metal having high thermal conductivity, such as aluminum. The heat sink 42 is formed sufficiently larger than the plane area of the MPU 38a. The heat radiating plate 42 is provided so as to overlap the MPU 38a, is opposed to the first surface 36a of the printed circuit board 36 substantially in parallel, and is in surface contact with the upper surface of the MPU through the heat transfer sheet 47, and is thermally It is connected to the. Two fixing pins 45 project from the center of the upper surface of the heat radiating plate 42.

  The stopper plate 44 as a pressing member is formed of, for example, a metal plate spring made of stainless steel or the like, and has a pressing portion 44a that is in contact with the center of the upper surface of the heat radiating plate 42 and a pair of arm portions that extend from the pressing portion to both sides. 48a and 48b. The pressing portion 44a has a pair of through holes 46 through which the fixing pins 45 of the heat radiating plate 42 are inserted, and is fixed to the upper surface of the heat radiating plate by caulking the tip portions of these fixing pins.

  The arm portions 48a and 48b extend obliquely upward from the pressing portion 44a, and attachment portions 50a and 50b bent substantially in an L shape are integrally formed at each extended end. . Mounting holes 52a and 52b are formed in the mounting portions 50a and 50b, respectively.

  Mounting portions 50a and 50b of the stop plate 44 are screwed to studs 54a and 54b provided on the printed circuit board 36, respectively. The stud 54a is temporarily fixed by solder on the first surface 36a of the printed circuit board 36, and is erected almost vertically on the first surface. The stud 54a is screwed to the printed circuit board by a stud fixing screw 62 screwed into the stud 54a from the second surface 36b side of the printed circuit board 36 through the printed circuit board. The attachment portion 50a of the stop plate 44 is screwed to the stud 54a from the first surface 36a side of the printed circuit board 36 by a set screw 60a screwed into the stud 54a through the attachment hole 52a.

  The other stud 54b is temporarily fixed to the second surface 36b of the printed circuit board 36 with solder, and is erected almost vertically on the second surface. The mounting portion 50a of the stop plate 44 is connected to the printed circuit board 36 and the printed circuit board 36 by a set screw 60a screwed into the stud 54a from the side of the first surface 36a of the printed circuit board 36 through the mounting hole 52a and the through hole 58 of the printed circuit board 36. It is screwed to the stud 54a.

  As described above, the attachment portions 52 a and 52 b located on both sides of the heat radiating plate 42 are fixed to the printed circuit board 36. The stopper plate 44 presses the pressing portion 44a against the heat radiating plate 42 by the elastic force of the arm portions 48a and 48b, and causes the heat radiating plate 42 to adhere to the MPU 38a via the heat transfer sheet 47. Thereby, the heat sink 42 receives heat from the MPU 38a and dissipates the heat into the housing 114, thereby forcibly cooling the MPU 38a.

  As shown in FIGS. 6 and 7, the stop plate 44 extends obliquely with respect to a pair of opposed side edges of the heat radiating plate 42. For this reason, the stopper plate 44 can stably fix the heat radiating plate 42 without rattling.

  On the other hand, as shown in FIG. 8, a plurality of electronic components including a plurality of semiconductor elements 66 and connectors 68 a and 68 b are mounted on the first surface 36 a of the printed circuit board 36. A memory board 70 as a second electronic component is connected to the connector 68 a, is adjacent to the second surface 36 b, and is disposed so as to overlap the stud fixing screw 62. An insulating sheet 71 is provided between the second surface 36 b of the printed circuit board 36 and the memory board 70. Further, the video board 72 is connected to the connector 38b and is adjacent to and opposed to the second surface 36b of the printed circuit board 36.

  According to the circuit board device 34 and the portable computer 110 configured as described above, the MPU 38a as a heat generating component and the cooling unit 40 for cooling the MPU 38a are mounted on the first surface 36a of the printed circuit board 36. The stud 54a to which the cooling unit 40 is fixed is erected on the first surface 36a of the printed circuit board 36, and is fixed to the printed circuit board by a stud fixing screw 62 screwed from the second surface 36b side. Yes. Therefore, the stud 54a does not protrude toward the second surface 36b of the printed circuit board 36, and other electronic components can be mounted and arranged on the second surface in a region overlapping with the stud 54a. . As a result, the space of the printed circuit board 36 can be effectively used, the mounting density can be improved, and the circuit board device and the computer can be reduced in size and thickness.

  Further, by fixing the stud 54a erected on the first surface 36a of the printed circuit board 36 from the second surface 36b side by the stud fixing screw 62, the stud 54a is reliably prevented from falling off when the heat sink 42 is attached. can do. Furthermore, the two set screws 60a and 60b for fixing the stop plate 44 can be screwed in from the same surface side of the printed circuit board 36, and the workability during assembly can be prevented from being lowered.

Examples Hereinafter, the present invention will be specifically described with reference to Examples.

Example 1
An inorganic filler added with a magnetic material obtained by kneading a magnetic material (ferrite (Fe ₂ O ₃ )) with respect to a part of the inorganic filler and the elastomer, and an elastomer added with the magnetic material were prepared.

  Underfill compositions were prepared by mixing materials having the following compositions.

Underfill composition Bisphenol A liquid epoxy resin 1% by weight
Bisphenol F type liquid epoxy resin 15% by weight
Silica filler with no magnetic material added 15% by weight
10% by weight of silicone elastomer without magnetic material
Silica filler with magnetic material ferrite added 20% by weight
Silicone elastomer to which the above magnetic material is added 20% by weight
Acid anhydride Methyl nadic acid anhydride 15% by weight
Carbon black Less than 1% by weight After mounting the BGA on the printed circuit board, apply the resulting underfill composition on one or three sides around the BGA, and the gap between the IC chip and the printed circuit board due to capillary action And then cured at a temperature of 160 ° C. for 15 minutes to obtain a printed circuit board.

  The silica filler used had a volume average particle size of 2 μm, and the elastomer had a volume average particle size of 9 μm.

Comparative Example 1
As a comparison,
Bisphenol A liquid epoxy resin 1% by weight
Bisphenol F type liquid epoxy resin 15% by weight
Silica filler with no magnetic material added 35% by weight
Acid anhydride Methyl nadic acid anhydride 15% by weight
By preparing a composition for underfill containing less than 1% by weight of carbon black and mounting BGA on a printed wiring board in the same manner, applying the composition for underfill and performing heat curing, a printed circuit is obtained. I got a plate.

  A thermal cycle test was performed using the obtained printed circuit board.

  In this thermal cycle test, the process of raising the temperature to 90 ° C. and then cooling to −25 ° C. was defined as one cycle.

  As a result, the BGA mounting structure of Comparative Example 1 was broken at 900 cycles, but the mounting structure of Example 1 was not broken even after 1400 cycles.

  From this, it was found that when the present invention is used, the stress relaxation action in the underfill is remarkably improved, and a more reliable connection can be obtained.

  Further, by increasing the blending ratio of the magnetic material to the elastomer, it becomes possible to sink the material that floats. According to the present invention, it is considered that the intended dispersion state can be created by controlling the positions of the inorganic filler and the elastomer.

Example 2
Prior to mounting, a printed circuit board was obtained in the same manner as in Example 1 except that a coating containing ferrite (Fe ₂ O ₃ ) was applied to the surface of the flip chip on the solder ball side.

  When a thermal cycle test was conducted in the same manner as in Example 1, no fracture occurred after 1400 cycles.

  From this, it was found that when the present invention is used, the stress relaxation action in the underfill is remarkably improved, and a more reliable connection can be obtained.

  The reason why the stress relaxation effect in the underfill is good is thought to be that the inorganic filler and elastomer to which the magnetic material was added floated without settling in the underfill, and the dispersibility of the filler became good. Inorganic fillers and elastomers to which magnetic materials are added have the property of being attracted to the chip-side wiring material or to the substrate-side wiring material due to the applied magnetism. Unlike inorganic fillers, which have a heavy specific gravity and tend to sink, it is thought that they can be lifted selectively.

Model diagram schematically showing distribution of filler in underfill according to the present invention Model diagram schematically showing distribution of filler in other examples of underfill according to the present invention The figure showing an example of the manufacturing process of the printed circuit board of this invention The figure showing an example of the manufacturing process of the printed circuit board of this invention FIG. 6 is a diagram for describing an example of an electronic device of the invention FIG. 6 is a diagram for describing an example of an electronic device of the invention FIG. 6 is a diagram for describing an example of an electronic device of the invention FIG. 6 is a diagram for describing an example of an electronic device of the invention

Explanation of symbols

  1 ... 2, ... 3 ... 4 ... 5 ..., 6 ..., 7 ..., 8 ..., 11 ..., 12 ..., 110 ... portable computer, 112 ... device main body, 113 ... display unit, 114 ... housing Body 114a ... bottom wall 116 ... top cover 22 ... keyboard 34 ... circuit board device 36 ... printed circuit board 36a ... first surface 36b ... second surface 40 ... cooling part 42 ... heat sink, 44 ... Stop plate, 50a, 50b ... Mounting portion, 54a, 54b ... Stud, 60a, 60b ... Set screw, 62 ... Stud fixing screw, 70 ... Memory board

Claims (5)

A resin composition for underfill, comprising a nonmagnetic filler containing at least one inorganic filler and an elastomer among a liquid epoxy resin, silica, and alumina , and a magnetic filler. The underfill resin composition according to claim 1, wherein the elastomer is at least one of a silicone resin and a urethane resin . A printed wiring board having a connection terminal, an electronic component joined to the connection terminal of the printed wiring board via a solder ball, an epoxy resin provided between the printed wiring board and the electronic component, and dispersed in the epoxy resin A printed circuit board comprising: a non-magnetic filler containing at least one inorganic filler of silica and alumina and an elastomer ; and an underfill containing a magnetic filler . The printed circuit board according to claim 3, wherein the elastomer is at least one of a silicone resin and a urethane resin. An electronic apparatus comprising the printed circuit board according to claim 3 .

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