Patent Application
20110198115
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-032521, filed on Feb. 17, 2010, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic component built-in module in which electronic components are covered with an insulating resin and a method of manufacturing the same.
2. Description of the Related Art
An electronic component built-in module is an electronic component in which a plurality of electronic components such as passive elements and active elements are mounted on a substrate by solder or the like to have a set of functions. When such an electronic component built-in module is mounted on a mounting substrate of an electronic device, terminal electrodes of the electronic component built-in module and terminal electrodes of the mounting substrate are bonded by solder. At this time, it is possible that solder which bonds the electronic components in the electronic component built-in module to the substrate melts and the solder moves or spreads. Japanese Laid-open Patent Publication No. 2007-234930 discloses a method in which a linear expansion coefficient of a sealing resin of the electronic component built-in module is regulated to be within a predetermined range.
An electronic component built-in module according to an aspect of the present invention includes an electronic component; a substrate on which the electronic component is mounted; a first resin that is formed of a resin including pores and covers the electronic component and the substrate and whose thickness on an area where the electronic component is not mounted on a surface of the substrate is larger than that on a surface of the electronic component opposite to a surface facing the substrate; and a second resin that covers a surface of the first resin and has a porosity smaller than that of the first resin.
A method of manufacturing an electronic component built-in module according to another aspect of the present invention includes mounting an electronic component on a substrate by solder; coating a first resin solution into which fillers are mixed on the electronic component mounted on the substrate and the substrate; reducing at least a thickness of the first resin solution coated on a surface of the electronic component opposite to a surface attached to the substrate; curing the first resin; covering the cured first resin with a second resin; and curing the second resin.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Hereinafter, an embodiment for implementing the present invention (an embodiment of the present invention) will be described with reference to the drawings. The embodiment described below does not limit the present invention. Constituent elements disclosed in the embodiment described below include those that can be easily assumed by those skilled in the art or that are substantially equivalent or within an equivalent range. Further, the constituent elements disclosed in the embodiment described below can be arbitrarily combined.
The electronic components 2 included in the electronic component built-in module 1 include, for example, passive elements such as a coil, a capacitor, and a resistor, however active elements such as a diode and a transistor, an Integral Circuit (IC), and the like may be mounted on the surface of the module substrate 3 or inside the module substrate 3 as the electronic components 2. The electronic components 2 are not limited to those. In the embodiment, a capacitor 2C, an IC 2P, and a resistor 2R are mounted on the module substrate 3, and the capacitor 2C, the IC 2P, and the resistor 2R are arbitrarily referred to as the electronic component 2 if necessary.
As shown in
As shown in
The shield layer 5 is formed on the surface of the second resin 4 that covers a plurality of electronic components 2. In the embodiment, the shield layer 5 is formed by a conductive material (material having an electrical conductivity: metal is used in the embodiment). In the embodiment, the shield layer 5 may be formed by a single conductive material or a plurality of layers of conductive materials. The shield layer 5 covers the surface of the second resin 4, and thereby shields the electronic components 2 encapsulated in the second resin 4 from high-frequency noises and electromagnetic waves coming from outside of the electronic component built-in module 1, and blocks high-frequency noises emitted from the electronic components 2. In this way, the shield layer 5 functions as an electromagnetic shield. In the embodiment, the shield layer 5 covers the entire surface of the second resin 4. However, the shield layer 5 only needs to cover the second resin 4 to exert a function as an electromagnetic shield, and does not necessarily need to cover the entire surface of the second resin 4. Therefore, the shield layer 5 only needs to cover at least a part of the surface of the second resin 4. When the shield layer 5 is not necessary, the shield layer 5 need not be formed.
The module substrate 3 includes terminal electrodes (module terminal electrodes) 7 on a surface opposite to the component-mounting surface. The module terminal electrodes 7 are electrically connected to the electronic components 2 included in the electronic component built-in module 1 and, as shown in
The mounting substrate 8 shown in
In the electronic component built-in module 1, the electronic components 2 are covered and sealed by the second resin 4, and thus, the solder 6 that bonds the electronic components 2 to the module substrate 3 is also covered and sealed by the second resin 4. As a result, the solder 6 that is sealed by the second resin 4 is melted again by the reflow in a secondary mounting operation (the reflow to mount the electronic component built-in module 1 on the mounting substrate 8). At this time, by forces caused by water vapor generated from moisture contained in the second resin 4 and gas generated from the re-melted solder 6 or residual flux, the solder 6 sealed by the second resin 4 moves or spreads in a gap between the component-mounting surface of the module substrate 3 and the second resin 4. The solder 6 expands when the solder 6 is melted by the reflow in the secondary mounting operation, so that the solder 6 may move rapidly.
In the embodiment, the first resin 10 that includes pores 11 as shown in
In particular, when the electronic component built-in module 1 is sealed by the shield layer 5, the water vapor, residues of the evaporated flux, and the gas generated from the solder 6 are enclosed in the electronic component built-in module 1, and an environment is created in which the solder 6 easily moves or spreads. However, the pores 11 of the first resin 10 included in the electronic component built-in module 1 effectively absorb the water vapor and the gas generated in the electronic component built-in module 1, so that it is possible to effectively prevent the solder 6 from moving or spreading. As described above, the embodiment is preferable, in particular when the electronic component built-in module 1 includes the shield layer 5.
The second resin 4 that covers the first resin 10 has a porosity smaller than that of the first resin 10. The porosity is a ratio (vol %) of the volume of the pores 11 per unit volume. By decreasing the porosity of the second resin 4 to a value smaller than that of the first resin 10, the second resin 4 becomes stronger than the first resin 10. Such a second resin 4 seals the electronic components 2 and the first resin 10 on the module substrate 3 to secure a sufficient strength of the electronic component built-in module 1. The porosity of the second resin 4 may be 0%.
The pores 11 included in the first resin 10 is formed by, for example, adding fillers to a resin that is a base material of the first resin 10 and curing the resin to dispose the resin into gaps between the fillers. When the porosity is smaller than or equal to 0.1 vol %, it is impossible to obtain a mitigation effect against thermal shock caused by a rapid movement of the melted solder 6 or rapid gas expansion. Thus, the solder 6 moves in the reflow process of the secondary mounting operation, so that there is a risk to cause a short circuit or a contact failure of the electronic components 2.
When the porosity is greater than or equal to 30 vol %, there is a risk that the strength of the first resin 10 decreases and cracks are easily generated. And at the same time, the pores 11 are easily connected to each other, so that the pores 11 are formed into a pipe shape. Therefore, in the reflow process of the secondary mounting operation, there is a risk that the solder 6 is melted along the pores 11 having a pipe shape. On the other hand, it is preferable to set the porosity to be smaller than or equal to 10 vol % because, when the porosity is smaller than or equal to 10 vol %, the number of connections between the pores 11 decreases and the melted solder 6 is highly prevented from moving. As described above, to effectively prevent the solder 6 from moving or spreading, it is preferable to set the porosity of the first resin 10 to be greater than or equal to 0.1 vol % and smaller than or equal to 30 vol %, and more preferable to set the porosity to be greater than or equal to 0.1 vol % and smaller than or equal to 10 vol %.
When the average diameter (D50) of the pores 11 shown in
The average diameter of the pores 11 was measured from images obtained by cutting off a completed electronic component built-in module 1 at an appropriate position, making a cut surface without resin dropping by ion milling the cut surface, and taking photographs of any three positions in the cut surface by using a scanning electron microscope (SEM). In the embodiment, the magnification was 3000 times. The distribution of the pores 11 was defined from D50 obtained from the images, D10 corresponding to a cumulative frequency diameter of 10%, and D90 corresponding to a cumulative frequency diameter of 90%. The porosity was measured from an image obtained by cutting off a completed electronic component built-in module 1 at an appropriate position, making a cut surface without resin dropping by ion milling the cut surface, and taking a photograph of the cut surface by using a SEM (magnification was 3000 times). The obtained image was binarized so that only the pores are blackened, and the porosity was calculated as a volume ratio of the pores. In the embodiment, the ratio of the area of the pores to the entire area of the obtained image is assumed to be the volume ratio of the pores.
The first resin 10 on the surface RD of the electronic component opposite to the substrate is present on the surface 2T (top surface) opposite to the surface 2B (the surface through which the electronic component 2 is attached to the module substrate 3; bottom surface) of the electronic component 2 facing the substrate surface 3P. By making the thickness of the first resin 10 on the surface RD of the electronic component opposite to the substrate smaller than the thickness of the first resin 10 on the area ND where nothing is mounted, heat generated from the electronic component 2 is released easily. In particular, when the electronic component 2 is an active element (for example, IC 22), it is advantageous because the amount of discharged heat is large.
As shown in
By making the thicknesses (ts1, ts2, ts3, tt1, tt2, and tt3) of the first resin 10 on the area ND where nothing is mounted larger than the thickness of the first resin 10 on the surface RD of the electronic component opposite to the substrate, the solder 6 that bonds the electronic components 2 to the terminal electrodes (substrate terminal electrodes) 3T of the module substrate 3 can be reliably covered by the first resin 10. Based on this, when the solder 6 is heated by the reflow in the secondary mounting operation, the pores 11 (see
For example, the IC 2P includes terminal electrodes (component terminal electrodes) 2TB on the bottom surface 2B, and the component terminal electrodes 2TB and the substrate terminal electrodes 3T are bonded together by the solder 6. By forming the first resin 10 into the structure described above, the solder 6 is reliably covered by the first resin 10 present on the area ND where nothing is mounted. Based on this, the first resin 10 on the area ND where nothing is mounted effectively absorbs the gas generated from the solder 6 and the thermal shock caused by the solder 6 in the reflow process of the secondary mounting operation, so that the first resin 10 can more reliably prevent the solder 6 from moving or spreading.
Regarding the capacitor 2C shown in
As shown in
In the embodiment, the thickness to of the first resin 10 on the surface RD of the electronic component opposite to the substrate and the thicknesses (ts1, ts2, ts3, tt1, tt2, and tt3) of the first resin 10 on the area ND where nothing is mounted are essentially lengths in a direction perpendicular to a surface of the electronic component 2 (top surface 2T, side surface 2S, end surface 2ST of component terminal electrode 2TS, or the like). In this case, the maximum value of the thickness of the first resin 10 on the area ND where nothing is mounted is the length from the side surface 2S of the electronic component 2 to the bottom position 10B of the U—shape of the first resin 10 (the position where the length between the surface of the first resin 10 on the area ND where nothing is mounted and the substrate surface 32 is smallest).
In the embodiment, in the first resin 10 on the area ND where nothing is mounted, the thickness from the side surface 2S of the electronic component 2 increases as the surface of the first resin 10 approaches the module substrate 3 (when the electronic component 2 has the component terminal electrode 2TS, the end surface 2ST corresponds to the side surface of the electronic component 2). For example, in the examples shown in
As the thickness of the first resin 10 on the area ND where nothing is mounted, the lengths (tt1, tt2, and tt3) in the direction perpendicular to the substrate surface 3P of the module substrate 3 may be used. In this case, the thickness of the first resin 10 on the area ND where nothing is mounted decreases as the surface of the first resin 10 goes away from the electronic component 2. Specifically, in the example shown in
For example, the module element body 3A is manufactured by the following procedure.
(1) Print a solder paste including the solder 6 on the terminal electrodes of the module substrate 3.
(2) Mount the electronic components 2 on the module substrate 3 by using a mounting apparatus (mounter).
(3) Bond the terminal electrodes of the electronic components 2 and the terminal electrodes of the module substrate 3 together by inserting the module substrate 3 on which the electronic components 2 are mounted into a reflow furnace and heating the solder paste so that the solder 6 in the solder paste is melted and thereafter hardened.
(4) Wash off fluxes attached to the surfaces of the electronic components 2 and the module substrate 3.
Next, when the module element body 3A is completed, the process proceeds to step S2, and, as shown in
The molecular weight of the thermo-setting resin that forms the first resin 10 is preferred to be 100 to 1000 before curing. If the molecular weight of the thermo-setting resin before curing is too high, viscosity of the thermo-setting resin before curing is too high, so that it is difficult to form the first resin 10 having an even film thickness. If the molecular weight is too low, viscosity of the thermo-setting resin before curing decreases, and the thermo-setting resin does not remain around the electronic components 2 but flows away. Therefore, the molecular weight of the thereto-setting resin that forms the first resin 10 is preferred to be within the range mentioned above.
The fillers included in the first resin 10 are preferred to have a near sphere shape. It is because, if such fillers are used, the size, shape, and distribution of the pores 11 included in the first resin 10 can be easily controlled. However, the shape of the fillers is not limited to this. The average diameter (D50) of the fillers included in the first resin is preferred to be greater than or equal to 1 μm and smaller than or equal to 10 μm, and more preferred to be greater than or equal to 2 μm and smaller than or equal to 7 μm. Regarding the particle size distribution of the fillers, D50/(D90-D10) is preferred to be set within a range of 0.1 to 0.8. By doing so, the fillers and the pores 11 in the first resin 10 can be easily distributed evenly. The average diameter (D50) is a diameter of the integrated value 50% (median diameter) when the diameters of a plurality of fillers are measured, D90 is a diameter when the integrated value is 90%, and D10 is a diameter when the integrated value is 10%. The particle size distribution of the fillers is defined from the number average value (median diameter) D50 measured by a particle size distribution meter, D10 corresponding to a cumulative frequency particle diameter of 10%, and D90 corresponding to a cumulative frequency particle diameter of 90%.
The type of the fillers is not particularly limited unless the fillers affect electrical characteristics of the electronic components 2 and circuits included in the electronic component built-in module 1. However, the fillers are preferred to have a good dispersibility in the thermo-setting resin included in the first resin 10. For example, when using fillers whose average diameter is smaller than 1 μm, the specific surface area increases. Therefore, the necessary amount of thermosetting resin increases and the porosity decreases, and thus the effect to prevent the solder 6 from moving or spreading decreases. When using fillers whose average diameter is greater than 10 μm, the film thickness of the first resin 10 coated on the surface of the module element body 3A needs to be large. Further, there are a risk that the strength of the formed first resin 10 decreases and cracks easily occur and a risk that the sizes of the pores 11 become large and the effect to prevent the solder from moving or spreading decreases.
Fillers having a large average diameter (D50) may be added to the fillers. The large average diameter (D50) of the fillers is preferred to be greater than or equal to 10 μm and smaller than or equal to 50 μm. The additive amount of the fillers having the large average diameter (D50) is preferred to be greater than or equal to 5 vol % and smaller than or equal to 30 vol % of the total amount of added fillers. In this way, by mixing fillers having different average diameters, it is possible to adjust a packing state among the fillers. It is easy to realize a desired pore diameter and pore distribution by an appropriate resin combination. When using fillers having different average diameters, the same type of fillers may be used, or different types (compositions) of fillers may be used. The types of the fillers are not particularly limited.
Since the spin coat method is a method for reliably removing the redundant first resin solution 10L, structures shown in
When the first resin solution 10L is coated on the surface of the module element body 3A, the first resin solution 10L is heated for a predetermined time period to cure the thermo-setting resin (first curing process). In this way, the first resin 10 is formed on the surface of the module element body 3A. Next, the process proceeds to step S3, and as shown in
Next, the process proceeds to step S4, and as shown in
When the shield layer 5 is formed, the process proceeds to step S6, and the module substrate 3 of the module aggregate body 3C is cut completely into units of the electronic component built-in modules 1 (units divided by Cl in
The first resin 10 of the electronic component built-in module 1 manufactured in this way is not exposed to the outside of the shield layer 5. If the first resin 10 including the pores 11 is exposed to the outside of the electronic component built-in module 1, there is a risk that water is introduced from the outside through the first resin 10. However, in the embodiment, the shield layer 5 is formed on the surface of the second resin 4, and the first resin 10 is covered by the shield layer 5, so that water is not introduced. As a result, water is highly prevented from entering into the electronic component built-in module 1, so that the risk that cracks or the like occur in the first resin 10 or the second resin 4 is extremely low. Based on this, the durability of the electronic component built-in module 1 improves.
Although a part of the first resin 10 appears on the surface of the second resin 4 by the half dice in step S4, the surface area is increased by the pores 11 of the first resin 10, so that the contact between the shield layer 5 and the first resin 10 is improved. As a result, when forming the shield layer 5, there is an advantage that the shape retaining effect of the shield layer 5 increases. When forming the shield layer 5, the first resin 10 may not be in contact with the shield layer 5. However, when manufacturing a plurality of electronic component built-in modules 1 from one substrate, it is difficult to make such a structure.
In the method for manufacturing the electronic component built-in module 1 according to the embodiment, although a part of the first resin 10 appears on the surface of the second resin 4 by the half dice, the first resin 10 appearing on the surface of the second resin 4 can be covered by forming the shield layer 5. As a result, water is not introduced into the completed electronic component built-in module 1, so that the durability of the electronic component built-in module 1 improves as described above.
In this way, as shown in
As described above, in the embodiment, in the electronic component built-in module 1, the electronic components and the substrate are covered by the first resin including pores, further the first resin is covered by the second resin, and thereby the electronic components are sealed by the second resin via the first resin. When the electronic component built-in module is heated by the reflow in the secondary mounting operation, the solder inside the electronic component built-in module melts, and thereby a phenomenon may occur in which the solder is moved or spread by the melting and expansion of the solder or the melted solder is moved or spread by volume expansion of flux residues and absorbed moisture due to evaporation.
In the embodiment, pores for absorbing a volume change of the electronic component built-in module and absorbing gas generated in the electronic component built-in module are provided in the first resin that covers the electronic components. Based on this, even when the solder is melted by the reflow in the secondary mounting operation, a volume expansion that causes the solder to move or spread is absorbed by the pores included in the first resin. As a result, it is possible to prevent the solder movement or the solder spreading from occurring, which is caused when the solder in the electronic component built-in module is melted by the heat generated when the electronic component built-in module is mounted.
The electronic component built-in module 1 (see
A method for evaluating the movement of the solder will be described. The evaluation body has been heated in a reflow furnace and the movement of the solder in the evaluation body after the reflow has been observed by using transmission X-ray. The evaluation body in which the movement of the solder is observed has been determined to be an evaluation body with movement, and the evaluation body in which the movement of the solder is not observed has been determined to be an evaluation body without movement. A plurality of electronic component built-in modules 1 have been created for each condition such as a porosity and an average diameter, and a ratio of the number of evaluation bodies in which the movement of the solder is observed to the total number of evaluation bodies has been evaluated on a percentage (%) basis. The condition of the reflow is as follows:
As preprocessing for drying, the evaluation body has been left in an environment of 1.25° C. for 24 hours. As preprocessing for moisture absorption, the evaluation body after the drying has been left in an environment of 60° C. and relative humidity of 60% for 120 hours. Thereafter, the reflow has been performed under the condition described below. The evaluation body after the drying and the moisture absorption is inserted into the reflow furnace, then the temperature in the reflow furnace is raised to 150° C., and thereafter the temperature is raised to 180° C. in 120 seconds. The temperature in the reflow furnace is raised to 230° C. and then the reflow is started. During the reflow, the temperature in the reflow furnace is controlled so that the temperature is least 230° C. and the maximum temperature is 260° C.±3° C., and the temperature is held for 30 seconds. Thereafter, the evaluation body is taken out from the reflow furnace, and the reflow is completed.
Evaluation bodies respectively including first resins 10 having different porositys have been manufactured by using spherical fillers with an average diameter of 3 μm. The evaluation result is shown in table 1. The porosity has been changed as shown in table 1. The average diameter of the pores is 0.7 μm. The average diameter of the pores is a value of D50. In the first evaluation example, the movement of the solder and the strength of the first resin 10 have been evaluated. The strength of the first resin 10 has been evaluated on the basis of presence or absence of the cracks. The cracks in the first resin 10 have been observed by transmission X-ray. As known from table 1, when the porosity is smaller than 0.1%, the movement of the solder 6 cannot be sufficiently prevented. On the other hand, when the porosity is 40%, the strength of the first resin 10 is not sufficient. For this reason, the porosity is preferred to be greater than or equal to 0.1% and smaller than or equal to 30%.
Evaluation bodies respectively including first resins 10 having different average diameters of the pores have been manufactured by changing a mixing ratio of one or at least two fillers among fillers respectively having average diameters of 1 μm, 3 μm, 5 μm, 7 μm, and 30 μm. The average diameter of the pores has been changed as shown in table 2. The average diameter of the pores is a value of D50. The evaluation result is shown in table 2. As known from table 2, when the average diameter of the pores is smaller than 0.1 μm, the movement of the solder 6 cannot be prevented. On the other hand, when the average diameter of the pores is 20 μm, the movement of the solder 6 cannot be sufficiently prevented. For this reason, the average diameter of the pores is preferred to be greater than or equal to 0.1 μm and smaller than or equal to 10 μm.
Evaluation bodies respectively including first resins 10 having different average diameters of the fillers have been manufactured by changing a mixing ratio of one or at least two fillers among fillers respectively having average diameters of 1 μm, 3 μm, 5 μm, 7 μm, and 30 μm. The average diameter of the fillers has been changed as shown in table 3. The average diameter of the fillers is a value of D50. The evaluation result is shown in table 3. As known from table 3, when the average diameter (D50) of the fillers is smaller than 1 μm, the movement of the solder 6 cannot be sufficiently prevented. On the other hand, when the average diameter (D50) of the fillers is 15 μm, the strength of the first resin 10 is not sufficient. For this reason, the average diameter (D50) of the fillers is preferred to be greater than or equal to 1 μm and smaller than or equal to 10 μm.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-032521 | Feb 2010 | JP | national |
