This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-091189, filed on Apr. 28, 2015, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to a substrate with embedded component.
Electronic devices such as a personal computer and a server incorporate various kinds of wiring substrates.
Among them, the substrate with embedded component such as a resistive element or a capacitor can have a small outer shape, because the component is not exposed on the surface of the substrate, thereby leading to downsizing of an electronic device.
Note that technologies related to the present application are disclosed in Japanese Laid-open Patent Publication No. 07-302970 and Japanese Examined Laid-open Patent Publication No. Hei 6-9302.
According to one aspect discussed herein, there is provided a substrate with embedded component including: an insulating base member; a conductive pad formed on the insulating base member; a component connected to the conductive pad with a solder; and a resin covering the component, wherein a hole is provided in the insulating base member and the conductive pad, and the insulating base member is exposed on a side surface of the hole.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.
Prior to the description of the embodiments, matters investigated by the inventors are described.
As illustrated in
Subsequently, as illustrated in
The component 3 may be, for example, a resistive element, a capacitor, or a coil.
The material of the solder 4 is preferably a lead-free solder, which is eco-friendly, and a SnAgCu solder is used in this example. The melting point of the SnAgCu solder depends on its composition ratio. For example, a Sn-3Ag-0.5Cu solder having a melting point of about 220° C. is used as the material of the solder 4.
Note that, the conductive pad 2, to which the component 3 is connected as described above, is also called as a foot print.
Next, a process illustrated in
Firstly, a first multi-layer wiring base member 7 and a second multi-layer wiring base member 8 are disposed over the insulating base member 1, to which the component 3 is connected as described above.
The multi-layer wiring base members 7 and 8 each include alternate layers of an insulating layer 9 and wiring 10. A resin sheet of epoxy resin may be used as the insulating layer 9. Then, a copper-plated layer may be formed as the wiring 10.
Then, prepreg as thermosetting resin 11 is adhered onto a surface of the first multi-layer wiring base member 7. In addition, an opening 7a having a dimension enough to house the component 3 is formed in the resin 11 and the first multi-layer wiring base member 7 by mechanical processing.
The resin 11 is, for example, a thermosetting epoxy resin, and is disposed also between the first multi-layer wiring base members 7 and 8. Note that the resin 11 is not yet cured at this step and is in an uncured state.
Subsequently, as illustrated in
The highest temperature of the resin 11 in this process is in a range of about 180° C. to 200° C. at which the resin 11 is thermally cured. Since this temperature is lower than the melting point of the solder 4, the solder 4 is not melted in this process.
By pressing in this manner, the resin 11 penetrates into the opening 7a, and the opening 7a is filled with the resin 11.
Subsequently, as illustrated in
Then, the solder bump 16 is subjected to reflow by heating it, thereby connecting the semiconductor element 17 to the wiring 10 with the solder bump 16.
Thus, the basic structure of the substrate 18 with embedded component according to this example is completed.
The substrate 18 can have a small outer shape because the component 3 is not exposed on the substrate surface, thereby leading to downsizing of an electronic device such as a server in which the substrate 18 is incorporated.
Here, according to the method of manufacturing the substrate 18 with the embedded component, the solder 4 and the resin 11 are also heated by heat for melting the solder bump 16 in the process of
Since the solder bump 16 and the solder 4 have the same melting point as described above, the solder 4 is also melted when the solder bump 16 is melted by heating. In addition, the resin 11 around the solder 4 thermally expands by this heat.
Accordingly, the melted solder 4 is pressurized by the resin 11 around the solder 4 and spreads along an interface between the resin 11 and the insulating base member 1 in the lateral direction. Then, in the worst case, the conductive pads 2 adjacent to each other in the lateral direction are electrically short-circuited via the solder 4.
Such a phenomenon is called solder flash, which adversely contributes to the reduction in the yield of the substrate 18 with embedded component.
Although the inventors investigated some methods for preventing the solder flash, these methods have difficulties.
For example, it is considered that the material having higher melting point than that of the Sn-3Ag-0.5Cu solder, which is the material of the solder bump 16, is employed as the material of the solder 4. In this case, the solder 4 having the higher melting point does not melt even when subjected to the reflow in the process of
In this method, however, the solder 4 needs to be heated at high temperature to be melted in the process of
In contrast, it is also considered that the solder having lower melting point than that of the Sn-3Ag-0.5Cu solder, which is the material of the solder 4, is employed as the material of the solder bump 16, for the purpose of preventing the solder 4 from melting when the solder bump 16 is subjected to the reflow. However, the solder having lower melting point than that of the Sn-3Ag-0.5Cu solder is mechanically fragile. Therefore, when such a solder is used as the solder bump 16, connection strength between the wiring 10 and the semiconductor element 17 is lowered.
Alternatively, the material, whose melting point rises once melted, is considered to be used for the solder 4.
For example, in the solder paste in which copper powder is added to the solder, since a part of the copper powder is melted into the solder at the first melting, composition ratio of copper in the solder becomes high. Thus, a higher temperature than that in the first melting is required to melt the solder at the next melting, and thus the solder 4 is considered to be not melted in the reflow of the solder bump 16 in the process illustrated in
However, since a rise in the melting point of the solder 4 is small, the solder 4 is potentially melted in the reflow of the solder bump 16 in the process illustrated in
Instead of changing the material of the solder 4 in this manner, it is considered that the opening 7a may be filled with an adhesive agent before the process of
However, this method requires an additional process of filling the adhesive agent into the opening 7a, resulting in an increase in the number of processes and also in manufacturing cost of the substrate 18. Moreover, it is technologically difficult to measure the adhesive agent having the same volume as that of the opening 7a and fill this adhesive agent into the opening 7a.
In the followings, embodiments capable of preventing the solder flash are described.
In the present embodiment, the solder flash in a substrate with embedded component is prevented as described below.
Note that in
First, as illustrated in
The material and thickness of the insulating base member 1 are not particularly limited. In this example, a glass epoxy substrate having a thickness of about 0.06 mm to 0.2 mm is used as the insulating base member 1.
Next, as illustrated in
Note that the holes 1a may be formed by laser processing instead of drilling. In this case, a portion of the conductive pad 2 corresponding to the holes 1a may be previously removed in the patterning of
In the present embodiment, metal film and the like is not formed on the side surface of the hole 1a, so that the material of the insulating base member 1 is left exposed in the hole 1a.
As illustrated in
Next, as illustrated in
An opening 19a is formed at a position of the metal mask 19 that corresponds to the conductive pad 2, and the position of the metal mask 19 is adjusted so that the opening 19a overlaps the conductive pad 2.
Then, by a printing method, solder paste is printed as the solder 4 on the conductive pad 2 in the opening 19a.
The solder 4 is preferably a lead-free solder, which is eco-friendly, and is a SnAgCu solder in this example. The melting point of this SnAgCu solder is also not particularly limited. In the present embodiment, Sn-3Ag-0.5Cu, which has a low melting point of about 220° C. and thus causes no damage on the insulating base member 1 when melted, is used.
As illustrated in
Subsequently, as illustrated in
Even when the solder 4 is melted in this manner, the solder 4 hardly enters into the hole 1a, because the insulating material of the insulating base member 1 having a low solder wettability is exposed on the side surface of the hole 1a.
Subsequently, as illustrated in
As explained in
Prepreg used as the resin 11 is, for example, a thermosetting epoxy resin, and is in the uncured state at this time. Although the thickness of the resin 11 is not particularly limited, the thickness of the resin 11 is about 0.06 mm to 0.2 mm in this example.
In addition, the thicknesses of the insulating layer 9 and the wiring 10 are not particularly limited. The insulating layer 9 is, for example, a resin sheet of epoxy resin having a thickness of about 0.06 mm to 0.2 mm. The wiring 10 is, for example, a copper-plated layer having a thickness of about 12 μm to 35 μm.
Then, as illustrated in
Thereafter, the insulating base member 1, the first multi-layer wiring base member 7, the resin 11, and the second multi-layer wiring base member 8 are pressed while heating these elements, thereby thermally curing the resin 11.
The highest temperature of the resin 11 in this process is in the range of about 180° C. to 200° C. at which the resin 11 is thermally cured. Since this temperature is lower than the melting point of the solder 4, the solder 4 is not melted in this process.
Moreover, by pressing in this manner, the resin 11 penetrates into the opening 7a, and the opening 7a is filled with the resin 11.
Subsequently, as illustrated in
The material of the solder bump 16 is not particularly limited. However, the solder having lower melting point than that of the solder 4 is mechanically fragile, and thus the connection strength between the semiconductor element 17 and the wiring 10 would be reduced when such a solder of low melting point is used as the solder bump 16.
In order to enhance the connection strength between the semiconductor element 17 and the wiring 10, it is preferable to use the solder having the melting point equal to or higher than that of the solder 4 for the material of the solder bump 16. In view of this, Sn-3Ag-0.5Cu, which is the same material having the same melting point (about 220° C.) as that of the solder 4, is used for the material of the solder bump 16.
Then, the solder bump 16 is subjected to reflow under heating at a temperature of about 220° C. so as to connect the semiconductor element 17 to the wiring 10 with the solder bump 16.
In this reflow, solder 4 having the same melting point of that of the solder bump 16 melts, and the resin 11 around the solder 4 thermally expands. Thus, the solder 4 is subjected to the pressure generated by the resin 11 around the solder 4. In the present embodiment, however, the melted solder 4 escapes into the hole 1a, and hence the melted solder 4 does not spreads in the lateral direction. As a result, the solder flash, in which the conductive pads 2 adjacent to each other in the lateral direction are electrically short-circuited via the solder 4, can be suppressed.
Moreover, since the insulating base member 1, which has a low solder wettability, is exposed on the side surface of the hole 1a, the hole 1a can be prevented from being filled with the solder 4 before this process, which allows the solder to escape into the hole 1a in the process.
By these steps, the basic structure of the substrate 25 with embedded components completes.
According to the present embodiment, since the melted solder 4 can escape into the hole 1a, solder flash can be suppressed.
Although the number of the holes 1a provided in the single conductive pad 2 is one in this example, a plurality of the holes 1a may be provided in the single conductive pad 2 to increase the amount of the solder 4 escaping into the hole 1a.
Next, explanation is given for the preferable positions of the hole 1a that effectively suppress the solder flash.
Unlike the example in
The component 3 and the solder 4 are not present at the part of the hole 1a located outside the conductive pad 2. Therefore, when the resin 11 is pressurized in the process of
On the other hand, in the present embodiment, all portions of the hole 1a is positioned inside the conductive pad 2 as illustrated in
The inventor further investigated the diameter of the hole 1a which can effectively suppress the solder flash.
In this investigation, the thermal expansion amounts of the solder 4 and the resin 11 was calculated.
In this model, the thickness of the insulating base member 1 is set as T, and the diameter of the hole 1a is set as D. Also, the height of the component 3 is set as Z, and the length of the component 3 is set as Y.
The size of the component 3 is represented by YxZ as a combination of the length Y and the height Z. Here, four types of the dimension YxZ were used, namely, 0.6 mm×0.3 mm, 1.0 mm×0.5 mm, 1.6 mm×0.8 mm, and 2.0 mm×1.2 mm.
Here, the thermal expansion rate of the solder 4 was set 21 ppm/° C., and the thermal expansion amount of the resin 11 was set 60 ppm/° C.
Then, the sum (ΔVs+ΔVr) of (1) the thermal expansion amount ΔVs of the solder 4 and (2) the thermal expansion amount ΔVr of the resin 11 is equal to (3) the amount ΔVh of the solder 4 entering the hole 1a.
Note that, for reference,
On the other hand,
Here, when the volume V of the hole 1a is smaller than the amount ΔVh (see
In order to prevent this problem, the volume V of the hole 1a is preferably set to be equal to or larger than the amount ΔVh (ΔVh≦V) to prevent the hole 1a from being fully filled with the solder 4.
According to
In contrast, when the diameter D is too large, the area of the portion of the conductive pad 2 which is connected to the solder 4 becomes small, which results in a reduction in the connection strength between the conductive pad 2 and the component 3. In order to prevent this reduction in the connection strength, the diameter D is preferably set to be equal to or smaller than 0.3 mm. As for an area ratio of the hole 1a and the conductive pad 2, such a reduction in the connection strength can be prevented by setting the area Sh of the hole 1a to be equal to or smaller than 20% of the area Sc of the conductive pad 2.
In the present embodiment, wiring is densely formed in a substrate with embedded component as described below.
First, as illustrated in
In the present embodiment, the hole 1a is formed in the conductive pad 2 at this patterning.
Subsequently, as illustrated in
As the insulating layer 9, a resin sheet of epoxy resin having a thickness of about 0.06 mm to 0.2 mm can be used, for example.
Then, as illustrated in
The power of the laser is set enough to evaporate the insulating base member 1 made of resin, and is insufficient to evaporate the conductive pattern 2a. Thus, the conductive pattern 2a is not opened in this process, and hence the structure in which the hole 1a is closed by the conductive pattern 2a is obtained.
Subsequently, as illustrated in
Thereafter, the processes illustrated in
According to the present embodiment described above, the conductive pattern 2a closes the hole 1a as illustrated in
All examples and conditional language recited herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2015-091189 | Apr 2015 | JP | national |
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Number | Date | Country | |
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20160324005 A1 | Nov 2016 | US |