Patent Application
20200137883
The present invention relates to a thin film capacitor and a circuit board incorporating the thin film capacitor and, more particularly, to a thin film capacitor capable of being embedded in a circuit board and used and a circuit board incorporating the thin film capacitor.
In general, a decoupling capacitor is mounted on a circuit board on which an IC is mounted for stabilizing the potential of a power supply to be fed to the IC. A laminated ceramic chip capacitor is generally used as the decoupling capacitor, and a required decoupling capacitance is ensured by mounting many laminated ceramic chip capacitors on the surface of a circuit board.
However, in recent years, it is often the case that a space on a circuit board for mounting many laminated ceramic chip capacitors is insufficient. Thus, there has been proposed a method of using a thin film capacitor in place of the laminated ceramic chip capacitor and embedding the thin film capacitor in the circuit board (see JP 2005-191559 A).
In order to enable the thin film capacitor to be embedded in the circuit board, it is necessary to reduce the overall thickness of the thin film capacitor as much as possible. However, when the thin film capacitor is reduced in thickness, it may be easily warped. To prevent the warpage of the thin film capacitor, the thicknesses and materials of metal films formed on the front and back sides of a capacitive insulating film are made the same as each other; however, it is not realistic to make the thicknesses and materials thereof the same as each other.
It is therefore an object of the present invention to provide a thin film capacitor whose warpage can be suppressed without making the thicknesses or materials of metal films formed on the front and back sides of a capacitive insulating film the same as each other and a circuit board incorporating the thin film capacitor.
A thin film capacitor according to the present invention includes a capacitive insulating film, a first metal film formed on one surface of the capacitive insulating film, and a second metal film formed on the other surface of the capacitive insulating film and made of a metal material different from that of the first metal film and has an opening penetrating the capacitive insulating film, first metal film, and second metal film. The second metal film is thicker than the first metal film. Assuming that the size of a part of the opening that penetrates the first metal film is a first size and that the size of a part of the opening that penetrates the second metal film is a second size, the first size is larger than the second size.
Further, a circuit board according to the present invention is a circuit board in which the above thin film capacitor is embedded and includes a via conductor that passes through the opening without contacting the first and second metal films.
According to the present invention, since the opening that penetrates the capacitive insulating film, first metal film and second metal film is formed, stress due to a difference in thickness or metal material between the first and second metal films is released through the opening. In addition, the second metal film is made thicker than the first metal film, and the first size is made larger than the second size, so that rigidity is ensured by the thicker second metal film, thereby significantly suppressing warpage. Thus, warpage of the thin film capacitor that may occur when it is embedded in the circuit board can be minimized.
In the thin film capacitor according to the present invention, the opening may comprise a plurality of openings, and assuming that an area where the capacitive insulating film is sandwiched between the first and second metal films in a plan view is a capacitive area and that an area where the capacitive insulating film is not present and an area where the capacitive insulating film is not sandwiched between the first and second metal films in a plan view is a non-capacitive area, the ratio of the capacitive area to the sum of the capacitive area and non-capacitive area may be set to 80% or less. This allows further suppression of warpage that may occur in the thin film capacitor.
In the present invention, assuming that the size of a part of the opening that penetrates the capacitive insulating film is a third size, the third size may be smaller than the first size. In addition, assuming that the size of a part of the opening that penetrates the second metal film at the boundary of the capacitive insulating film is a fourth size, the third size may be smaller than the fourth size. This increases the creepage distance between the first and second metal films inside the opening, thereby making it possible to improve withstand voltage.
In the present invention, the opening may be filled with an insulating material. This can improve product reliability.
As described above, according to the present invention, there can be provided a thin film capacitor whose warpage can be suppressed without making the thicknesses or materials of metal films formed on the front and back sides of a capacitive insulating film the same as each other and a circuit board incorporating the thin film capacitor.
The above and other objects, features and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein:
Preferred embodiments of the present invention will now be explained in detail with reference to the drawings.
As illustrated in
In the present embodiment, assuming that the thicknesses of the metal film 20, metal film 30 and capacitive insulating film 10 are set to T1, T2 and T3, respectively, the following relationship is satisfied:
T2>T1>T3.
T1 is in the range of 5 μm to 20 μm and set to, e.g., about 10 μm, and T2 is in the range of 8 μm to 50 μm and set to, e.g., about 15 μm. T3 is set to about 3 μm.
As described above, the overall thickness of the thin film capacitor 1 according to the present embodiment is very small. In addition, the metal films 20 and 30 formed on the front and back sides of the capacitive insulating film 10 differ from each other in terms of thickness and material. Thus, the capacitive insulating film 10 is very easily warped if no measure is taken. However, in the present embodiment, such warpage stress is partially released through an opening 40 formed so as to penetrate the capacitive insulating film 10 and the metal films 20 and 30. As illustrated in
The higher the formation density of the openings 40 is, the more stress is released to reduce warpage, but a capacitance value to be obtained is reduced. The following configuration is preferable in order to sufficiently reduce the warpage of the thin film capacitor 1. That is, assuming that an area that functions as a capacitor, i.e., an area where the capacitive insulating film 10 is sandwiched between the metal films 20 and 30 in a plan view is a capacitive area C1 and that an area that does not function as a capacitor, i.e., an area where the capacitive insulating film 10 is not present and an area where the capacitive insulating film 10 is not sandwiched between the metal films 20 and 30 in a plan view is a non-capacitive area C2, the ratio (C1/(C1+C2)) of the capacitive area C1 to the sum of the capacitive area C1 and non-capacitive area C2 is preferably set to 80% or less. However, in this case, a capacitance value is reduced by 20% or more as compared to the instance where the openings 40 are not formed.
Further, in the present embodiment, assuming that the sizes of a part of each opening 40 that penetrates the metal film 20, a part of each opening 40 that penetrates the metal film 30 and a part of each opening 40 that penetrates the capacitive insulating film 10 are ϕ1, ϕ2 and ϕ3, respectively, the following relationship is satisfied:
ϕ1>ϕ3>ϕ2.
In addition, assuming that the size of a part of each opening 40 that penetrates the metal film 30 at the boundary of the capacitive insulating film 10 is ϕ2a, the following relationship is satisfied:
ϕ1>ϕ2a>ϕ3.
When the opening 40 has an elongated shape in a plan view as illustrated in
As described above, in the thin film capacitor 1 according to the present embodiment, the size ϕ2 of the opening 40 in the metal film 30 having a larger thickness is smaller than the size ϕ1 of the opening 40 in the metal film 20 having a smaller thickness, so that rigidity is ensured by the thicker metal film 30 to thereby suppress the warpage of the thin film capacitor 1. In addition, in the present embodiment, the size ϕ3 of the opening 40 in the capacitive insulating film 10 is smaller than the sizes ϕ1 and ϕ2, causing the capacitive insulating film 10 to protrude to the inside of the opening 40 as illustrated in
The circuit board 100 illustrated in
In the thus configured circuit board 100, the thin film capacitor 1 according to the present embodiment is embedded between the wiring layers L5 and L6. As illustrated in
The bump electrode BS for transmitting/receiving a signal is connected to the wiring layer L5 in a lower layer through a via conductor 130 passing through the opening 40. As described above, the thin film capacitor 1 according to the present embodiment has the plurality of openings 40, so that it is possible to connect the bump electrode BS to a conductor pattern in a lower layer at the shortest distance without signal wire routing by thus providing the via conductor 130 passing through the opening 40 without contacting the metal films 20 and 30.
However, not all the via conductors that pass through the opening 40 need to be signal wiring, but some via conductors may be power supply wiring or ground wiring.
As described above, the thin film capacitor 1 according to the present embodiment has the plurality of openings 40, allowing the via conductor that passes through each of the openings 40 to be provided in the circuit board 100.
The following describes a manufacturing method for the thin film capacitor 1 according to the present embodiment.
First, as illustrated in
Then, as illustrated in
Then, as illustrated in
Then, as illustrated in
Then, as illustrated in
After the support panel S2 is peeled off, dicing is performed in predetermined locations, whereby the thin film capacitor 1 illustrated in
As described above, in the present embodiment, the metal film 30 is patterned so as to make the size ϕ2 smaller than the size ϕ1, allowing the rigidity of the metal film 30 to be ensured. In addition, the metal film 30 is overetched when the metal film 20 is patterned, allowing the capacitive insulating film 10 to protrude to the inside of the opening 40. As a result, the creepage distance between the metal films 20 and 30 inside the opening 40 is increased, thereby preventing deterioration in withstand voltage.
As illustrated in
The following describes a manufacturing method for the thin film capacitor 2 according to the present embodiment.
First, the processes illustrated in
Then, as illustrated in
Then, as illustrated in
As described above, in the thin film capacitor 2 according to the second embodiment, the inside of the opening is filled with the insulating resin 50, allowing improvement in product reliability in a shipping state before embedding in the circuit board.
As illustrated in
Even with such a configuration, it is possible to suppress warpage as in the thin film capacitor 1 according to the present embodiment. Further, the capacitive insulating film 10 protrudes to the inside of the opening 40, so that it is possible to prevent deterioration in withstand voltage.
The following describes a manufacturing method for the thin film capacitor 3 according to the present embodiment.
First, the processes illustrated in
Then, as illustrated in
Then, as illustrated in
As exemplified in the present embodiment, the metal films 20 and 30 may be patterned from the same direction in the present invention.
As illustrated in
As exemplified in the present embodiment, the capacitive insulating film 10 need not protrude from both the metal films 20 and 30 inside the opening 40.
It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.
A 15×15 mm thin film capacitor having the same configuration as the thin film capacitor 1 illustrated in
The results are illustrated in Table 1. The capacitance (%) shown in Table 1 is represented by a percentage when the capacitance in Sample 1 having no opening 40 is set as 100.
As shown in Table 1, the warpage amount in Sample 1 having no opening 40 is 55 μm. On the other hand, in Samples 4 to 7, 9 to 11, 15 to 20, and 23 to 25, in which both T1<T2 and ϕ1>ϕ2 are satisfied, the warpage amount is less than 20 μm and, thus, it is confirmed that the warpage is significantly suppressed. In Samples 2, 3, 8, 12 to 14, 21, and 22 in which the above conditions are not satisfied, the warpage amount is 30 μm or more. That is, the warpage cannot be sufficiently suppressed although many openings 40 are formed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-202468 | Oct 2018 | JP | national |
| 2019-187615 | Oct 2019 | JP | national |
