Patent Grant
9035740
The present invention relates to a circuit protecting element which is used in a variety of electronic devices and blown out by an over-current for protecting the devices.
Base layer 3 of the foregoing conventional circuit protecting element; however, is made of epoxy resin having a low heat resistance, so that its shape becomes unstable due to the heat produced by a laser beam with which trimming grooves are formed on element 4. This unstable shape of base layer 3 sometimes causes the shape of element 4 to be unstable, which invites dispersion in the blowout characteristics of the circuit protecting element.
Patent Document 1: Unexamined Japanese Patent Application Publication No. H05-225892
The present invention addresses the problem discussed above, and aims to provide a circuit protecting element of which blowout characteristics are stable. The circuit protecting element of the present invention comprises the following structural elements:
wherein the base layer is formed of a mixture of diatom earth and silicone resin.
Since the diatom earth and the silicone resin forming the base layer are excellent in the heat resistance, the base layer can be prevented its shape from being unstable caused by the heat produced by a laser beam with which the trimming grooves are formed on the element. As a result, the element becomes stable in its shape, so that the blowout characteristics can be stabilized.
An exemplary embodiment of the present invention is demonstrated hereinafter with reference to the accompanying drawings.
As shown in
To be more specific about the foregoing structure, insulating substrate 11 is shaped like a square, and contains Al2O3 in the range of 55-96%. The pair of surface electrodes 12 is provided to both the ends of the top face of substrate 11, and is formed by printing Ag on the top face. Element 13 is provided on the top faces of surface electrodes 12 and base layer 14 such that element 13 can cover the entire surface of substrate 11.
First element 13a is formed by sputtering Ti, Cu or Cr, CuNi in this order, and second element 13b is formed by electrolytic plating or electroless plating Ni, Cu, Ag in this order onto first element 13a that works as a base for the plating.
At the center of element 13, trimming groove 17 is formed with a laser beam at two places, i.e. from the upper side of element 13 toward the center, and from the lower side toward the center, namely, the grooves are formed along the vertical direction in
As shown in
Blowout section 18 can be covered with the metal, such as Sn, Zn, or Al, having a melting point lower than that of element 13. This preparation allows the metal having the lower melting point to melt faster than other parts, so that element 13 confined within blowout section 18 can be blown out faster. As a result, the circuit protecting element excellent in responsiveness can be obtained.
Base layer 14 is placed in the center of insulating substrate 11, and formed on almost the entire top face of substrate 11 such that both the ends of layer 14 can overlap with the top face of the pair of surface electrodes 12. In this case, at least parts of surface electrodes 12 are exposed. Base layer 14 does not necessarily overlap with the top face of surface electrode 12; however, the caution is preferably paid to element 13 so as not to touch substrate 11. In other words, base element 14 is placed between substrate 11 and element 13 that is located between the pair of surface electrodes 12.
On top of that, base layer 14 is formed of the mixture of diatom earth and silicone resin, and the heat conductivities of these materials are not greater than 0.2 W/m·K, so that the diffusion of the heat from element 13 into substrate 11 can be reduced. As a result, the circuit protecting element excellent in responsiveness can be obtained. Base layer 14 contains diatom earth at a mixed ratio in the range of 50-90 volumetric %, and the more preferable range is 55-70 volumetric %.
The diatom earth is used as one of the materials for wall plate or heat-proof brick, so that it is fire-proof and light-weight soil having an ultra-porous and hyperfine structure. Since the diatom earth is fire-proof, the blowout characteristics can be kept stable although element 13 becomes hot due to an over-current. Since element 13 becomes hot due to the over-current, the resin to be mixed with the diatom earth should be fire-proof. The silicone resin is best suited for this purpose, and epoxy resin and others do not suit to this application because they are inferior to the silicone resin in fire resistance. Both of the diatom earth and the silicone resin are available in ample volume at a low cost, so that the productivity can be improved.
On top of that, the silicone resin forming base layer 14 is colored by mixing a pigment of blue or red except white in approx. 1 wt % with the silicone resin. The insulating substrate including alumina looks, in general, white, so that if element 13 encounters a defect such as a print blur or a fracture, the defect cannot be recognized on the white-looking substrate. However, since this embodiment colors the silicone resin as discussed above, the defect can be recognized and then screened with ease by human eyes or an automatic inspection.
Base layer 14 can be formed not only in the center but also on almost all of the top face of substrate 11, and then the pair of surface electrodes 12 can be formed on both ends of base layer 14.
Base layer 14 can be formed by mixing silicone resin with alumina powder. In this case, since the silicone resin has the heat conductivity not greater than 0.2 W/m·K, so that the diffusion of the heat from element 13 into substrate 11 can be reduced. As a result, the circuit protecting element excellent in responsiveness can be obtained. Base layer 14 contains the alumina powder at a mixed ratio in the range of 50-80 volumetric %, and the heated alumina powder can tightly bond to alumina or silica contained in substrate 11. On top of that, the silicone resin can strongly adhere to the alumina of substrate 11. Base layer 14 thus adheres to substrate 11 more strongly.
If base layer 14 contains the alumina powder at a mixed ratio over 80 volumetric %, its heat conductivity increases due to the greater amount of the alumina powder, so that element 13 resists increasing its temperature even if an over current flows. As a result, the blowout characteristics of element 13 are degraded, and thixotropy of base element 14 is also degraded, which are not favorable for handling the circuit protecting element. On the other hand, if base layer 14 contains the alumina powder at a mixed ratio less than 50 volumetric %, the content ratio of the resin increases in base layer 14, so that base layer 14 tends to move its location due to the heat or stress when first element 13a is formed by the sputtering. First element 13a is thus subjected to cracks, so that the mixed ratio of the alumina powder at less than 50 volumetric % is not favorable.
The alumina powder to be mixed with silicone resin can be replaced with silica powder, or both of alumina powder and silica powder can be mixed with the silicone resin for forming base layer 14.
Insulating layer 15 covers element 13 and is formed of first insulating layer 15a made of resin such as silicone resin for covering blowout section 18 and second insulating layer 15b made of resin such as epoxy resin and placed on first insulating layer 15a.
Insulating layer 15 in parts (lateral section of layer 15) bulges out of base layer 14 as shown in
Shoulder electrode layer 16 made of silver-based material is formed on both the ends of insulating substrate 11 such that shoulder electrode layer 16 overlaps with element 13 in parts. Electrode layer 16 is coated with a plated film (not shown) on its surface.
A method of manufacturing the circuit protecting element in accordance with the embodiment is demonstrated hereinafter. In
Next, print the conductive paste of palladium silver alloy, of which a main ingredient is silver paste or silver, such that the paste strides across lateral dividing grooves 22b. The paste is then fired for forming multiple surface electrodes 12. A pair of surface electrodes 12 is thus formed on both the ends of the top face of insulating substrate 11 in the chip-like circuit protecting element.
Form dummy electrode 23 shaped like a square frame which surrounds the region where surface electrodes 12 are formed. Dummy electrode 23 is made of the same material as surface electrode 12 and formed by printing at the same time as surface electrode 12 is printed. Dummy electrode 23 is formed of a pair of lateral dummies 23a and a pair of vertical dummies 23b. The pair of lateral dummies 23a is connected to multiple surface electrodes 12. Dummy electrode 23 can be formed before or after the formation of surface electrodes 12.
Next, as shown in
The mixture of diatom earth in base layer 14 in the range of 50-90 volumetric % allows decreasing the difference in heat shrinkage rates between base layer 14 and first element 13a (thin film layer) formed by the sputtering. As a result, first element 13a can be free from cracks produced by the heat during the sputtering, so that the locations of element 13 and base layer 14 can be stabilized, which allows stabilizing the location of trimming grooves 17.
The silicone resin colored in blue allows for the recognition and screening of a defect on element 13 with ease by human eyes or an automatic inspection machine.
On top of that, a rear electrode (not shown) can be formed by printing and firing the paste made of palladium silver alloy, of which major ingredient is silver paste or silver, in order to stabilize the circuit protecting element when the element is mounted to a device.
Then form element 13 on the top faces of base layer 14 and the pair of surface electrodes 12 as shown in
When first element 13a is formed, the sputtering is carried out while sheet-like insulating substrate 21 is heated from the base layer side because the heat is accumulated in base layer 14, which can be thus kept hot so that first element 13a can be formed quickly. When second element 13b is formed by the electrolytic plating, one of dummy electrodes 23 is connected to a power feeder section. This preparation allows second element 13b to be formed with ease. Use of the electroless plating method allows second elements 13b to be formed simultaneously on numbers of chip-like circuit protecting circuits.
Next, as shown in
In this case, as shown in
A method of forming trimming grooves 17 is demonstrated hereinafter, i.e. forming first trimming grooves 25a, 25b for the blowout section and second trimming grooves 26a-26f for the adjustment of resistance value. First, measure a resistance value of element 13 located between a pair of surface electrodes 12. When this resistance value falls within a given range, irradiate element 13 with a laser beam at two places in the center, thereby cutting element 13 for forming a pair of first trimming grooves 25a, 25b along the direction from the lateral face toward the center of elements 13 confronting one another. The region surrounded by the pair of first trimming grooves 25a, 25b forms blowout section 18 which is supposed to blow itself out and cut off the current when an over current flows. These first grooves 25a and 25b are formed such that they overlap each other. The product of the length of the overlapped sections by the space between the overlapped sections of grooves 25a and 25b, i.e. the area (volume) of blowout section 18 will determine the blowout characteristics. Considering this fact, the pair of first trimming grooves 25a and 25b are preferably formed in advance, thereby reducing the possibility of dispersion in the blowout characteristics. Second trimming grooves 26a-26f for adjusting resistance value can be formed thereafter, and then the resistance value can be adjusted.
As discussed above, the resistance value of element 13 is firstly measured, and only when the resistance value falls within the given range, trimming grooves 25a, 25b are formed. The reason of this procedure is this: The area of blowout section 18 depends on the blowout characteristics and the rated current required by the specification, and the area will automatically determine the locations of the first trimming grooves 25a and 25b. The resistance value of element 13 after the formation of grooves 25a, 25b is also determined automatically. In other words, the formation of grooves 25a and 25b should not be carried out while the resistance value is adjusted.
When an initial resistance value of element 13 falls outside the given range, trimming grooves 25a, 25b cannot be formed at given locations, because the blowout characteristics and the rated current required by the specification cannot be satisfied. In this case, as shown in
Next, measure the resistance value of element 13 after the formation of grooves 25a and 25b. Only when the resistance value falls within the given range, irradiate elements 13 on both sides of grooves 25a and 25b with a laser beam, thereby cutting these elements along the direction from the lateral face toward the center of elements 13 confronting each other as shown in
In this case, the second trimming grooves 26a, 26c, 26e for the adjustment of the resistance value are formed on the same side where one of the first trimming grooves 25a for the forming of the blowout section is formed. The second trimming grooves 26b, 26d, 26f for the adjustment of the resistance value are formed on the same side where the other one of the first trimming grooves 25b for the blowout section is formed. To be more specific, on the left side of and closer to the first groove 25a, the second grooves 26b, 26c, 26f are formed in this order. On the right side of and closer to the other first groove 25b, the second grooves 26a, 26d, 26e are formed in this order.
The resistance value of element 13 after the formation of trimming grooves 25a and 25b is measured, and only when the value falls within a given range, the second trimming grooves 26a-26f are formed. The reason of this procedure is this: When the resistance value of element 13 is higher than the given range, the thickness of element 13 becomes thinner, so that the given blowout characteristics cannot be obtained, and it is necessary to exclude such element 13 having a thinner thickness and poor blowout characteristics. When the resistance value of element 13 after the formation of grooves 25a and 25b exceeds the range adjustable with trimming grooves 26a-26f, there is no need to form grooves 26a-26f.
When the resistance value of element 13 after the formation of grooves 25a and 25b falls outside the given range, open-cut groove 27 can be formed as shown in
Space “t1” between the first trimming grooves 25a and 25b is set smaller than length “t2” between each one of grooves 26a-26f and the lateral face confronting each one of grooves 26a-26f, of element 13. On top of that, grooves 26a-26f adjacent to each other are spaced away by space “t3”, and groove 25a is spaced away from groove 26b by space “t3”, and groove 25b is spaced away from groove 26a by also space “t3”, then the space “t1” is set equal to or smaller than space “t3”. The foregoing relation among t1, t2, and t3 allows blowout section 18 surrounded by grooves 25a and 25b to blow themselves out reliably.
In
After the formation of trimming grooves 17 (i.e. first grooves 25a, 25b for forming the blowout section and second grooves 26a-26f for adjusting resistance value), form first insulating layer 15a by using resin such as silicone resin for covering at least blowout section 18. Then form second insulating layer 15b by using, e.g. epoxy resin, on the top face of first insulating layer 15a, thereby forming dual-layered insulating layer 15.
Next, apply resin silver paste onto both the ends of insulating substrate 11 such that the paste overlaps with parts of element 13, and then harden the paste, thereby forming shoulder electrode layer 16, however, layer 16 can be formed through a thin-film process such as sputtering.
Finally, form a plated film (not shown) made of dual layers, i.e. one is a nickel layer and the other is a tin layer, on the top face of shoulder electrode layer 16. The circuit protecting element in accordance with this embodiment can be thus manufactured.
Before the formation of second element 13b, insulating substrate 11 (sheet-like insulating substrate 21) can be pasted with a stop-off sheet (not shown) on its rear face in order to prevent the rear face, in particular, electrodes on the rear face from being plated. This preparation prevents substrate 11 from being conductive on its rear face. In this case, the stop-off sheet can be pasted onto the rear face by using a temperature of the plating solution so that the stop-off sheet can more positively adhere onto the rear face without increasing the number of the manufacturing steps. To be more specific, when second element 13b is formed, dip it into the plating solution, which is heated to a temperature higher than the ordinary temperature (in both the cases of the electroless plating and the electrolytic plating), so that the stop-off sheet is also heated simultaneously. The stop-off sheet is increased its adhesiveness by the heating, so that the use of the higher temperature of the plating solution can eliminate an independent heating device, and yet, the adhesiveness of the stop-off can increase.
The stop-off sheet can be formed of pressure sensitive adhesive formed on a polyvinyl chloride film which works as a supporter. The stop-off sheet can preferably closely adhere to insulating substrate 11, and can be removed with ease.
In the foregoing embodiment, base layer 14 is formed of a mixture of diatom earth and silicone resin both of which are excellent in heat resisting characteristics. This structure prevents the heat due to the laser beam from making base layer 14 unstable in shape, so that element 13 can be stable in its shape, and thus the blowout characteristics can be stabilized.
The silicone resin can enter among the particles of the diatom earth, so that base layer 14 can be fixed strongly onto substrate 11, and atmospheric moisture or the plating solution cannot enter base layer 14, so that the resistance to humidity can be improved.
Since base layer 14 is formed of the mixture of diatom earth in 50-90 volumetric % and silicone resin in 50-10 volumetric %, base layer 14 strongly adheres to insulating substrate 11, and yet the yield rate can be improved.
The study of relations among the mixture ratio of the diatom earth in volumetric %, the adhesive strength between base layer 14 and insulating substrate 11, and the presence of cracks on first element 13a is done through the following procedures, and the study results in the following facts: First, the adhesive strength between layer 14 and insulating substrate 11 is tested this way: Paste up a scotch tape tentatively onto base layer 14 having undergone the printing and the curing processes, then peel off the scotch tape and confirm whether or not base layer 14 is peeled off together with the scotch tape from substrate 11. When base layer 14 is not peeled off, it is determined that base layer 14 strongly adheres to substrate 11. On top of that, form first element 13a on base layer 14 by sputtering Ti and Cu, and observe whether or not a crack happens on first element 13a.
The result of the forgoing test is this: When the mixture ratio of diatom earth is not greater than 90 volumetric %, base layer 14 never peels off substrate 11; however, when the mixture ratio exceeds 90 volumetric %, some base layers 14 peel off substrate 11. When the mixture ratio of diatom earth is not less than 50 volumetric %, no cracks occur on first element 13a; however, when the mixture ratio is less than 50 volumetric %, cracks occur on some elements 13a.
Since the adhesive strength between the silicone resin and the alumina forming substrate 11 is strong, a higher mixture ratio of the silicone resin in the mixture of the diatom earth and the silicone resin, both forming base layer 14, allows the adhesive strength between base layer 14 and substrate 11 to be increased. It means that the higher mixture ratio of the silicone resin can eliminate the step of firing base layer 14 at a temperature over 1000° C., and thus base layer 14 can be bonded to substrate 11 without the firing step.
A higher mixture ratio of the diatom earth in the mixture of the diatom earth and the silicone resin, both forming base layer 14, allows reducing a difference in heat shrinkable properties between element 13a formed by sputtering and base layer 14. First element 13a can be thus free from the cracks due to the difference in the heat shrinkage properties between first element 13a and base layer 14, so that the yield rate can be improved.
Base layer 14 formed of silicone resin, alumina powder, and silica powder allows itself to be stable in shape against the heat produced by the laser beam when trimming grooves 17 are formed by radiating the laser beam, because those materials are excellent both in heat resistant properties and in adhesion properties to insulating substrate 11 which contains alumina. The shape of element 13 can be thus stabilized, so that the blowout characteristics can be also stabilized.
The silicone resin can enter among the particles of the alumina powder and the silica powder, so that base layer 14 can be fixed strongly onto substrate 11, and atmospheric moisture or the plating solution cannot enter base layer 14, so that the resistance to humidity can be improved.
Since base layer 14 strongly adheres to substrate 11, base layer 14 can be bonded to insulating substrate 11 without the step of firing base layer 14 at a temperature over 1000° C., so that the productivity can be improved.
In this embodiment, after first trimming grooves 25a, 25b for forming the blowout section are formed, then second trimming grooves 26a-26f for adjusting resistance value are formed. This procedure allows grooves 25a and 25b to be formed such that those grooves can satisfy the given blowout characteristics before the resistance value of element 13 is adjusted, so that the blowout characteristics can be stabilized.
Since element 13 is made of metal, the formation of trimming grooves 25a and 25b by radiating a laser beam allows blowout section 18 between grooves 25a and 25b to heighten its resistance value, which is an important factor to the blowout characteristics, than a theoretical value because of the heat produced by the laser beam. However, in this embodiment, trimming grooves 26a-26f for adjusting the resistance value are formed after the formation of grooves 25a and 25b, and the resistance value can be adjusted later than the formation of grooves 25a and 25b. The heat thus dissipates with time, so that the resistance value of blowout section 18 approaches the theoretical value. The blowout characteristics thus can be stabilized.
The resistance value is adjusted with multiple trimming grooves 25a, 25b, and 26a-26f, so that the resistance value can be stabilized.
According to the foregoing method of manufacturing the circuit protecting element in accordance with the embodiment, three of the second trimming grooves for adjusting the resistance value are formed on the left side of one first trimming groove 25a which is used for forming the blowout section, and another three of the second trimming grooves for adjusting the resistance value are formed on the right side of the other one of the first trimming grooves 25b. However, the number of the grooves for adjusting the resistance value is not always three, and they are not always formed on both sides of grooves 25a and 25b in the same quantity. The formation of them on both sides in the same quantity, however, is preferable because this structure can heighten the temperature of blowout section 18.
The present invention advantageously stabilizes the blowout characteristics, and is useful particularly for a circuit protecting element which blows itself out when an over current flows, thereby protecting a variety of electronic devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-290314 | Nov 2007 | JP | national |
| 2008-008870 | Jan 2008 | JP | national |
| 2008-079619 | Mar 2008 | JP | national |
| 2008-216130 | Aug 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/003203 | 11/6/2008 | WO | 00 | 4/27/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/060607 | 5/14/2009 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4308514 | Kozacka | Dec 1981 | A |
| 4538756 | Trenkler et al. | Sep 1985 | A |
| 4626818 | Hilgers | Dec 1986 | A |
| 5367280 | Thiel et al. | Nov 1994 | A |
| 5399416 | Bujard | Mar 1995 | A |
| 5420560 | Hanada | May 1995 | A |
| 5450055 | Doi | Sep 1995 | A |
| 5572181 | Kiryu et al. | Nov 1996 | A |
| 5614881 | Duggal et al. | Mar 1997 | A |
| 5680092 | Yamada et al. | Oct 1997 | A |
| 5712610 | Takeichi et al. | Jan 1998 | A |
| 5815065 | Hanamura | Sep 1998 | A |
| 5877467 | Arnold et al. | Mar 1999 | A |
| 5907274 | Kimura et al. | May 1999 | A |
| 5917403 | Hashimoto et al. | Jun 1999 | A |
| 5990781 | Kambara | Nov 1999 | A |
| 6040754 | Kawanishi | Mar 2000 | A |
| 6078245 | Fritz et al. | Jun 2000 | A |
| 6087920 | Abramov | Jul 2000 | A |
| 6087921 | Morrison | Jul 2000 | A |
| 6094123 | Roy | Jul 2000 | A |
| 6153256 | Kambara et al. | Nov 2000 | A |
| 6304167 | Nakayama | Oct 2001 | B1 |
| 6388550 | Kanetaka et al. | May 2002 | B1 |
| 6452475 | Kawazu et al. | Sep 2002 | B1 |
| 6492885 | Murata et al. | Dec 2002 | B1 |
| 6535106 | Teramae | Mar 2003 | B2 |
| 6724295 | Tsukada | Apr 2004 | B2 |
| 6771476 | Fukuoka et al. | Aug 2004 | B2 |
| 6806167 | Kuriyama | Oct 2004 | B2 |
| 6864774 | Kanetaka et al. | Mar 2005 | B2 |
| 6867133 | Kanetaka et al. | Mar 2005 | B2 |
| 6982624 | Saito et al. | Jan 2006 | B2 |
| 7057490 | Hashimoto et al. | Jun 2006 | B2 |
| 7089652 | Akhtman et al. | Aug 2006 | B2 |
| 7173510 | Kono et al. | Feb 2007 | B2 |
| 7380333 | Tsukada et al. | Jun 2008 | B2 |
| 7907046 | Tsukada | Mar 2011 | B2 |
| 20010000215 | Oh | Apr 2001 | A1 |
| 20020097547 | Fukuoka et al. | Jul 2002 | A1 |
| 20030079904 | Sato et al. | May 2003 | A1 |
| 20050141164 | Bender et al. | Jun 2005 | A1 |
| 20060199031 | Kistner et al. | Sep 2006 | A1 |
| 20060255897 | Tanaka et al. | Nov 2006 | A1 |
| 20070075822 | Pachla et al. | Apr 2007 | A1 |
| 20080081454 | Sakoh | Apr 2008 | A1 |
| 20080191832 | Tsai | Aug 2008 | A1 |
| 20080303626 | Blum et al. | Dec 2008 | A1 |
| 20090009281 | Wang et al. | Jan 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 1-228101 | Sep 1989 | JP |
| 04-033230 | Feb 1992 | JP |
| 05-121122 | May 1993 | JP |
| 5-225892 | Sep 1993 | JP |
| 07-231061 | Aug 1995 | JP |
| 9-129115 | May 1997 | JP |
| 9-168233 | Jun 1997 | JP |
| 9-246384 | Sep 1997 | JP |
| 11-096886 | Apr 1999 | JP |
| 2000-279311 | Oct 2000 | JP |
| 2001-167909 | Jun 2001 | JP |
| 2001-345039 | Dec 2001 | JP |
| 2002-056767 | Feb 2002 | JP |
| 2002-260447 | Sep 2002 | JP |
| 2003-234057 | Aug 2003 | JP |
| 2004-319168 | Nov 2004 | JP |
| 2006-318896 | Nov 2006 | JP |
| Entry |
|---|
| International Search Report issued Jan. 20, 2009 in International (PCT) Application No. PCT/JP2008/003203. |
| Number | Date | Country | |
|---|---|---|---|
| 20100245028 A1 | Sep 2010 | US |
