CA1191178A - Fuse for thick film device - Google Patents
Fuse for thick film deviceInfo
- Publication number
- CA1191178A CA1191178A CA000441886A CA441886A CA1191178A CA 1191178 A CA1191178 A CA 1191178A CA 000441886 A CA000441886 A CA 000441886A CA 441886 A CA441886 A CA 441886A CA 1191178 A CA1191178 A CA 1191178A
- Authority
- CA
- Canada
- Prior art keywords
- fuse
- fusible link
- substrate
- terminal block
- solder
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
- H01H85/02—Details
- H01H85/04—Fuses, i.e. expendable parts of the protective device, e.g. cartridges
- H01H85/041—Fuses, i.e. expendable parts of the protective device, e.g. cartridges characterised by the type
- H01H85/046—Fuses formed as printed circuits
Landscapes
- Fuses (AREA)
Abstract
FUSE FOR THICK FILM DEVICE
Abstract of the Disclosure:
A fuse is disclosed for protecting thick film devices. The fuse comprises two blocks of material mounted to the substrate that carries the thick film device. The blocks are mounted in close proximity to one another, in axial alignment, but in a spaced apart relationship.
An electrically conductive fusible link (e.g. solder) straddles the two blocks so as to complete an electric circuit.
- i -
Abstract of the Disclosure:
A fuse is disclosed for protecting thick film devices. The fuse comprises two blocks of material mounted to the substrate that carries the thick film device. The blocks are mounted in close proximity to one another, in axial alignment, but in a spaced apart relationship.
An electrically conductive fusible link (e.g. solder) straddles the two blocks so as to complete an electric circuit.
- i -
Description
Backgrouncl oF the Invention This inven~ion relates generally to fuses, and more particularly to a fuse arrangement for thick Film circui-ts.
Thick film resistors are well known and are commonly formed by applying a paste of a resistive material onto an insulating substrate;
the applied resistive material is then dried and hardened by the application of heat. The magnitude of the resistance of such a resistor depends upon the thickness oF the resistive material, the composition of the material, and upon the extent of the area of the substrate covered with the resistive material.
One application of thick film resistors is as battery feed resistors in battery feed circuits for telephones. In such an app1ication a source of power (e.g. a battery) is connected to a balanced two-wire subscriber telephone line (sometimes reFerred to as a loop) via two battery feed resistors in order to provide current to the line. The two battery feed resistors should be closely matched to each other in order to maintain the balance oF the line, and are preferably small in physical size. The battery feed resistors should also be able to limit current on extremely short loops -to saFe values; at the same time they must be capable of carrying large currents thdt may arise from fault conditions (e.g. current surges due to lightning).
The following U,S. patents depict various thick Film resistors and attention is directed -to them: U.S. patent 3,573,703 dated April 69 1971 by D.P. Burks et al; U.S. patent 3,787,965 dated January 29, 1974 by T~Fo Cocca et al; and U.S~ patent 4,293,839 dated October 6, 1981 by E. Asada et al.
It can be seen that the above-mentioned patents are silent on the issue of fusing. U.S. patent 4,197,521 dated April 89 1980 by 3~
RoM. Rovnyak -is d-irecte(l to the issue oF fusing a resistor used in a telephone line circuit. In fact, that patent is directed -to making the resistor itselF be a fusible element, and does not describe a separate and discrete fuse.
Summary of the Invention:
The present inven-tion relates to a fuse particularly suited for mounting on the substrate of a thick film device, such as a substrate supporting a thick film resistor. The fuse is of course connected in series to the resistor and is designed -to rupture, thereby opening the electrical circuit, before darmage occurs to the resistor.
Two solder pads are provided on the substrate for mounting the fuse. The fuse itself comprises two blocks of material, one soldered to each solder pad, and a fusible link joining the two blocks. The fusible link is tubular in shape and protrudes into a mating hole in each block. The mating hole is a little larger than necessary to accept the fusible link; the purpose of this is to allow molten material from the fusible link to move into the hole (due to capillary action) when the fusible link melts due to excessive heat.
Stated in other terms, the present invention is a fuse for mounting on a substrate to protect a thick film device, also mounted on the substrate and connected electrically in series with the fuse, the fuse characterized by: two terminal block means, mounted to electrodes carried by the substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship; and an electrically conductive fusible link means straddling the two terminal block means so as to complete an electric circuit.
Brief Description of the ~ra ngs The invention will now be describe(l in more detail ~lith re-Ference -to the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference character~ and wherein:
Figure 1 is a plan view of a thick film device depicting a fuse constructed according to the present invention;
Figure 2 is a perspective view of the fuse from Figure l;
and Figure 3 is a sectional view of the fuse taken along the section line 3-3 of Figure 1.
Figure 1 depicts a thick fi'lm resistor 10 and a fuse 11.
Resistor 10 comprises a 'layer 12 oF resistive material deposited on the top face of a solid rectangular ceramic substrate 13. Electrodes 16 and 17 provide electrical connections to opposite ends of layer 12.
Electrode 16 serves as a terminal electrode For resistor lO, and electrode 17 provides an electrical connection from the other end of resistor 10 to terminal 18 of fuse 11.
Fusible link 21 provides an electrical connection between terminal blocks 18 and 19 of fuse 11, and terminal block 19 connects to electrode 22. In shortg the elec-trical path through the combination of resistor 10 and fuse 11 is as follows: electrode 16, layer 12 of resistive material, electrode 17, terminal block 18, fusible link 21, terminal block 19, and electrode 22; or vice-versa.
Figure 2 depicts a perspective view of fuse 11 by itself.
From Figure 2 it can be seen that terminal b'locks 18 and 19 are .'7~
rectangular in cross-section, and a ho'le extends lonyitudinal'ly throu(Jh -them for their complete length. Fusible link 21 extends between blocks 18 and 19 and extends through the holes in blocks 18 and 19 as can be seen in Figure 3. Blocks 18 and 19, in the exemplary embodiment, are each approximately 1/8 inch long and are spaced apart by approximately 1/16 inch.
Figure 3 depicts a cross-section of fuse 11 taken along -the section line 3-3 of Figure 1. It can be seen that there is a hole 23 that extends the full lenyth of terminal block 18 and a ho'le 24 that extends the full length of terminal block 19. Fusible link 21 extends between blocks 18 and 19 and also extends the full length of holes 23 and 24 as depicted.
Note tha-t blocks 18 and 19 are made of a material that is a good conductor of both heat and electricity, such as copper. Note also tha-t blocks 18 and 19 are coated on their end surfaces and the inside surface of holes 23 and 24, with a layer 26 of a relatively low me'lting point (e.g. 232C) solder. Layer 26 is preferably applied by an electrolysis process. Note also that fusible link 21 is preferably a length of flux-core solder wi-th a melting point (e.g. 301C) higher than 20 that of layer 26.
Note also that holes 23 and 24 are somewhat larger in diameter than is necessary to accept fusible link 21. The reason for this is to provide for a "capillary" effect when link 21 melts, thereby causing the link 21 which is in a liquid state to enter into holes 23 and 24 and to thereby minimi~e the escape of any of the material forming link 21.
To assemble fuse 11, the blocks 18 and 19 are aligned and the fusible link is inserted between and through the two blocks~ The .'7~
assembly is then heated to a temperature higher tharl -that of the meltirlg point of layer 26 (but lower tharl the meltirlg point of fusible link 21).
It is then allowed to cool to ambient temperatures. The assembly can then be soldered onto electrodes carried by substra-te 13 (Figure 1). In the preferred embodirnen-t this soldering is carried out with the use of a solder flux paste (95% tin, 5% silver), having a melting point of approximately 232C., applied to the electrodes.
~ In normal operation~ the temperature oF the resistor and - fuse assembly will rise. If the temperature rises too much (due either to electrical load, or ambient conditions, or both), then solder layer 26 becomes molten. If the temperature continues to rise, fusible link 21 will also become molten. ~hen link 21 becomes molten, the liquid material from link 21, is absorbed into holes 23 and 24 due to capillary action.
Note that in the preferred embodiment holes 23 and 2~ are approximately 0~03~ inches in diameter and fusible link 21 is a piece oF
Flux-core solder (with 5 -flux conduits) approximately 0. 350 i nches long, 0.02~ inches in diameter and is comprised of 93.5% l ead, 5.0% ti n, and 1.5% silver and melts at approximately 301C. Layer 26 is comprised of 100% tin and melts at approxirnately 232C.
Thick film resistors are well known and are commonly formed by applying a paste of a resistive material onto an insulating substrate;
the applied resistive material is then dried and hardened by the application of heat. The magnitude of the resistance of such a resistor depends upon the thickness oF the resistive material, the composition of the material, and upon the extent of the area of the substrate covered with the resistive material.
One application of thick film resistors is as battery feed resistors in battery feed circuits for telephones. In such an app1ication a source of power (e.g. a battery) is connected to a balanced two-wire subscriber telephone line (sometimes reFerred to as a loop) via two battery feed resistors in order to provide current to the line. The two battery feed resistors should be closely matched to each other in order to maintain the balance oF the line, and are preferably small in physical size. The battery feed resistors should also be able to limit current on extremely short loops -to saFe values; at the same time they must be capable of carrying large currents thdt may arise from fault conditions (e.g. current surges due to lightning).
The following U,S. patents depict various thick Film resistors and attention is directed -to them: U.S. patent 3,573,703 dated April 69 1971 by D.P. Burks et al; U.S. patent 3,787,965 dated January 29, 1974 by T~Fo Cocca et al; and U.S~ patent 4,293,839 dated October 6, 1981 by E. Asada et al.
It can be seen that the above-mentioned patents are silent on the issue of fusing. U.S. patent 4,197,521 dated April 89 1980 by 3~
RoM. Rovnyak -is d-irecte(l to the issue oF fusing a resistor used in a telephone line circuit. In fact, that patent is directed -to making the resistor itselF be a fusible element, and does not describe a separate and discrete fuse.
Summary of the Invention:
The present inven-tion relates to a fuse particularly suited for mounting on the substrate of a thick film device, such as a substrate supporting a thick film resistor. The fuse is of course connected in series to the resistor and is designed -to rupture, thereby opening the electrical circuit, before darmage occurs to the resistor.
Two solder pads are provided on the substrate for mounting the fuse. The fuse itself comprises two blocks of material, one soldered to each solder pad, and a fusible link joining the two blocks. The fusible link is tubular in shape and protrudes into a mating hole in each block. The mating hole is a little larger than necessary to accept the fusible link; the purpose of this is to allow molten material from the fusible link to move into the hole (due to capillary action) when the fusible link melts due to excessive heat.
Stated in other terms, the present invention is a fuse for mounting on a substrate to protect a thick film device, also mounted on the substrate and connected electrically in series with the fuse, the fuse characterized by: two terminal block means, mounted to electrodes carried by the substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship; and an electrically conductive fusible link means straddling the two terminal block means so as to complete an electric circuit.
Brief Description of the ~ra ngs The invention will now be describe(l in more detail ~lith re-Ference -to the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference character~ and wherein:
Figure 1 is a plan view of a thick film device depicting a fuse constructed according to the present invention;
Figure 2 is a perspective view of the fuse from Figure l;
and Figure 3 is a sectional view of the fuse taken along the section line 3-3 of Figure 1.
Figure 1 depicts a thick fi'lm resistor 10 and a fuse 11.
Resistor 10 comprises a 'layer 12 oF resistive material deposited on the top face of a solid rectangular ceramic substrate 13. Electrodes 16 and 17 provide electrical connections to opposite ends of layer 12.
Electrode 16 serves as a terminal electrode For resistor lO, and electrode 17 provides an electrical connection from the other end of resistor 10 to terminal 18 of fuse 11.
Fusible link 21 provides an electrical connection between terminal blocks 18 and 19 of fuse 11, and terminal block 19 connects to electrode 22. In shortg the elec-trical path through the combination of resistor 10 and fuse 11 is as follows: electrode 16, layer 12 of resistive material, electrode 17, terminal block 18, fusible link 21, terminal block 19, and electrode 22; or vice-versa.
Figure 2 depicts a perspective view of fuse 11 by itself.
From Figure 2 it can be seen that terminal b'locks 18 and 19 are .'7~
rectangular in cross-section, and a ho'le extends lonyitudinal'ly throu(Jh -them for their complete length. Fusible link 21 extends between blocks 18 and 19 and extends through the holes in blocks 18 and 19 as can be seen in Figure 3. Blocks 18 and 19, in the exemplary embodiment, are each approximately 1/8 inch long and are spaced apart by approximately 1/16 inch.
Figure 3 depicts a cross-section of fuse 11 taken along -the section line 3-3 of Figure 1. It can be seen that there is a hole 23 that extends the full lenyth of terminal block 18 and a ho'le 24 that extends the full length of terminal block 19. Fusible link 21 extends between blocks 18 and 19 and also extends the full length of holes 23 and 24 as depicted.
Note tha-t blocks 18 and 19 are made of a material that is a good conductor of both heat and electricity, such as copper. Note also tha-t blocks 18 and 19 are coated on their end surfaces and the inside surface of holes 23 and 24, with a layer 26 of a relatively low me'lting point (e.g. 232C) solder. Layer 26 is preferably applied by an electrolysis process. Note also that fusible link 21 is preferably a length of flux-core solder wi-th a melting point (e.g. 301C) higher than 20 that of layer 26.
Note also that holes 23 and 24 are somewhat larger in diameter than is necessary to accept fusible link 21. The reason for this is to provide for a "capillary" effect when link 21 melts, thereby causing the link 21 which is in a liquid state to enter into holes 23 and 24 and to thereby minimi~e the escape of any of the material forming link 21.
To assemble fuse 11, the blocks 18 and 19 are aligned and the fusible link is inserted between and through the two blocks~ The .'7~
assembly is then heated to a temperature higher tharl -that of the meltirlg point of layer 26 (but lower tharl the meltirlg point of fusible link 21).
It is then allowed to cool to ambient temperatures. The assembly can then be soldered onto electrodes carried by substra-te 13 (Figure 1). In the preferred embodirnen-t this soldering is carried out with the use of a solder flux paste (95% tin, 5% silver), having a melting point of approximately 232C., applied to the electrodes.
~ In normal operation~ the temperature oF the resistor and - fuse assembly will rise. If the temperature rises too much (due either to electrical load, or ambient conditions, or both), then solder layer 26 becomes molten. If the temperature continues to rise, fusible link 21 will also become molten. ~hen link 21 becomes molten, the liquid material from link 21, is absorbed into holes 23 and 24 due to capillary action.
Note that in the preferred embodiment holes 23 and 2~ are approximately 0~03~ inches in diameter and fusible link 21 is a piece oF
Flux-core solder (with 5 -flux conduits) approximately 0. 350 i nches long, 0.02~ inches in diameter and is comprised of 93.5% l ead, 5.0% ti n, and 1.5% silver and melts at approximately 301C. Layer 26 is comprised of 100% tin and melts at approxirnately 232C.
Claims (10)
1. A fuse for mounting on a substrate to protect a thick film device, also mounted on said substrate and connected electrically in series with said fuse, said fuse characterized by:
two terminal block means, mounted to electrodes carried by said substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship; and an electrically conductive fusible link means protruding into respective mating holes in each of said two terminal block means so as to complete an electric circuit whereby said mating holes are larger than necessary to accept said fusible link, so as to allow molten material from the fusible link to move into said mating holes due to capillary action when said fusible link melts due to excessive heat.
two terminal block means, mounted to electrodes carried by said substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship; and an electrically conductive fusible link means protruding into respective mating holes in each of said two terminal block means so as to complete an electric circuit whereby said mating holes are larger than necessary to accept said fusible link, so as to allow molten material from the fusible link to move into said mating holes due to capillary action when said fusible link melts due to excessive heat.
2. The fuse of claim 1 wherein said thick film device is a resistor.
3. The fuse of claim 2 wherein said fusible link is comprised of solder.
4. The fuse of claim 2 wherein said fusible link is a piece of flux-core solder.
5. The fuse of claim 3 wherein said two terminal block means are each rectangular parallelepipeds.
6. A fuse for mounting on a substrate in order to protect a thick film resistor, also mounted on said substrate and connected electrically in series with said fuse, from overheating, said fuse characterized by:
two terminal block means, mounted to electrodes carried by said substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship, and having holes extending therethrough; and an electrically conductive fusible link means interconnecting said two terminal block means so as to complete an electric circuit, whereby said fusible link means melts under a condition of elevated temperature and molten material from said fusible link means is drawn into said holes in said terminal block means by capillary action thereby breaking said electric circuit.
two terminal block means, mounted to electrodes carried by said substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship, and having holes extending therethrough; and an electrically conductive fusible link means interconnecting said two terminal block means so as to complete an electric circuit, whereby said fusible link means melts under a condition of elevated temperature and molten material from said fusible link means is drawn into said holes in said terminal block means by capillary action thereby breaking said electric circuit.
7. The fuse of claim 6 wherein said fusible link means is connected to said two terminal block means with a solder having a lower melting point than the melting point of said fusible link.
8. The fuse of claim 7 wherein said fusible link means is a piece of solder.
9. An insulating substrate having a layer of resistive material deposited on at least one face thereof, to form a resistor, and a fuse fixed to said substrate, said fuse and said resistor connected in a series electrical arrangement, said fuse characterized by:
two terminal blocks, fixed to said substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship, and having holes extending therethrough; and an electrically conductive fusible link means interconnecting said two terminal blocks so as to complete an electric circuit, whereby said fusible link means melts under a condition of elevated temperature and molten material from said fusible link means is drawn into said holes in said terminal block means by capillary action thereby breaking said electric circuit.
two terminal blocks, fixed to said substrate, in close proximity to one another, in axial alignment, but in a spaced apart relationship, and having holes extending therethrough; and an electrically conductive fusible link means interconnecting said two terminal blocks so as to complete an electric circuit, whereby said fusible link means melts under a condition of elevated temperature and molten material from said fusible link means is drawn into said holes in said terminal block means by capillary action thereby breaking said electric circuit.
10. The fuse of claim 9 further characterized by:
said terminal blocks being in the shape of rectangular parallelepipeds, and said fusible link being soldered to said terminal blocks with solder having a melting point lower than the melting point of said fusible link.
said terminal blocks being in the shape of rectangular parallelepipeds, and said fusible link being soldered to said terminal blocks with solder having a melting point lower than the melting point of said fusible link.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000441886A CA1191178A (en) | 1983-11-24 | 1983-11-24 | Fuse for thick film device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000441886A CA1191178A (en) | 1983-11-24 | 1983-11-24 | Fuse for thick film device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191178A true CA1191178A (en) | 1985-07-30 |
Family
ID=4126592
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000441886A Expired CA1191178A (en) | 1983-11-24 | 1983-11-24 | Fuse for thick film device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1191178A (en) |
-
1983
- 1983-11-24 CA CA000441886A patent/CA1191178A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |