JPH0821301B2 - Surface mount thin film fuse and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to electric fuses, and more particularly to a surface mount fuse using thin film technology and a method for manufacturing the same.

[0002]

[Cross-reference of Related Applications] This application was filed on July 2, 1992.
US Application No. 920113, filed on the 4th, "Method o
f Making Thin Film Surface Mount Fuses ”is a continuation-in-part application and a priority claim based on the part-continuation application. US Application No. 920113 was filed on February 28, 1992. US Application No. 84
This is a divisional application of No. 6264 "Thin Film Surface Mount Fuses". U.S. Application No. 846264 was patented as U.S. Patent No. 5,166,656, November 24, 1992.
A patent certificate is issued every day. US Application No. 846264
As a related application, there is a PCT application PCT / US93 / 01915 whose designated country is Japan.

[0003]

2. Description of the Related Art Surface mounting technology is widely used as a technology for assembling circuit boards. Virtually all electronic components have been or are being redesigned leadless for this surface mount application. Surface mount device (S
The rapid adoption of MD) in electronic circuits of all kinds has led to the demand for surface mount (SMD) fuses.

Fuses perform essential functions on many circuit boards. By providing a fuse in a partial circuit or a specific component, it is possible to prevent a local component failure from damaging the entire system. Examples of such damage include damage to the mainframe computer due to a failure of the tantalum capacitor, and damage to the entire telephone exchange due to a short circuit of one line card.

Circuit board fuses are required to have features such as small size, low cost, accurate current detection, quick reaction or blow time, and, in the case of time lag fuses, ability to show surge resistance.

The conventional tube type and lead type fuses occupy a large space on the circuit board designed for the SMD assembly, and the manufacturing cost increases significantly. Manufacturers have recognized the need for fuses that are also applicable to SMD assembly technology and have come to provide leadless molded fuses for standard SMD assemblies. However, even the device provided in this way is still bulky, expensive, and limited in performance, such as a package size of about 7 × 4 × 3 mm.
Most importantly, the prior art does not allow accurate control of fuse characteristics during manufacturing.

For example, using the thin film technology shown in the aforementioned US patents and applications, it is clear that all elements of the fuse can be precisely controlled and economically design standard fuses or custom fuses to meet various requirements. Became. That is, thin film technology has enabled the development of fuses whose electrical and physical properties can be precisely controlled. In particular, the advantages of thin film technology have become clear in the areas of design, reproducibility of fuse characteristics, and I ² t let-through. Moreover, with this thin film technology, line resolution of less than 1 μm and
Management of layer thickness up to 100 angstrom units is realized, so standard SMD with a standard package size of 1.6 x 0.8 mm or non-standard package size, for example.
The fuse can be manufactured.

In the method of manufacturing the surface mount type thin film electric fuse disclosed in the above-mentioned US patents and applications, first, a metal thin film of aluminum having a uniform thickness is deposited on the surface of an insulating substrate such as glass by sputtering or the like. The film thickness is determined in particular by the fuse rating. Next, a predetermined portion of the metal thin film is removed by a photolithography technique to form a repeating pattern including a plurality of specific fuse elements. Each fuse element includes a pair of contact portions and a fusing link that is narrower than the contact portions and connects the contact portions. The composition is then passivated and a glass insulation coating is glued onto the passivation layer with epoxy. Next, the assembly formed by the above process is cut into strip pieces along the end face perpendicular to the substrate surface. Each strip piece includes fuse elements arranged in a row. By this cutting step, the edge of each contact portion along the end surface of the strip piece is exposed. When the conductive terminal layer is deposited on the end face, the terminal layer is electrically connected to the exposed end of the contact portion. Finally, the strip pieces are cut laterally to obtain individual fuses.

By utilizing the manufacturing method by photolithography, various fuse chips can be manufactured by combining various fuse element designs and various kinds of substrates. Moreover, important characteristics such as the fusing rate can be set so as to optimally satisfy the requirements for use. Finally, the sealing structure of the thin film fuse sealed by the sealing glass cover plate provides excellent reliability against environmental changes.

[0010]

There are several problems with the glass / fuse / glass layer structure described in the aforementioned patent application. While glass has the favorable thermal properties required by "quick" rated thin film fuses, it is fragile, limiting the voltage rating of the fuse to, for example, 32 volts. This is because the fuse body is cracked when a high voltage is applied. The mechanical bending strength of the glass / fuse / glass layer structure is limited by the brittleness of the glass, as well as the thermal cycling properties of the structure.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface mount type thin film fuse capable of achieving a higher voltage rating than before while maintaining a "quick" rating.

It is another object of the present invention to provide a surface mount type thin film fuse structure having improved mechanical strength, reliability and heat cycle characteristics.

A further object of the present invention is to provide a method for manufacturing the surface mount type thin film fuse thus improved.

[0014]

In order to achieve the above object, according to the first invention, a step of attaching a metal thin film to the surface of an insulating substrate, and removing a specific portion of the metal thin film,
Forming a fuse element having a pair of contact parts and at least one fusing link narrower than the contact parts and connecting the contact parts; and bonding an insulating coating to the structure obtained by the above steps And a step of adhering a first coating layer made of a material having a mechanical strength higher than that of the insulating substrate and the insulating coating to the back surface of the insulating substrate, and And a step of adhering a second coating layer of a large material.

According to the second aspect of the invention, a substantially rectangular insulating substrate having a flat surface, an end surface orthogonal to the surface, and a flat back surface; and an end surface of the insulating substrate formed on the surface of the insulating substrate by vapor deposition. A conductive thin film forming a fuse element having a pair of contact portions whose outer edges are flush with each other and at least one fusing link which is narrower than the contact portions and connects the contact portions; and an insulating substrate. An insulating coating which is adhered to the surface of the insulating substrate with a similar spread, and which cooperates with the end face of the insulating substrate and the outer edge of the fuse element to form opposing end faces of the surface-mounted fuse, and is larger than the insulating substrate and the insulating coating The first coating layer having mechanical strength and being spread on the surface of the insulating coating with the same spread as the insulating coating, and the mechanical strength greater than that of the insulating substrate and the insulating coating, A second coating layer that is adhered to the back surface of the insulating substrate with a wide spread, and a conductive terminal that covers the opposite end surfaces of the surface-mounted fuse and is electrically connected to one of the outer edges of the fuse element. And each conductive terminal includes a leg that extends partially along a front surface of the first coating layer and a leg that extends partially along a back surface of the second coating layer. A thin film fuse is provided.

[0016]

According to a preferred embodiment of the present invention, there is provided a surface mount type thin film fuse manufactured by depositing a fuse element on a thin glass substrate. A thin alumina coating is adhered to the back or bottom surface of the glass substrate. A thin glass film is adhered to the fuse element layer, and a thin alumina film is adhered to the upper surface of the glass film. The alumina / glass / fuse / glass / alumina layer structure thus obtained not only provides the advantages of the conventional glass / fuse / glass layer fuse structure, but also reduces the disadvantages of such a structure and reduces the package size. Can be maintained. The "quick" rated fuse characteristics provided by the temperature characteristics of the glass are maintained, and the thin upper and lower alumina layers significantly enhance the strength of the fuse. At that time, the fuse speed does not change. Moreover, the voltage rating is substantially improved, being considerably higher, for example from 32 volts to 63 volts and even higher. Therefore, mechanical bending strength and heat cycle characteristics are improved. Due to its high mechanical strength, the new fuse structure can be used to protect circuits formed on plastic or ceramic substrates. This has been impossible in the past.

[0017]

1 and 2 show a laminated thin film SMD fuse 10 according to a preferred embodiment of the present invention. However, the thickness of each layer shown in the figure is exaggerated for ease of understanding and is not generally proportional to the actual size.

The fuse 10 has an insulating substrate 12. As the insulating substrate 12, for example, a substrate 12 having a thin glass plate having a thickness of 0.30 mm is preferable. The insulating substrate 12 has a back surface 14 and a flat surface 16 coated with a metal thin film such as aluminum. The metal thin film is arranged to form one or more fuse elements 18. The thickness of the metal thin film is, for example, 0.6.
About μm to 4.5 μm is preferable. The fuse element 18 is
A pair of contact points and a fusing link 22 that is considerably narrower than the contact points 20 and connects the contact points are provided.
For example, in the case of a fuse element rated at 0.2 amp, the total length is 116 mils, the width is 51 mils, the length of the fusing link is 10 mils, and the width thereof is about 1 mil. The thickness of the metal thin film of such a fuse is 0.6 μm
It is a degree.

The silica passivation layer 24 protects the thin film fuse element 18 and the surrounding surface 16. A thin glass coating 26 as an insulating coating having a similar extent to the insulating substrate 12 has a surface 28. The glass coating 26 is adhered to the passivation layer 24 by an epoxy layer 30. The epoxy layer 30 also serves to seal the fuse element 18. The thickness of the glass coating 26 is about 0.30 μm, like the insulating substrate 12.

A thin alumina coating 34 is adhered to the back surface 14 of the insulating substrate 12 by an epoxy layer 32. The thickness of the alumina coating 34 is set to about 0.25 mm.
Similarly, the alumina coating 36 having a thickness of about 0.25 mm is adhered to the surface of the glass coating 26 by the epoxy layer 38. It should be noted here that the alumina and the fuse layer cannot be in direct contact with each other. This is because alumina has a high heat transfer characteristic, so that the speed of the fuse becomes too high and the power loss becomes large. However, by bonding a thin layer of alumina to the top and bottom surfaces of the underlying glass / fuse / glass structure, the fuse strength is significantly improved and high voltage ratings can be achieved without changing the fuse speed. The fuse according to the present invention can have a high rated voltage of, for example, 63V or 125V. Also, since the bending strength is large, the allowable deflection is only 1 mm to 3 m, which is the conventional value.
improve to m. The new fuse of the present invention is, for example, 140 heat cycles (-
It has the characteristics of 55 ° C to + 125 ° C (rapid temperature cycle). Due to this improved strength and thermal cycling properties, the fuse of the present invention can be used to protect circuits formed not only on glass epoxy substrates, but also on plastic and ceramic substrates.

As described above, alumina has excellent mechanical properties in tensile strength, flexural strength, etc., and therefore considerably strengthens the final fuse structure. These properties are considerably superior to those of glass. One of ordinary skill in the art will recognize the use of other high strength insulation materials, such as sapphire, as an alternative to alumina. However, alumina has the advantage of low cost.

The above-mentioned alumina / glass / fuse / glass / alumina laminated fuse assembly is preferably a rectangular parallelepiped. The rectangular parallelepiped has two end faces 40 parallel to each other.
And a plurality of corners 42 connected to the end face 40. The edge 44 of the fuse element contact 20 is within the end face 40.

The end surface 40 is covered with a conductive terminal 46. Each conductive terminal 46 is formed of an inner layer 48 made of a material such as nickel or chromium and an outer solder coating 50. Each inner layer 48 contacts the edge 44 of the one contact portion 20 and electrically connects the conductive terminal 46 and the surface of the fuse element 18 facing the conductive terminal 46.

The conductive terminal 46 has a land 52 that bends along the corner 42 and extends partially along the back surface of the alumina coating 34 and the alumina coating 36.

The thin film fuse of the present invention has high reliability.
Since the protective cover plate is temperature stable and seals the fuse, the fuse element 18 can be protected when the fuse is placed in a high temperature and high humidity environment. The protective coating is also electrically stable under extreme conditions when the fuse operates. Circuit voltage is 125 V (maximum breaking current 5
0A), high insulation resistance (>
1 MΩ) is consistently maintained.

The above patents and applications describe a process for manufacturing a glass / fuse / glass fuse structure, which process is fully applicable to the manufacture of the fuse structure of the present invention. The contents related to the steps of the patent and application are cited or described in the present specification and the drawings.

[0027]

According to the present invention, the width of the fuse element,
The length, thickness, and conductivity can be very accurately limited or programmed, thus minimizing variations in fuse characteristics. Furthermore, various types of fuse element designs and substrate types can be combined to create fuses with a range of speed characteristics. For example, high speed fuses can be manufactured using low mass fuse elements on a conductive substrate. Low speed fuse characteristics can be obtained by combining a high mass fuse element with an insulating substrate. The unique five-stack fuse component structure in accordance with the present invention further provides superior mechanical and thermal properties, thus providing a "quick" fuse that can be used in higher voltage ratings and in a wider range of circuit board environments.

[Brief description of drawings]

FIG. 1 is a front view of a cross section of a fuse according to the present invention.

2 is a cross-sectional view of the fuse of FIG. 1 taken along line 2-2.

[Explanation of symbols]

10 fuse, 12 insulating substrate, 14 back surface, 16
Surface, 18 fuse element, 20 contact part, 22 fusing link, 24 silica passivation layer, 26 glass coating, 28 surface, 30, 32, 38 epoxy layer,
34,36 Alumina coating, 40 End face, 44 edges, 4
2 corners, 46 conductive terminals, 48 inner layers, 50 outer solder coating, 52 lands.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-170826 (JP, A) Tokuyo HEI 2-503969 (JP, A)

Claims (4)

[Claims] 1. A step of attaching a metal thin film to a surface of a glass substrate, a specific portion of the metal thin film being removed, and a pair of contact portions and at least a portion narrower than these contact portions and connecting the contact portions. Forming a fuse element with one fusing link; adhering a glass coating on the surface of the glass substrate with the metal thin film; and on the back surface of the glass substrate, from the glass substrate and alumina, which has greater mechanical strength than the glass coating. And a step of adhering a second coating layer made of alumina, which has a mechanical strength higher than that of the glass substrate and the glass coating, to the surface of the glass coating. Method of manufacturing thin film fuse. 2. The method for manufacturing a surface-mount thin film fuse according to claim 1, further comprising the step of passivating the surface of the metal thin film and the glass substrate adjacent thereto. . 3. A substantially rectangular glass substrate having a flat surface, an end surface orthogonal to the surface, and a flat back surface, and an outer edge exposed flush with the end surface of the glass substrate formed on the surface of the glass substrate by vapor deposition. A conductive thin film forming a fuse element having a pair of contact portions and at least one fusing link narrower than these contact portions and connecting the contact portions; A glass coating adhered to the surface of the substrate, which cooperates with the end surface of the glass substrate and the outer edge of the fuse element to form opposite end surfaces of the surface-mounted fuse, and has a mechanical strength greater than that of the glass substrate and the glass coating, The first alumina coating layer, which has the same spread as the glass coating and adheres to the surface of the glass coating, has greater mechanical strength than the glass substrate and the glass coating. The second alumina coating layer, which has the same spread as the glass substrate and is adhered to the back surface of the glass substrate, covers the opposite end faces of the surface-mounted fuse and is electrically connected to one of the outer edges of the fuse element. Conductive terminals, each conductive terminal including a leg extending partially along a surface of the first alumina coating layer and a leg extending partially along a back surface of the second alumina coating layer. Surface mount thin film fuse characterized by 4. The surface mount type thin film fuse according to claim 4, further comprising a passivation layer covering a fuse element formed of a thin film.