Patent Application
20090009281
1. Field of the Invention
This invention relates generally to a device configuration and manufacturing method for providing a fuse element. More particularly, this invention relates to an improved device configuration and manufacturing method for providing a fuse element by using resin coated copper (RCC) foil.
2. Description of the Prior Art
Even though there are many types of fuse elements implemented as over current protection, there are still technical limitations and difficulties as now available in the marketplace to provide fuse elements configured a micro-chip. Specifically, there are basically following types of fuse elements configured as chips.
The first type of fuse elements is fuse elements that are supported on a ceramic substrate. This type of fuse elements has the benefit of reliable operation at a higher operation because the ceramic substrate can sustain higher temperature. However, the thermal conductivity of the ceramic substrate is generally in the range of 8-10 W/m° K. while the thermal conductivity of glass is 2-4 W/m° K. and polymer substrates generally have a thermal conductivity of 0.2-0.5 W/m° K. Thus, compared with glass and polymer substrates, the ceramic substrate has a relatively higher thermal conductivity. Due to this higher thermal conductivity, a fuse element supported on a ceramic substrate often requires longer time to reach a fuse temperature to break the circuit for over-current protection.
Another type of fuse elements are produced with thick film technologies that are generally manufactured on a glass substrate by using thick film processes. The thick film processes are able to precisely pattern the fuse with accurately controllable resistance at room temperature thus provide better protection with well controlled fuse-breaking condition that is repeatable. The glass substrate further provides another benefit that the fuse breaking action would not lead to sparks, flame or burning, therefore, there no concerns of burning or smoke damages to nearby circuits or components. The thick film type of fuse elements further has adequate capacity to sustain higher current to pass through. However, similar to the first type of fuse elements, longer time is required to activate a fuse breaking action due to a higher thermal conductivity of the glass substrate. It is often required to use a thicker layer for fuse thus causes higher resistance and higher power consumption.
For the purpose of inducing a faster fuse breaking action, a fiberglass may be implemented that has a lower thermal conductivity. Many kinds of printed circuit boards (PCB) are available at lower cost to reduce the production costs. However, such substrate lacks characteristics of high temperature and high current reliabilities that are often required for many applications of over-current protections. The scopes of fuse elements using fiberglass as supporting substrates are therefore greatly limited.
In order to overcome the above discussed difficulties, another type of fuse elements is manufactured with a thin film technology on aluminum oxide (Al2O3) substrate. A laser scribing process can be conveniently carried out to form the fuse chips thus significantly speed up the production cycles for manufacturing such fuse chips. However, such fuse elements are conventionally configured with an aluminum oxide substrate cover with a polymer layer to function as a heat insulation layer. Since the polymer layer has a low thermal conductivity, there is a benefit of quick fuse breaking action for over-current protection. However, similar to the fuse elements that supported on the fiberglass substrates, the polymer layer is not stable in a high temperature. Therefore, the conventional thin-film fuse elements supported on the aluminum oxide substrate have limited scope applications due to the limited capacity to sustain high temperature and high current operations. Furthermore, a fuse layer and the substrate are not securely adhered to the heat insulation layer due to both surfaces of the heat insulation layer surface are formed smooth surfaces.
Therefore, a need still exists in the art of design and manufacture of fuse element to provide a novel and improved device configuration and manufacturing method to resolve the difficulties.
It is therefore an aspect of the present invention to provide a fuse element and a manufacturing method of the fuse element to sustain a high current and high temperature operation without the limitation of slower fuse breaking reaction as that generally encountered in the above-discussed conventional techniques such that the difficulties and limitations can be overcome.
Specifically, in one aspect of this invention, the surface roughness of the second surface of the heat insulation layer can increase the adhesion of the resin layer to the substrate, to the first seed layer, and to the fuse layer.
It is another aspect of this invention, the fuse element is implemented by laminating a substrate with a heat insulation layer having a good insulation characteristics and high glass transition temperature (Tg) above 150° Celsius to sustain high temperature operation and also to reduce the thermal conductivity to a range of approximately 0.2 W/m° K. In an exemplary embodiment, a top surface of the substrate insulated with the resin layer having a thermal conductivity of between 1.0 W/m° K. and 0.1 W/m° K.
It is another aspect of this invention that a copper foil laminated to the resin layer to laminated to the substrate is processed to have a roughness surface on both the copper surface and a top surface of the substrate such that secure and strong adhesion between the copper foil and the resin layer to the substrate are achieved to produce reliable fuse element that can sustain long term high temperature and high current operations. Furthermore, the copper foil is implemented as electrode terminal to achieve low resistance current conduction.
Another aspect of this invention is the application of the alloys of Au/Pt, Au/Co or Au/Pd as buffer layer to diffuse rapidly to an acceleration layer composed of tin such that the rate of fuse breaking can be well controlled with relatively increased amount of conducting current through the fuse element for broader scopes of over-current protection.
This invention discloses a method for manufacturing a fuse element by laminating a copper foil with a resin layer attached on a top surface of a substrate where the resin layer has a high glass transition temperature above 150° Celsius. The method further includes a step of carrying out a roughening process to roughen the top surface of the substrate and a bottom surface of the copper foil to increase the adhesion of the resin layer to the substrate and to the copper foil. Furthermore, the method further includes a step of carrying out a roughening process to roughen a surface of the resin layer to increase the adhesion of the resin layer to the substrate, to a first seed layer, and a fuse layer.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.
Referring to
The fuse element 100 begins with the substrate 110 for supporting the other elements of the fuse element 100. In the embodiment, the material of the substrate 110 is an aluminum oxide (Al2O3). Other material for the substrate 110 includes, but not limited to, glass. The substrate 110 includes a top surface 1101, a bottom surface 1102 opposite to the top surface 1101, and side surfaces 1103.
The heat insulation layer 115 includes a first surface 1151 and a second surface 1152 opposite to the first surface 1151. The second surface 1152 has a surface roughness in the range 300 nm to 400 nm. The first surface 1151 of the heat insulation layer 115 is disposed on the top surface 1102 of the substrate 110. The heat insulation layer 115 is a resin having a high glass transition temperature (Tg) above 150° Celsius and a thermal conductivity of between 1.0 W/m° K. and 0.1 W/m° K. The surface roughness of the second surface 1152 can increase the adhesion of the resin layer to the substrate 110, to the first seed layer 125, and to the fuse layer 130.
The copper terminal 120 is disposed at two opposite ends of the second surface 1152 of the heat insulation layer 115 to achieve low resistance current conduction. The other purpose of the copper terminal 120 is to increase the area that is electrically connected with the side terminal layers 160 and 165 due to the thickness of the fuse layer 130 is very low.
The first seed layer 125, for example, but not limited to, nickel (Ni) or NiCr, is disposed on the copper terminals 120 and the second surface 1152 of the heat insulation layer 115. The fuse layer 130 composed of copper (Cu) or copper-tin (CuSn) alloy is disposed on the first seed layer 125. The fuse layer 130 is adapted for conducting a current therethrough. The buffer layer 135 composed of Au/Pd, Au/Pt or Au/Co is disposed on the fuse layer 130 and the accelerated layer 140 composed of tin (Sn) is disposed on the buffer layer 135. The buffer layer 135 is disposed between the accelerated layer 140 and the fuse layer 130. The application of the alloys of Au/Pt, Au/Co or Au/Pd as buffer layer 135 to diffuse rapidly to an acceleration layer 140 such that the rate of fuse breaking can be well controlled with relatively increased amount of conducting current through the fuse element for broader scopes of over-current protection.
The protective layer 145 is disposed over the buffer layer 135 and the acceleration layer 140. The protective layer 145 can be includes a Polymer, or a combination of a first protective layer (not shown) composed of epoxy and a second protective layer (not shown) composed of polyimide (PI). The first protective layer is disposed between the acceleration layer 140 and the second protective layer. When a current is conducting over the fuse layer 130, the temperature starts to increase. The acceleration layer 140 will diffuse to the fuse layer 130 thus forming an alloy. While the melting alloy spill out, the second protective layer composed of PI can stop the residue of melting alloy to stay inside of the second protective layer, since the PI has characteristics, such as high melting point, flexibility, not easy to flame, low moisture absorption, and excellent thermal prosperity.
The bottom terminal layer 150 composed of NiCr/NiCu is formed on the bottom surface of the substrate 110 followed by the process of formation a side terminal. The second seed layer 155 composed of NiCr/NiCu wraps around the side surfaces 1103 of the substrate 110. Then the side terminal layers 160 and 165 composed of Cu/Ni/Sn wraps around the side surfaces 1103 of the substrate 110 and are disposed over the second seed layer 155. In the embodiment, the second seed layer 155, the side terminal layer 160, and the side terminal layer 165 are copper layer, Ni layer, and Sn layer respectively. The copper layer is formed to lower the resistance of the edge terminal. Since the fuse element is copper, and different thickness of the fuse layer is used for different currents, it is required to reduce the resistance of the edge terminal in order prevent the situation that a low current would limit the fuse action if the resistance of the edge terminal limits the current passes through the fuse element. The Ni layer functions as barrier layer and the Sn layer is applied as a soldering layer for conveniently soldering the circuits to be protected by the fuse element.
Referring to
In
In
In
A bottom terminal layer 150 is sputtered onto the bottom surface of the substrate 110 and composed of NiCr/NiCu having a thickness approximately 500±300 Angstroms. The fuse elements supported on the substrate 110 is then laser scribed and stacked to tooling for NiCr/NiCu sputtering as shown in
The fuse element 100 as disclosed in this invention has special structural features. The first structural feature is the use of an aluminum oxide (Al2O3) as the supporting substrate. The aluminum oxide substrate provides a benefit of reliable operation at high temperature. Moreover, because of the fact that it is more convenient to apply existing technologies and manufacturing processes on the aluminum oxide, the use of aluminum oxide further reduce the production cost. However, the substrate employed in this invention, e.g., an aluminum oxide, is a heat dissipation substrate. For the purpose of manufacturing a fuse element, a heat dissipation substrate such as the aluminum oxide is generally not suitable for application for supporting the fuse element due to the fact that a fuse element require to accumulate heat quickly to break the fuse layer when an over-current even occurs. For this reason, a thin layer of insulation, i.e., a coated resin layer as a heat insulation material is applied to reduce the heat dissipation from the substrate. Another structural feature of this invention is the surface roughness of the copper foil that provide secure adhesion to the coated resin layer and thus provide reliable fuse elements with secure adhesion to the substrate 110 and also to the first seed layer 125.
Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.
