This application claims the benefit of Taiwanese Application 104123186, filed Jul. 17, 2015.
1. Field of the Invention
The present invention is generally relates to a micro-resistor of small size. In particular, the present invention is directed to a small micro-resistor of particularly small temperature coefficient of electrical resistance so that products with such micro-resistor have a distribution of resistance as uniform as possible.
2. Description of the Prior Art
For the design of the current resistor pattern, the main features to design the resistor pattern are in accordance with the resistance demand to obtain the resistor pattern which meets the resistance demand. Usually, first the target resistance is confirmed before cupper electrodes are formed at two end of the resistor pattern with the help of the lithographic and of cupper-plating techniques. Later the resistance is fined-tuned by trimming the resistance so a resistor pattern of the target resistance is obtained.
The inventors found out that in the process of designing a resistor pattern, the prediction of positive or negative change of the temperature coefficient is too difficult so that the change of the resistance of a product is susceptible to the change of the temperature and it leads to the specification of the resistance of a product cannot be assured by the customers or by the end-users due to the great value of the temperature coefficient of electrical resistance of a product. Or the thickness distribution of the plated cupper is not even enough to make the resistance of a product too much dispersed, to adversely affect the product yield, the trimming time and the integrity of the product so that the temperature coefficient of electrical resistance of the product is too dispersed to fall within a small range. The above problems all adversely affect the product quality of a micro-resistor.
In the light of the above, the present invention proposes a micro-resistor of particularly small temperature coefficient of electrical resistance. Such micro-resistor facilitates the even distribution of the temperature coefficient of electrical resistance of the product as much as possible in order to overcome the undesirable situations.
A micro-resistor includes at least a resistor material layer, an electrode set and a first protective layer. The electrode set includes a first electrode and a second electrode. Both are disposed on the same side of the resistor material layer to define an opening which exposes the resistor material layer. The space between the first electrode and the second electrode defines an opening size of the opening. The first protective layer covers the opening completely and has a coverage size along a direction parallel with the space. The micro-resistor has a resistance less than 5 milliohm and the difference of the opening size and the coverage size is less than 3100 micrometer so that the temperature coefficient of electrical resistance of the micro-resistor is not greater than 150 ppm/° C.
In one embodiment of the present invention, the first electrode includes a first plating electrode layer and a first electrode contact. The first plating electrode layer is in direct contact with the resistor material layer and disposed between the resistor material layer and the first electrode contact.
In another embodiment of the present invention, the first protective layer partially covers the first plating electrode layer but not in direct contact with the first electrode contact.
In another embodiment of the present invention, the micro-resistor further includes a solder part which covers the first electrode contact.
In another embodiment of the present invention, the second electrode includes a second plating electrode layer and a second electrode contact. The second plating electrode layer is in direct contact with the resistor material layer and disposed between the resistor material layer and the second electrode contact.
In another embodiment of the present invention, the first protective layer partially covers the second plating electrode layer but not in direct contact with the second electrode contact.
In another embodiment of the present invention, the micro-resistor further includes a solder part which covers the second electrode contact.
In another embodiment of the present invention, the micro-resistor further includes a substrate which directly connects the resistor material layer.
In another embodiment of the present invention, the difference is less than 1000 micrometer when the micro-resistor has a resistance less than 2 milliohm.
In another embodiment of the present invention, the difference is less than 700 micrometer so that the temperature coefficient of electrical resistance is not greater than 100 ppm/° C. when the micro-resistor has a resistance less than 1 milliohm.
In another embodiment of the present invention, the difference is less than 450 micrometer so that the temperature coefficient of electrical resistance is not greater than 100 ppm/° C. when the micro-resistor has a resistance less than 0.5 milliohm.
In another embodiment of the present invention, the temperature coefficient of electrical resistance is not greater than 60 ppm/° C. when the difference is less than 300 micrometer.
In another embodiment of the present invention, the temperature coefficient of electrical resistance is a value between 25° C.-125° C.
In another embodiment of the present invention, the resistor material layer is selected from a group consisting of MnCu alloy, NiCu alloy, CuMnSn alloy and NiCrAlSi alloy.
In another embodiment of the present invention, the micro-resistor further includes a heat-dissipating layer disposed on a side of the substrate and away from the resistor material layer.
In another embodiment of the present invention, the micro-resistor further includes a connecting layer attached to the heat-dissipating layer and extending from the heat-dissipating layer to the resistor material layer.
In another embodiment of the present invention, the micro-resistor further includes a second protective layer to cover the resistor material layer.
In another embodiment of the present invention, the micro-resistor further includes a third protective layer together with the heat-dissipating layer for capping the substrate and the third protective layer is connected to the heat-dissipating layer and to the substrate.
Considering different resistance ranges of micro-resistor products, the present invention correspondingly adjusts the difference of the opening size and the coverage size, preferably the difference is close to 0 as much as possible so that the temperature coefficient of electrical resistance of the micro-resistor is not greater than 150 ppm/° C. Preferably, the temperature coefficient of electrical resistance is advantageously not greater than 100 ppm/° C. when the difference is not greater than 300 micrometer to overcome the undesirable situations which the current micro-resistor products suffer.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
The present invention provides a micro-resistor of particularly small temperature coefficient of electrical resistance. Taken different resistance ranges of micro-resistors into consideration, the difference of the opening size and the coverage size is correspondingly adjusted, preferably the difference is not greater than 300 micrometer, so that different resistance of different micro-resistors may advantageously obtain the temperature coefficient of electrical resistance of the micro-resistor not greater than 100 ppm/° C. In such a way, a smaller temperature coefficient of electrical resistance inhibits the great fluctuation of the resistance due to the change of the temperature so that the distribution of the product resistance may be as even as possible. The temperature coefficient of electrical resistance is defined as follows:
wherein T1 is a lower first temperature,
T2 is a higher second temperature,
R1 is a resistance value at the first temperature,
R2 is a resistance value at the second temperature.
Please refer to
The resistor material layer 120 usually has an alloy material, such as MnCu alloy, NiCu alloy, CuMnSn alloy or NiCrAlSi alloy . . . etc. Generally speaking, the thickness of the resistor material layer 120 may be 0.025 mm-0.3 mm. The electrode set 130 is disposed on the same side as the resistor material layer 120 is, for example the electrode set 130 is disposed on the first side 121 of the resistor material layer 120.
Table 1 shows different temperature coefficients of resistance of different alloy materials between the temperature range 20° C.-105° C. From Table 1 it is observed that the temperature coefficient of electrical resistance of the pure cupper material is by far greater than that of the alloy materials.
Please refer to
In one embodiment of the present invention, the first electrode 131 includes a first plating electrode layer 135 and a first electrode contact 136, preferably the first plating electrode layer 135, the first electrode contact 136 and the resistor material layer 120 collectively form a steps-like structure, as shown in
Similarly, the second electrode 132 includes a second plating electrode layer 137 and a second electrode contact 138, preferably the second plating electrode layer 137, the second electrode contact 138 and the resistor material layer 120 collectively form a steps-like structure. The second plating electrode layer 137 is disposed on the resistor material layer 120 and in direct contact with the resistor material layer 120. The second electrode contact 138 is disposed on the second plating electrode layer 137 but is slightly shorter than the second plating electrode layer 137 along the direction of the opening size L so the second plating electrode layer 137 is disposed between the resistor material layer 120 and the second electrode contact 138. In one embodiment of the present invention, the first plating electrode layer 135, the first electrode contact 136, the second plating electrode layer 137 and the second electrode contact 138 may have tapered side surfaces.
Preferably, both the first electrode 131 and the second electrode 132 are of cupper material. In other words, the first plating electrode layer 135, the first electrode contact 136, the second plating electrode layer 137 and the second electrode contact 138 are preferably made of cupper. The pure cupper material is known to have relatively large temperature coefficient of electrical resistance, for example about 3860 ppm/° C. for pure cupper material and about 3930 ppm/° C. for annealed cupper material. When in use, the electric current flows from one of the first electrode 131 and the second electrode 132 of the micro-resistor 100 into the resistor material layer 120 and leaves the micro-resistor 100 from still one of the first electrode 131 and the second electrode 132.
Because opening 133 exposes some of the resistor material layer 120, a first protective layer 140 is needed to keep the exposed resistor material layer 120 from outside damage. The first protective layer 140 may be a solder mask material to completely cover the opening 133. For example, methods such as printing laminating, heat pressing, spraying, electro-plating may be used to apply the solder mask material onto the opening 133 and resultantly to make the solder mask material solidified. Due to the natural reason of the printing application, the solder mask material may also be applied onto the first electrode 131 and onto the second electrode 132 which define the opening 133 in addition to the location of the opening 133. Accordingly, the first protective layer 140 would more or less cover the first electrode 131 and the second electrode 132. However, ideally speaking, the first protective layer 140 may possibly not cover the first electrode 131 and the second electrode 132. Optionally, there may be a third protective layer 142 together with the heat-dissipating layer 111 to cap the substrate 110 so that the third protective layer 142 is connected to the heat-dissipating layer 111 and to the substrate 110 to keep the substrate 110 from oxidation.
As shown in
The first protective layer 140 may cover the opening 133 in various possible ways but the first protective layer 140 covers the opening 133 with the coverage size D, or further covers some of the first electrode 131 and the second electrode 132. As shown in
Optionally, the micro-resistor 100 may further include a solder part. The solder part may have various shapes and a solder ball 150 or a solder layer 151 is given here as an example but is not limited to these. The solder part may be used to protect at least one of the first electrode 131 and the second electrode 132. For example, the solder part may cover the first electrode contact 136, or the solder part may further cover the second electrode contact 138. Or as shown in
The inventors found out that the temperature coefficient of electrical resistance of the micro-resistor may be advantageously not greater than 150 ppm/° C. when the micro-resistor 110 has a resistance not greater than 5 milliohm if the difference D-L of the coverage size D and the opening size L is less than 3100 micrometer. Preferably, the difference D-L is less than 1000 micrometer when the micro-resistor has a resistance less than 2 milliohm. In one embodiment of the present invention, the difference is less than 700 micrometer so that the temperature coefficient of electrical resistance may be not greater than 100 ppm/° C. when the micro-resistor has a resistance less than 1 milliohm. In another embodiment of the present invention, the difference is less than 450 micrometer so that the temperature coefficient of electrical resistance may be not greater than 100 ppm/° C. when the micro-resistor has a resistance less than 0.5 milliohm. More preferably, the temperature coefficient of electrical resistance may be not greater than 60 ppm/° C. when the difference is less than 300 micrometer. The temperature coefficient of electrical resistance in the present invention is an example of a range from room temperature to an elevated temperature, for instance the temperature coefficient of electrical resistance between 25° C.-125° C.
Table 2 shows the results of the difference D-L of the coverage size D and the opening size L, and the resistance difference of different resistance values between 25° C.-125° C. To be explained in advance, 1) the resistance difference ΔR is R2-R1; 2) T1 is the first temperature at 25° C.; 3) T2 is the second temperature at 125° C. as an example but it is not restricted to these conditions. In practice, T2-T1≦100° C. is workable. For example, T1 may also be 30° C. and T2 may be 130° C., or T1 may be 30° C. and T2 may be 60° C. An alloy material Cu0.907Mn0.07Sn0.023 is used in Table 2 to serve as the resistor material layer 120. The dimension of the resistor material layer 120 is 3.2 mm×6.4 mm. The coverage size D is changeable but the opening size L is kept unchanged so that there are various differences D-L present in each group.
Because the present invention takes different resistance ranges of micro-resistor products into consideration, the difference of the opening size and the coverage size is correspondingly adjusted, preferably the difference is as close to 0 as possible, so that the temperature coefficient of electrical resistance of the micro-resistor is not greater than 150 ppm/° C. Preferably, the temperature coefficient of electrical resistance is advantageously not greater than 100 ppm/° C. when the difference is not greater than 300 micrometer.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Number | Date | Country | Kind |
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104123186 | Jul 2015 | TW | national |