KR100986708B1 - Curable paste for thick film resistor - Google Patents

Abstract

The present invention provides a curable thick film resistor paste comprising a curable resin, a conductive filler, and an inorganic additive that simultaneously improves lead heat resistance and resistance temperature coefficient.

Thick Film Resistor Paste, Resistance Characteristics

Description

Curable thick film resistor paste {CURABLE PASTE FOR THICK FILM RESISTOR}

The present invention relates to a curable thick film resistor paste and a resistor produced using the same.

With the miniaturization of mobile communication devices, satellite broadcasting receivers, and computers, miniaturization, complexation, high functionality, and high precision have been progressed for electronic components used in them. To cope with the increase in speed is required. In response to the demand for higher density, there is a growing interest in embedded PCB technology in which three basic passive components, resistors (R), coils (L), and capacitors (C), are embedded inside the PCB. This technology reduces the size of the board by embedding passive components, and allows more ICs to be mounted on boards of the same size. In particular, since passive components are embedded in the PCB, undesirable phenomena such as noise and signal processing delays are reduced, thereby enabling high speed, miniaturization, and multifunction of electronic information communication service convergence terminals such as communication devices, digital home appliances, and mobile communication terminals.

Embedded resistor technology is one of the core technologies of embedded PCB, and various methods such as thin film type, plating type, high temperature fired ceramic thick film type, and low temperature hardened polymer thick film type have been devised and commercialized. The low temperature curing polymer thick film type resistor is expected to be advantageous for mass production because it has the advantage of being easy to implement on a substrate, and many substrate manufacturers are conducting research and development.

Low temperature curing polymer thick film resistance can be easily implemented by forming a polymer resistance paste on a PCB substrate patterned with copper foil using a screen printing method, drying it, and then thermosetting at a temperature of about 150 ° C to 200 ° C. First, circuit and resistor electrodes are formed by using a PCB substrate, such as FR-4 having copper foil, by photolithography or the like, a polymer thick film resist paste is printed on the electrodes, dried and heat treated, and thermally cured, and a protective film. It is a process of forming a thick-film resistor by printing a layer and hardening again. The laser trimming process is often added after curing to adjust the resistance. Placing another PCB substrate on the substrate on which the resistor is formed and compressing it creates a PCB having a low temperature thermosetting thick film resistor.

The general characteristics of the polymer thick film resistor formed by the prior art have the advantage of allowing a wide range of resistance values to be implemented, thereby increasing the degree of freedom in design, while allowing a large change in the characteristic value of the resistor with respect to temperature and allowing the resistance value. There is a disadvantage that the deviation is large. In order to reduce the deviation of the resistance value, it is common to finally perform the trimming using a laser. If the initial deviation is too large, it is not easy to perfectly set the target value even by trimming, so a method of minimizing the initial deviation is required. .

According to these requirements, we proposed a method of controlling the effect of the shape change of the resistor by using two separate circular electrodes, or a method of maintaining a dimension in the XY direction by forming a cavity by a lithography method using a photoresist. have. Also, after forming and filling the cavity in the electrode layer, a method of maintaining the shape of the resistor uniformly has been proposed by forming the secondary electrode plating layer and patterning by lithography.

However, the proposed methods require a separate work to connect the separated circular electrode to the circuit, or use a lithography method having a complicated process step such as PR treatment, plating, and photoetching to form a cavity. In addition, there are difficulties in process control because various solvents and chemical solutions must be used.

In addition, in the patterning method of the thick film resistor, the resistance value can be further improved and supplemented by the method of reducing the tolerance by increasing the accuracy of the shape of the resistor using the exposure and development methods or the roll coating, which is one of the methods of applying the photosensitive paste. Has been proposed to further reduce the tolerance.

However, the improvement of lead heat resistance and resistance temperature coefficient, which is another characteristic of the resistor, has not been considered, and in order to properly function as a thick film resistor, good lead heat resistance and resistance temperature coefficient should be secured.

Since polymer thick film resistors are cured at low temperatures, unlike polymers of high temperature firing, polymers remain in the resistors, making it difficult to control lead heat resistance and resistance temperature coefficients.

 The present invention is to solve the above problems, to produce a resist paste using a curable resin, such as photosolder resist (PSR) and a conductive filler, in particular can improve the lead heat resistance and resistance temperature coefficient of the thick film resistor at the same time It is an object to provide a curable thick film resistor paste containing an inorganic additive as an essential configuration.

As a means for achieving the above object,

The present invention provides a curable thick film resistor paste comprising a curable resin, a conductive filler, and an inorganic additive added at a weight ratio of 10 to 50 weight percent based on 100 weights of the conductive filler to improve lead heat resistance and resistance temperature coefficient at the same time.

In addition, the inorganic additive provides a curable thick film resistor paste, characterized in that at least one selected from SiO ₂ , NiCr, Si is used.

In addition, the inorganic additive provides a curable thick film resistor paste, which is added in a weight ratio of 20 to 40 to 100 weight of the conductive filler.

In addition, the conductive filler provides a curable thick film resistor paste, characterized in that at least one selected from carbon, such as carbon black, graphite.

The present invention also provides a curable thick film resistor paste, wherein the curable thick film resistor paste is coated and cured, wherein the TCR (resistance temperature coefficient) is in the range of -200 to 150 ppm / ° C.

In addition, the resistor provides a curable thick film resistor paste, characterized in that the resistance change after the lead heat resistance evaluation is within ± 5%.

Hereinafter, the present invention will be described in detail. The following description is a specific example of the present invention, but is not intended to limit the scope of the rights defined by the claims, even if there is an assertive, limited expression.

The curable thick film resistor paste according to an embodiment of the present invention is made of a curable resin, a conductive filler, and an inorganic additive added at a ratio of 10 to 50 by weight based on 100 weight of the conductive filler to simultaneously improve lead heat resistance and resistance temperature coefficient. It is characterized by.

The curable resin is not limited and the curable resin used in the thick film resistor paste may be used without limitation. Preferably, a curable resin having photosensitivity, which is easy to form a pattern by exposure, and which can be secondary cured by heat after pattern formation is preferable.

Preferred is PSR (Photo Solder Resist) having photosensitivity and alkali developability. In particular, in the case of PSR, the exact reason was not identified, but it was found that the organic composition with the inorganic additive to be described later during curing further improved lead heat resistance and resistance temperature coefficient. PSRs are commercially available and easily obtained and are well known, and thus detailed descriptions are omitted.

In order to thermoset the curable resin, a thermosetting agent or a thermosetting aid may be added and used.

The conductive filler may be used without limitation as long as the filler can provide conductivity, and preferably at least one or more of carbons such as carbon black and graphite may be used. In particular, when further lowering the resistance value, nano silver powder may be used in parallel. That is, when the resistance value is to be further lowered, it may be realized by further increasing the content of the nano silver powder.

The carbon black is particularly preferably carbon black having an oil absorption rate in the range of 100 to 200 cc / 100 g. Too low is difficult to realize a desired level of conductivity, and too large is difficult to prepare a paste due to high viscosity. Graphite is a plate-shaped filler having a relatively large particle diameter, and carbon black alone may not reduce the viscosity of the paste, and thus, it is preferable to mix the graphite when it is difficult to realize low resistance. Nano silver powder is preferably used in the average particle diameter range of 100 ~ 300nm, too small is difficult to uniformly disperse in the paste, if too large it is not effective to lower the resistance value when mixing with the carbon paste in the future.

The present invention is characterized in that an inorganic additive for improving lead heat resistance and resistance temperature coefficient at the same time is essential. While struggling with the content of the inorganic additive, it was found that the content is closely related to the content of the conductive filler. That is, as shown in the examples to be described later it was found that the addition of 10 to 50 weight ratio to the weight of the conductive filler 100 has a critical significance to improve the lead heat resistance and resistance temperature coefficient at the same time. Outside the above range, either or both of the lead heat resistance and the resistance temperature coefficient deteriorated sharply. Particularly preferred range was to be added in a 20 to 40 weight ratio to 100 weight of the conductive filler.

As the inorganic additive, at least one selected from SiO ₂ , NiCr, and Si had a significant effect. In addition, as a result of testing graphite, TiO ₂ , Ag (spherical, or flake type), there is a possibility of use, but the effect was not satisfactory. However, it is not excluded from the scope of the present invention.

In addition, a solvent may be further used, and the solvent may be a solvent used in a general curable paste, and is not limited. An organic solvent is more preferable, and it is preferable to use ketones, such as a lactone.

Hereinafter, a method of manufacturing a thick film resistive paste using PSR, for example, will be briefly described.

Proper conductive fillers must be mixed to prepare the thick film resist paste. As the conductive filler for the polymer resistor, one or a mixture of two or more carbons such as carbon black and graphite (graphite) may be used. In the case of using a two-part PSR, firstly, the main agent and the curing agent are mixed in an appropriate ratio, and then mixed with the dispersant for proper dispersion of the conductive filler. After the conductive filler is added and mixed, it is pasted using a 3 roll mill. Thereafter, in order to increase the uniformity, the mixture is mixed again with a high speed mixer to complete the paste preparation. In the case of using a one-part PSR, a paste can be prepared in a similar manner. Conductive fillers can be pushed to the limit of maintaining the developability of the PSR. After that, an inorganic additive that improves the lead heat resistance and resistance temperature coefficient of the resistive material is added and 3 roll milled to prepare a curable thick film resistor paste.

1A to 1F illustrate a method of forming an embedded polymer thick film resistor as a resistor according to an embodiment of the present invention. First, the board | substrate with which copper foil is formed is prepared. The substrate may be an epoxy substrate currently applied to a PCB substrate, a FR-4 substrate, or a hybrid substrate formed of a ceramic-polymer composite. The copper foil on the substrate is patterned using a conventional lithography method to pattern the circuit and the electrodes. The resist paste according to the present invention is applied thereto. As the coating method, various methods such as screen printing, spin coating, and roll coating may be used, but it is most preferable to use roll coating to minimize thickness variation. In the case of using a roll coating, the coating is repeated two or three times in order to further minimize the thickness variation, and when the coating is repeatedly applied, it is preferable to rotate the substrate by rotating the substrate 90 to 180 degrees. After application, pre-cure by drying at a temperature of about 80 ℃ for 10-20 minutes. Potential resistance patterns are exposed to the pre-cure resistive film using a chrome mask and an ultraviolet exposure apparatus in which the resistance patterns are formed. The exposed substrate is reacted with an aqueous alkali solution using a spin or spray developer to form a resistance pattern. Here, the exposed portion remains photocured and is masked by the mask to remove the uncured portion from the substrate by reaction with the developer. Na ₂ CO ₃ aqueous solution may be used as the developer. After development, it is washed with ultrapure water, and then dried with an air gun and put in an oven to remove residual moisture. After the photo-patterned thick film resistor is completed by post-cure at a temperature of 150 ~ 200 ℃. Subsequently, another PCB substrate is placed on the substrate on which the resistor is formed, pressed, or covered with a protective film, thereby forming a PCB structure having a low temperature thermosetting polymer thick film resistor.

As a result of measuring the resistance temperature coefficient (TCR) and the lead heat resistance of the resistor manufactured by applying and curing using the above-described curable thick film resistor paste, most of TCR was in the range of -200 to 150 ppm / ℃, and after evaluation of lead heat resistance As the resistance change was within ± 5%, it was found that the resistor had very excellent resistance characteristics.

 The curable thick film resistor paste according to the present invention having the above constitutive features contains an inorganic additive which can improve lead heat resistance and resistance temperature coefficient of the thick film resistor at the same time as a remarkable effect of excellent resistance characteristics of the resistor. To provide.

≪ Example 1 >

Experiments were conducted to introduce modifying filler to improve TCR and heat resistance of 10K composition paste. Conductive fillers are Vulcan XC72R (Cabot), PSR is PSR-4000 KT33R06 (topic) and CA-40 KT33R06 (curing agent) (Taiyo Ink, subject: curing agent = 4: 1 mixture), BYK-9076, Butyl Carbitol Acetate (BCA) was used as an additional solvent for viscosity control. The experiment was conducted using 20 g PSR, 1 g XC72R, and 0.4 g BYK-9076 as the basic composition. Primary fillers tested were graphite, NiCr metal alloy, and SiO ₂ (quartz) powder. Graphite used KS-6 from Timcal, NiCr used N-1091 (Ni / Cr = 80/20, 97% pure) from Cerac, and SiO ₂ powder using high purity chemical reagents. Table 1 shows the results of evaluating the characteristics of the fillers and the amount of the fillers by adding 0.1, 0.3, and 0.5 g of carbon black to 1 g, respectively. Here, sheet resistance is measured using multileter, and hot TCR is calculated by measuring the change of resistance value in the temperature range of 25 ~ 125 ℃. The lead heat resistance was evaluated by measuring resistance and calculating the rate of change before and after floating in a 260 ° C lead bath for 10 seconds.

According to Table 1, when the graphite is added, the sheet resistance is severely changed according to the addition amount, and the change rate is relatively poor after the evaluation of lead heat resistance. NiCr and SiO ₂ showed improved properties, especially when the addition amount was 0.3g. Both lead heat resistance and resistance temperature coefficient were found to be suitable.

TABLE 1

Sheet resistance (㏀ / sq) Hot TCR (ppm / ℃) △ R after solder float (%) 9.68 -148.1 -4.08 Graphite 0.1 8.00 -203.6 3.68 ~ 6.09 0.3 5.59 -124.2 3.83-4.14 0.5 4.86 -87.4 4.52 ~ 6.66 NiCr 0.1 10.73 130.72 -1.06 0.3 8.69 84.75 -2.47 0.5 10.09 123.46 -2.85 SiO2 0.1 9.80 -80.00 -2.75 0.3 8.99 -86.96 -2.72 0.5 9.90 78.13 -5.62

<Example 2>

Further modified fillers tested were TiO ₂ , Si, Ag (spherical) and Ag (flake). TiO ₂ and Si were used as reagents of high purity chemistry, and Ag powders were used as products of Changsung Co., Ltd. In the same manner as described above, 0.1, 0.3, and 0.5 g of carbon black were added to each of the fillers, and the results of evaluation of the characteristics of the fillers and the amount of the additives are shown in Table 2 below.

As a result of the evaluation, the characteristics of TCR and lead heat resistance of 0.3 to 0.5 g of Si were relatively good.

TABLE 2

Sheet resistance (㏀ / sq) Hot TCR (ppm / ℃) △ R after solder float (%) 9.68 -148.1 -4.08 TiO2 0.1 20.12 -252.4 4.72 0.3 17.17 -181.6 4.23 0.5 20.28 -142.1 3.54 Si 0.1 9.95 -183.1 2.34 0.3 10.80 -121.8 2.15 0.5 9.58 -127.0 1.24 Ag (spherical) 0.1 14.12 -221.7 3.03 0.3 11.39 -199.4 2.72 0.5 16.93 -121.3 3.23 Ag (flake) 0.1 12.31 -252.6 2.35 0.3 12.97 -220.7 1.40 0.5 12.95 -246.8 0.58

Overall, it is well within the range of 10 to 50 by weight based on the weight of the conductive filler 100, and when it is out of this, it is found that the effect of either or both of TCR and lead heat resistance is remarkably inferior, in particular, within the range of 20 to 40 weight by weight of the conductive filler 100 Optimum value was shown.

In addition, considering the results of Examples 1 and 2 as a whole, the inorganic additives that significantly improve the properties of both TCR and lead heat resistance can be compressed into three kinds: SiO ₂ , NiCr, and Si.

1A to 1F illustrate a method of forming an embedded polymer thick film resistor as a resistor according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: substrate 111112: copper foil

120,121: curable thick film resistance paste 122: resistance pattern

130: protective film 150: developer

200: mask

Claims (6)

It includes a photosensitive photo solder resist (PSR) resin, a conductive filler, and an inorganic additive added at a 20 to 40 weight ratio based on 100 weight of the conductive filler to improve lead heat resistance and resistance temperature coefficient at the same time. The inorganic additive is a curable thick film resistor paste, characterized in that Si. delete delete The curable thick film resistor paste of claim 1, wherein the conductive filler is selected from at least one of carbons such as carbon black and graphite. A resistor formed by applying and curing the curable thick film resistor paste according to claim 1 or 4, wherein the TCR (resistance temperature coefficient) is in the range of -200 to 150 ppm / ° C. 6. The curable thick film resistor paste of claim 5, wherein the resistance has a resistance change within ± 5% after lead heat resistance evaluation.

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