JPH0546117B2 - - Google Patents

Description

[Detailed description of the invention]

【0001】

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board equipped with a printed resistor.

【0002】

[Prior Art] As a circuit board used in electronic devices, a circuit board in which a conductive part such as copper foil to be soldered and a printed resistor are provided on an insulating board is widely used. In circuit boards,
If the printed resistor and the conductive part to be soldered are provided on different sides of an insulating substrate and it is necessary to connect the conductive part and the printed resistor, a through-hole conductor provided through the board is used. The two were electrically connected through the

【0003】

Problems to be Solved by the Invention Recently, in order to increase the integration density of components, it has become necessary to provide a resistor on the surface of an insulating substrate to which soldering is performed. Therefore, as shown in Japanese Patent Publication No. 49-26768, a circuit board has a structure in which a printed resistor is provided on the surface of the board to be soldered, and the printed resistor is covered with a heat-resistant insulating coating. was proposed. However, with this conventional circuit board,
Since the printed resistor is simply covered with a heat-resistant insulating coating, the thermal and mechanical strains generated in the insulating coating and the insulating substrate that cover the printed resistor during soldering are directly transmitted to the printed resistor. However, there is a problem in that the resistance value of the resistor changes greatly when soldering is performed, and it has been difficult to obtain a product that can withstand practical use.

[0004] Conventionally, when it is particularly required to provide resistors on both sides of an insulating board, a configuration has been adopted in which a chip resistor is soldered to the copper foil part (conductive part) on the soldering side. Ta. In this case, the chip resistor is temporarily attached to a predetermined location on the soldering surface of the board using adhesive, and by dipping the soldering surface of the board into a solder bath, the chip resistor is soldered to a predetermined location on the copper foil section along with other components. However, with this method, when the board is immersed in a solder bath, the chip resistor is likely to fall off, its mounting position may be shifted, or both ends of the chip resistor may be short-circuited by the solder.
It was inevitable that the product yield would deteriorate.

[0005] An object of the present invention is to provide a circuit board with a printed resistor, which is provided with a printed resistor on the soldering surface of an insulating substrate and can reduce changes in resistance value during soldering. It is in.

【0006】

[Means for Solving the Problems] The present invention shows one embodiment thereof. As seen in FIG. 1, in a circuit board P with a printed resistor, in which a printed resistor 2 is provided on an insulating substrate 3 having a surface 3a having a conductive portion 1 to be soldered, soldering is performed. This makes it possible to provide the printed resistor 2 on a surface having a conductive portion (hereinafter referred to as the soldering surface).

[0007] In the present invention, the printed resistor 2 is formed on the surface 3a of the insulating substrate 3 having the conductive portion 1 to which soldering is performed, with the base insulating layer 4 interposed therebetween. A buffer insulating layer 6 is formed to cover the printed resistor 2, and a heat-resistant protective insulating coating layer 7 is formed to cover the buffer insulating layer 6. The base insulating layer 4 and the buffer insulating layer 6 are made of an insulating material that has the property of softening when exposed to heat during soldering (the buffer insulating layer 6 may become fluid).

[0008] In the present invention, it is sufficient that the printed resistor provided on the soldering surface of the board is covered and protected by the buffer insulation layer and the protective insulation coating layer, and the buffer insulation layer and the protective insulation coating layer are There is nothing to prevent the printed resistor from being coated with other conductors, resistors, etc. in addition to the printed resistor.

[0009] For example, a conductor such as a jumper wire is provided on the soldering surface of a board, a printed resistor is formed on the conductor via an insulating layer, and this printed resistor is covered with a buffer insulating layer and a protective insulating coating layer. It can also be made into a covering structure.

[0010] The buffer insulating layer does not necessarily need to be in direct contact with the printed resistor, and the scope of the present invention also includes cases where the buffer insulating layer contacts the printed resistor through another insulating layer.

[0011] Furthermore, in the present invention, there is no hindrance to further covering the protective insulating coating layer with another insulating coating such as a solder resist.

[0012] The protective insulating coating layer needs to have heat resistance that can withstand the heat during soldering, but heat resistance here refers to a layer that does not lose its independence when exposed to heat during soldering. (Does not lose its shape)
This means that it maintains sufficient mechanical strength to a certain degree. Therefore, this protective insulating coating layer may be formed of a thermosetting resin or thermoplastic resin that hardly softens when exposed to heat during soldering. Alternatively, it may be formed of an insulating material that softens to some extent when subjected to heat during soldering, as long as it does not lose its independence.

【0013】

[Function] In the above structure, the base insulating layer and the buffer insulating layer suppress the transfer of heat to the printed resistor when it receives heat during soldering, and also prevent mechanical distortion from occurring in the printed resistor. The protective insulating coating layer functions to suppress the transfer of heat to the printed resistor during soldering and to mechanically protect the printed resistor. According to the invention, therefore:
When heat is applied to the soldering surface of the board during soldering, heat transfer to the printed resistor can be suppressed.
Printed resistors can be prevented from being exposed to high heat. In particular, in the present invention, when heat is received during soldering, the protective insulating coating layer and the buffer insulating layer block a considerable amount of heat, and at the same time, the base insulating layer and the buffer insulating layer soften and act as a buffer. High heat is not applied to the printed resistor, and thermal distortion of the protective insulating coating layer is not transmitted to the printed resistor.
Therefore, it is possible to prevent the printed resistor from being mechanically destroyed due to thermal shock during soldering, and to prevent the resistance value from significantly changing. This makes it possible to obtain a circuit board with high quality.

【0014】

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0015] FIGS. 1 and 2 show an embodiment of the present invention, with FIG. 1 being a sectional view of a main part, and FIG. 2 being a plan view showing an example of a pattern on a soldering surface.

[0016] In these figures, 3 is an insulating substrate made of any substrate material such as a paper phenolic resin laminate, a glass epoxy board, a ceramic board, etc. One surface of this insulating substrate 3 is a soldering surface 3a, and this solder Conductive parts 1 made of metal foil such as copper foil are provided in a predetermined pattern on the attachment surface 3a. The conductive part 1 is a part to be soldered (soldering part) 1a
A through hole 10 is provided through the soldering portion 1a and the substrate 3. A lead wire of an electronic component (not shown) is inserted into the through hole 10 from the other side of the board 3, and the lead wire is connected to the solder portion 1a.
is soldered to.

[0017] The conductive part 1 also has a pair of resistor connecting parts 1b, 1b to which the printed resistor is connected, and in this example, a jumper wire (such as copper foil) is connected between the pair of resistor connecting parts 1b, 1b. Conductor 1 comprising metal foil) etc.
1 is provided. Soldering surface 3a of board 3
In the region located between the opposite ends of the pair of resistor connecting parts 1b, 1b of the conductive parts, both the resistor connecting parts 1
A base insulating layer 4 is formed by printing so as to span between the opposing ends of the conductors 1b and 1b and to cover the conductor 11. The base insulating layer 4 has the function of fixing the printed resistor, and the insulating material forming this base insulating layer may be any material as long as it can withstand the heat during soldering and has good printability. However, it is preferable to use a resin paint that has the property of softening to some extent when exposed to heat during soldering. As such a resin, for example, a novolac type epoxy resin, a bisphenol A type epoxy resin, etc. can be used.

[0018] Pair of resistor connection parts 1b, 1 of the conductive part 1
A printed resistor 2 is formed on the base insulating layer 4 extending between the base and the resistor connection portions. The printed resistor 2 is formed by printing using a resistor paint such as carbon resin paint. As the resistor coating, it is preferable to use a thermosetting resin baked at a low temperature (baked at 200° C. or less) containing carbon. The printed resistor 2 is electrically connected by directly contacting the surfaces of the resistor connection parts 1b, 1b of the conductive part 1, but in this embodiment, the electrical connection between the resistor 2 and the conductive part 1 is In order to ensure proper connection, connect both ends of resistor 2 and resistor connection part 1.
A pair of conductive layers 5, 5 are formed spanning 1b and 1b. The conductive layers 5, 5 are provided so that their respective ends extend beyond the ends of the resistor 2 and overlap the resistor connection parts 1b, 1b. The conductive layers 5, 5 are formed by printing using a conductive paint such as silver paint or copper paint after the resistor 2 is fired.

[0019] The resistor 2 and the conductive layers 5, 5, the portion of the base insulating layer 4 where the printed resistor 2 is not provided, and the resistor connection portion 1b of the conductive part 1, so as to cover the vicinity of 1b. A thermally softenable buffer insulating layer 6 is formed, and this buffer insulating layer 7 and the conductive part 1
A protective insulating coating layer made of a thermosetting resin having heat resistance that can withstand the heat during soldering so as to cover the resistor connection parts 1b and 1b (portions not covered by the buffer insulating layer 6) of the resistor connection parts 1b and 1b. 7 is formed.

[0020] The buffer insulating layer 6 is formed by printing after the conductive layers 5, 5 are fired. This buffer insulating layer 6 is provided to suppress the transfer of heat to the printed resistor 2 when it receives heat during soldering, and to prevent mechanical distortion from occurring in the printed resistor 2. As the insulating material constituting the buffer insulating layer 6, an insulating material having a property of softening when exposed to heat during soldering is used. This heat-softening insulating material has good printability and is in a state where it is sufficiently flexible (fluid) when exposed to heat during soldering than the base insulating layer 4 and the protective insulating coating layer 7. (It is also possible to become sexually active)
Use a material that softens. Examples of this insulating material include polyester resins such as saturated copolymer polyester resins and saturated polyester resins, silicone rubber, silicone resins, and thermoplastic resins that soften sufficiently when exposed to heat during soldering (those with good printability). ) can be used.

[0021] The protective insulating coating layer 7 is provided to suppress the transfer of heat to the printed resistor 2 during soldering and to mechanically protect the printed resistor 2 and the buffer insulating layer 6. . This protective insulating coating layer 7 is formed by printing using a heat-resistant insulating resin after the buffer insulating layer 6 is fired. The resin constituting this protective insulating coating layer may be one that has good printability, high solvent resistance, and maintains sufficient mechanical strength when exposed to heat during soldering. It may be a curable resin or a thermoplastic resin, but it is preferably a resin that has the property of being softened by the heat during soldering without losing its independence, and that hardens when cooled. As such a resin, those considered to be preferable as resins for forming the base insulating layer 4, such as novolak type epoxy resin, bisphenol A type epoxy resin, etc., can be used.

[0022] Although not particularly illustrated, the protective insulating coating layer 7 may be covered with a solder resist layer if necessary.

[0023] As described above, if the printed resistor is covered with a protective insulating coating layer via a buffer insulating layer, the printed resistor can be protected from heat by the two layers of the protective insulating coating layer and the buffer insulating layer. In addition, the buffer insulating layer and the base insulating layer absorb the mechanical strain of the protective insulating coating layer and the insulating substrate to prevent distortion from occurring in the printed resistor, thereby reducing changes in the resistance value of the resistor. can.

In particular, as in the above embodiment, the printed resistor 2 is formed on the base insulating layer 4 made of a thermosetting insulating resin that has the property of being softened by heat during soldering, and the printed resistor 2 is is covered with a thermally softenable buffer insulating layer 6, and the buffer insulating layer is further covered with a protective insulating coating layer 7 made of a thermosetting resin that is softened by heat during soldering. The insulating coating layers 1 and 2 can protect the resistor 2 from heat during soldering, and can also completely protect the resistor from thermal shock, minimizing changes in the resistance value of the printed resistor 2. can do.

[0025] That is, when heat is applied during soldering, the protective insulating coating layer 7 and the base insulating layer 4 soften and absorb a portion of the thermal shock, and at the same time, the buffer insulating layer 6 softens and further absorbs the thermal shock. Absorb. In particular, since the buffer insulation layer softens to a state where it is more flexible than the protective insulation coating layer, most of the thermal shock is absorbed by this buffer insulation layer, causing distortion in the printed resistor and causing the resistor to become mechanically unstable. This can prevent the resistor from being destroyed or its resistance value changing significantly. The buffer insulating layer 6 is
Depending on the material (for example, when saturated polyester resin or saturated copolymerized polyester resin is used), it may become fluid due to the heat during soldering, but this buffer insulating layer 6
is covered with a protective insulating coating layer 7 made of a thermosetting resin that retains sufficient mechanical strength even though it may soften, so it will not cause any problems even if it becomes fluid. Not worth it.

[0026] As in the above embodiment, the base insulating layer 4 is formed under the printed resistor.
If the resistor is made of a resin that has the property of softening to some extent by the heat during soldering, the printed resistor can be protected from thermal shock on both sides, increasing the heat resistance of the printed resistor and reducing changes in its resistance value. can be minimized.

[0027] In order to confirm the above effects, as in the above example, a printed resistor was provided on the soldering surface of the board, and the printed resistor was covered with a buffer insulation layer and a protective insulation coating layer. When the circuit board was subjected to a soldering heat resistance test, the results shown in FIG. 5 were obtained.

[0028] In this test, we prepared 10 samples each with a printed resistor 2 having a sheet resistance value of 700KΩ/□, and repeated the test three times by dipping each sample in molten solder at 260°C for 5 seconds. . In the samples used in this test, the protective insulating coating layer 7 was formed of a novolak type epoxy resin, and the tests were conducted with various materials used to form the base insulating layer 4 and the buffer insulating layer 6. The vertical axis in Figure 5 shows the rate of change in resistance value ΔR/R.
The horizontal axis shows the number of dips. Further, in FIG. 5, the straight lines extending upward and downward from the plot points of the actual measured values of each polygonal line indicate the range of variation in the actual measured values.

In FIG. 5, the polygonal line indicates that the printed resistor is formed on the soldering surface of the board without providing a base insulating layer, and the printed resistor is directly formed with a protective insulating coating layer made of thermosetting resin without using a buffer insulating layer. The case where the body is covered, that is, the conventional example is shown.

[0030] Furthermore, the polygonal lines indicate the case where a printed resistor is formed on the soldering surface without providing a base insulating layer, and a saturated polyester resin and a novolak type epoxy resin are used as a buffer insulating layer and a protective insulating coating layer, respectively. There is. As described above, it can be seen that by covering the printed resistor with the buffer insulating layer and the protective insulating coating layer, the change in resistance value after soldering can be significantly suppressed compared to the conventional method.

In FIG. 5, the base insulating layer and the protective insulating coating layer are both made of novolak type epoxy resin (which has the property of softening to some extent when exposed to heat during soldering) to form the first insulating layer. This figure shows cases in which various materials are used to form the buffer insulation layer, and cases in which the buffer insulating layer is formed from silicone resin, silicone rubber, and saturated polyester resin. As is clear from these test results, if the base insulating layer and the protective insulating coating layer are made of a resin that softens to some extent when exposed to heat during soldering,
Changes in resistance after solder dipping can be further reduced.

[0032] In each of the examples of the present invention shown by polygonal lines ~ in Fig. 5, there were no samples in which the printed resistor was thermally destroyed, and it was confirmed that the examples were sufficiently practical.

[0033] Referring to FIG. 3, another embodiment of the invention is shown. In this embodiment, a printed resistor 2 is formed on a soldering surface 3a of an insulating substrate 3 via a base insulating layer 4, and both ends of each printed resistor 2 are covered with a conductive layer 5 made of conductive paint to form a conductive part 1. It is connected to the resistor connection part 1b. A wiring conductor 20 in a predetermined pattern is formed on the other surface 3b of the substrate 3 using metal foil such as copper foil or conductive paint.
A predetermined portion of the conductor 20 is electrically connected to a predetermined portion of the conductive portion 1 on the soldering surface 3a by a known through-hole conductive portion 21 provided through the through hole 3A of the substrate 3.

[0034] A buffer insulating layer 6 made of a heat-softening insulating material is formed so as to cover the printed resistor 2 on the soldering surface 3a. A protective insulating coating layer 7 made of a thermosetting resin is formed.

[0035] Also, the wiring conductor 2 on the other side 3b of the substrate
An intermediate insulating layer 22 is formed so as to cover 0, and a cross jumper line 23 made of conductive paint is printed on this intermediate insulating layer 22. An insulating coating layer (overcoat) 24 is formed to cover the cross jumper wire 23 and the intermediate insulating layer 22.

[0036] FIG. 4 shows still another embodiment of the present invention. In this embodiment, the other surface 3 of the insulating substrate 3
A printed resistor 2' is also formed on the b side with an undercoat 15 interposed therebetween, and this printed resistor 2' is covered with an insulating coating layer 24. In other respects, the structure is similar to that of the embodiment shown in FIG.

[0037] In the above embodiment, only one layer of the printed resistor is provided on the soldering surface of the board, but a base insulating layer is formed on the printed resistor formed on the soldering surface of the board via an undercoat. It is also possible to form another printed resistor through the base insulating layer and cover the printed resistor on the base insulating layer with a buffer insulating layer and a protective insulating coating layer. Further, even when other elements such as capacitance are formed on the substrate together with the printed resistor by printing, the present invention can be applied by covering the other elements together with the printed resistor with the first and protective insulating coating layers. Can be applied.

【0038】

Effects of the Invention As described above, according to the present invention, a printed resistor is formed on the soldering surface of a substrate via a base insulating layer that softens when exposed to heat during soldering, and the printed resistor is The body is covered with a buffer insulating layer that softens when exposed to heat during soldering, and the buffer insulating layer is further covered with a heat-resistant protective insulating coating layer, making it easy to solder onto the soldering surface of the board. When heat is applied, the transfer of heat to the printed resistor can be suppressed, and the printed resistor can be prevented from being exposed to high heat. In particular, in the present invention, when heat is received during soldering, the buffer insulation layer and the protective insulation coating layer block a considerable amount of heat, and at the same time, the buffer insulation layer softens to a state that is more flexible than the protective insulation coating layer. Since the thermal shock is absorbed by the thermal shock, it is possible to prevent the printed resistor from being mechanically destroyed or the resistance value changing due to thermal shock. In addition, if a base insulating layer is formed under the printed resistor and this base insulating layer is made of a resin that has the property of being softened to some extent by the heat during soldering, the printed resistor will be exposed to thermal shock and mechanical strain from both sides. The heat resistance and mechanical strength of the printed resistor can be increased, and changes in its resistance value can be minimized. Therefore, a highly practical circuit board having a printed resistor on the soldering surface of the board can be obtained, and there is an advantage that the component integration density of the circuit board can be increased.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part showing an embodiment of the present invention.

FIG. 2 is a plan view of a main part showing an example of a pattern on a soldering surface of a board in the embodiment of FIG. 1;

FIG. 3 is a sectional view showing a main part of yet another different embodiment of the present invention.

FIG. 4 is a sectional view showing a main part of yet another different embodiment of the present invention.

FIG. 5 is a diagram showing the results of a solder heat resistance test of the circuit board according to the present invention.

[Explanation of symbols]

1... Conductive part 1a...Soldering part 1b...Resistor connection part 2...Printed resistor 3...Insulating board 3a...Soldering surface 4...Base insulation layer 5... Conductive layer 6...Buffer insulation layer 7...Protective insulation coating layer.

Claims (4)

[Claims] 1. A printed resistor-equipped circuit board comprising a printed resistor provided on an insulating substrate having a surface having a conductive portion to which soldering is applied, wherein the printed resistor is provided with a printed resistor on which the soldering of the insulating substrate is performed. A buffer insulating layer is formed on a surface having a conductive portion to be applied via a base insulating layer to cover the printed resistor, and a heat-resistant protective insulating coating layer is formed to cover the buffer insulating layer. A circuit board with a printed resistor, wherein the base insulating layer and the buffer insulating layer are made of an insulating material that has a property of softening when exposed to heat during soldering. 2. The buffer insulating layer is selected from a group of substances including a saturated copolymer polyester resin, a saturated polyester resin, a silicone rubber, and a silicone resin, which soften to a state with higher flexibility than the resin forming the base insulating layer. 2. The printed resistor-attached circuit board according to claim 1, wherein the printed resistor-attached circuit board is made of an insulating material. 3. The base insulating layer is made of a novolak type epoxy resin or a bisphenol A type epoxy resin, which has the property of being softened by heat during soldering to the extent that it does not lose its independence. Circuit board with printed resistor as described. 4. The circuit board with a printed resistor according to claim 1, wherein the conductive portion is made of metal foil.