JPS605080B2 - Composition for protective film of circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition for a protective film of a circuit board, and in particular, the present invention relates to a composition for a protective film of a circuit board. In a circuit board on which a planar chip-type electrical element is mounted, the protective film that protects the soldering part is made suitable for soldering, and the adhesion to the adhesive for fixing the position of each of the electrical elements is increased. The present invention relates to a composition for a protective film as described above.

Among electrical elements such as resistors and capacitors, chip-type electrical elements that use electrodes instead of lead wires or have electrodes or lead wires in one horizontal plane are composed of, for example, square chips. In the case of a resistor element that has electrodes on both sides, this element can be attached to the soldered portion of the circuit pattern of the circuit board from the same side.

Therefore, if circuit patterns are formed on both sides of the circuit board, both sides of the circuit board can be used, which increases the wiring density of the circuit board, which allows the overall structure of the circuit board with elements mounted on it to be smaller and thinner. These electric elements have been used in a wide variety of ways in recent years. In order to solder each of the above-mentioned electrical elements to a circuit board, the elements to be soldered must be soldered while hanging from the circuit board, using either the commonly used bonding method or the jet method. The electrical element must be securely fixed to the circuit board in order to move it into contact with the circuit board. By the way, circuit boards are made by forming a circuit pattern on a synthetic resin laminate using steel foil, covering this circuit pattern with an insulating film leaving only the soldered parts, and then covering the soldered parts with a protective film and then using copper foil. Prevents oxidation. At this time, not only the soldered portion but also other insulating films are coated with the protective film. This is because the protective film is formed by roll coating, dipping, or spraying. Conventionally, this protective coating paint has a solid content that is a mixture of alkyd resin or polyester resin with a softening point of 10,000 or higher, petroleum resin, and vinyl copolymer resin, and in addition to these solid content, ethyl acetate, toluene, and methyl ethyl ketone are added. , methyl isobutyl ketone, isobutanol, and other solvents to reduce the solid content to 20~
A composition with a concentration of 45% has been used. However, as mentioned above, the protective film made of this paint also covers the insulating film, so the electrical element must be adhered to this protective film. However, if an epoxy adhesive or an acrylic UV-curable adhesive is used for this bonding, in the case of the former, it will be heated at 150°C for 5 to 20 minutes, and this heat will cause thermal deterioration of the protective film. This not only impedes the adhesion between the protective film and the insulating film, making it impossible to securely maintain the electrical element on the circuit board, but also causes the protective film to become insoluble, making it difficult to solder the parts later. When the molten solder comes in contact with the protective film, the protective film does not melt, and therefore the protective film is not pushed away by the molten solder. Therefore, the solder cannot make good contact with the copper foil, resulting in an unbridged state, which prevents the original soldering. You will not be able to achieve your purpose. In addition, if you try to avoid this by removing the protective film before using the above adhesive, not only will it be time consuming, but the copper foil on the exposed soldering area will oxidize due to the heat used to harden the adhesive. - or be contaminated by adhesive volatiles. In this case, soldering cannot be performed easily. On the other hand, when bonding an electric element to a protective film using the latter type of ultraviolet curable adhesive, the temperature rises only to about 100q0, and the curing time ranges from overnight to 3.
Since the amount of sand is small, there is no thermal deterioration of the protective film that would cause the unsealed condition described above, but the compatibility between the adhesive and the protective film becomes poor, and peeling between the adhesive and the protective film is likely to occur. The electrical elements bonded to the circuit board become extremely susceptible to falling off during handling operations such as transporting and stacking the board. Therefore, if the protective film is removed in the same way as above, the same problem will occur. Therefore, in the present invention, when a leadless electric element or a chip-type electric element is bonded and fixed to a protective film made of conventional paint using a thermosetting adhesive or an ultraviolet curing adhesive, the protective film is removed. In order to improve the problem that thermal deterioration occurs, making it impossible to solder or reducing the adhesive strength of the adhesive, and that removing the protective film to avoid this problem is cumbersome. The circuit board is provided with a protective film that is thermally stable and does not impair solder wettability or compatibility with adhesives and does not reduce its adhesive strength, and electrical elements can be inserted while covered with this protective film. The present invention provides a composition for a protective film of a circuit board, which can be fixed and soldered.

For this purpose, the composition for a protective film for a circuit board of the present invention is applied to a circuit board to protect its soldered portion, and to provide a leadless electric element having an electrode instead of a lead wire or a leadless electric element having an electrode instead of a lead wire. is a composition for forming a protective film to which a chip-type electric element having lead wires protruding horizontally in one plane is bonded via an adhesive, and the softening point of the protective film is 60q0 or more and 100°C or less, and The protective film is characterized in that it comprises at least a rosin resin contained in the circuit pattern so as to be corrosion resistant and insulating, and a solvent that dissolves the rosin resin. The protective film in the present invention contains a rosin resin as a basic component, has a softening point of 60° C. or higher and 100 qo or lower, and is bonded to a leadless electrical element or Even after a chip-type electric element is bonded to it, it has such thermal properties that it comes into contact with molten solder during soldering, melts, and is pushed away by the solder. These thermal properties include, in addition to the above-mentioned thermal stability, which prevents the adhesive from reacting and becoming infusible due to the heat generated during curing, and the adhesive that is applied due to the heat generated during curing. It is necessary to have flowability that allows easy miscibility. The flowability that allows for easy compatibility with this adhesive means that when the adhesive hardens, it does not impair the adhesive strength between the adhesive and the protective film, and the adhesive strength between the insulating film and the protective film of the circuit pattern. This is important in order to ensure that the electrical element is firmly fixed to the circuit board. If the protective film containing the rosin resin has a softening point exceeding 100° C. as described above, it cannot be expected to maintain the adhesive strength as described above. Furthermore, if the softening point of this protective film is too low, not only will the electrical element not be able to be stably bonded to the circuit board, but it will also be sticky even under normal conditions, making it difficult to handle the board. The lower limit of the softening point of this protective film is approximately 60 oo. From the above, it is preferable that the protective film has a softening point of 60 qo or more and 100 q0 or less, but the optimum softening point is 90 qo or less. Furthermore, the rosin resin contained in the protective film must be corrosion resistant to the copper foil, and this also includes properties such as air barrier properties and non-hygroscopic properties. Furthermore, this rosin-based resin must be of a type that does not impair electrical insulation. This is so that even if the circuit board comes into contact with other electrical wiring, it will not disturb the circuit of this wiring. Rosin-based resins having the above properties include gum rosin, wood rosin, polymerized rosin, hydrogenated rosin, esterified rosin, disproportionated rosin, phenol-modified rosin, maleic acid-modified rosin, and the like. The above-mentioned resin can be used alone for the protective film, and in that case, a resin with a softening point of 100°C or lower is used, but is not limited to this, and is not limited to dioctyl phthalate (DOP),
It is also possible to use a plasticizer such as dimethyl phthalate (DMP) in combination, and to form a protective film by mixing 5 to 15% by weight of these plasticizers with respect to the resin, and to lower the softening point to 100 qo or less.

Note that the softening point here is a value determined by the ring and ball method specified in JIS. In addition to the above, the composition of the present invention also includes 1
One property is that activators such as amines, amine hydrochloric acid, organic acids, and amino acids that reduce copper oxide are added to the resin.
．． 02 to 25% by weight may be mixed. The protective film mixed with this retention agent can have a function as a flux.

The rosin resin, plasticizer, and activator are dissolved in various organic solvents such as alcohol, aromatic, hydrocarbon, and ester to form a paint. This paint is coated on the circuit board and sealed, and can be applied by roll coating, dipping, or spraying.

When electrical elements are bonded to the protective film formed on the circuit board in this way using a thermosetting adhesive or an ultraviolet curable adhesive, the protective film will not deteriorate due to heat caused by the curing of these adhesives. , which exhibits thermal flowability and is well compatible with adhesives without impairing adhesive strength, melts when it comes into contact with molten solder and is pushed away by the solder, making direct contact between the solder and the copper foil possible. It exhibits thermal properties. Next, an embodiment of the present invention will be described based on FIGS. 1 and 2. Figure 1 is a cross-sectional view of a portion of the circuit board with electrical elements attached to it, and Figure 2 shows a protective film formed on a steel plate, which is applied under the curing conditions of a thermosetting adhesive or an ultraviolet curable adhesive. FIG. 3 is a characteristic diagram showing wetting of solder on a test piece after heating under the same conditions.

In the figure, 1 is the substrate body. This board body 1 has a circuit pattern 2 made of copper foil on its surface, and has a soldered portion 2a.
, 2a' are shown in the figure. The entire surface of the board body 1, except for the soldering parts 2a and 2a', is coated with an insulating film 3 made of an epoxy thermosetting film or an acrylic ultraviolet curing film.
, 2a' are coated with the paint of Experimental Example 1 and 5 of the present invention in Table 1 by roll coating, forming a protective film 4 of about 5 to 1 cape. The temperature was 120°C in Comparative Example 1 and 160o0 in Comparative Example 2, whereas the temperature in Experimental Examples 1 to 5 of the present invention was 100°C or less and 60q.
It is 0 or more.

In addition, Experimental Example 2 of the present invention has a softening point of 9000, and Experimental Example 5 has a softening point of 7yo. Next, the performance of this protective film 4 will be explained in comparison with the performance of protective films formed using the paints of Comparative Examples 1 and 2 shown in Table 1 in the same manner as above. For this purpose, as shown in FIG. 1, the electric element 5 is located between the soldering parts 2a and 2a', and the electric element is bonded there with a thermosetting adhesive or an ultraviolet curable adhesive.
Tables 2 and 3 show the results of the solder wetting test and the electrical element adhesive strength test. Here, the test piece was prepared by applying the paint shown in Table 1 to the main body of the board by roll coating, drying with natural ventilation to form a protective film, and applying epoxy adhesive to this protective film at 150°C for 10 minutes. The adhesive was bonded by irradiating ultraviolet rays with three ozone-less mercury lamps for 19 steps using an ultraviolet curable adhesive. The above wetting test is to immerse a test piece coated with flux in molten solder for 3 seconds at 250 oo in a jet-type automatic soldering machine, and visually observe whether the solder is repelled and does not get wet. The corresponding number is counted as the non-wetted number. Separately, a steel plate coated with a protective film and heated under the same curing conditions as the epoxy adhesive or ultraviolet curable adhesive described above was made into a 0.2 rib thickness. When this test piece is flux-treated and immersed in molten solder, it is measured whether the test piece receives upward or downward force over time, and this is shown in Figure 2. This latter test was conducted using M Yamaichi STD88$Method2022Menisco bait a
According to the ph Solderability test method.

In addition, in the adhesion test, the number of electrical elements that fall off due to the pressure of molten solder during soldering is counted from the same test piece as the one used when measuring the number of unbridges mentioned above. At the same time, we measured the tensile load that caused the electrical element to detach laterally.Furthermore, we repeatedly dropped a 10-strong test piece onto the concrete floor from above 1, and 1/2 of the 5-strong electrical element fell from the circuit board. This tells you how many times it will fall before it falls off. Table 2 shows the test results when the epoxy adhesive was cured at 150° C. for 10 minutes.

Table 2 Table 3 shows the test results when an acrylic ultraviolet curable adhesive was cured with sand using three ozoneless mercury lamps for an irradiation time of 19 hours.

Table 3 - Of the above wetting tests, the one shown in Figure 2 shows the force exerted on the test piece by the surface tension of the test piece immersed in molten solder in dyn/ka, where A is Comparative Example 1. , 2, and B' are those of Experimental Examples 1 to 5 of the present invention.

(It is the same regardless of whether the protective film is exposed to the curing conditions of epoxy adhesive or ultraviolet curable adhesive.) In this figure, the upper part with Myn/arc as a reference is the molten solder. The solder is shown to be repelled by the protective film, and the lower part shows that the protective film has melted and the solder comes into contact with the copper plate and becomes wet. From these results, Comparative Examples 1 and 2, in which the protective film has a softening point of 120°C and 16000°C, have better solder wetting and electrical element adhesion than the experimental examples of the present invention, in which the protective film has a softening point of 100°C or lower. It is clear that both are inferior.

As explained above, according to the present invention, it is possible to provide a composition that provides a protective film that is thermally stable and has solderability, especially on a circuit board on which a leadless electric element or a chip-type electric element is mounted. Because it is possible to securely fix a leadless electric element or a chip-type electric element to a circuit board through this protective film without removing this protective film, it is also possible to securely fix the electric element to the circuit board through this protective film. Soldering is possible, and the workability of soldering can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a part of a circuit board having a protective film formed using a composition according to an embodiment of the present invention, and FIG. 2 shows a protective film formed on a copper plate and bonded with a thermosetting adhesive or FIG. 3 is a characteristic diagram showing solder leakage from a test piece after heating under the same conditions as the curing conditions of the ultraviolet curable adhesive. In the figure, 1 is the board body, 2 is the circuit pattern, 2a, 2a'
3 is a soldering part, 3 is an insulating film, 4 is a protective film, 5 is an electric element, and 5a, 5a' are electrodes. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A leadless electric element that is coated on a circuit board to protect its soldered portion and has electrodes instead of lead wires, or has electrodes or has lead wires that protrude in a horizontal plane. A composition for forming a protective film to which a chip-type electric element is bonded via an adhesive, wherein the softening point of the protective film is 60°C or more and 100°C or less, and the protective film is 1. A composition for a protective film of a circuit board, comprising at least a rosin-based resin that is contained so as to have corrosion resistance and insulation properties, and a solvent that dissolves the rosin-based resin. 2. A leadless electrical element that is coated on a circuit board to protect its soldered parts and has an electrode instead of a lead wire, or a chip-type electrical element that has an electrode or a lead wire that protrudes in a horizontal plane. A composition for forming a protective film that is bonded via an adhesive, wherein the softening point of the protective film is 60°C or more and 100°C or less, and the protective film has corrosion resistance and insulation properties with respect to the circuit pattern. 1. A composition for a protective film for a circuit board, comprising: a rosin resin, an activator that reduces copper oxide, and a solvent that dissolves the rosin resin and the activator. 3. The composition for a protective film of a circuit board according to claim 1 or 2, characterized in that the composition contains a plasticizer.