JPH0543315B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a protective composition for preventing oxidation of a copper foil land before soldering of a printed wiring board, and to a printed wiring board in which a protective film is formed using the same.

Conventional technology Printed wiring boards are used to mount electronic components such as resistors and capacitors. A circuit pattern is formed by etching copper foil pasted onto the board, and the copper foil lands of this circuit pattern are etched. The above electronic components are connected and fixed by soldering.

By the way, recently, with the miniaturization and higher performance of electronic devices, there is a demand for high-density mounting of electronic components on printed wiring boards, and for this reason, surface mount technology (SMT) has been researched and rapidly developed. Progress has been made. Along with this, the wiring of circuit patterns has become more precise and delicate, and it is also important to reduce the soldering failure rate in so-called micro-soldering, which involves soldering electronic components at high density to copper foil lands. This requirement is becoming stricter, and even if several hundred solders are to be soldered, only a few can be soldered.

In order to reduce this soldering defect rate, it is necessary to optimize each process such as forming the circuit pattern by etching when creating a printed wiring board, applying flux during soldering to the printed wiring board, and performing soldering. The condition must be considered. Among these, when using a so-called reflow process, in which soldering is performed by supplying solder paste to the soldered part and heating it to melt the solder powder, the heating temperature is high and the solder powder is melted to speed up the melting time. Heat treatment conditions are becoming increasingly complex and severe, requiring shorter heating times.

On the other hand, one of the important measures is to prevent the copper foil land from rusting after the circuit pattern is formed and before the flux is applied.

To form a circuit pattern on a printed wiring board, an etching resist is screen printed on the copper-clad laminate, cured with ultraviolet light or heat, and then etched with a ferric chloride aqueous solution to remove the copper foil other than the circuit area. After dissolving and removing the etching resist, the etching resist is dissolved and removed with a solvent or alkaline liquid to expose the circuit portion, and then the solder resist is screen printed and cured with ultraviolet rays or heat to expose the soldered portion (land). It will be done. At this time, the exposed copper foil part is oxidized and rusts, so if you apply flux to it and then solder it, the solder will not wet well, weakening the soldering strength and causing soldering defects. It can happen.

Therefore, the oxide film on the copper foil land to be soldered is removed. It is considered preferable to perform a soft etching process, and when a considerable amount of time has elapsed before soldering, a preflux is applied and an oxidation-preventing film is provided.

This soft etching process involves immersing the copper foil land in an aqueous solution such as ammonium persulfate, sodium persulfate, or a mixture of sulfuric acid and hydrogen peroxide.
The oxide film is dissolved and removed.

Problem to be Solved by the Invention However, even if a protective film is provided to prevent oxidation of the copper foil land by forming a preflux film after performing the above-mentioned soft etching process, the above-mentioned recent reflow soldering cannot be performed. When the protective film is exposed to high temperatures, such as when the protective film is exposed to high temperatures, the oxidation resistance of the protective film may not be sufficient, resulting in poor soldering.

An object of the present invention is to provide a protective composition for a printed wiring board and a printed wiring board that have excellent oxidation resistance and do not impair solderability when performing reflow soldering at high temperatures.

Means for Solving the Problems In order to solve the above problems, the present invention provides a composition coated on the metal surface of a printed wiring board to be reflow soldered by high-temperature heating, the composition comprising a rosin ester resin, a rosin derivative, etc. , a petroleum resin, and a terpene resin with a softening point.
5 to 40 thermoplastic resins with a temperature higher than 100℃ and lower than 130℃
The present invention provides a protective composition for a printed wiring board characterized by containing 0.05 to 40% by weight of an antioxidant, and a printed wiring board using the composition as a protective film.

Next, the present invention will be explained in detail.

The protective composition of the present invention is preferably applied to a soft etched metal surface, but
It can also be applied to metal surfaces and other surfaces after etching treatment.

In other words, the copper foil land of the soldered part of the printed wiring board on which the circuit pattern is formed as described above oxidizes when exposed to air, so do not use ammonium persulfate, sodium persulfate, or sulfuric acid. A soft etching process is performed by immersing it in an aqueous solution, such as a mixture of hydrogen peroxide, to remove the rust.

After performing this soft etching treatment, the protective composition of the present invention is applied to the copper foil land of the wiring part,
It is preferable to form a protective film by drying.

The protective composition of the present invention contains a thermoplastic resin, which includes petroleum resins, terpene compounds, rosin ester resins, rosin derivatives, and the like. The softening point (according to the ring and ball method) of these resins is higher than 100°C and lower than 130°C.
If it is lower than 100℃, the molten resin may flow during high-temperature reflow soldering and the coated metal surface may be exposed. Prevents contact of solder with metal surfaces.

Specifically, Fuoral 85 manufactured by Herkyulis,
Examples include YS Polyster manufactured by Yasushi Oil Co., Ltd. and Neopolymer manufactured by Nippon Petrochemicals.

An antioxidant is used in combination with the above thermoplastic resin. Examples of the antioxidant include hindered phenol compounds and hydrazine compounds, and a specific example is Irganox manufactured by Ciba Geigy.

A polyamine, an organic acid salt or an inorganic acid salt of an amine may be used in combination with the protective composition of the present invention, if necessary. These salts act as reducing agents to reduce the oxides in the copper foil. Examples of the polyamine include ethylenediamine, and examples of the amine include cyclohexylamine.

In the protective composition of the present invention, in addition to the above-mentioned components, an organic solvent is used, and examples of the solvent include alcohol solvents, aromatic solvents, and ester solvents.

The composition ratio in the protective composition of the present invention is such that the thermoplastic resin is preferably 5 to 40% by weight, more preferably 10 to 30% by weight, and the antioxidant is 0.5% by weight based on 100 parts by weight of the thermoplastic resin. It is preferably 0.05 to 40% by weight, more preferably 10 to 30% by weight, and the remainder is an organic solvent. If the amount of resin is more than this, it is uneconomical. Furthermore, when the above-mentioned polyamine or amine salt is used in combination, it is preferably used in an amount of 20 to 25% by weight.

To apply the protective composition of the present invention, after performing the soft etching treatment as described above, it is washed in a wet state with deionized water for 30 to 60 seconds, then lower alcohol, then ester solvent, etc. It is preferable to wash the copper foil with solvents of decreasing polarity in order to thoroughly degrease the surface of the copper foil, and then dry and apply the coating.

To apply the protective composition of the present invention, the printed wiring board to be protected may be immersed in the protective composition after being diluted with a solvent as necessary.
This protective composition may be applied by spray or roll coater. After this, it may be left to dry, or may be dried with cold air, hot air, or further dehydrated with a water-absorbing material.

In this way, a protective film is formed on the copper foil land of the wiring part of the printed wiring board that has been soft etched, but when soldering electronic components,
In particular, a reflow soldering method using high-temperature heating is also preferably used.

Function: The protective film is made of a thermoplastic resin such as a rosin ester resin with a softening point higher than 100°C and lower than 130°C, combined with an antioxidant, so the protective film maintains oxidation resistance even when exposed to high temperatures. Yes, it can protect metal surfaces from oxidation.

Example Next, examples of the present invention will be described.

A 7mm x 15mm x 0.2mm copper plate was treated with 11% sulfuric acid, 3.8% by weight.
60 at 20±1°C in an aqueous solution containing wt% hydrogen peroxide.
After immersing it for a second to perform soft etching, take it out and wash it with ion-exchanged water for 30 seconds. Thereafter, it was washed with isopropyl alcohol and ethyl acetate in order, the surface was thoroughly dehydrated, and then air-dried.

This copper plate is mixed with 9.8% by weight of rosin ester resin,
A test piece was prepared by immersing it in a solution in which 0.2% by weight of an antioxidant was dissolved in isopropyl alcohol and air drying it at room temperature and pressure.

For this test piece, in order to examine the solderability of molten solder, the solder wetting time was measured using a solder graph manufactured by Tamura Kaken Co., Ltd. The measurement method is as follows.

Prepare six of the above test pieces and heat each one at 200℃ for 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes.
For each test piece that had undergone these heat treatments, flux manufactured by Tamura Kaken Co., Ltd.
After flux treatment using CF-220V,
Wetness of the molten solder to the copper plate was measured using a digital solder graph manufactured by Tamura Kaken Co., Ltd. That is, each test piece was placed in molten solder (63 wt% tin/37 wt% lead eutectic solder) at a solder bath temperature of 250°C.
The test piece is immersed in a depth of mm, and the time (seconds) it takes for the force acting on the test piece of molten solder to change from upward to downward and for the force acting in the vertical direction to balance out and become 0 is measured.

The measurement results are shown in the graph of the figure as a solid line.

Comparative Example In Example 1, rosin ester resin was
Test pieces were prepared in the same manner as in Example 1 using the same solution except that 10% by weight was used instead of 9.8% by weight and no antioxidant was used, and these were also tested in the same manner as in Example 1. The results are shown in the graph in the figure as a dotted line.

From the above results, the time required for the molten solder to wet the test piece of the example which was heated for more than 30 minutes was significantly shorter than that of the comparative example. This is because the copper plate of the comparative example was oxidized due to the heating of the test piece. Although the molten solder is difficult to wet, the copper plate of the test piece of the example has sufficient oxidation prevention effect, and the film melts and is pushed away by the molten solder, allowing the molten solder to come into good contact with the copper plate. I understand that.

Effects of the Invention According to the present invention, an antioxidant is used in combination with a thermoplastic resin having a softening point higher than 100°C and lower than 130°C, which is made of at least one of rosin ester resin, rosin derivative, petroleum resin, and terpene resin. Since we can provide a protective composition for printed wiring boards, a protective film coated on a metal surface such as copper foil using this composition can be soldered not only in air but also by heating at high temperature for a short time. It shows a sufficient oxidation prevention effect even when heated under severe conditions such as in recent reflow soldering methods, and it melts due to the temperature of the molten solder and is easily pushed away by the molten solder. It can provide a protective film that cannot be obtained with conventional preflux.

Since such a printed wiring board with a protective film can be provided, it is possible to significantly reduce soldering defects of electronic components to the printed wiring board, and it is possible to improve the reliability of the printed wiring board and the workability of soldering thereto.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of a solderability test.

Claims (1)

[Scope of Claims] 1. A composition to be coated on the metal surface of a printed wiring board to be reflow soldered by high-temperature heating, the composition being made of at least one of rosin ester resin, rosin derivative, petroleum resin, and terpene resin. 1. A protective composition for a printed wiring board, comprising 5 to 40% by weight of a thermoplastic resin having a softening point higher than 100°C and lower than 130°C, and 0.05 to 40% by weight of an antioxidant. 2. A printed wiring board characterized in that a metal surface of the printed wiring board is protected using the protective composition for a printed wiring board according to claim 1.