JP3066090B2 - Liquid preflux composition and printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid preflux composition which functions as a protective film for preventing printed wiring boards from being damaged or stained before soldering, and for preventing rust and oxidation of metal surfaces. The present invention relates to a coated printed wiring board.

[0002]

2. Description of the Related Art Conventionally, a rosin-based preflux composition has been used for protecting printed wiring boards. or,
A preflux composition using a thermoplastic resin and an antioxidant in combination and a composition containing a polyurethane oligomer have also been proposed as a preflux (JP-A-2-49492).
No. 2,104,494).

On the other hand, with the recent demand for higher performance, smaller size and lighter weight of electronic equipment, printed wiring boards are rapidly changing from the conventional insertion mounting method to a high-density surface mounting method (SMT). There is the present situation. As described below, the surface mounting method is subjected to severe heat history repeatedly, so high heat resistance is required for pre-flux, but conventional pre-flux has sufficient performance to respond to this Was not obtained.

To improve heat resistance, for example, a pre-flux composition in which an antioxidant is used in combination with a petroleum resin has also been proposed, but this composition suffers from deterioration in performance due to exhaustion of the antioxidant due to repeated heat treatment. In addition, due to repetition of expansion and contraction of the printed wiring board due to heat treatment, a part of the film having poor flexibility is lost.

The thermal history of such a printed wiring board will be described below using a double-sided surface mounting / lead-through mounting mixed mounting method as an example. FIG. 1 is a flow sheet illustrating an example of the above method. The solder paste 3 is printed on the A surface 2 of the printed wiring board 1 to which the pre-flux has been applied, and after mounting the chip component 4, soldering 5 is performed in a reflow furnace process. At this time, the printed wiring board 1
It is exposed to an ambient temperature of 00 to 250 ° C. Next, B
Adhesive 7 for temporary fixing is applied to surface 6, and after mounting chip components 8, printed wiring board 1 is cured to cure the adhesive.
The treatment is performed at an ambient temperature of 50 to 170C. Further, the discrete component 9 is inserted, and the chip component 8 on the B side 6 and the discrete component 9 are soldered 10 and 11 in a flow solder bath. At the time of soldering in this flow soldering tank, the printed wiring board using the conventional pre-flux under the heat conditions received in the reflow process, the oxidation of the copper surface causes insufficient soldering and reduced adhesive strength of chip components At present, it is becoming impossible to perform highly reliable soldering due to dropping of components. The process of receiving such a heat history tends to require more complicated and severer conditions in the future.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to maintain the performance of a protective film even when a printed wiring board is repeatedly heated and cooled under a high temperature atmosphere in a reflow process. A pre-flux composition that maintains the anti-oxidation function of the surface and removes this protective film during soldering, allowing molten solder to come into contact with the metal surface of the printed wiring board via a post-flux to ensure sufficient soldering An object and a printed wiring board using the same are provided.

[0007]

According to the present invention, there is provided a cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group in a molecule as a pre-flux, and 5 to 100 parts of the cellulose compound.
The object has been achieved by using a composition consisting of a phenolic antioxidant and a solvent by weight and applying the composition to a printed wiring board before soldering.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a cellulose compound as a component of a preflux composition is tough, soluble in a wide variety of solvents, and forms a thin film without losing flexibility even under extreme temperature changes. It is necessary to choose what can be used.

[0009] Such a cellulose compound is represented by the following reaction formula, for example, in the form of cellulose ether produced by reacting ethyl chloride with alkali cellulose. RONa + C ₂ H ₅ Cl → ROC ₂ H ₅ + NaCl (R represents a cellulose group) The structural formula of the cellulose molecule is a chain of β-anhydroglucose linked by an acetal bond, and this long chain has flexibility and toughness. Things.

The introduction of an ethylhydroxyethyl group into cellulose is described by the following reaction formula.

Embedded image Specific examples of such a cellulose compound include ethyl cellulose and ethyl hydroxyethyl cellulose manufactured by Hercules, USA.

The phenolic antioxidants used in the present invention include, for example, para-tert-amylphenol, 2,6-di-tert-butyl-para-cresol, 2,2'-methylenebis (4-methyl -6-tert-
Butylphenol) and the like. These antioxidants can be used alone or in combination as needed.

Next, the solvents used in the present invention include, for example, esters, aromatics, alcohols, ketones,
It is an organic solvent comprising a chlorinated solvent or the like and a mixture thereof.

The content of the cellulose compound in the preflux composition of the present invention is suitably in the range of 1 to 20% by weight, preferably 3 to 10% by weight.

The amount and quality of the antioxidant may be selected as required, but the amount is preferably 5 to 1 based on the weight of the cellulose compound.
00% by weight and preferably 20 to 50% by weight.

The pre-flux composition of the present invention comprises the above-mentioned cellulose compound, antioxidant and organic solvent, and may optionally use a rust preventive or the like, if necessary.

In the present invention, in order to obtain a printed wiring board having a protective film using the above-mentioned preflux composition, the printed wiring board before soldering is washed by an appropriate method, and the copper foil surface is cleaned. Then, a preflux composition is applied by a method such as roll coat application, spray application, brush application, dip application, or the like. After the application, the protective film is formed by natural drying or drying with warm air.

The printed wiring board on which the protective film is formed by the liquid preflux composition as described above is preferably soldered by a normal soldering method for electronic components, that is, reflow fixing, dipping soldering, jet soldering or the like. Can be applied.

[0018]

The cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group used as a component of the preflux in the present invention has the following features.
(1) Since it has flexibility in a wide temperature range, it has excellent impact resistance, and can maintain its performance as a protective film even if any impact is given in handling the printed wiring board. (2) It has good electrical characteristics and has a sufficient function as a protective film such as the insulation property of a printed wiring board. (3) It is easily soluble in various organic solvents, is compatible with common post-flux solvents used in soldering, and has features that facilitate the soldering action.

The printed wiring board on which the liquid pre-flux composition containing such a cellulose compound is applied to form a film has a metal surface covered with the film, so that storage management, storage and handling are easy. In addition, the protective film is stable even when exposed to a high temperature in a manufacturing process such as a reflow process. Further, even if the printed wiring board is repeatedly heated and cooled by heat history, the cellulose compound in the present invention forms a tough film having flexibility not found in rosin-based and petroleum resin-based preflux. As a result, the film adhered to the printed wiring board does not cause partial loss with the metal surface.

Since the film of the cellulose compound is soluble in various organic solvents at the time of soldering, for example, it is easily dissolved in the solvent of the post-flux composition, and the film maintained as the protective film of the printed wiring board is removed. As a result, the molten solder, the post-flux component, and the metal of the printed wiring board come into direct contact with each other, so that good soldering can be performed.

[0021]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. Example 1 The following components were mixed by a conventional method to obtain a liquid composition. Ethyl cellulose Hercules (N-4) 10 parts by weight Antioxidant 2,2'-methylenebis (4-methyl-tert-butylphenol) Ouchi Shinko Chemical (NS-6) 5 Solvent Isopropyl alcohol 228 Toluene 57

Comparative Example 1 Petroleum resin Neon Zeon (U-185) 10 parts by weight Antioxidant Irganox 1010 Ciba-Geigy 5 5 Solvent Toluene 228 Ethyl acetate 57

Comparative Example 2 Rosin Raw rosin 15 parts by weight Solvent Toluene 228 {ethyl acetate 57}

Example 2 Ethyl hydroxyethyl cellulose Hercules (EHEC) 10 parts by weight Antioxidant Irganox 1010 Ciba-Geigy 5 Solvent Toluene 228 Ethyl acetate 57

The preflux compositions of Examples 1 and 2 were dip-coated on a printed wiring board for a through hole test using FR-4 as a base material, and dried at a temperature of 70 ° C. for 5 minutes. The printed circuit board is subjected to a reflow process at a temperature of 23.
The heat treatment at 0 ° C. for 3 minutes was repeated once to five times. Five kinds of test specimens were soldered in a jet soldering process by a conventional method. The soldering of the through-holes was performed according to Examples 1 and 2 regardless of the number of reflow heat treatments.
In both cases, stable soldering was confirmed.

Examples 1 and 2 using the composition of Comparative Example 2
As a result of performing the heat treatment under the same conditions as above, it was not possible to solder to the copper wall of the through hole by one heat treatment, and no solder lift of the through hole was confirmed.

Similarly, the results of heat treatment using the composition of Comparative Example 1 showed that soldering of the through-holes was confirmed by two heat treatments.
It was 0%. Specimens subjected to 5 heat treatments had a solder fried amount of 10% or less of the number of through holes.

[0028]

According to the present invention, a liquid preflux composition comprising a cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group in a molecule as a component is applied to a printed wiring board to form a film at a high temperature. A metal surface such as a copper foil exposed to an atmosphere is protected from adverse effects such as oxidation, and a film having high heat resistance, which cannot be obtained with a film made of a conventional preflux composition, is formed. In addition, since the cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group is easily dissolved in an organic solvent, the film is easily removed by the organic solvent of the post flux composition used at the time of soldering.

The test method for evaluating solderability is JIS
Z 3197-1986 defines a spread test. On the copper surface, the spread rate of the solder is measured, and a material having a high spread rate is said to have good solderability. Although the evaluation can be performed by this method, the test time for the spread of the solder on the copper surface is 3 hours.
It is set to 0 seconds.

The conditions for soldering to a printed wiring board in an actual manufacturing process are as follows. In a high productivity line such as recent automation, the contact time between the molten solder and the printed wiring board is 4,5.
Because of the harsh conditions of seconds, the above-mentioned cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group can be easily dissolved in an organic solvent such as isopropyl alcohol used in the composition of the post flux. This is a feature of the present invention as compared with a protective film insoluble in alcohol solvents such as urethane resin and the like.
Cellulose protective film containing ethoxyl group or ethylhydroxyethyl group dissolves quickly with post-flux solvent immediately before contact with the printed wiring board of the molten jet solder. Since the molten solder and the activator of the post flux composition can effectively contact each other, a sufficiently reliable soldered printed wiring board can be provided.

[0031]

[Brief description of the drawings]

FIG. 1 is a flow sheet for explaining a thermal history in a double-sided surface mounting / lead-through mixed mounting system.

FIG. 2 is a graph comparing the spread ratio of solder after applying to a copper plate using the preflux compositions of Example 1 and Comparative Examples 1 and 2 and performing heat treatment for each time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 The A side 3 Solder paste 4 Chip part 5 Soldering 6 B side of printed wiring board 7 Adhesive 8 Chip part 9 Discrete part 10 Soldering 11 Soldering solid line Example of this invention Dashed line Comparative example 1 Spread rate Dashed line Spread rate of Comparative Example 2

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 35/363 C09D 5/08 H05K 3/28 H05K 3/34 503 B23K 101: 42

Claims (2)

(57) [Claims] 1. A liquid preflux for a printed wiring board comprising a cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group in a molecule, and a phenolic antioxidant and a solvent in an amount of 5 to 100% by weight based on the cellulose compound. Composition. 2. A liquid preflux composition comprising a cellulose compound containing an ethoxyl group or an ethylhydroxyethyl group in a molecule and a phenolic antioxidant and a solvent in an amount of 5 to 100% by weight based on the cellulose compound. Printed wiring board.