JPH06269979A - Solder precipitation composition and method for precoating circuit board with solder - Google Patents

Abstract

PURPOSE:To prevent the oxidation of solder as germanium preferentially adsorbs oxygen at the time of precoating and to enable good soldering even with a flux of low activity. CONSTITUTION:This solder precipitation compsn. consists essentially of org. acid lead salt and powder of a tin-germanium alloy contg. 0.001 to 0.1% germanium and the balance tin and the ratio of the lead in the org. acid lead salt and the tin in the alloy is 20 to 50:50 to 80. The precoating method is executed by applying the solder precipitation compsn. on a circuit board and heating this circuit board for 0.5 to 5 minutes at 180 to 250 deg.C, thereby depositing the lead-tin-germanium alloy on the pads of the circuit board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder deposition composition for depositing a solder containing tin and lead as main components, and a solder deposition composition which is necessary for soldering on a pad of a circuit board using the solder deposition composition. The present invention relates to a solder precoating method for forming a solder layer.

[0002]

2. Description of the Related Art Conventionally, a solder layer is pre-coated on a pad of a circuit board, an electronic component is placed on the pad and heated, and the solder layer is remelted to solder the electronic component to the circuit board. Attaching is done.

As a method of pre-coating a circuit board with a solder layer, a solder deposition composition containing an organic acid lead salt and a tin powder as main components has been recently applied to a circuit board by solid coating and heating the composition on the pad. A method of selectively precipitating a solder alloy to form a solder layer has been proposed and is attracting attention.

[0004]

However, in this method, when the solder alloy is deposited, the solder alloy adsorbs oxygen in the air and is easily oxidized. Physically preventing the adsorption of oxygen has also been attempted, but it is not perfect, and in particular, oxygen adsorbed inside the solder alloy cannot prevent oxidation from proceeding inside.

Therefore, in order to reduce the oxide of the solder alloy, a flux having a strong activity must be used, and the electrical reliability is impaired.

Further, Japanese Patent Laid-Open No. 62-230493 describes that a small amount of germanium is added to the solder alloy to prevent the solder alloy from being oxidized. For a circuit board having a small pitch, it is difficult to reliably pre-coat the pads with solder.

The present invention has been made in view of the above circumstances, and germanium is added to tin in a solder deposition composition to precipitate germanium-containing solder on a pad, thereby giving priority to the germanium. The purpose of this is to adsorb oxygen to and to prevent oxidation inside the alloy of tin and lead.

[0008]

Therefore, the solder deposition composition of the present invention contains an organic acid lead salt and a germanium content of 0.001 to 0.001.
A powder of a tin-germanium alloy whose main component is 0.1% and the balance is tin, and the ratio of lead in the organic acid lead salt and tin in the alloy is 20 to 50:50 to 80. It is what

Further, the precoating method of the present invention comprises, as a main component, an organic acid lead salt and a tin-germanium alloy powder having a germanium content of 0.001 to 0.1% and the balance being tin. The ratio of lead in salt and tin in alloy is 20 to 5
The solder deposition composition of 0:50 to 80 is applied to a circuit board and heated at 180 to 250 ° C. for 0.5 to 5 minutes to deposit a tin-lead-germanium alloy on the pad of the circuit board. It is characterized by causing precipitation.

As the organic acid lead salt in the present invention, a lead salt of an organic acid such as rosin acid, naphthenic acid and higher fatty acid can be used.

As the tin-germanium alloy, one having a germanium content of 0.001 to 0.1% and the balance of tin is used. Germanium content is 0.001%
If it is less than 0.1%, there is no effect, and if it exceeds 0.1%, the content of germanium becomes excessive and the performance as a solder alloy deteriorates.

In the present invention, the ratio of lead in the organic acid lead salt and tin in the tin-germanium alloy is from 20 to 50:50.
Should be 80. If the ratio is out of this range, the solderability will deteriorate. Similar to the ratio of normal lead-tin eutectic alloy, 3
Most preferably, the ratio is 8:62.

In addition to the above organic acid lead salt and tin-germanium alloy, the solder deposit composition of the present invention may optionally contain additives similar to those used in ordinary solder deposit compositions. You can

For example, rosins, waxes, solvents such as carbitol and mineral spirits, and additives such as amine-based activators can be added.

When the solder deposition composition is applied to a circuit board, it may be printed by a method such as screen printing according to the pad pattern of the circuit board as in the case of a normal solder paste, but a portion where the pad pitch is small. In, it is also possible to apply a solid coating to the entire pad group.

By heating the circuit board coated with the solder deposition composition at a temperature of 180 to 250 ° C. for 0.5 to 5 minutes, the lead ions in the organic acid lead salt and the metal in the alloy powder are separated. Ion-exchange reaction occurs between the two, and tin-lead-
A germanium alloy, that is, a solder alloy containing a small amount of germanium, is deposited and a solder layer is precoated on the pad.

[0017]

In the present invention, the solder alloy is deposited on the pad by the ion exchange reaction between the organic acid lead salt and the metal tin, and the solder layer is precoated on the surface of the pad. At this time, since a small amount of germanium is contained in the metal tin powder, germanium preferentially adsorbs oxygen and prevents the progress of oxidation of tin and lead in the solder layer.

In the ion exchange reaction, lead ions are converted into metallic lead, and at this time, highly active metallic lead is produced,
This bonds with oxygen and is easily oxidized. Therefore, the solder deposited from the solder deposition composition is more likely to be oxidized than ordinary powdered solder, but according to the present invention, germanium adsorbs oxygen, so the opportunity for active lead to bond with oxygen is lost. , It effectively blocks oxidation.

[0019]

As described above, according to the present invention, the solder composed of tin and lead is less oxidized, and even the flux having weak activity can be soldered well, and the electrical reliability of the circuit is improved. .

[0020]

【Example】

 Example Preparation of Solder Deposition Composition A solder deposition composition was prepared according to the following composition.

Lead rosin acid salt (lead content 10% by weight) 50 parts by weight Rosin 10 parts by weight Wax 2 parts by weight Butyl carbitol 10 parts by weight Mineral spirits 10 parts by weight Diethanolamine 8 parts by weight Tin-germanium alloy powder 10 parts by weight ( Germanium content 0.01% by weight, particle size 20-6
0 μm)

Precoat The solder deposition composition was printed on a copper plate (40 × 10 × 0.3 mm) with an applicator at a thickness of 200 μm, heated at 220 ° C. for 2 minutes, cooled at room temperature, and washed with toluene to remove the residue. A solder layer was formed on the surface of the copper plate. A solder layer was similarly formed on the back surface.

Comparative Example A copper plate was immersed in a molten solder bath of tin-lead alloy at 250 ° C. to form a solder layer on both sides of the copper plate.

Solder wettability test The wettability of solder was tested by a meniscograph on copper plates having solder layers formed on both sides according to the examples and comparative examples.

Test conditions Bath temperature: 235 ° C. Immersion depth: 2 mm Immersion speed: 16 mm / min Immersion time: 5 seconds Post-flux: 4 types of aqueous solution resistance 50,000 cΩ RA system aqueous solution resistance 100,000 cΩ RMA system aqueous solution resistance 20 10,000 cΩ RMA system Aqueous solution resistance 400,000 cΩ R system

Test Results The solder wettability for each post flux is shown in Table 1 as the zero cross time (seconds) in the above-mentioned Examples and Comparative Examples.

[0027]

[Table 1]

From the results shown in Table 1, it can be understood that the solder deposit composition of the present invention has good solder wettability and suppresses oxidation of the solder alloy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Noriko Katayama Inventor Noriko 4 471 67 Mizumizu, Kakogawa-shi, Kakogawa, Central Research Laboratory, Harima Kasei Co., Ltd. (72) Takao Fukunaga 2-6-1 Marunouchi, Chiyoda-ku, Tokyo No. Furukawa Electric Co., Ltd. (72) Inventor Kazuto Hikasa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Within Furukawa Electric Co., Ltd.

Claims (2)

[Claims] 1. A lead-alloy of an organic acid lead salt, which comprises a lead-organic acid salt and a tin-germanium alloy powder having a germanium content of 0.001 to 0.1% and the balance being tin, as a main component. Solder deposition composition, characterized in that the ratio with the tin in it is 20-50: 50-80 2. A lead-alloy in an organic acid lead salt, comprising a lead-organic acid salt and a tin-germanium alloy powder having a germanium content of 0.001 to 0.1% and the balance being tin, as a main component. The circuit board is coated with a solder deposition composition having a ratio of tin in the range of 20 to 50:50 to 80, and this is applied at 180 to 250 ° C.
A method for pre-coating a solder on a circuit board, which comprises depositing a tin-lead-germanium alloy on a pad of the circuit board by heating for 0.5 to 5 minutes.