JP2564151B2 - Coating solder powder - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating solder powder, and more particularly to a solder powder used in a solder paste for a printed wiring board to prevent oxidation.

BACKGROUND ART A printed circuit board has a circuit pattern formed by etching a copper foil attached to the surface of a laminated board according to an electric circuit, and a circuit board on which electric parts such as resistors and capacitors can be mounted. There is a ceramic substrate in which a circuit pattern of silver-palladium is baked on a ceramic plate. The electrical components are attached to these boards by, for example, soldering the lead terminals to the soldering lands of the circuit pattern.

In this case, the circuit pattern is formed on the opposite side of the printed circuit board on which the electrical components are mounted and the soldering lands are formed, but the circuit pattern is formed on the side of the printed circuit board on which the electrical components are mounted and the soldering lands are formed. There is a so-called plane mounting type. In any of these cases, molten solder is supplied and soldered to the soldering parts of the soldering land and the electric component, but in the former case, jet solder is supplied and soldered, and in the latter case. In many cases, a solder paste is applied in advance to the soldering land, and the coating film of this solder paste is melted and soldered at the time of soldering.

This solder paste is composed of solder powder, resin components such as rosin and a solvent as essential components, and further, if necessary, composed of an activator such as amine hydrochloride, a fluidity imparting agent, etc., which is screen-printed, dispenser, It is applied to the soldering land of the printed circuit board by transfer or the like.
After that, after the electric components are supplied, the solder paste coating film is melted and cooled to complete the soldering work. In order to perform such soldering work, a solder paste is manufactured in advance, and this is brought to the soldering work site,
Normally, the steps from application of the solder paste to soldering by melting the solder are performed in a continuous process.

Problems to be Solved by the Invention In such a case, since the solder paste manufacturer and the soldering operator are different from each other, the solder paste may not be used immediately in the pre-manufactured solder paste and may be used after a certain number of days. During this period, even if the solder paste is stored in a closed container, the powder of lead and tin reacts with the vehicle at room temperature to increase the viscosity. This may double, for example, in one week. Such thickening is accelerated when the solder powder is oxidized, and finally does not exhibit screen-printing fluidity.

Further, the oxidized solder powder does not completely melt when the solder powder that is not oxidized during melting of the solder is melted and agglomerated, is separated from the agglomerated solder and remains at the application position, or is dispersed after the melting is delayed. However, there are also problems that these become solder balls to short-circuit between the conductors, the soldering strength is reduced, and the appearance of the finished soldering is deteriorated.

In order to eliminate such a problem associated with the oxidation of the solder powder, the solder paste may contain a large amount of an activator that reduces the oxide of the solder, and for example, an amine hydrochloride is used as the activator. Therefore, after soldering, if much of it remains on the soldering land, its corrosion is promoted. In order to avoid this, it is necessary to sufficiently perform cleaning after the soldering is completed, so that it is difficult to complete the work while reducing the work efficiency. Further, when a large amount of amine hydrochloride is used in this way, there is a problem that the reaction product with the solder powder thickens the solder paste.

In order to prevent such a reaction between the solder powder and the vehicle and oxidation of the solder powder, the solder paste is stored in a refrigerator, but this involves using the solder paste and returning it to room temperature. It is necessary and has a problem that workability is deteriorated.

In addition, when manufacturing a solder paste, it is also possible to knead the ingot of the solder with the hivicle immediately after forming the powder particles by, for example, an atomizing method, but after manufacturing the solder powder for the convenience of the work, wait for a while. It may be kneaded with the vehicle and the solder powder may be transported during this time. Even in such a case, the solder powder is oxidized when exposed to air, and when it is made into a solder paste, the viscosity is remarkably increased as described above. For this reason, the solder powder is stored in vacuum or in an inert gas to avoid its oxidation. However, since this also requires equipment, and its handling is troublesome, its improvement has been desired.

Means for Solving the Problems In order to solve the above problems, the present invention is characterized in that a vehicle used for a solder paste is coated with solder powder particles with an insoluble or sparingly soluble coating agent. To provide a coating solder powder.

 Next, the present invention will be described in detail.

The coated solder powder in the present invention is obtained by coating solder powder with a coating agent. As what is used as this solder powder, for example, the atomization method, that is, the solder ingot is melted and dropped,
It is produced by spraying an inert gas or the like on the way to form particles, and those having various particle sizes (for example, a particle size of 100 mesh or less) and shapes (spherical or amorphous) can be used. The composition is, for example, 63Sn / 37Pb, 62Sn / 36Pb.
In addition to / 2Ag, those shown in the table below are used.

Further, as the coating agent, those which are insoluble or hardly soluble in the vehicle of the solder paste described later can be used, and for example, silicon oil, silcon-based polymer, fluorinated silicon oil, fluorosilicone resin, fluorinated hydrocarbon. Examples of silicon-based polymers such as silicon and fluorine-based polymers are given below.

Silicon Polon L, Polon T, KF96, KS-701, KS-707, KS-70
5F, KS-706, KS-709, KS-709S, KS-711, KSX-71
2, KS-62F, KS-62M, KS-64, Siliconube G-430, Si
licolube G-540, Siliconeube G-541 or above SH-200, SH-210, SH-1109, SH-3109, SH-3107, manufactured by Shin-Etsu Chemical Co., Ltd.
SH-3108, SH-8011, FS-1265, Syli-off23, DC pan
Glaze62 or above Fluoro series Die-free MS-443, MS-543, MS-743, MS-043, ME manufactured by Toray Silicon Co., Ltd.
-413, ME-810 and above Daikin Industries, Ltd. Fluorad FC-93, FC-95, FC-98, FC-129, FC-1
34, FC-430, FC-431, FC-721 or higher Sumitomo 3M Co., Ltd.Sumiflunon FP-81, FP-81R, FP-84C, FP-84R, F
P-86 and above Sumitomo Chemical Co., Ltd. Surflon SR-100, SR-100X and above Kiyomi Chemical Co., Ltd. EF-125DS, EF-1200 and above Shin-Akita Kasei Co., Ltd. These can be used alone or in combination. . Polymers are particularly preferable.

In order to coat the solder powder with such a coating agent, the coating solution is mixed with a solvent to prepare a treatment liquid, and the solder powder produced by, for example, an atomizing method is immediately dipped and stirred in that order. . The solvent is preferably a halogenated hydrocarbon such as 1,1,1 trichloroethane, and the concentration of the solid content of the coating agent is preferably 0.01% to 2%.

After stirring in this way, it is allowed to stand for 5 minutes to 1 hour, and then solid-liquid separation can be performed by a gradient method, a centrifugal separation method, or a filtration method. After this, it is dried, and this drying may be either natural or air drying, may be drying in an inert gas or in vacuum, and either normal temperature or heat drying may be used, and these may be used in combination. good.

Although an inert gas is blown when the solder powder is produced by the atomizing method, the surface of the solder powder may be covered by blowing the treatment liquid together with this gas. At this time, the method of dipping in the above-mentioned treatment liquid may be used together.

In this way, the coating solder powder is obtained, the type of this coating film can be confirmed by pyrolysis gas chromatography, the coating amount can be estimated by Auger electron spectroscopy analysis, carbon-containing compound in the coating agent When used, carbon is preferably 30 mol% to 70 mol% as a quantitative analysis value.

To form the coating solder powder of the present invention as a solder paste, it is mixed with a vehicle, but in the solder paste, a flux is used as a vehicle, and as the flux, a resin and a solvent are essential components, and if necessary, a thixotropic agent. It is made by blending a solvent, etc. There are three types of flux in the United States MIL standard (MIL-F-14256) depending on the activity (R: inactive, RMA: moderately active, R
A: activity), but it is generally preferable to mainly use RA or RMA grade for solder paste, but it is not limited to these. Inorganic acid salts of amines such as aniline hydrochloride, organic acid salts of amines, amines, organic acids, and halogenated hydrocarbons are used as activators of this vehicle.

In the solder paste thus obtained, the solder powder is coated with the coating agent, and since the film of this coating agent is insoluble or hardly soluble in the resin of the vehicle, the solvent, etc., the solder powder is coated by the coating film. By being shielded from the outside world, the reaction with the vehicle and the reaction with oxygen in the air are blocked. This maintains the viscosity stability of the solder paste.

On the other hand, when this solder paste is applied to the soldering lands of the printed circuit board, dried and melted to wet the soldered parts of the supplied electric components, the coating solder powder melts and separates from the coating film on its surface. To do. After this, the solder melts are fused together, cooled and the electrical components are soldered to the soldering lands.
At this time, if the film of the coating agent is made thin, its influence can be ignored. This film is preferably one that melts at the melting temperature of the solder, but it may be one that does not melt.

Example Next, an example of the present invention will be described.

Example 1 A solder alloy (Sn 63 wt%, Pb 37 wt%) ingot was melted to form 250 to 400 mesh solder alloy powder particles by an atomization method, and the particles were immediately treated with 20 kg of a treatment liquid.
And stir. This treatment liquid is the above-mentioned Florard FC
-721 was dissolved in 500g Freon TF (DuPont) 1Kg
It is a 50% (solid content 1%) solution. The above operation is continued until the amount of the solder powder in the treatment liquid reaches 10 kg, and then left for 30 minutes. After that, the supernatant liquid is removed by a gradient method and naturally dried.

Thus, the coated solder powder was obtained, which was analyzed by Auger electron spectroscopy, and was as shown in FIG. The analysis results of the solder powder before coating by Auger electron spectroscopy were as shown in FIG. From these, carbon (C) was hardly detected in the solder powder before coating, whereas a sharp peak of carbon (C) was detected in the solder powder after coating, and C58.6mol%, Sn17.8mo
It was calculated that the coating amount was 1% and O2 was 3.6 mol%, and the coating amount was about 60 mol% in the case of C off.

Even after the above coated solder powder was left in the air at room temperature for 30 days, the result of analysis by Auger electron spectroscopy in the same manner as above showed a spectrum similar to that shown in FIG. No change with time was observed in the coating film.

In applying the Auger electron spectroscopy, the coating solder powder obtained above was held under pressure on an indium (In) plate for measurement.

In addition, gas chromatography manufactured by Shimadzu Corporation
Using GC-7APTF with PYR-2A (pyrolysis device) manufactured by the same company, 0.16 g of the above coating solder powder in nitrogen gas was used.
When the generated gas when heated at 00 ° C was analyzed,
The results shown in the figure were obtained. Further, when 1 ml of the above treatment liquid was analyzed in the same manner, FIG. 4 was obtained. The retention time of the peaks shown in each of these figures and the area ratio of the peaks are calculated as follows.

From these, it was confirmed that the main peaks coincided with each other, and the coating film of the coating solder powder was the same as the resin Florard-721 used in the treatment liquid. The measurement conditions for gas chromatography are: column: PEG-6000 (polyethylene glycol) 10%, column temperature: 3 ° C / min 100
Temperature rise from ℃ to 180 ℃, carrier gas: nitrogen, flow rate:
50 ml / min, detector: FID (hydrogen ion detector), injection temperature: 230 ° C.

Next, the following solder paste was prepared using the coating solder powder obtained above.

Coated solder powder (63Sn / 37Pb) 90 parts by weight Polymerized rosin 5.8 parts by weight Hydrogenated castor oil 0.4 parts by weight Dimethylamine hydrochloride 0.05 parts by weight Butyl carbitol 3.75 parts by weight After mixing for 30 minutes at room temperature with solvent or solder powder The mixture was further mixed with stirring to adjust the viscosity to 360,000 centipoise. The solid line of this solder paste is shown in FIG. 5 when refrigerated, stored at 20 ° C., and stored at 40 ° C. Further, when the solder paste prepared in the same manner except that the solder powder before coating was used instead of the coating solder powder in the above solder paste, the viscosity was measured in the same manner, and it was as shown by the dotted line in FIG. A Brookfield HBT viscometer was used for the measurement.

From this, it can be seen that the solder paste using the coated solder powder has good viscosity stability at 20 ° C (room temperature).

Example 2 A coating solder powder was prepared in the same manner as in Example 1 using an ingot of a solder alloy (62Sn / 36Pb / 2Ag),
Using this, a solder paste having the following composition was prepared in the same manner as in Example 1 and measured in the same manner as in Example 1.
It was as shown in the figure.

Coating solder powder (62Sn / 36Pb / 2Ag) 90 parts by weight Polymerized rosin 5.8 parts by weight Hydrogenated castor oil 0.4 parts by weight Dimethylamine hydrochloride 0.05 parts by weight Butylcalcitoleol 3.75 parts by weight According to the present invention, coating solder Since powder can be provided, its oxidation is prevented even if it is stored or transported in the air, so it is extremely easy to handle, and solder powder production and solder paste production are separated separately with time. It is possible to facilitate the production planning of the solder paste.

Further, by using the coating solder powder of the present invention,
The viscosity change of the solder paste can be remarkably suppressed, and the printability can be maintained for a long time.
Especially this solder paste can be stored at room temperature,
Since refrigeration is not required, the storage cost can be reduced and the handling can be facilitated.

[Brief description of drawings]

FIG. 1 is an Auger electron spectroscopic analysis spectrum of the coated solder powder of one embodiment of the present invention, FIG. 2 is an Auger electron spectroscopic analysis spectrum of the solder powder before the coating, and FIG. 3 is the same sample heat as FIG. Decomposed gas chromatogram, Fig. 4 is a gas chromatogram of the same sample as Fig. 2, Fig. 5 is Fig. 1 and Fig. 2 is a viscosity measurement graph of solder paste using the same sample as each sample, and Fig. 6 is 7 is a viscosity measurement graph of a solder paste using the coated solder powder of another example.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Yuhiro Miyano 1336 Kitairi, Sayama City, Saitama Prefecture, Saitama Prefecture (72) Inventor Nobuo Tajima 31-32, Shinmeicho, Kawagoe City, Saitama Prefecture (72) Makoto Inoue Tokyo Metropolitan Government Kita-ku Akabanedai 1-2-8-209 (56) Reference JP-A-57-52588 (JP, A)

Claims (1)

(57) [Claims] 1. A coated solder powder, characterized in that a vehicle used in a solder paste is coated with solder powder particles with an insoluble or sparingly soluble coating agent.