JP4457070B2 - Solder paste composition - Google Patents

Description

  The present invention relates to a lead-free solder paste that is excellent in viscosity stability, reduces flux scattering and decomposition in a soldering process, and reduces the generation of voids in a soldered portion.

In recent years, surface mounting technology has rapidly developed along with the multi-functionalization, miniaturization, and miniaturization of wiring boards for electronic devices. When surface mounting electronic components, reflow soldering methods that use solder paste are mostly used. ing. The solder powder used for the solder paste is mostly Sn-Pb-based.
However, if the electronic equipment is disposed of after it has been used, etc., it is disassembled and part of it is recovered, but the mounting board on which the electronic components are mounted is crushed and landfilled without being recovered. The current situation is that some are left in nature.
Since electronic components are soldered on the mounting board that is dumped in nature, if this solder contains lead, it will be eluted as a soluble lead compound due to acid rain, etc., and pollutes nature. In addition, contaminated water and animal and plant foods may be ingested by humans through groundwater, which is becoming a serious problem because of its high toxicity.
Accordingly, lead-free solder materials have been developed, and so-called lead-free solder alloy powders such as Sn—Ag alloys and Sn—Ag—Cu alloys have been used.

By the way, in order to solder an electronic component to a printed wiring board, solder paste is applied to the soldering land of the printed wiring board, and the chip-shaped electronic component is placed so that its electrode or lead is positioned on the soldering land. Temporarily fastening with the adhesive strength of the coating film, then heating, and soldering by melting the solder powder of the solder paste film is performed, but solder paste is applied to the through hole provided in the printed wiring board. In addition, a lead wire of an electronic component is inserted into this, and heating and soldering are performed in the same manner as described above.
Such solder paste contains, for example, solder powder, rosin resin, activator, solvent and thixotropic agent, but the application is performed by screen printing using a metal mask, for example, so the viscosity of the solder paste is moderate. And so-called viscosity stability is required, the viscosity of which must be maintained moderately after production. Further, when applied to a printed wiring board, it is also necessary to suppress the scattering of the flux and the decomposition of the flux film, and to prevent the generation of voids in the molten solder due to the decomposition gas.

In order to increase the viscosity stability of the solder paste, a device for suppressing the reactivity of the solder metal is also performed. For example, the solder powder is insoluble or difficult to coat with glycerin (Patent Document 1 below), the solder paste solvent, or the like. A method of coating solder powder with a soluble coating agent (silicone-based, fluorine-based compound, etc.) is also known (Patent Document 2 below), and malonic acid and succinic acid are used to stabilize lead-free solder. This is also known (Patent Document 3 below).
In addition, methods for reducing solder-based flux scattering and methods for reducing voids in soldered portions (Patent Documents 4 to 6 below) are also known.

JP-A-60-261689 Japanese Patent Laid-Open No. 1-113197 Japanese Patent Laid-Open No. 10-43882 JP 2004-322139 A JP 2000-42786 A JP 2003-264367 A

  However, unlike the conventional Sn / Pb solder containing lead (63Sn / 37Pb), the lead-free solder has a high Sn content (higher than 63%) and Sn is highly reactive. There exists a problem that it is easy to react with a resin component etc. and it is easy to impair the viscosity stability of a solder paste. For this reason, even the methods described in Patent Documents 1 to 3 that touch this problem solution cannot be said to have been sufficiently improved for lead-free solders, apart from lead-based solders. In particular, soldering of electronic parts is performed at many places on a single wiring board, and a large number of microscopic and lightweight 0603 chips (length 0.6 mm, width 0.3 mm) are also used. Is miniaturized and multi-functionalized, and a large number of leads are arranged at narrow intervals. For example, in an integrated circuit component such as QFP or SOP, the number of leads is 100 or more and the lead interval is 0.5 mm or less. In addition, as the mounting density for mounting electronic components progresses more and more, as the finer one with a lead interval of 0.3 mm has been put into practical use, printing of a solder paste with higher definition is required. For this purpose, the stability of viscosity is becoming more and more important, and further improvement is desired.

  In addition, since the lead-free solder has a high melting point of 200 to 220 ° C., the reflow soldering method using the solder paste containing the solder powder needs to have a peak temperature during heating of 230 to 240 ° C., In the case of a lead-based Sn—Pb alloy, the eutectic composition (63Sn / 37Pb) has a melting point as low as 183 ° C., and in the reflow soldering method using the solder paste containing the solder powder, the peak temperature of the heating Compared with the temperature of about 230 ° C., flux is likely to be scattered in the soldering process, and the insulating performance and antioxidation performance of the soldered land due to the leakage of coating are likely to be impaired. Further, when the flux film is exposed to a high temperature, decomposition is likely to occur, and if gas is generated in the decomposition product, voids (vacuum) are likely to be generated in the soldered portion, resulting in a problem that the bonding strength is reduced. Therefore, even if the solder paste viscosity is stabilized using lead-free solder stabilized with malonic acid or succinic acid, the flux is easily scattered by these malonic acid or succinic acid, and the flux film is decomposed. About the point which is easy to generate and a void tends to generate | occur | produce in a soldering part, even if it is the method of the said patent documents 4-6 touching solution of these problems, it is the improvement about a lead-type solder irrespective of a lead-type solder Is not done enough.

The first object of the present invention is to provide a lead-free solder paste that has excellent viscosity stability over time, reduces flux scattering and decomposition in the soldering process, and provides a soldered state with reduced void generation. There is to do.
A second object of the present invention is to provide a lead-free solder paste capable of obtaining a highly reliable mounting board for circuit conductors.

As a result of intensive studies to solve the above problems, the present inventor has found that a solder paste using a flux component containing a low molecular dibasic acid dialkyl ester compound in lead-free solder powder has viscosity stability. When using this to reflow soldering electronic components to a printed circuit board, flux scattering hardly occurs, the flux film does not easily decompose, and voids are generated in the soldered portion due to the decomposition gas. It was found difficult to complete the present invention.
Accordingly, the present invention provides (1) a lead-free solder powder having a Sn content of more than 63% by mass and a solder paste containing at least a resin component, or a lead-free solder having a Sn content of more than 63% by mass. In the solder paste containing a powder, a resin component, an activator, a solvent, and a thixotropic agent, a solder paste composition containing a low-molecular dibasic acid dialkyl ester compound is provided.
The present invention also relates to (2) a solder paste containing a low molecular dibasic acid dialkyl ester compound in a solder paste containing a lead-free solder powder, a resin component, an activator, a solvent, and a thixotropic agent. A solder paste composition that is excellent in viscosity stability over time, is less likely to cause flux scattering and decomposition in the soldering process, and is less likely to generate voids in the soldered portion; (3) low The molecular dibasic acid dialkyl ester compound is a compound having 4 to 21 carbon atoms, the solder paste composition of (1) or (2), (4), a solder containing at least a lead-free solder powder and a resin component Low molecular dibasic in paste or solder paste containing lead-free solder powder, resin component, activator, solvent and thixotropic agent A solder paste composition containing an acid dialkyl ester compounds, low molecular dibasic acid dialkyl ester compound is a compound from 4 carbon atoms 21, the low-molecular dibasic acid dialkyl ester compound 0 A solder paste composition containing 3% by mass to 1% by mass is provided.
In addition, " (1) Solder containing a low molecular dibasic acid dialkyl ester type compound in a solder paste containing at least a lead-free solder powder and a resin component used when soldering an electronic component to a circuit board, for example " A paste composition is provided.
Further, the present invention provides (2) a solder paste containing a lead-free solder powder, a resin component, an activator, a solvent, and a thixotropic agent, for example, used when soldering an electronic component to a circuit board. Solder paste composition comprising a low molecular dibasic acid dialkyl ester compound, (3), and the low molecular dibasic acid dialkyl ester compound is a compound having 4 to 21 carbon atoms. (4) A low-molecular dibasic acid dialkyl ester compound is provided in the solder paste composition according to any one of (1) to (3) above, which is contained in an amount of 0.1% to 10.0%. . It can also be said.

In the present invention, the lead-free solder powder is a solder powder containing no lead component, and includes Sn / Ag, Sn / Ag / Cu, Sn / Ag / Bi, Sn / Bi, and Sn / Ag / Cu. / Bi, Sn / Ag / Bi / In, Sn / Zn, Sn / Zn / Bi, Sn / Zn / Al, Sn / Sb and the like.
The lead-free solder powder used in the solder paste of the present invention is used in the solder paste in an amount of 85 to 92% (flux: 8 to 15%, “%” represents mass%, hereinafter the same), and is spherical and has a particle size of 1 A solder powder of ˜40 μm is preferable for reflow soldering for the recent printed circuit board and solder bump formation in which the pitch of the soldering land is becoming narrower.

  Examples of the resin component used in the solder paste of the present invention include rosin-based resins. Examples of rosin-based resins include rosin and derivatives thereof such as modified rosin, and these can be used in combination. Examples include gum rosin, wood rosin, polymerized rosin, phenol-modified rosin and derivatives thereof, but acrylic resins can also be used in combination. The content of the rosin resin can be 30 to 70% in the so-called flux, which is another component excluding the solder powder of the solder paste composition. If it is less than this, oxidation of the copper foil surface of the soldering land is prevented and the solder is easily wetted on the surface, so-called solderability is deteriorated, and solder balls are easily formed. Become more.

Examples of the activator include organic amine hydrohalides and organic acids. Specifically, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide as organic amine hydrohalates. Salts, diethylamine hydrochloride, triethanolamine hydrobromide, monoethanolamine hydrobromide, and organic acids include malonic acid, succinic acid, maleic acid, glutaric acid, suberic acid, adipine An acid, sebacic acid, etc. are mentioned.
These activators are preferably 0.1 to 3% in the flux from the viewpoint of suppressing the corrosiveness caused by the flux residue and not impairing the insulation resistance, and further from the viewpoint of preventing solderability and solder balls.

In addition, a thixotropic agent may be used. For example, hydrogenated castor oil, fatty acid amides, and oxy fatty acids are fluxed so that the solder paste can be adjusted to a viscosity suitable for its printability. It is preferable to contain 3 to 15%.
Moreover, as a solvent, what is used for the normal solder paste is mentioned. Examples thereof include hexyl carbitol (boiling point: 260 ° C.), butyl carbitol (boiling point: 230 ° C.), ethylene glycol monobutyl ether, and the like, and it is preferably contained in the flux by 30 to 50%.

In the present invention, the low molecular dibasic acid dialkyl ester compound is added to the solder paste. Specifically, the solder paste is added to the flux and the flux is stirred and mixed with the lead-free solder powder. Obtained (flux is obtained by removing solder powder from solder paste). Specific examples of the low molecular dibasic acid dialkyl ester compounds include dimethyl malonate, diethyl malonate, dipropyl malonate, diisopropyl malonate, and dibutyl malonate (C5-13). Is mentioned. In addition, succinic acid di-lower alkyl esters (carbon number 5 to 14) such as dimethyl succinate corresponding to each of these may also be mentioned, and low molecular dibasic acid di-lower alkyl ester compounds (carbon numbers 5 to 14). (“Lower alkyl” means an alkyl group having 1 to 5 carbon atoms.) Low molecular dibasic acid dialkyl ester compounds are low molecular dicarboxylic acid dialkyl ester compounds, low molecular dibasic acid dilower alkyl esters. The low-molecular dicarboxylic acid di-lower alkyl ester compound may be a low-molecular organic acid ester compound, which is a monomolecular compound, but may be a multimer. The dialkyl ester compounds include those having 4 to 21 carbon atoms, and these compounds can be used alone or in combination. , Alkyl groups may have a substituent on the lower alkyl group, a dialkylamino group, a di-lower alkyl groups that two alkyl groups, two lower alkyl groups may be the same or different.
The addition amount of the low molecular dibasic acid dialkyl ester compound and the like is preferably 0.1% to 10.0%, particularly preferably 0.3% to 1%. When the addition amount is less than 0.1%, the effect of adding to the solder paste is not observed, and when the addition amount is 10.0% or more, the solderability is deteriorated.

  By adding the low-molecular dibasic acid dialkyl ester compound (especially the low-molecular dibasic acid di-lower alkyl ester compound) to the flux, the solder paste is said to be an essential component for maintaining viscosity stability. Since the added substances (for example, malonic acid and succinic acid) can be omitted, the disadvantages (addition of voids and flux scattering described above) due to the addition of this substance can be reduced. That is, especially in solder paste using lead-free solder powder with a lot of Sn, malonic acid and succinic acid have a low decomposition temperature, and flux scattering frequently occurs due to the effect of decomposition of the organic acid. This is a cause of void generation in the soldered part, but the addition of the low molecular dibasic acid dialkyl ester compound improves the viscosity stability by the same mechanism as malonic acid and succinic acid. On the other hand, since the decomposition temperature is high, flux scattering can be reduced, and furthermore, these compounds are not easily gasified (the molecular weight is large and stabilized because of esterification). Therefore, voids are less likely to occur in the soldered portion.

  According to the present invention, since it is possible to provide a solder paste containing a low molecular dibasic acid dialkyl ester-based compound, it has excellent viscosity stability over time, reduces flux scattering and decomposition in the soldering process, and solders To provide a solder paste using lead-free solder that enables soldering with reduced generation of voids in the part, and that does not deteriorate the solderability and can provide a highly reliable circuit board. Can do.

  Details will be described with reference to the following examples, but the objects of the present invention can be well realized by those having a scope similar to the above description of the present invention centering on these examples.

Hereinafter, examples will be described, but the present invention is not limited to the following examples.
A solder paste having the following composition was prepared.
Hydrogenated rosin (rosin resin) 50.0g
Diphenylguanidine hydrobromide (active agent) 0.5 g Adipic acid (active agent) 0.5 g
Hydrogenated castor oil (thixotropic agent) 6.0g
Ethylene glycol monobutyl ether (solvent) 38.0g
Dimethyl malonate 5.0g
(Flux 100g)
Flux 11.0g
Lead-free solder powder (Sn / 3Ag / 0.5Cu, particle size 1-12μm) 89.0g
(Solder paste 100g)
A solder paste was obtained by stirring and mixing the flux and the solder powder. When this solder paste was measured with a Malcolm viscometer, it was 210 Pa · s (measurement temperature 25 ° C.) (initial viscosity).

Table 1 shows the results of the following tests using the solder paste obtained above.
(i) Flux scattering test Using a test board (copper-clad laminate) manufactured by Tamura Kaken Co., Ltd., soldering is performed using a peak 245 ° C profile for soldering temperature. Count the number of flux scattered per 25 cm ² at that time (pieces / 25 cm ² ).
(ii) Void generation test A test board (copper-clad laminate) manufactured by Tamura Kaken Co., Ltd. is used, a BGA (ball grid array) is mounted, and soldering is performed using a peak 245 ° C profile. At that time, the area ratio (%) of voids generated in the soldered part of the BGA (ratio of the planar area of the void to the total area of the solder in the plan view) is measured.
(iii) Viscosity change test after 1 month After making the solder paste, store it under constant temperature and humidity (10 ° C, 50% relative humidity) for 1 month, and then measure the viscosity (conforms to JIS Z 3284 (1984)) .

A solder paste was prepared in the same manner as in Example 1 except that 5 g of diethyl malonate was used instead of 5 g of dimethyl malonate, and the results of tests conducted in the same manner as in Example 1 are shown in Table 1.
In addition, when the viscosity of the solder paste was measured in the same manner as in Example 1, it was 215 Pa · s (measurement temperature 25 ° C.) (initial viscosity).

A solder paste was prepared in the same manner as in Example 1 except that 5 g of dibutyl malonate was used instead of 5 g of dimethyl malonate, and the results of testing this in the same manner as in Example 1 are shown in Table 1.
In addition, when the viscosity of the solder paste was measured in the same manner as in Example 1, it was 214 Pa · s (measurement temperature 25 ° C.) (initial viscosity).
[Comparative Example 1]

A solder paste was prepared in the same manner as in Example 1 except that 5 g of dimethyl malonate was not used and that part was used instead of ethylene glycol monobutyl ether. Table 1 shows.
In addition, when the viscosity of the solder paste was measured in the same manner as in Example 1, it was 210 Pa · s (measurement temperature 25 ° C.) (initial viscosity).
[Comparative Example 2]

A solder paste was prepared in the same manner as in Example 1 except that 5 g of malonic acid was used instead of 5 g of dimethyl malonate, and the results of testing this in the same manner as in Example 1 are shown in Table 1.
In addition, when the viscosity of the solder paste was measured in the same manner as in Example 1, it was 210 Pa · s (measurement temperature 25 ° C.) (initial viscosity).

In Examples 1 to 3, even if ethylene glycol monobutyl ether (solvent) was used instead of adipic acid, the effect was almost unchanged under the use of adipic acid, instead of malonic acid diester. Moreover, it is considered that an effect equivalent to this can be obtained when a succinic diester corresponding to this is used.
From the results of Table 1, Examples 1 to 3 have no change in viscosity after 1 month relative to the initial viscosity, compared to Comparative Example 1, and are about 6 to 10 times better than Comparative Examples 1 and 2 in the flux scattering test. The test shows 50-120% better.

The “low molecular dibasic acid dialkyl ester compound” means “low molecular aliphatic dibasic acid dialkyl ester compound”, “low molecular dibasic carboxylic acid dialkyl ester compound” [general formula R ₁ -AR]. ₂ compounds (R ₁ and R ₂ are carboxylate groups (R ₁ is —COOR ₁₁ , R ₂ is —COOR ₂₁ (R ₁₁ and R ₂₁ are alkyl groups, which may be the same or different)), A Is a substituted or unsubstituted saturated or unsaturated hydrocarbon group (the saturated hydrocarbon group includes a substituted or unsubstituted alkylene group (— (CH ₂ ) n — (n is an integer including 0))) or A low molecular weight aliphatic dibasic carboxylic acid dialkyl ester compound ”(in the above general formula, A is a substituted or unsubstituted saturated or unsaturated hydrocarbon group (saturated carbon). The hydrogen group may be a substituted or unsubstituted alkylene group.)) May be used, and the “low molecular dibasic acid di-lower alkyl ester compound” may be referred to as “low molecular aliphatic dibasic acid di-lower alkyl ester compound”. ", A low molecular dibasic carboxylic acid di-lower alkyl ester compound" (in the above general formula, R ₁₁ and R ₂₁ are lower alkyl groups which may be the same or different) or "low molecular aliphatic dibasic carboxylic acid A di-lower alkyl ester compound ”(in the above general formula, A is a substituted or unsubstituted saturated or unsaturated hydrocarbon group (the saturated hydrocarbon group includes a substituted or unsubstituted alkylene group), and R _11. R ₂₁ is a lower alkyl group which may be the same or different. “Dibasic carboxylic acid” may be “dicarboxylic acid”, and “dibasic” may be “dibasic”.
In addition, the invention of “a reflow soldering method in which an electronic component is reflow soldered to a soldered portion of a printed circuit board using the solder paste composition according to any one of the above (1) to (4)” is configured. May be.

Claims (4)

In a lead-free solder powder having a Sn content higher than 63% by mass and a solder paste containing at least a resin component, or a lead-free solder powder having a Sn content higher than 63% by mass , a resin component, and an activator A solder paste composition containing a low molecular dibasic acid dialkyl ester compound in a solder paste containing a solvent and a thixotropic agent. A solder paste containing a low molecular weight dibasic acid dialkyl ester compound in a solder paste containing a lead-free solder powder having a Sn content higher than 63 mass% , a resin component, an activator, a solvent, and a thixotropic agent. A solder paste composition that is excellent in viscosity stability over time, is less likely to cause flux scattering and decomposition in a soldering process, and is less likely to generate voids in a soldered portion. The solder paste composition according to claim 1 or 2, wherein the low-molecular dibasic acid dialkyl ester compound is a compound having 4 to 21 carbon atoms. In a solder paste containing at least a lead-free solder powder and a resin component, or in a solder paste containing a lead-free solder powder, a resin component, an activator, a solvent, and a thixotropic agent, a low-molecular dibasic acid dialkyl ester a solder paste composition containing a system compound, the low molecular dibasic acid dialkyl ester compound is a compound from 4 carbon atoms 21, the low-molecular dibasic acid dialkyl ester compound 0.3 mass Solder paste composition containing 1% to 1% by mass .