JP3480634B2 - Flux for soldering - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux used when soldering a printed circuit board or the like.

[0002]

2. Description of the Related Art When soldering a printed circuit board or the like, a flux is used to remove a natural oxide film on the surface of a conductor metal. A usual flux is composed of an activator for removing a natural oxide film, a rosin for maintaining reliability after soldering, and alcohols as their solvent. Since the conventional rosin-based flux uses a strong activator such as a hydrohalide salt, if it remains on the board after soldering, it will affect the insulation reliability of the board. Therefore, after soldering, it was necessary to wash and remove the flux residue on the substrate.

Therefore, recently, attention has been paid to rosin-based flux which does not require cleaning after soldering. This flux uses an organic acid having a relatively weak activity as an activator. The activator remaining on the board after soldering is captured by rosin,
High insulation reliability can be maintained without cleaning. However, in the rosin-based flux for no-cleaning, the rosin may remain on the substrate after soldering, which may cause contact failure of the checker pins.

By using a solvent such as polyalkylene glycol dialkyl ether, which is immiscible with water, as the flux for no-cleaning without adding rosin, the hygroscopicity of the residue after soldering is suppressed, and thus the insulation reliability of the board is improved. To secure the above (Japanese Patent Laid-Open No. 3-7779).
No. 3), or containing a deactivator, which reacts with a halogen-based activator at the temperature at the time of soldering to make the activator harmless so as to ensure the insulation reliability of the substrate ( Japanese Patent Laid-Open No. 4-143093) has been proposed. However, in the former flux, when the solvent decomposes and disappears after soldering, the activator is exposed and exists, and the insulation reliability may decrease. In addition, the latter flux is due to the shape of parts, etc.
If the temperature of the substrate is not sufficiently high during soldering, the activator may not be completely deactivated and the insulation reliability may decrease.

[0005]

[Problems to be Solved by the Invention] As described above,
In the conventional non-cleaning flux, the addition of rosin was essential in order to ensure insulation reliability. Therefore, it is an object of the present invention to provide a flux for no-cleaning which has excellent insulation reliability without using rosin.

[0006]

In order to solve the above problems, the present invention provides a soldering flux with a chelating agent that forms a complex with at least tin and copper. The soldering flux of the present invention is a sublimation.
Chelating agent having solubility and dissolving it to form a chelate
It contains a solvent that suppresses sublimation of the agent. The complex is water insoluble
It is preferable that the complex is a complex and is insoluble in the solvent.
Preferably there is. The chelating agents of the oxalic acid, A Ntoraniru acid, at least one selected from the group consisting of contact and quinoline-8-carboxylic acid are preferably used. As the solvent, at least one selected from dihydric alcohols represented by the following formulas (1) and (2) is preferably used.

[0007]

[Chemical 2] (In the formula, r and s are 1 or 2.)

When the above solvent is used, the chelating agent is preferably a chelating agent which forms an insoluble complex with copper and tin. Such chelating agents include anthranilic acid and quinoline-8-
At least one selected from the group consisting of carboxylic acids is suitable.

As described above, the soldering flux of the present invention contains, as an activator, at least a chelating agent which forms a complex with tin and copper. When this flux is used, tin, which is the main component of the solder, and a chelating agent form a complex after soldering, and a complex film is formed on the solder. This complex has a chelate structure and has a very strong binding force between the chelating agent and the metal. In particular, oxalic acid, iminodiacetic acid, nitrilotriacetic acid, anthranilic acid, quinaldic acid, and quinoline-8-carboxylic acid complexes with tin do not dissociate with water, so the presence of this complex coating results in the presence of a substrate after soldering. Shows excellent insulation reliability even without cleaning. In addition, since the complex film is similarly formed on the copper portion, which is the main component of the conductor metal, even if flux is attached to the portion where soldering is not performed, the insulation reliability is not affected. Furthermore, since the rosin does not remain on the substrate after soldering, contact failure of the checker pin does not occur.

Further, when a chelating agent which forms a water-insoluble complex with tin and copper is used, the complex is not dissolved and ionized by water even under a high humidity condition, so that the insulation reliability is more excellent. . If the chelating agent that forms a complex with copper and tin has a subliming property, it decomposes by heat during soldering, so that the residue after soldering is reduced. When a sublimable chelating agent is used, the chelating agent is decomposed before the solder is completely spread during soldering, reoxidation of the substrate occurs, and the solderability may deteriorate. On the other hand, by using a solvent that suppresses sublimation of the chelating agent as a part of the solvent component, excellent solderability can be obtained.

Further, in the flux containing the solvent that suppresses the sublimation of the chelating agent, by using the chelating agent that forms a complex that does not dissolve in water and the solvent used for suppressing the sublimation, the solvent remains after soldering. Even in the case, the complex does not elute, and the insulation reliability is superior to that of the above flux. The complex of the chelating agent anthranilic acid or quinoline-8-carboxylic acid with copper or tin does not dissolve in the solvent represented by the above formulas (1) and (2), which suppresses the sublimation of the chelating agent, and water. Therefore, the complex does not elute even under high humidity conditions or when the solvent remains on the substrate after soldering, and excellent insulation reliability can be obtained.

As a solvent for suppressing the sublimation of the chelating agent, one having an ethylene glycol group addition mole number of ethylene oxide group of 3 or more, or one having a propylene glycol group addition mole number of propylene glycol group compound of 3 or more Has a high boiling point and does not decompose at the soldering temperature. Therefore, it remains on the substrate after soldering, and there is an undesirable problem such as stickiness.

[0013]

DETAILED DESCRIPTION OF THE INVENTION I with a flux, including at least constituting a chelating agent and a solvent are preferred. The chelating agent functions as an activator for removing the natural oxide film on the conductor metal and facilitating the joining of the conductor metal and the solder, and as described above, the copper of the conductor metal and the tin of the solder metal are used. And has a role of forming a complex that is an insulating substance and ensuring insulation reliability after soldering. The solvent is preferably one in which the chelating agent is dissolved and dispersed in the solvent, and which is evaporated during soldering and does not become a residue after soldering. Solvents that satisfy such conditions include water, hydrocarbons, ketones, ethers, esters, monohydric alcohols, dihydric alcohols, glycol ethers, etc. that evaporate at the soldering temperature.

When the chelating agent has sublimability, it is more preferable to include a solvent that suppresses the sublimation. Solvents that satisfy this include ethylene glycol, diethylene glycol, and propylene glycol. Since these do not dissolve the complex formed by anthranilic acid and quinoline-8-carboxylic acid with copper and tin, it is preferable to form a flux in combination with these chelating agents. When anthranilic acid is included as a chelating agent and only a solvent selected from the group of ethylene glycol, diethylene glycol, and propylene glycol is used as a solvent, the solvent does not completely evaporate during soldering and remains as a residue after soldering. Therefore, these solvents 10
It is more preferable to use a solvent in which 50 to 95 parts by weight of 0 parts by weight is replaced with a low boiling point solvent. As the low boiling point solvent to be substituted, there are water, hydrocarbons, ketones, ethers, esters, monohydric alcohols and glycol ethers that evaporate at the soldering temperature.

When the flux is composed of the chelating agent and the solvent, if the amount of the chelating agent is less than 3 parts by weight with respect to 100 parts by weight of the solvent, the natural oxide film on the conductor metal cannot be completely removed. , Solderability deteriorates. Further, if the amount of the chelating agent exceeds 10 parts by weight, especially 15 parts by weight or more with respect to 100 parts by weight of the solvent, it is excessive for removing the natural oxide film and does not form a complex after soldering. Since a large amount of the remaining chelating agent remains, a large amount of residue remains.
From these, the amount of the chelating agent is preferably 3 to 10 parts by weight with respect to 100 parts by weight of the solvent. The components other than the chelating agent and the solvent may include solid components such as rosin and synthetic resin. However, if these solids remain on the substrate after soldering, contact failure of the checker pins may occur. In order to avoid contact failure of the checker pins as much as possible, it is desirable to adjust the solid content to 10 parts by weight or less based on 100 parts by weight of the solvent and the chelating agent in total.

[0016]

EXAMPLES Examples of the present invention will be described below. The flux was prepared by placing the flux components in a 300 ml glass beaker and stirring. Next, the flux performance of the obtained flux was evaluated according to Test Example 1 to Test Example 3. The flux constituents and evaluation results are summarized in Table 1.

[Test Example 1] Evaluation of Solderability The solder spread rate was measured by the method specified in JIS Z 3197, and the obtained value was evaluated in the following four stages. Judgment criteria ◎: Solder spread rate is 90% or more ○: Solder spread rate is 85% or more and less than 90% △: Solder spread rate is 80% or more and less than 85% ×: Solder spread rate is less than 80%

[Test Example 2] Evaluation of Flux Residue 30 μl of flux was uniformly applied to the copper comb-shaped electrode portions 2 and 3 of the evaluation substrate 1 having the structure shown in FIG.
Soldering was performed by immersing the substrate in a solder bath at a temperature of 2 ° C. twice for 3 seconds each. Next, the flux residue on the board after soldering was visually evaluated. In addition, in FIG. 1, 4 and 5 are leads of the electrodes 2 and 3, respectively. Judgment criteria ◎: No residue at all ○: Almost no residue ×: With residue

Test Example 3 Evaluation of Insulation Reliability The sample substrate used in Test Example 2 was tested at a temperature of 60 ° C. and a humidity of 95%.
Put in a constant temperature and humidity chamber of RH, DC 50V between the electrodes 2 and 3.
The insulation resistance test was performed for 1000 hours with the applied voltage applied. The measurement of the insulation resistance value was performed once per hour at a temperature of 60 ° C. and a humidity of 95% RH. The change with time of the obtained insulation resistance value was evaluated in the following four stages. Judgment criteria ◎: Insulation resistance value is always 10 ¹⁰ Ω or more ○: Insulation resistance value is decreased to 10 ⁹ Ω or more and less than 10 ¹⁰ Ω △: Insulation resistance value is decreased to 10 ⁸ Ω or more and less than 10 ⁹ Ω ×: Insulation resistance value Drops below 10 ⁸ Ω

[0020]

[Table 1]

The symbols in the table indicate the following. Solvent; IPA: Isopropyl alcohol, DEG: Diethylene glycol TEG: Triethylene glycol Evaluation result; Evaluation 1: Solderability, Evaluation 2: Flux residue, Evaluation 3: Insulation reliability

[ Reference Example 1] Iminodiacetic acid was used as a chelating agent and isopropyl alcohol was used as a solvent. As is clear from Table 1, this flux has excellent solderability and insulation reliability, and almost no residue is found after soldering. Similar results were obtained by using nitrilotriacetic acid instead of iminodiacetic acid as a chelating agent. As described above, when a chelating agent that forms a complex with at least tin and copper is used, a flux having excellent solderability and insulation reliability and having almost no residue after soldering can be obtained. On the other hand, the flux of Comparative Example 1, which uses sebacic acid that is less likely to form a complex with tin and copper in place of iminodiacetic acid, is inferior to Reference Example 1 in insulation reliability.

[ Reference Example 2] A quinaldic acid was used as a chelating agent.
Since quinaldic acid forms a water-insoluble complex with each of tin and copper, insulation reliability superior to that of Reference Example 1 can be obtained. [ Reference Example 3] Oxalic acid was used as a chelating agent. Oxalic acid forms a water-insoluble complex with each of tin and copper, and therefore has better insulation reliability than Reference Example 1. Further, since oxalic acid has sublimability, it is decomposed by heat during soldering, and the chelating agent does not remain on the substrate after soldering. Therefore, the residue is less than that in Reference Example 2.

[Example 1 ] Oxalic acid was used as a chelating agent, and diethylene glycol was used as a solvent. Since diethylene glycol suppresses sublimation of oxalic acid, it has better solderability than Reference Example 3. However, the complex of oxalic acid with tin and copper is insoluble in water, but is soluble in diethylene glycol, and thus the insulation reliability is inferior to that of Reference Example 3. Also,
Since diethylene glycol having a high boiling point is used as the solvent, the residue after soldering is larger than in Reference Example 3. Comparative Example 2 uses triethylene glycol instead of diethylene glycol. Since triethylene glycol does not decompose at the soldering temperature, a large amount of solvent residue remains after soldering, causing an undesirable problem such as stickiness.

[Example 2 ] A flux comprising anthranilic acid and diethylene glycol. Since anthranilic acid is a chelating agent having a sublimation property, good solderability can be obtained by combining it with a solvent diethylene glycol that suppresses the sublimation. Moreover, the complex formed by anthranilic acid with copper and tin is not dissolved in water and diethylene glycol, and thus the insulation reliability is superior to that in Example 1 . Note that, instead of anthranilic acid, quinoline-8-carboxylic acid, which is a chelating agent having a subliming property and forming a complex insoluble in water and diethylene glycol with each of copper and tin, was used as in the case of anthranilic acid. Similar results were obtained for flux.

Example 3 In the composition of Example 2 , a part of diethylene glycol was replaced with isopropyl alcohol. This flux has less solvent residue after soldering than in the case of Example 2 . The solderability and insulation reliability are the same as those in the second embodiment. Next, the 50 check boards after soldering were tested for continuity of the checker pins in the comb-shaped electrode portion. As a result, no checker pin contact failure occurred.

In Example 3 , isopropyl alcohol was used as the solvent for substituting diethylene glycol, but a solvent that evaporates at the soldering temperature and does not dissolve the complex, such as other monohydric alcohols, water, or hydrocarbons, is used. The same effect can be obtained by using a ketone or the like. In Example 3 , anthranilic acid was used as the chelating agent, but it has a sublimation property like anthranilic acid,
Quinoline-8- which is a chelating agent which forms a complex insoluble in water and a solvent for suppressing sublimation with copper and tin, respectively.
Similar results were obtained with carboxylic acids.

As shown in Examples 1 to 3 , the soldering flux of the present invention is excellent in solderability and insulation reliability, has almost no residue after soldering, and has a solid content such as rosin. Since it does not include, the contact failure of the checker pin does not occur. Among these, the flux of Example 3 has the most excellent flux performance.

Further, the soldering flux of the present invention can use water as the main component of the solvent, and therefore can comply with volatile solvent regulations and the like. Furthermore, since the chelating agent used in the present invention forms a complex with all the metals used in solder, it can be applied to lead-free solder and the like.

[0030]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a flux which is excellent in solderability and insulation reliability and which does not cause poor contact of checker pins. Further, since the flux of the present invention does not need to be cleaned after soldering, the cleaning cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a plan view of an evaluation substrate used in an example of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Onishi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-237593 (JP, A) JP-A-7- 88686 (JP, A) JP 7-290278 (JP, A) JP 62-187595 (JP, A) JP 60-127096 (JP, A) JP 5-185284 (JP, A) JP-A 7-116889 (JP, A) JP-A 5-320918 (JP, A) JP-B 7-240 (JP, B2) JP-B 6-92034 (JP, B2) International Publication 94/011148 ( WO, A1) International Publication 94/017950 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) B23K 35/363

Claims (6)

(57) [Claims] 1. A complex is formed with at least copper and tin.
Sublimation chelating agents and sublimation of chelating agents
A flux for soldering, which contains a solvent that suppresses 2. The complex is a water-insoluble complex.
Flux for soldering according to 1 . 3. A chelating agent, oxalic acid, at least one type of claim 1 soldering flux according selected from the group consisting of anthranilic acid and quinoline-8-carboxylic acid,. Wherein the solvent is the following formula (1) and (2) at least one a soldering flux according to claim 1, wherein is selected from dihydric alcohols represented by. [Chemical 1] (In the formula, r and s are 1 or 2.) 5. The complex is insoluble in water and the solvent.
The soldering flux according to claim 4, which is a complex of 6. The soldering flux according to claim 5 , wherein the chelating agent is at least one selected from the group consisting of anthranilic acid and quinoline-8-carboxylic acid.