JP4819624B2 - Soldering flux and solder paste composition - Google Patents

Description

  The present invention relates to a soldering flux and a solder paste composition used, for example, when soldering circuit components or the like to a circuit board.

  Conventionally, various soldering fluxes and solder paste compositions have been used for soldering electronic circuit components and the like. However, in the conventional flux and solder paste composition, there is a problem that a crack is generated in the flux residue after soldering, and moisture is condensed in the cracked portion to cause a short circuit failure between the component leads. there were. This problem is particularly likely to occur on a vehicle-mounted substrate that has a large temperature difference during use and a large amount of vibration.

  As a method for improving this problem, the following crack preventing means has been proposed. That is, a) In a solder paste using rosin as a base resin, a high-boiling plasticizer is added and soldered as in a method of adding an ester of trimellitic acid that is a high-boiling plasticizer (see Patent Document 1). Means for leaving the plasticizer in the residue afterwards, b) a flexible synthetic resin such as a polymer of ethylene or propylene, such as a soldering flux using an ethylene-acrylic copolymer (see Patent Document 2) A means for forming a base resin; c) a means for cleaning after soldering to remove a flux residue.

JP-A-9-234588 JP-A-9-122975

  However, the means a) has a problem in that the occurrence of cracks in the flux residue is reduced, but there is a concern that the reliability may be lowered due to the residual liquid substance. The means b) has a problem in that it becomes difficult to ensure the wettability of the solder and the solderability is deteriorated by using a synthetic resin as compared with the rosin flux. In the means c), there is a problem that the cost of the product increases due to the need for a post-process for cleaning and the addition of cleaning equipment, and environmental pollution is concerned by the solvent used for cleaning.

  Therefore, the present invention can sufficiently suppress the occurrence of cracks in the flux residue after soldering, has high reliability, has good solderability, and has the same manufacturing cost and environmental load as conventional ones. An object is to provide a soldering flux and a solder paste composition.

  As a result of intensive research to solve the above-mentioned problems, the present inventors have used a rosin having a softening point below a specific temperature as a base resin for soldering flux. Flexibility is provided, cracking in the flux residue can be effectively suppressed, and it has the same activity and high insulation as conventional rosins, ensuring high reliability and good soldering. The present inventors have found a new fact that the manufacturing cost and the load on the environment can be kept at the same level as before, and have completed the present invention.

That is, the present invention has the following configuration.
(1) A soldering flux comprising a low softening point rosin having a softening point of 60 ° C. or less as a base resin.
(2) The soldering flux according to (1), wherein the low softening point rosin contains secodehydroabietic acid.
(3) The soldering flux according to (1) or (2), wherein the low softening point rosin contains a thermal decomposition component of rosin.
(4) The soldering flux according to the above (2) or (3), wherein the content of secodehydroabietic acid and / or a thermal decomposition component contained in the low softening point rosin is 5% by weight or more.
(5) The soldering flux according to any one of (1) to (4), wherein the content of the low softening point rosin is 0.5 to 80% by weight based on the total amount of the flux.
(6) The soldering flux according to any one of (1) to (5), which also contains an acrylated rosin and / or an acrylic resin as a base resin.
(7) A solder paste composition comprising the soldering flux according to any one of (1) to (6) and a solder alloy powder.

  According to the present invention, it is possible to sufficiently suppress the occurrence of cracks in the flux residue after soldering, and to obtain high reliability and good solderability. As a result, it is possible to prevent short circuit due to cracks in the flux residue, dropout of joined parts due to insufficient soldering, disconnection due to corrosion, etc., so that highly reliable and high quality electronic equipment can be easily manufactured. An effect is obtained. In particular, even when used in harsh environments such as low temperature and high temperature cycles (cooling cycles) or exposure to vibration, it is possible to maintain corrosion resistance and high electrical insulation, Reliability can be improved. Further, according to the present invention, since there is no need to clean the residual flux after soldering as in the prior art, there is no possibility that the product cost will rise, and there is no possibility that the cleaning solvent will adversely affect the human body and the environment.

Hereinafter, an embodiment of the present invention will be described in detail.
The soldering flux of the present invention (hereinafter sometimes simply referred to as “flux”) contains, as a base resin, a low softening point rosin having a softening point of 60 ° C. or less. A low softening point rosin having a softening point of 60 ° C. or lower generally has a flexible structure, and has an active force equivalent to that of a conventional rosin having a softening point exceeding 60 ° C. and high insulation. Therefore, by using such a low softening point rosin as a base resin, it is possible to obtain good solderability and high reliability while effectively suppressing the occurrence of cracks in the flux residue after soldering. Can do it. When the rosin has a softening point exceeding 60 ° C., the flexibility of the resin is lowered, and the effect of the present invention that suppresses the generation of cracks in the residue cannot be obtained.

The low softening point rosin preferably contains secodehydroabietic acid. Due to the presence of secodehydroabietic acid in the flux, corrosion resistance and high electrical insulation can be maintained even when used in an environment exposed to low temperature and high temperature cycles or vibrations.
The secodehydroabietic acid has a structure represented by the following formula (I), and has a conjugated double bond contained in various rosins (for example, abietic acid type such as neoabietic acid, parastrinic acid, levopimaric acid) The resin acid having a conjugated double bond is modified. Specifically, the secodehydroabietic acid is formed by ring-opening a resin acid having an abietic acid type conjugated double bond simultaneously with disproportionation while retaining its carboxylic acid moiety.

  The low softening point rosin containing secodehydroabietic acid includes, for example, various rosins containing the component having a conjugated double bond (resin acid having an abietic acid type conjugated double bond) such as iodine, sulfur and iron. It can be obtained by a method of heating at 150 to 300 ° C., preferably 250 to 280 ° C. for about 3 to 24 hours in the presence of a catalyst. By this method, the resin acid having an abietic acid type conjugated double bond in rosin is disproportionated and simultaneously ring-opened to produce secodehydroabietic acid. In this method, in order to promote the ring-opening reaction simultaneously with the disproportionation reaction, an alkylphenol disulfide oligomer having a structure represented by the following formula (II) as a catalyst to be present during heating as in the following production example (for example, , Nonylphenol disulfide oligomer, t-amylphenol disulfide oligomer, etc.) are effective. Further, in the above method, temperature control during heating is important in order to suppress side reactions other than desired disproportionation and ring opening and prevent other decomposition products from being by-produced.

The low softening point rosin preferably contains a thermal decomposition component of rosin. The presence of the thermal decomposition component of rosin in the flux makes it possible to maintain corrosion resistance and high electrical insulation even when used in environments exposed to low temperature and high temperature cycles and vibrations.
The thermal decomposition component of the rosin is usually obtained by thermally decomposing various components (for example, abietic acid, neoabietic acid, parastrinic acid, pimaric acid, isopimaric acid, etc.) contained in various rosins. Specifically, for example, pinoline or rosin oil obtained by thermally decomposing gum rosin can be used.
The low softening point rosin containing the thermal decomposition component can be obtained, for example, by a method in which various rosins are heated at a temperature of 250 to 300 ° C. for several hours in an inert gas atmosphere. In this method, unlike the above-described method for obtaining a low softening point rosin containing secodehydroabietic acid, a catalyst such as iodine, sulfur, iron, etc. is not present during heating. Only decomposition reactions occur.
The low softening point rosin may contain only one of the secodehydroabietic acid and the heat decomposition component, or may contain both.

  The content of the secodehydroabietic acid and / or the thermal decomposition component in the low softening point rosin is preferably 5% by weight or more, and more preferably 20% by weight or more. If the secodehydroabietic acid and / or the thermal decomposition component is less than 5% by weight, it becomes difficult to make the softening point of rosin 60 ° C. or lower, and the low softening point resin may not be obtained. In addition, when both the said secodehydroabietic acid and the said thermal decomposition component are contained in the low softening point rosin, the total amount of both should just be the said range. In the present invention, the content of secodehydroabietic acid and / or a thermal decomposition component can be measured by gas chromatography.

  The content of the low softening point rosin is preferably 0.5 to 80% by weight, more preferably 2 to 60% by weight, based on the total flux. When the low softening point rosin is less than 0.5% by weight, the solid content in the flux decreases, so that the film property at the time of soldering is lowered and sufficient solderability may not be obtained. On the other hand, if the low softening point rosin exceeds 80% by weight, the flux has a high viscosity and the workability may be significantly reduced.

  The soldering flux of the present invention preferably contains an acrylated rosin and / or an acrylic resin as the base resin together with the low softening point rosin. By including an acrylated rosin, solderability can be further improved. On the other hand, by adding an acrylic resin, the flexibility of the flux residue is further reduced while suppressing the influence on solderability and reliability. It is possible to improve and prevent the occurrence of cracks more reliably. Accordingly, at least one of the acrylated rosin and the acrylic resin, preferably both, should be contained.

As the acrylated rosin, those obtained by addition reaction of various rosins with acrylic acid or methacrylic acid may be used.
The content of acrylated rosin is preferably 0.1 to 60% by weight, more preferably 1 to 45% by weight, based on the total flux. If the acrylated rosin is less than 0.1% by weight, there is a high possibility that the effect of improving the solderability cannot be expected. On the other hand, when the acrylated rosin exceeds 60% by weight, the amount of the low softening point rosin is relatively decreased, and the crack resistance of the residue may be deteriorated.

  Acrylic resins include monomers having polymerizable unsaturated groups (for example, (meth) acrylic acid, various esters thereof, crotonic acid, itaconic acid, (anhydrous) maleic acid and esters thereof, (meth) acrylonitrile, (meth) acrylamide. , Vinyl chloride, vinyl acetate, etc.) using a polymerization catalyst such as a bulk polymerization method, a liquid polymerization method, a suspension polymerization method, an emulsion polymerization method or the like. .

  The content of the acrylic resin is preferably 0.1 to 60% by weight, more preferably 1 to 45% by weight, based on the total amount of the flux. If the acrylic resin is less than 0.1% by weight, there is a high possibility that the effect of improving the flexibility of the residue cannot be expected. On the other hand, when the acrylic resin exceeds 60% by weight, the ratio of the low softening point rosin in the flux solid content is relatively decreased, which may cause a decrease in solderability.

  The soldering flux of the present invention may further contain rosin and its derivatives or synthetic resins conventionally used in the flux as a base resin, if necessary. In that case, it is preferable that the low softening point rosin (acrylic rosin and acrylic resin, if necessary) is contained in a range that can sufficiently ensure the proportion of the base resin in the base resin.

  Examples of rosin and derivatives thereof that have been generally used for flux conventionally include normal gum rosin, tall rosin, and wood rosin. Examples of these derivatives include heat-treated resins, polymerized rosins, hydrogenated rosins, formylated rosins, rosin esters, rosin-modified maleic resins, rosin-modified phenol resins, and rosin-modified alkyd resins. Examples of synthetic resins conventionally used for fluxes include styrene-maleic acid resins, epoxy resins, and urethane resins.

  The soldering flux of the present invention usually contains an activator in addition to the above-described base resin, and also contains a thixotropic agent as necessary. Further, when the flux is used in a liquid state, an appropriate organic solvent can be contained.

Examples of the activator include hydrohalide salts such as ethylamine, propylamine, diethylamine, triethylamine, ethylenediamine, and aniline, and organic carboxylic acids such as lactic acid, citric acid, stearic acid, adipic acid, and diphenylacetic acid.
The content of the activator is preferably 0.1 to 30% by weight with respect to the total flux. When the activator is less than 0.1% by weight, there is a risk that the activity is insufficient and the solderability is lowered. On the other hand, when the activator exceeds 30% by weight, the film property of the flux is lowered and the hydrophilicity is increased, so that the corrosivity and the insulating property may be lowered.

  Examples of the thixotropic agent include hardened castor oil, beeswax, carnauba wax, stearamide, hydroxystearic acid ethylenebisamide, and the like. The thixotropic agent content is preferably 1.0 to 25% by weight based on the total flux.

  Examples of the organic solvent include alcohol solvents such as ethyl alcohol, isopropyl alcohol, ethyl cellosolve and butyl carbitol, ester solvents such as ethyl acetate and butyl acetate, hydrocarbon solvents such as toluene and turpentine oil, and the like. . Among these, isopropyl alcohol is preferable in terms of volatility and solubility of the activator.

  The content of the organic solvent is preferably 20 to 99% by weight with respect to the total flux. When the organic solvent is less than 20% by weight, the viscosity of the flux increases, and the applicability of the flux may deteriorate. On the other hand, when the organic solvent exceeds 99% by weight, the active component (such as rosin) as a flux is relatively decreased, and thus solderability may be deteriorated.

  Furthermore, in addition to the components described above, the flux of the present invention is a conventionally known synthetic resin (for example, polyester resin, phenoxy resin, etc.) that is generally used as a base resin for the flux, as long as the effects of the present invention are not impaired. Terpene resins, etc.), additives such as antioxidants, antifungal agents, and matting agents can also be included.

The solder paste composition of the present invention contains the aforementioned soldering flux of the present invention and a solder alloy powder.
There is no restriction | limiting in particular as solder alloy powder, The tin-lead alloy etc. which added silver, bismuth, or indium etc. which were generally used, and also silver-bismuth etc. can be used. Moreover, you may use lead-free alloys, such as a tin-silver type, a tin-copper type, and a tin-silver-copper type. The particle size of the solder alloy powder is preferably about 5 to 50 μm.

  The weight ratio of the flux to the solder alloy powder (flux: solder alloy powder) in the solder paste composition of the present invention is not particularly limited, but is preferably about 5:95 to 20:80.

  The solder paste composition of the present invention is applied onto a substrate by a dispenser, screen printing or the like when soldering electronic device parts or the like. And after application | coating, it preheats, for example at about 150-200 degreeC, and performs reflow at the maximum temperature of about 170-250 degreeC. Application and reflow on the substrate may be performed in the air or in an inert atmosphere such as nitrogen, argon, helium, or the like.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to a following example.
In addition, evaluation of the obtained flux and solder paste composition was performed by the following method.

<Solderability test>
Flux was applied to a glass epoxy substrate having 15 SOP (Shrink Outline Package) patterns with a pitch of 20 mm having 20 leads. After soldering the substrate after flux application with a jet soldering device (for soldering, Sn—Ag—Cu alloy (Sn: Ag: Cu = 96.5: 3.0: 0.5 (weight ratio)) The solder alloy powder consisting of the above is used), and the presence or absence of a bridging defect in the SOP pattern portion is determined by visual observation. Evaluation was performed by obtaining a value indicating the percentage of the number of defects as a percentage (%).

<Solder ball test>
A solder paste composition was printed on a substrate having a 0.8 mm pitch QFP (Quad Flat Package) pattern using a metal mask having the same pattern and a thickness of 200 μm. Within 10 minutes after printing, preheating was performed at 175 ± 5 ° C. for 80 ± 5 seconds in the atmosphere, and reflow was performed at a maximum temperature of 235 ± 5 ° C. Then, by measuring the number of solder balls generated around the 80 pads (80 soldering portions) using a 20 × stereo microscope, the number of solder balls (pieces) generated as a solderability index is counted. evaluated.

<Residual crack test>
The board after the solderability test or the solder ball test described above was used as a test piece, and a thermal cycle load was applied to the test piece under the condition of −30 ° C. × 30 minutes → 85 ° C. × 30 minutes for 100 cycles. Then, the crack generation state in the soldering part of the SOP pattern or QFP pattern on a board | substrate was observed visually, and the following references | standards evaluated.
○: No cracks are observed.
Δ: Cracks are generated, but cracks that adversely affect reliability, that is, cracks that straddle two or more adjacent soldered portions (hereinafter referred to as “connected cracks”) are not recognized.
X: The connection crack has generate | occur | produced.

<Insulation resistance test>
1) In the case of flux: Flux was applied to a comb substrate (type II) defined in JIS-Z-3197. After flux application, soldering was performed with a jet soldering apparatus (for soldering, from Sn—Ag—Cu alloy (Sn: Ag: Cu = 96.5: 3.0: 0.5 (weight ratio)) Used solder alloy powder). Electrical reliability by measuring the resistance value (Ω) over time (initial, after 500 hours and after 1000 hours) by leaving the soldered board in a constant temperature and humidity chamber at 85 ° C. and 85%. The insulation resistance was evaluated as a property.
2) In the case of solder paste composition: The solder paste composition was printed on a comb-shaped substrate (type II) defined in JIS-Z-3197 using a metal mask having the same pattern and a thickness of 100 μm. Within 10 minutes after printing, preheating was performed at 175 ± 5 ° C. for 80 ± 5 seconds in the atmosphere, and reflow was performed at a maximum temperature of 235 ± 5 ° C. The substrate after reflow was subjected to a thermal cycle load under the same conditions as the above-mentioned residual crack test, and then left in a constant temperature and humidity chamber at 85 ° C. and 85% over time (initial, 500 hours and 1000 hours later). The insulation resistance was evaluated as electrical reliability by measuring the resistance value (Ω).

<Corrosion test>
The copper plate corrosion test piece prescribed | regulated to JIS-Z-3197 was produced using the flux or the solder paste composition, and the thermal cycle load was applied to this test piece on the same conditions as the said residual crack test. Thereafter, each test piece was left in a constant temperature and humidity chamber at 40 ° C. and 85%, and after 500 hours and 1000 hours, the presence or absence of pitting or corrosion was confirmed by visual observation.

(Production Example 1)
To 100 parts by weight of gum rosin, 0.5 part by weight of nonylphenol disulfide oligomer (sulfur content: 10% by weight) was added, heated to 260 ° C., and held at the same temperature for 6 hours to obtain synthetic rosin A. .
This synthetic rosin A had a softening point of 57 ° C. and contained 3.6% by weight of secodehydroabietic acid and 2.2% by weight of pinoline as a thermal decomposition product.

(Production Example 2)
To 100 parts by weight of gum rosin, 0.35 part by weight of nonylphenol disulfide oligomer (10% by weight of sulfur), 0.14 part by weight of iodine and 0.013 part by weight of iron naphthenate were added and the temperature was raised to 250 ° C. After warming, the mixture was held at the same temperature for 3 hours to obtain synthetic rosin B.
This synthetic rosin B had a softening point of 44 ° C. and contained 14.8% by weight of secodehydroabietic acid.

(Production Example 3)
To 100 parts by weight of gum rosin, 0.56 parts by weight of nonylphenol disulfide oligomer (sulfur content 10% by weight), 0.05 parts by weight of iodine and 0.01 parts by weight of iron naphthenate were added and the temperature was raised to 250 ° C. After warming, the same temperature was maintained for 3 hours to obtain synthetic rosin C.
This synthetic rosin C had a softening point of 48 ° C. and contained 11.2% by weight of secodehydroabietic acid.

(Production Example 4)
To 100 parts by weight of gum rosin, 0.30 part by weight of t-amylphenol disulfide oligomer (sulfur content 23% by weight), 0.05 part by weight of iodine and 0.01 part by weight of iron naphthenate are added, 260 After raising the temperature to 0 ° C., the same temperature was maintained for 3 hours to obtain a synthetic rosin D.
This synthetic rosin D had a softening point of 35 ° C. and contained 21.2% by weight of secodehydroabietic acid.

(Production Example 5)
A synthetic rosin E was obtained by heating 100 parts by weight of gum rosin to 280 ° C. in a nitrogen gas atmosphere and holding at that temperature for 10 hours.
This synthetic rosin E had a softening point of 56 ° C. and contained 6.1% by weight in total of pinoline and diterpene, which are thermal decomposition components of gum rosin.

(Examples 1-4 and Comparative Example 1)
As the base resin, the synthetic rosin, acrylic resin (weight average molecular weight 5000, acid value 50 mgKOH / g), acrylated rosin (softening point 110 ° C., acid value 210 mgKOH / g) and gum rosin (softening point) obtained in each of the above production examples. 79 ° C., acid value of 168 mg KOH / g), the activator and solvent shown in Table 1 are mixed in the composition shown in Table 1, and dissolved by applying sufficient heat so that they are uniform. , Flux was obtained respectively.
Using each of the obtained fluxes, a solderability test, a residual crack test, an insulation resistance test, and a corrosion test were performed. The results are shown in Table 1.

(Examples 5 to 8 and Comparative Example 2)
As the base resin, the synthetic rosin, acrylic resin (weight average molecular weight 8000, acid value 75 mgKOH / g), acrylated rosin (softening point 105 ° C., acid value 200 mgKOH / g) and gum rosin (softening point) obtained in each of the above production examples. 77 ° C., acid value of 165 mg KOH / g), and the activator, thixotropic agent and solvent shown in Table 2 are mixed in the composition shown in Table 2, and heat is applied sufficiently so as to be uniform. To obtain fluxes.
Next, solder alloy powder (particle size: 38 to 25 μm) composed of each obtained flux and Sn—Ag—Cu alloy (Sn: Ag: Cu = 96.5: 3.0: 0.5 (weight ratio)) Were mixed at a ratio of flux: solder alloy powder = 12: 88 (weight ratio) to obtain solder paste compositions, respectively.
Using each of the obtained solder paste compositions, a solder ball test, a residual crack test, an insulation resistance test, and a corrosion test were performed. The results are shown in Table 2.

  From Tables 1 and 2, Examples 1 to 8 using synthetic rosins A to D, which are low softening point rosins, are suppressed from poor soldering and the generation of solder balls, and are also reliable after a thermal cycle load. It can be seen that the reduction and the occurrence of corrosion are suppressed, and excellent performance is obtained. In particular, Examples 2 to 4 and Examples 6 to 8 using synthetic rosins B to D containing 5% by weight or more of secodehydroabietic acid are found to be excellent in the effect of suppressing the occurrence of cracks in the thermal cycle. .

As is apparent from the above, according to the present invention, the solderability is excellent, and the corrosion resistance and high electrical insulation can be maintained even when used in an environment exposed to low temperature and high temperature cycles or vibrations. The reliability of the part can be improved.

Claims (5)

A soldering flux containing a low softening point rosin having a softening point of 60 ° C. or lower as a base resin , wherein the low softening point rosin contains secodehydroabietic acid and / or a thermal decomposition component of rosin Soldering flux. 2. The soldering flux according to claim 1 , wherein the content of secodehydroabietic acid and / or a thermal decomposition component contained in the low softening point rosin is 5% by weight or more. The soldering flux according to claim 1 or 2 , wherein the content of the low softening point rosin is 0.5 to 80% by weight based on the total amount of the flux. The soldering flux according to any one of claims 1 to 3 , further comprising an acrylated rosin and / or an acrylic resin as a base resin. A solder paste composition comprising the soldering flux according to any one of claims 1 to 4 and a solder alloy powder.