JP6700570B1 - Flux and solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux and a solder paste capable of reducing generation of precipitates due to heating sag, voids, and low temperature storage, having excellent reflowability, having a high degree of aggregation of solder powder, and easily forming solder balls. . A flux contains rosin, a solvent, an organic acid, and an amine. Organic acids include dibasic carboxylic acids having 3 to 6 carbon atoms. The amine is a primary to tertiary amine, the molecular weight is 80 or less when the amine is a primary amine, the molecular weight is 160 or less when the secondary amine, and the molecular weight is 200 or less when the tertiary amine is used. 0.3 to 2.0% by mass based on the total mass of [Selection diagram] None

Description

  The present invention relates to flux and solder paste.

  The solder paste is composed of flux and solder powder. Electrodes are provided on a substrate on which electronic components are mounted. Solder paste is printed on the electrodes, and solder bumps are formed by reflow processing. Printing of the solder paste is performed by placing a metal mask with an opening on the substrate, moving the squeegee while pressing it against the metal mask, and applying the solder paste to the electrodes of the substrate all at once from the opening of the metal mask. .

  In recent years, the size of electrodes has become smaller as electronic components have become smaller, and the spacing between electrodes has become narrower accordingly. Therefore, the electrodes may be short-circuited due to heating sag during reflow. Solder paste is a mixture of solder powder and flux, and when the storage period is long, the viscosity of the solder paste increases and the solder paste is not applied from the opening of the metal mask depending on the storage conditions. May not be able to exert its printing performance.

  Therefore, for example, Patent Document 1 discloses a solder paste that contains malonic acid or an amine salt of malonic acid in the flux in order to suppress a change with time that affects printing performance, such as a bounce phenomenon of the solder paste. . The document describes that malonic acid functions as a protective film for the solder powder to cover the surface of the solder powder and prevents the solder powder from reacting with components such as an activator and a solvent.

JP-A-3-216292

  However, with the recent miniaturization of electrodes, it is necessary to reduce the particle size of the solder powder contained in the solder paste. If the particle size of the solder powder is small, the surface area is large, so that the surface of the solder powder is easily oxidized. When such a solder powder is applied to the solder paste described in Patent Document 1, malonic acid or an amine salt of malonic acid more sufficiently exhibits the function as a protective film for the solder powder. Then, the flux is softened at the time of reflow and flows together with the solder powder, so that the flux gets wet and spreads out of the electrode, causing heating sag. Due to the heating sag, a bridge due to solder occurs. Further, in the invention described in Patent Document 1, when the flux is softened, the solder powder also flows, so that it is difficult to form solder bumps on the electrodes.

  Further, due to the reduction in diameter of solder powder due to the downsizing of electronic parts in recent years, the weight per particle is also reduced, and the number and range of solder powder that flows out due to the softening and spreading of flux increases. .. Due to the miniaturization of electronic components, there has been a problem in that the gap between electrodes is narrowed and a bridge due to solder is generated.

  As described above, since the conventional solder paste cannot cope with the recent narrowing of the electrode pad, further study is necessary in view of the actual situation when forming the solder bump.

  An object of the present invention is to provide a flux and a solder paste which are excellent in heating sagging and easily form a solder bump on an electrode pad.

  The present inventors have paid attention to the cause of heating sag, which is one of the problems at the time of mounting, among various problems that have been recently demanded. Even if the flux wets and spreads to the outside of the electrode, if the solder powder does not flow out, a short circuit between the solder bumps due to heating sag is suppressed. In order to prevent the solder powder from flowing out of the electrode pad together with the flux, it is necessary that the solder powder stays on the electrode pad even if the flux gets wet and spreads.

  Conventional flux contains a thixotropic agent to suppress heating sag, but the flux softens during reflow by adding a low molecular weight organic acid and a low molecular weight amine having a predetermined molecular weight instead of the thixotropic agent. It was found that the oxide film on the surface of the solder powder is reduced and removed at a temperature lower than the temperature so that the solder powder particles are fixed to each other and the outflow of the solder powder from the electrode can be suppressed. Along with this, good solder ball test results were obtained, the occurrence of voids and precipitates was suppressed, and it was also found that the reflow property was excellent.

  Although the reason why this phenomenon occurs is not clear, in the present invention, when a low molecular weight organic acid and a low molecular weight amine having a predetermined molecular weight are added to the flux, the low molecular weight organic acid and the amine having a predetermined molecular weight are added. Salt is produced. Therefore, it is presumed that the activation action occurred at a temperature lower than the softening temperature of the flux.

The present invention obtained from this finding is as follows.
(1) A flux containing rosin, a solvent, an organic acid, and an amine, wherein the organic acid is a dibasic carboxylic acid having 3 to 6 carbon atoms , and the amine is a primary to tertiary amine, When the amine is a primary amine, the molecular weight is 80 or less, when the amine is a secondary amine, the molecular weight is 160 or less, and when the amine is a tertiary amine, the molecular weight is 200 or less. The content of the flux is 0.3 to 2.0% with respect to the total mass of the flux.

(2) The flux according to (1) above, which further contains an activator and/or a thixotropic agent.
(3) The flux according to (1) or (2) above, wherein the organic acid is at least one of malonic acid, succinic acid, glutaric acid, adipic acid, and maleic acid.
(4) The flux according to any one of (1) to (3) above, wherein the amine is at least one of n-propylamine, tributylamine, monoethanolamine, and triethylenetetramine.

  (5) A solder paste having the flux according to any one of (1) to (4) above.

The invention will be described in more detail below. In the present specification, “%” is “mass %” unless otherwise specified.
1. Flux The flux according to the present invention contains a rosin, a solvent, an organic acid, and an amine. Each configuration will be described in detail.

(1) Rosin Examples of the rosin used in the present invention include the following. Examples thereof include raw rosins such as gum rosin, wood rosin and tall oil rosin, and derivatives obtained from the raw rosins. Examples of the derivative include purified rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin and α,β unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumarized rosin, etc.), and the polymerized rosin. , Purified products, hydrides and disproportionated products, and purified products of the α,β-unsaturated carboxylic acid modified products, hydrides and disproportionated products, and the like. Good.

In addition to rosin, at least one resin selected from terpene resin, modified terpene resin, terpene phenol resin, modified terpene phenol resin, styrene resin, modified styrene resin, xylene resin, and modified xylene resin is further included. You can As the modified terpene resin, aromatic modified terpene resin, hydrogenated terpene resin, hydrogenated aromatic modified terpene resin and the like can be used. As the modified terpene phenol resin, a hydrogenated terpene phenol resin or the like can be used. As the modified styrene resin, styrene acrylic resin, styrene maleic acid resin or the like can be used. Examples of the modified xylene resin include phenol-modified xylene resin, alkylphenol-modified xylene resin, phenol-modified resole-type xylene resin, polyol-modified xylene resin, polyoxyethylene-added xylene resin, and the like. Two or more of these may be contained at the same time.
The content of rosin is preferably 15 to 50% by mass and more preferably 20 to 45% by mass with respect to the total mass of the flux.

(2) Solvent Examples of the solvent used in the present invention include those exemplified below. Examples thereof include alcohol solvents, glycol ether solvents, ester solvents, terpineols and the like. As the alcohol solvent, 1,2-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl- 2,5-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2,3-butanediol ,1,1,1-tris(hydroxymethyl)ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis(methylene)bis(2-ethyl-1,3-propane Diol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-hexanetriol, bis[2,2,2-tris(hydroxymethyl)ethyl]ether, 1-ethynyl- 1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, erythritol, threitol, guaiacol glycerol ether, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7 , 9-tetramethyl-5-decyne-4,7-diol and the like. Examples of the glycol ether solvent include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol. Examples thereof include dimethyl ether, butyl propylene triglycol, butyl propylene diglycol and the like. As the ester solvent, diisobutyl succinate, dibutyl succinate, dimethyl adipate, diethyl adipate, dibutyl adipate, diisopropyl adipate, diisobutyl adipate, diisodecyl adipate, dibutyl maleate, dimethyl sebacate, diethyl sebacate, Examples thereof include dibutyl sebacate, dioctyl sebacate, diisopropyl decanedioate and the like. Two or more of these may be contained at the same time.

  The content of the solvent is preferably 25 to 80 mass% with respect to the total mass of the flux, and more preferably 20 to 45 mass %.

(3) Organic acid: dibasic carboxylic acid having 3 to 6 carbon atoms Since the flux according to the present invention suppresses heating sag and promotes aggregation of solder powder, it has 3 to 6 carbon atoms. Contains a basic carboxylic acid. When the carbon number exceeds 6, it becomes difficult for the activation effect to occur at low temperatures. As a result, heating sag, voids, reflowability are poor, and solder balls are likely to occur.

Examples thereof include malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, tartaric acid, malic acid and diglycolic acid. Preferred are malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, and phthalic acid. Two or more of these may be contained at the same time.
Preferred is at least one of malonic acid, succinic acid, glutaric acid, adipic acid and maleic acid. You may combine 2 or more types of these amines.
The content of the organic acid is preferably 0.3 to 5 mass% and more preferably 0.3 to 4.1 mass% with respect to the total mass of the flux.

(4) Amine: Primary to tertiary amine The flux according to the present invention contains a primary to tertiary amine in order to suppress heating sag.
At least one of the above-mentioned low molecular weight organic acid and primary to tertiary amine does not exhibit an active action at a low temperature, heat sagging occurs, and the cohesiveness of the solder powder is poor. Therefore, in the present invention, the above-mentioned low molecular weight organic acid and the primary to tertiary amines are essential addition substances.

  The amine used in the present invention has a predetermined molecular weight according to each grade in order to prevent heating sagging and prevent the degree of aggregation of the solder powder from deteriorating due to the reducing action of the solder powder surface in a low temperature range. is necessary. When it is a primary amine, its molecular weight is 80 or less, preferably 70 or less. When the amine is a secondary amine, the molecular weight is 160 or less. When the amine is a tertiary amine, the molecular weight is 200 or less.

  Examples of primary amines include monoalkylamines [eg, alkylamines such as methylamine, ethylamine, propylamine, butylamine, etc.], alkanolamines [eg, monoethanolamine (2-aminoethyl alcohol), monopropanol]. Amine, monoisopropanolamine, etc.], amines having a plurality of amino groups [eg, diaminopropane, propylenediamine, etc.] and the like.

  Examples of secondary amines include dialkylamines (eg, dialkylamines such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, etc.), alkylalkanolamines (eg, N-methylethanolamine, etc.). N-C1-3 alkyl monoalkanolamine), dialkanolamine (for example, dialkanolamine such as diethanolamine, dipropanolamine, diisopropanolamine), alkylcycloalkylamines (for example, methylcyclohexylamine), alkylarylamine (Eg, N-methylaniline), alkylaralkylamines (eg, N-methylbenzylamine), cyclic amines (eg, pyrrolidine, piperidine, hexamethyleneimine, morpholine, and other 5- to 8-membered cyclic amines) ) And triethylenetetramine.

Examples of the tertiary amine include trialkylamines (eg, dimethylethylamine, diethylmethylamine, triethylamine, tripropylamine, tributylamine, and other trialkylamines), alkylalkanolamines [eg, N-methyldiethanolamine, etc. Such as N-alkyl dialkanol amine, N,N-dimethyl ethanol amine (dimethylamino ethanol), dialkyl monoalkanol amine such as dimethyl amino propanol], trialkanol amine (eg, triethanol amine, tripropanol amine, triisopropanol amine , Etc., cycloalkyldialkylamines (eg, cyclohexyldimethylamine, etc.), dialkylarylamines (eg, N,N-dimethylaniline, etc.), dialkylaralkylamines (eg, N,N-dimethylbenzyl, etc.) Amines), cyclic amines (for example, 5- to 8-membered cyclic amines such as pyridine, picoline, quinoline, N-methylpyrrolidine, N-methylpiperidine, etc.) and the like.
Preferred is at least one of n-propylamine, tributylamine, monoethanolamine, and triethylenetetramine. You may combine 2 or more types of these amines.

  The content of the amine needs to be 0.3 to 2.0 mass% with respect to the total mass of the flux. If the content of amine is less than 0.3% by mass, the effect of adding amine is difficult to be exhibited, while if it exceeds 2.0% by mass, precipitates are generated due to low temperature storage. The content of amine is preferably 0.3 to 1.8% by mass. Further, it is more preferably 0.3 to 0.9 mass% from the viewpoint of suppressing the formation of precipitates during low temperature storage.

(3) Activator Examples of the activator used in the present invention include low molecular weight organic acids, amine hydrohalides, and organic halogen compounds. For example, examples of the low molecular weight organic acid include those that do not correspond to the above-mentioned organic acids, and examples thereof include phthalic acid, pimelic acid, suberic acid, and azelaic acid. Examples of the amine compound of the amine hydrohalide include those not corresponding to the above-mentioned amines, such as diethyleneamine, diphenylguanidine, cyclohexylamine, and aniline. Examples of the hydrohalic acid include hydrochloric acid and hydrogen bromide. Acid, hydroiodic acid are mentioned. Examples of the organic halogen compound include 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol and 1,4-dibromo-2-butanol. , 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 2,3-dibromo-2-butene-1,4-diol, Triallyl isocyanurate 6 bromide and the like can be mentioned. Two or more of these may be contained at the same time.

In addition to the low molecular weight organic acids described above, other organic acids may be added, citric acid, glycolic acid, salicylic acid, picolinic acid, sebacic acid, terephthalic acid, dodecanedioic acid, eicosanedioic acid, parahydroxyphenylacetic acid. , Phenylsuccinic acid, fumaric acid, lauric acid, benzoic acid, isocyanuric acid tris(2-carboxyethyl), 1,3-cyclohexanedicarboxylic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis( (Hydroxymethyl)butanoic acid, 2,3-dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, p-anisic acid, stearic acid, 12-hydroxystearic acid, oleic acid , Linoleic acid, linolenic acid, dimer acid, hydrogenated dimer acid, trimer acid, hydrogenated trimer acid and the like may be contained.
The content of the activator is preferably 0 to 5 mass% and more preferably 0 to 2 mass% with respect to the total mass of the flux.

(4) Thixotropic agent The thixotropic agent used in the present invention includes, for example, a wax type thixotropic agent and an amide type thixotropic agent. Examples of the wax thixotropic agent include castor hydrogenated oil and the like.

As the amide thixotropic agent, lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, saturated fatty acid amide, oleic acid amide, erucic acid amide, unsaturated fatty acid amide, p-toluenemethane amide, Aromatic Amide, Methylenebisstearic Acid Amide, Ethylenebislauric Acid Amide, Ethylenebishydroxystearic Acid Amide, Saturated Fatty Acid Bisamide, Methylenebisoleic Acid Amide, Unsaturated Fatty Acid Bisamide, m-Xylylenebisstearic Acid Amide, Aromatic Bisamide , Saturated fatty acid polyamide, unsaturated fatty acid polyamide, aromatic polyamide, substituted amide, methylol stearic acid amide, methylol amide, fatty acid ester amide and the like. Two or more of these may be contained at the same time.
The content of the thixotropic agent is preferably 1 to 10 mass% and more preferably 5 to 7 mass% with respect to the total mass of the flux.

2. Solder Paste The solder paste according to the present invention contains the above flux and solder powder.
The content of the flux in the solder paste is preferably 8 to 20% by mass, more preferably 8 to 15% by mass, based on the total mass of the solder paste. Within this range, the thickening suppressing effect due to the solder powder is sufficiently exhibited.

  The solder powder may be any of Sn-Pb-based solder powder and lead-free solder powder such as Sn-3Ag-0.5Cu. The particle size of the solder powder is preferably 10 to 50 μm.

  The solder paste according to the present invention is manufactured by a method commonly used in the art. First, in the production of solder powder, a known method such as a dropping method of dropping a molten solder material to obtain particles, a spraying method of centrifugal spraying, or a method of pulverizing a bulk solder material can be adopted. In the dropping method or the spraying method, the dropping or the spraying is preferably performed in an inert atmosphere or a solvent in order to form particles. Then, the above components can be heated and mixed to prepare a flux, and the solder powder can be introduced into the flux, stirred and mixed to manufacture.

  The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples. In the examples, “%” is “mass %” unless otherwise specified. Moreover, the number of the alloy composition of the solder powder means the content in mass %.

  A solder powder having an alloy composition of Pb-63Sn and a particle size of 20 to 38 μm was prepared. A flux prepared as shown in Table 1 was mixed with solder powder to prepare a solder paste. The numerical values shown in Table 1 are "mass %". The mass ratio of the flux to the solder powder is flux:solder powder=10:90. With respect to each solder paste, heating sag, reflowability, agglomeration state of solder powder, void rate, and presence/absence of precipitates were evaluated. Details are as follows.

-Heating sag JIS Z 3284-3 (2014) After the solder paste is printed on a copper plate using a stainless metal mask having a solder paste printing part formed in a predetermined pattern shown in FIG. 6, and after removing the metal mask The heating sag property of the solder paste was quantified by performing heat treatment at 150° C./10 min. The metal mask has a thickness of 0.2 mm, the solder paste printing portion has a square opening, and the size is 3.0×1.5 mm. In the solder paste printing section, a plurality of openings of the same size are arranged at different intervals, and the intervals L of the openings are 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, It was 0.8 mm, 0.9 mm, and 1.0 mm.

  When the frontage gap L is 0.2 mm and no short circuit has occurred, “◎”; when the frontage gap L is 0.3 to 0.4 mm and no short circuit occurs, “◯”; When a short circuit occurred at 0.5 mm or more, it was evaluated as "x". "○" and "○" indicate that there was no problem in practical use.

-Reflow property A solder mask was printed on a copper plate using a metal mask having an opening diameter of 500 μm and a thickness of 150 μm, and the solder paste was melted in a reflow furnace to prepare a test piece. The reflow was performed under the condition that the preheat was maintained at 150 to 180° C. for 80 seconds and then maintained at 220° C. or higher for 40 seconds. The peak temperature is 240°C. The solder after reflow was observed with a stereoscopic microscope at a magnification of 30 times. "◎" when the solder is evenly wet to the land and there is almost no generation of solder balls, "○" when the solder is evenly wet to the land but there is solder balls, "○", When the solder did not get wet and the solder powder remained unmelted, it was marked with "x". "○" and "○" indicate that there was no problem in practical use.

・Agglomeration state of solder powder (solder ball test)
The solder ball test of JIS Z 3284-4 (2014) was followed. "⊚" when the solder cohesion degree is "1" or "2", "○" when the solder cohesion degree is "3", and "O" when the solder cohesion degree is "4" or "5"X".

・Void ratio: On a printed circuit board with a copper pad of 10 mm square, use a metal mask with a mask thickness of 150 μm to print solder paste on the copper pad in a 10 mm square, and place an 8 mm square Si chip on the paste after application. After placing, the solder paste was melted in a reflow furnace to prepare a test piece. The reflow was performed under the condition that the preheat was maintained at 150 to 180° C. for 80 seconds and then maintained at 220° C. or higher for 40 seconds. The peak temperature was 240°C. After that, the generation of voids after reflow was confirmed using an X-ray inspection apparatus. The X-ray magnification was set to 7 and the void ratio was measured by image processing software. When the void rate was 15% or less, “⊚” was given, when the void rate was more than 15% and 30% or less, “◯” was given, and when the void rate exceeded 30%, it was given as “x”.

-Presence or absence of precipitate The flux was refrigerated for 24 hours. The presence or absence of precipitates in the flux was visually confirmed. When there was no precipitate, it was marked with "O", and when there was precipitate, it was marked with "X".
The evaluation results are shown in Table 1.

  As shown in Table 1, it was found that all of Examples 1 to 13 satisfy all the requirements of the present invention.

On the other hand, in Comparative Example 1, since the amine and the low-molecular organic acid were not contained, heating sagging occurred, the degree of agglomeration of the solder powder was poor, and the void ratio was high. Since Comparative Examples 2 and 3 did not contain amine, heat sagging occurred and the degree of aggregation of the solder powder was poor. In Comparative Example 4, since the low molecular organic acid was not contained, heating sagging occurred and the degree of aggregation of the solder powder was poor. In Comparative Example 5, a precipitate was generated because the content of the amine was too large. In Comparative Example 6, since the primary amine having a molecular weight of more than 80 was used, heating sagging occurred and the degree of aggregation of the solder powder was poor.

Claims (5)

A flux containing rosin, solvent, organic acid, and amine,
The organic acid is a carboxylic acid having 2 bases a carbon number of 3-6,
The amine is a primary to tertiary amine, the molecular weight when the amine is a primary amine is 80 or less, the molecular weight when the amine is a secondary amine is 160 or less, the amine is a tertiary amine. A flux having a molecular weight of 200 or less when it is an amine, and the content of the amine is 0.3 to 2.0% with respect to the total mass of the flux.   The flux according to claim 1, further comprising an activator and/or a thixotropic agent.   The flux according to claim 1 or 2, wherein the organic acid is at least one of malonic acid, succinic acid, glutaric acid, adipic acid, and maleic acid.   The flux according to claim 1, wherein the amine is at least one of n-propylamine, tributylamine, monoethanolamine, and triethylenetetramine.   The solder paste which has the flux of any one of Claims 1-4.