JP2011115855A - Solder paste having blackening preventive effect, and lead-free solder blackening preventive method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that if resin-based flux containing organic halide is contained in a lead-free solder employed through lead-free solder, a soldered portion is secularly discolored black and advanced to the inside of the solder, resulting in separation of the soldered portion or degradation of the conductivity of the solder. <P>SOLUTION: When using flux containing organic halide in soldering a lead-free solder, phosphor compound is added to the flux containing the organic halide, or phosphor is added to lead-free solder powder to be used, and the reaction of halogen remaining in flux residue after the soldering can be suppressed thereby. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for soldering a printed circuit board with solder paste, and more particularly to a soldering method for preventing blackening of a solder alloy generated by lead-free soldering.

In joining and assembling electronic components to electronic equipment, soldering using solder is most advantageous in terms of cost and reliability, and is most commonly performed.
As soldering methods, manual soldering method that solders the cored solder using a soldering iron, flow soldering method that performs soldering by bringing a printed circuit board and electronic parts into contact with molten solder, solder paste, There is a reflow soldering method in which solder preforms, solder balls, etc. are remelted in a reflow furnace for soldering. However, reflow soldering suitable for soldering fine parts has become the most common as electronic parts become smaller. ing.

  In soldering using solder, flux is used as an auxiliary agent that makes it easier for solder to adhere to printed circuit boards and electronic components. The flux in soldering is the surface cleaning action that chemically removes the oxide film on the metal surface of the printed circuit board and electronic parts to create a clean surface that can be soldered. The metal surface of the printed circuit board and electronic parts when soldering Reoxidation prevention action that covers contact with oxygen and prevents reoxidation by heating, and the effect of lowering the surface tension of molten solder to lower the interfacial tension that helps solder wetting Therefore, flux is always used for soldering.

Soldering fluxes used for soldering printed circuit boards and electronic components are roughly classified into two types: resin-based fluxes and water-soluble fluxes.
Resin flux consists of rosin, the main component, dissolved in alcohol together with organic acid and activator. Even if flux residue remains, it is insulative and has little adverse effect on the soldered part. After that, it can be used without washing.
On the other hand, the water-soluble flux is obtained by dissolving a water-soluble organic acid or an activator in water, but there is also one in which alcohol is added to prevent scattering.
Since a water-soluble flux requires cleaning after soldering, a resin-based flux is generally used.

  As the solvent used for the resin flux, an alcohol ether such as diethylene glycol monobutyl ether or diethylene glycol monohexyl ether is often used as a solder paste flux used for flow soldering. The activator used in the resin flux must be soluble in these solvents, and amine hydrohalides and organic halides such as ethylamine hydrobromide and diethylamine hydrochloride are used. It has been.

  As the organic halide used in the flux, as disclosed in JP-A-10-128573, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1, 2-propadiol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 1,4 dibromo-2,3-butanediol, 2,3-dibromo-2 -Butene-1,4-diol, 1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, bromomethylbenzyl stearate, bromomethylphenyl Stearate, ethyl bromoacetate, ethyl α-bromocaprylate, ethyl α-bromopropionate , Ethyl β-bromopropionate, ethyl α-bromobutyrate, 2,3-dibromosuccinic acid, 2-bromosuccinic acid, 2,2-bromoadipic acid, tetrabromostearic acid, hexabromostearic acid, hexabromocyclododecane, Examples include 2,4-dibromoacetophenone, 1,1-dipromotetrachloroethane, 1,2-dibromo-1-phenylethane, 1,2-dibromostyrene, and the like. These organic halides are also used for post soldering for flow soldering, solder paste for flow soldering, and flux of flux cored solder.

  By the way, when an electronic device soldered using a solder breaks down or becomes unusable because it is old, it has been disposed of without being repaired or used excessively. When disposing of electronic equipment, plastic, glass, metal, etc. that make up the electronic equipment may be recovered and reused, but the printed circuit board has copper foil adhered to the resin part and solder adheres to the copper foil. Therefore, it is difficult to separate and recover these and reuse them, so they were finely crushed and buried, or were disposed of as landfills. The rain that falls on the ground due to the recent heavy use of fossil fuel is acid rain, and when the acid rain penetrates into the ground and contacts the printed circuit board that has been disposed of in landfill, the Pb component in the solder is eluted and Pb Acid rain containing ingredients penetrates deeper into the ground and enters groundwater. And if human beings drink groundwater containing Pb component for many years, it is said that Pb component accumulates in the body and eventually causes Pb poisoning. Therefore, the use of Pb is now being regulated on a global scale, and Pb—Sn eutectic solder used for soldering printed circuit boards is also subject to regulation.

  Since the use of Pb-Sn solder is regulated in this way, it is now recommended to use lead-free solder that does not contain Pb at all. The lead-free solder is a solder based on Sn to which one or more elements such as Ag, Sb, Cu, Zn, Bi, In, Ni, Cr, Fe, P, Ge, and Ga are added. Presently proposed lead-free solders include Sn-Ag-Cu lead-free solder, Sn-Cu lead-free solder, Sn-Ag lead-free solder, Sn-Bi lead-free solder, and the like. Sn-Ag-Cu-based lead-free solder is an alloy of Sn, Ag, Cu and an alloy obtained by adding a small amount of additive elements to Sn, Ag, Cu. Among these, currently available solders are Sn-3Ag-0.5Cu (solidus temperature 217 ° C, liquidus temperature 220 ° C), Sn-8Zn-3Bi (solidus temperature 190 ° C, liquidus) 197 ° C), Sn-2.5Ag-0.5Cu-1Bi (solidus temperature 214 ° C, liquidus temperature 221 ° C). These lead-free solders have a melting temperature of about 40 ° C. higher than that of conventional Sn63-Pb37 solder.

  Sn-Ag-Cu lead-free solder is one of the most practical lead-free solders currently available. Sn-Ag-Cu lead-free solder has a melting point of around 220 ° C. In addition to Sn-3Ag-0.5Cu, Sn-3.5Ag-0.75Cu, Sn-3.9Ag-0.6Cu, Sn-4.0Ag -0.5Cu has been put to practical use. In addition, there is also one in which phosphorus is added as a wettability improving element for preventing oxidation of lead-free solder for flow soldering (Japanese Patent Laid-Open No. 2003-094195).

  Also, since lead-free solder has poor wettability compared to conventional Pb-Sn solder, as the solder used for soldering printed circuit boards is replaced by lead-free solder, the flux used for soldering is also lead-free solder. A special one has become necessary. In other words, since the lead-free solder has a high melting temperature, the flux used therein must be usable at a high temperature. Since the flux used for soldering needs to be activated based on the soldering operation temperature, the lead-free solder flux activator works effectively at higher temperatures than conventional Sn-Pb solder alloys You must choose one.

  Of the activators that have been used in conventional fluxes for Pb-Sn solders, many amine hydrohalides are active at around 150-200 ° C, while organic halides have higher temperatures than 200. Active at around ~ 230 ° C. Therefore, as the activator of the lead-free solder flux, even when an amine hydrohalide and an organic halide coexist, a flux that increases the specific gravity of the organic halide is increasing. In particular, in solder paste, if the amount of amine hydrohalide is large, the lead-free solder powder and the flux are likely to react with each other, and the viscosity of the solder paste immediately increases, so the specific gravity of the organic halide increases. Yes.

However, it has been found that when a resin flux containing an organic halide in lead-free solder is used, the soldered portion turns black. In particular, when a voltage is applied for a long time under a high temperature and high humidity environment such as 120 ° C. and 100% RH, discoloration of the solder surface proceeds to the inside of the solder. If the solder turns black as described above, the soldered portion is peeled off or the conductivity of the solder is lowered.
JP 2003-094195 A

  The problem to be solved by the present invention is that when a resin-based flux containing an organic halide is used in the lead-free solder adopted by the lead-free solder, the soldered portion turns black over time and the solder It is a point which progresses to the inside and a soldering part peels or the electroconductivity of solder falls.

  The inventors of the present invention have the cause that the lead-free solder turns black due to the residue of the organic halide remaining in the resin-based flux residue after soldering. By adding the phosphorus compound, the phosphorus compound is converted into the resin-based solder. The present invention was completed by finding that it reacts with the organic halide residue remaining in the flux residue to prevent blackening of the solder.

  When the resin flux contained in the solder paste is used for soldering, the solvent in the resin flux diffuses, and the functional groups necessary for soldering contained in pine resin and activator are decomposed to oxidize the solder. It reacts with objects and works to remove solder oxides. A part unnecessary for soldering at this time and a residue after reacting with the oxide of the solder are called a flux residue and remain around the solder after soldering. The main component of the flux residue is mainly heat-modified pine resin. This residue repels moisture and acts as an insulator. Therefore, resin-based flux is sufficiently reliable without cleaning the residue after soldering. .

  However, the surface of the resin-based flux residue is porous, and water molecules are easily taken into the surface. The particles of water taken in do not penetrate into the flux residue because rosin does not pass through water, but in high temperature and high humidity environments, the flux residue and water molecules always come into contact. The flux activator decomposes during soldering. The amine hydrohalides and organic halides used as flux activators are decomposed by the heat of soldering to produce free halogens, which are then soldered to electronic component terminals, printed circuit board copper foil and solder. It reacts with the solder material to remove the oxide.

  Even with the same flux of activator, the reaction method differs between amine hydrohalides and organic halides. In the amine hydrohalide, halogen is partially dissociated in the solvent such as alcohol in the flux to form an ionic state, but the organic halide is not dissociated in the solvent and is not heated for the first time during soldering. Decomposition and halogen dissociation. For this reason, the amine hydrohalide easily undergoes a dissociation reaction, and there is no undissociated halogen after soldering. On the other hand, in the case of organic halides, the dissociation reaction does not occur unless heated to the decomposition temperature, and undissociated halogen may remain after soldering depending on the heating conditions. Furthermore, the degree of oxidation of electronic parts, printed circuit boards, and solder materials to be soldered is not necessarily uniform. In order to solder even oxidized parts with poor wettability, a flux with strong activity is required. In particular, since the solder has been replaced with lead-free solder, it is necessary to use a large amount of halogen in the activator used in the solder paste.

In the case of organic halides, the active power of the soldering flux must be matched to that of a part with poor wettability, so that a portion of excess halogen is formed in the residue after soldering. Since these halogens are covered with rosin and sealed, they will not react, but in high temperature and high humidity environments, they react with water molecules attached to the surface of the flux residue and gradually become ionic. The substance changes to. Then, the solder portion to which the moisture containing these ions is soldered, particularly the oxidation of Sn, proceeds to the inside, and the solder changes to black.
The black change in lead-free solder tends to occur when the soldered part is covered with flux residue. This is thought to be because if the soldered part is covered with flux, the soldered part will always come into contact with the flux residue, and the solder will easily come into contact with the ionized halogen.

  The black change in lead-free solder occurs in all Sn-based lead-free solders because it is a reaction between Sn and organic halides. Examples of Sn-based lead-free solders include Sn-Ag-Cu lead-free solder, Sn-Cu lead-free solder, Sn-Ag lead-free solder, and Sn-Bi lead-free solder.

  In order to prevent the black change of the lead-free solder, it is conceivable to add a substance that reacts with the reactive halogen remaining in the residue to the flux. For example, a basic substance such as an amine is an example, but the addition of a base such as an amine reduces solderability such as generation of solder balls. Therefore, the thing which is not a base is good. Examples of the substance that reacts with the reactive halogen remaining in the residue instead of the base include phosphorus, which is a metalloid belonging to Group 5 of the periodic table. As is considered to have the same effect, but it is harmful and cannot be used. Since phosphorus is highly reactive, a compound is used instead of a simple substance. Since phosphorus is a semimetal, it has the property of forming both inorganic and organic compounds.

  The phosphorus compound of the present invention brings about the same effect when added to either the solder powder or the flux in the solder paste. The present invention prevents black discoloration of solder by adding a phosphorus compound to the lead-free solder powder and flux of the solder paste when using a flack containing an organic halide for soldering the lead-free solder paste. Is the method.

  When using a flux containing an organic halide for soldering the lead-free solder of the present invention, by using a flux containing a phosphorus compound and a lead-free solder containing phosphorus, the black change of the lead-free solder It is possible to prevent the soldered portion from turning black and progressing to the inside of the solder with the passage of time, and preventing the soldered portion from peeling off or the solder conductivity from being lowered.

The phosphorus and phosphorus compound of the present invention bring about the same effect when added to either the solder powder or the flux in the solder paste. If the amount of the phosphorus compound added to the lead-free solder paste is less than 0.01% by mass with respect to the flux weight in the flux, the blackening prevention effect does not appear, and if it exceeds 10% by mass, the balance of other flux components is lost. As a result, the properties of the paste are impaired and the soldering is adversely affected. Therefore, the addition amount of the phosphorus compound in the lead-free solder paste flux is desirably 0.01 to 10% by mass of the flux weight. In addition, if phosphorus addition to the solder powder is less than 0.0005% by mass with respect to the solder weight, the blackening prevention effect does not appear, and if it exceeds 0.02% by mass, the solder liquidus temperature rises and the soldering temperature also increases. , Solder may not melt completely and wetting is reduced. However, since the soldering temperature varies depending on the workpiece, the upper limit of the P addition amount is preferably a composition in which the liquidus temperature of the solder is equal to or lower than the soldering temperature of the workpiece. On the other hand, at a soldering temperature of 250 ° C., phosphorus addition of about 0.02 mass% does not significantly affect the wettability of the solder.

  When a phosphorus compound is added to the lead-free solder powder, a phosphorus alloy or an inorganic phosphorus compound that easily reacts with the solder powder is desirable. Phosphorus alloys suitable for the present invention include Sn-P, Ag-P, Cu-P, Bi-P, Sn-Ag-Cu-P, Sn-Cu-P alloys, inorganic phosphorus compounds include phosphoric acid, Examples thereof include phosphoric acid such as sodium phosphate, hypophosphorous acid, sodium hypophosphite, sodium pyrophosphate, sodium metaphosphate, and sodium hexametaphosphate, and salts of phosphoric acid and alkali metal. It is better to add the phosphorus alloy or inorganic phosphorus compound to the lead-free solder powder while the solder is melted to produce a lead-free solder powder alloyed with phosphorus. When the inorganic phosphorus compound is added to the surface of the resulting lead-free solder powder and added, the inorganic phosphorus compound may react excessively with the lead-free solder powder, resulting in corrosion.

  When a phosphorus compound is added to a flux containing an organic halide, an organic phosphorus compound that is easily dissolved in the flux is desirable. Suitable organic phosphate compounds for the present invention include triphenyl phosphate, phenyl diisodecyl phosphate, octadecyl phosphite, trisdiphenyl phosphate, 9,10-dihydro-9oxa-10-phosphaphenane-10-oxide, 10- Examples thereof include phenyl phosphates such as decidroxy-9,10-dihydro-9oxa-10-phosphaphenanthrene and tris (2,4-di-t-butyl-phenyl) phosphate.

  Since these phosphorus compounds do not react with halogen at room temperature and are stable, they do not react with the activator even when added to the solder paste. However, since it reacts with ionic halogen, it reacts only when the residual halogen contained in the resin flux residue is ionized in the presence of water. Thus, the phosphorus compound is an optimal material for preventing the black change of lead-free solder. However, if a phosphorus compound is used in the flux of the solder paste, it tends to be acidic in the flux, so that the blending of the flux is limited, such as adding a basic one. On the other hand, when adding a phosphorus compound to the solder powder, it is not necessary to limit the blending of the flux. Therefore, the best addition method of the phosphorus compound in the solder paste is to add the phosphorus compound to the solder powder.

  A solder paste flux was prepared with the following composition, and mixed with solder powder made of each solder alloy to prepare the solder paste shown in Table 1. A high accelerated life test was performed on each solder paste to compare the deterioration of the fillet at the solder joint.

Advanced accelerated life test method Solder paste is printed on a test substrate with a 200 μm thick metal mask and reflow soldered.
2. After cooling to room temperature, it is stored for 63 hours in a constant temperature and humidity chamber set at a temperature of 120 ° C., a humidity of 100%, and an applied voltage of DC 20V.
3. Check the state of black color change of the fillet at the solder joint after 63 hours.
4). Criteria for advanced accelerated life test Level 1: No blackening Level 2: Black streaks appear Level 3: Partially blackened Level 4: Blackened entirely Photo of judgment criteria is shown in FIG. The results of the advanced accelerated life test are shown in Table 1.

(Table 1)
Results of highly accelerated life test of solder paste made from each flux and solder powder.

1. Solder paste formulation Solder powder 89% by mass
Flux 11% by mass
2. Formulation of flux
1). Flux 1
Polymerized rosin 45% by mass
Adipic acid 0.5% by mass
2,3-dibromo-1-propanol 2% by mass
Hydrogenated castor oil 5wt%
Diethylene glycol monohexyl ether
2). Flux 2
Polymerized rosin 45% by mass
Adipic acid 0.5% by mass
Hydrogenated castor oil 5% by mass
Diethylene glycol monohexyl ether
3). Flux 3
Polymerized rosin 45% by mass
Adipic acid 0.5% by mass
2,3-dibromo-1-propanol 2% by mass
9,10-dihydro-9oxa-10-phosphaphenane-10-oxide 2% by weight
Hydrogenated castor oil 5% by mass
Diethylene glycol monohexyl ether
4). Flux 4
Polymerized rosin 45% by mass
Adipic acid 0.5% by mass
2,3-dibromo-1-propanol 2% by mass
9,10-Dihydro-9-Oxa-10-phosphaphenane-10-oxide 2% by mass
Hydrogenated castor oil 5% by mass
2. Diethylene glycol monohexyl ether Lead-free solder powder
1). Solder powder 1
Sn-3.0% by mass Ag-0.5% by mass Cu lead-free solder with a particle size of 25-36μm
2). Solder powder 2
Sn-0.7Cu lead-free solder powder with a particle size of 25-36μm
3). Solder powder 3
Sn-3.0 mass% Ag-0.5 mass% Cu lead-free solder, 0.0005 mass% phosphorus master alloy Sn-Ag-P dissolved into powder with a particle size of 25-36μm
4). Solder powder 4
Sn-3.0% by mass Ag-0.5% by mass Cu lead-free solder 0.002% by mass of phosphorus master alloy Sn-Ag-P dissolved into a powder with a particle size of 25-36μm
5). Solder powder 5
Sn-3.0% by mass Ag-0.5% by mass Cu lead-free solder 0.02% by mass of phosphorus master alloy Sn-Ag-P dissolved into a powder with a particle size of 25-36μm
6). Solder powder 6
Sn-0.7Cu Mass Lead-free solder dissolves 0.0005% by mass of phosphorus master alloy Sn-P, particle size 25-36μ
m powder
7). Solder powder 7
Sn-0.7Cu Mass Lead-free solder dissolves 0.002% by mass of phosphorus master alloy Sn-P, particle size 25-36μ
m powder
8). Solder powder 8
0.02% by mass of phosphorus master alloy Sn-P dissolved in Sn-0.7Cu mass lead-free solder, particle size 25-36μm
Made into powder
9). Solder powder 9
Sn-3.0 mass% Ag-0.5 mass% Cu lead-free solder, 0.01 mass% of germanium master alloy Sn-Ag-Ge dissolved into a powder with a particle size of 25-36μm

From the result of the advanced accelerated life test, solder paste with phosphorus compound added can suppress the blackening of the fillet at the solder joint even under high temperature and humidity conditions, but no phosphorus compound is added to the solder paste. In the case, the blackening has progressed to the inside of the fillet of the solder joint (FIG. 2).

The present invention is also effective in preventing blackening of lead-free solder by a flux containing dicarboxylic acid. The flux containing an epoxy resin often uses 10% by mass or more of dicarboxylic acid and dicarboxylic acid anhydride as a curing agent for the epoxy resin. Although this dicarboxylic acid is not activated in the flux, it is decomposed during soldering and exhibits activity. Although not as abrupt as organic halides, dicarboxylic acids can also cause black changes in lead-free solder if they remain in the flux residue.
By adding a phosphorus compound to a flux containing dicarboxylic acid and an anhydride of dicarboxylic acid or adding a phosphorus compound to lead-free solder to be soldered, it is possible to prevent the black color of the solder.

It is the photograph of the pass / fail judgment which showed the blackening level in 1-4 steps. It is a cross-sectional photograph of a soldered joint that has been blackened.

Claims (3)

  In solder paste consisting of lead-free solder powder mixed with flux containing organic halide, the lead-free solder powder is Sn-P alloy, Ag-P alloy, Cu-P alloy, Bi-P alloy, Sn -Ag-Cu-P alloy, Sn-Cu-P alloy, phosphoric acid, sodium phosphate, hypophosphorous acid, sodium hypophosphite, sodium pyrophosphate, sodium metaphosphate, sodium hexametaphosphate A solder paste characterized in that the above phosphorus alloy or inorganic phosphorus compound is added to molten solder and powdered using lead-free solder alloyed with phosphorus.   The solder paste uses a lead-free solder alloyed with phosphorus in which a phosphorus alloy or an inorganic phosphorus compound is added to the molten solder and the content of P in the solder becomes 0.0005 to 0.02%. 2. The solder paste according to claim 1, wherein the solder paste is a powder.   A method of preventing blackening of lead-free solder, wherein soldering using a solder paste is used to prevent blackening of a soldered portion using the solder paste of claim 1.