JP3273757B2 - Solder paste and flux for forming solder joints - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solder paste and a flux for forming a lead-free solder joint for joining electrical, electronic or mechanical components. More specifically, the present invention relates to a solder paste and a flux capable of forming a joint of an electric or electronic component such as a circuit board with tin / zinc solder.

[0002]

2. Description of the Related Art Soldering is a technique for joining objects using a substance having a relatively low melting point, and has been used for a long time, and it is said that its origin can be traced back to the ancient Mesopotamian civilization. In modern industry, soldering is widely used for joining and assembling electronic devices. For example, in a mounting substrate, it is used for bonding for mounting electronic components such as a semiconductor, a microprocessor, a memory, and a resistor on the substrate. The advantage of soldering is that, in addition to fixing the component to the substrate, an electrical connection is formed by the conductivity of the metal contained in the solder, which is different from the organic adhesive in this point.

A commonly used solder is a eutectic solder composed of tin and lead, and has a theoretical eutectic point of 183 ° C.
Since many thermosetting resins are lower than the temperature at which gasification starts, tin / lead eutectic solder is used for joining substrates, etc., and has the feature that printed boards, etc., do not need to be damaged by heat. I have. It is also known that in this eutectic solder, the tin component forms a specific metal compound layer at the interface of the copper plate, and the adhesion between the solder and copper is further strengthened.

[0004] The eutectic solder made of tin and lead having such features is important in joining and assembling parts in the manufacture of electronic equipment. In fine soldering processes such as thick film formation, conductor circuit formation and semiconductor mounting,
A screen printing method using a solder paste in the form of a paste in which solder powder and flux are mixed is used, and with the rapid spread of personal devices such as personal computers, mobile phones and pagers, electronic components have become increasingly popular. The demand for solder in the mounting technology is increasing.

[0005] The spread of electronic devices has enriched people's lives. However, on the other hand, it is also true that a large amount of electronic equipment that is no longer used is discarded, and there is a danger that environmental problems due to waste will occur. For this reason,
Recycling of waste and production methods that do not use harmful substances have been proposed. In particular, the elimination of harmful substances is desirable from the viewpoint of preventing environmental pollution beforehand, and it is considered that development is required also in the joining technique using solder.

[0006]

SUMMARY OF THE INVENTION Tin / lead eutectic solder is
It has the property that it has better wettability to the base material than other metal mixtures, but the lead contained in this solder is exposed to acid rain etc. for many years when discarded electronic equipment is landfilled Therefore, there is a concern that lead ions may be eluted into the soil to cause toxicity. In order to solve this, a technique for immobilizing lead has been proposed, but sufficient long-term data on the diffusion into soil has not been obtained. Furthermore, with the recent increase in the density of memory elements, the effects of lead radiation (α-rays) on electronic equipment have been highlighted, and the use of lead has also been reduced in response to high-density packaging in semiconductor devices. Need to be reviewed.

[0007] Under such circumstances, there is a need for a joining technique using lead-free solder. However, solder in which lead is replaced by another metal or a combination of other metals has very poor wettability and does not exhibit satisfactory bonding properties. For example, the use of tin and zinc solder and tin and silver solder has been attempted, but the wettability is poor and bonding is difficult. Moreover, since silver itself is a noble metal, it is difficult to use a large amount of solder containing silver as a general-purpose product, and the application is easily limited to a special area.

[0008] In the current state of joining and assembling electric and electronic parts, since a screen printing type apparatus and equipment using a solder paste has penetrated a manufacturing site, it is necessary to commercialize a solder paste containing no lead. Have been. However, at present, only a few attempts have been made to put the solder paste into practical use in complex systems such as tin / silver / bismuth solder, and component assembly using a lead-free solder paste has hardly been put to practical use. The reason is that a special atmosphere, environment, or the like must be used as a working environment, so that it is not economically feasible in a process such as assembly of parts.

[0009]

Means for Solving the Problems Accordingly, the present inventors have:
In order to solve the environmental problems caused by lead in waste, we conducted intensive research on soldering using a highly versatile metal solder that does not contain lead, and as a result, to prepare a solder paste of zinc-containing solder Found that adding a catechin compound to the flux to be mixed in the process reduces the use of highly reactive components that require a special work environment during reflow, and provides a solder paste that is safe and easy to handle. Thus, the solder paste and the flux of the present invention have been completed.

[0010] The solder paste of the present invention is a solder paste in which a flux containing catechin or a catechin derivative and a solder powder containing zinc and tin are mixed.

The above solder powder has a binary tin / zinc binary eutectic composition, and contains no metallic impurities other than tin and zinc.
At 1 wt% or less, the oxygen content is 1000 ppm or less.

The flux for forming a solder joint according to the present invention comprises:
Contains catechin or catechin derivative.

[0013] The flux contains a component that dissolves, decomposes or reduces the metal oxide, and a binder.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Solder paste is obtained by mixing a solder powder prepared by heating and melting a plurality of kinds of metals into granulated solder powder and a separately prepared flux. By applying and reflowing (heating), the flux is vaporized or decomposed, and a bond is formed by the molten solder. The role of the flux is to chemically remove and clean the natural oxide film on the surface of the solder powder and the surface of the member to be soldered and to prevent re-oxidation during the reflow process, and mechanically solder until the joining is completed. There is a role of temporarily fixing the members. Therefore, basically, a component that dissolves, decomposes, or reduces a metal oxide and a binder (binder) component are essential components of the flux. Such a flux is formed by blending various substances as necessary in order to efficiently exhibit a chemical action and a mechanical action. In general, the main component of the flux is a resin that coats the surface of a solder powder and a member to be soldered. Generally, a rosin-based resin (pine resin) mainly containing abietic acid is used. Gum rosin, wood rosin,
There are tall rosin and modified rosins and rosin esters obtained from these. The rosin-based resin also plays a chemical function of the flux. Thermoplastic synthetic resins such as polyester resins and acrylic resins are also used. In such a resin component, an activator for supplementing a chemical action such as a detergency of the resin and improving the bonding property of the solder, an auxiliary activator for assisting the action of the activator, and a printability as a paste are maintained. A thixotropic agent, a solvent for dissolving and mixing these, and the like are appropriately selected and added as needed, and a solder paste is prepared. An organic acid is added to impart gloss to the solder, and an amine compound or the like is added to adjust the pH to prevent dripping or to form a solder ball. Commonly used, for example, monoethanolamine, stearylamine, amine compounds such as diphenylamine, ethylamine, propylamine,
Examples include hydrohalides of amine compounds such as diethylamine and aniline, and organic acids such as citric acid, lactic acid, adipic acid and stearic acid.

When the flux used for tin / lead solder is used for tin / zinc solder, the viscosity of the solder paste immediately after preparation is about 200 Pa · s, which is similar to that of tin / lead solder. In the case of tin / zinc solder, the viscosity of the tin / zinc solder reaches several times or more and almost hardens. This is considered to be caused by the bonding between the zinc of the solder and the organic component of the flux, the polymerization of the organic component, and the oxidation of the solder by a small amount of oxygen mixed in the solvent or the like. In order to eliminate such a cause, it is necessary to devise the components to be used, such as by reducing the amount of addition of a substance having a high acidity.

In the present invention, catechin or a catechin derivative, ie, a catechin derivative, is used as a component of a milder flux.
A catechin compound is used. Catechin compounds are water-soluble natural polyhydric phenols widely contained in trees. In a broad sense, it is a kind of tannin and is considered to be a precursor of condensed tannin, and is sometimes referred to as a class of pigment compounds generally called flavonoids. Specifically, it means epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, catechin, gallocatechin, epicatechin digallate, epigallocatechin digallate, etc., and naturally (-)-epicatechin, (−) −
Epigallocatechin, (−)-epicatechin gallate,
There are (-)-epigallocatechin gallate, (+)-catechin, (+)-gallocatechin, (-)-epicatechin digallate and (-)-epigallocatechin digallate. It is known that catechins are contained in tea buds in a large amount.
Can be obtained as crude catechin. Methods for obtaining higher purity crude catechins have also been proposed. The main catechin compounds contained in tea are (-)-epicatechin,
(-)-Epigallocatechin gallate, (-)-epicatechin gallate and (-)-epigallocatechin gallate,
These make up about 90% of the crude catechins. Studies have been conducted on the chemical, biochemical and pharmacological usefulness of various catechin compounds.
It has been reported that (-)-epigallocatechin gallate contained at a ratio of 0 to 60% is a substance having particularly high functionality.

The properties of catechin compounds include 1) reaction with metal (precipitation by calcium, blue-black color reaction by iron), 2) reaction with protein (precipitation, etc.), 3) antioxidant activity , 4) Astringency, 5) Antibacterial action (caries, periodontal disease bacteria, food poisoning bacteria), 6) Pharmacological action (lowering blood cholesterol level, anti-allergy, etc.), 7) Deodorant action (prevent fishy odor, bad breath) Etc.). When used as a flux component of the solder paste, the catechin compound suppresses a reaction due to oxygen by its antioxidant property and function as a radical scavenger. In addition, when a catechin compound is added to food, it exhibits an antioxidant effect on lipids in the food, and similarly prevents oxidation of lipids in a flux. The antioxidant effect of catechins on lipids is very good.
Of crude catechin was added and the peroxide value was measured.
0 ppm of dl-α-tocopherol (vitamin E) or 5 ppm
Shows better antioxidant activity than 0 ppm butylhydroxyanisole (BHA).

The antioxidant properties of catechin compounds are synergistically increased when used in combination with amino acids and vitamins. Amino acids that exhibit a synergistic effect depending on the combination include L-methionine, and vitamins such as L-ascorbic acid (vitamin C) and tocopherol (vitamin E).
And the like. Vitamin A, Vitamin C, Vitamin D and Vitamin E have antioxidant properties. Addition of them suppresses the time-dependent change of the solder paste and improves the storage stability. Vitamin K enhances the flux reactivity during reflow, vitamin L ₁ can be used as a reducing agent, vitamins U, and amino acids so can be used for pH adjustment of the flux, catechin compound and combinations of these are very effective for the preparation of the flux.

The catechin compounds and the amino acids and vitamins used in combination therewith act like a chelating agent in the solder paste to form a chelate complex with the metal on the surface of the solder powder. This suppresses the active metal species from reacting with components such as activators contained in the flux, and prevents the active metal species from being eluted into the flux and being deteriorated with time or having reduced stability. Therefore, a decrease in the joining property of the solder is suppressed. In the tin / zinc solder powder, zinc is an active metal species, so that the zinc reacts with the activator or the like and is eluted into the flux, thereby preventing the deterioration and the decrease in stability, and maintaining the solder bondability. You.

The active metal species acts as a catalyst in the solder paste to cause a polymerization reaction of organic components in the flux to increase the viscosity of the flux. Catechin compounds suppress such a reaction. Can be. Furthermore, it is necessary to suppress the direct oxidation reaction of solder by active oxygen species in the atmosphere and the indirect oxidation reaction of solder generated by peroxide generated by the oxidation of organic or inorganic components in flux by active oxygen species. Can be.

When the solder paste according to the present invention is heated, the catechin compounds, amino acids and vitamins are decomposed and vaporized, and the activator in the flux reacts with the metal on the surface of the solder powder, thereby purifying the metal surface. Good soldering is performed.

Catechin compounds having the above-mentioned properties are contained in the solder paste flux in an amount of 1 ppm to 10 ppm.
wt%, preferably about 10 ppm to 3 wt%. When using amino acids or vitamins together,
The added amount of amino acids is preferably about 100 ppm to 5 wt%, and the added amount of vitamins is preferably about 100 ppm to 10 wt%. Both amino acids and vitamins may be used. These additives are added and mixed together with other components at the time of preparing the flux according to a conventional method.

Such a flux has a particle size of 4 to 100.
about μm, preferably about 10 to 50 μm or less by mixing with paste solder powder prepared in a granular form,
A suitable solder paste is prepared. The solder powder and the flux are usually mixed at a ratio of about 9: 1. The volume of the solder paste applied on the metal member to be soldered is reduced to about 1/2 by reflow. The amount of solder paste to be applied to the members to be soldered is 150
An amount that gives a thickness of about 200 μm is preferable.

The flux containing the catechin compound of the present invention is suitable for producing a solder paste of tin / zinc solder, but is not limited thereto.
It is also possible to add a catechin compound to the flux as an activator in other metal solders. Also, tin /
The zinc solder powder is not limited to the alloy particles having the tin / zinc eutectic composition, but may be alloy particles having a composition other than the eutectic composition.
It may be a mixture of simple powders of tin and zinc. In particular,
Mixtures of tin and zinc plain powders in eutectic composition have particular advantages. That is, when the heating temperature reaches the eutectic point temperature in the reflow operation, the eutectic solder powder begins to melt on the entire outer surface of the particles, whereas tin and zinc plain particles are tin particles and zinc particles. Liquid starts to be melted from the contact interface of the solder powder, and a liquid susceptible to air oxidation is generated inside the mass of the solder powder, so that a decrease in wettability due to oxidation of the solder can be suppressed.
This is easily understood from the tin / zinc binary phase diagram. Furthermore, considering that zinc is easily oxidized, the most preferable form is a solder powder in which zinc is coated with tin and the composition of the entire solder powder becomes an eutectic composition. The solder powder having such a multilayer structure can be easily produced through rolling and pressing and cutting of a metal block.
Oxidation of the solder increases the melting temperature and significantly lowers the wettability. Therefore, it is desirable that the solder powder used has a low oxygen and oxide content. If there is much oxygen or oxide contained in the solder powder used, even if the surface of the solder powder is activated and melted by the flux, the inside does not melt because the oxide has a high melting temperature, and the reflow temperature is increased. It has to be done.
As a result, air oxidation on the liquid phase surface also proceeds more easily, and sufficient wettability cannot be obtained even when a strong flux is used. Metal impurities other than tin and zinc, including unavoidable metal impurities, are 0.1 wt% or less and the oxygen content is 1000
Tin / zinc solder purified to less than ppm, preferably less than 100 ppm, has good wettability and does not require a highly active substance as a flux.

After the solder paste prepared as described above is applied to a member to be soldered by using a technique such as a screen printing method, the members to be joined are brought into contact with each other and reflowed. In the reflow process, 100 to
By heating to a temperature of about 170 ° C., the above-mentioned flux activates the surface of the solder powder, and the solder powder comes into contact with the member surface. Subsequently, the solder powder is melted by heating to a reflow temperature at which the solder melts. Thereafter, by cooling, the metal members are joined by solder. The heating time at the reflow temperature is preferably 200 ° C. or more and 30 seconds or less, and 240 ° C. or less is preferably 10 seconds or less. If heating is continued more than necessary, the oxidation of the solder tends to proceed. The reflow can be performed in an air atmosphere, but is preferably performed in a non-oxidizing atmosphere. In the reflow in a non-oxidizing atmosphere, the tin / zinc alloy in the molten state is cut or has low viscosity due to the prevention of oxidation of the solder powder, and it can cope with the formation of dense joints such as those of high-density mounting substrates. .

The solder plague of the present invention is made of copper, silver, gold,
The present invention can be applied not only to a single type of metal member such as nickel, aluminum, and SUS stainless steel, but also to a member such as an alloy material and a composite metal material. In addition, fine soldering can be adequately performed, and a thin line-shaped metal member having a narrow interval can be used for soldering a member having a line width and a line interval of about 0.3 mm. Therefore, it can be used for soldering for mounting a substrate or joining various electric and electronic components. Examples of electric and electronic components include an IC package used in the semiconductor field, a conductive portion of a CPU, a hard disk built in a personal computer, an electric circuit of a liquid crystal panel, an IC card, a cable connector used for connecting a personal computer or a printer, Examples include an optical connector used for a communication cable, a radiator of an automobile, and the like. The mounting form of the board includes single-sided surface mounting, double-sided surface mounting, component mounting with double-sided surface mounting leads, component mounting with single-sided surface mounting leads, lead-through mounting, etc., all using the bonding material of the present invention. be able to. Also, as mounted components, ceramic capacitors, inductors, jumpers, transistors,
Examples include a diode, an aluminum electrolytic capacitor, a tantalum semi-fixed resistor, a trimmer, a coil, and the like, and typical examples of the active component include an IC and an SI. Package shapes include SOIC, SOP, QIP, QFP, PLCC,
LCC, SOJ, MSP, BGA, FC-BGA, CS
P, PLC, MCM, OE-MCM, and a high-density chip in which a plurality of chips are stacked.

Depending on the material of the member to be joined, the member may be pre-coated in advance, and the composition of the pre-coat and the pre-coating method can be appropriately selected.

The flux containing the catechin compound of the present invention may be used as it is, without preparing a solder paste, applied to the surface of the member to be joined as it is to activate the surface of the member at the time of soldering. Further, a flux may be applied to the surface of a solder material such as a wire solder and used for soldering. In this case, since a paste-like physical property is not required, a component having a binder (binder) function is not essential, but a paste-like one is more convenient in order for the necessary component to remain on the metal surface. Further, the flux of the present invention can be used as a protective agent for preserving a solder material.

It is more effective to use a reducing atmosphere in the reflow step. Examples of the reducing atmosphere include an atmosphere containing a suitable amount of a reducing gaseous substance in an inert gas such as nitrogen. The reducing gaseous substance includes hydrogen; methanol vapor, ethanol vapor, propanol vapor, and the like. Alcohol vapors, and acid vapors such as formic acid and acetic acid.

As described above, when the solder paste of the present invention is used, a lead-free general-purpose device and equipment that are used in the current assembly and manufacturing process of electric and electronic assemblies are used. It is possible to join parts using tin / zinc-based solder having high performance.

The use of a tin / zinc binary alloy solder having a simple composition facilitates the recovery and recycling of the joined parts and the joined body after joining, and is advantageous in reusing the collected metal.

[0032]

The present invention will be described below in detail with reference to examples.

Example 1 91.2 parts by weight of metallic tin and 8.8 parts by weight of metallic zinc were heated and melted under reduced pressure, and the composition was 91.1% by weight or more of tin, 8.8% by weight of zinc and other trace amounts. A tin / zinc solder having a total oxygen content of less than 0.1 wt% and an oxygen concentration of 10 ppm was prepared. This solder was granulated in a nitrogen atmosphere to obtain a solder powder having a particle size distribution of 20 to 40 μm.

On the other hand, 54 parts by weight of polymerized rosin (pine resin), 35 parts by weight of hexyl diglycol as a solvent, 5 parts by weight of hydrogenated castor oil (thixotropic agent), 4 parts by weight of citric acid, 1 part by weight of ethylamine hydrochloride and the following composition Was heated while mixing, followed by cooling to prepare a homogeneous flux. 11 parts by weight of this flux and 89 parts by weight of the above-mentioned solder powder were stirred and mixed in a nitrogen atmosphere to obtain a solder paste.

[Crude catechin] (-)-epicatechin 6.0 wt% (-)-epigallocatechin 17.5 wt% (-)-epicatechin gallate 12.5 wt% (-)-epigallocatechin gallate 54.0 wt % (+)-Gallocatechin 1.5 wt% (+)-catechin, (−)-epicatechin digallate and (−)-epigallocatechin digallate Residual JIS Z
The spread ratio and the viscosity in soldering were measured according to 3197. Further, after the remainder was stored in a refrigerator set at 0 to 10 ° C. for one month, the spreading ratio and the viscosity were measured in the same manner. From these measured values, the spread change rate (%) [100 × (spread rate after storage−initial spread rate) / initial spread rate] is used as a measure of wet retention, and the viscosity change rate (% is used as a measure of preservability. ) [100 × (viscosity after storage−initial viscosity) / initial viscosity] was determined. The results are shown in Table 1 as A for less than 1%, B for 1% or more and less than 5%, and C for 5% or more.

Example 2 Example 1 was repeated except that 1 part by weight of crude catechin was replaced by 1 part by weight of a mixture of crude catechin and L-methionine at a weight ratio of 1:10.
The same operation as in was repeated, and the spread rate and the viscosity were measured to determine the spread change rate and the viscosity change rate. Table 1 shows the results.

(Example 3) Instead of 1 part by weight of crude catechin, crude catechin and dl-α-tocopherol were mixed at a ratio of 1: 2
The same operation as in Example 1 was repeated except that 1 part by weight of the mixture mixed at a weight ratio of 0 was used, and the spread rate and the viscosity were measured to obtain the spread change rate and the viscosity change rate. Table 1 shows the results.

Example 4 A mixture 1 in which crude catechin, L-methionine and dl-α-tocopherol were mixed at a weight ratio of 1:10:20 instead of 1 part by weight of crude catechin was used.
The same operation as in Example 1 was repeated except that the parts by weight were used, and the spread rate and the viscosity were measured to obtain the spread change rate and the viscosity change rate. Table 1 shows the results.

(Comparative Example) The same operation as in Example 1 was repeated except that 1 part by weight of crude catechin was not used, and the spread rate and the viscosity were measured to determine the spread change rate and the viscosity change rate. Table 1 shows the results.

[0040]

Table 1 ------------------ Retention (%) (Pa · s) −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Example 1 Crude catechin 80 250 BA Example 2 Crude catechin + L-methionine 82 230 BA (1:10) Example 3 Crude catechin + dl-α-84 200 BA Tocopherol (1:20) Example 4 Crude catechin + L-methionine 83240 B A + dl-α-tocopherol (1:10:20) Comparative Example-61 440 C C-------------------------------------------------------------------- −−−−−− As can be understood from the results of the comparative examples in Table 1, the flux without the addition of the catechin compound does not Immediately after the preparation of the paste, the viscosity was already large and the spreading rate was low, indicating that the change in the properties of the solder and the flux had already progressed during the preparation. On the other hand, by adding the catechin compound, the wettability of the solder paste is maintained even one month after the preparation, and the storage stability is improved. Excellent effects are also seen when L-methionine or dl-α-tocopherol is used in combination.

[0041]

According to the present invention, when a tin / zinc solder paste is prepared using a flux containing a catechin compound, the flux deteriorates due to active oxygen species, organic or inorganic peroxides, and the like. Is prevented, and the quality of the solder paste is stably maintained for a long period of time, so that good bonding can be formed.
Further, soldering at a low melting temperature is possible, and mechanical characteristics such as creep characteristics of solder joint can be improved. Therefore, it is extremely effective for practical use of soldering without using lead, it is possible to reduce lead contained in waste, and it is also effective for recycling waste.
Also, the working environment for soldering is improved. Therefore, the present invention is extremely useful in industrial and environmental measures.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-243782 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 35/363 B23K 35/22 B23K 35 / 26

Claims (3)

(57) [Claims] 1. A solder paste comprising a mixture of a flux containing catechin or a catechin derivative and a solder powder containing zinc and tin. 2. The solder powder according to claim 1, wherein the overall composition is a tin / zinc binary eutectic composition, metal impurities other than tin and zinc are 0.1 wt% or less, and the oxygen content is 1000 ppm or less. The solder paste as described. 3. A flux for forming a solder joint, comprising catechin or a catechin derivative.