JPH0929480A - Solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress Manhattan phenomenon by including >=2 kinds of solder particles, alloy particles contg. one kind of metals for solder at a ratio higher than the ratio of a compsn. which fonts eutectic with other metals for solder and allay particles contg. these metals at a lower ratio into solder paste. SOLUTION: The solder particles formed of >=2 kinds of the metals for solder contain at least >=2 kinds of the solder particles ; the alloy particles in which at least one kind of the metals for solder are included at the ratio higher than the ratio in the compsn. which form eutectic with the other metals for solder and the alloy particles in which these metals are included at the lower ratio. The viscosity of the solder paste at the time of soldering is increased and the occurrence of a difference in melting time is prevented by using the paste contg. at least one kind of the solder particles consisting of the alloy particles composed of the compsn. exhibiting a half-molten state and, therefore, the Manhattan phenomenon is prevented and the joint parts having the high reliability are formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solder paste. More specifically, the present invention relates to a solder paste having improved soldering characteristics by improving the composition of alloy particles constituting solder particles. The solder paste of the present invention can be suitably used, for example, when connecting a printed wiring board and an electronic component.

[0002]

2. Description of the Related Art In recent years, there have been demands for miniaturization, multifunctionalization and high performance of electronic equipment. For this reason, printed wiring boards used in electronic equipment have been reduced in diameter of through holes, increased in wiring density, and multilayered in order to meet the above demand.
In addition, a surface mount method (SMT: Surface Mounted Tech) in which components are directly attached to the surface of the substrate.
The technology requires a higher level of technology than the conventional through-hole mounting method. With this SMT mounting method, high-density mounting is possible, self-alignment by soldering is possible, and other advantages are very great.

In this SMT mounting method, after solder paste is applied by screen printing and components are mounted, reflow (for example, vapor phase soldering (VSP; Vapor) is carried out.
Phase Soldering), infrared rays and / or soldering with a hot air reflow furnace, etc.) to heat and melt to form a joint. Particularly in recent years, since soldering in an oxidizing atmosphere has poor wettability, soldering is performed in a nitrogen atmosphere in order to improve quality. The conventional solder paste contains Sn63%, Pb
An alloy having a eutectic composition of 37% and made into particles by an atomizing method is often used.

However, in the above reflow, a phenomenon in which a component rises, a so-called Manhattan phenomenon occurs, which is a problem. This phenomenon occurs because a difference in melting time occurs at a portion (for example, an electrode portion) where soldering of a component is desired at the time of reflow, and a rotational moment generated by the surface tension of the solder on the melting side causes the component to rise. . Therefore, the parts where this Manhattan phenomenon occurred are
There arises a problem that the portion desired to be joined is not joined.

[0005]

In the above-mentioned conventional soldering utilizing reflow, in order to prevent the Manhattan phenomenon, the land design is optimized, preheating is performed before the reflow treatment, and the required amount of heat is exceeded. Methods such as supplying solder paste are used. However, these methods cannot be said to be a fundamental solution to the Manhattan phenomenon caused by the difference in solder melting time.

On the other hand, JP-A-58-28889 and JP-A-59-112689 describe the use of solder pastes having different melting points, but in both publications, one surface of the substrate is used. Uses a solder paste containing only solder particles composed of alloy particles having the same melting point. Therefore, even the methods described in these publications cannot prevent the Manhattan phenomenon.

[0007]

Thus, according to the present invention, in solder particles formed from two or more kinds of soldering metals, at least one kind of soldering metal forms a eutectic crystal with another soldering metal. There is provided a solder paste containing at least two kinds of solder particles, that is, alloy particles contained in a larger proportion and alloy particles contained in a smaller proportion.

Further, according to the present invention, there is provided a solder paste containing at least one kind of solder particles, the solder particles being alloy particles having a composition showing a semi-molten state.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The solder particles usable in the present invention are alloy particles composed of two or more kinds of soldering metals capable of forming a eutectic. Here, the eutectic refers to a mixture of two or more kinds of crystals that are simultaneously precipitated as crystals from the liquid phase. Specifically, the solder particles are Sn, Pb, Bi, I
Alloy particles formed by combining two or more kinds of n and Ag metals,
Alternatively, it is preferable to be composed of alloy particles in which one or more kinds of Cu, Sb, Ga, Ge, P and Cd are further combined with the metal. As more preferable solder particles, Pb-Sn, Sn
-Bi, Sn-In, In-Pb, Sn-Ag, Pb-
Binary alloy particles such as Ag, Ag-In, Bi-In, P
Examples include ternary alloy particles such as b-Sn-Ag Pb-Sn-Sb. In addition to these binary and ternary alloy particles, Cu, Ag, Sb, Ga, Ge, In and B are further added.
You may use the multi-component alloy particle which further combined 1 or more types of i, P, and Cd. In addition, Sb, Cu, Bi, Zn,
Impurities derived from the raw material of the solder particles such as Fe, Al, As, and impurities (unavoidable impurities) that are expected to be mixed in during the production of the solder particles may be included.

It is one of the features that the solder particles of the present invention include at least one kind of solder particles composed of alloy particles having a composition showing a semi-molten state. By using a solder paste containing at least one kind of solder particles consisting of alloy particles composed of a composition showing a semi-molten state,
It is possible to prevent the Manhattan phenomenon from increasing because it is possible to increase the viscosity of the solder paste at the time of soldering (to reduce the rotation moment generated by surface tension) and to prevent the difference in melting time. Here, the semi-molten state means a state in which the solid and the liquid coexist when changing from the solid to the liquid and from the liquid to the solid.

Further, the solder particles in the present invention preferably contain at least one alloy particle having a composition adjusted so that the temperature range in the semi-molten state is 5 ° C. or more. When the temperature range is 5 ° C. or more, it is possible to prevent the solder paste from having a higher viscosity and to prevent a difference in melting time, and it is possible to prevent the Manhattan phenomenon.

Further, the solder particles in the present invention may contain one kind or two kinds or more of the alloy particles exemplified above. Furthermore, in solder particles formed from two or more kinds of soldering metals, at least one kind of soldering metal is
It is preferable to contain at least two kinds of solder particles, that is, alloy particles contained in a larger proportion and alloy particles contained in a smaller proportion than the composition forming a eutectic with another solder metal. Furthermore, two or more kinds of alloy particles made of the same metal but different in composition may be combined. More preferably, solder particles composed of two or more kinds of alloy particles having different compositions adjusted in advance so that the composition in the molten state shows a composition forming a eutectic (eutectic composition). Is. By adjusting the composition in the molten state to be the eutectic composition, the composition of the joint after the actual soldering also becomes the eutectic composition. The joint having the eutectic composition is mechanically superior to the joint having a composition other than the eutectic composition in values such as tensile strength and shearing force. Here, the eutectic composition means a composition at a time point (eutectic point) at which the metals simultaneously precipitate as crystals from a liquid phase containing two or more kinds of metals.

The average diameter of the solder particles is 10-5.
It is about 0 μm. However, it is not limited to this range. The shape of the solder particles is not particularly limited, but a spherical shape is preferable. Furthermore, when solder particles composed of two or more kinds of alloy particles are used, among the two or more kinds of alloy particles, the average diameter of alloy particles having a low temperature on the liquidus line (hereinafter, referred to as liquidus temperature) is More preferably, it is larger than the average diameter of the alloy particles having a high liquidus temperature. Here, the liquidus line means a curve representing the relationship between the composition (% by weight) of the liquidus phase and the temperature. By changing the size of the average diameter in this way, alloy particles having a low liquidus temperature and a large average diameter are melted quickly. The molten alloy particles take in the alloy particles having a high liquidus temperature, so that the melting phenomenon proceeds smoothly. Therefore, the temperature required for soldering can be kept low. The average diameter of the alloy particles having a low liquidus temperature is preferably 5 μm or more larger than the average diameter of the alloy particles having a high liquidus temperature.

In the present invention, particularly preferable solder particles are solder particles composed of Pb—Sn alloy particles and composed of two kinds of alloy particles having different compositions. Here, FIG.
[Fig. 4] is a state diagram showing how the state of metal changes in relation to the composition and temperature of Pb-Sn. Hereinafter, a more detailed description will be given using a state diagram. In FIG. 1, a means a melting point of Pb, c means a melting point of Sn, b means a eutectic point, L means a liquid phase, α means a solid phase consisting essentially of Pb, and β means a solid phase consisting essentially of Sn. Further, the curve abc (L) means the liquidus line, and dbe means the eutectic line. The semi-molten state in the present invention specifically means a state of a liquid phase and a solid phase in adb (α + L) and bec (β + L).

Here, when the solder particles are composed only of alloy particles composed of 53 wt% Pb and 47 wt% Sn, such as the AA line, the solder particles exist as a solid phase at a temperature lower than the eutectic line dbe. To do. When the temperature is raised to a temperature higher than the eutectic line dbe, the solid phase α substantially made of Pb and the liquid phase substantially made of Sn are in a semi-molten state. When the temperature is further increased to a temperature higher than the liquidus line abc, the solder particles exist as a liquid phase. Next, when the temperature is lowered, the liquid phase becomes a semi-molten state at a temperature lower than the liquidus line abc, and becomes a solid phase at a temperature lower than the eutectic line dbe. Therefore, the solder particles having the above composition are in a semi-molten state, and during soldering, it is possible to gain time until completely melting. As a result, it is possible to prevent a difference in melting time, so that it is possible to prevent the Manhattan phenomenon.

In the present invention, more preferably, Pb is 35 to 40% by weight, Sn is 60 to 65% by weight, and particularly Pb is 37% by weight and Sn is 63% by weight (eutectic composition) after melt solidification. In addition, it is preferable to previously adjust the composition of the soldering metal of the alloy particles constituting the soldering particles. Therefore, the solder particles before melting and solidification are the first alloy particles composed of Pb of 38 to 53% by weight and Sn of 47 to 62% by weight, and Pb of 20 to 35% by weight and Sn of 65 to 80% by weight.
It is particularly preferable that the second alloy particles consist of
When solder particles composed of two kinds of alloy particles having such a composition are used, soldering can be performed at 190 to 210 ° C.

Here, after melting and solidification, Pb is 37% by weight,
The state during soldering of the solder particles, which are adjusted in advance so that the Sn content will be 63% by weight (eutectic composition) and made of alloy particles having a particularly preferred composition, will be described with reference to FIG. The solder particles are a mixture of the first alloy particles having the composition of Pb53 wt% and Sn47 wt% used in the above description and the second alloy particles having the composition of Pb73 wt% and Sn27 wt%. To use. First, the first alloy particles are in a semi-molten state at a temperature higher than the eutectic line dbe, and when the temperature is further raised, they are in a molten state at a temperature higher than the liquidus line abc (see line AA in FIG. 1). ). On the other hand, the second
The alloy particles of No. 2 also go into a semi-molten state after undergoing the same state as the first alloy particles (see line BB in FIG. 1). When the temperature is further raised, the first and second alloy particles are mixed in a liquid phase at a temperature higher than the liquidus line abc, and have a eutectic composition.
After that, when the temperature is lowered, the temperature becomes lower than the temperature of the eutectic point b to become a solid phase (that is, a joint) without passing through a semi-molten state, and the soldering is completed.

The solder paste of the present invention contains solder particles and other additives necessary to form the solder paste. Here, the solder particles are contained in an amount of 80 to 95 parts by weight with respect to 100 parts by weight of the solder paste. Further, other additives include activators, thickeners, thixotropic agents, solvents and the like. The activator has a function of cleaning the surface of a metal to be soldered, amine hydrochloride such as dimethylamine hydrochloride, amine hydrobromide such as ethylamine hydrobromide, adipic acid, maleic acid, etc. Examples of organic acids include The addition ratio of the activator is 0.001 to 0.01 part by weight with respect to 100 parts by weight of the solder paste.

The thickener has the functions of cleaning the metal surface to be soldered and improving the tackiness for holding parts, and examples thereof include rosin, rosin ester and polybutene. The addition ratio of the thickener is 1 to 10 parts by weight with respect to 100 parts by weight of the solder paste.
The thixotropic agent has a function of preventing dispersion and dripping, and examples thereof include castor wax (hardened castor oil) and carnauba wax. The addition ratio of the thixotropic agent is the solder paste 100.
It is 0.1 to 0.5 parts by weight with respect to parts by weight.

The balance of the solder paste is a solvent, which has the function of optimizing the characteristics of the paste, and polyhydric alcohol compounds such as butyl carbitol, ethylene glycol and glycol ether are used. Solder paste, solder particles formed by a known atomizing method,
Other additives required to form the solder paste can be prepared by mixing. It is preferable that the mixing is performed so that the components of the solder paste are uniform.

The solder paste of the present invention is suitably used, for example, when connecting a printed wiring board and an electronic component. The method of use can be used, for example, by applying a solder paste to a portion desired to be soldered by a printing method or the like and then heating it to melt and solidify the solder particles. In the solder paste of the present invention, in the solder particles formed from two or more kinds of soldering metals, at least one kind of soldering metal is contained in a proportion higher than that of a composition forming a eutectic with another soldering metal. Since it is characterized by containing at least two kinds of solder particles, that is, the alloy particles and the alloy particles contained in a small proportion, it is possible to gain time until the solder particles are completely melted. Therefore, it is possible to prevent the melting time difference from occurring and suppress the Manhattan phenomenon.

Further, since the solder particles have a composition that forms a eutectic in the molten state, the values of tensile strength, shearing force, etc. are higher than those of the solder particles having a composition other than the eutectic composition in the molten state.
A mechanically superior joint is obtained. Further, since the solder particles include at least one kind of solder particles composed of alloy particles having a composition showing a semi-molten state, a large amount of time can be gained until melting and the Manhattan phenomenon is suppressed.

Moreover, since the solder particles contain at least one kind of alloy particles composed of two or more kinds of soldering metals having a composition showing a semi-molten state having a temperature range of 5 ° C. or more, the viscosity of the solder paste can be improved. It can be increased and the Manhattan phenomenon is suppressed. Further, the solder particles are Sn, P
Alloy particles formed by combining two or more metals of b, Bi, In, and Ag, or Cu, Sb, Ga, Ge, and
Since it is composed of alloy particles in which one or more of P and Cd are further combined, a mechanically excellent joint can be obtained.

Further, the solder particles are composed of two or more kinds of alloy particles composed of compositions having different liquidus temperatures, and among the alloy particles, alloy particles having a low liquidus temperature are alloy particles having a high liquidus temperature. Since it has a larger average diameter than that of, the temperature required for soldering can be kept low. Furthermore, alloy particles having a low liquidus temperature are 5 μm smaller than alloy particles having a high liquidus temperature
Since it has a large average diameter, the temperature required for soldering can be kept low.

[0025]

【Example】

Example 1 Other additives (resin component) necessary for forming a solder paste by adding 46 g of butyl carbitol, 1 g of adipic acid, 3 g of hydrogenated castor oil, and 0.02 g of dimethylamine hydrochloride to 50 g of polymerized rosin. Was adjusted.

The solder particles are alloy particles of 73% by weight Sn-27% by weight Pb produced by the atomization method (semi-molten temperature range: about 12.5 ° C., average diameter 40 μm).
Alloy particles of 450 g, 53 wt% Sn-47 wt% Pb (semi-molten temperature range: about 22.5 ° C., average diameter 30 μ
m) 450 g were used. The resin component was mixed with solder particles to prepare a solder paste, which was subjected to the following tests. (Test method) 1005 type parts (size 1
A printed wiring board having lands (size 0.8 mm × 0.6 mm) on which 50 mm × 0.5 mm square chip parts can be mounted was used. Solder paste was applied to the lands of this printed wiring board by a printing method. After this,
Place 50 pieces of 1005 type parts on the land, and
Soldered using a reflow machine. The number of defects (number of Manhattan phenomenon occurrences) after soldering was measured by visual inspection. Table 1 shows the number of occurrences of the Manhattan phenomenon together with the occurrence rate.

Example 2 Solder particles were alloy particles of 68 wt% Sn-32 wt% Pb (semi-molten temperature range: about 7 ° C., average diameter 40 μm).
m) 500 g, alloy particles of 53 wt% Sn-47 wt% Pb (semi-molten temperature range: about 22.5 ° C., average diameter 3
0 μm) A solder paste was prepared in the same manner as in Example 1 except that the amount was 400 g. The solder paste of Example 2 was evaluated based on the same test method as that of Example 1.
Table 1 shows the number of occurrences of the Manhattan phenomenon together with the occurrence rate.

Example 3 A solder paste was prepared in the same manner as in Example 1 except that the alloy particles of 53 wt% Sn-47 wt% Pb had an average diameter of 35 μm. The solder paste of Example 3 was evaluated based on the same test method as that of Example 1. Table 1 shows the number of occurrences of the Manhattan phenomenon together with the occurrence rate.

Example 4 Solder particles were made of alloy particles of 61 wt% Sn-39 wt% Pb (semi-molten temperature range: about 3 ° C., average diameter 40 μm).
m) 450 g, alloy particles of 65 wt% Sn-35 wt% Pb (temperature range in semi-molten state: about 5 ° C., average diameter 30 μm
m) In the same manner as in Example 1 except that the amount was 450 g,
A solder paste was prepared. The solder paste of Example 5 was evaluated based on the same test method as that of Example 1. Table 1
The number of occurrences of the Manhattan phenomenon is shown together with the occurrence rate.

Example 5 A solder paste was prepared in the same manner as in Example 1 except that the alloy particles of 53 wt% Sn-47 wt% Pb had an average diameter of 36 μm. The solder paste of Example 4 was evaluated based on the same test method as that of Example 1. Table 1 shows the number of occurrences of the Manhattan phenomenon together with the occurrence rate.

Example 6 Solder particles were mixed with 61.5 wt% Sn-38.5 wt% P.
b alloy particles (semi-molten state temperature width: about 2 ° C., average diameter 40 μm) 450 g, 64.5 wt% Sn-35.5 wt% Pb alloy particles (semi-molten state temperature range: about 4 ° C., A solder paste was prepared in the same manner as in Example 1 except that the average diameter was 30 μm and the weight was 450 g. The solder paste of Example 6 was evaluated based on the same test method as that of Example 1. Table 1 shows the number of occurrences of the Manhattan phenomenon together with the occurrence rate.

Comparative Example 1 A solder paste was prepared in the same manner as in Example 1 except that the solder particles were 900 g of one type of alloy particles of 63 wt% Sn-37 wt% Pb (average diameter 40 μm).

The solder paste of Comparative Example 1 was evaluated based on the same test method as in Example 1. Table 1 shows the number of occurrences of the Manhattan phenomenon together with the occurrence rate.

[0034]

[Table 1]

From Table 1 above, it can be seen that the solder pastes of Examples 1 to 6 according to the present invention have a lower number and rate of occurrence of the Manhattan phenomenon than the conventional solder paste of Comparative Example 1. Further, by comparing Examples 1 to 4 and Example 5, it is found that the difference in average diameter between the alloy particles having a low liquidus temperature and the alloy particles having a high liquidus temperature is preferably 5 μm or more.

Further, by comparing Examples 1 to 4 with Example 6, at least alloy particles composed of two or more kinds of soldering metals having a composition showing a semi-molten state in a temperature range of 5 ° C. or more are obtained. It turns out that it is preferable to include one kind.

[0037]

In the solder paste of the present invention, in the solder particles formed from two or more kinds of soldering metals, at least one kind of soldering metal is more than the composition forming a eutectic crystal with another soldering metal. Since it is characterized by containing at least two kinds of solder particles, that is, alloy particles contained in a proportion and alloy particles contained in a small proportion, it is possible to earn time until the solder particles are completely melted. Therefore, it is possible to prevent the melting time difference from occurring and suppress the Manhattan phenomenon. Therefore, it becomes possible to form a highly reliable joint portion in the joint between the component and the substrate, which is required to be finer in the future.

Furthermore, since the solder particles have a composition that forms a eutectic in a molten state, the strength of the tensile strength, shearing force, etc. are higher than those of the solder particles having a composition other than the eutectic composition, and the mechanically excellent joint is obtained. Can be obtained. Moreover, since the solder particles include at least one kind of solder particles composed of alloy particles having a composition showing a semi-molten state, it is possible to obtain a large amount of time until melting and suppress the Manhattan phenomenon.

Further, since the solder particles contain at least one alloy particle composed of two or more kinds of soldering metals having a composition showing a semi-molten state having a temperature range of 5 ° C. or more, the viscosity of the solder paste is further improved. It can be increased and the Manhattan phenomenon can be suppressed. In addition, the solder particles are alloy particles formed by combining two or more metals of Sn, Pb, Bi, In, and Ag, or Cu, Sb,
Since it is composed of alloy particles in which one or more kinds of Ga, Ge, P, and Cd are further combined, a mechanically excellent bonded portion can be obtained.

Further, the solder particles are composed of two or more kinds of alloy particles composed of compositions having different liquidus temperatures, and among the alloy particles, alloy particles having a low liquidus temperature are alloy particles having a high liquidus temperature. Since it has a larger average diameter than that of, the temperature required for soldering can be kept low. Also,
Since the alloy particles having a low liquidus temperature have an average diameter larger than that of the alloy particles having a high liquidus temperature by 5 μm or more, the temperature required for soldering can be further suppressed.

[Brief description of drawings]

FIG. 1 is a state diagram showing how the state of a metal changes depending on the composition and temperature of Pb—Sn.

[Explanation of symbols]

 a Melting point of Pb c Melting point of Sn b Eutectic point L Liquid phase α Solid phase consisting essentially of Pb Solid phase consisting essentially of Sn abc Liquidus line dbe Eutectic line

Claims (7)

[Claims] 1. A solder particle formed from two or more kinds of soldering metal, wherein at least one kind of soldering metal is contained in an amount higher than that of a composition forming a eutectic crystal with another soldering metal. And a solder paste containing at least two kinds of solder particles of alloy particles contained in a small proportion. 2. The solder paste according to claim 1, wherein the solder particles have a composition that forms a eutectic in a molten state. 3. At least one solder particle, wherein the solder particle is an alloy particle composed of a composition exhibiting a semi-molten state.
Solder paste containing seeds. 4. The solder particles according to claim 1, wherein the solder particles include at least one kind of alloy particles composed of two or more kinds of solder metals having a composition showing a semi-molten state having a temperature range of 5 ° C. or more. The listed solder paste. 5. The solder particles are Sn, Pb, Bi, I
Alloy particles formed by combining two or more kinds of n and Ag metals,
Alternatively, it is composed of alloy particles in which one or more kinds of Cu, Sb, Ga, Ge, P and Cd are further combined with the metal.
Solder paste according to any one. 6. The solder particles are composed of two or more kinds of alloy particles composed of compositions having different liquidus temperatures, and among the alloy particles, alloy particles having a low liquidus temperature are alloy particles having a high liquidus temperature. The solder paste according to any one of claims 1 to 5, which has a larger average diameter than that of. 7. The solder paste according to claim 6, wherein the alloy particles having a low liquidus temperature have an average diameter larger than that of the alloy particles having a high liquidus temperature by 5 μm or more.