JP2000158179A - Solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain paste with good storage stability and superior wetting/ spreading properties by coating metallic solder powder with the other fine metallic powder. SOLUTION: Solder metal is Sn/Zn alloy, Sn/Zn/Bi alloy, or Sn/Zn/Bi/In alloy with average grain diameter of 20-60 μm. The metallic solder powder is coated using fine powder of one type or two types or more of Ag, Cu, In, Ge, Bi, and Ni with average grain diameter of 10 μm or less. The fine metallic powder is preferably 0.1-10 weight % against the total amount with the metallic solder powder. The metallic solder powder is added to the mixture of fine metallic powder and binder and mixed, and the coating is done with the fine metallic powder. The binder is rosin of a flux component. The metallic solder powder including the coating fine metallic powder is 86-92 weight % against the total amount with the flux. Reactivity of active Zn is controlled and oxidation in a reflow process is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor integrated circuit (I).
C) The solder paste used for mounting, etc., is more specifically improved in oxidation resistance and wet spreadability.
The present invention relates to a solder paste that can be b-free.

[0002]

2. Description of the Related Art In general, in mounting an IC or the like, a solder paste is applied on a printed circuit board by screen printing or the like, and the IC or the like is mounted thereon, and the solder paste is melted in a reflow furnace to fix the IC to the substrate. are doing. The solder paste mainly comprises a solder alloy and rosin as a flux, and generally contains a part of a solvent and an additive.

[0003] Solder alloys are Pb, Sn, Bi, In, Z
Although alloys containing n and the like are generally known, lead-free alloys containing no Pb have recently been proposed due to environmental problems. Various lead-free alloy compositions have been proposed and are known from ternary to quaternary systems. In particular, Sn / Zn
Due to the activity of Zn, the alloy preferentially reacts with an activator such as a halide of an organic compound incorporated in the flux, and the viscosity increases so that the paste cannot withstand storage. Further, the solder powder is oxidized during the reflow process, so that the wet spreadability is extremely deteriorated, and a large amount of solder balls are generated.

To solve these problems, there has been proposed a method of coating solder powder particles with electroless plating using Sn, Ni, Cu, Ag, Au, or the like, or coating with an organic compound. In the case of plating, it is expensive and mass production is difficult.
In the case of coating with an organic compound, it is difficult to unite and fuse the solder particles, and the wet-spreadability is also poor.

[0005]

The solder paste containing active Zn has the above-mentioned problems, but the present invention has good stability during storage even with a solder paste containing Zn.
It is another object of the present invention to provide a solder paste which has excellent solder wettability and does not have the drawbacks of frequent occurrence of solder balls.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its gist is to coat the solder powder particles with other metal fine powders to suppress the reactivity of active Zn. And prevents oxidation during the reflow process. That is, the present invention is a solder paste characterized in that, in a solder paste containing solder metal powder and flux as main components, the solder metal powder is coated with another metal fine powder.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be applied to a solder paste containing Pb, but is particularly effective for a solder paste containing Pb and containing active Zn. As the solder metal (including alloy), Sn / Zn alloy, Sn /
A Zn / Bi alloy, a Sn / Zn / Bi / In alloy or the like is used. If the particle size of these solder metal powders is too small, it is difficult to coat with other metal powders. If the particle size is too large, solder balls will be generated.
60 μm is preferred.

[0008] Other metal fine powders for coating the solder metal powder include Ag, Cu, In, Ge, Bi and Ni.
One or more fine powders are used. When two or more kinds are used, the alloy may be used in advance. Furthermore, if the above-mentioned metal is the main component (50% by weight or more),
An alloy containing a metal other than the above metals may be used. The particle size of these metal fine powders is smaller than the particle size of the solder metal powder, and the average particle size is preferably 10 μm or less, more preferably 5 μm or less. If the average particle size exceeds 10 μm, it is difficult to dissolve during reflow.

In order to obtain a sufficient coating effect, the quantitative ratio of the solder metal powder and the other metal powder to be coated is such that the metal powder to be coated is 0.1% by weight based on the total amount of the solder metal powder. The above is preferable, and if the amount is too large, the adhesive strength of the solder is reduced.

In order to coat the solder metal powder with another metal fine powder, for example, a method in which a binder is mixed with the metal fine powder, and then the metal powder is added to the mixture and sufficiently kneaded can be used. . Rosin, a component of the flux, is preferred as the binder. Rosin is dissolved in alcohol or the like, and the viscosity is adjusted before use. It is preferable that alcohol and the like be evaporated after coating. The solder paste of the present invention contains the above-mentioned coated solder metal powder and flux such as rosin as main components, but may further contain an activator, a thixotropic agent, an antioxidant and the like. The amount of the solder metal powder including the coating metal fine powder is preferably 86 to 92% by weight based on the total amount with the flux.

[0011]

Next, the present invention will be described specifically with reference to examples and comparative examples. (Example) Polymerized rosin as a resin component was dissolved in isopropyl alcohol so as to have a concentration of 80% by weight. 1.8 g of Ag fine powder having an average particle size of 0.5 μm was added to 8.2 g of the solution and mixed well. 2 g in 10 g of this mixture
Sn having a particle size in the range of 5-45 μm (average particle size 38 μm)
90 g of Pb-free solder alloy powder having a composition of / 8 Zn / 3 Bi (molar ratio) was added and kneaded in a mortar until solidified to obtain a coated solder metal powder using 100 g of rosin as a binder.

As a solvent, 50% by weight of disproportionated rosin, 6% by weight of hydrogenated castor oil as a thixotropic agent, 0.01% by weight of diphenyl guanidine hydrobromide and 0.35% by weight of isopropylamine hydrobromide. Diethylene glycol monohexyl ether was added to 100% by weight,
This was used as flux. 90 parts by weight of the above-mentioned coated solder metal powder was added to 10 parts by weight of the flux and kneaded by a planetary mill to obtain a solder paste. The obtained solder paste was printed on a substrate in a standard test pattern. The reflow was performed in a nitrogen atmosphere having an oxygen concentration of 2% by volume so that the peak temperature was 230 ° C. at the substrate temperature. The occurrence rate of solder balls and the spreadability of the solder metal powder were evaluated according to JIS Z3284. The state of generation of solder balls was 2 or less in terms of the cohesion degree of the solder according to JIS, and the solder metal powder wet spreadability was 2 or less in JIS. The storage stability was evaluated by printing a 0.6 mm pitch QFP pattern after refrigerated storage at 5 ° C. for one month. If one of the products has a missing plate, it is rejected (x). If no missing plate is passed, it is passed (o).
And The results are shown in Table 1. It is shown in FIG. Similarly, No. 1 shown in Table 1 was used. Solder pastes were obtained using various types of solder alloy powders 1 to 13 and 15 to 27 (Examples and Comparative Examples) and coating metal fine powders, and the characteristics were evaluated. In addition,
Conditions not shown in Table 1 were the same as above.

[0013]

[Table 1]

The solder paste of the present invention contains Zn,
Even when a solder alloy containing no Pb is used, the storage stability is excellent, the occurrence rate of solder balls is low, and the wet spreadability is good.

Claims (7)

[Claims] 1. A solder paste comprising solder metal powder and flux as main components, wherein the solder metal powder is coated with another metal fine powder. 2. The solder paste according to claim 1, wherein the solder metal powder contains Sn and Zn and does not contain Pb. 3. Other metal fine powders are Ag, Cu, In, G
The solder paste according to claim 1, wherein the solder paste is at least one of e, Bi, and Ni. 4. An average particle size of the solder metal powder is 20 to 60.
4. The solder paste according to claim 1, wherein the other metal fine powder has an average particle size of 10 μm or less. 5. 5. The solder paste according to claim 1, wherein the other metal powder to be coated is 0.1 to 10% by weight based on the total amount of the solder metal powder and the other metal fine powder. 6. The coating according to claim 1, wherein the coating with another metal fine powder is performed using rosin as a binder.
The solder paste according to any one of the above. 7. A solder metal powder coated with another metal fine powder has an amount of 8% with respect to the total amount of flux.
The solder paste according to any one of claims 1 to 6, which is 6 to 92% by weight.