JP2013237088A - Solder alloy powder and solder paste for bump, and solder bump using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide solder alloy powder and solder paste for a bump, which can suppress generation of a needle-like protrusion, and to provide a solder bump using the same.SOLUTION: Solder alloy powder for a bump has a component composition containing 2.8-4.2 wt.% Ag and 0.4-0.6 wt.% Cu and also containing 50-500 ppm of Pb and the balance consisting of Sn and unavoidable impurities. A solder paste for a bump is formed by mixing the solder alloy powder with flux together. Furthermore, a solder bump is formed by using the solder alloy powder for the bump.

Description

  The present invention relates to a solder alloy powder for a bump, a paste, and a solder bump using the same, which can suppress protrusions generated during bump formation.

  As a high-density mounting technique for semiconductors, a joining technique using solder bumps is generally used. As a solder alloy powder used for this solder bump, for example, a Pb—Sn solder alloy powder described in Patent Document 1 is known. Also, lead-free solder alloys have been developed in response to environmental considerations in recent years, and SnAg-based and SnAgCu-based alloy solders are known as the lead-free solder alloys.

  For example, Patent Document 2 conventionally proposes a SnAgCu-based high-temperature solder. This high-temperature solder is a solder alloy having a composition composed of 3.0 to 5.0% by weight of Ag, 0.5 to 3.0% by weight of Cu, and the balance Sn.

JP 2009-233686 A Japanese Patent No. 3027441

The following problems remain in the conventional technology.
That is, when SnAgCu solder powder, which is a typical lead-free solder, is made into a paste, and printing / reflow processing is performed using the paste to form solder bumps, needle-shaped protrusions are generated on the solder bumps, resulting in poor bump shape There was a case. This needle-shaped protrusion may cause a short circuit by coming into contact with other adjacent solder bumps. Particularly, in recent fine-pitch solder bumps, adjacent bumps are close to each other. Occurrence becomes a big problem. Further, when the needle-like protrusion is generated, the uniformity of the bump height is deteriorated, and there is a disadvantage that the bonding cannot be performed at the time of the assembly at the time of flip chip bonding.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a solder alloy powder for a bump, a paste, and a solder bump using the same, which can suppress the occurrence of needle-like protrusions.

  As a result of intensive studies on SnAgCu-based solder alloy materials, the present inventors have found that the generation of needle-like protrusions can be suppressed by adding a specific element in a trace amount.

  Therefore, the present invention has been obtained from the above findings, and the following configuration has been adopted in order to solve the above problems. That is, the bump solder alloy material according to the first invention contains Ag: 2.8 to 4.2% by weight, Cu: 0.4 to 0.6% by weight, and further contains 50 to 500 ppm of Pb. And the remainder has the component composition which consists of Sn and an unavoidable impurity, It is characterized by the above-mentioned.

Since this solder alloy powder for bumps contains 50 to 500 ppm of Pb, the formation of needle-like protrusions can be suppressed when a solder bump is formed by reflow treatment or the like, and a good bump shape can be obtained.
Needle-like protrusions, _beta-Sn constituting the alloy, Ag 3 Sn, of _Cu 6 Sn _5, in _{which Ag} 3 which Sn becomes plate coarsened was out bumps occur during solidification However, in this solder alloy powder for bumps, Pb is contained in an amount of 50 to 500 ppm, and a clear mechanism is not known at present, but the solder structure is refined by addition of Pb in this content range, or It is thought that the coarsening of Ag ₃ Sn was suppressed.

  The reason why Pb is set in the addition amount range is that when the amount is less than the lower limit value or exceeds the upper limit value, the effect of suppressing the generation of the needle-like protrusion is not recognized.

The range of Pb addition is preferably 50 ppm or more and less than 150 ppm. That is, when the amount of Pb added is 50 ppm or more and less than 150 ppm, usually a large amount of impurities has an effect on the void characteristics, but Pb also realizes needle suppression, and if this amount is void, The effect on characteristics is small.
The reason why the contents of Ag and Cu are in the above range is that, in the industry, Sn ₃ Ag _0.5 Cu and Sn ₄ Ag _0.5 Cu alloys are the main components of lead-free alloys with high Ag contents. It is because it is general.

The bump solder paste according to the second invention is characterized by mixing the bump solder alloy powder of the first invention and a flux.
A solder bump according to a third invention is formed using the solder alloy powder for bumps of the first invention.
That is, these bump solder pastes and solder bumps are formed using the bump solder alloy powder of the first aspect of the invention, so that no needle-like protrusions are produced and the bumps have a good bump shape. Even with a fine pitch flip chip, good bonding is possible.

The present invention has the following effects.
That is, according to the solder alloy powder for bumps, the paste and the solder bump using the same according to the present invention, since Pb is contained in 50 to 500 ppm, the generation of needle-like protrusions is suppressed, and a good bump shape is obtained. Can be obtained. Therefore, according to the present invention, even a fine pitch high density flip chip can be satisfactorily bonded, and high density mounting with high reliability becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified cross-sectional view showing a state when printing a solder paste in one embodiment of a solder alloy powder for a bump, a paste and a solder bump using the same according to the present invention. In this embodiment, it is a graph which shows the profile of a reflow process. It is a SEM photograph which shows a good solder bump. It is a SEM photograph which shows the solder bump which the needle-like projection produced.

  Hereinafter, an embodiment of a solder alloy powder for a bump, a paste, and a solder bump using the same according to the present invention will be described with reference to FIG. 1 and FIG.

  The solder alloy powder for bumps in this embodiment contains Ag: 2.8 to 4.2% by weight, Cu: 0.4 to 0.6% by weight, and further contains 50 to 500 ppm of Pb, with the balance being It has a component composition consisting of Sn and inevitable impurities. The bump solder alloy powder has a particle size of, for example, 5 to 15 μm, and an average particle size of 10 μm. The average particle size is measured by a laser diffraction / scattering particle size analyzer (MT3300 manufactured by Nikiso). The content of the element is analyzed using a high-frequency inductively coupled plasma emission spectrometer (ICAP-577 manufactured by Nippon Jarrell-Ash).

  In this method of producing solder alloy powder for bumps, first, in addition to each raw material of Sn, Ag, and Cu weighed to have a predetermined content, an additive element of Pb weighed to have a predetermined content is contained in the crucible. For example, Sn-3 wt% Ag-0.5 wt% Cu solder alloy powder (solidus temperature) is obtained by melting the alloy into a molten alloy and granulating the alloy using a gas atomizing method or the like. : 217 ° C, liquidus temperature: 217 ° C).

  In order to produce a solder bump using this bump solder alloy powder, first, the bump solder alloy powder and the flux are mixed at, for example, a flux ratio of 11% by mass to form a solder paste. The solder paste has a viscosity of about 150 Pa · s. Next, as shown in FIG. 1, for example, a dry film F provided with a bump forming hole H is attached to a Si wafer W, and the under bump metal UBM arranged in the bump forming hole H on the Si wafer W The solder paste P is printed on. Further, the solder paste B is manufactured by performing reflow processing (1st reflow and 2nd reflow) twice on the solder paste P.

As the flux, a general flux can be used, and this flux usually includes rosin, an activator, a solvent, a thickener, and the like. Moreover, as a flux, RA, RMA flux, etc. are preferable from a wettability viewpoint of a paste.
In addition, in order to arrange bump shape after 1st reflow, after removing the dry film F, RMA post flux is applied, 2nd reflow is performed again, and the solder bump B is obtained.
The under bump metal UBM is obtained by subjecting Cu or Cu to OSP (organic film treatment), Au / Ni plating treatment, or Sn plating treatment.

The above-described two reflow processes (1st reflow and 2nd reflow) are performed using, for example, the profile shown in FIG. The reflow process is performed in a nitrogen atmosphere using a belt furnace.
The solder bumps thus produced have a diameter of about 100 μm and a height of about 70 μm, for example. The bump pitch is, for example, 150 μm.

Thus, since the solder alloy powder for bumps of this embodiment contains Pb in an amount of 50 to 500 ppm, the generation of needle-like protrusions is suppressed when solder bumps are formed by reflow treatment or the like, and a good bump shape Can be obtained.
Needle-like protrusions, _beta-Sn constituting the alloy, Ag 3 Sn, of _Cu 6 Sn _5, in _{which Ag} 3 which Sn becomes plate coarsened was out bumps occur during solidification However, in this solder alloy powder for bumps, Pb is contained in an amount of 50 to 500 ppm, and a clear mechanism is not known at present, but the solder structure is refined by addition of Pb in this content range, or It is thought that the coarsening of Ag ₃ Sn was suppressed.

  In addition, since the solder bumps of this embodiment are formed using the solder alloy powder for bumps, needle-like protrusions are not generated, the bumps have a good shape, and are fine pitch flip chips. However, good bonding is possible.

  Next, the results of evaluating the presence or absence of needle-like protrusions in Examples in which solder bumps were produced based on the solder alloy powder for bumps and pastes in the above embodiment and the solder bumps using the same will be described.

  First, as an example of the present invention, a solder alloy powder having the component composition shown in Table 1 was prepared, and flux was mixed at a flux ratio shown in Table 1 to obtain a solder paste. That is, the Example of this invention contains 50-500 ppm of Pb as an additive element. Using each solder paste of the present example, solder bumps were formed by the above-described reflow process. Then, the produced solder bumps were observed with an SEM and an optical microscope to examine whether or not the needle-like protrusions were generated, and the generation rate (hereinafter referred to as needle generation rate) was calculated.

In addition, as a comparative example, a plurality of the additive elements having a content outside the scope of the present invention were produced, solder bumps were produced, and the needle generation rate was similarly obtained. These results are also shown in Table 1. In addition, Comparative Examples 1 and 3 to 7 contain Pb less than the range of the present invention, and Comparative Example 2 contains Pb more than the range of the present invention.
In each example and comparative example, the number of bumps measured was 756.

As can be seen from the results, in all the comparative examples, the needle generation rate exceeded 1%. On the other hand, in all the examples of the present invention, the needle generation rate is less than 1%, and the generation of needle-like protrusions is suppressed.
In addition, about the example of a favorable normal bump shape, a SEM photograph is shown in FIG. In addition, FIG. 4 shows an SEM photograph of an example of a bump shape in which needle-like protrusions found in the study are generated.

  The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

  B ... Solder bump, F ... Dry film, P ... Solder paste, UBM ... Under bump metal, W ... Si wafer

Claims (3)

Ag: 2.8 to 4.2 wt%, Cu: 0.4 to 0.6 wt%,
Furthermore, the solder alloy powder for bumps containing 50-500 ppm of Pb, and the remainder has a component composition consisting of Sn and inevitable impurities.   A solder paste for bumps, wherein the solder alloy powder for bumps according to claim 1 and a flux are mixed.   A solder bump formed using the solder alloy powder for a bump according to claim 1.