KR20020031098A - Soldering method and soldered joint - Google Patents

Abstract

The present invention provides a soldering method and a solder joint without cost increase, without adversely affecting the environment and ensuring a bond strength comparable to soldering using a conventional Pb-Sn solder alloy.

The soldering method of the present invention is a process of coating a Cu electrode of an electronic device with a rust-proofing film made of an organic compound containing N, and Ag 2.0 wt% or more and less than 3wt%, Cu 0.5-0.8wt% And a step of forming a solder joint at the coated Cu electrode by using a brazing material made of residual Sn and inevitable impurities. The brazing material used in the present invention may further contain at least 3 wt% or less of at least one element selected from the group consisting of Sb, In, Au, Zn, Bi and Al.

Description

Soldering Method and Solder Joint {SOLDERING METHOD AND SOLDERED JOINT}

Lead-tin (Pb-Sn) solder alloys have been widely used for soldering in various electric and electronic devices in view of low melting point and good wettability in an oxidizing atmosphere.

Since Pb is toxic, various restrictions are made on the handling of materials such as Pb or an alloy containing Pb.

In addition, with the recent increase in environmental protection, regulations on disposal of electronic devices and the like using Pb-containing braze alloys have been tightened.

Conventionally, used electronic devices, which have a large amount of Pb-containing braze alloy, have been generally disposed of by landfill, similarly to ordinary industrial waste or general waste.

However, if the used electronic device which used a large amount of Pb containing solder alloy is discarded as it is by landfill etc., there exists a possibility that it may adversely affect an environment or a living thing by elution of Pb.

In the near future, used electronic devices that use large amounts of Pb-containing braze alloys will be obliged to be disposed of after recovery of Pb.

However, until now, a technique for efficiently and effectively removing Pb from used electronic devices and the like has not been established. In addition, the cost of recovery of Pb may cause an increase in the product cost.

Therefore, development of the soldering technique by a lead-free soldering material is strongly desired.

As the lead-free solder alloy, for example, alloys in which Sb (antimony), Ag (silver), Ge (germanium), Ti (titanium), etc. are added to Sn are partially used, but are limited to special applications. It reacts with all the properties required for the general use of conventional Pb-Sn braze alloys, namely low melting point and good wettability, reflow treatment, and the base material. This is because characteristics such as not forming a weak compound layer or brittle layer cannot be obtained.

The present invention relates to a soldering method of an electronic device by a lead-free soldering material and a solder joint formed by the same.

BRIEF DESCRIPTION OF THE DRAWINGS The chemical structural formula which shows the specific example of the antirust film which consists of N containing organic compounds used for this invention.

FIG. 2 is a graph showing a melting point change of an alloy with respect to Ag content for a 0 to 3.5 wt% Ag-0.7 wt% Cu-Sn braze alloy. FIG.

3 is a graph showing a change in melting point of an alloy with respect to Cu content with respect to 3 wt% Ag-0 to 3 wt% Cu-Sn braze alloy.

4 is a graph showing the relationship between the Ag content and the occurrence frequency of needle-like foreign matter in the 0-4 wt% Ag-0.7wt% Cu-Sn braze alloy.

Fig. 5 is a sectional view schematically showing a rust preventive film / flux mixture extruded at a solder joint of the present invention.

Fig. 6 shows the intermetallic compound layer growth at the thickness of the? Layer alone when heated at 125 ° C. and 150 ° C. for 100 hours, respectively, for a solder joint formed of a 2 wt% Ag-0 to 1.5 wt% Cu—Sn braze alloy. Graph representing.

Fig. 7 shows the intermetallic compound layer growth in the thickness of the? Layer alone when the solder joint formed of 2wt% Ag-0 to 1.5wt% Cu-Sn braze alloy was heated at 125 캜 and 150 캜 for 100 hours, respectively. Graph representing.

Fig. 8 shows the intermetallic compound layer growth in the case of a solder joint formed of 2wt% Ag-0 to 1.5wt% Cu-Sn braze alloy at 100 ° C. and 150 ° C. for 100 hours, respectively. Graph of the thickness of the graph.

9 shows the thickness of the ε layer alone for the intermetallic compound layer growth when the solder joint formed of 2.5 wt% Ag-0 to 1.5 wt% Cu-Sn braze alloy was heated at 125 ° C. and 150 ° C. for 100 hours, respectively. The graph represented by.

FIG. 10 shows the intermetallic compound layer growth when the solder joint formed of 2.5 wt% Ag-0 to 1.5 wt% Cu-Sn braze alloy was heated at 125 ° C. and 150 ° C. for 100 hours, respectively. The graph represented by.

11 shows an interlayer compound layer growth of an intermetallic compound layer when heated at 125 ° C. and 150 ° C. for 100 hours for a solder joint formed of a 2.5 wt% Ag-0 to 1.5 wt% Cu—Sn braze alloy. Graph of total thickness.

Fig. 12 shows the intermetallic compound layer growth when the solder joint formed of 3 wt% Ag-0 to 1.5 wt% Cu-Sn braze alloy was heated at 125 ° C. and 150 ° C. for 100 hours, respectively. Graph representing.

Fig. 13 shows the intermetallic compound layer growth when the solder joint formed of 3 wt% Ag-0 to 1.5 wt% Cu-Sn braze alloy was heated at 125 ° C. and 150 ° C. for 100 hours, respectively. Graph representing.

Fig. 14 shows the intermetallic compound layer growth in the solder joint formed by 3 wt% Ag-0 to 1.5 wt% Cu-Sn braze alloy at 100 ° C. and 150 ° C. for 100 hours, respectively. Graph of the thickness of the graph.

Fig. 15 is a graph showing the bonding strength per connection terminal of an electronic component before and after heating of a solder joint formed of a 2.5 to 3.5 wt% Ag-0.7 wt% Cu-Sn solder alloy in comparison with a Pb-Sn solder alloy.

An object of the present invention is to provide a soldering method and a solder joint which can secure a joint strength comparable to soldering using a conventional Pb-Sn solder alloy without any adverse effect on the environment, without increasing the cost.

According to the present invention, the following process:

Coating a Cu electrode of an electronic device with a rust-proofing film made of an organic compound containing N, Ag 2.0 wt% or more and less than 3 wt%, Cu 0.5 to 0.8 wt% and the balance Sn and The above object is achieved by a soldering method comprising the step of forming a solder joint on the coated Cu electrode using a brazing material made of inevitable impurities.

The brazing material used in the present invention may further contain at least 3 wt% or less of at least one element selected from the group consisting of Sb, In, Au, Zn, Bi and Al.

One typical application of the present invention is a printed wiring board for electronic components, and the Cu electrode to be soldered is coated with an antirust film made of an organic compound containing N (nitrogen), thereby ensuring long-term storage and solder wettability. do.

Conventionally, a method of performing Ni plating on a Cu electrode and then performing Au plating again has been performed, but there is a drawback in that the manufacturing period is long because the cost is high and the plating process is complicated. Moreover, there was a possibility that the environmental pollution by the waste liquid treatment of plating might generate | occur | produce.

In this invention, cost is reduced and manufacturing period is shortened by using said antirust film.

Conventionally, resin coatings such as rosin (natural rosin) and resin (synthetic resin) have been formed as rust-proofing treatments of Cu electrodes. However, since the film thickness was thicker than 20 micrometers, the washing process was necessary after soldering because probing at the time of an electrical test became difficult.

On the other hand, in order to make film thickness thin so that the washing process after soldering can be skipped, using water-soluble antirust agent is performed. In other words, the Cu electrode is cleaned by etching with a copper sulfate solution or the like, and then immersed in a solution containing 1000 to 5000 ppm of a water-soluble rust inhibitor to form a coordination bond film.

In the present invention, a very thin rust preventive film is formed by the coordination bond (chelate bond) by N and a metal in an N-containing organic compound. It is thought that the film thickness is 3000 kPa or less.

As the N-containing organic compound constituting the antirust coating of the present invention, cyclic forms such as imidazole, benzoimidazole, alkylimidazole, benzotriazole, mercaptobenzothiazole, pyrrole, and thiazole shown in FIG. Compounds are used.

The necessary properties as the brazing material are as follows.

(1) Wetting property with a base material is high.

(2) Soldering is possible at a temperature low enough to prevent thermal damage to the electronics to be soldered. That is, melting | fusing point is equivalent to melting | fusing point 456K (183 degreeC) of the conventional Pb-Sn soldering.

(3) It does not form a weak intermetallic compound or embrittlement layer by reaction with a base material.

(4) Can be supplied in the form of paste, powder, thread solder, etc. applicable to automation.

(5) Defects such as poor wetting, voids, and bridges do not occur due to the metal component oxide in the brazing material.

In particular, in soldering electronic devices, it is necessary to inject molten solder into a narrow gap, so surface tension, viscosity, fluidity, and the like of the soldering material are important.

The conventional Pb-Sn braze alloy satisfies the above conditions sufficiently, but it is difficult to avoid environmental pollution by Pb.

The soldering material used for this invention is Ag-Cu-Sn alloy which contains Ag 2.0 wt% or more and less than 3.0 wt% and Cu 0.5-0.8 wt%, remainder consists essentially of Sn, and contains Pb. Without this, the alloy components Ag, Cu, and Sn are all elements of high safety, so there is no fear of environmental pollution, and the above-mentioned characteristics are sufficiently satisfied.

The reason for limitation of Ag-Cu-Sn braze alloy composition of this invention is demonstrated below.

[Ag: 2.0wt% or more but less than 3.0wt%]

As for the melting point, which is the most basic characteristic of the brazing material, it is necessary to ensure a low melting point (220 ° C. or lower) equivalent to that of a conventional Pb-Sn braze alloy. If Ag content is 2.0 wt% or more, low melting | fusing point of 220 degrees C or less can be ensured. When the Ag content is less than 2.0 wt%, the melting point increases rapidly. On the other hand, when the Ag content is 3.0 wt% or more, needle-shaped crystals are generated in a large amount, short circuits occur between the electronic components, and the joining reliability is lowered. For applications in which short-circuit prevention by means of needle-shaped crystals and joining reliability are particularly important, the Ag content is limited to 2.5 wt% or less within the scope of the present invention to almost completely prevent the occurrence of needle-shaped crystals. It is preferable because it can. Conversely, for applications in which it is necessary to give particular importance to the suppression of the thickness of the intermetallic compound layer described below, if the Ag content is further limited to 2.5 wt% or more within the scope of the present invention, the thickness of the intermetallic compound layer can be further reduced. It is preferable because it can. As the Ag content satisfying both of these conditions at the same time, 2.5 wt% is most preferred.

[Cu: 0.5-0.8wt%]

The intermetallic compound is generated at the interface between the braze alloy and the Cu electrode, whereby the braze alloy and the Cu electrode are joined. In other words, the production of intermetallic compounds is essential for bonding. However, when the intermetallic compound layer is too thick, it becomes weak and the bonding strength is lowered. Therefore, it is preferable to produce an intermetallic compound layer as thin as possible at the time of joining, and it is preferable that it is difficult to grow by the heat history after joining. This inventor measured the thickness of the intermetallic compound layer of a joining interface with respect to the temperature up to 150 degreeC considered as the thermal history which an electronic device receives in a use environment. As a result, when the Ag content is in the range of the present invention and the Cu content is in the range of 0.5 to 0.8 wt%, it was found that the thickness of the intermetallic compound layer can be stably suppressed to about 4 μm or less. When Cu content is less or more than the said range, the thickness of an intermetallic compound layer will increase. As the Cu content which can suppress the thickness of the intermetallic compound layer to be the thinnest, most preferred is 0.1 wt%.

For the above reasons, in the Ag-Cu-Sn braze alloy of the present invention, the Ag content is limited to 2.0 wt% or more and less than 3.0 wt%, and the Cu content is limited to 0.5 to 0.8 wt%. Ag content can select any one of 2.0 wt% or more and 2.5 wt% or less or 2.5 wt% or more and less than 3.0 wt% as needed. The most preferred composition is 2.5 Ag-0.7 Cu-Sn.

In general, when the soldering temperature of an electronic device is lowered by 10K (10 占 폚), the lifetime of the electronic component is doubled, so that the low melting point of the soldering material is very important.

In addition, the Ag-Cu-Sn braze alloy of the present invention has a property very close to Sn as a main component, good wettability with Cu, and high conductivity.

In addition, since the amount of Ag added is small, it is inexpensively provided to the same extent as the conventional Pb-Sn alloy.

The braze alloy of the present invention is selected from Sb (antimony), In (indium), Au (gold), Zn (zinc), Bi (bismuth) and Al (aluminum) in addition to the above-described Ag-Cu-Sn base composition. One type or multiple types of elements can be contained in total 3 wt% or less.

These elements (in particular, In and Bi) further lower the melting point of the braze alloy and further improve the wettability. However, when the total amount exceeds 3 wt%, the appearance, particularly the gloss, of the solder joint is deteriorated. Moreover, especially when content of Bi alone exceeds 3 wt%, the bonding reliability with a Pb containing material falls.

The braze alloy of the present invention contains O (oxygen), N, H (hydrogen) and the like as unavoidable impurities. In particular, O is likely to embrittle the alloy, so it is preferable to be as small as possible.

In a braze alloy containing Sn as a main component, Sn is easily oxidized at the time of soldering. Therefore, it is preferable to carry out the soldering in a N ₂ or Ar (argon) ratio (非) an oxidizing atmosphere, such as. Thereby, generation | occurrence | production of the wet defect or electrical connection defect by oxidation of soldering can be prevented.

The soldering of the present invention can also be performed while applying ultrasonic waves to promote wetting similarly to conventional soldering.

Example 1

The reason for limitation of the Ag content range in this invention is demonstrated more concretely by a present Example.

The influence of Ag content and Cu content on the melting point of Ag-Cu-Sn alloy was investigated. Specifically, the melting point was measured for 0 to 3.5 wt% Ag-0 to 3 wt% Cu-Sn braze alloy. The melting point change of the alloy with respect to Ag content is shown in FIG. 2 and Table 1 about 0-3.5 wt% Ag-0.7 wt% Cu-Sn braze alloy. As shown in FIG. 2 and Table 1, the low melting | fusing point of 220 degrees C or less is obtained at the lower limit of 2.0 or more of Ag content prescribed | regulated by this invention. When the Ag content is less than 2.0 wt%, the melting point rises rapidly. The relationship between the Ag content and the melting point is the same for the range of 0.5 to 0.8 wt% of the Cu content defined in the present invention. In addition, Pb-Sn in Table 1 is a conventional 37 wt% Pb-Sn braze alloy.

In FIG. 3 and Table 2, the melting point change of the alloy with respect to Cu content is shown about 3 wt% Ag-0-3 wt% Cu-Sn braze alloy. It is understood that a low melting point of 220 ° C. or less is obtained in a wide range of Cu content including 0.5 to 0.8 wt% of the range Cu of the present invention. About the relationship between Cu content and melting | fusing point, the same result was obtained about 2.0 wt% or more and less than 3.0 wt% of Ag content range of this invention.

Next, the soldering strength was investigated about 0-3.5 wt% Ag-0.7 wt% Cu-Sn alloy and 3 wt% Ag-0.5-1.3 wt% Cu-Sn alloy. The bonding sequence is the same as in Example 2. As shown in Table 3 and Table 4, the braze alloy of the composition range of the present invention obtains a higher bonding strength than the conventional Pb-Sn braze alloy.

In addition, the frequency of occurrence of needle crystals affecting the bonding strength was investigated. In FIG. 4, the relationship between the Ag content and the frequency of occurrence of needle-like crystals (needle foreign matter) is shown for 0 to 4 wt% Ag-0.7 wt% Cu-Sn braze alloy. As shown in Fig. 4, when the Ag content is 3.0 wt% or more, needle-shaped crystals are generated in a large amount. As described above, when a large amount of needle-shaped crystals occur, a short circuit occurs between the electronic components, and the joining reliability is lowered. For applications in which the short-circuit prevention and the joining reliability by the needle-shaped crystals are particularly important, by limiting the Ag content to 2.5 wt% or less, the generation of the needle-shaped crystals can be almost completely prevented as shown in FIG. It is more preferable because there is. 4 shows the result of measuring about 0-4 wt% Ag-0.7 wt% Cu-Sn braze alloy, but the same result is obtained about 0.5-0.8 wt% of the range of Cu content prescribed | regulated by this invention.

Example 2

By the present Example, the reason for range limitation of Cu content in this invention is demonstrated more concretely.

Each braze alloy having a composition of Sn-2.0 to 3.0 Ag-0 to 1.5 Cu was solvent.

An antirust film of an alkylbenzotriazole compound was formed as an N-containing organic compound on a Cu electrode of a printed wiring board made of a copper-clad laminate.

On the Cu electrode provided with the said film, the solder joint was formed with the said braze alloy in the following procedure.

1) A solder paste was prepared by mixing 90 wt% of the braze powder (particle diameter of about 20 to 42 μm) prepared with the above alloys and 10 wt% of the flux powder (active agent + resin powder). The said solder paste was screen-printed on the Cu electrode provided with the said film, and the solder paste layer of uniform thickness (about 150 micrometers) was formed.

2) The connection terminal of an electronic component was mounted on each Cu electrode provided with the solder paste layer. The connection terminal consists of 42 alloys (Fe-42wt% Ni alloy).

3) After the solder paste layer was heated to 498 K (225 ° C.) or more to melt the solder, heating was stopped to cool to room temperature. This formed the solder joint which joins a Cu electrode and 42 alloy connection terminals.

The antirust film made of an organic compound containing N is decomposed by the above heating and reacted with the acidic flux contained in the solder paste to be removed from the Cu electrode / 42 alloy junction. That is, as shown in FIG. 5, it is thought that the mixture 3 of an antirust film and a flux is extruded from the interface with Cu electrode 1 by the molten braze alloy 2. As shown in FIG. Therefore, the antirust film coated on the Cu electrode does not remain at the soldering interface.

After the rust preventive coating was removed, Sn in the molten braze alloy reacted with Cu of the electrode to react with the two kinds of intermetallic compounds (ε phase: Cu ₃ Sn, η phase: Cu ₆ Sn ₅ ) at the solder alloy / Cu electrode interface. ) Is generated. That is, the interface structure is made of Cu / ε layer / η layer / solder alloy.

The intermetallic compound is produced to bond the braze alloy and the Cu electrode. In other words, the production of intermetallic compounds is essential for bonding. However, when the intermetallic compound layer is too thick, it becomes weak and the bonding strength is lowered. Therefore, it is preferable to produce an intermetallic compound layer as thin as possible at the time of joining, and it is preferable that it is difficult to grow by the heat history after joining.

6 to 14 and Tables 5 to 7 show the intermetallic compound layer growth when heated at 125 ° C. and 150 ° C. for 100 hours at 125 ° C. and 150 ° C., respectively. It represents with the thickness of (epsilon) layer + (eta) layer total. 8, 11, and 14, the intermetallic compound layer thickness (total thickness) after the said heating is about 4 micrometers or less when the braze alloy of the composition within the range of this invention is used. In particular, by setting the Cu content to 0.5 to 0.8 wt%, which is the range of the present invention, the thickness of the intermetallic compound layer can be reduced stably. In addition, the Ag content tends to be thinner in the range of 2.5 wt% or more than the range of 2.5 wt% or less within the scope of the present invention.

As described above, the solder joint according to the present invention has a slow growth of the intermetallic compound and high reliability over a long period of time.

Example 3

Bonding strength after heat processing was investigated. In FIG. 15, the bonding strength after heating at 125 degreeC for 100 hours, and heating at 150 degreeC for 100 hours about the 2.5-3.5 wt% Ag-0.7 wt% Cu-Sn braze alloy is shown. From the result of FIG. 15, it turns out that the joint strength equivalent to the conventional Pb-Sn braze alloy is obtained by this invention. In particular, while the joint strength by the conventional Pb-Sn braze alloy falls monotonically by heating (heat history), it is recognized that the bonding strength according to the present invention is rather improved by heating.

TABLE 1

0-3.5 Ag-0.7 Cu-Sn

Ag concentration (wt%) Melting Point (℃) 0.0 226.50 0.3 226.50 1.5 222.70 2.0 218.03 2.5 217.50 3.0 217.60 3.5 218.42 Pb-Sn 183.00

TABLE 2

3 Ag-0 to 3 Cu-Sn

Cu concentration (wt%) Melting Point (℃) 0.0 221.63 0.1 220.63 0.2 218.47 0.3 218.10 0.4 218.17 0.5 218.80 0.6 218.17 0.7 217.60 0.8 217.73 1.3 217.45 1.5 217.83 3.0 218.67

TABLE 3

Ag concentration (wt%) Bond strength (N) Pb-Sn 4.80 0.0 6.10 0.3 7.60 2.5 7.06 3.0 7.25 3.5 8.38

TABLE 4

Cu concentration (wt%) Bond strength (N) 0.5 8.04 0.6 8.29 0.7 7.08 0.8 8.43 1.3 7.29

TABLE 5

2Ag system unit: μm

ε layer η layers ε layer + η layer 150 ℃ / 100H 125 ℃ / 100H 150 ℃ / 100H 125 ℃ / 100H 150 ℃ / 100H 125 ℃ / 100H Sn-2Ag 1.07 0.80 5.60 5.33 6.67 6.13 Sn-2Ag-0.5Cu 0.67 0.53 3.33 3.07 4.00 3.60 Sn-2Ag-0.6Cu 0.67 0.40 2.80 2.80 3.47 3.20 Sn-2Ag-0.7Cu 0.67 0.46 2.67 2.50 3.34 2.96 Sn-2Ag-0.8Cu 0.67 0.40 3.47 2.67 4.13 3.07 Sn-2Ag-1.5Cu 0.93 0.53 3.60 3.33 4.53 3.87

TABLE 6

2.5Ag Unit: μm

ε layer η layers ε layer + η layer 150 ℃ / 100H 125 ℃ / 100H 150 ℃ / 100H 125 ℃ / 100H 150 ℃ / 100H 125 ℃ / 100H Sn-2.5Ag 1.00 0.80 3.50 1.90 4.50 2.70 Sn-2.5Ag-0.5Cu 0.53 0.33 2.46 2.00 2.99 2.33 Sn-2.5Ag-0.6Cu 0.70 0.30 2.00 1.90 2.70 2.20 Sn-2.5Ag-0.7Cu 0.60 0.50 2.70 2.10 3.30 2.60 Sn-2.5Ag-0.8Cu 0.70 0.50 3.30 2.80 4.00 3.30 Sn-2.5Ag-1.5Cu 1.00 0.70 3.60 3.50 4.60 4.20

TABLE 7

3.0Ag Unit: μm

ε layer η layers ε layer + η layer 150 ℃ / 100H 125 ℃ / 100H 150 ℃ / 100H 125 ℃ / 100H 150 ℃ / 100H 125 ℃ / 100H Sn-3.0Ag 0.20 0.00 4.47 4.20 4.67 4.20 Sn-3.0Ag-0.5Cu 0.73 0.60 2.60 2.00 3.33 2.60 Sn-3.0Ag-0.6Cu 0.73 0.47 2.07 2.07 2.80 2.53 Sn-3.0Ag-0.7Cu 0.47 0.47 2.07 2.00 2.53 2.47 Sn-3.0Ag-0.8Cu 0.67 0.67 2.00 2.00 2.67 2.67 Sn-3.0Ag-1.3Cu 1.33 0.80 2.67 1.87 4.00 2.67

As described above, according to the present invention, it is possible to secure an equivalent bonding strength without generating environmental pollution due to Pb and without increasing the cost as compared with conventional Pb-Sn braze alloys.

Claims (5)

The following process: Coating a Cu electrode of an electronic device with a rust-proofing film made of an organic compound containing N, and Forming a solder joint in the coated Cu electrode using a brazing material composed of Ag 2.0 wt% or more and less than 3 wt%, Cu 0.5 to 0.8 wt%, and residual Sn and inevitable impurities. Soldering method characterized in that. The soldering method according to claim 1, wherein the soldering material contains 2.0 to 2.5 wt% of Ag. The soldering method according to claim 1, wherein the soldering material contains at least 2.5 wt% of Ag and less than 3.0wt%. The soldering material according to any one of claims 1 to 3, wherein the brazing material further contains at least one element selected from the group consisting of Sb, In, Au, Zn, Bi, and Al in a total of 3 wt% or less. Soldering method. The solder joint part formed by the soldering method in any one of Claims 1-4.