Field of technology

The invention concerns the composition of a soft solder for ultrasonic soldering of mainly non-metal and metal materials, or of two non-metal materials, at higher application temperatures. The invention falls into the field of soldering in the electrotechnical industry.

Prior state of the art

The state of the art shows that currently used ceramic materials (e.g. AI2O3, S1O2, T1O2 and so on), some non-metal materials (Si, Ge, graphite and so on) and metal materials that are difficult to solder (W, Mo, Ta and so on) are soldered indirectly in such a way that the solderable coating is applied to the surface of the ceramic material and the actual soldering is realized only after this application. The metallization of the ceramics removes the problems related to wettability of the ceramic and some non-ceramic materials. From the point of view of the type of metallization one needs to know the operation temperature at which the soldered component will work. Pursuant to this one uses either soft or hard solder, whereby the temperature boundary between them is approximately 450 °C. The required metal solderable coating is the obtained by firing (burning) of metal solutions - either fireproof metals Mo, Mn, W (with subsequent galvanization) or precious metals Ag, Au, Pt and so on. Or the requested solderable coating is obtained through physical and chemical deposition which produces thin coatings, for example Au, Ag, Ni and their combinations. The realized metal solderable coating ensures excellent wettability of the surface of the material by the solder, even though the material itself is otherwise non-wettable. The disadvantage of the abovementioned solder technology with the melt is a need to realize intermediate operation consisting of metallization.

Broad group of soft solders is on the basis of tin where these solders, together with other components, have a melting point usually at 180 °C to 230 °C. The disadvantage of the soft solders is weaker mechanical features such as shear strength, tensile strength and so on. Publication JP2011235294 discloses a tin-based solder which contains 0,5 to 9,0% of mass of Zn, 0,1 to 4,0% of mass of Sb, and as an active metal it contains Ti at 0,005 to 0,3% of mass. Such solder has good long-term resistance against oxidation and aging, but it has weaker mechanical features.

Solder pursuant to EP0351462 A1 , US4758407 A contains tin and antimony, but it does not contain an active metal and it is designed only for soldering of the metal materials. The tin-bas solder pursuant to DE 19816671 A1 contains Sb in up to 3,5% of the mas and Ag in up to 3,0% of the mass; in order to improve strength characteristics it needs to increase the share of Ag and without active metal this solder is not suitable for surfaces that are difficult to wet.

Pursuant to the abovementioned one strives to produce a new technology of direct soldering without the intermediate operation of metallization, which resulted in the further disclosed composition, according to this invention, of the soft solder for ultrasonic soldering of the metal and non-metal materials or two non-metal materials at higher application temperatures.

Essence of the invention

The abovementioned deficiencies are significantly remedied by the composition of the new soft solder for the ultrasonic soldering of non-metal and metal materials, or two non-metal materials, at higher application temperatures, pursuant to this invention. The solution is based on the design of the suitable basis and on the choice of suitable active metal. A basis in this invention is the composition Sn-Sb. The solder based on Sn-Sb is a perspective substitute of the solders for the lead solders for higher application temperatures in general for soldering of the metal materials. Multiple active metals have been tested with this basis. Following criteria have been used when designed and producing the solder: producibility of the solder with the active metal, acceptable costs, relatively low toxicity, structural compatibility with the Sn-Sb basis, sufficient reaction ability of the active metal with as large number of the soldered materials as possible. Doping with titanium and lanthanum is the best choice. The essence of the invention is that the composition of the soldering alloy is on Sn-Sb basis and it contains at least one active metal - Ti (0,5 to 4% of the mass) and/or La (0, 1 to 2% of the mass). The soldering alloy can also contain Ag in share of 1 to 30% of the mass. The titanium with tin produces four intermetallic phases; these phases can appear in the structure of the soft solder, too. Aside from the mentioned essential components the solder can contain trace amounts of impurities, usually up to 0, 1 to 0,5% of the mass.

The essential advantage of the composition of the solder according to this invention is an achievement higher mechanical feature of the resulting joint at higher wettability of various surfaces of metal and non-metal materials. The solder according to the proposed invention is especially suitable for ultrasonic soldering, when the components Sn, Sb and active solder support the effective cavitation in broad spectrum of frequencies. The active metal creates a reaction layer which reacts with the surface of a difficult-to-solder material. The synergetic effect of the cooperation of the components and the active metal in the mention amounts is also manifested in the fact that the resulting joint keeps its mechanical features for a long time, it does not corrode, it does not suffer from a tin plague, and so on. The maintenance of these features, which are known in the prior art in cases of solders used with easy-to-solder materials (mainly metals), is ensured, by use of the proposed invention, for the difficult-to-solder materials, too.

The advantages of the soft active solder for the ultrasonic soldering of the metal and non-metal materials, or two non-metal materials at higher application temperatures according to this invention are obvious from the outwardly manifested effects. In general, one can state that, compared to the original technology with the intermediate operation of metallization, the proposed solution has multiple advantages. The offered solution is a technology of direct soldering by use of a special, so-called active, solder which contains small amount of active metal. The time needed to produce the joints decreases; the hygiene of the working environment improves, and the production of soldered joints is more cost-effective. The active solder is an important part of the solder since it ensures the wettability, and the creation of a joint between the metal solder and the ceramic material. Such soldering alloy in combination with the ultrasound activation is suitable for the direct soldering of the ceramic and other hard-to-solder materials without the use of coating and without the use of melt. The absence of melt is possible thanks to the use of ultrasonic solder where the erosion of the ultrasonic cavitation keeps the required purity of the joint during the soldering. The Sn, Sb components and the active metal in the composition of the solder according to this invention prevent the oxidation of the soldered surfaces; the melted joint in contact with the oscillating tip disrupts and removes the layer of oxides on the surface of the soldered material. The solder on Sn-Sb basis is a perspective substitute of the solders for the lead solders for higher application temperatures. The main consumption of the solders for higher application temperatures is within the electronic industry, mainly in progressive technologies of casing during the gradual soldering. There are technologies such as ball grid array (BGA), flip-chip technology (C4), chip-scale package (CSP) or multi chip module (MCM). Casing (Die Attach) is a process of connection of the silicon chip to the substrate or carrier construction of the semiconductor case. During the production of the electronics the casing of the electronic circuits is a final phase in the production of the semiconductor devices where the small semiconductor material is closed into the support casing which prevents its physical or corrosion damage.

A high solidity of the soldered joint, mainly the high shear strength above the level of 40MPa, is achieve not only by increase of the mechanical features of the solder itself, but also by high wettability of the materials connected with the liquid solder. The invention brings advantage in this direction where the mutually opposite demands are met thanks to the synergetic cooperation of multiple components at their defined ratio.

Description of drawings

Soft active solder for the ultrasound soldering of the metal and non-metal, or of two non-metal materials at higher application temperatures according to this invention is further disclosed on drawings where figure 1 depicts shear strength of various joints soldered by SnSb5Ti1 solder in a graph.

Examples of realization

It is understood that individual realizations of the soft active solder for the ultrasonic soldering of non-metal and metal materials, or of two non-metal materials, at higher application temperatures, according to this invention, are presented only for purposes of illustration and cannot be interpreted as limiting the scope of protection. The person skilled in the art will be able to find many equivalents of the specific realization of the invention, within the mentioned ratios of the components, by use of no more than a routine experimentation. Such equivalents will fall into the scope of the subsequent patent claims, too. The shares of the mass in percent present the share in relation to a complete mass of the resulting solder.

Example 1

In this example of particular realization of the invention a composition of the soft active solder for ultrasonic soldering of two ceramic materials AI2O3/AI2O3 at higher application temperatures is disclosed. An SnSb5Ti1 solder is used as the active solder in a liquid state in following composition: Sb in 5% of the mass, Ti in 1 % of the mass, whereby Sn is in additional, remaining amount of 94% of the mass. The solder can contain trace amounts of impurities, too.

Soldering has been realized by the heating of the hot board with help of the activation by ultrasound at 40 kHz frequency. The temperature of soldering was 240 °C. Titanium is in general a very reactive metal. It has high affinity to the oxygen and other elements which are parts of the soldered materials. In the process of soldering the titanium from the solder reacts with the surface of the soldered substrate which ensures the wettability and subsequently the creation of the solid joint. The solidity of joints was at the level from approx. 45 to 53 MPa, which is sufficient for the solders of similar type.

Example 2

In this example of the particular realization of the subject matter of the invention a composition of the soft active solder for the ultrasonic soldering of the metal material with the S13N4/CU ceramic material at higher application temperatures is disclosed. An SnSb10Ti3 solder in a form of an ingot in following composition: Sb in 10% of the mass, Ti in 3% of the mass, whereby Sn is in additional amount of 87% of the mass. The soldering can be realized by the heating with a hot board with the support of ultrasound activation at 40 kHz frequency. The temperature of soldering was 240 °C. The hot board brings a significant part of the added heat; the ultrasonic peak brings energy to the melted solder for the cavitation processes in the solder.

Example 3

In this example of the particular realization of the subject matter of the invention an analogical composition of the soft active solder for the ultrasonic soldering of the metal material with the ceramic S13N4/CU material at higher application temperatures is disclosed. An SnSb7La1 solder has been used as active soft solder in following composition: Sb in 7% of the mass, La in 1 % of the mass, whereby Sn is in remaining, additional amount of approx. 92% of the mass. Figure 1 depicts in a graph the shear strength of various soldered joints with SnSb5Ti1 solder.

Example 4

In this example of the particular realization of the subject matter of the invention an analogical composition of the soft active solder for the ultrasonic soldering of the metal material with the AIN/Cu ceramic material at higher application temperatures is disclosed. An SnSb5Ag15La2 solder has been used as active soft solder in following composition: Sb in 5% of the mass, La in 2% of the mass, Ag in 15% of the mass, whereby Sn is in additional amount of approx. 78% of the mass.

Industrial applicability

Industrial applicability of the soft active solder for ultrasonic soldering of the non-metal and metal materials, or two non-metal materials, at higher application temperatures, according to this invention, is mainly in electrotechnics industry.