SK9070Y1 - Soft active Zn-based lead-free solder for higher application temperatures and its use - Google Patents

Abstract

The soft active lead-free solder consists of 0.3 to 4% by weight. Sr, 0.1 to 2 weight Mg, the balance Zn. The brazing alloy may also contain Al in the range of 0 to 6% by weight. This soft active solder binds the non-metallic material to the non-metallic / metallic material directly or sequentially, by ultrasound or laser.

Description

Technical field

The technical solution relates to the composition of a soft active lead-free solder for soldering non-metallic materials with non-metallic or metallic materials at higher application temperatures and its use. The technical solution belongs to the field of soldering with lead-free solders in the electronics industry.

Prior art

In the manufacture of power electronics devices, it is now often necessary to use solders for higher application temperatures. Solder joints of non-metallic materials with metallic / non-metallic materials present in such equipment must meet the conditions of reliability for temperature cycles at elevated temperatures and longer joint life than the current industry standard. The basic ceramic materials used in encapsulated power components are Si3N4, A1N, SiC and Al2O3. Solders suitable for higher application temperatures must have a melting point in the range of approximately 260 ° C to 420 ° C. Solder alloys based on Zn, Sn, Au or Bi with a correctly selected combination of alloying elements are suitable for these conditions. Solders for higher application temperatures based on Zn-Al, Zn-Sn, Zn-Al-Ag, Bi-Ag, Au-Sn or Sn-Ag-Cu are known in the prior art. These solders for higher application temperatures are most often used in the electronics industry, especially in progressive encapsulation technologies for sequential soldering. For joining ceramic or semiconductor substrates, it is necessary to pre-treat non-metallic surfaces by plating. This eliminates the problems associated with the wettability of ceramic and other non-metallic materials. From the point of view of the choice of the type of plating, it is necessary to know at what operating temperature the soldered component will work. Accordingly, either soft or hard solder is used for soldering. The desired metal solder coating is then obtained:

• either by burning metal solutions of either refractory metals Mo, Mn, W (followed by nickel plating), or precious metals Ag, Au, Pt, etc., • or by physical and chemical deposition, which form thin coatings, e.g. Au, Ag, Ni and their combinations.

The formed metal solder coating ensures excellent wettability of the surface of the material by the solder, otherwise it is non-wettable.

Another possibility is the use of solders with an active element, which under certain conditions and the used soldering technology can react with the surface of the ceramic material. These elements have an electronic structure that allows them to react more easily with many compounds, and thus can be integrated (when thermally or otherwise activated) into many compounds on metal, semiconductor and ceramic surfaces. The most common active elements that are added to solder alloys are titanium and magnesium, but it is also possible to use other active metals. Direct soldering using the so-called active solder is known e.g. from patent application US 2013323530 A1 describing the soldering of metallic materials with non-metallic ones, the essence of the invention being the inclusion of active metal (e.g. Ti, Mg etc.) in a Sn-Zn-based solder with the addition of e.g. Bi or In. Such a solder is designed for lower application temperatures from 150 ° C to 200 ° C. The basis of most active solders known in the prior art is Sn or Pb. Pb is gradually being replaced by alternative elements as it is considered harmful. Sn, in turn, causes a reduction in the application temperature of the solder. Thus, such solders are not directly comparable to the present Zn-based solder according to this technical solution. In order to reduce the time required to make a brazed joint of two ceramic materials or to join a ceramic material to a metal without coating, an attempt has been made to solve this problem by technical means. The result of this effort is further described the composition of a soft active lead-free solder for soldering non-metallic materials with non-metallic / metallic materials at a higher application temperature and its use in ultrasonic, laser or sequential soldering methods according to the technical solution.

The essence of the technical solution

These shortcomings are substantially eliminated by the soft active lead-free solder for higher application temperatures according to this technical solution. The benefit lies in the design of a suitable base and in the selection of a suitable active metal. Zinc was designed as the basis of the solder. Zn-based solder is a promising replacement for solders with lead solders for higher application temperatures. Several active metals have been tested with this base. The following criteria were used in the design and production of the solder: manufacturability of the solder with active metal, acceptable price, relatively low toxicity, structural compatibility with the basic base Zn, the active metal must have sufficient reactivity with the widest possible range of soldered materials. The alloying Mg and Sr can be considered the best choice. Strontium is a soft light metal that reacts violently with oxygen. Magnesium is also a soft light metal, which reacts quickly with oxygen. Both elements are generally very reactive

SK 9070 Υ1 metals. They have a high affinity for oxygen and other elements that are components of soldered materials. The essence of the technical solution is a solder alloy based on Zn, which contains two active metals Mg and Sr. The solder consists of 0.3 to 4% by weight. Sr, 0.1 to 2 wt. Mg, the residue being Zn. The brazing alloy may also contain A1 in the range of 0 to 6% by weight. This solder alloy, in combination with ultrasonic activation, is suitable for direct soldering of ceramic and other difficult-to-solder materials without the use of coating and without the use of flux at higher application temperatures in the range from 350 to 420 ° C. In the soldering process, the active solder metals Mg and Sr react with the surface of the soldered substrate, which ensures wettability and subsequent formation of a strong bond. The strength of the joints was from 21 to 35 MPa.

The advantages of soft active lead-free solder according to the technical solution are obvious from the effects which are manifested externally. In general, it can be stated that the solder according to this technical solution is in combination with e.g. with ultrasonic or laser or other activation (wave soldering or reflow soldering) suitable for direct soldering of ceramic and other difficult to solder materials without the use of coating and without the use of flux. This reduces the time required to make the joints, improves the hygiene of the working environment and improves the economy of the production of soldered joints. Active elements are an important part of the solder, as they ensure wettability and the formation of a bond between the metal solder and the ceramic material. A significant advantage of the solder in question is its applicability at higher application temperatures without the use of flux. The higher application temperature predetermines the usability of this solder, especially in the process of gradual soldering.

Overview of figures in the drawings

In FIG. 1 is a graph showing the shear strength of a soldered joint for different soldered pairs of materials.

Examples of embodiments

Individual embodiments of a soft active lead-free Zn-based solder for higher application temperatures in soldering a non-metallic material with a non-metallic / metallic material according to the technical solution are presented for illustration and not as limitations of technical solutions. Those skilled in the art will find, or be able to ascertain using no more than routine experimentation, many equivalents to specific embodiments of the invention. Such equivalents will also fall within the scope of the following protection claims.

Example 1

In this example of a specific embodiment of the technical solution, the composition of a soft active solder based on Zn with the addition of Mg and Sr is described. The soft active solder consists of 1.5% by weight. Sr, 2 wt. Mg, the residue being Zn.

Example 2

An active solder ZnMg2Sr1.5 in the cast state was used for the soldering of the ceramic material AI2O3 / AI2O3. During soldering, the joint was heated with a hot plate with the aid of ultrasonic activation at a frequency of 40 kHz. The soldering temperature was 380 ° C.

Example 3

In this example of a specific embodiment, an active ZnMg2Sr1.5 solder in the form of an ingot was used on the A1N copper solder. During soldering, the joint was heated with a hot plate with the aid of ultrasonic activation at a frequency of 40 kHz. The soldering temperature was 380 ° C.

Example 4

In this example according to Figure 1, various pairs of materials, namely Al 2 O 3 / Al 2 O 3, AlN / AlN, Si 3 N 4 / Si 3 N 4 and SiC / CuSiC, were soldered with ZnMg 2 S 15. The achieved shear strengths of the joints are shown in the graph in Figure 1.

Industrial applicability

The industrial applicability of soft active lead-free solder based on Zn according to the technical solution is a promising replacement of solders for lead solders for higher application temperatures. He can find an application

SK 9070 Υ1 in the electronics and electrical engineering industry. It can be used in sequential soldering in progressive encapsulation technologies, such as e.g. technologies: Grid Array (BGA), Flip-Chip technology (C4), Chip-Scale-Package (CSP) or Multi-Chip Module (MCM).

Claims (3)

1. A soft active solder, characterized in that it comprises 0.3 to 4% by weight. Sr, 0.1 to 2 wt. Mg, the residue being Zn. 5 Soft active solder according to Claim 1, characterized in that it comprises A1 in a proportion of at most 6% by weight. Use of a soft active solder according to claims 1 or 2 for direct or sequential ultrasonic or laser soldering of non-metallic materials with non-metallic / metallic materials.