An objective of the present invention is to provide a flux that suppresses occurrence of flux drying up during soldering and occurrence of precipitation during storing.

The flux comprising, based on the whole flux, 3.5 to 11% by mass of a rosin ester, more than 0% by mass and 18% by mass or less of a rosin resin other than a rosin ester, and 70% by mass or more and less than 96.5% by mass of a solvent.

A flux containing an organic acid, a water-soluble base agent, and a solvent, but not containing water is adopted. In this flux, the organic acid includes 1,2,3-propanetricarboxylic acid. The water-soluble base agent is one or more selected from the group consisting of a nonionic surfactant and a weak cationic surfactant. The content of the 1,2,3-propanetricarboxylic acid is 1% by mass or more and 15% by mass or less with respect to the total amount of the entire flux, the total content of the water-soluble base agent is 30% by mass or more and 65% by mass or less with respect to the total amount of the entire flux, and the total content of the solvent is 30% by mass or more and 65% by mass or less with respect to the total amount of the entire flux. According to this flux, the wettability of solder can be enhanced and ball missing after reflow and flux residue washing is suppressed.

A metal composition that includes a metal component and a flux. The metal component is composed of a first metal powder of a Sn-based metal, and a second metal powder of a Cu-based metal that has a higher melting point than the Sn-based metal. The flux includes a rosin, a solvent, a thixotropic agent, an activator, and the like. When the metal composition is heated to a temperature equal to or higher than the melting point of the first metal powder, the first metal powder is melted. The melted Sn and the CuNi alloy powder produce an intermetallic compound phase of a CuNiSn alloy through a TLP reaction.

A brazing material for brazing aluminum or an aluminum alloy includes fluoride-based flux, a solidifying agent, and a coating film uniformity agent, and is solid at 25° C.

Compositions and methods for coupling metals to aluminum surfaces are provided. The compositions are prepared as aqueous solutions or suspensions, and can be applied to the aluminum surface using conventional printing techniques. Rheology of the printable composition can be adjusted to provide a gel or a cream. Curing steps, if necessary, are performed at low temperatures that are compatible with plastic/polymer components of mass produced devices, such as aluminum RFID antennae.

Undercooled liquid metallic core-shell particles, whose core is stable against solidification at ambient conditions, i.e. under near ambient temperature and pressure conditions, are used to join or repair metallic non-particulate components. The undercooled-shell particles in the form of nano-size or micro-size particles comprise an undercooled stable liquid metallic core encapsulated inside an outer shell, which can comprise an oxide or other stabilizer shell typically formed in-situ on the undercooled liquid metallic core. The shell is ruptured to release the liquid phase core material to join or repair a component(s).

By using a solder alloy consisting essentially of 0.2-1.2 mass % of Ag, 0.6-0.9 mass % of Cu, 1.2-3.0 mass % of Bi, 0.02-1.0 mass % of Sb, 0.01-2.0 mass % of In, and a remainder of Sn, it is possible to obtain portable devices having excellent resistance to drop impact and excellent heat cycle properties without developing thermal fatigue even when used in a high-temperature environment such as inside a vehicle heated by the sun or in a low-temperature environment such as outdoors in snowy weather.

A flux composition includes a component (A) that is a powder of an alkali metal zinc fluoroaluminate represented by “M.sub.wZn.sub.xAl.sub.yF.sub.z (1)” (wherein M is K or Cs, and w, x, y, and z are a positive integer, the greatest common divisor of w, x, y, and z being 1), the content of the component (A) in the flux composition being 50 mass % or more. The flux composition prevents occurrence of a brazing defect and discoloration even when an aluminum alloy is brazed in an atmosphere having a high oxygen concentration, or an atmosphere having high humidity.

A method for fabricating a semiconductor device with a heterogeneous solder joint includes: providing a semiconductor die; providing a coupled element; and soldering the semiconductor die to the coupled element with a first solder joint. The first solder joint includes: a solder material including a first metal composition; and a coating including a second metal composition, different from the first metal composition, the coating at least partially covering the solder material. The second metal composition has a greater stiffness and/or a higher melting point than the first metal composition.

A processing method of formic acid soldering includes providing a solder, performing a formic acid providing step, performing a soldering step and performing a cooling step. The solder is disposed at a soldering object. In the formic acid providing step, a water-containing formic acid vapor extracted from a formic acid source is introduced to a soldering object so as to form a water-containing formic acid atmosphere surrounding the soldering object. In the soldering step, the solder and the soldering object are soldered in the water-containing formic acid atmosphere at a soldering temperature so as to form a soldered object with high temperature. In the cooling step, the soldered object with high temperature is cooled by a cooling method so as to form a soldered object. A range of a moisture content of the formic acid source is greater than or equal to 0.1 wt % and less than 15 wt %.