Provided is a preform solder including a first metal containing Sn and a second metal formed of an alloy containing Ni and Fe. Alternatively, provided is a preform solder (1) having a metal structure including a first phase (10) that is a continuous phase and a second phase (20) dispersed in the first phase (10), the first phase (10) contains Sn, the second phase (20) is formed of an alloy containing Ni and Fe, and a grain boundary (15) of a metal is present in the first phase (10).

A solder ball with a concave-convex structure is provided. The solder ball with a concave-convex structure includes tin-bismuth alloy including a plurality of concave portions and convex portions on its surface. The height difference between the concave portions and the convex portions is between about 10 nanometers and about 200 nanometers. The proportion of tin in the tin-bismuth alloy is between about 28% and about 52%. A method for preparing the solder ball with a concave-convex structure is also provided.

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).

A solder preform in the shape of a solder tube or washer includes: a cylindrically shaped solder alloy body including an inner surface, an outer surface, a first end, a second end, a first opening located at the first end, and a second opening located at the second end, the second end interlocking with the first end, and the first opening and the second opening cut along an entire height of the solder alloy body; and a flux core embedded in the solder alloy body between the inner surface and the outer surface, the flux core including a thermochromic indicator. During reflow soldering, the flux core including the thermochromic indicator flows out of the first opening of the first end and the second opening of the second end to coat the inner surface of the solder alloy body and the outer surface of the solder alloy body.

A solder preform in the shape of a solder tube or washer includes: a cylindrically shaped solder alloy body including an inner surface, an outer surface, a first end, a second end, a first opening located at the first end, and a second opening located at the second end, the second end interlocking with the first end, and the first opening and the second opening cut along an entire height of the solder alloy body; and a flux core embedded in the solder alloy body between the inner surface and the outer surface, the flux core including a thermochromic indicator. During reflow soldering, the flux core including the thermochromic indicator flows out of the first opening of the first end and the second opening of the second end to coat the inner surface of the solder alloy body and the outer surface of the solder alloy body.

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.

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 solder alloy essentially consists of tin, silver, copper, bismuth, antimony, and cobalt. Relative to a total amount of the solder alloy, the silver content is 2 mass % or more and 4 mass % or less, the copper content is 0.3 mass % or more and 1 mass % or less, the bismuth content is more than 4.8 mass % and 10 mass % or less, the antimony content is 3 mass % or more and 10 mass % or less, the cobalt content is 0.001 mass % or more and 0.3 mass % or less, and the tin content is the remaining portion.

Some implementations of the disclosure are directed to liquid metal pastes that can be used as thermal interface materials. In one implementation, a liquid metal paste configured to be applied as a thermal interface material between electronic components, includes: 92.5 wt % of 99.9 wt % of a liquid gallium or liquid gallium alloy; and 0.1 wt % to 7.5 wt % of a powder of metal particles, the metal particles including Ag, Au, Cu, W, Ti, Cr, Ni, Cu or Ni. The liquid metal paste can also include an organic compound coating a surface of the metal particles, the organic compound configured to prevent the metal particles from forming an intermetallic compound with the liquid gallium or liquid gallium alloy.

A solder composition for use in solder joints of printed circuit boards (PCBs), including a compound layer comprising an alloy of bismuth and tin; and a graphene coating positioned on the compound layer.