Abstract: 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.

Abstract: Some implementations of the disclosure are directed to a solder preform, comprising: a solder alloy body, the solder alloy body comprising at least one opening; and a flux core embedded in the solder alloy body, the flux core comprising a thermochromic indicator, wherein during reflow soldering, the flux core comprising the thermochromic indicator is configured to flow out of the at least one opening of the solder alloy.

Abstract: Some implementations of the disclosure are directed to a solder preform, comprising: a solder alloy body, the solder alloy body comprising at least one opening; and a flux core embedded in the solder alloy body, the flux core comprising a thermochromic indicator, wherein during reflow soldering, the flux core comprising the thermochromic indicator is configured to flow out of the at least one opening of the solder alloy.