Flux core solder- Flux is the element used to reduce the oxidized metals to their metallic state. It is in essence a reducing agent that undoes the effects of oxidization. Rosin-coated solder on the other hand is a type of flux extracted from the sap of pine trees and exhibits various electrical characteristics depending on its temperature. In its natural state, it does not conduct electricity and is non-corrosive. However, at higher temperatures, it becomes corrosive and has the ability to reverse oxidization in metals.
FR4- This is the base material that gives a PCB its thickness. For most printed circuit boards, this is usually fiberglass or kapton. The substrate, often known as FR4, gives the PCBs the rigidity required to hold several components in place. The thickness and weight of the substrate will vary from one manufacturer to the other.
Fumes- This is a significant health hazard present in the use of solder. When lead is heated, it turns to lead oxide and through naturally occurring can cause serious health problems..The elements contained in solder and flux coating in solder cause dangerous fumes once exposed to temperatures above a certain level. Resin for example turns to a wide range of toxic gases that have been known to cause respiratory problems especially if one is exposed consistently to the fumes for a significant period of time.
Fire hazard- This is perhaps the most significant potential risk in soldering that may arise as a result of electrical failures. Soldering iron contain e heat resistive element through which an electric current is passed. Failure in this or another component of the iron could cause a fire. Fires could also result from any other point within the electrical connection.
Flux residue- This is an impurity present in a solder joint that arises from contamination related to use of flux in soldering.