| 摘要 |
When applying solder paste to substrates, for example circuit boards, a jet comprising a fluxing agent (15) on top of a core of molten solder (11) is used. It is achieved by making a jet of molten solder (11) pass through a space filled with the fluxing agent. For suitable conditions the jet (19) is divided into drops (21), when it has passed out of the space filled with fluxing agent. Those drops, which hit the substrate, the consist of a core (22) of solidified solder surrounded by an enclosure (25) of fluxing agent. The applied solder paste thereby becomes completely fresh, which means that only an extremely small amount of oxide exists in the paste. Furthermore, in the corresponding way individual drops of solder can be ejected through the space filled with fluxing agent, which allows a very accurate dosing of the amount of solder paste, since the amount is determined by the number of solder balls and this number can be digitally controlled. This method can generally be used to apply a first liquid material having an enclosure of another liquid material, the first material advantageously being a material such as molten metal, which is significantly more heavy than the material of the enclosure. |
