1. Field of the Invention
The present invention relates to an apparatus and a method of manufacturing a plug. More particularly, the present invention relates to an apparatus and an improved method of manufacturing a plug in a plated-through hole.
2. Description of the Related Art
Plated-through holes (PTH) are widely used in many applications such as printed circuit boards (PCB), Multi-Chip Module-Laminate (MCM-L), ceramic substrates, thick film devices and integrated circuit packaging carriers such as ball grid array (BGA), chip scale package (CSP) and so on.
Solder masks (S/M), epoxies, or conductive pastes such as silver, copper or silver-copper mixed pastes are commonly used to plug the plated-through holes. Currently, a stencil printer is used to form plugs in the plated-through holes.
During the printing step, a stencil is aligned to a printed circuit board. A large amount of paste is applied on the stencil by an operator. A squeegee is used to plug the plated-through holes with the paste. Plugs are formed in the plated-through holes. However, the plugs usually have a problem of void formation, which voids affect the reliability of the packages and decrease the surface uniformity of the plugs.
Because the printing step is performed in atmospheric conditions, air mixes into the paste during the printing step. Bubbles are formed in the paste. Thus, voids are formed in the plug because of air. Further, the paste itself also causes the voids. The paste usually consists of flux and solvent, and is mixed in atmospheric conditions. Air is easily mixed into the paste, so voids are easily formed in the plug when the paste is used to plug the plated-through holes. Furthermore, the paste is applied on the stencil during the printing step, in a large amount. The solvent mixed in the paste continually evaporates. As a result, the viscosity of the paste continuously changes during the printing step. The surface uniformity of the plugs is worse because the paste viscosity continuously increases during the printing step.
Accordingly, the present invention provides an apparatus for manufacturing a voidless plug, as well as an improved method of manufacturing a voidless plug.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an apparatus for manufacturing a plug. The apparatus includes a closed printing chamber having a baseplate on the bottom of the closed printing chamber. A pressure controlling system is connected to the closed printing chamber. The baseplate includes a heating unit. A paste source tank is located in the closed printing chamber.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of manufacturing a plug. The method includes the following steps. A baseplate located on the bottom of a closed printing chamber is provided. A printed circuit board and a stencil are mounted on the baseplate in sequence. The stencil is aligned to the printed circuit board. An amount of preheated paste is placed on the stencil. A pressure of the closed printing chamber is adjusted to a first pressure. A printing step is performed to form plugs in the printed circuit board. The pressure of the closed printing chamber is adjusted to a second pressure to remove voids trapped in the plugs. The pressure of the closed printing chamber is adjusted to a third pressure. A scraping step is performed to remove the redundant paste.
The apparatus and the method according to the invention both avoid forming trapped voids in a plug; the reliability of the packages is thus improved and the surface uniformity of the plug is also improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.