Metal fusion bonding – Including means to apply flux or filler to work or applicator
Reexamination Certificate
1998-07-08
2001-02-06
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Including means to apply flux or filler to work or applicator
C228S041000, C228S039000, C228S049500, C029S840000
Reexamination Certificate
active
06182883
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the repair of printed circuit boards and, in particular, to the precise application of solder paste to the surface mount pads of the printed circuit board that are to used to receive a replacement printed circuit board component.
PROBLEM
It is a problem in the field of printed circuit board repair to efficiently and accurately replace circuit elements on the printed circuit board, once the printed circuit board has been populated with components. In the manufacturing process, the bare (devoid of components) printed circuit board is overlaid with a global solder mask that contains a plurality of apertures that correspond to the component contacts. Once the global solder mask is in place on the printed circuit board, a layer of solder paste is applied to the global solder mask and thus also to the printed circuit board surface mount pads that are exposed through the mask apertures. The global solder mask is then removed and automated equipment is used to both position the numerous components that populate the printed circuit board and solder these components to the surface mount pads. However, once the printed circuit board is populated with components, the global solder mask can no longer be used to apply solder paste to desired surface mount pads during the replacement of a component due to the presence of the remaining components on the printed circuit board.
This is a problem in the case of surface mount devices, especially mini Ball Grid Array active devices and bare die circuit elements. This is due to the fact that these component packages are of small dimensions (typically 50*50 mils) and contain a large number of fine pitch conductors (typically 15 mil centers or less), which conductors are located under the device and can not be seen by the human eye. Therefore, the registration of the component conductors with the printed circuit board surface mount pads is critical and the interconnection of these elements is highly dependent upon the precise placement of solder paste on the surface mount pads of the printed circuit board. However, when one of these components needs to be replaced after the printed circuit board is manufactured, the failed component must be unsoldered, removed and the printed circuit board surface mount pads cleaned to receive the replacement component. As part of the replacement component installation process, the printed circuit board surface mount pads must be coated with solder paste. If the solder paste overprints or is misregistered on to the surface of the printed circuit board, the solder flow can bridge the space between adjacent component conductors under the component and short out the component. Therefore, the precise application of the solder paste to the printed circuit board surface mount pads is necessary and requires a tedious, labor intensive process, which has a high failure rate. Therefore, there is presently no process to efficiently and accurately apply solder paste to the printed circuit board surface mount pads to interconnect replacement components once the printed circuit board is manufactured.
SOLUTION
The above described problems are solved and a technical advance achieved in the field by the present process for precisely registering solder paste in a printed circuit board repair operation (termed “precise solder paste registration process” herein). The precise solder paste registration process entails the basic component removal steps of the prior art, coupled with a novel method of precisely applying solder paste to the printed circuit board surface mount pads. The precise solder paste application process makes use of mask registration apertures that are formed in the printed circuit board and that are adapted to receive a component solder paste mask that conforms to the conductor pattern of the component to be replaced. The component solder paste mask comprises a mask sized for the single component that is being replaced and that has formed therein apertures that correspond to the pattern of solder paste that is to be applied to the printed circuit board surface mount pads to correspond to the conductors of the component. The component solder paste mask includes registration features (such as tooling pins) that mate with the registration apertures (such as tooling holes) formed in the printed circuit board to thereby ensure precise placement of the component solder paste mask over the area of the printed circuit board that receives the replacement component. The repair person can therefore simply and precisely place the component solder paste mask on the printed circuit board, apply the solder paste to the printed circuit surface mount pads exposed through the apertures formed in the component solder paste mask and thereby ensure that the pattern of solder paste precisely corresponds to the printed circuit board surface mount pads. This ensures that the component, when placed on the printed circuit board surface mount pads, can be soldered to these surface mount pads without solder overflow. The component solder paste mask also optionally includes one or more gripping elements that protrude from the top surface of the component solder paste mask to enable the repair person to grasp and position the component solder paste mask. The one or more gripping elements can be extensions of the registration features. Furthermore, fasteners can be used to secure the registration features once they are placed in the mask registration apertures.
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Duft, Graziano & Forest,P.C.
Edmondson L.
Lucent Technologies - Inc.
Ryan Patrick
LandOfFree
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