Metal fusion bonding – Process – With protecting of work or filler or applying flux
Reexamination Certificate
1997-10-31
2001-10-02
Shaw, Clifford C. (Department: 1725)
Metal fusion bonding
Process
With protecting of work or filler or applying flux
C228S254000, C228S258000, C228S180210
Reexamination Certificate
active
06296174
ABSTRACT:
BACKGROUND OF THE INVENTION
According to the present invention, a circuit board and a method for assembling electronic devices, in particular an effective and simple solution for assembling electronic devices onto a circuit board having dense soldering pads and/or dense traces is disclosed.
Due to the facts that surface-mounting electronic devices onto the surface of a circuit board eliminates drilling of the circuit board as well as considerably increases the circuit density, and that soldering paste can be precisely applied over soldering pads by screen printing, Surface Mounting Technology (SMT) has become the primary method for assembling electronic devices onto circuit boards.
However, the trend of electronic industry is to produce electronic devices, such as integrated circuits (“IC's”), having considerably more and denser contacts, which require more, smaller, and denser soldering pads on the circuit board. The gaps between neighboring soldering pads and/or distance between soldering pads and neighboring traces must be reduced as a result of such smaller soldering pads, on which only tiny amount of soldering paste is applicable so as to eliminate the possibility of joining neighboring soldering pads or neighboring traces that ultimately result in short-circuits. Nevertheless, the tiny amount of soldering paste being applied onto the smaller soldering pads is insufficient to facilitate ideal soldering joints and thus reduces the reliability of soldering, and further deteriorates the quality of the entire circuits after completion.
To ensure the reliability of soldering, the measure generally adopted by the industry relates to limiting soldering pads to a predetermined dimension. However, such a limitation prevents further development of denser soldering pads and/or traces printed on the circuit board, and thus indirectly impedes development of electronic industry. An alternative measure adopted by the industry includes applying solder directly over the soldering pads, placing contacts of devices on the soldering pads plated with solidified solder, and melting the solder to connect the contacts and soldering pads. However, such a measure frequently causes bending of the contacts due to inconsistent thickness in solder plating, while controlling thickness of solder plating involves great difficulty.
An effective soldering solution for high-density soldering pads and/or closely neighboring soldering pads and traces is thus immediately required.
SUMMARY OF INVENTION
It is an objective of this invention to provide an effective and simple solution for assembling electronic devices onto a circuit board having dense soldering pads and/or dense traces
It is another objective of this invention to provide a novel circuit board having dense soldering pads and/or dense traces, which circuit board facilitates reliable soldering process for assembling electronic devices thereon.
Based on research conducted by the Applicant, it is known that because the soldering pads are either located at terminated ends of or a part of the conductive zone (such as copper foils), a stronger bond is formed between its conductive substance and the soldering paste. Therefore, when contacts of electronic devices are soldered to the soldering pads, the molten soldering paste eventually agglomerates the soldering paste extending to periphery insulated zones or applied insulated zones approaching the soldering pads and the contacts of electronic devices due to its surface tension whereby sufficient amount of soldering paste is provided between the soldering pads and the contacts to form ideal soldering joints.
Accordingly, the method disclosed in this invention primarily relates to applying soldering paste to soldering pads allowing the soldering paste to extend outwardly from at least one soldering pad to locations not in contact with other soldering pads or traces; and soldering contacts of electronic devices to the circuit board having the portion of soldering pads including said one soldering pad. Furthermore, the method and circuit board disclosed in this invention relate to applying at least an insulated zone onto a circuit board at locations having high-density soldering pads or locations having closely neighboring soldering pads and traces, wherein the insulated zone is in various configurations so as to abut on one or more than one soldering pads. The insulated zone primarily provides a region to which soldering paste extends. As for densely aligned soldering pads, soldering paste being applied to the soldering pads is extendible to the neighboring insulated zone, whereby the soldering paste being additionally applied to the soldering pads facilitates an effective soldering process. As for closely neighboring soldering pads and traces, the insulated zone provides a region to which soldering paste extends, wherein the insulated zone covers traces that closely abut on the soldering pads to facilitate application of soldering paste and to provide effective shielding whereby any possibility of short-circuits is eliminated.
The electronic devices referred in this invention include various semiconductor devices, resistors, capacitors, inductors, connectors, sockets for device contacts, signal routes, leads, or other circuit components or devices that is solderable to circuit boards.
In summary, the problems encountered in the process of soldering electronic devices as a result of high-density soldering pads and/or closely neighboring soldering pads and traces are solved by the technical measures disclosed in this invention.
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Frommer William S.
Frommer Lawrence & Haug LLP.
Johnson Jonathan
Ryan Matthew K.
Shaw Clifford C.
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