Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1998-04-15
2001-01-30
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S698000, C257S738000, C174S260000
Reexamination Certificate
active
06181551
ABSTRACT:
BACKGROUND
The disclosures herein relate generally to circuit boards and more particularly to a soldering enhancement for bonding the pins of the circuit board components in the pin holes formed through the multiple board layers.
A common method of soldering components on a circuit board, such as a motherboard used in a computer, is a wave solder process. A multi-layer board includes through holes. Component pins are inserted into a bore or barrel formed by the through holes. The board is pre-heated and then moved by a conveyor at a preset speed across a molten solder pot. The component pins which extend beyond the underside of the board are soldered to the board when contacted by the wave of solder. Thus, there is a critical time of exposure controlled by the speed of the board and a critical temperature of the solder material.
As the solder contacts the protruding component pins, the solder wicks up by capillary action through the barrel and along the pins. Ultimately, the solder material reaches the top side of the board where the pins connect to their host component which is being soldered to the board. As the pins pass through the various board layers, the pins are bonded to certain layers. This is accomplished by a copper pad surrounding the hole. The pad is tied, i.e. electrically connected, to a copper plane in the board layers and to each other component tied to the plane. The ties between the pad and the copper plane are copper traces.
This is illustrated in U.S. Pat. No. 4,654,102 wherein a component pin is inserted through a bore formed in a multi-layer board. Solder material is wicked upward through the bore by a wave solder or flow solder process to secure the component pin in the bore.
The copper traces also conduct heat away from the solder material while it wicks up through the barrel. Because the circuit boards are multi-layered, the more copper layers contacting the pin, the more heat is conducted away from the solder. Thus, it sometimes occurs that the solder cools sufficiently so as to solidify before the wicking up process is completed. In such a case, a weak physical bond may occur between the pin and the hole but no molecular bond is achieved by the solder material. In fact, the weak bond may even fail due to handling during installation.
Certain components compound the solder cooling problem. For example, aluminum electrolyte caps, which have a substantial mass of metal and fluid, act as a heat shield during pre-heating and wave soldering. The caps are part of the voltage regulating circuity that assist in running the processor. If the caps are not properly soldered and fail, the processor will fail causing a shut down of the system being controlled by the board.
Therefore, what is needed is a device and a method for providing proper wicking up of solder material in the solder barrel formed in a multi-layer circuit board which avoids premature cooling of the solder material.
SUMMARY
On embodiment, accordingly, enhances solder flow and wicking up by retaining heat at the pad site surrounding the pin connections of components being soldered onto the board. To this end, a pad site in a multi-layer circuit board includes a metallic ring surrounding a pin hole formed in a metallic layer of the board. The ring is isolated from the layer by a gap formed of non-metallic material. A plurality of metal traces interconnect the ring and the layer. The traces extend radially outwardly from the ring and segment the gap. Each trace has a width of about 0.010 mils and has a length of about 0.050 mils.
A principal advantage of this embodiment is that the gap forms a thermal barrier around the pad site and isolates the pad site from the metallic layer. Thus, heat is retained at the pad site long enough to permit a good solder bond. The length and width of the traces permit current to flow between the pin and the layer and delay the heat dissipation from the solder barrel around the component pin.
REFERENCES:
patent: 4127830 (1978-11-01), Chalifour et al.
patent: 4316171 (1982-02-01), Miyabayashi et al.
patent: 4453033 (1984-06-01), Duff et al.
patent: 4654102 (1987-03-01), Wery et al.
patent: 5371653 (1994-12-01), Kematani et al.
Green David Scott
Herman Patricia
Dell USA L.P.
Duong Hung Van
Haynes and Boone L.L.P.
Picard Leo P.
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