Metal working – Method of mechanical manufacture – Disassembling
Reexamination Certificate
1999-11-10
2002-09-24
Chang, R (Department: 3729)
Metal working
Method of mechanical manufacture
Disassembling
C029S739000, C029S426100, C029S832000, C029S402210, C228S119000, C228S264000, C257S715000, C361S719000, C361S700000, C165S104210, C165S185000, C174S016300, C174S252000
Reexamination Certificate
active
06453537
ABSTRACT:
FIELD OF THE INVENTION
The present invention is in the field of integrated circuits. More particularly, the present invention provides a method and apparatus for maintaining the temperature of adjacent electronic components below their solder reflow temperature during the rework processing of a primary electronic component.
BACKGROUND OF THE INVENTION
Electronic components, such as integrated circuit chips, are commonly attached to a substrate (e.g., a printed circuit board (PCB) or printed circuit card (PCC)) with solder ball connecters using a ball grid array (BGA) packaging technique. Occasionally, an electronic component may be found to be defective, and will therefore have to be removed and replaced with a functional electronic component using a rework process. In a conventional rework process, the defective electronic component is removed by first heating the solder material, used to connect the component's solder balls to corresponding contact pads on the substrate, to its melting, or “reflow” temperature. Then, the defective electronic component is pulled off the substrate and replaced. Unfortunately, during a rework process, enough heat may be transferred to adjacent electronic components, either directly or through the substrate, to unintentionally heat their solder connections beyond a reflow temperature. This may compromise, or even destroy, the connections between the affected adjacent electronic components and the substrate.
SUMMARY OF THE INVENTION
A block of a porous, thermally conductive material, saturated with a liquid, is positioned on an electrical component to be cooled. During the rework processing of an adjacent electrical component, the liquid in the porous, thermally conductive block vaporizes, thereby maintaining the temperature of the electrical component below its reflow temperature. A second thermally conductive block is positioned between the electronic component to be cooled and the electronic component undergoing rework. The second thermally conductive block is in thermal contact with the porous, thermally conductive block, and the substrate on which the electronic component to be cooled is attached. The second thermally conductive block acts both as a heat shield, absorbing and directing heat from the hot gases of the nearby rework process into the porous, thermally conductive block, and as a thermal shunt, wherein heat from the substrate is drawn away from the electrical component to be cooled and into the porous, thermally conductive block. A supply of liquid is provided to the porous, thermally conductive block to maintain the temperature of the electronic component to be cooled at a predetermined level for a specified period of time.
Generally, the present invention provides a cooling structure for electronic components, comprising:
an electrical component to be cooled, positioned on a substrate;
a second electrical component positioned on the substrate, the second electrical component having a higher temperature than the electronic component to be cooled;
a porous, thermally conductive body positioned on the electronic component to be cooled;
a second thermally conductive body, positioned between the electronic component to be cooled and the second electronic component, the second thermally conductive body in thermal contact with the substrate and the porous, thermally conductive body; and
a quantity of a liquid having a specified boiling temperature located in the porous, thermally conductive body.
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Heim Craig G.
Hooker Wade Leslie
Trivedi Ajit Kumar
Chang R
Fraley Lawrence R.
International Business Machines - Corporation
Schmeiser Olsen & Watts
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