Fluxless solder transfer and reflow process
First Claim
1. A process for transfer of molten solder from cavities in a mold plate to wettable pads on a substrate without the use of flux, the process comprising the steps of:
- aligning the mold plate with the substrate, whereby the solder in the cavities is in contact with the wettable pads of the substrate;
placing the mold plate and the substrate into an oxide reducing atmosphere;
heating the substrate above the melting temperature of the solder, whereby an oxide which may have formed on the wettable pads is removed thereby permitting wetting of the solder to the wettable pads;
cooling the substrate to solidify solder and thereafter removing the mold plate from the substrate while leaving behind the solder on the wettable pads;
reheating said substrate in said oxide reducing atmosphere whereby the solder may reflow into a spherical shape; and
cooling the substrate to solidify the solder in the spherical shape.
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Accused Products
Abstract
Disclosed is a new process that permits the transfer and reflow of solder features produced by Injection Molded Solder (IMS) from a mold plate to a solder receiving substrate without the use of flux. Several embodiments produce solder transfer and reflow separately or together and use either formic acid vapor or partial concentration of hydrogen, both in nitrogen, as the oxide reducing atmosphere. A final embodiment produces fluxless transfer and reflow in only nitrogen through the use of ultrasonic vibration between the solder filled mold plate and solder receiving substrate.
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Citations
10 Claims
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1. A process for transfer of molten solder from cavities in a mold plate to wettable pads on a substrate without the use of flux, the process comprising the steps of:
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aligning the mold plate with the substrate, whereby the solder in the cavities is in contact with the wettable pads of the substrate; placing the mold plate and the substrate into an oxide reducing atmosphere; heating the substrate above the melting temperature of the solder, whereby an oxide which may have formed on the wettable pads is removed thereby permitting wetting of the solder to the wettable pads; cooling the substrate to solidify solder and thereafter removing the mold plate from the substrate while leaving behind the solder on the wettable pads; reheating said substrate in said oxide reducing atmosphere whereby the solder may reflow into a spherical shape; and cooling the substrate to solidify the solder in the spherical shape. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A process for transferring molten solder from cavities in a mold plate to wettable pads on a substrate, the process comprising the steps of:
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aligning the mold plate to the substrate so that said solder in the cavities is in abutting contact with the wettable pads; placing the mold plate and substrate in a nitrogen atmosphere, wherein said mold plate is attached to an actuator capable of providing lateral motion at ultrasonic frequencies and vertical Z motion; heating the mold plate and substrate above the melting temperature of the solder; abrasively removing an oxide which may have formed through vibrational contact with the wettable pads thereby permitting wetting of the solder to the wettable pads; cooling the substrate to solidify the solder and thereafter removing the mold plate from the substrate while leaving behind the solder on the wettable pads; reheating said substrate in said nitrogen atmosphere whereby the solder may reflow into a spherical shape; cooling the substrate to solidify the solder in the spherical shape.
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Specification