Composite solder paste for flip chip bumping
AssigneeDelco Electronics Corporation
InventorsShing Yeh, Bradley Howard Carter
Life of this patent
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Abstract
Composite solder paste compositions adapted to be deposited using a dry film photoresist mask to form solder joints for flip chip integrated circuit devices. The composite solder paste compositions are characterized by the ability to flow at a first temperature during bumping reflow while the photoresist mask is present, yet upon subsequently reheating to a higher temperature yield solder joints capable of withstanding temperatures of 200.degree. C. and higher. As such, the present invention retains the advantages associated with using a dry film photoresist as a mask during deposition of the solder, yet results in the formation of solder joints that exhibit enhanced reliability in severe thermal environments.
Claims17
A solder paste composition comprising multiple solder paste constituents, a first solder paste constituent of the multiple solder paste constituents having lower liquidus and solidus temperatures than a second solder paste constituent of the multiple solder paste constituents, wherein the first solder paste constituent establishes a bumping reflow temperature at which the solder paste composition flows without liquefying all of the multiple solder paste constituents, and wherein a chip mount reflow temperature is established that is higher than the bumping reflow temperature and at which all of the multiple solder paste constituents liquefy in a manner that yields a solder having a homogenous alloy composition, the first and second solder paste constituents comprising indium-lead alloy powders.
A spherical solder bump comprising:
- a first solder constituent comprising a first metal alloy;
- and
- a second solder constituent comprising a second metal alloy dispersed in the first solder constituent, the second solder constituent having higher liquidus and solidus temperatures than the first solder constituent, the second metal alloy being an indium-lead alloy containing up to about 2.5 weight percent silver and about 2.5 to about 5 weight percent indium;
- wherein the first solder constituent establishes a bumping reflow temperature for the solder bump at which the solder bump is formed without liquefying the second solder constituent, and the second solder constituent establishes a chip mount reflow temperature that is sufficient to cause both the first and second solder constituents to liquefy and form a solder having a liquidus temperature that is between that of the first and second solder constituents.
A method for forming solder bumps for a flip chip circuit device, the method comprising the steps of:
- separately forming first and second solder paste constituents such that the second solder paste constituent has higher liquidus and solidus temperatures than the first solder paste constituent, the first and second solder paste constituents comprising indium-lead alloy powders;
- combining the first and second solder paste constituents to form a solder paste composition;
- depositing the solder paste composition on a substrate through a photoresist mask;
- heating the solder paste composition to a bumping reflow temperature at which the second solder paste constituent does not liquefy and at which the first solder paste constituent liquefies and causes the solder paste composition to flow and form a solder bump;
- cooling the solder paste composition so as to solidify the solder bump;
- registering the solder bump with a mounting surface;
- and
- heating the solder bump to a mount reflow temperature that is higher than the bumping reflow temperature, the mount reflow temperature being sufficient to liquefy both the first and second solder paste constituents so as to yield a solder joint having a composition based on the first and second solder paste constituents.
Dependencies are inferred from the claim text.