A two-step electronic assembly process whereby a flip chip is soldered to a substrate with a pre-applied underfill. The step-one underfill has a low coefficient of thermal expansion and the step-two underfill contains a polymer flux that has a high coefficient of thermal expansion. The two portions can also be intermixed and inter-reacted.

A method for making an underfilled flip chip assembly using a pre-applied underfill.

1. An encapsulant is applied, which may contain a silica powder-filled polymer, to at least a portion of a bumped flip chip
2. A second encapsulant is then applied, which contains a curable fluxing agent between the encapsulated chip and a printed circuit.
3. The encapsulated chip is then placed on the printed circuit substrate so that a thin layer of second portion encapsulant is present between the solder bumps and the printed circuit substrate.
4. The combination is then heated to melt the solder and harden the polymers.

The second encapsulant can be applied to either the chip or the printed circuit. The encapsulants may include materials that allow rework of the flip chip assembly.

A solder-bumped flip chip with a pre-coated underfill. For improved reliability, the underfill can include a mixture of a polymer and an inorganic filler. The underfill can also contain at least one meltable portion, which provides for easy rework. When used with an adhesive having fluxing properties, this unique invention allows simultaneous flip chip soldering and underfill curing in a reworkable structure.

A method for making an underfilled flip chip assembly using a pre-applied underfill.

1. An encapsulant is applied to a solder-bumped flip chip while exposing the tips of the solder bumps.
2. A polymer with fluxing properties is then applied either to the encapsulated chip or to a printed circuit.
3. The encapsulated chip is placed on the printed circuit.
4. The combination is heated to melt the solder bumps and simultaneously harden the polymer.

Electronic assembly process whereby a flip chip with a multipart pre-applied underfill is soldered to a printed circuit. The first portion of the underfill has a low coefficient of thermal expansion and a second portion, comprising a polymer flux, has a high coefficient of thermal expansion. The underfill may also include materials that allow rework of the flip chip assembly.

Fabrication process that allows one to solder a flip chip to a printed circuit using a pre-applied, two-part underfill. The underfill comprises a laminated film and an adhesive with fluxing properties. The underfill can also include a printed circuit, as well as materials that allow rework of the flip chip assembly.

Fabrication process whereby a flip-chip can be soldered to a substrate containing a pre-applied underfill. The underfill contains a layer of adhesive with fluxing properties between the encapsulant and the substrate, which may include materials that allow rework of the flip chip assembly.