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Method for prepatterned solid film UF with TCB

IP.com Disclosure Number: IPCOM000033147D
Publication Date: 2004-Nov-29
Document File: 4 page(s) / 105K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for prepatterned solid film underfill (UF) with thermocompression bonding (TCB). Benefits include improved functionality, improved performance, improved reliability, improved process simplification, and improved throughput.

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Method for prepatterned solid film UF with TCB

Disclosed is a method for prepatterned solid film underfill (UF) with thermocompression bonding (TCB). Benefits include improved functionality, improved performance, improved reliability, improved process simplification, and improved throughput.

Background

      The conventional underfill process includes three steps, prebake, no-flow underfill (NUF) dispensing, and chip placement (see Figure 1).

 

      The NUF can become entrapped in bumps, presenting a very high risk for first-level interconnect reliability. Entrapped NUF can limit the circuit maximum current draw (Imax capability). Bump cracks due to entrapped NUF, which can cause device failure, occur as early as post preconditioning. (see Figure 2 , please remove this image!!). 

      A solution to these problems has not been found yet.

General description

      The disclosed method includes a prepatterned solid UF sheet. It is made to match the product bump patterns and pitches. The pre-patterned solid UF films are applied to flip-chip assembly substrate, where substrate presolders are placed in prepatterned holes. The TCB chip-attach process is used to place the die and instantly join the die the substrate while the solid film UF is being flowed and cured.

              The key elements of the method include:

•             Solid film UF is pre-patterned to match the bump pattern of a specific product using mechanical punching, laser drilling, or imprinting for thermal-set material.

•             Prepatterned UF film enables die bumps to be in direct contact with substrate solders so that UF entrapment inside the bump is eliminated.

•             The method uses solid resin-based or B-stage solid-film UF material, which are commercially available, with filler loading.

•             UF material is in-line cured during the TCB process, providing die interlayer dielectric (ILD) protection.

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to using die-side flux dip to provide sufficient flux capability where compatible no-clean flux is the ideal selection

•             Improved performance due to using UF material that is inline cured during the TCB process, which provides die ILD protection

•             Improved reliability due to enabling die bumps to be in direct contact with substrate solders, eliminating UF entrapment inside the bumps

•             Improved process simplification due to using the local flow properties of solid film UF

•             Improved throughput due to processing more units per hour because of the solid film UF local flow properties

•             Improved cost effectiveness due to using resin-based and B-stage solid-film UF material, which are c...