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Method for a BCB encapsulant for gold-to-gold and gold-to-copper bonding applications

IP.com Disclosure Number: IPCOM000010733D
Publication Date: 2003-Jan-15
Document File: 4 page(s) / 127K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a benzocyclobutene (BCB) encapsulant for gold-to-gold and gold-to-copper bonding applications. Benefits include improved reliability.

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Method for a BCB encapsulant for gold-to-gold and gold-to-copper bonding applications

Disclosed is a method for a benzocyclobutene (BCB) encapsulant for gold-to-gold and gold-to-copper bonding applications. Benefits include improved reliability.

Background

      Conventional epoxy-based nonconductive adhesive encapsulants cannot stand the gold-to-gold and gold-to-copper thermocompression temperatures (280-350ºC) due to their relatively low decomposition temperatures. As a result, a requirement exists for an effective encapsulant for gold-to-gold bonded, gold-to-copper bonded, and gold-stud bump flip-chip applications.

      Conventionally, gold-to-gold bonding is used in many electronics packaging applications such as 3-D die or wafer stacking and die-on-polyamide flex substrate. The Au-to-Au and Au-to-Cu bonding is performed using a thermocompression bonder at a high temperature (~350ºC) for 10-20 seconds. Encapsulants are typically required to compensate the CTE mismatch and enhance device reliability.

              Two approaches are used to introduce the encapsulant:

•             Introduce encapsulant after the Au-Au or Au-Cu bonding is made. This approach is not successful for fine pitch and tight gap devices because uniform encapsulant flow is difficult and process voiding can occur.

•             Introduce the encapsulant before bonding, and perform bonding and curing in one step. This process is suitable for fine pitch and tight gap applications and low cost due to its simpler process. However, this approach requires an encapsulant which cures (solidify) rapidly and does not decompose at the bonding temperature. Conventional epoxy-based encapsulants cannot meet these requirements.

General description

              The disclosed method is a BCB-based encapsulant for gold-to-gold and gold-to-copper bonding in electronics packages.

              Gold-to-gold and gold-to-copper bonding is achieved by thermocompression bonding at 280-350ºC for 10-60 seconds. BCB material is suitable as an encapsulant for this high-temperature application due to its high curing speed at this temperature range, low CTE, low moisture absorption, and low curing shrinkage (see Figure 1).

      BCB encapsulant compensates for the CTE mismatch between die/substrate and improves the integrity of the assembly. Using an unfilled BCB encapsulant, a high interconnection yield is achieved during assembly

Advantages

      The disclosed method provides advantages, including:

•             Improved throughput due to the fast curing speed at the gold-to-gold and gold-to-copper bonding temperature

•             Improved...