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Method for a metallurgical bonded via

IP.com Disclosure Number: IPCOM000028046D
Publication Date: 2004-Apr-21
Document File: 3 page(s) / 144K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for forming metallurgical bonded copper via in organic packaging substrate. Benefits include improved functionality and improved performance.

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Method for a metallurgical bonded via

Disclosed is a method for forming metallurgical bonded copper via in organic packaging substrate. Benefits include improved functionality and improved performance.

Background

Via delamination (see Figure 1) in organic substrates causes electrical opens or high resistance failures. Via delamination failure can be intermittent and is usually difficult to screen out by electrical test. As a result, impacted materials are typically scrapped to prevent adverse consequences to customers.

When the organic substrate passes through the assembly and test processes, it is subject to varying degrees of thermal treatments. Difference in thermal expansion of the organic based dielectric material and copper interconnect produces a vertical tensile stress on the copper via structure. This tensile stress can easily cause via delamination if the via bottom interface is weak. Sometimes the stress is high enough to delaminate the healthy stacked vias.

The adhesion between the via’s bottom and underlying Cu trace is strongly influenced by the cleanliness of the interface. Presence of organic dielectric residue, metal oxide or contaminant can easily weaken the adhesion strength between via and Cu trace, causing via delamination to occur easily when stressed.

Other steps conventionally taken to prevent via delamination include tightening the process control on via laser milling, soft etching, rinsing and electroless copper plating. No complete solution is available. The via delamination issues still occur periodically, depending on the substrate manufacturing process controls, which vary from one supplier to another.

General description

The disclosed method is a via structure consisting of a metallurgical bond that welds the via to the underlying copper trace/ plane as illustrated in Figure 2. A thin layer of immersion Sn is introduced to the via-trace interface to form copper-tin (CuSn) intermetallic compound (IMC) that provides the strong mechanical and chemical adhesion. Key elements of the method include:

         •         Immersion Sn on via interface.

§         Metallurgical bonded via

Advantages

The disclosed method provides advantages, including:

§         Improved functionality due to providing a robust substrate via interconnect with a metallurgical bond that welds the bottom surface of the...