Browse Prior Art Database

Inter-Metallic Surface Energy Modifiers to Increase Solder Joint Reliability for Ball Attach

IP.com Disclosure Number: IPCOM000103397D
Publication Date: 2005-Mar-17
Document File: 3 page(s) / 86K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that adds small amounts of alkaline metals (e.g. sodium, potassium, calcium, etc.) or rare earths (lanthanum, cerium, actinium, etc.) to lead-free solder alloys. The disclosed method modifies the faceted growth of the inter-metallic compound (IMC) formed at the interface of the plated pad/solder. Benefits include a solution the requires no additional equipment or major process modifications, and can be implemented with current packaging materials.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Inter-Metallic Surface Energy Modifiers to Increase Solder Joint Reliability for Ball Attach

Disclosed is a method that adds small amounts of alkaline metals (e.g. sodium, potassium, calcium, etc.) or rare earths (lanthanum, cerium, actinium, etc.) to lead-free solder alloys. The disclosed method modifies the faceted growth of the inter-metallic compound (IMC) formed at the interface of the plated pad/solder. Benefits include a solution the requires no additional equipment or major process modifications, and can be implemented with current
packaging materials.

Background

During ball attach and surface mounting, alloys are soldered to gold/nickel plated copper pads. The solder alloy reacts with the pad and the plating covering the pad. The reaction produces inter-metallic compounds that are brittle in nature, but also necessary since they are part of the bonding process.

Inter-metallic compounds are similar to ceramics, and they grow like crystals with faceted sides. Since many crystals nucleate on the surface of the gold/nickel plated copper pad, growth of the IMC is made up of many individual crystals, each one growing in its own preferential crystallographic orientation. The result is an uneven layer with sharp edges (see Figures 1 and 2). These sharp edges are concentration sites for stresses that can cause cracks and reduce the resistance of an alloy to shear and tensile loads. Current lead-free alloys are known to be stiffer than lead-based alloys. This additional stiffness reduces the solder joint reliability (SJR) for second-level interconnects, since the joints are not normally surrounded by an underfill to distribute stress.

General Description

The disclosed method adds alloying elements that modify the growth pattern of the inter-metallic compounds and eliminate the sharp edges and unevenness of the layer; this significantly reduces stress concentrations and cracks. Modification of the growth is achieved by adding alkaline elements or rare earths. These elements are known to have an affinit...