Gold-tin solder suitable for self-aligning applications

Inactive Publication Date: 2001-01-02
AMERICAN TELEPHONE & TELEGRAPH CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

In accordance with the teachings of the present invention, a tin-rich Au/Sn solder (Au.sub.80-x Sn.sub.20+x, 0<x.ltoreq.6) is utilized, preferably in the range of 78/22 to 74/26 (weight % composition). Therefore, if solid state (or liquid state) diffusion of tin into a contacting gold plating layer occurs, the melt temperature will actually drop as the tin is depleted in the solder composition, until the eutectic composition is reached. The use of the tin-rich solder thus insures that the alloy will remain molten during solder reflow.
Further, the soldering process of the present invention may be optimized by heating the solder preform withi

Problems solved by technology

There are many known disadvantages to this procedure.
First, the reproducibility of the reflow is questionable and sensitive to process variations, particularly since commonly available eutectic Au/Sn solder may only be guaranteed .+-.1% around the eutectic 80

Method used

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  • Gold-tin solder suitable for self-aligning applications
  • Gold-tin solder suitable for self-aligning applications
  • Gold-tin solder suitable for self-aligning applications

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Embodiment Construction

An exemplary process for providing self-aligned solder attachment of a pair of components is illustrated in FIGS. 1-3. The inventive bonding process will be particularly described in association with the self-aligned attachment of an LED to a bond pad. However, it is to be understood that the tin-rich solder of the present invention is ubiquitous in nature and can be utilized within virtually any desired soldering process. Referring back to FIG. 1, a device submount 10, which may be formed of silicon, is illustrated as including a bond pad 12. Conventionally, bond pad 12 is formed of a highly conductive material and, in particular, may comprise a tri-layer structure of titanium, platinum and gold. Gold, in general, is often used for bond pads due to its inert nature and relatively high conductivity. A device 14, such as an LED, is illustrated in FIG. 1 as positioned above bond pad 12. Device 14 also includes a conductive layer 16 (which may also comprise a tri-level, or gold plated ...

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Abstract

A tin-rich gold-tin solder is disclosed which is particularly advantageous for self-aligning applications. When utilized with gold-plated bond locations, the out-diffusion of tin from the solder during heating functions to shift the composition of the remaining solder closer to the eutectic value, thus preserving the liquid state of the solder and improving its reflow quality with respect to conventional eutectic solders.

Description

BACKGROUND OF THE INVENTION1. Technical FieldThe present invention relates to a gold-tin solder and, more particularly, to a tin-rich, gold-tin solder.2. Description of the Prior ArtSoldering is a well-known technique for securing metal piece parts in a permanent fashion. Solder material must have the capacity to form metallurgical bonds with the two base metals that are to be joined. The bonding process results in the formation of an alloy in the surface of the base metal characterized by atoms of the soldering composition interspersed between atoms of the base metal.When the solder is heated to a molten state, it exists as a round droplet as a result of the attraction between the molecules forming the alloy. This attraction is commonly referred to as surface tension. For many technologically advanced applications, such as semiconductor and lightwave technologies, a solder composition of choice is a eutectic gold-tin material which is approximately 80% by weight gold and 20% by wei...

Claims

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Application Information

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IPC IPC(8): B23K35/30B23K35/00
CPCB23K35/3013B23K35/001B23K2035/008
Inventor DAUTARTAS, MINDAUGAS FERNAND
Owner AMERICAN TELEPHONE & TELEGRAPH CO
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