WO1997029216A1

WO1997029216A1 - Alloy c11004

Info

Publication number: WO1997029216A1
Application number: PCT/US1997/002030
Authority: WO
Inventors: Joseph P. Mennucci; Charles R. Mead; Kiran Dalal; Shelley J. Wolf; David Ross
Original assignee: Brush Wellman Inc.
Priority date: 1996-02-09
Filing date: 1997-02-07
Publication date: 1997-08-14
Also published as: EP0866883A4; EP0866883A1

Abstract

An enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm, an iron content generally less than about 20 ppm, a zinc content generally less than about 24 ppm, a silicon content generally less than about 31 ppm, generally less than about 31 ppm aluminum, a tin content generally less than about 10 ppm, generally less than about 10 ppm lead and about 10 ppm magnesium, a manganese content generally less than about 10 ppm, generally less than about 10 ppm cobalt, generally less than about 31 ppm nickel, and a cadmium content generally less than about 10 ppm, the balance copper.

Description

This application is a continuation-in-part of application Serial No. 08/474,090 filed June 7, 1995, which is a

continuation of application Serial No. 08/182,288 filed January 14, 1994, now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to alloys and more particularly to a novel high performance alloy of copper having superior bonding characteristics.

BACKGROUND OF THE INVENTION

Commercially pure copper is notable for its superior electrical conductivity and its exceptional ability to conduct and dissipate heat. For these reasons, pure copper is often a material of choice in the construction of heat sinks for microelectronic packaging.

When constructing heat sinks, sheeting of pure copper is often bonded to a non-metal such as a ceramic substrate. This is preferably done by a process known as direct bonding. Direct bonding requires that the bonding surface of the copper be oxidized so that covalent bonds can form with the ceramic during thermal bonding. By conventional methods, both sides of the sheeting are coated with (or dipped in) a chemical solution that promotes oxidation. This forms a low melting temperature eutectic of copper oxide on each side of the sheeting which, upon heating, bonds the substrate to the sheeting, and the sheeting to adjacent copper layers.

For improved bond strength and reliability, instead of using a chemical coating, the copper may be impregnated with oxygen. Materials of this general description are found for example, in a co-pending patent application, S.N. 08/474,090, filed June 7, 1995, entitled MULTILAYER LAMINATE PRODUCT AND PROCESS, the disclosure of which is hereby incorporated by reference in its entirety.

While the foregoing methods and materials are useful, they often yield inconsistent results in bond integrity, durability, reliability and dimensional stability. This unpredictability in bond quality may be especially problematic in ultra high performance applications where heat sinks must perform consistently under extreme temperature conditions. Also, materials and bonding techniques which require the use of a chemical coating have been found costly and to produce excessive chemical waste.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a high performance alloy with enhanced bonding

characteristics.

Another object of the present invention to provide a high performance alloy with superior heat transfer properties.

Still another object of the present invention is to provide a material with enhanced bonding characteristics.

Yet another object of the present invention is to provide a material which yields consistent bond integrity, durability, reliability and dimensional stability.

A further object of the present invention is to provide a material that withstands high temperatures while rapidly

dissipating heat.

Still a further object of the present invention is to provide a material which eliminates the use of chemical coating techniques for direct bonding. Yet a further object of the present invention is to provide for the economical production of heat sinks without excessive chemical waste.

Still another object of the present invention is to provide simple and efficient manufacture of high performance heat sinks using direct bonding technology.

Yet another object of the present invention is to maximize the energy transfer properties of copper alloys.

A further object of the present invention is to facilitate low cost production of high performance heat sink structures which have acceptable acoustics, cooling rates and pressure drop.

Another object of the present invention is to facilitate rapid dissipation of heat from microelectronic packaging.

In accordance with one aspect of the present invention, there is provided an enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm and generally less than about 10 ppm of any one impurity, the balance copper.

In accordance with another aspect of the present invention is a higher order copper alloy containing controlled oxygen and impurity contents represented by the formula (350-709 ppm O₂) + (0-30 ppm Ni) + (0-19 ppm Fe) + (0-30 ppm Si) + (0-30 ppm Al) + (0-23 ppm Zn) + (0-9 ppm Co) + (0-9 ppm Sn) + (0-9 ppm Pb) + (0- 9 ppm Mg) + (0-9 ppm Mn) + (0-9 ppm Ca), the balance copper.

In accordance with a further aspect of the present

invention, there is provided an enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm, an iron content generally less than about 20 ppm, and a zinc content generally less than about 24 ppm, the balance copper. In accordance with still another aspect of the present invention, there is provided an enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm, an iron content generally less than about 20 ppm, a zinc content generally below about 24 ppm, a silicon content generally less than about 31 ppm, generally less than about 31 ppm aluminum, a tin content generally less than about 10 ppm, generally below about 10 ppm lead and about 10 ppm magnesium, a manganese content generally less than about 10 ppm, generally less than about 10 ppm cobalt, generally below about 31 ppm nickel, and a cadmium content of generally less than about 10 ppm, the balance copper.

In accordance with yet another aspect of the present invention, there is provided an enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm, an iron content generally less than about 20 ppm, a zinc content below about 24 ppm, a silicon content generally less than about 31 ppm, generally less than about 31 ppm aluminum, a tin content generally less than about 10 ppm, generally below about 10 ppm lead and about 10 ppm magnesium, a manganese content generally less than about 10 ppm, generally less than about 10 ppm cobalt, generally below about 31 ppm nickel, a cadmium content generally less than about 10 ppm, less than about 10 ppm calcium, below about 10 ppm beryllium, less than approximately 10 ppm chromium, and generally less than about 10 ppm phosphorus, the balance copper.

Although the present invention is shown and described in connection with oxygen-rich copper, it may be adapted for improving bonding characteristics of other materials such as those containing precious metals, aluminum, titanium, nickel, iron and their alloys. The present invention will now be further described by reference to the following drawings which are not intended to limit the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a micrograph of an enhanced bonding copper alloy strip at 120 x magnification containing about 700 ppm oxygen, in accordance with one aspect of the present invention;

FIG. 2 is a micrograph of an enhanced bonding copper alloy strip at 120 x magnification containing about 380 ppm oxygen, in accordance with another aspect of the present invention;

FIG. 3 is a graph for Alloy C11004 showing impurities as a function of oxygen content for cobalt, tin, lead, magnesium, manganese and calcium;

FIG. 4 is a graph for Alloy C11004 showing impurities as a function of oxygen content for zinc;

FIG. 5 is a graph for Alloy C11004 showing impurities as a function of oxygen content for nickel;

FIG. 6 is a graph for Alloy C11004 showing impurities as a function of oxygen content for silicon;

FIG. 7 is a graph for Alloy C11004 showing impurities as a function of oxygen content for iron; and

FIG. 8 is a graph for Alloy C11004 showing impurities as a function of oxygen content for aluminum.

The same numerals are used throughout the figure drawings to designate similar elements. Still other objects and

advantages of the present invention will become apparent from the following description of the preferred embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a discovery of the extraordinary bonding characteristics of Alloy C11000 at relatively high oxygen contents and minimal impurity levels. According to one aspect of the present invention is a higher order copper alloy containing a controlled balance of oxygen and various impurities, the alloy being represented generally by the formula (350-709 ppm O₂) + (0-30 ppm Ni) + (0-19 ppm Fe) + (0-30 ppm Si) + (0-30 ppm Al) + (0-23 ppm Zn) + (0-9 ppm Co) + (0-9 ppm Sn) + (0-9 ppm Pb) + (0-9 ppm Mg) + (0-9 ppm Mn) + (0-9 ppm Ca), the balance copper.

According to another aspect of the present invention is a higher order copper alloy containing a controlled balance of oxygen and various impurities, the alloy being represented by the formula (350-709 ppm O₂) + (0-30 ppm Ni) + (0-19 ppm Fe) + (0-30 ppm Si) + (0-30 ppm Al) + (0-23 ppm Zn) + (0-9 ppm Co) + (0-9 ppm Sn) + (0-9 ppm Pb) + (0-9 ppm Mg) + (0-9 ppm Mn) + (0-9 ppm Ca) + (0-9 ppm Be) + (0-9 ppm Cr) + (0-9 ppm P), the balance copper.

The foregoing formulas indicate the ranges of oxygen and impurities which have consistently yielded acceptable direct bonding of Alloy C11000 to a ceramic substrate, e.g., beryllium oxide, for relatively high performance heat transfer applications. An exemplary definition of a successful bond, according to one aspect of the present invention, is one which gives a minimum of 15 lbs./in. peel strength for a 0.015 in. thick copper sheet direct bonded to a 0.025 in. thick ceramic, e.g., beryllium oxide, using a 90 degree peel strength test.

It has been found that outside the stated oxygen and impurity ranges, the suitability of high oxygen content C11000 to bonding for the high energy transfer demands of state-of-the- art electronics is unpredictable. Ranges of acceptable impurity levels for bonding high oxygen content Alloy C11000 are

illustrated in FIGS. 3-8. Copper alloys with constituents falling within these parameters are hereinafter referred to as Alloy C11004.

For consistent results in bond uniformity and strength, it is preferred that the oxygen content be controlled to remain within a selected envelope, e.g., generally within a range of 380 ppm and 700 ppm oxygen. In one embodiment of the present invention, the concentration of oxygen is about 700 ppm, as shown in FIG. 1. In another embodiment, as shown in FIG. 2, the oxygen concentration is about 380 ppm. Oxygen appears as heavy black spots at the grain boundaries, as is the case when the material is in the as-cast state. Upon hot working, the oxygen becomes randomly distributed m a new microstructure.

Oxygen content is determined, e.g., by inert gas fusion using a LECO analyzer, LECO TC-436. Utilizing a 0.5 gram sample of C11004, concentrations of oxygen which may be detected fall generally within a range of 0.001% and 0.200%. Testing is conducted according to usual industry standards and procedures, though it may be modified according to common practice.

During direct bonding, temperature and other conditions cause C11004 sheeting to anneal simultaneously to like sheets of the alloy and/or substrates, e.g., beryllium oxide, metallurgically bonding the various layers to one another. After direct bonding, a fine grain structure is produced in the layers (See FIG. 1). Various methods of direct bonding metals to ceramics (and metals to other metals) are described, for example, in U.S. Patent No. 3,944,430, which issued on November 30, 1976, and in U.S. Patent No. 4,129,243, which issued on December 12, 1978, the disclosures of which are hereby incorporated by reference in their entireties. Oxygen impregnated copper provides oxygen to the copper-ceramic or copper-copper interface more uniformly than does chemically coated copper. This improves substantially bond integrity and part reliability. Moreover, by eliminating the three chemical baths required to chemically coat copper, there is significant reduction in cost, chemical waste, and health risks alleged to be associated with hauling the waste. The dimensional stability and durability of oxygen impregnated copper is also superior.

It has now been discovered that by minimizing impurity levels, particularly of those impurities which combine readily with oxygen, achieves a tremendous advancement in bond integrity and part reliability over that of conventional oxygen

impregnated copper.

Set forth in FIG. 3 is a graph for Alloy C11004 showing maximum acceptable impurity levels for cobalt, tin, lead, magnesium, manganese and calcium as a function of oxygen.

Acceptable ranges shown are linear, as illustrated by cross-hatching.

FIG. 4 shows maximum acceptable impurity levels of zinc as a function of oxygen. Acceptable ranges are shown by the shaded region below the line. As this demonstrates, the correlation between high oxygen levels and zinc are generally nonlinear and erratic.

Maximum acceptable impurity levels of nickel for Alloy C11004 are provided as a function of oxygen in FIG. 5.

Acceptable ranges are shown by the shaded region below the line. As with zinc, there is also a nonlinear correlation between relatively high oxygen levels in the alloy and nickel. The same is true for the relationship between high oxygen levels and silicon, as demonstrated in FIG. 6. A combination of linear and nonlinear relationships is found between relatively high oxygen levels and each of iron and aluminum, as demonstrated in FIGS. 7 and 8. In the case of iron, the relationship is linear at the lowest and highest of the high oxygen levels, but nonlinear in the mid range.

Aluminum, on the other hand, shows nonlinearities at the low end of oxygen content, but becomes linear from about the mid range to higher oxygen levels.

Other impurities which may be present in the alloy include, but are limited to, chromium, beryllium, and phosphorus. The level of each additional impurity is preferably well below 10 ppm. In general, given an oxygen content as specified by the present invention, and commensurate minimums of each impurity, the balance of the alloy contents are desirably copper.

Although the embodiments illustrated herein have been shown and described in connection with oxygen-rich copper alloys, e.g., 99.50% Cu (Mill Standard C11000), it is understood that an analogous process could be practiced on other materials, giving consideration to the purpose for which the present invention is intended. For example, the present invention may be adapted for improving bonding characteristics of other materials such as those containing precious metals, aluminum, titanium, nickel, iron, and their alloys.

In Table I below is an illustrative Chemical Analysis

Summary of Alloy C11004 listing oxygen, various impurities, and effective oxygen data which yield successful bonding. As this demonstrates, the composition of C11004 which achieves acceptable bonding results may be outside the ranges of impurities defined and claimed herein, though the precise correlation between levels of copper, oxygen and impurities is not fully understood nor has acceptable bondability been accurately predicted outside such ranges.

Effective oxygen is calculated according to the following equation :

O_{2 effective} = total O₂- (atomic weight O₂) × [((Fe/(atomic

weight Fe)) + (Pb/(atomic weight Pb)) +

(Zn/(atomic weight Zn)) + (Sn/(2 × atomic weight Sn))]

FeO, PbO, ZnO and SnO, are oxides typically present in the copper matrix. Excluded from the equation are those elements and their oxides usually at or beyond detection limits. If other constituents are present in detectable quantities, however, it is considered prudent to include them in the equation. Such materials and their oxides include Be, BeO, Si,

SiO₂, Al, Al₂O₃, Cr, Cr₂O₃, Mg, MgO, Ca, CaO, Zr and Zr₂O.

The balance of the oxygen is believed present as a cuprous oxide (Cu₂O) in the matrix material. These oxides appear as black spherical particles under normal lighting conditions (or cherry red particles under polarized light).

The present invention is beneficial in permitting the use of pure copper which has a substantially higher thermal

conductivity than that of Cu thick film, Mo-Mn thick film or As- Pd thick film and a substantially lower resistivity. The use of direct bond copper technology, it is noted, typically maintains the electrical conductivity within about 5 % of that of pure copper.

In this connection, the use of a BeO substrate has similar benefits in having a thermal conductivity substantially higher than that of AIN. Together, Alloy C11004 and BeO provide superior thermal resistance performance over AIN-Cu, AI203-Cu, or high oxygen content copper clad laminates. A substantially higher maximum conductor current is also provided without the need for an intermediate bonding layer.

During direct bonding, there is diffusion bonding (or interdiffusion) not only at metal to metal interfaces, but also between the metal and ceramics. This facilitates the formation of a solidified, heterogeneous, multilayer laminate or other structure for use in heat sink applications. Application of C11004 to net shape articles is also considered within the spirit and scope of the present invention.

The present invention has been found particularly desirable for use in heat exchangers for high technology applications. Heat exchangers of this general type are shown, for example, in a co-pending continuation-in-part of application Serial No.

08/474,090, filed by Joseph P. Mennucci and Charles R. Mead on the same date herewith, entitled HEAT EXCHANGER ASSEMBLY AND METHOD FOR MAKING THE SAME, the disclosure of which is hereby incorporated by reference in its entirety.

Alloy C11004 advantageously permits cost-effective mass production of high performance heat sink structures, extending the superior cooling characteristics of Alloy Cl1000 to leading edge microelectronic applications. C11004, through its

extraordinary bondability, permits the economical construction of reliable heat sink structures for ultra high performance applications, such as control modules of electric car motors, and the Pentium™ and POWERPC™microchips.

Various modifications and alterations to the present invention may be appreciated based on a review of this

disclosure. These changes and additions are intended to be within the scope and spirit of this invention as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. An enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm and generally less than about 10 ppm of any one impurity, the balance copper.

2. A higher order copper alloy containing controlled oxygen and impurity contents represented by the formula (350-709 ppm O₂) + (0-30 ppm Ni) + (0-19 ppm Fe) ₊ (0-30 ppm Si) + (0-30 ppm Al) + (0-23 ppm Zn) + (0-9 ppm Co) + (0-9 ppm Sn) + (0-9 ppm Pb) + (0-9 ppm Mg) + (0-9 ppm Mn) + (0-9 ppm Ca), the balance copper.

3. The higher order copper alloy of claim 2 having less than about 10 ppm of any one impurity.

4. The higher order copper alloy of claim 2 having a minimum of 15 lbs./in. peel strength for a 0.015 in. thick specimen of the alloy bonded to a 0.025 in. thick ceramic using a 90 degree peel strength test.

5. An enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm, an iron content generally less than about 20 ppm, and a zinc content generally less than about 24 ppm, the balance copper.

6. An enhanced bonding copper alloy characterized by an oxygen content generally within a range of 350 ppm to 709 ppm, an iron content generally less than about 20 ppm, a zinc content generally below about 24 ppm, a silicon content generally less than about 31 ppm, generally less than about 31 ppm aluminum, a tin content generally less than about 10 ppm, generally below about 10 ppm lead and about 10 ppm magnesium, a manganese content generally less than about 10 ppm, generally less than about 10 ppm cobalt, generally below about 31 ppm nickel, and a cadmium content of generally less than about 10 ppm, the balance copper.

7. A net shape article comprised of a higher order copper alloy containing controlled oxygen and impurity contents represented by the formula (350-709 ppm O₂) + (0-30 ppm Ni) + (0-19 ppm Fe) + (0-30 ppm Si) + (0-30 ppm Al) + (0-23 ppm Zn) + (0-9 ppm Co) + (0-9 ppm Sn) + (0-9 ppm Pb) + (0-9 ppm Mg) + (0-9 ppm Mn) + (0-9 ppm Ca), the balance copper.

8. The net shape article of claim 7 having a minimum of 15 lbs./in. peel strength for a 0.015 in. thick specimen of the alloy bonded to a 0.025 in. thick ceramic using a 90 degree peel strength test.

9. The net shape article of claim 7 having less than about 10 ppm of any one impurity.

10. A higher order copper alloy containing controlled oxygen and impurity contents represented by the formula (350-709 ppm O₂) + (0-30 ppm Ni) + (0-19 ppm Fe) + (0-30 ppm Si) + (0-30 ppm Al) + (0-23 ppm Zn) + (0-9 ppm Co) + (0-9 ppm Sn) + (0-9 ppm Pb) + (0-9 ppm Mg) + (0-9 ppm Mn) + (0-9 ppm Ca) + (0-9 ppm Be) + (0-9 ppm Cr) + (0-9 ppm P), the balance copper.

11. A high performance material containing a commercially pure metal and a controlled balance of oxygen and

impurities to maximize the material's capacity for direct bonding to a like material or ceramic substrate.

12. A high performance material containing an alloy and a controlled balance of oxygen and impurities to maximize the material's capacity for direct bonding to a like material or ceramic substrate.