KR101339025B1 - Solder alloy - Google Patents

Abstract

Alloy for ball grid arrangement, 0.15-1.5 wt% copper, 0.1-4 wt% silver, 0-0.1 wt% phosphorus, 0-0.1 wt% germanium, 0-0.1 wt% gallium, 0-0.3 wt% One or more rare earths Element, 0-0.3 wt% indium, 0-0.3 wt% magnesium, 0-0.3 wt% calcium, 0-0.3 wt% silicon, 0-0.3 wt% aluminum, 0-0.3 wt% zinc, 0-1 wt% antimony And at least one of 0.02-0.3 wt% nickel, 0.008-0.2 wt% manganese, 0.01-0.3 wt% cobalt, 0.005-0.3 wt% chromium, 0.02-0.3 wt% iron, and 0.008-0.1 wt% zirconium and inevitable impurities Together with the alloy containing the remaining tin.

Description

Solder Alloy {SOLDER ALLOY}

TECHNICAL FIELD The present invention relates to alloys, and more particularly to lead-free solders. This alloy is particularly suitable for use in chip scale packages and ball grid arrays in the form of solder spheres, but not exclusively.

For environmental reasons, there is an increasing demand for lead-free products that replace conventional alloys containing lead. Many conventional solder alloys are based on a tin-copper eutectic composition, Sn-0.7 wt.% Cu.

A ball grid array joint is a beaded solder between two substrates, typically a circular pad. This arrangement of joints is used to mount the chip on the circuit board.

There is a great demand for solder alloys suitable for use in ball grid arrangements and chip scale packages. First, this alloy should exhibit good wetting characteristics with respect to various substrate materials such as copper, nickel, nickel-phosphorus, nickel-boron ("electroless nickel"). Solder alloys degrade the substrate material to form intermetallic compounds at the interface with the substrate. For example, tin in the solder alloy will react with the substrate at the interface to form the intermetallic material. If the substrate is copper, then a Cu ₆ Sn ₅ layer will be formed. Such layers generally have a thickness of a fraction of a micron to several microns. There may be an intermetallic compound of Cu ₃ Sn at the interface between this layer and the copper substrate. Such intermetallic compounds can result in brittle solder joints. In certain cases, voids occur, which can contribute to premature failure of the stressed joint.

Other important factors include (i) the presence of the intermetallic material of the alloy itself resulting in strong mechanical properties, (ii) oxidation resistance in multiple reflows, (iii) drossing rate, and (iv) alloy stability. This latter consideration is important in use, in which case the alloy remains in the tank or bath for a long period of time.

It is an object of the present invention to address at least some of the problems associated with the prior art and to provide an improved solder alloy. Accordingly, the present invention provides an alloy suitable for use in a ball grid arrangement or chip scale package, the alloy comprising:

0.15-1.5 wt% copper,

0.1-4 wt% silver,

0-0.1 weight percent phosphorus,

0-0.1 wt% germanium,

0-0.1 wt% gallium,

0-0.3 weight percent of one or more rare earth elements,

0-0.3 wt% indium,

0-0.3 wt% magnesium,

0-0.3 wt% calcium,

0-0.3 wt% silicone,

0-0.3 wt% aluminum,

0-0.3 wt% zinc,

0-1 weight percent antimony,

And at least one of the following elements:

0.02-0.3 wt% nickel,

0.008-0.2 wt% manganese,

0.01-0.3 weight percent cobalt,

0.005-0.3 wt% chromium,

0.02-0.3 wt% iron,

0.008-0.1 wt% zirconium,

And balance tin along with unavoidable impurities.

The invention will be explained below. Various aspects of the invention are defined in more detail below. Each aspect so defined may be combined with other aspects or may be combined with the opposite aspect although not explicitly shown. In particular, the desired or advantageously presented features can be combined with other features or features that are preferred or advantageously shown.

Copper forms a eutectic compound with tin, which increases alloy strength and lowers melting point. Copper content in the hyper- eutectic range increases liquidus temperature and also improves alloy strength.

This alloy preferably comprises 0.15 to 1% by weight Cu, more preferably 0.5 to 0.9% by weight Cu, even more preferably 0.6 to 0.8% by weight Cu.

Silver lowers the melting point and improves the wetting properties of the solder on copper and other substrates.

This alloy preferably comprises 0.1 to 3% by weight Ag, more preferably 0.1 to 2% by weight Ag. Most preferably, this alloy comprises 0.1 to 1 weight percent Ag. Within this range, the preferred range is 0.1 to 0.5% by weight Ag, more preferably 0.1 to 0.4% by weight Ag, even more preferably 0.1 to 0.3% by weight Ag. The lower limit for the Ag range can be raised to 0.2% by weight.

Low silver content has been known to be beneficial because it provides reduced alloy stiffness with the result of improved drop shock resistance. In drop shock or other high strain tests, stiffness and acoustic impedance play a major role in determining how stress is transferred to the interface (ie solder / IMC / substrate) through the solder alloy. Preferably this stress or stress wave is attenuated by the alloy. Low silver content has been known to improve alloy characteristics in this respect. Ag ₃ Sn intermetallic materials have also been known to be generally formed as high aspect ratio laths and plates. In forming solder joints, Ag ₃ Sn IMC tends to nucleate at the interface (ie solder / IMC / substrate). This structure can act as a stress riser, thereby making the solder joint additionally brittle. For this reason, the silver content in the alloy according to the invention is advantageously ≤1% by weight, preferably ≤0.4% by weight, more preferably ≤0.35% by weight, even more preferably ≤0.3% by weight. .

If present, the alloy preferably comprises from 0.02 to 0.2 wt% of at least one of nickel, cobalt, iron and chromium, more preferably from 0.02 to 0.1 wt% of at least one of nickel, cobalt, iron and chromium. It includes.

If present, the alloy preferably contains 0.005 to 0.3% by weight magnesium. In this case, improved properties can be obtained by the presence of 0.02 to 0.3% by weight Fe.

If present, the alloy preferably contains 0.01 to 0.15% by weight manganese, more preferably 0.02 to 0.1% by weight manganese.

Nickel, cobalt, chromium, manganese, iron, antimony and zirconium can act as intermetallic compound growth modifiers and grain refiners. For example, although not wishing to be connected theoretically, nickel forms an intermetallic of CuNiSn with tin and with copper, and the presence of low solubility elements in the intermetallic material slows the diffusion of Cu. This reduces the amount of IMC formed over time.

Manganese, cobalt and chromium each have low solubility in tin and also form an intermetallic material with copper and tin. The presence of the intermetallic material affects the microstructure formed when cooling the alloy from molten to the solid state. Finer grain structures are observed, which is beneficial for the strength and appearance of the alloy.

The growth rate of CuNiSn intermetallic material is known to be less than that of an alloy without nickel.

Cobalt is known to slow down the formation of interfacial intermetallic materials.

In a preferred embodiment of the invention, the alloy contains from 0.005 to 0.3 wt% chromium, preferably from 0.01 to 0.3 wt% chromium, more preferably from 0.02 to 0.2 wt% chromium, even more preferably from 0.03 to 0.1 wt% chromium. Include. As mentioned above, 0.3 wt% or less of Cr together with 1 wt% or less of Ag is an alloy having improved properties. In particular, alloys containing Cr additions have reduced ball traction for so-called mode 1 failure. Mode 1 is the preferred failure mode. This is tensile failure and necking in the solder, not at the interface. In addition, preferred results are obtained by the presence of Ni in addition to Cr.

Chromium is also known to soften alloys and improve oxidation resistance.

Manganese is known to reduce the intermetallic growth rate.

Zirconium is known to reduce solder interface growth.

Indium, zinc, magnesium, calcium, gallium and aluminum can act as diffusion compensators. The addition of suitably fast diffusing species may be effective, for example, in balancing pure atomic flux from the solder-substrate interface and thereby forming voids (Horsting or Kirkendall). Indium is known to have a beneficial effect on solder wetting. Indium lowers the melting point of the solder. Indium may also act to reduce the formation of voids in the solder joint. Indium can also improve the strength of the Sn-rich matrix. Zinc is known to work in a similar way to indium.

Aluminum is known to change the shape of the metal phase. Aluminum can also be combined with antimony, which may be present. In addition, aluminum (as well as chromium, germanium, silicon and phosphorus) may be advantageous in terms of redox.

Phosphorus, germanium, and gallium can act as dross reducers.

If present, the alloy preferably contains at least 0.05% by weight of one or more rare earth elements. The at least one rare earth element preferably comprises at least two elements selected from cerium, lanthanum, neodymium and praseodymium.

The alloy according to the invention is lead free or essentially lead free. This alloy offers advantages in environmental issues over conventional lead containing solder alloys.

The alloy according to the invention will generally be supplied as a solder sphere for CSP use, and may also optionally be supplied as a bar, stick or ingot with flux. The alloy may also be provided in the form of a wire, for example a cored wire comprising a preform, sphere or flux stamped or cut from a strip or solder. It may only be an alloy or may be coated with the appropriate flux as required by the soldering process. The alloy may also be supplied as a powder mixed with flux to provide a solder paste.

The alloy according to the invention can be used in a molten solder bath as a means for coating a substrate and / or for soldering two or more substrates together.

The alloy according to the invention may contain unavoidable impurities, provided that the total amount does not exceed 1% by weight of the composition. Preferably this alloy contains unavoidable impurities in an amount of up to 0.5% by weight of the composition, more preferably up to 0.3% by weight of the composition, even more preferably up to 0.1% by weight of the composition.

The alloy according to the invention may comprise the mentioned components in essential constructions. Thus, as well as mandatory components (ie, at least one of Sn, Cu, Ag and Ni, Co, Mn, Fe, Zr and Cr), other non-specified components may be present in this composition, in which case The essential features of the composition are not materially affected by the presence of such components.

It will generally be at least 90% by weight tin, preferably 94 to 99.5% tin, more preferably 95 to 99% tin, even more preferably 97 to 99 wt% tin. Accordingly, the present invention further provides an alloy used in a chip scale package or ball grid arrangement, the alloy comprising:

95-99 wt% tin,

0.15-1.5 wt% copper,

0.1-4 wt% silver,

0-0.1 weight percent phosphorus,

0-0.1 wt% germanium,

0-0.1 wt% gallium,

0-0.3 weight percent of one or more rare earth elements,

0-0.3 wt% indium,

0-0.3 wt% magnesium,

0-0.3 wt% calcium,

0-0.3 wt% silicone,

0-0.3 wt% aluminum,

0-0.3 wt% zinc,

0-1 weight percent antimony,

And at least one of the following ingredients:

0.02-0.3 wt% nickel,

0.008-0.2 wt% manganese,

0.01-0.3 weight percent cobalt,

0.005-0.3 wt% chromium,

0.02-0.3 weight percent iron, and

0.008-0.1 wt% zirconium,

Together with inevitable impurities.

The alloy according to the invention is particularly suitable for use comprising a ball grid arrangement or a chip scale package. Thus, the present invention provides the use of a solder alloy as described in a ball grid arrangement or chip scale package.

The present invention also provides a chip scale package joint or ball grease arrangement comprising a solder alloy composition as described herein.

Yes

The following are non-limiting examples that further illustrate the invention.

Example 1

The alloy was prepared by melting Sn in a cast iron crucible (alternatively a ceramic crucible could be used). To the molten Sn, an alloy of Sn-3% by weight Cu and an alloy of Sn-5% by weight Ag and Sn-0.35% by weight Ni were added. This addition was made at an alloy bath temperature of 350 ° C. This bath was cooled to 300 ° C. for the addition of phosphorus in the form of alloy Sn-0.3% P.

This alloy,

Ag 0.3 wt%

Cu 0.7 wt%

Ni 0.03 wt%

P 0.006 wt% and

Samples were made to identify the composition of the remaining tin.

This alloy composition was then sprayed as a metal stream into an inserted vertical column. This metal stream became spherodised by applying magnetostrictive vibrational energy applied at or near the exit orifice and through the melt pot.

Equally, the alloy composition can be punched and then spherical as a sphere.

Alloys provided in spherical form may be used in ball grid array joints or chip scale packages. The flux is pinned or printed to the pad of the CSP. This sphere is then picked and shaken or positioned through a stencil with a fluxed pad. The package is then reflowed in a standard reflow oven at a peak temperature of 240 ° C. to 260 ° C.

Alloy and solder joint performance was evaluated in a package maintained at 150 ° C. for up to 1000 hours. IMC growth was measured by standard metallographic techniques. Mechanical ball pulling testing was used to evaluate the solder joint failure mode (brittle or ductile).

Example 2

The following alloy compositions were prepared in a similar manner to Example 1 (all wt%).

Ag 0.3

Cu 0.7

Ni 0.2

P 0.006

Sn rest

This alloy can be provided in spherical form and can be used in ball grid array joints or chip scale packages.

Example 3

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Co 0.2

P 0.006

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 4

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Cr 0.05

P 0.006

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 5

Alloys were prepared corresponding to the compositions of Examples 1-4, in which Ge replaced the phosphorus content.

Example 6

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Co 0.2

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 7

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Ni 0.10

Ge 0.10

P 0.006

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 8

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Ni 0.2%

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 9

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Fe 0.1

Mg 0.05

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 10

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Cr 0.05

Co 0.2

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 11

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Cr 0.05

Ni 0.2

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 12

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Cr 0.05

Fe 0.2

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Example 13

The following alloy composition was prepared in a similar manner to Example 1.

Ag 0.3

Cu 0.7

Cr 0.05

Fe 0.2

Mg 0.1

Sn rest

This alloy may be provided in spherical form and may be used in ball grid array joints or chip scale packages.

Claims (35)

As an alloy for a ball grid array or chip scale package, As an essential component 0.15-1.5 wt% copper, 0.1-4 wt% silver, 0.02-0.3 wt% nickel, 0.005-0.3 wt% chromium, As an optional component 0-0.1 weight percent phosphorus, 0-0.1 wt% germanium, 0-0.1 wt% gallium, 0-0.3 weight percent of one or more rare earth elements, 0-0.3 wt% indium, 0-0.3 wt% magnesium, 0-0.3 wt% calcium, 0-0.3 wt% silicone, 0-0.3 wt% aluminum, 0-0.3 wt% zinc, Contains 0-1 weight percent antimony, 0.008-0.2 wt% manganese, 0.01-0.3 weight percent cobalt, 0.02-0.3 weight percent iron, and 0.008-0.1 wt% zirconium optionally comprising one or more components, and Containing the rest of the tin together with unavoidable impurities, Alloy for ball grid array or chip scale. The method of claim 1, Comprising 0.15 to 1 weight percent copper, Alloy for ball grid array or chip scale. The method of claim 2, Comprising 0.5 to 0.9 weight percent copper, Alloy for ball grid array or chip scale. The method of claim 3, wherein Comprising 0.6 to 0.8 wt% copper, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.1 to 1 weight percent silver, Alloy for ball grid array or chip scale. 6. The method of claim 5, 0.1 to 0.4 wt% silver, Alloy for ball grid array or chip scale. The method of claim 6, 0.1 to 0.35 wt% silver, Alloy for ball grid array or chip scale. The method of claim 7, wherein Comprising 0.1 to 0.3 wt% silver, Alloy for ball grid array or chip scale. delete 5. The method according to any one of claims 1 to 4, Comprising 0.01 to 0.3 wt% chromium, Alloy for ball grid array or chip scale. 11. The method of claim 10, Comprising 0.02 to 0.2 wt% chromium, Alloy for ball grid array or chip scale. The method of claim 11, Comprising 0.03 to 0.1 weight percent chromium, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, 0.02-0.2 wt% of at least one of nickel, cobalt, iron and chromium, Alloy for ball grid array or chip scale. 14. The method of claim 13, 0.02-0.1 weight percent of at least one of nickel, cobalt, iron and chromium, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.01 to 0.3 wt.% Magnesium, Alloy for ball grid array or chip scale. 16. The method of claim 15, Comprising 0.02 to 0.3 wt% iron, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.01 to 0.15 wt.% Manganese, Alloy for ball grid array or chip scale. 18. The method of claim 17, Comprising 0.02 to 0.1 weight percent manganese, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.05 to 0.3 wt.% Indium, Alloy for ball grid array or chip scale. 20. The method of claim 19, Comprising 0.1 to 0.2 weight percent indium, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.01 to 0.3 wt% calcium, Alloy for ball grid array or chip scale. 22. The method of claim 21, Comprising 0.1 to 0.2 wt% calcium, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.01 to 0.3 wt% silicone, Alloy for ball grid array or chip scale. 24. The method of claim 23, Comprising 0.1 to 0.2 wt% silicone, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.008 to 0.3 weight percent aluminum, Alloy for ball grid array or chip scale. 26. The method of claim 25, Comprising 0.1 to 0.2 wt% aluminum, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.01 to 0.3 wt% zinc, Alloy for ball grid array or chip scale. 28. The method of claim 27, Comprising 0.1 to 0.2 wt% zinc, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Comprising 0.05 to 1 weight percent antimony, Alloy for ball grid array or chip scale. 30. The method of claim 29, Comprising 0.1 to 0.5 wt% antimony, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, The at least one rare earth element comprises at least one element selected from cerium, lanthanum, neodymium and praseodymium, Alloy for ball grid array or chip scale. 5. The method according to any one of claims 1 to 4, Preformed solder pieces, or solder spheres for ball grid array joints, powders or pastes (mixtures of powder and flux), preforms, foils or strips, solid or flux cored wires in the form of a cored wire, stick, or bar, Alloy for ball grid array or chip scale. A soldered ball grid arrangement or chip scale package joint, comprising an alloy as defined in claim 1. delete 5. The method according to any one of claims 1 to 4, Wherein the at least one rare earth element comprises at least two elements selected from cerium, lanthanum, neodymium and praseodymium, Alloy for ball grid array or chip scale.