Die attach adhesives for use in microelectronic devices

Details Die attach adhesives for use in microelectronic devices Die attach adhesives for use in microelectronic devices

1999-06-18

2001-07-24

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S117000, C528S211000, C528S172000, C528S253000, C528S248000, C526S262000, C525S182000, C525S185000, C525S279000, C525S282000, C525S422000

Reexamination Certificate

active

06265530

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to compositions that are suitable for use as adhesives in microelectronic devices or semiconductor packages.
BACKGROUND OF THE INVENTION
Adhesive compositions, particularly conductive adhesives, are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses are the bonding of integrated circuit chips to lead frames or other substrates, and the bonding of circuit packages or assemblies to printed wire boards.
The requirements for conductive adhesives in electronic packaging are that they have good mechanical strength, curing properties that do not affect the component or the carrier, and thixotropic properties compatible with existing application equipment currently used in the industry.
Another important aspect of an adhesive bonding or interconnection technology is the ability to rework the bond. For single chip packaging involving high volume commodity products, a failed chip can be discarded without significant loss. However, it becomes expensive to discard multi-chip packages with only one failed chip; consequently, the ability to rework the failed chip would be a manufacturing advantage. Today, one of the primary thrusts within the semiconductor industry is to develop adhesives that will meet all the requirements for adhesive strength and flexibility, but that will also be reworkable, that is, will be capable of being removed without destroying the substrate.
SUMMARY OF THE INVENTION
This invention is an adhesive composition for use in electronic devices that comprises one or more mono- or polyfunctional maleimide compounds, or one or more mono- or polyfunctional vinyl compounds other than maleimide compounds, or a combination of maleimide and vinyl compounds, a curing initiator, and optionally, one or more fillers. The composition can be designed to be reworkable.
In another embodiment, this invention is the cured adhesive that results from the just described curable adhesive composition.
In another embodiment, this invention is a microelectronic assembly comprising an electronic component bonded to a substrate with a cured adhesive composition prepared from a composition comprising one or more mono- or polyfunctional maleimide compounds, or one or more mono- or polyfunctional vinyl compounds, or a combination of maleimide and vinyl compounds, a curing initiator, and optionally one or more fillers.
DETAILED DESCRIPTION OF THE INVENTION
The maleimide and vinyl compounds used in the adhesive compositions of this invention are curable compounds, meaning that they are capable of polymerization, with or without crosslinking. As used in this specification, to cure will mean to polymerize, with or without crosslinking. Cross-linking, as is understood in the art, is the attachment of two polymer chains by bridges of an element, a molecular group, or a compound, and in general will take place upon heating. As cross-linking density is increased, the properties of a material can be changed from thermoplastic to thermosetting.
It is possible to prepare polymers of a wide range of cross-link density by the judicious choice and amount of mono- or polyfunctional compounds. The greater proportion of polyfunctional compounds reacted, the greater the cross-link density. If thermoplastic properties are desired, the adhesive compositions can be prepared from mono-functional compounds to limit the cross-link density. A minor amount of poly-functional compounds can be added to provide some cross-linking and strength to the composition, provided the amount of poly-functional compounds is limited to an amount that does not diminish the desired thermoplastic properties. Within these parameters, the strength and elasticity of individual adhesives can be tailored to a particular end-use application.
In those cases where it is necessary to rework the assembly and thermoplastic materials are used, the electronic component can be pried off the substrate, and any residue adhesive can be heated until it softens and is easily removed.
The cross-link density can also be controlled to give a wide range of glass transition temperatures in the cured adhesive to withstand subsequent processing and operation temperatures.
In the inventive adhesive compositions, the maleimide compounds and the vinyl compounds may be used independently, or in combination. The maleimide or vinyl compounds, or both, will be present in the curable package adhesive compositions in an amount from 2 to 98 weight percent based on the organic components present (excluding any fillers).
The adhesive compositions will further comprise at least one free-radical initiator, which is defined to be a chemical species that decomposes to a molecular fragment having one or more unpaired electrons, highly reactive and usually short-lived, which is capable of initiating a chemical reaction by means of a chain mechanism. The free-radical initiator will be present in an amount of 0.1 to 10 percent, preferably 0.1 to 3.0 percent, by weight of the organic compounds (excluding any filler). The free radical curing mechanism gives a fast cure and provides the composition with a long shelf life before cure. Preferred free-radical initiators include peroxides, such as butyl peroctoates and dicumyl peroxide, and azo compounds, such as 2,2′-azobis(2-methyl-propanenitrile) and 2,2′-azobis(2-methyl-butanenitrile).
Alternatively, the adhesive compositions may contain a photoinitiator in lieu of the free-radical initiator, and the curing process may then be initiated by UV radiation. The photoinitiator will be present in an amount of 0.1 to 10 percent, preferably 1 to 5.0 percent, by weight of the organic compounds (excluding any filler). In some cases, both photoinitiation and thermal initiation may be desirable. For example, the curing process can be started by UV irradiation, and in a later processing step, curing can be completed by the application of heat to accomplish a free-radical cure.
In general, these compositions will cure within a temperature range of 80-200° C., and curing will be effected within a length of time of less than 1 minute to 60 minutes. As will be understood, the time and temperature curing profile for each adhesive composition will vary, and different compositions can be designed to provide the curing profile that will be suited to the particular industrial manufacturing process.
Suitable conductive fillers for the adhesives are silver, copper, gold, alladium, platinum. In some circumstances, nonconductive fillers may be needed, for example to adjust rheology, such as, alumina, silica, and teflon.
As used throughout this specification, the notation C(O) refers to a carbonyl group.
Maleimide Compounds
The maleimide compounds suitable for use in the adhesive compositions of this invention have a structure represented by the formula: [M—X
m
]
n
—Q , or by the formula: [M—Z
m
]
n
—K. For these specific formulae, when lower case “n” is the integer 1, the compound will be a mono-functional compound; and when lower case “n” is an integer 2 to 6, the compound will be a poly-functional compound.
[M—X
m
]
n
—Q, or by the formula: [M—Z
m
]
n
—K.
Formula [M—X
m
]
n
—Q represents those compounds in which:
M is a maleimide moiety having the structure
in which R
1
is H or C
1
to C
5
alkyl;
each X independently is an aromatic group selected from the aromatic groups having the structures (I) through (IV):
Q is a linear or branched chain alkyl, alkyloxy, alkylene, alkyleneoxy, aryl, or aryloxy alkyl amine, alkyl sulfide, alkylene amine, alkylene sulfide, aryl sulfide species, which may contain saturated or unsaturated cyclic or heterocyclic substituents pendant from the chain or as part of the backbone in the chain, and in which any heteroatom present may or may not be directly attached to X;
or Q is a urethane having the structure:
in which each R
2
independently is an alkyl, aryl, or arylalkyl group having 1 to 18 carbon atoms; R
3
is an alkyl or alkylox

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