Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-06-25
2003-03-04
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S413000, C156S330000, C523S400000, C525S523000, C525S529000, C525S530000
Reexamination Certificate
active
06528169
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to adhesive compositions comprising epoxy resins and more particularly to such adhesive compositions used as underfill adhesives for integrated circuits.
BACKGROUND OF THE INVENTION
Early integrated circuit packaging involved wire bonding for connecting the integrated circuit to the printed circuit board. One alternative to wire bonding is solder bump interconnections. This method of interconnection is increasing in usage due to improved performance and increasing Input/Output (I/O) density. Flip chip bonding using solder bumped chips has allowed the use of area arrays on chips.
In flip chip bonding using solder bumped chips, a solder paste (flux) is applied to the circuit board, the chip pads are aligned with the traces on the substrate, and then the assembly is heated in a reflow oven. During this heating, the solder melts and a metallurgical bond between the chip and the substrate is formed. The surface tension of the solder during melting also leads to self-alignment of the pad pairs. After this reflow process, the solder flux must be washed away to remove corrosive residue. The assembly must be dried after this washing step.
The electronic assembly then requires additional environmental protection. In most cases, the underside of the assembly is encapsulated using an epoxy adhesive containing an inorganic filler. This adhesive is applied by allowing capillary forces to pull the resin underneath the chip. The filler, typically silica, is added to reduce the coefficient of thermal expansion of the underfill resin.
As chip sizes and the number of solder bumps on them increase, the method of adding an underfill material to the package using capillary forces will become less effective. An alternative to the capillary method of underfilling is to pre-apply, to the substrate, an adhesive that has fluxing properties. The adhesive, after fluxing the solder and allowing interconnection to occur, cures and becomes the underfill.
However, fluxing adhesives that contain liquid or easily volatilized anhydrides for example, provide bondlines that contain voids after cure. These voids can lead to premature solder fatigue failure in underfill applications. Fluxing adhesives that contain fluxing crosslinking agents can have poor shelf life or premature gelation or both, inhibiting solder flow.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a one-part, thermally curable, adhesive composition comprising epoxy resin substantially free of hydroxyl functionality; anhydride curing agent, wherein the anhydride has a weight loss of less than 10 percent as determined by thermogravimetric analysis wherein the temperature is ramped from ambient to 140° C. at a rate of 90° C./minute, held isothermal for 1 minute, then ramped to a temperature of 225° C. at a rate of 90° C./minute and then held isothermal for 2 minutes; hydroxyl containing compound that is substantially insoluble in the epoxy resin at a temperature of less than 80° C.; and optionally, catalyst. A preferred use of the adhesive composition is as a fluxing adhesive composition.
In another aspect, the invention provides an electrical component assembly comprising an electrical component having a plurality of electrical terminations, each termination including a solder bump; a component carrying substrate having a plurality of electrical terminations corresponding to the terminations of the electrical component; and an adhesive disposed between and bonding the electrical component and the substrate together, the solder bumps being reflowed and electrically connecting the electrical component to the substrate, the adhesive comprising the reaction product of an adhesive composition of the invention.
In another aspect, the invention provides a method of bonding an electrical component assembly comprising the steps of providing an electrical component having a plurality of electrical terminations, each termination including a solder bump; providing a component carrying substrate having a plurality of electrical terminations corresponding to the terminations of the electrical component; providing a sufficient amount of an adhesive composition of the invention to bond the electrical component and the component carrying substrate together onto the substrate; contacting the electrical component with the adhesive composition; and curing the adhesive composition.
In yet another aspect, the invention provides a thermally-curable one-part adhesive composition comprising an epoxy resin substantially free of hydroxyl functionality and an anhydride curing agent. The adhesive compositions of this aspect are stable in that they are expected to have a relatively long shelf-life as compared to other epoxy resin/anhydride compositions. The adhesive compositions of this aspect have utility bonding substrates where a fluxing agent is not necessary.
“Substantially free of hydroxyl functionality” means the epoxide equivalent weight is at or near the theoretical epoxide equivalent weight (that is, within 5 percent or less of the theoretical epoxide weight) and there is no hydroxyl group inherent in the monomeric form of the epoxide.
“Substantially insoluble” means that when a particulate form (1-10 mil (0.025-0.25 mm)) of the insoluble component is added to a liquid component, an opaque blend is formed which remains unchanged and only goes translucent upon heating of the mixture to a temperature of 80° C. or greater.
“Fluxing agent” means a material that cleans a metal, for example solder, surfaces of oxides.
“Adhesive” means a cured adhesive composition.
“Parts per hundred” means parts per 100 parts by weight of the total amount of epoxy resin, anhydride curing agent, hydroxyl containing compound, and catalyst.
Advantages of the adhesives and adhesive compositions of the invention include processing stability (as measured by gel time), a shelf life of greater than 4 weeks at ambient temperature under a nitrogen atmosphere, a pot life of greater than 8 hours at 80° C. (defined as a doubling of viscosity), minimal outgassing during cure (as measured by thermogravimetric analysis), and high fluxing activity (as measured by solder spread). Additionally, the adhesives and adhesive compositions of the invention do not substantially interfere with the surface tension/self-alignment feature of the solder. It has also been observed that only minimal force for short periods of time is required during placement to provide constructions that yield metallurgically and electrically bonded component during a reflow process with no additional added pressure required.
The preferred adhesive compositions and resulting adhesives of the invention provide a balance of fluxing properties and improved potlife. This balance is achieved by using a combination of purified epoxy resins, less volatile, relatively high molecular weight anhydrides, and hydroxyl containing compounds that are substantially insoluble in the epoxy resin-anhydride mixture at temperatures less than about 80° C. The adhesive compositions of the invention improve potlife and maintain fluxing capability by generating a fluxing agent just prior to the melting point of the solder. The fluxing agent is generated by the reaction of the hydroxyl containing compound (which becomes soluble at an elevated temperature) and the anhydride, neither of which provide fluxing individually. The purified epoxy resins prevent premature gellation and the substantially insoluble hydroxyl containing compound provide improved potlife since the hydroxyl containing compound reacts with the anhydride at temperatures of about 80° C. and above. Anhydrides having low volatility prevent void formation in the adhesive bondline during cure.
The adhesives and adhesive compositions of the invention do not include polyimide oligomers having a molecular weight of up to about 8,000 g/mol (Mn) having a backbone that is unreactive with an epoxy resin as described in U.S. Ser. No. 09/611,450, entitled Polyimide Hybrid Adhesives, filed on Jul. 6, 2000, now U.S. Pat. No. 6,294,259.
DETAILED DESCRIPT
Charles Scott B.
Kinney Robert J.
Kropp Michael A.
Mader Roger A.
3M Innovative Properties Company
Bardell Scott A.
Feely Michael J.
Harts Dean M.
Moore Margaret G.
LandOfFree
No-flow flux adhesive compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with No-flow flux adhesive compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and No-flow flux adhesive compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3034021