Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/40—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the curing agents used
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W74/00—Encapsulations, e.g. protective coatings
  • H10W74/40—Encapsulations, e.g. protective coatings characterised by their materials
  • H10W74/47—Encapsulations, e.g. protective coatings characterised by their materials comprising organic materials, e.g. plastics or resins
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/14—Polycondensates modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/40—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the curing agents used
  • C08G59/42—Polycarboxylic acids; Anhydrides, halides or low molecular weight esters thereof
  • C08G59/4284—Polycarboxylic acids; Anhydrides, halides or low molecular weight esters thereof together with other curing agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L63/00—Compositions of epoxy resins; Compositions of derivatives of epoxy resins
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W74/00—Encapsulations, e.g. protective coatings
  • H10W74/01—Manufacture or treatment
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W74/00—Encapsulations, e.g. protective coatings
  • H10W74/01—Manufacture or treatment
  • H10W74/012—Manufacture or treatment of encapsulations on active surfaces of flip-chip devices, e.g. forming underfills
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W74/00—Encapsulations, e.g. protective coatings
  • H10W74/10—Encapsulations, e.g. protective coatings characterised by their shape or disposition
  • H10W74/15—Encapsulations, e.g. protective coatings characterised by their shape or disposition on active surfaces of flip-chip devices, e.g. underfills
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W72/00—Interconnections or connectors in packages
  • H10W72/851—Dispositions of multiple connectors or interconnections
  • H10W72/853—On the same surface
  • H10W72/856—Bump connectors and die-attach connectors

Definitions

• the present invention relates to an underfill encapsulant that may be utilized in no-flow underfilling processes.
• This invention relates to underfill encapsulant compounds prepared from epoxies to protect and reinforce the interconnections between an electronic component and a substrate in a microelectronic device.
• Microelectronic devices contain multiple types of electrical circuit components, mainly transistors assembled together in integrated circuit (IC) chips, but also resistors, capacitors, and other components. These electronic components are interconnected to form the circuits, and eventually are connected to and supported on a carrier or a substrate, such as a printed wire board.
• the integrated circuit component may comprise a single bare chip, a single encapsulated chip, or an encapsulated package of multiple chips. The single bare chip can be attached to a lead frame, which in turn is encapsulated and attached to the printed wire board, or it can be directly attached to the printed wire board.
• the connections are made between electrical terminations on the electronic component and corresponding electrical terminations on the substrate.
• One method for making these connections uses polymeric or metallic material that is applied in bumps to the component or substrate terminals. The terminals are aligned and contacted together and the resulting assembly is heated to reflow the metallic or polymeric material and solidify the connection.
• the electronic assembly is subjected to cycles of widely varying temperature ranges. Due to the differences in the coefficient of thermal expansion for the electronic component, the interconnect material, and the substrate, this thermal cycling can stress the components of the assembly and cause it to fail.
• the gap between the component and the substrate is filled with a polymeric encapsulant, hereinafter called underfill or underfill encapsulant, to reinforce the interconnect material and to absorb some of the stress of the thermal cycling.
• underfill or underfill encapsulant to reinforce the interconnect material and to absorb some of the stress of the thermal cycling.
• the material helps absorb impact energy and improve so- called "drop test" performance.
• CSP chip scale packages
• BGA flip-chip ball grid array
• the underfill dispensing and curing takes place after the reflow of the metallic or polymeric interconnect.
• flux is initially applied on the metal pads on the substrate.
• the chip is placed on the fluxed area of the substrate, on top of the soldering site.
• the assembly is then heated to allow for reflow of the solder joint.
• a measured amount of underfill encapsulant material is dispensed along one or more peripheral sides of the electronic assembly and capillary action within the component-to-substrate gap draws the material inward.
• additional underfill encapsulant may be dispensed along the complete assembly periphery to help reduce stress concentrations and prolong the fatigue life of the assembled structure.
• the underfill encapsulant is subsequently cured to reach its optimized final properties.
• the no-flow underfill process provides a more efficient procedure than that described above for attaching electronic components to a substrate and protecting the assembly with an underfill encapsulant.
• the flux is contained in the underfill which is applied to the assembly site prior to the component placement. After the component is placed, it is soldered to the metal pad connections on the substrate by passing the full assembly, comprising the component, underfill and substrate, through a reflow oven. During this process the underfill fluxes the solder and the metal pads, the solder joint reflows, and the underfill cures.
• the separate steps of applying the flux and post-curing the underfill are eliminated via this process.
• the underfill must remain at a low viscosity to allow melting of the solder and the formation of the interconnections. It is also important that the cure of the underfill not be unduly delayed after the cure of the solder. It is desirable that the underfill in the no-flow process cure rapidly after the melting of the solder. Preferably the viscosity will be suitable to allow the underfill to be dispensed from a syringe.
• Most commercially available underfill encapsulants utilize epoxy anhydride chemistry. For example, U.S. Patent No.
• 6,180,696 describes an underfill that contains a separate anhydride component.
• the use of anhydrides in underfills has raised toxicity issues. Accordingly, it would be preferable to develop an underfill encapsulant that does not contain a free anhydride component.
• the system is fully cured after the completion of the reflow process.
• Figure 1a is an image of a eutectic solder ball after fluxing using the formulation of the underfill having an imidazole-anhydride adduct.
• Figure 1b is an image of a eutectic solder ball after fluxing using the formulation of the underfill having a physical blending of imidazole and anhydride.
• the invention relates to a curable underfill encapsulant composition which is especially useful in the no-flow encapsulation process.
• the composition contains a thermal curable resin system comprising an admixing of at least one epoxy resin and a phenol-containing compound, such as a phenol or phenolic resin, an imidazole-anhydride adduct as a catalyst, and a fluxing agent.
• a thermal curable resin system comprising an admixing of at least one epoxy resin and a phenol-containing compound, such as a phenol or phenolic resin, an imidazole-anhydride adduct as a catalyst, and a fluxing agent.
• Various additives such as air release agents, flow additives, adhesion promoters and rheology modifiers may also be added as desired.
• the resins used in the underfill encapsulant composition of the present invention are curable compounds, which means that they are capable of polymerization.
• to cure will mean to polymerize, with cross-linking.
• Cross-linking as 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 takes place upon heating.
• Ingredients of the underfill encapsulant composition of the present invention include an admixture of one or more epoxy resins and a phenol- containing compound such as phenol or phenolic resin, an imidazole- anhydride adduct which acts as a catalyst, and a fluxing agent.
• a phenol- containing compound such as phenol or phenolic resin
• an imidazole- anhydride adduct which acts as a catalyst
• a fluxing agent e.g., phenol-containing compound such as phenol or phenolic resin
• air release agents, flow additives, adhesion promoters, rheology modifiers, surfactants and other ingredients may be included.
• the ingredients are specifically chosen to obtain the desired balance of properties for the use of the particular resins.
• epoxy resins suitable for use in the present underfill composition include monofunctional and multifunctional glycidyl ethers of Bispheno!-A and Bisphenol-F, aliphatic and aromatic epoxies, saturated and unsaturated epoxies, or cycloaliphatic epoxy resins or a combination thereof.
• aliphatic epoxy include Flex Epoxy 1. Flex Epoxy 1
• Example of aromatic epoxies include RAS-1 , RAS-5, and Flex Epoxy-3.
• Example of unsaturated epoxy includes Cardolite NC513.
• non-glycidyl ether epoxides examples include 3,4- epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, which contains two epoxide groups that are part of the ring structures and an ester linkage, vinylcyclohexene dioxide, which contains two epoxide groups and one of which is part of the ring structure, 3,4-epoxy-6-methyl cyclohexyl methyl-3,4- epoxycyclohexane carboxylate and dicyclopentadiene dioxide.
• Glycidyl ether epoxides are preferred in the invention, either separately or in combination with the non-glycidyl ether epoxides.
• a preferred epoxy resin of this type is bisphenol A resin.
• Another preferred epoxy is aliphatic epoxy including Flex-1 epoxy.
• a most preferred epoxy resin is bisphenol F type resin. These resins are generally prepared by the reaction of one mole of bisphenol F resin and two moles of epichlorohydrin.
• a further preferred type of epoxy resin is epoxy novolac resin. Epoxy novolac resin is commonly prepared by the reaction of phenolic resin and epichlorohydrin.
• a preferred epoxy novolac resin is poly(phenyl glycidyl ether)-co-formaldehyde.
• Biphenyl type epoxy resin may also be utilized in the present invention. This type of resin is commonly prepared by the reaction of biphenyl resin and epichlorohydrin. Dicyclopentadiene-phenol epoxy resin, naphthalene resins, epoxy functional butadiene acrylonitrile copolymers, epoxy functional polydimethyl siloxane and mixtures thereof are additional types of epoxy resins which may be employed.
• Commercially available bisphenol-F type resin are available from CVC Specialty Chemicals, Maple Shade, New Jersey, under the designation 8230E and Resolution Performance Products LLC under the designation RSL1739.
• Bisphenol-A type epoxy resin is commercially available from Resolution Technology as EPON 828, and a blend of bisphenol-A and bisphenol-F is available from Nippon Chemical Company under the designation ZX-1059.
• the desired phenol-containing compound such as phenol or phenolic resin
• phenolic resins are phenolic novolac resins.
• phenol are bisphenol-A and dially bisphenol A phenolic resins.
• Commercially available examples of phenolic novolac resins are Durez 12686 (Oxychem), HRJ -2190 (Schenectady), SP-560 (Schenectady), HRJ-2606 (Schenectady), HRJ-1 166 (Schenectady), HRJ-11040
• SP-6701 (Schenectady), HRJ-1 1945 (Schenectady), SP-6700 (Schenectady), HRJ-11995 (Schenectady), SP-553 (Schenectady), HRJ-2053 (Schenectady), SP-560 (Schenectady),
• BRWE5300 (Georgia-Pacific Resins), BRWE5555 (Georgia-Pacific Resins), and GP2074 (Georgia- Pacific Resins).
• an imidazole-anhydride adduct is included in the underfill composition as a catalyst.
• the adduct provides different properties to the underfill than the properties provided by the inclusion of imidazole and anhydride as separate components.
• Preferred imidazoles that may be included in the adduct include non-N-substituted imidazoles such as 2-phenyl-4-methyl imidazole, 2-phenyl imidazole and imidazole.
• Other useful imidazole components include alkyl-substituted imidazole, N-substituted imidazole and mixtures thereof.
• the adduct also comprises an anhydride component.
• the preferred anhydride is preferably a cycloaliphatic anhydride and most preferably pyromellitic dianhydride, commercially available as PMDA from Aldrich. Additional preferred anhydrides include methylhexa- hydro phthalic anhydride, commercially available as MHHPA fror ⁇ Lonza Inc. Intermediates and Actives.
• anhydrides that may be utilized include methyltetra-hydrophthalic anhydride, nadic methyl anhydride, hexa-hydro phthalic anhydride, tetra-hydro phthalic anhydride, phthalic anhydride, dodecyl succinic anhydride, bisphenyl dianhydride, benzophenone tetracarboxylic dianhydride, and mixtures thereof.
• a fluxing agent is also incorporated into the underfill composition.
• the fluxing agent primarily removes metal oxides and prevents reoxidation. While many different fluxing materials may be employed, the fluxing agent is preferably chosen from the group carboxylic acids. These carboxylic acids include Rosin Gum, dodecanedioic acid (commercially available as Corfree M2 from Aldrich), adipic acid, tartaric acid, and citric acid. The flux agent may also be chosen from the group that includes alcohols, hydroxyl acid and hydroxyl base. Preferable fluxing materials include polyols such as ethylene glycol, glyercol, 3-[bis(glycidy! oxy methyl) methoxy]-1 ,2-propane diol, D- ribose, D-cellobiose, cellulose, 3-cyclohexene-1 ,1-dimethanol, and similar materials.
• carboxylic acids include Rosin Gum, dodecanedioic acid (commercially available as Corfree M2 from Aldrich), adipic acid, tart
• diluents can incrementally delay the increase in viscosity without adversely affecting the physical properties of the cured underfill.
• Preferred diluents include p-tert-butyl-phenyl glycidyl ether, allyl glycidyl ether, glycerol diglycidyl ether, glycidyl ether of alkyl phenol (commercially available from Cardolite Corporation as Cardolite NC513), and Butanediodiglycidylether (commercially available as BDGE from Aldrich), although other diluents may be utilized.
• Surfactants may -be utilized to aid in the prevention of process voiding during the flip-chip bonding process and subsequent solder joint reflow and material curing.
• Various surfactants which may be utilized include organic acrylic polymers, siiicones, polyoxyethylene/polyoxypropylene block copolymers, ethylene diamine based polyoxyethylene/polyoxypropylene block copolymers, .polyol-based polyoxyalkylenes, fatty alcohol-based polyoxyalkylenes, fatty alcohol pojyoxyalkylene alkyl ethers and mixtures thereof.
• coupling agents, air release agents, flow additives, adhesion promoters and other ingredients may also be added as desired.
• a preferred embodiment of the underfill encapsulant of the present invention comprises an admixture of at least one epoxy resin and at least one phenol/phenolic resin as a cross-link agent, an imidazole-anyhydride adduct as a catalyst, a fluxing agent and other ingredients as desired.
• the resin admixture will comprise in the range of about 0.1 wt % to about 99.9 wt % of the epoxy resin and about 0.1 to about 99.9 wt %. of the phenolic resin.
• the admixture will be comprised of in the range of about 40 wt % to about 95 wt % of the epoxy resin and about 5 to about 60 wt % of the phenol/phenolic resin.
• the admixture will comprise in the range of about 80 wt % to about 99.9 wt % of the underfill composition.
• An imidazole-anhydride adduct is also added as a catalyst.
• the adduct comprises in the range about 0.01 wt % to about 10 wt % of the underfill composition and preferably about 0.1 wt % to about 5 wt % of the composition.
• a fluxing agent is added comprising in the range of about 0.5 wt % to about 20 wt % of the composition and preferably in the range of about 1 wt % to about 10 wt % of the composition.
• composition in the range of about 0.01 wt % to about 5 wt % of the composition.
• surfactants such as surfactants, air release agents, flow additives, rheology modifiers, and adhesion promoters may be added to the composition in the range of about 0.01 wt % to about 5 wt % of the composition.
• adhesion promoters may be added to the composition in the range of about 0.01 wt % to about 5 wt % of the composition.
• EXAMPLE 1 Six underfill compositions were formulated utilizing Bisphenol F epoxy (RSL1739), phenolic epoxy (HRJ1 166), 2-phenyl-4-methyl imidazole (2P4MZ) and pyromellitic dianhydride (PMDA) both as an adduct and as separate components.
• RSL1739 Bisphenol F epoxy
• HRJ1 166 phenolic epoxy
• 2P4MZ 2-phenyl-4-methyl imidazole
• PMDA pyromellitic dianhydride
• EXAMPLE 2 Six underfill composition formulations were made according to the procedure set out in Example 1. The epoxy utilized in each formulation was either RSL1739, Flex-1 epoxy or a blend of RSL1739 and a second epoxy. In addition to the epoxy, HRJ1166 was included for the phenolic component, a 2P4MZ-PMDA imidazole-anhydride adduct catalyst and a fluxing agent of dodecanedioic acid (Corfree M2) were also added to the composition. The viscosity of each composition was tested and the results are listed in Table 3. Table 3: Viscosity of epoxy/phenolic/imidazole-anhydride adduct underfills
• underfill compositions It is preferable for underfill compositions to have a curing reaction that occurs at a temperature near the 183°C melting point of eutectic Sn/Pb solder bumps. Minimal curing should ideally occur below the melting temperature of the solder bump and, to allow complete curing in one reflow process, a rapid curing reaction should take place at a temperature just higher than the melting temperature of the solder ball.
• the underfill compositions of Example 2 were characterized using a DSC and the results are illustrated in Table 4. Table 4: DSC Results of the Underfill Compositions
• the peak temperature of the formulations containing the imidazole-anhydride adduct are generally in the range of 180°C to 185°C which is a good indication that the curing of the underfill composition is delayed sufficiently to allow the solder bail to melt before the cross-linking network forms.
• Example 3 The capability of fluxing of the compositions of Example 3 was tested using the hot plate method set out in Example 1 , except two different substrates, an OSP Cu substrate and a Ni/Au substrate, were utilized. All of the formulations in Table 3 exhibited enlargement of the solder bumps in the range of about 100% to about 300% which indicates that the underfills provide excellent capability of fluxing. At the same time, the surface tackiness of these packages was checked after the samples were cooled down to ambient temperature after being heated for one minute on the 240°C hot plate. Under these conditions, non-tacky surfaces were observed on all of the formulations.
• PB-8 is a peripheral array flip chip with die size of 200 x 200 mil, 8 mil pitch, 4 mil gap, and 88 l/Os
• TV-46 is a full area array micro BGA with die size of 226 x 310 mil, 13 mil gap, and 46 I/Os.
• Approximately 6 to 14 mg of the samples were dispensed using a syringe onto the substrate. The board was then placed on the pick and place machine manufactured by Universal Instrument and the chips were automatically picked and placed on the board.
• the entire package was sent to a reflow oven and passed through the standard reflow process where the soaking time is about 2 minutes at 150 °C and the solder fluxing and resin curing time is about 1 minute ramping from 150 C C to 240 °C.
• This reflow process is to allow the solder bumps to flux and form an interconnect between the chip and board.
• a 100% interconnection was established with all four formulations using the PB8 chips and formulations F and G obtained a 100% interconnection utilizing the TV46 chips. No residual curing was observed by DSC after the samples went through the reflow process.
• EXAMPLE 4 A drop of each of the underfill compositions of Table 3 was placed on a 1" x 3" glass slide. Four 20 mil solder balls were then buried inside each droplet and a 1" x 1" glass slit covered each droplet on the glass slide. The package was heated for two minutes on a 150°C hot plate and then transferred to a 240°C hot plate upon which it was heated for an additional one minute. The package was allowed to cool to ambient temperature. Following the cooling, the package was observed for the presence of any bubbles or void formations. Except for voids trapped in the underfill materials on formulation E, no bubbles or void formations were observed. This illustrates that an epoxy and phenolic resin composition which utilizes an imidazole-anhydride adduct with a fluxing agent will produce an underfill which minimizes voids and bubbles.
• underfill composition may also be employed in conjunction with lead free solder (Sn 96.5/Ag 3.5, melting point 225 °C).
• lead free solder Sn 96.5/Ag 3.5, melting point 225 °C.

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• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Epoxy Resins (AREA)
• Structures Or Materials For Encapsulating Or Coating Semiconductor Devices Or Solid State Devices (AREA)
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• 2002
  • 2002-01-31 US US10/062,902 patent/US20030162911A1/en not_active Abandoned
• 2003
  • 2003-01-21 JP JP2003564107A patent/JP4481651B2/ja not_active Expired - Fee Related
  • 2003-01-21 KR KR1020047011760A patent/KR100953579B1/ko not_active Expired - Fee Related
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